版权声明: 2018 地球科学进展 编辑部
River damming transforms allotropic natural rivers into autotrophic 'impound river' (referred to "reservoir"), which changes the processes of river biogenic substance cycle and the matter properties as well as export flux from land to ocean, thus becoming one of the key problems of element biogeochemical cycle. Due to the different behavior of biogenic substances (C, N, P, Si) in biological processes, biogenic substances cycle efficiency is different, in turns, Silicon (Si)>Organic Carbon (OC)>Phosphorus (P). The migration and transformation processes of C and Si are significantly affected by phytoplankton and water retention time. Nitrogen (N) and P are mainly affected by water pH, temperature, Dissolved Oxygen (DO) and retention time. The retention efficiency of biogenic substances is shown as N>C>P>Si at the global scale. Besides, the sedimentation and burial processes of reservoirs constitute the net sink of OC in rivers. River damming alters the stoichiometric characteristics of water elements, nutrient constraints, aquatic communities composition and the coupling effect of C/N/P/Si. The stable isotopic compositions of C, N and Si can effectively trace the source, migration and transformation of biogenic matter. A combination of elements stoichiometric characteristics and stable isotopic composition could effectively indicate the change of source materials in reservoirs. With the increasing demand for clean energy, the intensity of river damming and reservoir construction will increase. Thus, a series of scientific problems including changing law of biogenic substance migration and transformation dynamic, as well as accumulation effect of ecological environment in watershed systems by river cascade damming, should need to be concerned in the biogeochemistry cycle study.
Table 1 The main forms of biogenic elements in reservoirs
根据公式(1)估算2000年全球水库浮游植物生长吸收DIC形成POC为14.4 Tg,占水库总有机碳(Total Organic Carbon,TOC)的15%。
水库中POC的沉积埋藏和矿化过程受水体滞留时间和水温的制约。Maavara等根据公式(2)和(3)分别估算了全球水库POC的埋藏通量(Fb, Tg/a)和矿化通量(Fm, Tg/a):
Fig.1 Biogenic elements cyclic processes in reservoirs
The wide arrow refers to influx and outflux, and the dotted box is element cyclic process, all fluxes are given in units of Tg/a; (a) modified after reference, (b) modified after references[11,17], (c) modified after reference, (d) modified after reference
根据公式(5)计算出新加坡Upper Peirce水库硝化速率为0.77 g/(m3·a),反硝化速率为0.63 g/(m3·a)。
据估算,Upper Peirce水库NH4-N转化速率为0.030.06 h-1,硝酸盐转化速率较低,为0.00050.0009 h-1。截止目前,全球尺度的水库N循环研究尚未报道。
式中:Rmax为硅藻最大生产率状态下的吸收量(mol/ (m2·a)),[DSi]为DSi含量(mol/m2),Ks为硅藻生物吸收DSi的半饱和恒量。Maavara等根据全球17个水库的Rmax值(0.514.7 mol/ (m2·a))建立了Rmax与DSi之间的关系,如公式(10)所示:
Harrison等根据水体滞留时间(Rt/a),建立了溶解无机磷 (Dissolved Inorganic Phosphorus, DIP)的滞留效率计算公式:
对全球湖泊和水库N的滞留量(Tg/a)估算,Harrison等则利用了NiRReLa(Nitrogen Retention in Reservoirs and Lakes)模型:
另外,常用的流域分布式水文模型(Soil and Water Assessment Tool,SWAT)也用于估算水库对TN和TP的滞留效应。但是上述模型在计算水库对各生源要素的滞留效应时,均忽视了水库中各要素迁移转化过程的影响。
Fig.2 Biogenic element retention efficiency in global scale reservoir[
统计分布在不同大陆上20个水库(分别是亚洲11个,欧洲5个,美洲3个和非洲1个)的实测数据得出:水库对不同生源要素的平均滞留率从大到小依次是P(39%) >C(30.5%)>N(28.4%)> Si(22.5%)(图3),均高于依据模型估算的全球尺度水库生源要素的滞留率(图2)。TOC滞留效率接近,分别为31%和30%[25,26]。比较发现:大型水库(如罗马尼亚的铁门水库和我国的三峡水库)的N滞留效率较低(分别为5%和1%),低于中小型水库的相应值(7.8%54%)[25,34]。我国乌江渡水库(-19.7%)和东南沿海山区梯级水库(1%)对TP滞留效率较低,其他水库P的滞留效率变化于12%72%[25,27,31,32,34,40];水库对Si的滞留率为-7.3%72%,其中BSi(44%和72%)较DSi(-7.3%42%)具有更高的滞留效率[25,30,31,41,46]。
Fig.3 Retention efficiency of regional reservoir
Dotted line isaverage retention rate;N data from references[
对比三峡水库、乌江渡水库、铁门大坝和法国Marne, Seine和Aube 水库群(M.S.A水库群)不同生源要素的滞留量,发现水库对不同元素的滞留量均呈现出:N,Si>P(图4)。而且三峡水库和乌江渡水库滞留N的量明显小于法国M.S.A水库群和罗马尼亚的铁门水库的相应值,表明我国长江流域河
Fig.4 The difference of elements retention efficiency[
N和P是限制自养生物生长的主要元素,N∶ P可作为限制性养分判断指标之一。在湖泊和海洋生态系统中,缺N的生态系统N∶ P<20,而缺P的生态系统N∶ P>50,当N∶ P在2050则指示水体N和P都可能不足。水库出入库水体的元素化学计量特征与其元素限制状况有关:在缺N水库系统中,出库水体N∶ P是入库水体的2倍,这是由于缺N的水库系统对P的滞留效率高于N所导致[52,53]。水库营养程度不同,其生态化学计量特征变化存在差异。在富营养化的水库中,出库水体N∶ P是入库的25倍,其中P的滞留率(约90%)较N的相应值(约50%)高,此时库区水体N∶ P<20,属于N缺乏;在中营养化的水库中,由于P含量降低,水库的滞留率差异不大,导致其入库、出库和滞留的N∶ P高于富营养水库,此时P成为生物生长的制约因子。
水体的生态化学计量特征变化影响水生生物群落结构和组成。Schindler等对富营养化湖泊37年的观察,发现减少N输入不能改善湖泊富营养化。湖泊中N∶ P降低会改变湖泊浮游植物群落结构(具有固N功能的蓝藻大量生长)应对湖泊缺N的情况。乌江梯级水库随着流域N输入的增加和Si滞留的增强,下游水库Si∶ N下降导致库区蓝藻增加,改变了原有水库浮游植物群落结构。Turner研究发现当Si∶ DIN<1时鞭毛藻超过硅藻。筑坝减少河流DSi向河口的输出通量从而改变河口近岸的生物群落组成,如罗马尼亚铁门大坝的修建减少了多瑙河输入黑海80%的DSi通量,导致黑海浮游植物中硅藻比例减少,非硅藻成为优势种。三峡大坝拦截大量泥沙和长江中下游地区化肥使用量的增加,长江口水域Si∶ N持续下降(1999年为1.66,2003年为1.09和2004年为0.42),引起甲藻赤潮频发。
Table 2 C, N and Si stable isotopic composition equation
Fig.5 The δ13CDIC value of influx,outflux and in reservoir(data from references[
Different small letters indicate statistically significant differences(p<0.05)
硅酸盐矿物风化过程中存在着 Si 同位素动力学分馏,使得较多的30 Si 进入水循环,导致陆地河流、湖泊水体和海水的δ30Si 值较大。
Fig.6 The distribution of δ30Si value in lake, river and groundwater[
The authors have declared that no competing interests exist.
The world ocean silica cycle[J]. ,
Over the past few decades, we have realized that the silica cycle is strongly intertwined with other major biogeochemical cycles, like those of carbon and nitrogen, and as such is intimately related to marine primary production, the efficiency of carbon export to the deep sea, and the inventory of carbon dioxide in the atmosphere. For nearly 20 years, the marine silica budget compiled by Treguer et al. (1995), with its exploration of reservoirs, processes, sources, and sinks in the silica cycle, has provided context and information fundamental to study of the silica cycle. Today, the budget needs revisiting to incorporate advances that have notably changed estimates of river and groundwater inputs to the ocean of dissolved silicon and easily dissolvable amorphous silica, inputs from the dissolution of terrestrial lithogenic silica in ocean margin sediments, reverse weathering removal fluxes, and outputs of biogenic silica (especially on ocean margins and in the form of nondiatomaceous biogenic silica). The resulting budget recognizes significantly higher input and output fluxes and notes that the recycling of silicon occurs mostly at the sediment-water interface and not during the sinking of silica particles through deep waters.
Anthropogenic perturbation of the carbon fluxes from land to ocean[J]. ,
A substantial amount of the atmospheric carbon taken up on land through photosynthesis and chemical weathering is transported laterally along the aquatic continuum from upland terrestrial ecosystems to the ocean. So far, global carbon budget estimates have implicitly assumed that the transformation and lateral transport of carbon along this aquatic continuum has remained unchanged since pre-industrial times. A synthesis of published work reveals the magnitude of present-day lateral carbon fluxes from land to ocean, and the extent to which human activities have altered these fluxes. We show that anthropogenic perturbation may have increased the flux of carbon to inland waters by as much as 1.0 Pg C yr611 since pre-industrial times, mainly owing to enhanced carbon export from soils. Most of this additional carbon input to upstream rivers is either emitted back to the atmosphere as carbon dioxide (~0.4 Pg C yr611) or sequestered in sediments (~0.5 Pg C yr611) along the continuum of freshwater bodies, estuaries and coastal waters, leaving only a perturbation carbon input of ~0.1 Pg C yr611 to the open ocean. According to our analysis, terrestrial ecosystems store ~0.9 Pg C yr611 at present, which is in agreement with results from forest inventories but significantly differs from the figure of 1.5 Pg C yr611 previously estimated when ignoring changes in lateral carbon fluxes. We suggest that carbon fluxes along the land–ocean aquatic continuum need to be included in global carbon dioxide budgets.
