High Water Level Period Research Articles

Mapping inundation dynamics in a heterogeneous floodplain: Insights from integrating observations and modeling approach

Determining the spatiotemporal dynamics of surface water in a heterogeneous floodplain is difficult, especially for its surrounding isolated lakes. Seasonal inundation patterns of these isolated lakes can be misestimated in a hydrodynamic model due to their short and erratic appearances. A surface water time series of Poyang Lake having an 8-day revisit frequency with a 30 m spatial resolution from 2000 to 2016 was conducted for the first time. This study was produced with a modified hierarchical spatiotemporal adaptive fusion model (HSTAFM) by integrating both Landsat and MODIS data. Discrepancies between model-based surface water and remotely-sensed surface water were evaluated, and possible causes were discussed. Results show that the modified HSTAFM can better detect the water features of a floodplain, thereby providing more detailed information in an seasonal isolated lake system than the MODIS MOD13Q1 product. With the fusion product, we found that Poyang Lake evidently shrank after experiencing a longer low-water period after the impoundment of the Three Gorges Dam. A large proportion of these discrepancies (averaging 36%) between model-based and remotely-sensed surface water distributed in seasonal isolated lakes, mainly occurred during high-water level periods. Uncertainties in the hydrodynamic model might attribute to smaller defined lake boundaries, bathymetric variations, human disturbance, and unconsidered groundwater recharge/discharge. These results provide a new insight into the temporally continuous and spatially dynamic assessment of simulated surface water, which is essential for the future improvement in the hydrodynamic model.

Fish Distribution in the Middle Course of a Large Lowland River under the Effect of Hydrophysical Factors

The spatial distribution of fish in two 9-km-long sections of the Khoper River, both in the Khoper Nature Reserve and outside it, has been studied using a horizontal-beam echo sounder. Fish densities in the river-bed stretches with a different degree of meandering and depths and the effect of islands and accumulations of woody debris on fish distribution have been investigated. During the period of high water level (end of spring), all factors under consideration affect the spatial distribution of fish. In autumn, as the water level drops, the difference in densities of fish assemblages decreases in stretches with different degrees of meandering, as well as in those with and without islands, but it increases in parts of the river with different depths.

Periphytic algal community in lentic environments of the Upper Paraná River floodplain: seasonal and spatial variation

Abstract Aim: This study aimed to evaluate the influence of seasonal variation in the hydrological regime and of limnological variables on species richness of periphytic algae in lakes of the Upper Paraná River floodplain. Methods The study area is located in the last undammed stretch of the Paraná River in this floodplain, in which three lakes were sampled quarterly (May, August and November 2014, and February and May 2015) for one year. The periphytic material was obtained from petioles of the aquatic macrophyte Eichhornia azurea (Sw.) Kunth. Results We registered 149 taxa of periphytic algae, distributed in 9 classes. Algal richness changed as a function of the seasonal dynamics of the Paraná River’s hydrological regime. Water level fluctuations directly influenced periphytic algae species. During periods of high water level, species richness increased. Limnological variables showed a close relationship with the hydrological regime, and the dissolved nutrients and turbidity were the abiotic factors that most influenced the algal community. The following species were present in all lakes: Fragilaria capucina Desmazières, Gomphonema gracile Ehrenberg and Navicula cryptotenella Lange-Bertalot (Bacillariophyceae) and two species of the genus Oedogonium (Oedogoniophyceae). Conclusions The hydrological regime of the Paraná River played an important role in structuring communities of periphytic algae. Seasonal variation in hydrological regime and in limnological variables together influenced the species richness of these organisms in these floodplain lakes.

Hydrodynamic and water quality modeling of a large floodplain lake (Poyang Lake) in China.

