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1.
This 10-year field data study explores the relevance of water level fluctuations in driving the shift from a free-floating plant (FFP) to a phytoplankton dominated state in a shallow floodplain lake from the Lower Paraná River. The multi-year natural flood pulse pattern in the Lower Paraná River drove the ecosystem regime from a FFP-dominant state during very high waters (1998–1999) to absolute phytoplankton prevalence with blooms of nitrogen fixing Cyanobacteria during extreme low waters (2008–2009). Satellite images support the observed changes over the decade and show the decrease of the surface lake area covered by FFP as well as the modification of the spectral firm in open waters, which documents the significant increases in phytoplankton chlorophyll a concentrations. We discuss the possibility that, despite a slow eutrophication in these highly vegetated systems, water level changes and not nutrients account for the shift from a floating macrophyte community to phytoplankton dominance. Cyclic shifts may occur in response to the seasonal floodpulse, but more strongly, as indicated by our results, in association to the extreme drought and flood events related to the El Niño Southern Oscillation, which is linked to discharge anomalies in the Paraná River.  相似文献   

2.
Hydrological connectivity between floodplain wetlands and rivers is one of the principal driving mechanisms for the diversity, productivity and interactions of the major biota in river–floodplain systems. This article describes a method of quantifying flood‐induced overbank connectivity using a hydrodynamic model (MIKE 21) to calculate the timing, the duration and the spatial extent of the connections between several floodplain wetlands and rivers in the Tully–Murray catchment, north Queensland, Australia. Areal photogrammetry and field surveyed stream cross data were used to reproduce floodplain topography and rivers in the model. Laser altimetry (LiDAR)–derived fine resolution elevation data, for the central floodplain, were added to the topography model to improve the resolution of key features including wetlands, flow pathways and natural and artificial flow barriers. The hydrodynamic model was calibrated using a combination of in‐stream and floodplain gauge records. A range of off‐stream wetlands including natural and artificial, small and large were investigated for their connectivity with two main rivers (Tully and Murray) flowing over the floodplain for flood events of 1‐, 20‐ and 50‐year recurrence intervals. The duration of the connection of individual wetlands varied from 1 to 12 days, depending on flood magnitude and location in the floodplain, with some wetlands only connected during large floods. All of the wetlands studied were connected to the Tully River for shorter periods than they were to the Murray River because of the higher bank heights and levees on the Tully River and wetland proximity to the Murray River. Other than hydrology, land relief, riverbank elevation and levee banks along the river were found key factors controlling the degree of connectivity. These variations in wetland connectivity could have important implications for aquatic biota that move between rivers and off‐stream habitats during floods. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

3.
River streamflows are excellent climatic indicators since they integrate precipitation over large areas. Here we follow up on our previous study of the influence of solar activity on the flow of the Paraná River, in South America. We find that the unusual minimum of solar activity in recent years have a correlation on very low levels in the Paraná's flow, and we report historical evidence of low water levels during the Little Ice Age. We also study data for the streamflow of three other rivers (Colorado, San Juan and Atuel), and snow levels in the Andes. We obtained that, after eliminating the secular trends and smoothing out the solar cycle, there is a strong positive correlation between the residuals of both the Sunspot Number and the streamflows, as we obtained for the Paraná. Both results put together imply that higher solar activity corresponds to larger precipitation, both in summer and in wintertime, not only in the large basin of the Paraná, but also in the Andean region north of the limit with Patagonia.  相似文献   

4.
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5.
In the Senegal River valley and Niger Inner Delta, the annual floods inundate a wide floodplain consisting of a complex network of lakes and channels, where topographic information needed by standard hydraulic models is difficult to obtain. To represent the flood propagation between mainstream and floodplain, we use a model designed for flood propagation in river mainstreams with flat bed and large overflow and without topographic data. Depending on the water level in the riverbed, the model calibrated on the levels observed at two stations gives the level in the floodplains and propagation time between stations. Several cases are tested for various types of hydraulic connections between mainstream and floodplain. The model could correctly reproduce the flood rise and fall in the floodplain, even for a lake connected by a single channel to the riverbed or in the case of a strong attenuation of the flood between very distant stations.  相似文献   

