High Water-level Fluctuations Research Articles

Uncertainties in wetland methane-flux estimates.

The wetland at Old Woman Creek National Estuarine Research Reserve, with flux tower US-OWC, which is characterized by high methane fluxes, high spatial heterogeneity, dynamic hydrology and water level fluctuations, and high lateral transport of dissolved organic carbon and nutrients, embodies many of the challenges in modeling methane fluxes.

Are Water Level Fluctuations and Pelagic Water Quality in Lake Kinneret Directly Related? Perspectives of Nutrient Dynamics

Long-term records of Water Level Fluctuations (WLF) and nutrient dynamics in Lake Kinneret have indicated an independence between them. The winter’s high WLF with nutrient-rich conditions and the summer’s low WLF with nutrient-poor conditions are recurrent states. Are Water Level Fluctuations and Lake Kinneret’s pelagic water quality related directly or indirectly? Overall, the results found that WLF and nutrient dynamics in the pelagic zone of Lake Kinneret are not co-partners, but independent escorts. The common periodical (monthly) distribution of nutrient concentrations in the epilimnion of Lake Kinneret indicates that a 20 m deep epilimnion formed following a decline in water input, temperature, and evaporation elevation, resulting in the decline of WL. There was a seasonal correlation between summer’s natural conditions and pelagic nutrients’ deficiency. Low WL in summer is the result of natural subtropical climate conditions, whilst dry or high rainfall seasons induce water input modification and consequently, the WL decline of nutrient inputs and independent followers.

Role of Reef-Flat Plate on the Hydrogeology of an Atoll Island: Example of Rangiroa

On atoll islands, the fresh water lens (FWL) constitutes, for the island population, a very important fresh water resource for various usages. Its shape and thickness highly depend on the underground characteristics of several rock formations which constitute the underground of the island: upper Holocene sediments and lower Pleistocene limestone rocks separated by the Holocene Pleistocene Unconformity. In this study, several very simple investigation methods were applied on the Pacific atoll of Rangiroa in order to characterize the aquifer hydrodynamics and their impact on the FWL. A water budget of the aquifer was proposed, including the deep infiltration to the FWL. Pumping tests and tidal analysis demonstrated the confined character of the aquifer and its main hydrodynamic properties (storage and hydraulic conductivity). The role of the reef-flat plate on the hydrogeology of the atoll was highlighted. Its impermeable nature contributes to reduce the deep infiltration to the aquifer. It also contributes to the confined flow regime of the aquifer, inducing high and fast water level fluctuations due to tide forces, and consequently contributes to increase the thickness of the saline mixing zone. Both phenomena contribute to reduce the thickness of the FWL, which is only 2 m-thick in that atoll.

Nitrogen and Phosphorous Retention in Tropical Eutrophic Reservoirs with Water Level Fluctuations: A Case Study Using Mass Balances on a Long-Term Series

Nitrogen and phosphorous loading drives eutrophication of aquatic systems. Lakes and reservoirs are often effective N and P sinks, but the variability of their biogeochemical dynamics is still poorly documented, particularly in tropical systems. To contribute to the extending of information on tropical reservoirs and to increase the insight on the factors affecting N and P cycling in aquatic ecosystems, we here report on a long-term N and P mass balance (2003–2018) in Valle de Bravo, Mexico, which showed that this tropical eutrophic reservoir lake acts as a net sink of N (−41.7 g N m−2 y−1) and P (−2.7 g P m−2 y−1), mainly occurring through net sedimentation, equivalent to 181% and 68% of their respective loading (23.0 g N m−2 y−1 and 4.2 g P m−2 y−1). The N mass balance also showed that the Valle de Bravo reservoir has a high net N atmospheric influx (31.6 g N m−2 y−1), which was 1.3 times the external load and likely dominated by N2 fixation. P flux was driven mainly by external load, while in the case of N, net fixation also contributed. During a period of high water level fluctuations, the net N atmospheric flux decreased by 50% compared to high level years. Our results outlining water regulation can be used as a useful management tool of water bodies, by decreasing anoxic conditions and net atmospheric fluxes, either through decreasing nitrogen fixation and/or promoting denitrification and other microbial processes that alleviate the N load. These findings also sustain the usefulness of long-term mass balances to assess biogeochemical dynamics and its variability.