Global riverine N and P transport to ocean increased during the 20th century despite increased retention along the aquatic continuum[J]. ,
Various human activities ??? including agriculture, water consumption, river damming, and aquaculture ??? have intensified over the last century. This has had a major impact on nitrogen (N) and phosphorus (P) cycling in global continental waters. In this study, we use a coupled nutrient-input???hydrology???in-stream nutrient retention model to quantitatively track the changes in the global freshwater N and P cycles over the 20th century. Our results suggest that, during this period, the global nutrient delivery to streams increased from 34 to 64???Tg???N???yr???1 and from 5 to 9???Tg???P???yr???1. Furthermore, in-stream retention and removal grew from 14 to 27???Tg???N???yr???1 and 3 to 5???Tg???P???yr???1. One of the major causes of increased retention is the growing number of reservoirs, which now account for 24 and 22???% of global N and P retention/removal in freshwater systems, respectively. This increase in nutrient retention could not balance the increase in nutrient delivery to rivers with the consequence that river nutrient transport to the ocean increased from 19 to 37???Tg???N???yr???1 and from 2 to 4???Tg???P???yr???1. Human activities have also led to a global increase in the molar N???:???P ratio in freshwater bodies.
The continental Si cycle and its impact on the ocean Si isotope budget[J]. ,
The silicon isotope composition of biogenic silica (δ30SiBSi) in the ocean is a function of the δ30Si of the available dissolved Si (DSi; H2SiO4), the degree of utilisation of the available DSi, and, for some organisms, the concentration of DSi. This makes δ30SiBSiin sediment archives a promising proxy for past DSi concentrations and utilisation. At steady-state, mean δ30SiBSimust equal a weighted average of the inputs, the majority of which are of continental origin. Variation in the functioning of the continental Si cycle on timescales similar to the residence time of DSi in the ocean (~10ka) may therefore contribute to downcore variability in δ30SiBSion millennial or longer timescales. The direction and magnitude of change in published δ30SiBSirecords over the last few glacial cycles is consistent among ocean basins and between groups of silicifiers. They document glacial values that are typically 0.5 to 1.0‰ lower than interglacial values and together hint at coherent and predictable glacial–interglacial variability in whole-ocean δ30Si driven by a change in mean δ30Si of the inputs. In this contribution, we review the modern inputs of DSi to the ocean and the controls on their isotopic composition, and assess the evidence for their variability on millennial-plus timescales. Today, 9.55×1012molyr611DSi enters the ocean, of which roughly 64% and 25% are direct riverine inputs of DSi, and DSi from dissolution of aeolian and riverborne sediment, respectively. The remainder derives from alteration or weathering of the ocean crust. Each input has a characteristic δ30Si, with our current best estimate for a weighted mean being 0.74‰, although much work remains to be done to characterise the individual fluxes. Many aspects of the continental Si cycle may have differed during glacial periods that together can cumulatively substantially lower the mean δ30Si of DSi entering the ocean. These changes relate to i) a cooler, drier glacial climate, ii) lowered sea level and the exposure of continental shelves, iii) the presence of large continental ice-sheets, and iv) altered vegetation zonation. Using a simple box-model with a Monte-Carlo approach to parameterisation, we find that a transition from a hypothesised glacial continental Si cycle to the modern Si cycle can drive an increase in whole ocean δ30Si of comparable rate and magnitude to that recorded in δ30SiBSi. This implies that we may need to revisit our understanding of aspects of the Si cycle in the glacial ocean. Although we focus on the transition from the last glacial, our synthesis suggests that the continental Si cycle should be seen as a potential contributory factor to any variability observed in ocean δ30SiBSion millennial or longer timescales.
High-resolution mapping of the world's reservoirs and dams for sustainable river-flow management[J]. ,
Impact of humans on the flux of terrestrial sediment to the global coastal ocean[J]. ,
Here we provide global estimates of the seasonal flux of sediment, on a river-by-river basis, under modern and prehuman conditions. Humans have simultaneously increased the sediment transport by global rivers through soil erosion (by 2.3 0.6 billion metric tons per year), yet reduced the flux of sediment reaching the world's coasts (by 1.4 0.3 billion metric tons per year) because of retention within reservoirs. Over 100 billion metric tons of sediment and 1 to 3 billion metric tons of carbon are now sequestered in reservoirs constructed largely within the past 50 years. African and Asian rivers carry a greatly reduced sediment load; Indonesian rivers deliver much more sediment to coastal areas.
The effects of weathering variability. The effects of weathering variability and anthropogenic pressures upon silicon cycling in an intertropical watershed(Tana River,Kenya)[J]. ,
78 First study of Si isotopes in river water at the basin scale. 78 In headwaters, the isotopic signature seems linked to soil drainage. 78 The impact of diatoms in dam reservoir is clearly observed. 78 δ30Si ratio remains stable in the estuary.
Human activities directly alter watershed dissolved silica fluxes[J]. ,
Controls on chemical weathering, such as bedrock geology, runoff, and temperature, are considered to be the primary drivers of Si transport from the continents to the oceans. However, recent work has highlighted terrestrial vegetation as an important control over Si cycling. Here we show that at the regional scale (Southern New England, USA), land use/land cover (LULC) is an important variable controlling the net transport of Si from the land to the sea, accounting for at least 40% of dissolved Si (DSi) fluxes. A multiple linear regression model using average DSi fluxes from 25 rivers (>2,300 observations) shows the percent forest cover, as well as development and agricultural land use, to be significant (p < 0.05) drivers of DSi flux. This was true regardless of watershed size and lithology. Furthermore, forest cover is significantly negatively correlated, while development is significantly positively correlated, with Si concentrations and fluxes. We hypothesize that these relationships are due to several mechanisms, specifically the ability of terrestrial vegetation to store large amounts of Si within its biomass, the altered watershed hydrology that accompanies LULC change, and the capability of urban regions to serve as sources of Si to aquatic systems. Thus, we conclude that anthropogenic activities may be directly perturbing the global Si cycle through land use change and we offer a conceptual model which highlights a new approach to understanding the non-geochemical controls on Si fluxes.
Carbon, nitrogen, and phosphorus transport by world rivers[J]. ,
A review of CO2 and associated carbon dynamics in headwater streams: A global perspective[J]. ,
Terrestrial carbon export via inland aquatic systems is a key process in the global carbon cycle. It includes loss of carbon to the atmosphere via outgassing from rivers, lakes, or reservoirs and carbon fixation in the water column as well as in sediments. This review focuses on headwater streams that are important because their stream biogeochemistry directly reflects carbon input from soils and groundwaters. Major drivers of carbon dioxide partial pressures (pCO) in streams and mechanisms of terrestrial dissolved inorganic, organic and particulate organic carbon (DIC, DOC, and POC) influxes are summarized in this work. Our analysis indicates that the global river average pCOof 3100 ppmV is more often exceeded by contributions from small streams when compared to rivers with larger catchments (> 500 km). Because of their large proportion in global river networks (> 96% of the total number of streams), headwaters contribute large ut still poorly quantified mounts of COto the atmosphere. Conservative estimates imply that globally 36% (i.e., 0.93 Pg C yr) of total COoutgassing from rivers and streams originate from headwaters. We also discuss challenges in determination of COsources, concentrations, and fluxes. To overcome uncertainties of COsources and its outgassing from headwater streams on the global scale, new investigations are needed that should include groundwater data. Such studies would also benefit from applications of integral COoutgassing isotope approaches and multiscale geophysical imaging techniques.
Nitrogen dynamics at the sediment-water interface in a tropical reservoir[J]. ,
Nitrogen dynamics at the sediment–water interface were examined in a tropical reservoir, Upper Peirce Reservoir, Singapore to provide information on the relative importance of each process and evaluated the spatial differences of nitrogen dynamics. The intact sediment cores were collected from three locations with different depths and distances to the artificial aeration system. The flow-through system combined with the isotope pairing technique was applied to estimate the nitrogen fluxes, potential denitrification rates and anammox rates. A mass balance model was developed and calibrated with the experimental results, and calculated mineralization, nitrification and dissimilatory nitrate reduction process rates. The sediment had a strong mineralization rate (13.39mmolm612d611) at shallow section, thus, had obvious NH4-N fluxes (17.61mmolm612d611). The total N2removal rates through denitrification and anammox processes ranged from 0.08 to 0.28mmolm612d611, relatively lower than that in estuaries and coastal systems. Denitrification was performed as the main loss pathway, dominating up to 98% of total N2removal rates. The coupled nitrification–denitrification (Dn) was dominant as compared to denitrification that happened from water column nitrate (Dw). Nitrification and N2removal rates increased with water column depth. The artificial aeration around the deeper section might have contributed to the bacteria activities, and thus might stimulate high microbial processes converting NH4-N to NO3-N and bioactive nitrogen to N2gas. The discovery of nitrogen transformation pathways in tropical freshwater systems are proposed to be incorporated into future conceptual models of global nitrogen cycles.
Global phosphorus retention by river damming[J]. ,
More than 70,000 large dams have been built worldwide. With growing water stress and demand for energy, this number will continue to increase in the foreseeable future. Damming greatly modifies the ecological functioning of river systems. In particular, dam reservoirs sequester nutrient elements and, hence, reduce downstream transfer of nutrients...
Worldwide retention of nutrient silicon by river damming: From sparse data set to global estimate[J]. ,
Abstract Damming of rivers represents a major anthropogenic perturbation of the hydrological cycle, with the potential to profoundly modify the availability of nutrient silicon (Si) in streams, lakes, and coastal areas. A global assessment of the impact of dams on river Si fluxes, however, is limited by the sparse data set on Si budgets for reservoirs. To alleviate this limitation, we use existing data on dissolved Si (DSi) retention by dams to calibrate a mechanistic model for the biogeochemical cycling of DSi and reactive particulate Si (PSi) in reservoir systems. The model calibration yields a relationship between the annual in-reservoir siliceous primary productivity and the external DSi supply. With this relationship and an estimate of catchment Si loading, the model calculates the total reactive Si (RSi65=65DSi65+65PSi) retention for any given reservoir. A Monte Carlo analysis accounts for the effects of variations in reservoir characteristics and generates a global relationship that predicts the average reactive Si retention in reservoirs as a function of the water residence time. This relationship is applied to the Global Reservoirs and Dams database to estimate Si retention by damming worldwide. According to the results, dams retain 163 Gmol yr611 (9.8 Tg SiO2 yr611) of DSi and 372 Gmol yr611 (22.3 Tg SiO2 yr611) of RSi, or 5.3% of the global RSi loading to rivers.