6.
We examined the distribution of submerged and emergent macrophyte species and the entire macrophyte community within and between five lake types (highland reservoirs, alkali lakes, large shallow lakes, small to medium sized shallow lakes, marshes) in the Pannon Ecoregion, Hungary. The lowest submerged, emergent and total species richness was found in alkali lakes. The highest submerged macrophyte richness was in small to medium sized lakes, while the highest emergent macrophyte species richness was in reservoirs, small to medium sized lakes, and marshes. The values of within-lake type beta diversity were generally lower than the values of alpha diversity, especially for submerged macrophytes, indicating between site homogeneity in species composition within the lake types. Emergent macrophyte communities contributed the most to within and between lake type diversity and total (gamma) diversity. Canonical correspondence analyses showed that the main environmental variables which influenced the distribution of submerged macrophytes were conductivity, Secchi transparency and water nitrogen contents. For emergent macrophytes conductivity, lake width, altitude and water depth proved to be the most influential variables. Our results contribute to the knowledge of large-scale distribution of macrophytes in the Pannon Ecoregion and to the identification of conservation value of lakes using macrophytes. The results support the importance of small lakes and artificial lakes in the conservation of macrophyte diversity compared to large and natural lakes in the Pannon Ecoregion.  相似文献   

7.
The interactions among hydrogeomorphic features of large lowland rivers regulate the spatio-temporal fluvial dynamics and influence the occurrence and understanding of the ecological patterns in these systems. We studied the hydrogeomorphic features that explain the fluvial dynamics of the Paraná River floodplain and investigated the usefulness of NDVI patterns in summarizing these dynamics. Information layers related to elevation, drainage network, geomorphic units, runoff dynamics, and NDVI patterns of the study area were generated from multi-source remote sensing data and fieldwork measurements. All these layers were integrated and analysed in a GIS environment, and the statistical association among them was corroborated. In our study area, the interaction among hydrogeomorphic features determined a centrifugal flooding pattern through which inundation occurs when water from remote courses, fluvial lakes, and secondary tributaries reaches the main channel. The areas closest to the main channel are flooded only when it overflows. Five NDVI patterns statistically different in terms of their means and standard deviations were identified and characterized. These NDVI patterns were significantly associated with elevation, geomorphic units, and runoff dynamics, highlighting their usefulness to characterize the fluvial dynamics and support understanding of the ecological patterns. © 2020 John Wiley & Sons, Ltd.  相似文献   

8.
To test if phytobenthic algae provide additional important information to macrophytes and phytoplankton for lake monitoring, we sampled two large lakes in Norway. In each lake, we analyzed water chemistry and phytoplankton above the deepest site, recorded macrophytes and non-diatom phytobenthic algae at 20 sites around the shoreline and estimated site-specific nutrient input from land cover. Since no ready-to-use phytobenthos index exists for lakes in Norway, we tested the PIT index developed for rivers, commonly perceived signs of disturbance such as high algal cover, and taxon richness as well as similarity patterns. Both lakes were nutrient poor, but had potential local nutrient inputs (villages, agriculture). In neither of the lakes did phytobenthos indicate a worse overall ecological status than macrophytes and phytoplankton. Our data therefore, did not suggest that it would be useful to add phytobenthos into surveillance monitoring of lakes in Norway. There was a loose correlation between macrophyte and phytobenthic site-specific taxon richness and similarities. This means that macrophytes and phytobenthos do indeed give partly redundant information. High algal cover was found at sites with both high and low phosphorus input. Using algal cover as indicator of site-specific nutrient input is therefore overly simplistic. Urban and cultivated areas were associated with a more eutrophic PIT. This indicates that the PIT, despite being developed for lotic waters, may be used to detect site specific nutrient input in lakes.  相似文献   