Floodplain lakes are valuable to humans because of their various functions and are characterized by dramatic hydrological condition variations. In this study, a two-dimensional coupled hydrodynamic and water quality model was applied in a large floodplain lake (i.e., Poyang Lake), to investigate spatial and temporal water quality variations. The model was established based on detailed data such as lake terrain, hydrological, and water quality. Observed lake water level and discharge and water quality parameters (TN, TP, CODMn, and NH4-N) were used to assess model performance. The hydrodynamic model results showed satisfactory results with R2 and MRE values ranging between 0.96 and 0.99 and between 2.45 and 6.14%, respectively, for lake water level simulations. The water quality model basically captured the temporal variations in water quality parameters with R2 of TN, TP, CODMn, and NH4-N simulation ranges of 0.56-0.91, 0.44-0.66, 0.64-0.67, and 0.44-0.57, respectively, with TP of Xingzi Station and CODMn of Duchang Station excluded, which may be further optimized with supplementation of sewage and industrial discharge data. The modeled average TN, TP, CODMn, and NH4-N concentrations across the lake were 1.36, 0.05, 1.99, and 0.48mg/L, respectively. The modeled spatial variations of the lake showed that the main channel of the lake acted as a main pollutant passageway, and the east part of the lake suffered high level of pollution. In addition, consistent with previous water quality evaluations based on field investigations, water quality was the highest (average TN = 1.35mg/L) during high water level periods and the poorest (average TN = 1.96mg/L) during low water level periods. Scenario analysis showed that by decreasing discharge of upstream flow by 20% could result in the increase of TN and TP concentrations by 25.6% and 23.2% respectively. In summary, the model successfully reproduced the complex water and pollutant exchange processes in the systems involving upstream rivers, the Poyang Lake, and the Yangtze River. The model is beneficial for future modeling of the impact of different load reduction and other hydrological regime changes on water quality variation and provides a relevant example for floodplain lake management.

Iron speciation at the riverbank surface in wetland and potential impact on the mobility of trace metals

Fe oxyhydroxides in riverbanks and their high binding capacity can be used to hypothesize that riverbanks may act as a “biogeochemical filter” between wetlands and rivers and may constitute a major mechanism in the trapping and flux regulation of chemical elements. Until now, the properties of Fe minerals have been very poorly described in riverbanks. The goals of the present work are to identify Fe speciation in riverbanks where ferric deposits are observed and to determine their impact on the metal behavior (As, Co, Cu, Ni, Pb, Zn, etc.).At the surface, Fe speciation is mainly composed of small poorly crystalline Fe phases, i.e. ferrihydrite (~30%), Fe-OM associations (~40%) as well as crystalline Fe phases, i.e. goethite (~35%). At the subsurface, the Fe distribution is dominated by goethite (~35%) and Fe-mica (~35%), the proportion of which increases at the expense of ferrihydrite and the Fe-OM associations.At the riverbank surface, ferrihydrite and the Fe-OM associations are therefore the main Fe hosting phases in response to (i) the fast Fe(II) oxidation induced by the presence of O2 and (ii) the high amount of OM favoring the formation of nano-phases bound to OM (Fe monomers, polymers and nanoparticles) and preventing mineralogical transformation (ferrihydrite into goethite).During the high-water level period (high flow), a strong erosion of the riverbank transfers these ferric deposits into the river. However, the physicochemical parameters of the river (pH 6.6–7.6 and continuous oxic conditions) do not promote the dissolution of Fe oxyhydroxides and OM. Ferric deposits and the associated trace metals are therefore maintained as colloids/particles and are exported to the outlet. All of the results presented here demonstrate that the ferric deposits trap metals on a seasonal basis and are therefore a key factor in the mobilization of metals during riverbank erosion by river flow.

Pollution Characteristics and Source Identification of Polycyclic Aromatic Hydrocarbons and Phthalic Acid Esters During High Water Level Periods in the Wuhan Section of the Yangtze River, China

Persistent organic pollutants (POPs) have been detected extensively in water and sediments in China, causing potential risks to the environment and human beings. In this study, the content level, distribution characteristics, and pollution sources of PAHs and PAEs in the water and sediments collected from 15 sites in the Wuhan section of the Yangtze River in August of 2016 were analyzed systematically. The following conclusions were made. The total PAHs concentrations were 20.8-90.4 ng·L-1 (mean value 40.7 ng·L-1) in water and 46.1-424.0 ng·g-1 (mean value 191.8 ng·g-1) in the sediments, while for PAEs, they were 280.9-779.0 ng·L-1 (mean value 538.6 ng·L-1) in water and 1346.2-7641.1 ng·g-1 (mean value 3699.5 ng·g-1) in the sediment. Both PAH and PAE concentrations in water meet the Chinese national water environmental quality standard (GB 3838-2002) with a low degree of pollution. PAH monomers with two to three rings were dominant in water, while those with two to three rings and four rings were dominant in the sediment. DEHP and DBP were the dominant PAE pollutants in both the water and sediment. The ratio and principal component analysis showed that the main source of PAHs in water and the sediment were the emission from coal, biomass combustion, and petroleum sources, while the main sources of PAEs include the plastic and chemical industries and municipal solid wastes. Two types of POPs (PAHs and PAEs) in water and sediment have potentially detrimental effects on human health and monitoring needs to be strengthened. This research provides basic data and technical support for the protection of the Yangtze River.