Evaluation of the Open Diversion Channel Capacity on Margatiga Dam Construction Project using 6D BIM Analysis

The Margatiga Dam is designed to combine a gravity concrete dam and rockfill with an upright core. In the Margatiga Dam Project, river diversion is carried out in 2 stages. Stage 1 through a trapezoidal open channel with discharge plan of Q10 years approximately 789.10 m3/second and stage 2 with the diversion discharge of Q25 years approximately 976.90 m3/second. During construction, the stage 1 diversion channel is built with a capacity that exceeds the planned design due to the very high water level fluctuations. Moreover, an evaluation is needed regarding the annual plan discharge that passes through stage 1. The Evaluation is based on data from the desk study and 6D BIM analysis. Based on the analysis, the water level is at elevation +19.50. The discharge through the diversion channel on this stage is 884.69 m3/second; this discharge exceeds the planned discharge design for diversion channel stage 1 with an annual Q10 discharge of approximately 789.10 m3/second.

Does the size structure of the littoral community reflect water level fluctuations in shallow waterbodies?

The littoral zone of shallow water bodies (SWB) is highly susceptible to water level fluctuations (WLF) caused by ongoing climate-related hydrologic regime changes. The present study assessed the macrozoobenthos structure in the littoral of three temperate SWB after pronounced WLF and accompanying reduction of macrophyte coverage caused by excessive precipitation. The three SWB differed in environmental conditions – S1 (transparent lake covered with submerged macrophytes dominated by Ceratophyllum demersum); S2 (turbid lake without macrophyte coverage) represented the two interconnected backwater basins of the Sutla River watershed; and SK (Škrčev kut oxbow; highly turbid lake sparsely covered by floating-leaved Nuphar lutea) located in the Krapina River watershed (Croatia). With the aim to disentangle the littoral food web structure, and interactions among environmental conditions as well as structural and functional traits of the littoral community within the three SWB, the macrozoobenthos functional traits, trophic guilds and body size were correlated with the littoral environmental conditions, and with the traits of the potential macrozoobenthos prey (zooplankton) and predators (fish). Our results suggest that the littoral macrozoobenthos assemblage responded to the water level increase mainly by the decline of macroinvertebrate diversity and abundance. Due to loss of habitat heterogeneity, in general, larger-sized macroinvertebrates dominated the littoral zone of turbid SWB, particularly with high WLF, while smaller-sized detritivores and grazers prevailed in the littoral zone of the transparent SWB covered by submerged macrophytes. The correlations between different macrozoobenthos, zooplankton and fish size classes indicated that the larger-sized predatory macroinvertebrates prey on smaller-sized zooplankters and avoid predation of mid-sized fish. On the other hand, the abundance of smaller-sized macroinvertebrate detritivores and grazers, which were significantly correlated with concentrations of suspended detritus and algae, prevailed in the SWB covered by submerged macrophytes. Within the macrophyte-covered littoral habitats, macroinvertebrates coexisted with small-sized fish and zooplankters as well as with large-sized pelagic zooplankters, likely seeking shelter from fish. We assume that the increased abundance of larger-sized specimens affected macroinvertebrates and fish within the littoral community upon water level increase. Such a pattern could be recognized as an indicative trait in the evaluation of ecosystem functioning. Furthermore, we conclude that the structural and functional traits of the SWBs’ littoral communities could help us predict the ecological consequences of the climate-induced WLF.

Water level as the key controlling regulator associated with nutrient and gross primary productivity changes in a large floodplain-lake system (Lake Poyang), China

A floodplain lake system can be described as a water conveyance-type lake system that is subject to high water-level fluctuations (WLFs). This study investigated the effects of WLF on the nutrient status and the gross primary productivity (GPP) of phytoplankton in Lake Poyang, a large floodplain-lake system in China. This study hypothesized that WLF is the key controlling regulator of the lake’s nutrient status, phytoplankton growth and GPP, driven by its influence on the lake’s hydrological connectivity in combination with water-flow velocity as well as other environmental parameters. The results showed that the intra-annual water levels in this lake varied from 7.61 m to 20.82 m while inter-annual water levels significantly decreased throughout 1989–2018 (P < 0.05). Except for pH, most environmental variables and nutrients differed significantly each season. Mean GPP and chlorophyll a (Chl a) concentration during the water rising period was clearly higher compared to the dry season, wet season and falling period. Moreover, nutrient concentration was the main determining factor of phytoplankton growth and GPP during different periods, while water temperature (WT) also played a key role in influencing phytoplankton biomass and GPP during the water rising period. There was also a direct correlation between WLF and GPP during the water rising period, and WLF significantly affected nutrient concentration, subsequently impacting GPP. This study can benefit our overall knowledge of hydrological and ecological dynamics in floodplain-lake systems, while providing an important reference for policymakers in the management of dams and water quality in floodplain-lake systems globally.