9.
We analysed total bacterial number and mean volume of cells at three sites in each of ten floodplain lakes in the Middle Basin of the Biebrza River, North-Eastern Poland to test bacterioplankton communities change according to the distance to the river. The composition of the bacterial communities was determined by fluorescent in situ hybridization method. Total number of bacteria in the lakes ranged from 4.0 to 7.48 cells × 106 mL−1 with dominance by Actinobacteria, the contribution of which was positively correlated with water level. Old river channels (side-arms) featured Alpha- and Gammaproteobacteria. The community of Betaproteobacteria was limited by concentration of dissolved organic carbon. Archaea, in spite of a minor role (<3.65% of DAPI-4′,6-diamidino-2-phenylindole) in the communities, showed a positive relation to floodplain lake isolation. Multivariate analysis demonstrated that bacterioplankton in riverine lakes was similar to that in rivers, while lakes with limited water exchange showed a similarity to fertile lakes. Water level and nutrients were among the factors determining bacterial community structure.  相似文献   

10.
长江中游通江湖泊江湖关系研究进展   总被引：27，自引：8，他引：19  
自然通江的洞庭湖和鄱阳湖与长江之间形成复杂的江湖水沙交换关系,其变化影响着区域洪水灾害防治、水资源利用、水环境保护和水生态安全维护,是长江中游水问题的核心.从长江中游大型通江湖泊江湖关系的概念与内涵、江湖关系演变过程、江湖关系变化的影响因素及效应等方面,系统梳理了长江中游通江湖泊江湖关系研究的进展.针对当前研究现状和存在的问题,提出了研究江湖关系表征指标体系是正确认识江湖关系的前提;定量区分人类活动和气候变化影响的贡献率是江湖关系研究的重点和难点;深入跟踪研究三峡等重大工程对江湖关系变化的影响是一项长期任务;评估江湖关系调整背景下江湖关系的健康状况,研究以江湖水系重大水利工程群联合调度为核心的江湖关系优化调控原理,维持江湖两利的长江中游健康河湖系统格局和相互作用关系是江湖关系研究的根本目标.  相似文献   

11.
Floodplains show a high biodiversity due to their spatial heterogeneity and temporal variability, which are governed by environmental dynamics resulting from the flood pulse. We evaluated the importance of this driving force, the flood pulse, in the structuring of environmental gradients that influence species diversity in a neotropical floodplain. Gamma (γ) and alpha (α) zooplankton diversities were higher in the year with a typical flood pulse (2010), indicating that flood dynamics contributed to high diversity component values. We found significant relationships between α- and β-diversity and local environmental gradients, indicating that in years with a flood pulse, environmental filters might be the dominant mechanisms that structure the zooplankton community. Additive partitioning of γ-diversity showed that even in 2000 with atypical flood conditions, zooplankton diversities showed non-random patterns of spatial distribution and temporal variation in the floodplain. Our results indicate that the driving force of a floodplain can determine the spatial distribution of α- and β-diversity of aquatic communities owing to its primary effect on environmental filters. Therefore, if human activities that influence this driving force, such as water regulation, affect those environmental filters, floodplain biodiversity may decline.  相似文献   

12.
太湖西部环湖河道污染物输移速率变化特征   总被引：8，自引：2，他引：6  
阐明污染物出入湖输移速率对于湖泊陆域污染控制具有重要意义.本文研究了太湖西部主要环湖河道总氮（TN）、溶解性总氮（DTN）、总磷（TP）、溶解性总磷（DTP）和高锰酸盐指数（CODMn）输移速率变化特征.结果表明环湖河道上述指标净输入速率分别为707.9、727.0、28.8、18.2和700.9 g/s.城东港、百渎港、大浦港和沙塘港4条河道TN、DTN、TP、DTP和CODMn输入速率分别占西部河道总输入速率的62.7%、63.6%、67.1%、66.6%和64.8%.太浦河、长兜港和大钱港TN、DTN、TP、DTP和CODMn输出速率占总输出的86.5%、86.9%、85.0%、85.3%和80.6%.污染物净输入速率受水情影响,TN和DTN浓度汛前最大,而TP、DTP、CODMn浓度汛期增大,汛后分别降低44.2%、48.8%和39.8%.城东港氮、磷输入速率受浓度控制,其他河道各指标输移速率受流量控制.近岸湖体TN浓度与入湖速率呈显著正相关,而离岸湖体TN、TP、CODMn浓度对入湖速率的变化响应不明显.  相似文献   

