Investigating the effects of point source and nonpoint source pollution on the water quality of the East River (Dongjiang) in South China

Understanding the physical processes of point source (PS) and nonpoint source (NPS) pollution is critical to evaluate river water quality and identify major pollutant sources in a watershed. In this study, we used the physically-based hydrological/water quality model, Soil and Water Assessment Tool, to investigate the influence of PS and NPS pollution on the water quality of the East River (Dongjiang in Chinese) in southern China. Our results indicate that NPS pollution was the dominant contribution (>94%) to nutrient loads except for mineral phosphorus (50%). A comprehensive Water Quality Index (WQI) computed using eight key water quality variables demonstrates that water quality is better upstream than downstream despite the higher level of ammonium nitrogen found in upstream waters. Also, the temporal (seasonal) and spatial distributions of nutrient loads clearly indicate the critical time period (from late dry season to early wet season) and pollution source areas within the basin (middle and downstream agricultural lands), which resource managers can use to accomplish substantial reduction of NPS pollutant loadings. Overall, this study helps our understanding of the relationship between human activities and pollutant loads and further contributes to decision support for local watershed managers to protect water quality in this region. In particular, the methods presented such as integrating WQI with watershed modeling and identifying the critical time period and pollutions source areas can be valuable for other researchers worldwide.     

Development and application of watershed-scale indicator to quantify non-point source P losses in semi-humid and semi-arid watershed,China

Quantifying non-point source (NPS) phosphorus (P) pollution loads is essential for watershed nutrients management. This study intended to develop a NPS P indicator which (1) was suitable in semi-humid and semi-arid watersheds of Northern China; (2) integrated the key NPS P loss factors and constructed them in a simple and physically understandable way and (3) kept P loss forms distinctively separate. An inverse distance-based delivery ratio was proposed to count for the P delivery efficiency from source to watercourses. We applied this P indicator in Luan River Watershed (LRW) of northern China under typical hydrological years and seasons. Results demonstrated that this NPS P indicator predicted reasonable NPS TP loads using simple methods and readily obtainable inputs. The sub-watersheds located in the south of LRW were recognized as the high risk areas of NPS P loss to Panjiakou reservoir. The upland and paddy fields near the river channels were particularly posing high risk and thus should be treated with prioritized management practices such as soil conservation and recommended fertilization. Rainfall-runoff related variables rather than P source variables explained more of the spatial variation in NPS P load and percentages. Using this tool could give policy makers insight into the component and location of NPS P pollution that needs to be the focus of policy at watershed scales before sophisticated studies were conducted in smaller scales.     

河流干支流水质与土地利用的相关关系

为探索不同等级河流水质状况及其对土地利用构成响应的差异,以江苏北部的灌河流域为研究对象,基于2006—2007年两个年度灌河及其支流的水质监测数据和研究区的Landsat TM影像,在河流两侧长度0.0—10.0 km、宽度0.0—0.5 km的范围内,运用多元回归分析,对研究区干、支流主要水质指标及其与相应土地利用构成的关系进行了研究。结果表明:2006—2007年间,研究区干流水质总体上显著好于支流,支流的总氮(TN)、总磷(TP)等营养盐指标显著高于干流,而干流的有机污染指标显著高于支流;比较不同观测尺度上土地利用构成对河流水质变化的方差贡献率发现,缓冲区宽度一定时,支流在所有观测尺度上的土地利用构成与水质变化皆存在显著相关关系,而干流仅在缓冲区长度0.0—4.0 km的观测尺度上其土地利用构成与水质变化的相关关系显著;缓冲区长度一定时,干、支流河道两侧0.0—0.3 km间土地利用状况对水质变化的解释能力较大。同时发现,氮、磷等营养盐浓度多与较大尺度上的土地利用构成相关,而化学需氧量(COD)、生化需氧量(BOD)等多与较小尺度上的土地利用构成相关。研究结果显示,有必要区分不同河流等级,选择适宜的观测尺度,分别研究不同水质指标与土地利用构成间的相关关系。     

Application of watershed analyses and ecosystem modeling to investigate land–water nutrient coupling processes in the Guadalupe Estuary, Texas