Global perturbation of organic carbon cycling by river damming[J]. ,
The damming of rivers has large impacts on the balance of riverine carbon (C) processes and fluxes to the oceans.
Evolution of phosphorus limitation in lakes[J]. ,
Nutrient limitation of phytoplankton in freshwater and marine environments: A review of recent evidence on the effects of enrichment[J]. ,
Phytoplankton can become limited by the availability of nutrients when light and temperature are adequate and loss rates are not excessive. The current paradigms for nutrient limitations in freshwater, estuarine, and marine environments are quite different. A review of the experimental and observational data used to infer P or N limitation of phytoplankton growth indicates that P limitation in freshwater environments can be demonstrated rigorously at several hierarchical levels of system complexity, from algal cultures to whole lakes. A similarly rigorous demonstration of N limitation has not been achieved for marine waters. Therefore, we conclude that the extent and severity of N limitation in the marine environment remain an open question. Culture studies have established that internal cellular concentrations of nutrients determine phytoplankton growth rates, and these studies have shown that it is often difficult to relate growth rates to external concentrations, especially in natural situations. This should lead to a greater reliance on the composition of particulate matter and biomass-based physiological rates to infer nutrient limitation. Such measurements have demonstrated their utility in a wide variety of freshwater and marine environments, and, most importantly, they can be applied to systems that are difficult to manipulate experimentally or budget accurately. Dissolved nutrient concentrations are most useful in determining nutrient loading rates of aquatic ecosystems. The relative proportions of nutrients supplied to phytoplankton can be a strong selective force shaping phytoplankton communities and affecting the biomass yield per unit of limiting nutrient.
A modelling approach to determine systematic nitrogen transformations in a tropical reservoir[J]. ,
The systematic nitrogen transformations were investigated in a tropical freshwater system using a three-dimensional Hydro-Eutrophication model, which simulated hydrodynamics, phytoplankton processes and nutrients cycling in Delft3D. The nitrification and denitrification processes were explicitly considered as the functions of water temperature and oxygen conditions in the model. The validated model was able to capture the thermal differences in vertical direction, reproduce the characteristics of nutrients cycles and primary productions across years with the forcing functions from the area-specific meteorological conditions, discharges and input loads. The modelled nitrification and denitrification process rates were verified by the lab process-oriented measurements. The validated model preformed as a monitor, supplying the knowledge that sediment played an important role in nitrogen cycling, producing twice of the total external nitrogen load to water column. The water column bioactive nitrogen was controlled dominantly by phytoplankton assimilation, which had a nitrogen uptake rate of fifteen fold the external nitrogen loads. The bioactive nitrogen turnover rate by algal growth in this tropical water system was lower than the conditions in the other eutrophic lakes. Fifty-eight percent of the total external nitrogen load was retained via denitrification and burial processes in the Upper Peirce Reservoir. The discovery of the systematic nitrogen transformations in tropical freshwater systems is proposed to be incorporated into future conceptual models of global nitrogen cycles.
Adsorption and release of phosphorus in the surface sediment of a wastewater stabilization pond[J]. ,
In wastewater stabilization ponds, sedimentary phosphorus usually presents significant release and adsorption differences from that in lakes. However, their mobile potentials in stabilization pond have seldom been studied. In this study, the transformation characteristics of sedimentary phosphate in a wastewater stabilization pond are studied. The adsorption and release potential under different pH and E h conditions is investigated and possible mechanisms involved are also proposed. Additionally, the forming process of iron-bound-phosphorus with E h steadily increasing is also discussed. Results of this study show that the binding capability of each phosphorus fraction differed greatly under different pH conditions as follows: iron–phosphorus (Fe–P) and aluminium–phosphorus (Al–P) possessed the greatest binding capability at pH 7–8; and organic phosphorus extracted at alkaline conditions (OP alk) and calcium–phosphorus (Ca–P) showed the greatest binding capability at pH 5 and pH 9, respectively. Mainly through changing the proportion of Fe(III) in Total-Fe and the subsequent binding of its possible forms with phosphate, E h can effectively affect the adsorptive and releasing behaviors of sedimentary phosphorus. With E h increasing from 61650 mV to 6150 mV, Fe(II) was gradually oxidized to Fe(III), and Fe(III)–P significantly formed at the same time. Furthermore, the results show that there was no E h threshold for phosphorus adsorption with increasing E h.
Input-output models-With special reference to the phosphorus loading concept in limnology[J]. ,
Production and dissolution of biogenic silica in the ocean: Revised global estimates, comparison with regional data and relationship to biogenic sedimentation[J]. ,
We estimate the global rate of biogenic silica production in the ocean to be between 200 and 280 0103 1012 mol Si yr0908081. The upper limit is derived from information on the primary productivity of the oceans, the relative contribution of diatoms to primary production and diatom Si/C ratios. The lower limit is derived independently using a multi-compartment model of nutrient transport and biogenic particle flux, and field data on the balance between silica production and dissolution in the upper ocean. Our upper limit is 3009000950% lower than several previous estimates, due to new data indicating lower values for both the relative contribution of diatoms to primary productivity and their Si/C ratios. Globally, at least 50% of the silica produced by diatoms in the euphotic zone dissolves in the upper 100 m, resulting in an estimated export of 100090009140 0103 1012 mol Si yr090808l to the deep ocean. Our estimates correspond to a global mean rate of biogenic silica production between 0.6 and 0.8 mol Si m0908082 yr0908081. Incubation experiments indicate that silica production rates exceed that mean by a factor of 309000912 in coastal areas and are 20900094 times less than the global average in the oligotrophic mid-ocean gyres. The mean silica production rate in waters overlying diatomaceous sediments (approximately 1009000912% of the surface area of the oceans) is 0.70900091.2 mol Si m0908082 yr0908081. That rate is only slightly higher than the global average, indicating that the silica produced in those regions is only 1009000925% of the global total. The estimated production of biogenic silica in surface waters of the mid-ocean gyres is approximately equal to that for all major areas of opal sediment accumulation combined. Regional comparison of silica production and accumulation rates suggests a strongly bimodal character in the efficiency of opal preservation in the sea. In waters overlying diatom-rich sediments 1509000925% of the silica produced in the surface layer accumulates in the seabed, while virtually none of the silica produced in other areas is preserved. The global burial/production ratio of 0908 3% is a composite of those two very different systems. The mechanisms leading to more efficient opal preservation in regions of silica accumulation are presently unknown, but they have no simple relationship to primary productivity. Regional differences in opal preservation appear to be controlled by factors such as low surface temperature, selective grazing and aggregate formation, which diminish the rate of silica dissolution in surface waters and/or accelerate its transport to the seafloor.
Dissolved inorganic phosphorus export to the coastal zone: Results from a spatially explicit, global model[J]. ,
 Here we describe, test, and apply a spatially explicit, global model of river-borne dissolved inorganic phosphorus (DIP) export called NEWS-DIP. Among the innovations in NEWS-DIP are increased spatial resolution (0.5 0103 0.500°), explicit treatment of sewage, fertilizer, manure, and weathering P sources, and inclusion of reservoir retention and consumptive water use terms. The NEWS-DIP model performed better than pre-existing global models in predicting DIP yield for both calibration and validation basins (r2 = 0.72 and 0.56, respectively). NEWS-DIP predicts that of the 34 Tg of P yr0908081 loaded on watersheds by human activity globally, approximately 3% reaches river mouths as DIP; anthropogenic sources account for 65% (0.71 Tg yr0908081) of the DIP exported to the coastal zone, with the remainder (0.38 Tg yr0908081) attributable to natural weathering processes; DIP yields range over 5 orders of magnitude, from less than 0.01 to 1153 kg P km0908082 yr0908081 with highest predicted DIP yields clustering in East Asia, Europe, and Indonesia; human sewage is the largest anthropogenic source of DIP to the coastal zone on all continents and to all ocean basins. NEWS-DIP also suggests that despite regional variability, at the global scale, non-point sources of DIP such as inorganic P fertilizer and manure are much less important in determining coastal export of DIP than point sources and natural weathering processes.
The regional and global significance of nitrogen removal in lakes and reservoirs[J]. ,
Human activities have greatly increased the transport of biologically available nitrogen (N) through watersheds to potentially sensitive coastal ecosystems. Lentie water bodies (lakes and reservoirs) have the potential to act as important sinks for this reactive N as it is transported across the landscape because they offer ideal conditions for N burial in sediments or permanent loss via denitrification. However, the patterns and controls on lentie N removal have not been explored in great detail at large regional to global scales. In this paper we describe, evaluate, and apply a new, spatially explicit, annual-scale, global model of lentie N removal called NiRReLa (Nitrogen Retention in Reservoirs and Lakes). The NiRReLa model incorporates small lakes and reservoirs than have been included in previous global analyses, and also allows for separate treatment and analysis of reservoirs and natural lakes. Model runs for the mid-1990s indicate that lentie systems are indeed important sinks for N and are conservatively estimated to remove 19.7 Tg N year6301 from watersheds globally. Small lakes (<50 km05) were critical in the analysis, retaining almost half (9.3 Tg N year6301) of the global total. In model runs, capacity of lakes and reservoirs to remove watershed N varied substantially at the half-degree scale (0-100%) both as a function of climate and the density of lentie systems. Although reservoirs occupy just 6% of the global lentie surface area, we estimate they retain ~33% of the total N removed by lentie systems, due to a combination of higher drainage ratios (catchment surface areailake or reservoir surface area), higher apparent settling velocities for N, and greater average N loading rates in reservoirs than in lakes. Finally, a sensitivity analysis of NiRReLa suggests that, on-average, N removal within lentie systems will respond more strongly to changes in land use and N loading than to changes in climate at the global scale.