13.
This study tested the hypothesis that the flood pulse affects the diet composition and the niche breadth of Moenkhausia forestii, a small characid fish inhabiting the littoral zone of lakes. To this end, we compared the diet composition (at the population and individual levels) between hydrological periods (high and low water phases) in a floodplain lake of the Upper Paraná River. PERMANOVA revealed differences in the diet between periods (pseudoF1,38 = 8.5; p < 0.001), with predominant consumption of chironomid larvae and Ephemeroptera (aquatic resources) in the low-water period and an increase in the contribution of terrestrial resources (Hymenoptera, Coleoptera, and Orthoptera) during the high-water period. Based on the PERMDISP results, inter-individual variability in M. forestii diet also differed between periods (F1,38 = 5.80; p = 0.02), with higher values during the high-water period resulting in a dietary niche expansion. During the low-water period, we observed the dominance of chironomid larvae in the diets of most individuals, resulting in lower inter-individual variability and thus narrower niche breadth. The diet of M. forestii was affected by the flood pulse at both the population and individual levels. The most important difference was found in the origin of food items; during the low-water period, the diet consisted mainly of aquatic resources, and during the high-water period, there was a large contribution of terrestrial resources. This variation is related to the increased availability of allochthonous resources in the high period, when terrestrial areas are flooded by the overflow of the river, thereby increasing the input of resources into the aquatic environment. The increased availability of food resources during this period allowed the expansion of the trophic niche of M. forestii, accompanied by the highest richness (19 items) and the highest evenness of food items. Our findings demonstrated that the flood pulse affected the composition of the M. forestii diet at both the population and individual levels. These results support the importance of the flood pulse, which connects aquatic and terrestrial ecosystems, in providing food resources for fish.  相似文献   

14.
Abstract

A large dam is planned at Stiegler’s Gorge in Tanzania. The change in the Rufiji River flood pattern will affect downstream ecosystems. This paper concentrates on the highly productive floodplain lakes that play a vital role in local livelihoods. A participatory monitoring system with village-based observers collected water level, rainfall, fisheries and food data from 2001 to 2011. Water balances of the lakes show dependence on the Rufiji River flood, with varying vulnerability. With the dam design flood of 2500 m3 s-1, lakes with a high threshold and small catchment will dry out quickly. Lakes with a lower threshold and substantial catchment are more robust but may still dry out during prolonged local drought. Analysis of rainfall (1923–2012) indicates a recent decrease. The data were analysed through feedback workshops with local observers, government technical staff and researchers. Through this collaborative approach, local capacity in preparing for the post-dam future was enhanced.
Editor D. Koutsoyiannis; Guest editor M. Acreman

Citation Duvail, S., Mwakalinga, A.B., Eijkelenburg, A., Hamerlynck, O., Kindinda, K., and Majule, A., 2014. Jointly thinking the post-dam future: exchange of local and scientific knowledge on the lakes of the Lower Rufiji, Tanzania. Hydrological Sciences Journal, 59 (3–4), 713–730.  相似文献   