Estuarine nutrient enrichment is thought to be controlled by land use patterns in coastal watersheds. Hence, the objective of this work was to conduct a watershed analysis in two adjacent river basins with different land use characteristics to determine their influence on estuarine ecosystem response in the Guadalupe Estuary, Texas, U.S.A. All data sources for this study were available electronically on the Internet; the data were mined, managed, analyzed and transformed to simulate the estuarine ecosystem response to watershed-derived nutrient loads. Between 1992 and 2001, developed land use/land cover increased the most while forest cover decreased the most in both basins. Two hydrologic units nearest the coast were responsible for the greatest change in land cover. Nutrient concentrations and loads were significantly higher in the San Antonio River Basin than in the Guadalupe River Basin. Both river basins exhibited the highest flows ever recorded in 1992, however the magnitude of difference in loads between the two coastal hydrologic units for a wet and dry year was much greater in the Guadalupe River Basin (GRB) than in the San Antonio River Basin (SARB); this difference supports the concept that the GRB is a nonpoint source dominated system and SARB is a point source dominated system. There was a strong correlation between developed land use and nutrient concentrations in river water; the GRB had less developed land use and lower nutrient concentrations while the SARB had more developed land use and higher nutrient concentrations. Estuarine ecosystem response differed in the timing, duration and magnitude of DIN, phytoplankton and zooplankton when nitrogen loads from the Lower Guadalupe River were used as opposed to the Lower San Antonio. The two basins studied differ in their fundamental characteristics, i.e. precipitation, flow, human population density, etc., resulting in different drivers of nitrogen loading, point sources in the San Antonio River Basin and nonpoint sources in the Guadalupe River Basin, therefore, differing estuarine ecosystem responses.     

辽宁中部城市群城市非点源污染负荷评估

过去几十年我国经历了快速城市化过程,这使得不透水面大幅度增加,导致地表径流和洪峰流量增加,进入水体的污染物增多。城市非点源污染已成为河流水体恶化、生态系统退化的重要原因。在快速城市化过程中,城市群已成为城市化发展的新阶段。位于同一流域的各城市所产生的城市非点源污染导致城市群流域水环境问题越来越突出,成为制约城市群流域可持续发展的关键因素之一。现有的关于城市非点源的研究多集中于城市内部小尺度,对城市群大尺度的研究亟需发展。以位于浑河太子河流域的辽宁中部城市群为例,在沈阳市不同功能区和不同下垫面进行降雨径流采样,基于事件平均浓度（Event Mean Concentration, EMC）法和SWMM（Storm Water Management Model）模型相结合的方式,定量评估城市群流域城市非点源污染负荷。研究结果表明：路面径流中城市非点源污染物浓度、负荷量及其单位面积负荷要高于屋面径流和透水面径流。辽宁中部城市群TP、TN、COD、TSS的年均城市非点源污染负荷分别为265.52、852.89、2249.71、192496.74 t/a,重金属Cd、Ni、Pb、Cr、Cu、Zn的年均城市非点源污染负荷分别为347.99、9932.62、25861.29、28360.41、36068.30、138840.42 kg/a。沈阳市城市非点源污染负荷最高,但其单位面积负荷最低。本研究基于更为精细的城市下垫面划分,综合考虑城市功能区划、下垫面类型和降雨强度,更为准确的评估了辽宁中部城市群流域的城市非点源污染负荷。该研究能够为高度城市化流域城市非点源污染防控和水环境综合治理提供科学依据。     

不同土地覆被格局情景下多种生态系统服务的响应与权衡——以雅砻江二滩水利枢纽为例

在二滩水库集水区,按照当地生态政策发展以坡度为指标构建了10种未来土地覆被格局情景,研究生态系统减轻水库泥沙淤积、减轻水库面源污染、产水发电服务及价值对未来覆被格局的响应程度,并兼顾相关产业收益的变化,权衡各种情景格局的服务效益,优选利益相关方福祉提升幅度最大的情景格局。结果表明:1)现有土地覆被格局对减轻水库泥沙淤积功效的发挥不合理,而以退耕还林政策指导区域土地覆被格局变化,对集水区减轻河道和水库泥沙淤积具有较好功效。10种情景下,保沙价值的高低关系同入库泥沙量正好相反,遵循"随地表林地和草地面积比例的增加,保沙价值增加"的规律。随产沙总量的增加,高产沙强度像元呈现从水库周边逐渐向中上游蔓延的趋势。2)退耕还林政策单纯以坡度作为指标,指导土地覆被的转化,对集水区减轻水环境磷素非点源污染功效较差。除了全为未利用地覆被的情景10,余下9类情景模拟的入库磷素量及过滤磷素经济价值的高低关系完全一致,呈农田草地林地的规律。随入库磷素总量的增加,高强度磷素输出像元从雅砻江流域源区和大河湾区,逐渐蔓延扩散至集水区整个水网。3)随着集水区地表林地覆盖面积比例的减少,集水区生态系统总发电净利润值增加,且高净利润像元呈现从冕宁和喜德县的东部逐渐向整个集水区东南部乃至整个下游蔓延的趋势。4)从减轻对环境的负效应以及提升利益相关方福祉的角度,以坡度6°上下划分林地和耕地的情景5和以坡度15°和6°为阈值划分林草农的情景3为除极端的情景外,综合指标提升最高的两种情景。     