Anthropogenic sediment retention: Major global impact from registered river impoundments[J]. ,
In this paper, we develop and apply a framework for estimating the potential global-scale impact of reservoir construction on riverine sediment transport to the ocean. Using this framework, we discern a large, global-scale, and growing impact from anthropogenic impoundment. Our study links information on 633 of the world's largest reservoirs (LRs) (≥0.5 km 3 maximum storage capacity) to the geography of continental discharge and uses statistical inferences to assess the potential impact of the remaining >44,000 smaller reservoirs (SRs). Information on the LRs was linked to a digitized river network at 30′ (latitude×longitude) spatial resolution. A residence time change (Δ τ R) for otherwise free-flowing river water is determined locally for each reservoir and used with a sediment retention function to predict the proportion of incident sediment flux trapped within each impoundment. The discharge-weighted mean Δ τ R for individual impoundments distributed across the globe is 0.21 years for LRs and 0.011 years for SRs. More than 40% of global river discharge is intercepted locally by the LRs analyzed here, and a significant proportion (≈70%) of this discharge maintains a theoretical sediment trapping efficiency in excess of 50%. Half of all discharge entering LRs shows a local sediment trapping efficiency of 80% or more. Analysis of the recent history of river impoundment reveals that between 1950 and 1968, there was tripling from 5% to 15% in global LR sediment trapping, another doubling to 30% by 1985, and stabilization thereafter. Several large basins such as the Colorado and Nile show nearly complete trapping due to large reservoir construction and flow diversion. From the standpoint of sediment retention rates, the most heavily regulated drainage basins reside in Europe. North America, Africa, and Australia/Oceania are also strongly affected by LRs. Globally, greater than 50% of basin-scale sediment flux in regulated basins is potentially trapped in artificial impoundments, with a discharge-weighted sediment trapping due to LRs of 30%, and an additional contribution of 23% from SRs. If we consider both regulated and unregulated basins, the interception of global sediment flux by all registered reservoirs ( n≈45,000) is conservatively placed at 4–5 Gt year 611 or 25–30% of the total. There is an additional but unknown impact due to still smaller unregistered impoundments ( n≈800,000). Our results demonstrate that river impoundment should now be considered explicitly in global elemental flux studies, such as for water, sediment, carbon, and nutrients. From a global change perspective, the long-term impact of such hydraulic engineering works on the world's coastal zone appears to be significant but has yet to be fully elucidated.
Cascade Dam-induced hydrological disturbance and environmental impact in the upper stream of the Yellow River[J]. ,
Abstract/s, after the appearance of the cascade dams between 1977 and 2006. In the same period, the correlation coefficient () of monthly streamflow between the inlet and outlet of Longliu dropped from 0.959 to 0.375. The peak of streamflow shifted from June to May and October. The difference in sand concentration between two sections decreased from 0.52 to 0.3902kg/m, which was the direct consequence of the operation of the reservoirs. The value of sand concentrations of the inlet and outlet were also reduced from 0.504 to 0.356. A -test analysis indicates that the original hydrological nature was significantly disturbed by the cascade dams. The influence of the dams on nutrient pollutant transport was simulated by the SWAT model. This simulation suggests that the cascade dams decreased the discharge of total nitrogen and total phosphorus from 15.4 × 1002t and 1,99602t to 0.4 × 1002t and 32802t, respectively. In conclusion, the accumulated impact of cascade dams on streamflow, sand concentration and nutrient pollutant discharge were analyzed, which were helpful for understanding the environmental features of the entire watershed.
The qualitative and quantitative analysis of the coupled C, N, P and Si retention in complex of water reservoirs[J]. ,
The Solina–Myczkowce complex of reservoirs (SMCR) accounts about 1502% of the water storage in Poland. On the base of historical (2004–200602years) data, the mass balance of nitrogen, phosphorus, total organic carbon and dissolved silicon were calculated. Large, natural affluents were the main source of the biogenic compounds in the studied ecosystem, delivering 9002% of TOC, 8702% of TN and 8102% of TP and DSi load. Moreover, results show that SMCR is an important sink for all the analysed biogenic elements. About 15–3002% of external loads were retained in the reservoir mainly in upper Solina. Due to the intensive processes of primary production, inorganic forms of nitrogen and phosphorus were mainly retained. Internal production of organic matter lead to an amount of the organic matter deposited in the sediments greater than was anticipated on the basis of the mass balance calculations. A constant load of dissolved silicon originating only from natural sources did not contribute to supplement deficits of Si present in the body of water in the reservoirs, promoting disturbances in N:C:P:Si ratios and another growth condition for other types of algae.
Carbon, nitrogen, phosphorus, and sediment sources and retention in a small eutrophic tropical reservoir[J]. ,
Rapid urbanization and the absence of efficient water management policies are increasingly degrading the water quality of tropical reservoirs in developing countries. The small tropical reservoir of C
Retention of sediments and nutrients in the Iron Gate I Reservoir on the Danube River[J]. ,
This work addresses an intensively debated question in biogeochemical research: "Are large dams affecting global nutrient cycles?" It has been postulated that the largest impoundments on the Lower Danube River, the Iron Gates Reservoirs, act as a major sink for silica (Si) in the form of settling diatoms, for phosphorus (P) and to a lesser extent for nitrogen (N). This retention of P and N in the reservoir would represent a positive contribution to the nutrient reduction in the Danube River. Based on a 9-month monitoring scheme in 2001, we quantified the nutrient and the sediment retention capacity of the Iron Gate I Reservoir. The sediment accumulation corresponded to 5% TN (total nitrogen), 12% TP (total phosphorus) and 55% TSS (total suspended solids) of the incoming loading. A mass balance revealed that more N and P are leaving the reservoir than entering via the inflow. Based on these current results, the reservoir was temporarily acting as a small nutrient source. The nutrient accumulation in the sediments of the Iron Gate I Reservoir represents only 1% of the "missing" load of 1068 t N and 1.3 × 1067 t P defined as the difference between the estimated nutrient export from the Danube Basin and the measured flux entering the Black Sea. This result disproves the hypothesis that the largest impoundment on the Danube River, the Iron Gates Reservoir, plays a major role in N and P elimination.
Reservoirs are hotspots of nitrogen cycling in peatland catchments[J]. ,
Abstract This study presents input–output budgets of total dissolved nitrogen (TDN), dissolved organic N (DON) and dissolved inorganic N (DIN) for a reservoir in a peatland catchment in the south Pennines (UK). This site receives high levels of atmospheric inorganic N deposition, in the range of 2665kg65N65ha611 yr611. The results show that the reservoir retains ~21 to 31% of the annual TDN input (880665±6574165kg65N). Approximately 39 to 55% of DON (378265±6565365kg65N) and 6 to 13% of DIN (502465±6534965kg65N) were retained/processed. A long water retention time (10465days), average annual pH of 6.5, high concentrations of DIN in the reservoir water and a deep water column suggest that denitrification is potentially a key mechanism of N retention/removal. The results also demonstrate that DON is potentially photodegraded and utilized within the reservoir, particularly during the summer season when 58 to 80% of DON input (68265±6524165kg65N) was retained, and a net export of DIN (~3465kg65N) was observed. The findings therefore suggest that DON may play a more crucial role in the biogeochemistry of peat-dominated acid sensitive upland freshwater systems than previously thought. Reservoirs, impoundments and large lakes in peatland catchments may be important sites in mediating downstream N transport and speciation. Copyright 08 2016 John Wiley & Sons, Ltd.
Nitrogen transport, transformation, and retention in the Three Gorges Reservoir: A mass balance approach[J]. ,
Dam construction in river systems affects the biogeochemistry of nitrogen (N), yet most studies on N cycling in reservoirs do not consider the transformations and retention of the different N species. This study addresses the N inputs, transport, transformations, and retention in the Three Gorges Reservoir (TGR) in the Changjiang River, the world largest water storage project, during its filling phase in 2004 2007. The results indicate that dissolved inorganic nitrogen (DIN) was the most abundant N form in the TGR and particulate N was only 2% to the total N flow and retention. About 34% of the dissolved organic nitrogen (DON), 64% of nitrite, and 44% of ammonia were retained by transformation within the TGR in 2007. Time-series data show that about 8% of inflowing total dissolved N was lost by denitrification and sedimentation. Transformations of DON, nitrite and ammonia caused an increase of the nitrate load by 6%; and at the same time the DIN flux increased by 4% while the water moved through the TGR, which is the balance between formation and retention of DIN. The large contribution of biogeochemical transformations to nitrate loading in the TGR indicates the importance of internal processing for the river N species composition.
Biogeochemical mass-balances (C, N, P, Si) in three large reservoirs of the Seine Basin (France)[J]. ,
Three major reservoirs (Marne, Seine and Aube), situated in the upstream basin of the river Seine represent a storage capacity of 800 106 m3. In order to quantify the possible role of these...
Distribution, origin and cycling of carbon in the Tana River (Kenya): A dry season basin-scale survey from headwaters to the delta[J]. ,
The Tana River basin (TRB) is the largest in Kenya (~120 000 km2). We conducted a survey during the dry season throughout the TRB, analyzing a broad suite of biogeochemical parameters. Biogeochemical signatures in headwater streams were highly variable. Along the middle and lower river course, total suspended matter (TSM) concentrations increased more than 30-fold despite the absence of tributary inputs, indicating important resuspension events of internally stored sediment. These resuspended sediment inputs were characterized by a lower and 14C-depleted OC content, suggesting selective degradation of more recent material during sediment retention. Masinga Dam (a large reservoir on the upper river) induced a strong nutrient retention (~50% for inorganic N, ~72% for inorganic phosphate, and ~40% for dissolved silicate). Moreover, while DOC pools and ??13C signatures were similar above, in and below the reservoir, the POC pool in Masinga surface waters was dominated by 13C-depleted phytoplankton, which contributed to the riverine POC pool immediately below the dam, but rapidly disappeared further downstream, suggesting rapid remineralization of this labile C pool in the river system. Despite the generally high turbidity, the combination of relatively high oxygen saturation levels, low ??18O signatures of dissolved O2 (all <+24.2 ), and the relatively low pCO2 values suggest that in-stream primary production was significant, even though pigment data suggest that phytoplankton makes only a minor contribution to the total POC pool in the Tana River.
Distribution and retention efficiency of Nitrogen and phosphorus in cascade reservoirs in Wujiang River Basin[J]. ,
Multiple time-scale analysis of nitrogen retention characteristics and influencing factors in Shanmei Reservoir[J]. ,
An integrated modeling approach to total watershed management: Water quality and watershed assessment of Cheney Reservoir, Kansas, USA[J]. ,
Degradation of water quality is the major health concern for lakes and reservoirs in the central regions of the United States as a result of heavily devoted agricultural production. A vital key to the development of a reservoir management strategy is to identify nutrient loading that describes associated water quality conditions in reservoirs. This study integrated AnnAGNPS watershed and BATHTUB lake models to simulate actual lake water quality conditions of Cheney Reservoir, KS, and demonstrated the use of the coupled model for simulating lake response to changes in different watershed land use and management scenarios. The calibrated current-conditions model simulated in-lake reductions as much as 52% for TN, 48% for TP, and 70% for chlorophyll a due to conversion to native grass, and increases as much as 4% for TN, 9% for TP and 6% for chlorophyll a due to conversion of land from the Conservation Reserve Program (CRP) to cropland (15.5% of watershed). This model also demonstrated an increase in chlorophyll a (19%) as the lake sediment capacity was reached over the next century.