15.
Phosphorus has been traditionally regarded as the controlling nutrient for phytoplankton growth, however, N-limitation is likely to occur in several environments. For example, nitrogen is considered the main nutrient limiting phytoplankton in floodplain lakes of the Paraná River basin. However, N2-fixing heterocystous cyanobacteria (N2-cyano) are usually absent in these water bodies. The low pH values frequently found may limit the development of these algae. We hypothesise that long-term lake isolation allows conspicuous phytoplankton growth during summer, resulting in high photosynthetic rates and pH. This scenario combined with low DIN (dissolved inorganic nitrogen) would favour the development of N2-cyano. Phytoplankton composition was studied during 16 months in a vegetated and isolated floodplain lake in the Paraná basin. Additionally, pH was artificially increased in in situ mesocosms to test effects on phytoplankton structure. Lake phytoplankton was dominated by flagellates (cryptophytes and euglenophytes) and small coccoid algae (chlorophytes and colonial cyanobacteria). Algal biomass was highest during warm periods. Although pH increased up to 8.8 during the second summer period, N2-cyano remained rare, most likely because of the high DIN concentration recorded. The alkalophilic diatom Cyclotella meneghiniana dominated and was positively correlated with pH. Conversely, PO4= concentrations in the mesocosm experiment were high and DIN remained relatively low. pH enhancement in the treated mesocosms (avg. pH = 8.2) promoted the development of N2-cyano (Anabaena spp.) and C. meneghiniana, which after 1 month of incubation accounted together for 50% of the biomass in contrast to less than 1.6% in control containers. Our results support the hypothesis that during the warm season and under low DIN concentration, high pH favours N2-cyano growth in these lakes. We provide new evidence supporting the idea that even under optimal nutrient conditions, N2-cyano do not thrive unless other requirements are satisfied.  相似文献   

16.
The ecological functioning of floodplain lakes is largely influenced by the interaction with the river mainstem. In this study, seasonal variation in water chemistry and the relationship with the river conditions were compared between floodplain lakes that differ in the level of connection to the Usumacinta River, the largest river of Mesoamerica. Samples for suspended solids, nutrients, and chlorophyll a were collected through the year in lakes permanently connected to the river and in lakes that only received water from the Usumacinta for a short period during peak flow. Floodplain lakes showed higher total suspended solids than the river during the dry season while during the rainy season greater differences were observed between the river and the lakes, probably explained by higher concentrations in the river and greater sedimentation in the lakes. Greater organic matter content in the suspended solids was observed in the floodplain lakes, particularly in the more isolated lakes, likely related to high algal biomass. Nitrate concentrations were always higher in the river than in the lakes and lower nitrate concentrations occurred at the isolated lakes, suggesting that processes that remove nitrate occur through the year and are a common feature of floodplain lakes. Phosphorus in the connected lakes was higher than in the river only during the dry season, while in the isolated lakes concentrations were always greater than in the river. Chlorophyll a concentrations were higher in the connected lakes than in the river only during the dry season, while the more isolated lakes exhibited higher values through the year, showing signs of eutrophication. Suspended organic matter, nitrate, and chlorophyll showed larger differences between lake and river sites in the more isolated lakes, probably related to greater water residence time and its influence on primary production. Less connected lakes are more vulnerable to flow alteration because the brief period of connection to the river can be compromised and the effects of eutrophication exacerbated.  相似文献   

17.
This study models climate change impacts on the natural flow regime of braided rivers and inflows to hydropower lakes in a New Zealand mountain basin. Flow metrics include the magnitude, frequency, timing and duration of unaltered flows. The TopNet hydrological model was used to simulate impacts in the Upper Waitaki Basin of the South Island for the 1990s, 2040s and 2090s. An average emissions scenario and results from 12 global circulation models were used as input. Indicators of hydrological alteration and Kruskal-Wallis tests were used to evaluate flow differences. Modelled total inflows increase over time for all lakes, with most increases in winter/early spring and small decreases in summer/autumn. High flows generally increase, while low flows decrease. Although these changes may benefit hydropower and floodplain ecology, they may increase flood risk in winter and spring and drought risk in summer and autumn, causing additional challenges managing hydropower operations.
EDITOR M.C. Acreman