Monitoring and assessment of seasonal land cover changes using remote sensing: a 30-year (1987-2016) case study of Hamoun Wetland, Iran.

The availability of Landsat data allows improving the monitoring and assessment of large-scale areas with land cover changes in rapid developing regions. Thus, we pretend to show a combined methodology to assess land cover changes (LCCs) in the Hamoun Wetland region (Iran) over a period of 30-year (1987-2016) and to quantify seasonal and decadal landscape and land use variabilities. Using the pixel-based change detection (PBCD) and the post-classification comparison (PCC), four land cover classes were compared among spring, summer, and fall seasons. Our findings showed for the water class a higher correlation between spring and summer (R2 = 0.94) than fall and spring (R2 = 0.58) seasons. Before 2000, ~ 50% of the total area was covered by bare soil and 40% by water. However, after 2000, more than 70% of wetland was transformed into bare soils. The results of the long-term monitoring period showed that fall season was the most representative time to show the inter-annual variability of LCCs monitoring and the least affected by seasonal-scale climatic variations. In the Hamoun Wetland region, land cover was highly controlled by changes in surface water, which in turn responded to both climatic and anthropogenic impacts. We were able to divide the water budget monitoring into three different ecological regimes: (1) a period of high water level, which sustained healthy extensive plant life, and approximately 40% of the total surface water was retained until the end of the hydrological year; (2) a period of drought during high evaporation rates was observed, and a mean wetland surface of about 85% was characterized by bare land; and (3) a recovery period in which water levels were overall rising, but they are not maintained from year to year. After a spring flood, in 2006 and 2013, grassland reached the highest extensions, covering till more than 20% of the region, and the dynamics of the ecosystem were affected by the differences in moisture. The Hamoun wetland region served as an important example and demonstration of the feedbacks between land cover and land uses, particularly as pertaining to water resources available to a rapidly expanding population.

Source and Distribution of Dissolved Metal Ions in the Backwater Area of Pengxi River in Three Gorges Reservoir

This study uses the Gaoyang Lake section of the Pengxi River, the largest tributary on the northern bank of the Three Gorges Reservoir (TGR), as an example for exploring the distributions and dynamics of Ca, Zn, Fe, Cr, Pb, Cu, and Hg ions in the tributaries of TGR where the water level fluctuates due to dam regulation. Samples were taken 21 times, once every 17.3 days, at four sampling sites in Gaoyang Lake, which is in a perennial backwater zone of the Pengxi River, during one year from June 5, 2013 to May 29, 2014. At each sampling site, water samples were taken from the surface layer (0-0.5 m), middle layer, and bottom layer (0.5 m above the bed mud). During winter when the water was not stratified, the middle layer samples were taken at 1/2 depth, and when water was stratified in other seasons, the middle layer samples were taken from the thermal layer. Inductively coupled plasma atomic emission spectrometry (ICP-AES) and cold-vapor atomic absorption methods were adopted to determine the concentrations of the metals. Excel and SPSS were used for data analysis and Matlab for building 3-D prisms displaying concentration distributions of Hg ions in the high water level period (175 m, November-April in the ensuing year), sluicing period (May-middle June), low water level in the flooding season (145 m, June-August), and the storage period (September-November). The results provided the following observations ① Concentrations of Cr, Pb, Cu, Zn, and Hg ions were lower than those in Class Ⅲ of the water environment quality standard (GB 3838-2002). ② Cr, Pb, and Cu had high peak values during the storage and sluicing period, and the lowest values during the high water level period. Cr, Pb, and Cu were derived from the main stream of Yangtze, while Fe and Zn were from the Pengxi River locally. The concentration of Hg ions was affected by both the main stream and endogenous sources. As the water column stratified, metal ions did not mix among the stratified layers in Gaoyang Lake. ③ The conductivity was significantly lower during the high water level period than during other water level periods. The main material that affects the conductivity of Gaoyang Lake could be nonmetallic ions.