Ecological responses to nutrients in streams and rivers of the Colorado mountains and foothills

1. Abundance and composition of periphyton and benthic macroinvertebrates were treated as potential nutrient response variables for 74 streams in montane Colorado. The streams ranged from unenriched to mildly enriched with nutrients (N, P). 2. The study showed no meaningful relationship between periphyton biomass accumulation and concentrations of total or dissolved forms of nitrogen or phosphorus. Nutrient concentrations were also unrelated to periphyton and macroinvertebrate richness, diversity and community composition. Macroinvertebrate communities did, however, show a strong positive relationship to periphyton abundance. 3. A positive response of periphyton biomass to increasing nutrient concentrations has been well documented over large ranges of nutrient concentrations. Our study suggests that the nutrient response is suppressed by other controlling factors on the lower limb of the nutrient response curve (i.e. at low nutrient concentrations); a quantitatively significant response occurs only in excess of a threshold beyond which nutrients become dominant over other controlling factors. This interpretation of the results is consistent with published meta‐analyses showing lack of nutrient response for a high proportion of experimentally enriched periphyton communities, and division of responses between N and P for communities that do show growth in response to enrichment. 4. Grazing probably is not the key controlling variable for periphyton in Colorado mountain streams, given that the highest chlorophyll concentrations are associated with the highest abundances of macroinvertebrates. Modelling indicates that the initial amount of periphyton biomass at the start of the growing season, in conjunction with elevation‐related length of the growing season and water temperature, explains most of the variation in periphyton accumulation among these streams, but there is a yet unexplained suppression of periphyton growth rates across all elevations.     

Inter-annual,seasonal and spatial variability in nutrient limitation of phytoplankton production in a river impoundment

We characterize seasonal and spatial patterns in phytoplankton abundance, production and nutrient limitation in a mesotrophic river impoundment located in the southeastern United States to assess variation arising from inter-annual differences in watershed inputs. Short-term (48 h) in situ nutrient addition experiments were conducted between May and October at three sites located along the longitudinal axis of the lake. Nutrient limitation was detected in 12 of the 18 experiments conducted over 2 years. Phytoplankton responded to additions of phosphorus alone although highest chlorophyll concentrations were observed in enclosures receiving combined (P and N) additions. Growth responses were greatest at downstream sites and in late summer suggesting that those populations experience more severe nutrient limitation. Interannual variation in nutrient limitation and primary production corresponded to differences in the timing of hydrologic inputs. Above average rainfall and discharge in late-summer (July–October) of 1996 coincided with higher in-lake nutrient concentrations, increased production, and minimal nutrient limitation. During the same period in 1995, discharge was lower, nutrient concentrations were lower, and nutrient limitation of phytoplankton production was more pronounced. Our results suggest that nutrient limitation is common in this river impoundment but that modest inter-annual variability in the timing of hydrologic inputs can substantially influence seasonal and spatial patterns.     

流域水文模型在面源污染模拟与管控中的应用研究进展

面源污染是影响流域水环境和水安全的重要污染来源,对其进行有效防控需要对其负荷以及防控措施效果进行科学高效精准的预测。流域水文模型(Hydrological Simulation Program-FORTRAN,HSPF)具有突出的综合性和灵活性,是面源污染模型的典范。近年来,HSPF模型应用于我国流域面源污染相关的研究和实践有了飞速发展,但同样也面临着模型机理和参数本地化、模型构建精细化、模型结构不确定性较大等方面的挑战。围绕该模型在面源污染模拟与管控中的研究进展,对其在变化环境下的模拟方法和成果,以及应对参数识别、不确定性分析、措施效果评估和总量控制的思路和方法等方面进行了总结,并分析了现代化环境模拟形势下HSPF模型的延伸发展。结合模型相关研究的总结,强调了面向我国流域特色的本地化模型改进、服务河长制精细监管的大尺度精细化模拟、以及模型与大数据统计及人工智能耦合的互馈集合模拟等后续研究是需要重点关注的发展动向。     