Phosphorus speciation, transformation and retention in the Three Gorges Reservoir, China[J]. ,
Damming of river systems allowing the transformation of former rivers into artificial lakes will increase the transformation and retention of dissolved and sediment-associated phosphorus (P). The reservoir is therefore a ‘filter’ or ‘converter’, reducing and delaying the transport of nutrients to marine systems. Our study of the Three Gorges Reservoir (TGR) found that no stratification of phosphorus occurred, and the high particulate phosphorus (PP) concentrations upstream decreased gradually in the reservoir. Detrital P was found in greater concentrations in the surface sediment, accounting for 39% of PP; exchangeable P was rare and contributed very little to the total P budget. P forms and their concentrations in the suspended particulate matter varied throughout the TGR, with a significant increase of bioavailable P in the <8-μm particle fraction from 27% of PP in Fuling to 60% in Yichang, and decreasing detrital P and authigenic P in each grain size class. The TGR acted as a ‘converter’ for the dissolved reactive phosphorus, and it therefore plays a minor role in trapping incoming total dissolved phosphorus; whereas the TGR behaved as a ‘filter’ for the PP, especially for the coarse fraction, which resulted in the retention of 70% of the non-bioavailable PP. The controlling mechanism of P species and retention in the reservoir is particulate settling and its associated effects.
Hydrological controls on cascade reservoirs regulating phosphorus retention and downriver fluxes[J]. ,
Many coastal rivers have a system of cascade reservoirs, but the role of these reservoirs in regulating nutrient transport from watershed to coast is still unknown. In this study, phosphorus (P) in surface water and top sediment was investigated along the North Jiulong River (southeast China) under three hydrological conditions (high flow, medium flow and low flow) in 2012-2013, and P dynamics in a cascade reservoir (Xipi Reservoir) were studied on a monthly scale. Results showed that the concentrations of dissolved reactive phosphorus (DRP) consistently decreased longitudinally in the upper river with the lowest values observed in the section of cascade reservoirs, likely due to tributary inputs and in situ uptakes. The decrease was most rapid during base flow when DRP was highest in the free-flowing river section and lowest in cascade reservoirs. Results from monthly monitoring on the Xipi Reservoir showed general downriver decreases in DRP, total particulate phosphorus (TPP) and total phosphorus (TP) in the riverine zone and transition zone. Mass balance results on an annual basis suggest that the Xipi Reservoir (lacustrine zone) was an overall sink for TPP (6 % retention) but somewhat a source of DRP ( 0.3 %) with TP retention (1 %). Even scaled up to the whole cascade reservoir system, P retention was low compared with worldwide reservoirs, which we ascribe to the high P loading and short hydraulic residence time. Nevertheless, major processes controlling P retention in coastal rivers with cascade reservoirs varied from sedimentation in the dry-cold season to biotic transformation in the wet-warm season, thereby affecting loading and composition of P from watershed to the coast. This study highlights the hydrological controls on the role of cascade reservoirs in regulating P retention and downriver fluxes in different seasons.
Spatial pattern and temporal dynamics of limnological variables in Liuxihe Reservoir, Guangdong[J]. ,
The influence of upstream input on phosphorus retention in Miyun Reservoir[J]. ,
External phosphorus load estimates and P-budget for the hydroelectric reservoir of Bort-Les-Orgues, France[J]. ,
This paper presents two methods used to estimate the externalphosphorus load for the hydroelectric reservoir ofBort-Les-Orgues (in France's `Massif Central' region). The Pload calculated from export coefficients (150 t yr -1 ) agreedwith field measurements taken during a one-year survey carriedout from March 1996 to February 1997 (121 t yr -1 ). Exportcoefficients represent a good option for estimating phosphorusloads of other reservoirs in the region of Bort-Les-Orgues,provided that they display similar characteristics. Theseexternal load estimates are greater than the maximum permissibleload for a mesotrophic lake calculated from the OECD equations(40 t yr -1 ); thus, a yearly reduction of about 60 t shouldideally be achieved. This target, however, is probably tooambitious, and measures to reduce both point and non-pointsources must be implemented for the reservoir to tbe mesotrophic.Moreover, Bort-Les-Orgues is a tourist area. As such, thepresence of algal blooms (a regular occurrence on the lake) dueto an excess of P in the lake's water inflow could actuallyexert a negative impact on regional economy.
Nutrient budget for Saguling Reservoir, West Java, Indonesia[J]. ,
A preliminary nutrient budget for Saguling Reservoir is reported as a first attempt to quantify the behaviour of nutrients entering this reservoir. This work is part of a larger Indonesia ustralia collaborative research and training project, involving Padjadjaran University and Monash University, established to study nutrient dynamics in Saguling Reservoir. Saguling Reservoir, the first of a chain of three large reservoirs (Saguling, Cirata and Jatilahur), built on the Citarum River in central Java, was completed in 1985. It has already become highly polluted, particularly with domestic and industrial effluent (organic matter, nutrients, heavy metals) from the urban areas of Bandung (population 2 million). The reservoir experiences major water quality problems, including excessive growths of floating plants, toxic cyanobacterial blooms and regular fish-kills. The work reported in this paper shows that Saguling receives a very large nutrient load from the city of Bandung and because of this, is highly eutrophic. It is unlikely that the water quality of Saguling will improve until a substantial part of Bandung is sewered and adequate discharge controls are placed on the many industries in the region upstream of the reservoir.
Reactive silicon dynamics in a large prairie reservoir (Lake Diefenbaker, Saskatchewan)[J]. ,
61Current annual dissolved Si retention in Lake Diefenbaker is approximately 28% of the influx.61Most Si retention takes place in the mid-reservoir region, that is, in the fluvial–lacustrine transition zone.61Dissimilar retentions of nitrogen, phosphorus and silicon indicate a decoupling of nutrient cycles in reservoirs.
Silicon and sediment transport of the Changjiang River (Yangtze River): Could the Three Gorges Reservoir be a filter?[J]. ,
Water samples were collected from the Changjiang River (Yangtze River) in May 2005, after the impoundment of the Three Gorges Reservoir (TGR), to examine the influence of the TGR and large lakes on material delivery to the estuary of the Changjiang River. The concentrations of suspended particle material (SPM), dissolved silica (DSi) and biogenic silica (BSi) in the main stream were analyzed. The concentrations of DSi and BSi in the main channel of the Changjiang varied between 73 and 100 and 1.1-15 mu mol/l, with a distance weighted average of 81 and 8.0 mu mol/l, respectively. A calculation shows that live diatom comprises only an average value of 5.2 % of the BSi in the Changjiang River, and most of BSi may come from drainage basin. The concentrations of BSi and the ratios of BSi/SPM were relatively low in the Changjiang River compared to other rivers throughout the world, but the BSi carried in suspension by the Changjiang River was an important component of the rivers silicon load (i.e. similar to 13 %). SPM, DSi and BSi concentrations as observed in the Changjiang River tend to decrease from the upper sections of the river to the Three Gorges Dam (TGD), reflecting sedimentation associated with BSi trapping and DSi retention in the TGR in the normal-water period. SPM and BSi retention are more strongly influenced by the TGD compared to DSi. About 98 % of SPM, 72 % of BSi and 16 % of DSi were retained within the TGR in May 2005. The fluxes variations of DSi, BSi and SPM suggested that the large lakes and dams had a coupled effect on the transportation of DSi, BSi and SPM in the normal-water period. Such a change in silicon (DSi and BSi) balances of the Changjiang River will affect the ecological environment of the Changjiang estuary and its adjacent sea to some extent.
Silica retention in the Three Gorges Reservoir[J]. ,
A mass balance of dissolved silica (DSi) based on daily measurements at the inflow and outflow of the Three Gorges Reservoir (TGR) in 2007 and a more precise budget, with inflow, outflow, primary production, biogenic silica (BSi) settlement, dissolution of BSi in the water column and flux of DSi at the sediment-water interface in the dry season (April) of 2007 were developed. We address the following question: How much does the Three Gorges Dam (TGD) affect silica transport in the TGR of the Changjiang River (Yangtze River)? The DSi varied from 71.1 to 141 mu mol/l with an average of 108 mu mol/l, and it ranged between 68.1 and 136 mu mol/l, with an average of 107 mu mol/l in inflow and outflow, respectively, in the TGR in 2007. The linear relationship of DSi between inflow and outflow water is significant (r = 0.87, n = 362, p < 0.01). Along the main stream of the TGR, the DSi concentration decreases with an average concentration of 84.0 mu mol/l in the dry season. However, the stratification of DSi was not obvious in the main channel of the TGR in the dry season. The BSi is within the range of 0.04-5.00 mu mol/l, with an average concentration of 2.1 mu mol/l in the main channel of the TGR, while it is much higher in Xiangxi Bay (1.30-47.7 mu mol/l, 13.1 mu mol/l) than in the main stream of the TGR and the other bays. After the third filling of the TGR, approximately 3.8% of the DSi was retained by the TGR based on a 12-month monitoring scheme in 2007, which would slightly reduce nutrient fluxes of the Changjiang River to the East China Sea (2%). DSi was lost during January to June and November, whereas the additions of DSi were found during the other months in 2007. The budget results also indicate that there is a slight retention of DSi. The retention of DSi in the reservoir is approximately 2.9%, while BSi is approximately 44%. Compared with the total silica load, the retention of DSi and BSi in the reservoir is only 5.0% in the dry season. With its present storage capacity, the reservoir does not play an important role as a silica sink in the channel of the TGR. The DSi load is significantly related to discharge both in inflow and outflow waters (p < 0.01). DSi retention, to some extent, is the runoff change due to impoundment.