Biogeochemical characterization of a Mediterranean shallow lake using stable isotopes: Laguna del Cristo (NW Iberian Peninsula)

The present multi-isotopic study (δ18O–δDwater, δ34S–δ18Odissolved-sulphate, δ13Cdissolved-inorganic-carbon, δ13C–δ18Oshells-modern-gastropods, δ13Cplants, and δ13Csedimentary-organic-matter) is aimed at assessing the hydrogeochemical changes and biogeochemical dynamics in a Mediterranean shallow lake fed by a Quaternary–Tertiary aquifer, the “Laguna del Cristo” (NW Iberian Peninsula), a system sensitive to climate fluctuations, between 2010 and 2011. Lake water is of the bicarbonate type, and there are no major pollutants. δ18O-δDwater values plot on a local evaporation line (δD=5.29δ18O–12.29) indicating that evaporative enrichment had a significant impact on lake water isotopic features. Periods of high water levels are characterized by lower δ34S–δ18Odissolved-sulphate and δ13Cdissolved-inorganic-carbon values and suggest sulphate derived from weathering of sulphides in the catchment area, delivered to the lake by surface run-off or via groundwater, and in situ decay of organic matter. During lower water levels, sulphate reduction and enhanced primary productivity lead to higher δ34Sdissolved-sulphate and δ13Cdissolved-inorganic-carbon values. Evaporation induced enrichment in 18Osulphate, 13Cdissolved-inorganic-carbon and 13C–18Oshells-Galba-Gyraulus. δ13Cplant confirms the C3 photosynthetic pathway. Enrichment in 13C submerged aquatic plants indicates that HCO3− is the main carbon source, except for 13C-depleted Potamogeton. The TOC, δ13Corg values, and TC/TN ratios in sediments all confirm the autochthonous character of organic matter contribution. This study provides a baseline for isotopic research into shallow, flow-through lakes fed by siliciclastic aquifers, and stresses the importance of evaporation and refilling (direct precipitation and groundwater discharge) in controlling the solute chemistry and stable isotopic composition in temperate regions with contrasting seasonal climates. The results also provide a snapshot of modern lake isotope variability that can be applied to paleoenvironmental reconstructions.

Middle Permian environmental changes and shale oil potential evidenced by high-resolution organic petrology, geochemistry and mineral composition of the sediments in the Santanghu Basin, Northwest China

Shales in the Middle Permian Lucaogou Formation have been considered as one of the most important unconventional reservoirs in NW China, due to their excellent shale oil and tight oil potential. Based on the data of previous organic geochemical studies, the overall evolution of the ecosystem in the lake, water conditions and organic matter sources have been outlined. Here we present the results of the mineralogical and organic-petrological examinations and the Rock-Eval pyrolysis, on samples of a fine-grained, mixed carbonate-clastic sedimentary succession from the Santanghu Basin, providing new detailed insights into paleoenvironmental evolution and lake level changes. In addition, shale oil potential was further evaluated on this oil-prone shale.Analytical results from a total of 196 shale samples from the second member of the Lucaogou Formation, collected from one newly drilled core, indicate algal/microbial sources of organic matter, classified by Rock-Eval pyrolysis as type I kerogen. Samples characterized by lower hydrogen index (HI) values (type II kerogen) contain increased contributions of terrigenous organic matter, evidenced by enhanced inertinite and vitrinite contents. Vertical variations in mineralogical and bulk geochemical composition reflect an evolution from a saline, anoxic to a deep, freshwater lake. Two environmental changes subdivided the sequence into three units. The boundary between the lower Unit I and the middle Unit II is characterized by the drastic decrease of smectite and K-feldspar contents and a sharp increase in total organic carbon (TOC) content. The upper Unit III is distinguished by high TOC/S ratios. Based on variations in petrography and carbon isotopes of hopanes, the middle Unit II can be further subdivided into two parts reflecting changes in water level of the lake. All the periods of high-water level are characterized by higher lamalginite contents (>40vol%) and higher HI values than those obtained from sediments deposited during periods of shallower water levels. Deposition in a shallow lake is evidenced by increased dolomite and decreased lamaginite contents. Lake level fluctuations, indicated by mineralogical and geochemical parameters, are associated with changes in organic matter sources, leading to the great variability in mineral content, organic petrography and hydrocarbon generation potential. High TOC and brittle minerals contents, micro-nanopores system and large thickness of the shale show that the Lucaogou Formation holds a significant shale oil potential in areas where oil window maturity is reached.