中国东北地区非点源污染研究进展

为掌握东北地区非点源污染研究动态和明确研究中存在的问题和不足,对近20年（1991-2008年）东北地区有关非点源污染研究成果进行检索、分类和统计分析,以便更好地进行区域水环境治理和污染防治.东北地区非点源污染研究总体呈增加趋势;研究内容包括水环境污染源调查分析与评价、污染负荷量化、机理探索、模型模拟和污染防治5类;研究对象包括氮、磷、泥沙、农药和重金属;经验方法估算污染负荷较多,机理模型应用成功实例较少;研究性论文中以农业非点源污染较多,城市非点源污染较少;治理措施停留在水土保持措施层面上,缺乏对水土保持措施的优选评价和对最佳管理措施的评价研究.目前,东北地区非点源污染研究处在理论探索阶段,非点源污染是否是主要污染源还存在争议.今后应着力于措施应用、评价和基础数据收集及区域非点源污染物的确定和污染负荷的量化研究;尝试新技术和多领域交叉合作,为区域水环境治理提供科学依据.     

Vertical Variation of Nonpoint Source Pollutants in the Three Gorges Reservoir Region

Nonpoint source (NPS) pollution is considered the main reason for water deterioration, but there has been no attempt to incorporate vertical variations of NPS pollution into watershed management, especially in mountainous areas. In this study, the vertical variations of pollutant yields were explored in the Three Gorges Reservoir Region (TGRR) and the relationships between topographic attributes and pollutant yields were established. Based on our results, the pollutant yields decreased significantly from low altitude to median altitude and leveled off rapidly from median altitude to high altitude, indicating logarithmic relationships between pollutant yields and altitudes. The pollutant yields peaked at an altitude of 200–500 m, where agricultural land and gentle slopes (0–8°) are concentrated. Unlike the horizontal distributions, these vertical variations were not always related to precipitation patterns but did vary obviously with land uses and slopes. This paper also indicates that altitude data and proportions of land use could be a reliable estimate of NPS yields at different altitudes, with significant implications for land use planning and watershed management.     

Periphyton nutrient status in a temperate stream with mixed land-uses: implications for watershed nitrogen storage

We sampled periphyton communities in a highly productive stream to characterize how longitudinal changes in watershed geology and land use affect periphyton nutrient status and elemental composition. Nutrient status was evaluated from measures of periphyton nutrient composition (carbon, nitrogen, and phosphorus), stable isotope signatures (δ¹⁵N and δ¹³C), and the response of periphyton to experimental enrichment with nitrogen. Biomass and nutrient content increased dramatically from the headwaters to downstream, while tissue nutrient ratios (C:P and C:N) were more consistent and did not indicate strong N- or P-limitation. Nitrogen enrichment experiments did not exhibit a consistent response upstream or downstream, and periphyton C:N:P stoichiometry showed no significant response to N-enrichment. Absolute densities of periphyton N were 5- to 90-fold greater than the overlying N concentrations in stream water (159- to 353-fold greater for P), and the δ¹⁵N signal indicates downstream enrichment from likely watershed sources (urban and agriculture land-use). These results suggest that periphyton in Spring Creek are not N-limited and store large quantities of both N and P, which in turn can be transported downstream during high flow events. Handling editor: David Hamilton     

农业政策环境扩展模型在我国农业面源污染研究中的应用

我国的面源污染问题逐渐受到政府和科学界的重视,然而面源污染是一个复杂的系统过程,涉及多种因素和多个过程。面源(NPS)污染模型作为解决面源污染相关问题的研究和管理工具,在进行面源污染总量估算和严重程度评价、污染物流失路径和影响因素分析、治理策略制定等方面都有重要的作用。在我国,虽然针对面源污染模型进行了大量相关研究,既包含对基于国外模型的应用与验证,也包含基于观测数据自主研发的模型,但仍然存在模型应用和验证案例不足、已有的模型应用同中国面源污染特征结合不足、模型发展同面源污染机理研究结合不足等问题,而农业政策环境扩展(APEX)模型在应对这些问题上具有一定的优势。结合我国面源污染模型相关研究存在的问题、APEX模型模块和研究进展进行了介绍,对APEX模型在我国面源污染相关问题的研究中涉及的畜禽养殖、复杂耕作系统、特定BMP和水稻田的模拟等相关问题的应用前景进行了探讨,以期能够促进我国农业面源污染模型的发展。     