Dissolved silicate retention and transport in cascade reservoirs in Karst area, Southwest China[J]. ,
Presently, the fluvial fluxes of Dissolved silicate (DSi) by many famous rivers in the world have been reported significantly decreased in the past several decades. DSi retention by river damming hence becomes a great concern. In this study, the impact on DSi retention and transport by cascade reservoirs in the Karst area were investigated. Based on the monitoring data for four seasons, budget of DSi in these reservoirs were calculated. Results showed that, only the downstream eutrophic Wujiangdu reservoir (WJD) was the sink for DSi, with a value of ca. 3.5 kT DSi trapped annually. The new Hongjiadu reservoir (HJD) in the headwater area revealed to be an important source for DSi. Both Dongfeng (DF) and Suofengyin (SFY) reservoirs also released more DSi to the downstream than entering them. The great discrepancy of DSi source and sink effects among these reservoirs indicates that, (i) DSi was obviously taken up in summer and spring, and the concentration of DSi could be dropped down to below 30 ; (ii) during the period of thermal stratification, the concentration stratification of DSi is also developed along the water column. Possibly DSi releasing from inundation soil and bottom sediment was the important compensation for the silicon depletion in the epilimnion. In the newly constructed reservoirs ( e.g. HJD and SFY), the releasing flux of DSi can significantly exceed the assimilating flux by diatom; and (iii) due to the hypolimnion introducing for hydropower operation, water leaving the dam generally had high DSi content, and then masked the DSi taking up in the epilimnion. This process also decreased the ratio of DIN to DSi, mitigating the silicon limiting situation in the downstream.
Silica retention in the Iron Gate I reservoir on the Danube River: The role of side bays as nutrient sinks[J]. ,
There are longstanding concerns about the environmental impacts of super-dams such as Iron Gate I, the Danube River's largest hydropower scheme. Iron Gate I is suspected of trapping up to 80% (590 000 tons per year) of dissolved silica in the form of sedimenting diatom frustules and 30 000 000 tons per year of suspended solids. This study, however, indicates that (i) conditions are unfavorable for primary production in Iron Gate I except for the small quiescent center of Orsova Bay, and the diatom production is much too low for the suspected silica uptake; (ii) Orsova Bay is the most important sediment trap as resuspension does not occur, with 1% (82 000 tons per year) suspended solids retention, and (iii) also the only significant silica trap, with 0.2% (1000 tons per year) retention. It is most conservatively estimated that no more than 5% of dissolved silica can be retained by the Iron Gate I reservoir, and therefore the earlier estimate of the huge retention can definitely be ruled out. Copyright 2006 John Wiley & Sons, Ltd.
Is the Iron Gate I reservoir on the Danube River a sink for dissolved silica?[J]. ,
Damming rivers changes sediment and nutrient cycles downstream of a dam in many direct and indirect ways. The Iron Gates I reservoir on the Yugoslavian-Romanian border is the largest impoundment by volume on the Danube River holding 3.2 billion m3 of water. Silica retention within the reservoir in the form of diatom frustules was postulated to be as high as 600 kt year-1 in previous studies using indirect methods. This amount of dissolved silicate was not delivered to the coastal Black Sea, and presumably caused a shift in the phytoplankton community there, and subsequent drastic decline in fishery. We directly quantified the amount of dissolved silicate (DSi) entering and leaving the reservoir for 11 continuous months. The budget based on these data reveals two important facts: (1) only about 4% of incoming DSi was retained in the reservoir; (2) the DSi concentrations were relatively low in the rivers upstream of the reservoir compared to regional and global averages. Thus damming the Danube at the Iron Gates could not have caused the decline in DSi concentrations documented downstream of the impoundment. Rather, this change in DSi must have occurred in the headwaters of the Danube River. Potential reasons include the construction of many dams upstream of the Iron Gates, hydrologic changes resulting in lower groundwater levels, and clogging of the riverbed limiting groundwater-river exchange.
Advances of eco-environmental effects and adaptive management in river cascading development[J]. ,
Effects of dams on riverine biogeochemical cycling and ecology[J]. ,
The influence of organism on the composition of seawater[M]∥Hill M N, ed. T,
Sources and delivery of carbon, nitrogen, and phosphorus to the coastal zone: An overview of Global Nutrient Export from Watersheds (NEWS) models and their application[J]. ,
 An overview of the first spatially explicit, multielement (N, P, and C), multiform (dissolved inorganic: DIN, DIP; dissolved organic: DOC, DON, DOP; and particulate: POC, PN, PP) predictive model system of river nutrient export from watersheds (Global Nutrient Export from Watersheds (NEWS)) is presented. NEWS models estimate export from 5761 watersheds globally as a function of land use, nutrient inputs, hydrology, and other factors; regional and global scale patterns as of 1995 are presented here. Watershed sources and their relative magnitudes differ by element and form. For example, anthropogenic sources dominate the export of DIN and DIP at the global scale, although their anthropogenic sources differ significantly (diffuse and point, respectively). Natural sources dominate DON and DOP export globally, although diffuse anthropogenic sources dominate in several regions in Asia, Europe and N. America. 090008Hot spots090009 where yield (kg km0908082 yr0908081) is high for several elements and forms were identified, including parts of Indonesia, Japan, southern Asia, and Central America, due to anthropogenic N and P inputs in some regions and high water runoff in others. NEWS models provide a tool to examine past, current and future river export of nutrients, and how humans might impact element ratios and forms, and thereby affect estuaries and coastal seas.
Total nitrogen, total phosphorus, and nutrient limitation in lakes and oceans: Is there a common relationship?[J]. ,
Abstract Total nitrogen (TN) and total phosphorus (TP) measurements and contemporaneous measurements of chlorophyll a (Chl a) and phytoplankton nutrient deficiency have been made across a broad range of lakes and ocean sites using common methods. The ocean environment was nutrient rich in terms of TN and TP when compared with most lakes in the study, although Lake Victoria had the highest values of TN and TP. TN concentrations in lakes rose rapidly with TP concentrations, from low values to TN concentrations that are similar to those associated with the ocean sites. In contrast, the TN concentrations in the oceans were relatively homogeneous and independent of TP concentrations. The hyperbolic shape of the TN:TP relationship created a broad range of TN:TP values for both lakes and oceans. The TN:TP ratios of the surface ocean sites were usually well in excess of the Redfield ratio that is noted in the deep ocean. Phytoplankton biomass, as indicated by Chl a, was strongly dependent upon TP in the lakes, and there was a weaker relationship with TN. Oceanic Chl a values showed a positive relationship with TP, but at much higher TP values than were observed in the lakes; there was no relation with TN.P-deficient phytoplankton growth was inferred using independent indicators when TP was >0.5 mol L 1 at both freshwater and marine sites. N-deficiency indicators were highly variable and did not show any clear dependence on TN concentration. The TN:TP ratio was indicative of which nutrient would become limiting for growth in both lakes and oceans. When all sites are compared, N-deficient growth was apparent at TN:TP 20 (molar), whereas P-deficient growth consistently occurred when TN:TP 50 (molar). At intermediate TN:TP ratios, either N or P can become deficient. We conclude that N or P limitation of algal growth is a product of the TN and TP concentration and the TN:TP ratio rather than a product of whether the system of study is marine or freshwater.
Retention of nitrogen, phosphorus and silicon in a large semi-arid riverine lake system[J]. ,
Lakes and reservoirs (impoundments) are often viewed as a sink for nutrients within the river continuum. To date, most studies on nutrient retention within impoundments are derived from the temperate climate zones of Europe and North America, only consider one nutrient, and are often shortterm (1-2 years). Here, we present a long-term (17 year) data set and nutrient (nitrogen, phosphorus and silica) budget for two connected semi-arid lakes (the Lower Lakes) at the terminus of the River Murray, Australia. Most of the filterable reactive phosphorus and nitrate entering the lakes were retained (77 and 92%, respectively). Total phosphorus (TP) was also strongly retained (55% of the annual TP load on average) and the annual TP retention rates could be predicted as a function of the areal hydraulic loading rate (annual lake outflow/lake surface area). On average, there was a slight net retention (7%) of the annual total nitrogen (TN) load but a slight net export (6% of the load) of organic N. TN retention as function of the areal hydraulic loading rate was lower than expected from existing models, possibly because of high nitrogen fixation rates in the Lower Lakes. Silica was retained (39%) at similar rates to those observed in previous studies. There was also a marked increase in the TN: TP and TN: Si ratios within the lake (TN: TP-30 and TN: Si~ 0.67) compared to those entering (TN: TP~ 15, TN: Si~ 0.45), as a consequence of the relatively low net retention of nitrogen.
Nutrient stoichiometry of linked catchment-lake systems along a gradient of land use[J]. ,
1. Catchments export nutrients to aquatic ecosystems at rates and ratios that are strongly influenced by land use practices, and within aquatic ecosystems nutrients can be processed, retained, lost to the atmosphere, or exported downstream. The stoichiometry of carbon and nutrients can influence ecosystem services such as water quality, nutrient limitation, biodiversity, eutrophication and the sequestration of nutrients and carbon in sediments. However, we know little about how nutrient stoichiometry varies along the pathway from terrestrial landscapes through aquatic systems.2. We studied the stoichiometry of nitrogen and phosphorus exported by three catchments of contrasting land use (forest versus agriculture) and in the water column and sediments of downstream reservoirs. We also related stoichiometry to phytoplankton nutrient limitation and the abundance of heterocystous cyanobacteria.3. The total N : P of stream exports varied greatly among catchments and was 18, 54 and 140 (molar) in the forested, mixed-use and agricultural catchment, respectively. Total N : P in the mixed layers of the lakes was less variable but ordered similarly: 35, 52 132 in the forested, mixed-use and agricultural lake, respectively. In contrast, there was little variation among systems in the C : N and C : P ratios of catchment exports or in reservoir seston.4. Phytoplankton in the forested lake were consistently N limited, those in the agricultural lake were consistently P limited, and those in the mixed-use lake shifted seasonally from P- to N limitation, reflecting N : P supply ratios. Total phytoplankton and cyanobacteria biomass were highest in the agricultural lake, but heterocystous (potentially N fixing) cyanobacteria were most abundant in the forested lake, corresponding to low N : P ratios.5. Despite large differences in catchment export and water column N : P ratios, the N : P of sediment burial (integrated over several decades) was very low and remarkably similar (4.3 7.3) across reservoirs. N and P budgets constructed for the agricultural reservoir suggested that denitrification could be a major loss of N, and may help explain the relatively low N : P of buried sediment.6. Our results show congruence between the catchment export N : P, reservoir N : P, phytoplankton N versus P limitation and the dominance of heterocystous cyanobacteria. However, the N : P stoichiometry of sediments retained in the lakes was relatively insensitive to catchment stoichiometry, suggesting that a common set of biogeochemical processes constrains sediment N : P across lakes of contrasting catchment land use.