Fast shoreline erosion induced by ship wakes in a coastal lagoon: Field evidence and remote sensing analysis.

An investigation based on in-situ surveys combined with remote sensing and GIS analysis revealed fast shoreline retreat on the side of a major waterway, the Malamocco Marghera Channel, in the Lagoon of Venice, Italy. Monthly and long-term regression rates caused by ship wakes in a reclaimed industrial area were considered. The short-term analysis, based on field surveys carried out between April 2014 and January 2015, revealed that the speed of shoreline regression was insignificantly dependent on the distance from the navigation channel, but was not constant through time. Periods of high water levels due to tidal forcing or storm surges, more common in the winter season, are characterized by faster regression rates. The retreat is a discontinuous process in time and space depending on the morpho-stratigraphy and the vegetation cover of the artificial deposits. A GIS analysis performed with the available imagery shows an average retreat of 3˗4 m/yr in the period between 1974 and 2015. Digitization of historical maps and bathymetric surveys made in April 2015 enabled the construction of two digital terrain models for both past and present situations. The two models have been used to calculate the total volume of sediment lost during the period 1968˗2015 (1.19×106 m3). The results show that in the presence of heavy ship traffic, ship-channel interactions can dominate the morphodynamics of a waterway and its margins. The analysis enables a better understanding of how shallow-water systems react to the human activities in the post-industrial period. An adequate evaluation of the temporal and spatial variation of shoreline position is also crucial for the development of future scenarios and for the sustainable management port traffic worldwide.

Evidence of exceptional oyster-reef resilience to fluctuations in sea level.

Ecosystems at the land–sea interface are vulnerable to rising sea level. Intertidal habitats must maintain their surface elevations with respect to sea level to persist via vertical growth or landward retreat, but projected rates of sea‐level rise may exceed the accretion rates of many biogenic habitats. While considerable attention is focused on climate change over centennial timescales, relative sea level also fluctuates dramatically (10–30 cm) over month‐to‐year timescales due to interacting oceanic and atmospheric processes. To assess the response of oyster‐reef (Crassostrea virginica) growth to interannual variations in mean sea level (MSL) and improve long‐term forecasts of reef response to rising seas, we monitored the morphology of constructed and natural intertidal reefs over 5 years using terrestrial lidar. Timing of reef scans created distinct periods of high and low relative water level for decade‐old reefs (n = 3) constructed in 1997 and 2000, young reefs (n = 11) constructed in 2011 and one natural reef (approximately 100 years old). Changes in surface elevation were related to MSL trends. Decade‐old reefs achieved 2 cm/year growth, which occurred along higher elevations when MSL increased. Young reefs experienced peak growth (6.7 cm/year) at a lower elevation that coincided with a drop in MSL. The natural reef exhibited considerable loss during the low MSL of the first time step but grew substantially during higher MSL through the second time step, with growth peaking (4.3 cm/year) at MSL, reoccupying the elevations previously lost. Oyster reefs appear to be in dynamic equilibrium with short‐term (month‐to‐year) fluctuations in sea level, evidencing notable resilience to future changes to sea level that surpasses other coastal biogenic habitat types. These growth patterns support the presence of a previously defined optimal growth zone that shifts correspondingly with changes in MSL, which can help guide oyster‐reef conservation and restoration.

Impact of upstream river inputs and reservoir operation on phosphorus fractions in water-particulate phases in the Three Gorges Reservoir

The impoundment of the Three Gorges Reservoir (TGR) has changed water-sand transport regime, with inevitable effects on phosphorus transport behavior in the TGR. In this study, we measured phosphorus fractions in water and suspended particles transported from upstream rivers of the TGR (the Yangtze River, the Jialing River and the Wu River) to reservoir inner region over the full operation schedule of the TGR. The aim was to determine how phosphorus fractions in water and particulate phases varied in response to natural hydrological processes and reservoir operations. The results showed that total phosphorus concentration (TP) in water in the TGR inner region was 0.17±0.05mg/L, which was lower than that in the Yangtze River (0.21±0.04mg/L) and the Wu River (0.23±0.03mg/L), but higher than that in the Jialing River (0.12±0.07mg/L). In the TGR inner region, there was no clear trend of total dissolved phosphorus (TDP), but total particulate phosphorus (TPP) showed a decreasing trend from tail area to head area because of particle deposition along the TGR mainstream. In addition, the concentrations of TPP in water and particulate phosphorus in a unit mass of suspended particles (PP) in the TGR inner region were higher in October 2014 and January 2015 (the impounding period and high water level period) than that in July 2015 (the low water level period). The temporal variations of PP and TPP concentrations in the TGR may be linked to the change of particle size distribution of suspended particles in the TGR. The particle size tended to be finer due to large-size particle deposition under stable hydrodynamic conditions in the process of TGR impoundment, resulting in high adsorption capacities of phosphorus in suspended particles. The results implied that phosphorus temporal variations in the TGR could exert different impacts on water quality in the TGR tributaries.