基于非点源污染控制的景观格局优化方法与原则

对目前国内外较为常用的基于非点源污染控制的景观格局优化方法及其设计原则进行了系统的评述 ,以促进其推广应用并提高其污染控制效果。还通过分析这些方法在我国的应用前景 ,强调了探索适合我国国情的景观格局优化方法对于控制非点源污染的重要意义。     

Nitrogen Loss Estimation Worksheet (NLEW): an agricultural nitrogen loading reduction tracking tool

The Neuse River Basin in North Carolina was regulated in 1998, requiring that all pollution sources (point and nonpoint) reduce nitrogen (N) loading into the Neuse Estuary by 30%. Point source N reductions have already been reduced by approximately 35%. The diffuse nature of nonpoint source pollution, and its spatial and temporal variability, makes it a more difficult problem to treat. Agriculture is believed to contribute over 50% of the total N load to the river. In order to reduce these N inputs, best management practices (BMPs) are necessary to control the delivery of N from agricultural activities to water resources and to prevent impacts to the physical and biological integrity of surface and ground water. To provide greater flexibility to the agricultural community beyond standard BMPs (nutrient management, riparian buffers, and water-control structures), an agricultural N accounting tool, called Nitrogen Loss Estimation Worksheet (NLEW), was developed to track N reductions due to BMP implementation. NLEW uses a modified N-balance equation that accounts for some N inputs as well as N reductions from nutrient management and other BMPs. It works at both the field- and county-level scales. The tool has been used by counties to determine different N reduction strategies to achieve the 30% targeted reduction.     

Ecological responses of aquatic macrophytes and benthic macroinvertebrates to dams in the Henares River Basin (Central Spain)

The ecological responses of aquatic macrophytes and benthic macroinvertebrates to deep-release dams in three impounded rivers of the Henares River Basin (Central Spain) were studied, specially focusing on the effects of nutrient enrichment caused by deep releases on these two freshwater communities. Three sampling sites, one upstream and two downstream from the reservoir, were established in each impounded river. Sampling surveys to collect submersed macrophytes and benthic macroinvertebrates at each sampling site were carried out in spring–summer of 2009 and 2011. Water temperature tended to decrease downstream from dams, whereas nitrate and phosphate concentrations tended to increase. These abiotic changes, particularly the downstream nutrient enrichment, apparently affected the macrophyte and macroinvertebrate communities. In the case of submersed macrophytes, total coverage and taxa richness increased downstream from dams. In the case of benthic macroinvertebrates, total density and total biomass also increased downstream, but taxa richness tended to decrease. Scrapers appeared to be the macroinvertebrate feeding group most favored downstream from dams as a probable consequence of the positive effect of nutrient enrichment on periphyton and perilithon abundance. Nutrients would ultimately come from water runoff over agricultural lands and over semi-natural forests and pastures, being subsequently accumulated in the hypolimnion of reservoirs.     

A Topography Analysis Incorporated Optimization Method for the Selection and Placement of Best Management Practices

Best Management Practices (BMPs) are one of the most effective methods to control nonpoint source (NPS) pollution at a watershed scale. In this paper, the use of a topography analysis incorporated optimization method (TAIOM) was proposed, which integrates topography analysis with cost-effective optimization. The surface status, slope and the type of land use were evaluated as inputs for the optimization engine. A genetic algorithm program was coded to obtain the final optimization. The TAIOM was validated in conjunction with the Soil and Water Assessment Tool (SWAT) in the Yulin watershed in Southwestern China. The results showed that the TAIOM was more cost-effective than traditional optimization methods. The distribution of selected BMPs throughout landscapes comprising relatively flat plains and gentle slopes, suggests the need for a more operationally effective scheme, such as the TAIOM, to determine the practicability of BMPs before widespread adoption. The TAIOM developed in this study can easily be extended to other watersheds to help decision makers control NPS pollution.     