Stoichiometric imbalance in rates of nitrogen and phosphorus retention, storage, and recycling can perpetuate nitrogen deficiency in highly-productive reservoirs[J]. ,
We measured the nutrient stoichiometry of inputs, outputs, retention, storage, and recycling in three seasonally nitrogen (N)-deficient reservoirs by incorporating watershed mass balances with measurements of internal N and phosphorus (P) transformations. Our objective was to determine if the reservoirs were accumulating N and thereby likely to develop strict P deficiency over time. For the eutrophic reservoirs, the N : P (by atoms) of annual outputs was two to five times greater than that of inputs, reflecting higher retention efficiency for P than N (65 90% vs. 65 50%, respectively) and resulting in retention stoichiometry indicative of N deficiency (N : P 50). Denitrification (12–2302g N m61202yr611) removed 65 50–100% of N retained by the reservoirs annually, increasing N deficiency in storage relative to retention for all the reservoirs (N : P 2</sub> fixation (7–1102g N m61202yr611) was inefficient in balancing system N deficits and did not increase the low N : P of annual watershed inputs or seasonal epilimnion nutrient concentrations into the range of strict P deficiency. Low N : P storage and internal recycling strongly suggested that these reservoirs are not accumulating N relative to P and are thereby unlikely to become strictly P deficient over time.
Eutrophication of lakes cannot be controlled by reducing nitrogen input: Results of a 37-year whole-ecosystem experiment[J]. ,
Lake 227, a small lake in the Precambrian Shield at the Experimental Lakes Area (ELA), has been fertilized for 37 years with constant annual inputs of phosphorus and decreasing inputs of nitrogen to test the theory that controlling nitrogen inputs can control eutrophication. For the final 16 years (1990-2005), the lake was fertilized with phosphorus alone. Reducing nitrogen inputs increasingly favored nitrogen-fixing cyanobacteria as a response by the phytoplankton community to extreme seasonal nitrogen limitation. Nitrogen fixation was sufficient to allow biomass to continue to be produced in proportion to phosphorus, and the lake remained highly eutrophic, despite showing indications of extreme nitrogen limitation seasonally. To reduce eutrophication, the focus of management must be on decreasing inputs of phosphorus.
Responses of aquatic environment to river damming—From the geochemical view[J]. ,
Element ratios and aquatic food webs[J]. ,
Organic matter is the result of concentrating a few non-metals that are relatively rare in the earth’s crust. Most of these essential elements are in a rough proportionality within phylogenetic groupings. Life is thus working against a concentration gradient to extract or accumulate these elements, and this metabolic work is accomplished in interrelated and often subtle ways for many other elements. The physiological requirement to sustain these elemental ratios (commonly discussed in terms of the N∶P ratios, but also C∶N, C∶P, and Si∶N ratios) constrains organization at the cellular, organism, and community level. Humans, as geochemical engineers, significantly influence the spatial and temporal distribution of elements and, consequently, their ratios. Examples of these influences include the changing dissolved Si: nitrate and the dissolved nitrate: phosphate atomic ratios of water entering coastal waters in many areas of the world. Human society may find that some desirable or dependent ecosystem interactions are compromised, rather than enhanced, as we alter these elemental ratios. Human-modulated changes in nutrient ratios that cause an apparent increase in harmful algal blooms may compromise the diatom-zooplankton-fish food web. It will be useful to improve our understanding of aquatic ecosystems and for management purposes if the assiduous attention on one element (e.g., N or P) was expanded to include the realities of these mutual interdependencies.
Effect of Danube River dam on Black Sea biogeochemistry and ecosystem structure[J]. ,
Distributions of DSi, DIN and changes of Si∶ N ratio on summer in Changjiang Estuary before and after storage of Three Gorges Reservoir[J]. ,
对长江口水域1999、2003、2004年3个夏季航次和1959年历史数据的比较,分析 研究了长江三峡水库蓄水前后长江口溶解硅酸盐（DSi）和无机氮（DIN）含量的变化,发现与1999年相比,2003年和2004年DIN浓度分别增加 了1.3倍和2.2倍,DIN浓度还在增加中,而且有加快的趋势;三峡水库蓄水前DSi浓度每年减少约为0.60μmol/L,而蓄水后一年内就减少了 3.92μmol/L;Si/N比的平均值分别从1999年的1.66下降到2003年1.09,再下降到2004年的0.42,大面积区域比值已经小于 1,下降趋势比较明显,DSi含量的下降与长江径流输沙量减少有显著关系,DIN的增加则与长江中下游化肥的使用有关;同时长江口营养盐结构已经趋于不平 衡,营养盐结构的变化已经引起了长江口生态系统结构的改变,如甲藻赤潮频发等,这可能是人类活动影响的直接结果.
Thick-shelled, grazer-protected diatoms decouple ocean carbon and silicon cycles in the iron-limited Antarctic Circumpolar Current[J]. ,
Diatoms of the iron-replete continental margins and North Atlantic are key exporters of organic carbon. In contrast, diatoms of the iron-limited Antarctic Circumpolar Current sequester silicon, but comparatively little carbon, in the underlying deep ocean and sediments. Because the Southern Ocean is the major hub of oceanic nutrient distribution, selective silicon sequestration there limits diatom blooms elsewhere and consequently the biotic carbon sequestration potential of the entire ocean. We investigated this paradox in an in situ iron fertilization experiment by comparing accumulation and sinking of diatom populations inside and outside the iron-fertilized patch over 5 wk. A bloom comprising various thin-and thick-shelled diatom species developed inside the patch despite the presence of large grazer populations. After the third week, most of the thinner-shelled diatom species underwent mass mortality, formed large, mucous aggregates, and sank out en masse (carbon sinkers). In contrast, thicker-shelled species, in particular Fragilariopsis kerguelensis, persisted in the surface layers, sank mainly empty shells continuously, and reduced silicate concentrations to similar levels both inside and outside the patch (silica sinkers). These patterns imply that thick-shelled, hence grazer-protected, diatom species evolved in response to heavy copepod grazing pressure in the presence of an abundant silicate supply. The ecology of these silica-sinking species decouples silicon and carbon cycles in the iron-limited Southern Ocean, whereas carbon-sinking species, when stimulated by iron fertilization, export more carbon per silicon. Our results suggest that large-scale iron fertilization of the silicate-rich Southern Ocean will not change silicon sequestration but will add carbon to the sinking silica flux.
Coupling of carbon and silicon geochemical cycles in rivers and lakes[J]. ,
Abstract Krabbe disease (KD) is a neurodegenerative disorder caused by the lack of - galactosylceramidase enzymatic activity and by widespread accumulation of the cytotoxic galactosyl-sphingosine in neuronal, myelinating and endothelial cells. Despite the wide use of Twitcher mice as experimental model for KD, the ultrastructure of this model is partial and mainly addressing peripheral nerves. More details are requested to elucidate the basis of the motor defects, which are the first to appear during KD onset. Here we use transmission electron microscopy (TEM) to focus on the alterations produced by KD in the lower motor system at postnatal day 15 (P15), a nearly asymptomatic stage, and in the juvenile P30 mouse. We find mild effects on motorneuron soma, severe ones on sciatic nerves and very severe effects on nerve terminals and neuromuscular junctions at P30, with peripheral damage being already detectable at P15. Finally, we find that the gastrocnemius muscle undergoes atrophy and structural changes that are independent of denervation at P15. Our data further characterize the ultrastructural analysis of the KD mouse model, and support recent theories of a dying-back mechanism for neuronal degeneration, which is independent of demyelination.
Extreme drought decouples silicon and carbon geochemical linkages in lakes[J]. ,
How to find the multicollinearity of CPD data. This data is used in the research of OLDF.
Present limitations and future prospects of stable isotope methods for nitrate source identification in surface-and groundwater[J]. ,
Nitrate (NO 3 61) contamination of surface- and groundwater is an environmental problem in many regions of the world with intensive agriculture and high population densities. Knowledge of the sources of NO 3 61 contamination in water is important for better management of water quality. Stable nitrogen ( δ 15N) and oxygen ( δ 18O) isotope data of NO 3 61 have been frequently used to identify NO 3 61 sources in water. This review summarizes typical δ 15N- and δ 18O-NO 3 61 ranges of known NO 3 61 sources, interprets constraints and future outlooks to quantify NO 3 61 sources, and describes three analytical techniques (“ion-exchange method”, “bacterial denitrification method”, and “cadmium reduction method”) for δ 15N- and δ 18O-NO 3 61 determination. Isotopic data can provide evidence for the presence of dominant NO 3 61 sources. However, quantification, including uncertainty assessment, is lacking when multiple NO 3 61 sources are present. Moreover, fractionation processes are often ignored, but may largely constrain the accuracy of NO 3 61 source identification. These problems can be overcome if (1) NO 3 61 isotopic data are combined with co-migrating discriminators of NO 3 61 sources (e.g. 11B), which are not affected by transformation processes, (2) contributions of different NO 3 61 sources can be quantified via linear mixing models (e.g. SIAR), and (3) precise, accurate and high throughput isotope analytical techniques become available.
Preliminary research on the feature of dissolved inorganic carbon in Wulixia Reservoir in summer, Guangxi, China[J]. ,
为更加清晰地认识无机碳在岩溶水库水体中的循环转化过程,2013年7月初对位于岩溶区的广西五里峡水库沿流程方向不同地点不同深度水体进行现场监测.结果表明：1研究区水体水化学主要受碳酸盐平衡体系控制,水化学类型为HCO3-Ca＋Mg型.2水体溶解无机碳（dissolved inorganic carbon,DIC）含量及其同位素组成δ^13DIC分布特征：沿流程方向从库尾到坝前同一深度不同取样点DIC含量呈减小趋势（DIC（平均）：1.03～0.78 mmol·L^-1）,δ^13DIC则逐渐变重（δ^13DIC（平均）：-10.21‰～-6.62‰）.沿垂直方向从表层向库底DIC含量呈增加趋势（DIC（平均）：0.86～1.05 mmol·L^-1）,δ^13DIC则逐渐变轻（δ^13DIC（平均）：-7.88‰～-13.39‰）.分析认为：1碳酸盐岩溶解沉淀过程对研究区水体DIC含量及δ^13DIC的影响有限或被其它过程平抑.2研究区水体存在热分层现象,其通过影响水库不同部位、不同深度水生生物新陈代谢的方向及强度、有机质分解强度等对水体DIC及δ^13DIC产生影响,使之出现前述变化趋势.