Analysis of zooplankton assemblages from man-made ditches in relation to current velocity

Abstract Because of the slow current velocity, man-made ditches may create distinct physical and ecological conditions that are suitable for the growth of zooplankton populations. However, the influence of drainage ditches on zooplankton communities has not been studied yet. This study aims to answer the following questions: i) Are man-made ditches a rich source of zooplankton? ii) What current velocity value leads to abundant zooplankton in man-made ditches? iii) Do zooplankton communities differ between man-made ditches and connected natural streams? In man-made drainage ditches with a water current lower than 0.1 m s-1, the abundance of zooplankton was greater than in the majority of streams. Sometimes this level of abundance was equivalent to the densities of zooplankton in lakes or dammed reservoirs. The presence of zooplankton in man-made ditches may be of great importance to the establishment of food webs, particularly during periods of high water levels or heavy rainfall, both of which may accelerate the water current, causing the dispersion of zooplankton along the ditches and into natural streams.

Relations between vegetation and water level in groundwater dependent terrestrial ecosystems (GWDTEs)

Alkaline wetlands and fens are groundwater dependent, terrestrial ecosystems (GWDTEs) existing throughout the temperate zone. They contain a large number of protected and endangered plant species and their ecological status is threatened by insufficient groundwater quality and quantity. However, management and conservation of fens are constrained by limited knowledge on the relations between vegetation and measurable hydrological conditions. This study investigates the relations between vegetation and water level dynamics in groundwater dependent wetlands in Denmark.A total of 35 wetland sites across Denmark were included in the study. The sites represent a continuum of wetlands with respect to vegetation and hydrological conditions. Water level was measured continuously using pressure transducers at each site. Metrics expressing different hydrological characteristics, such as mean water level and low and high water level periods, were calculated based on the water level time series. A complete plant species list was recorded in plots covering 78.5m2 at each site. Community metrics such as total number of species and the number of bryophytes were generated from the species lists and Ellenberg Indicator scores of moisture, pH and nutrients were calculated for each site.The water level correlates with the number of typical fen species of vascular plants, whereas bryophytes are closer connected to the stable water level conditions provided by groundwater seepage. The water level variability is proved to be a significant limiting factor for species diversity in wetlands, which should be considered along with the fertility in order to access the habitat quality. The study provides new insight in the water level preferences for GWDTEs which is highly needed in the management and assessment of anthropogenic damage to these ecosystems.

Restoration of Eutrophic Lakes with Fluctuating Water Levels: A 20-Year Monitoring Study of Two Inter-Connected Lakes

Eutrophication continues to be the most important problem preventing a favorable environmental state and detrimentally impacting the ecosystem services of lakes. The current study describes the results of analyses of 20 year monitoring data from two interconnected Anatolian lakes, Lakes Mogan and Eymir, receiving sewage effluents and undergoing restoration. The first step of restoration in both lakes was sewage effluent diversion. Additionally, in hypertrophic Lake Eymir, biomanipulation was conducted, involving removal of benthi-planktivorous fish and prohibition of pike fishing. The monitoring period included high (H) and low (L) water levels (WL) enabling elucidation of the effects of hydrological changes on lake restoration. In shallower Lake Mogan, macrophyte abundance increased after the sewage effluent diversion in periods with low water levels even at turbid water. In comparatively deeper Lake Eymir, the first biomanipulation led to a clear water state with abundant macrophyte coverage. However, shortly after biomanipulation, the water clarity declined, coinciding with low water level (LWL) periods during which nutrient concentrations increased. A second biomanipulation was conducted, mostly during high water level (HWL) period, resulting in a major decrease in nutrient concentrations and clearer water, but without an expansion of macrophytes. We conclude that repetitive fish removal may induce recovery but its success may be confounded by high availability of nutrients and adverse hydrological conditions.