ASSOCIATE EDITOR S. Kanae  相似文献   

18.
We evaluated wind as the main structuring force in driving phycoperiphyton structure, community composition and succession in a warm, polymictic shallow lake in southern Brazil. Mangueira Lake is continuously mixed due to its exposure to wind, and during cold fronts the wind changes from the dominant NE direction to a SSW direction. Our question was: could changes in wind forces induce phycoperiphyton succession and determine population structure? To answer this question, we studied the phycoperiphyton successional response to a change in wind forces under three different situations: on clean macrophyte leaves in an open site (Open) and in an enclosed site protected from the wind (Enclosure), and the Natural community growing on uncleaned macrophyte leaves in an open site. Cold fronts improved nutrient availability and changed the algal community. The phycoperiphyton natural community was dominated by Epithemia spp bound in gross masses of green filaments during cold fronts. However, the wind direction typically changes when cold fronts are over (NE-E) and wind blowing from the off-shore direction dislodged the attached algae biomass and pushed it toward to lake shore, inducing community changes. The macrophyte bank exhibited rapid colonization and acted as a refuge for phycoperiphyton, providing habitat heterogeneity, whereas the enclosure acted as a buffer against wind forces, delaying the succession derived from settlement of loosely adhered algae. Furthermore, in the enclosure, the succession only started after a strong disturbance (rain and wind > 10 m s−1) in which lake water flooded the mesocosm inducing colonization. Phycoperiphyton showed resilience and recovered rapidly after the disturbance, when the rain supplied inocula and wind favored colonization with growth forms that take advantage of local conditions, depending of wind dynamics.  相似文献   

19.
Hydrological monitoring in complex, dynamic northern floodplain landscapes is challenging, but increasingly important as a consequence of multiple stressors. The Peace-Athabasca Delta in northern Alberta, Canada, is a Ramsar Wetland of International Importance reliant on episodic river ice-jam flood events to recharge abundant perched lakes and wetlands. Improved and systematic monitoring of landscape-scale hydrological connectivity among freshwater ecosystems (rivers, channels, wetlands, and lakes) is needed to guide stewardship decisions in the face of climate change and upstream industrial development. Here, we use water isotope compositions, supplemented by measurements of specific conductivity and field observations, from 68 lakes and 9 river sites in May 2018 to delineate the extent and magnitude of spring ice-jam induced flooding along the Peace and Athabasca rivers. Lake-specific estimates of input water isotope composition (δI) were modelled after accounting for influence of evaporative isotopic enrichment. Then, using the distinct isotopic signature of input water sources, we develop a set of binary mixing models and estimate the proportion of input to flooded lakes attributable to river floodwater and precipitation (snow or rain). This approach allowed identification of areas and magnitude of flooding that were not captured by other methods, including direct observations from flyovers, and to demarcate flow pathways in the delta. We demonstrate water isotope tracers as an efficient and effective monitoring tool for delineating spatial extent and magnitude of an important hydrological process and elucidating connectivity in the Peace-Athabasca Delta, an approach that can be readily adopted at other floodplain landscapes.  相似文献   

20.
长江中下游安庆沿江湖泊湿地夏季鸟类多样性调查   总被引：3，自引：3，他引：0  
湖泊湿地是鸟类的重要栖息地,湖泊湿地鸟类是湖泊生态系统重要的监测生物,湖泊湿地鸟类多样性及其影响因素的研究对湿地管理具有重要意义.2011年7-8月,采用样线法对长江中下游安庆沿江7个湖泊湿地的夏季鸟类资源进行了调查,以期为湖泊湿地资源管理提供依据.共记录到安庆沿江湖泊湿地鸟类14目35科82种,其中留鸟27种(占32.9%),夏候鸟37种(占45.1%);水鸟28种(占34.6%);肉食性、食虫和杂食性鸟类占多数,分别占30.5%、30.5%和23.2%;须浮鸥、夜鹭、丝光椋鸟、黑脸噪鹛、树麻雀、家燕等6种鸟类为优势种.物种数以黄大湖最高(50种),白荡湖和破罡湖最低(各28种);Shannon-Wiener指数以黄大湖最高(2.123),白荡湖最低(1.918);均匀度指数以龙感湖最高(0.865),菜子湖最低(0.739).进一步分析显示,鸟类物种数、多样性指数与湖泊面积呈显著正相关,鸟类物种数、多样性指数与干扰强度呈显著负相关.采取退田还湖、恢复湿地等途径增加湿地面积、生境类型和植被资源对于保护湖泊湿地的鸟类资源具有积极意义.  相似文献   

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