The impact of damming on geochemical behavior of dissolved inorganic carbon in a karst river[J]. ,
为探究筑坝对河流溶解性无机碳（DIC）地球化学行为的影响， 对乌江流域的水库及河流进行了半月1次为期1年的现场监测和取样分析. 相对于入库河流， 库区叶绿素a浓度平均提高了5.6倍， 库区表层DIC中HCO3-和溶解CO2比重下降， CO32-比重和DIC碳同位素值（δ13CDIC）上升， 而水库下泄水中DIC各组分却表现出与库区表层相反的地球化学行为. δ13CDIC变化范围为-10.2‰~2.5‰， 表明碳酸盐岩风化、光合作用及呼吸作用共同控制了δ13CDIC的变化. 河流筑坝后浮游植物生物活动增强， 显著影响了原始河流DIC的地球化学行为， δ13CDIC可以用来判断这种变化过程. 河流-水库水体高频率监测对于准确评估筑坝河流CO2释放通量和明确碳循环过程中的源汇关系是非常必要的.
Dissolved inorganic carbon and its isotopic differentiation characteristic in cascade reservoirs in Wujiang River Basin[J]. ,
选择长江右岸最大支流乌江干流上三座不同时期建造的梯级水库作为研究对象, 于2006年4月、7月、10月和2007年1月按水体表层、水深20, 40, 60和80 m分别采集了三座水库的坝前水体分层水样. 分析其中水化学特征、溶解无机碳含量及其同位素组成. 水库表层水体中溶解无机碳(DIC)及其同位素(δ13CDIC)组成总体特征表现为: DIC浓度夏、秋季较低, 冬、春季较高; δ13CDIC值则相反, 夏、秋季节偏正, 冬、春季节相对偏负. 在垂直剖面上, 水体中DIC浓度随水深的增加逐渐上升, 而δ13CDIC随水体深度增加而偏负. 各水库的溶解无机碳同位素组成与天然河流中的差异较大, 而接近自然湖泊情况. 另外, 通过调查不同拦截时间的水库, 发现在水库的上层水体中, δ13CDIC随着水库库龄的增长而偏负, 水库的营养水平随着库龄的增长而逐渐增高. 上述结论表明水坝拦截后河流水化学性质发生了改变, 蓄水河流趋向于向湖沼化方向发展; 溶解无机碳同位素组成分异在一定程度上可用于示踪水库的演化过程.
Spatial difference and causes analysis of the δ15N of suspended particulate matter in the Lancang River Basin[J]. ,
澜沧江流域水体悬浮颗粒物δ15N 空间差异及成因分析[J]. ,
梯级水电建设对澜沧江流域生源物质迁移转化及其生态环境的影响目前受到国内外学者的广泛关注,本文通过使用稳定同位素技术,分析了澜沧江流域悬浮颗粒物氮同位素的空间分布差异及其成因.结果表明,澜沧江上游自然河道水体溶解无机氮(DIN)质量浓度变化范围为0. 28～0. 60 mg·L~(-1),下游水库段DIN质量浓度显著增高,变化范围为0. 39～1. 15mg·L~(-1);上游自然河道段悬浮颗粒物δ~(15)N变化范围为4. 52‰～6. 72‰,下游水库段明显增重其变化范围为2. 3‰～11. 8‰.利用Isosource软件对悬浮颗粒物来源进行分析,结果表明澜沧江流域内工业及生活污水为悬浮物颗粒物氮素的主要贡献源,占比约为42. 43%;土壤有机质、大气沉降、农业化肥的贡献率分别为22. 38%、18. 16%和17. 03%;在该流域内上游自然河道段受工业及生活污水、土壤有机质以及大气沉降共同影响,下游水库段则主要受工业及生活污水的影响.同时小湾、漫湾、大朝山这3个库区内存在藻类吸收同化作用而使得悬浮颗粒物δ~(15)N变轻的现象.
Silicon isotopic composition of dissolved silicon and suspended particulate matter in the Yellow River, China, with implications for the global silicon cycle[J]. ,
The silicon isotopic composition of dissolved silicon and suspended particulate matter (SPM) were systematically investigated in water samples from the mainstem of the Yellow River and 4 major tributaries. The SPM content of the Yellow River varied from 1.4 to 38,560 mg/L, averaging 3568 mg/L, and the δ 30Si of suspended particulate matter (δ 30Si SPM) varied from 0.3‰ to 610.4‰, averaging 610.02‰. The major factors affecting the SPM content and the δ 30Si SPM values in the Yellow River were inferred to be the mineralogical, chemical and isotopic characteristics of the sediments from the Loess Plateau and a combination of the climate and the flow discharge of the river. The major ions in the Yellow River water were Na +, Ca 2+, Mg 2+, HCO 3 61, SO 4 261 and Cl 61. High salt concentration was observed in samples from the middle and lower reaches, likely reflecting the effects of evaporation and irrigation because the Na +, Mg 2+, SO 4 261 and K + concentrations were correlated with the Cl 61 concentration. The dissolved Si concentration (D Si) increased downstream, varying from 0.016 to 0.323 mM. The δ 30Si of dissolved Si (δ 30Si Diss) varied from 0.4‰ to 2.5‰, averaging 1.28‰. The major processes controlling the D Si and δ 30Si Diss of the Yellow River are (a) the weathering of silicate rocks, (b) the formation of phytoliths in plants, (c) the evaporation of water from and the addition of meteoric water to the river system, which only affects concentrations, (d) the adsorption and desorption of aqueous monosilicic acid on iron oxide, and (e) the dissolution of phytoliths in soils. The D Si and δ 30Si Diss values of global rivers vary spatially and temporally in response to changes in climate, chemical weathering intensity and biological activity. The moderately positive δ 30Si Diss values observed in the Yellow River may be attributed to the higher rates of chemical weathering and biological activities that have been observed in this catchment in comparison with those of other previously studied catchments, excluding the Yangtze River. Human activities may also potentially influence chemical weathering and biological activities and affect the D Si and δ 30Si Diss values of the major rivers of the world. Further river studies should be performed to gain a better understanding of the global Si isotope budget.
Silicon isotope compositions of dissolved silicon and suspended matter in the Yangtze River, China[J]. ,
Insights into the transfer of silicon isotopes into the sediment record[J]. ,
The first ??30Sidiatom data from lacustrine sediment traps are presented from Lake Baikal, Siberia. Data are compared with March surface water (upper 180???m) ??30SiDSi compositions for which a mean value of +2.28<mspace width="0.125em" linebreak="nobreak"/>???<mspace linebreak="nobreak" width="0.125em"/>???????????0.09 (95???% confidence) is derived. This value acts as the pre-diatom bloom baseline silicic acid isotopic composition of waters (??30SiDSi???initial). Open traps were deployed along the depth of the Lake Baikal south basin water column between 2012 and 2013. Diatom assemblages display a??dominance (???>???85???%) of the spring/summer bloom species Synedra acus var radians, so that ??30Sidiatom compositions reflect predominantly spring/summer bloom utilisation. Diatoms were isolated from open traps and, in addition, from 3-monthly (sequencing) traps (May, July and August??2012) for ??30Sidiatom analyses. Mean ??30Sidiatom values for open traps are +1.23<mspace width="0.125em" linebreak="nobreak"/>???<mspace linebreak="nobreak" width="0.125em"/>???????????0.06 (at 95???% confidence and MSWD of 2.9, n???=???10). Total dry mass sediment fluxes are highest in June 2012, which we attribute to the initial export of the dominant spring diatom bloom. We therefore argue that May ??30Sidiatom signatures (+0.67<mspace linebreak="nobreak" width="0.125em"/>???<mspace width="0.125em" linebreak="nobreak"/>???????????0.06,???2??) when compared with mean upper water ??30SiDSi initial (e.g. pre-bloom) signatures can be used to provide a snapshot estimation of diatom uptake fractionation factors (??uptake) in Lake Baikal. A ??uptake estimation of ???1.61?????? is therefore derived, although we emphasise that synchronous monthly ??30SiDSi and ??30Sidiatom data would be needed to provide more robust estimations and therefore more rigorously test this, particularly when taking into consideration any progressive enrichment of the DSi pool as blooms persist. The near-constant ??30Sidiatom composition in open traps demonstrates the full preservation of the signal through the water column and thereby justifies the use and application of the technique in biogeochemical and palaeoenvironmental research. Data are finally compared with lake sediment core samples, collected from the south basin. Values of +1.30<mspace width="0.125em" linebreak="nobreak"/>???<mspace width="0.125em" linebreak="nobreak"/>???????????0.08 (2??) and +1.43<mspace linebreak="nobreak" width="0.125em"/>???<mspace linebreak="nobreak" width="0.125em"/>???????????0.13 (2??) were derived for cores BAIK13-1C (0.6???0.8???cm core depth) and at BAIK13-4F (0.2???0.4???cm core depth) respectively. Trap data highlight the absence of a fractionation factor associated with diatom dissolution (??dissolution) (particularly as Synedra acus var radians, the dominant taxa in the traps, is very susceptible to dissolution) down the water column and in the lake surface sediments, thus validating the application of ??30Sidiatom analyses in Lake Baikal and other freshwater systems, in palaeoreconstructions.
Quantifying the impact of freshwater diatom productivity on silicon isotopes and silicon fluxes: Lake Myvatn, Iceland[J]. ,
78 Freshwater diatoms affect continental silicon isotope signal and Si fluxes to ocean. 78 Evidence of the pH dependency of diatom recycling rates in Lake Myvatn, Iceland. 78 Si isotope mass balance highlights up to 33% of biogenic Si recycling in the summer. 78 pH forcing on BSi recycling rates in lakes is crucial for diatom Si supply in ocean. 78 Ocean acidification would reduce diatom productivity and oceanic C storage capacity.