Highlighting the wide variability in arsenic speciation in wetlands: A new insight into the control of the behavior of arsenic

Although the behavior of Arsenic (As) under reducing conditions in periods of high water levels in wetlands is well understood and documented, there is a lack of information under oxidizing conditions when the water level decreases. In this study, we were interested in the first stage of the oxidizing period, when oxidation products are still in suspension. A soil sample from the Naizin Kervidy wetland (France) was incubated in the laboratory to produce a reduced soil solution. The reduced solution was subsequently oxidized, filtered and ultrafiltered using decreasing pore size membranes (5μm, 3μm, 0.2μm, 30kDa and 5kDa). The distribution of As and Fe was investigated in each size fraction of the oxidized solution and their speciations were studied using XAS, HPLC and SEC-ICP-MS. Organic matter was characterized using thermally assisted hydrolysis and methylation gas chromatography–mass spectrometry (THM-GC–MS) and fluorescence spectroscopy. The majority of the As was present as As(V) but a small amount of As(III) still remained despite the advanced oxidized conditions. In the >0.2μm fractions, the XAS analyses showed that As was associated, in the second shell, with Fe (As–Fe=3.35Å) as bidentate binuclear complexes and C (As–C=2.90Å), suggesting the integration of As in biological objects. In the <30kDa fraction, As was directly bound to C (As–C=1.96Å) in the first shell indicating the presence of organic As species. In the second shell, an As–Fe distance of 3.35Å was found showing that part of the As was still complexed with Fe. The 0.2μm–30kDa fraction was a transitional fraction in terms of the Fe species and OM composition. In this fraction, organic matter exhibited a more humic character (aromatic molecules) inducing an increasing cation binding capacity. As a consequence, in this fraction and in the smallest one, As, Fe and OM seemed to form ternary complexes in which the Fe or nano-oxides in the >30kDa fraction and as monomer, or cluster in <30kDa fraction acted as a bridge. In all of the fractions, a proportion of As(V) was present as organic methylated species. These organic species might be produced by several organisms (animal or plant) via a detoxification process. They seemed to be bound to the particulate and colloidal Fe/OM phases as well as integrated in the remains of the organisms. Mass calculations provided evidence that 90% of the As was contained in the >5μm particulate fraction and thus was hardly mobile. This study showed that although wetlands have been identified as a potential source of As, a number of biological and geochemical trapping mechanisms also favor As stabilization in wetlands.

Relationship of the water supply and drainage in a typical wetland of Lake Poyang