Simulation of watershed hydrology and stream water quality under land use and climate change scenarios in Teshio River watershed,northern Japan

Quantitative prediction of environmental impacts of land-use and climate change scenarios in a watershed can serve as a basis for developing sound watershed management schemes. Water quantity and quality are key environmental indicators which are sensitive to various external perturbations. The aim of this study is to evaluate the impacts of land-use and climate changes on water quantity and quality at watershed scale and to understand relationships between hydrologic components and water quality at that scale under different climate and land-use scenarios. We developed an approach for modeling and examining impacts of land-use and climate change scenarios on the water and nutrient cycles. We used an empirical land-use change model (Conversion of Land Use and its Effects, CLUE) and a watershed hydrology and nutrient model (Soil and Water Assessment Tool, SWAT) for the Teshio River watershed in northern Hokkaido, Japan. Predicted future land-use change (from paddy field to farmland) under baseline climate conditions reduced loads of sediment, total nitrogen (N) and total phosphorous (P) from the watershed to the river. This was attributable to higher nutrient uptake by crops and less nutrient mineralization by microbes, reduced nutrient leaching from soil, and lower water yields on farmland. The climate changes (precipitation and temperature) were projected to have greater impact in increasing surface runoff, lateral flow, groundwater discharge and water yield than would land-use change. Surface runoff especially decreased in April and May and increased in March and September with rising temperature. Under the climate change scenarios, the sediment and nutrient loads increased during the snowmelt and rainy seasons, while N and P uptakes by crops increased during the period when fertilizer is normally applied (May through August). The sediment and nutrient loads also increased with increasing winter rainfall because of warming in that season. Organic nutrient mineralization and nutrient leaching increased as well under climate change scenarios. Therefore, we predicted annual water yield, sediment and nutrient loads to increase under climate change scenarios. The sediment and nutrient loads were mainly supplied from agricultural land under land use in each climate change scenario, suggesting that riparian zones and adequate fertilizer management would be a potential mitigation strategy for reducing these negative impacts of land-use and climate changes on water quality. The proposed approach provides a useful source of information for assessing the consequences of hydrology processes and water quality in future land-use and climate change scenarios.     

Nutrient budgets and biogeochemistry in an experimental agricultural watershed in Southeastern China

During a two-year field study, an annual nutrient budget and cycles were developed for a small agricultural watershed. The study emphasized the integrated unit of the watershed in understanding the biogeochemistry. It was found that the total nutrient input was 39.1× 10⁴ kg nitrogen and 3.91×10⁴ kg phosphorus in the year 1995, of which the greatest input of nutrients to the watershed was chemical fertilizer application, reaching 34.7×10⁴ kg (676 kg/ha) nitrogen and 3.88×10⁴ kg (76 kg/ha) phosphorus. The total nutrient output from the watershed was 13.55×10⁴ kg nitrogen and 0.40×10⁴ kg phosphorus, while the largest output of nitrogen was denitrification, accounting for 44.1% of N output; the largest output of phosphorus was sale of crops, accounting for 99.4% of P output. The results show that the nutrient input is larger than output, demonstrating that there is nutrient surplus within the watershed, a surplus which may become a potential source of nonpoint pollution to area waters. The research showed that both denitrification and volatilization of nitrogen are key ways of nitrogen loss from the watershed. This suggests that careful management of fertilizer application will be important for the sustainable development of agriculture.The research demonstrated that a multipond system within the watershed had high retention rate for both water and nutrients, benefiting the water, nutrient and sediment recycling in the terrestrial ecosystem and helping to reduce agricultural nonpoint pollution at its source. Therefore, this unique watershed system should be recommended due to its great potential relevance for sustainable agricultural development.     

Macroinvertebrate food web structure in a floodplain lake of the Bolivian Amazon

Two stable isotopes δ¹³C and δ¹⁵N were used to identify the energy sources and trophic relationships of the main freshwater macroinvertebrates in a floodplain lake of the Beni River (Bolivian Amazonia). Four energy sources (seston, bottom sediment, periphyton, and aquatic macrophytes) and macroinvertebrate communities were collected during three periods of the river hydrological cycle. Macroinvertebrates showed greater temporal variation in isotope values than their food sources. Six trophic chains were identified: four were based on seston, periphyton, C₃ macrophytes, and bottom sediments, and the last two chains on a combination of two carbon sources. One mixed seston and periphyton sources during the wet season while the other mixed periphyton and macrophytes sources during the wet and dry seasons. Periphyton was the most important energy source supporting the highest number of trophic levels and consumers. The macrophytic contribution was only significant during the dry season. Bottom sediments constituted a marginal energy source. As each season is associated with different physical and chemical conditions, processes organizing macroinvertebrate food web structure in the Beni floodplain seem strongly linked to hydrological seasonality.