湿地水分在地下水含水层-土壤-植物-大气界面的运移和转换是维持能量和营养物平衡的重要环节，水分运移是湿地生态水文过程研究的关键.数值模型模拟已成为水分运移研究的重要手段，然而限于复杂的湿地自然条件及有限的监测手段，部分界面水分通量连续动态变化数据的获取及定量化工作较为困难，目前应用数值模拟法于湿地水分运移研究的案例仍不多见.本文以鄱阳湖典型湿地为研究区，构建垂向一维数值模型，阐释了湖泊水位显著季节性变化条件下，湿地水分在不同界面的传输过程，量化了湿地水分的补排关系.结果表明：（1）界面水分通量季节性差异大，降雨入渗地面和根系层水分渗漏均对降雨变化响应敏感，主要集中在4-6月，分别占年总量（1450和1053 mm）的65%和73%.土面蒸发和植物蒸腾年总量为176和926 mm，土面蒸发主要受气候条件影响，植物蒸腾还与植物生长特征有关，均集中在7-8月，分别占年总量的30%和47%.深层土壤向浅层根系层的水分补给集中发生在地下水浅埋时段-68月，占年总量（609 mm）的76%；（2）湿地植物根系层水分补排受鄱阳湖水位季节性波动影响显著.除丰水期（7-9月）主要补给为深层土壤水外，退、枯、涨水期的主要补给均为降水入渗.涨水期（4-6月）和枯水期（12-3月）的主要排泄为根系层水分渗漏，丰水期以植物蒸腾排泄为主，退水期（10-11月），土面蒸发与植物蒸腾为主要排泄，且比重相当.本文定量了鄱阳湖典型湿地不同界面水分连续交换关系，区分了土面蒸发和植物蒸腾，辨析了各界面水分的主要影响因子，研究结果有助于深入理解水分在湿地生态系统地下水含水层-土壤-植物-大气界面的相互作用机制，认识湖泊洲滩湿地水量平衡，为揭示湖泊水情变化对湿地生态的可能影响提供依据，为湿地生态水文过程研究提供重要方法和理论参考.;Water movement within the groundwater-soil-plant-atmosphere continuum (GSPAC) plays an important role in maintaining energy and nutrient balance in wetland, and water movement is a key to wetland eco-hydrological process. Numerical simulation is an important method for the study of water movement. However there are few examples of numerical simulation on water movement in wetlands, due to the limitation of complicated natural conditions and restricted monitoring methods. In this paper, a typical wetland in Lake Poyang was selected as a study area. One-dimensional vertical numerical model was used to investigate the water movement process through different interfaces and to quantify relationship of the water supply and drainage. The results showed that, (1) the water fluxes through interfaces were in a significant seasonal variation. The rainfall infiltration and the soil water drainage were sensitive to rainfall, which mainly occurred during April and June, taking 65% and 73% of the annual amount (1450 and 1053 mm), respectively. The soil evaporation and vegetation transpiration were related to climatic conditions and the character of plant growth, which were highest in July-August, taking 30% and 47% of their annual amount (176 and 926 mm), respectively. The upward fluxes from deep soil into root zone mainly occurred in June-August, accounting for 76% of the annual amount (609 mm). (2) The water supply and drainage in plant root zone of the wetland were strongly influenced by the seasonal changes of water level of the Lake Poyang. The main water supply of the root zone is rainfall infiltration except for the high water level period (July-September), in which the upward flow from deep soil is the major water source. In the rising water level (rainy seasons of April-June) and low water level (December-March) periods, the main drainage way is via deep leakage. In the high water level period, the vegetation transpiration is the major water discharge. In lake water level recession period, soil water drainage is mainly via vegetation transpiration and soil evaporation. Our study quantified the water transformation relationship through different interfaces in the typical wetland in Lake Poyang and differentiated the soil evaporation and vegetation transpiration. The results help to better understand the water movement in the GSPAC system and the water balance of lake wetlands, which are essential for lake and wetland managements.

Rule curve for seasonal increasing of water concessions in reservoirs with low regularized discharges

ABSTRACT Regions with high hydrological variability are usually supplied by reservoirs that regularize discharges inter-annually, with low discharge of regularization, seasonally subject to large overflow and evaporation losses in their periods of high water levels. The Brazilian semiarid is one of such regions. This work looks at the possibility of using water that would be evaporated and/or spilled, in regions with such characteristics, to supply demands that would not be otherwise provided by the maximum legally allowed withdrawal discharge. The proposed method was applied to the operation of a large reservoir, located in the semiarid region of Brazil. Through simulation of the water budget and optimization, a rule curve was developed for reservoir operation for achieving the maximum exploitable reservoir withdrawal in rainy periods. The results show that it is possible to use the excess water in periods of large inflows with no damage to water supply during dry periods.

Impact of large water level fluctuations on geomorphological processes and their interactions in the shore zone of a dam reservoir

Abstract Bratsk Reservoir is the second largest reservoir in the world in terms of volume (170 km 3 ) and one of the largest in terms of area (about 5500 km 2 ). It was created in 1967 and is characterized by a long-term exploitation regime, with water level fluctuations of 1.1 to 6.6 m per year and up to 10 m per decade. We summarize a series of detailed field investigations and monitoring conducted in 2001–2013, concerning various geomorphological processes in the shore zone of Bratsk Reservoir. The processes were initiated (bluff recession, accumulation processes, aeolian processes, linear erosion) or intensified (karst processes and landslides) as a result of creation of the reservoir. The course of geomorphological processes is conditioned by water level fluctuations in the reservoir. In periods of high water level, coastal slope erosion with bluff recession and activation of landslides are observed, whereas during low water level, aeolian processes are activated, while karst processes and linear erosion are intensified. Geomorphological processes occurring near the shore of Bratsk Reservoir often interact. Although the reservoir has been exploited for nearly 50 years, the rate of geomorphological processes taking place in its shore zone is not declining, and the area where these processes take place is increasing.