Metal bioavailability during the periodic drying and rewetting process of littoral anoxic sediment

High water-level fluctuations (WLFs) usually lead to the periodic drying and rewetting of littoral sediment, proven to influence the transformation of various sediment contaminants. However, details regarding metal bioavailability variations remain unclear. In this study, oxidation–reduction status transition, metal fraction transformation, and the development of the acid volatile sulfide (AVS) and the simultaneously extracted metals (SEM) were investigated to assess the variations of metal bioavailability in the littoral anoxic sediment during the drying–rewetting process. A series of sediment cores were collected from the littoral area near the mouth of Nanfei River in Lake Chaohu, China, with half of them exposed to dark conditions with an overlying water cover (the control treatment). The other half was dried through the removal of overlying water and then exposed to air and sunlight (the drying treatment). Every 5 days, three of the dried sediment cores were rewetted for 3 days with lake water collected in situ. Various characteristics were analyzed for both the control and drying sediment cores. The drying and rewetting experiment was carried out for 30 days, and the bioavailability of metals was then evaluated thoroughly through data analyses. The periodic drying and rewetting process led to the oxidation of the anoxic sediment with a pronounced increase in oxygen penetration depth and redox potential, and a decrease in AVS concentrations in the drying treatment after 15 days of experimentation. Significant increases in the values of the ratio of SEM and AVS, the difference between SEM and AVS, and the organic carbon normalized difference between ΣSEM and AVS were retrieved for the drying treatment after process completion. The increase of metal bioavailability to aquatic organisms was consequently predicted, with the most significant concerns noted regarding Cd and Pb due to their transformation to less firmly bound fractions. The periodic drying and rewetting process could increase the bioavailability of metals in littoral anoxic sediment. Therefore, this process should be given more attention during future management of water level and remediation of littoral sediment in similar areas.

Contrasting exchanges of nitrogen and phosphorus across the sediment–water interface during the drying and re-inundation of littoral eutrophic sediment

High water level fluctuations (WLFs) lead to periodic drying and re-inundation of sediments in the littoral area of eutrophic lakes. In this study, a series of littoral sediment cores were dried for different periods (5–30 d) and rewetted for 48 h. The sediment cores that dried for 30 d were then re-inundated for 90 d. The exchanges of nitrogen (N) and phosphorus (P) across the sediment–water interface (SWI) and the mechanisms were studied. The results showed that ammonium nitrogen (NH4+–N) fluxes increased after 5–25 d of drying, which was followed by an obvious decrease after 30 d of drying. The decreased NH4+–N fluxes remained at low levels during the 90 d re-inundation period. The soluble reactive P (SRP) fluxes decreased significantly after 15 d of drying. However, further re-inundation increased the SRP fluxes to their initial levels. The decreased water content and porosity, the oxidation of the sediment during drying, and the associated transformations of the N and P fractions in the sediment from drying to re-inundation influenced the exchanges of NH4+–N and SRP across the SWI. The decrease of labile NH4+–N in the sediment during drying was non-reversible, while the transformations between redox sensitive P (Fe-P) and aluminum-bound P were more likely to be reversible from drying to re-inundation. The increase of Fe-P during drying and dissolution of Fe-P during the re-inundation were responsible for the development of SRP fluxes from drying to re-inundation. Therefore, the periodic drying and re-inundation of the littoral eutrophic sediments reduced the release of NH4+–N but accelerated the release of SRP from the sediment. This should be given more consideration for the remediation and management of eutrophication in the lake and other similar lakes with high WLFs.

Estimated light compensation depth explains growth of Stuckenia pectinata in Te Waihora

Loss of a long-term stable submerged macrophyte community reverses shallow lakes from a clear into a turbid water state. Stuckenia pectinata densely colonised the marginal area of a shallow coastal lagoon Te Waihora (Lake Ellesmere) before its removal by the 1968 “Wahine” storm. This study aims to understand the current light availability for S. pectinata growth in Te Waihora with high turbidity and water level fluctuations. In a greenhouse experiment, acclimations in S. pectinata to lower light intensities involved elongation in stems and leaves, and an increase in photosynthetic efficiency per unit dry weight for both leaves and stems. However, these acclimations did not reduce the daily compensation irradiance (under which daily net photosynthesis equals zero) that was identified at 8.8 ± 0.9 μmol photons m−2 s-1. Subsequently, we estimated light compensation depth (LCD), based on the derived daily compensation irradiance, incident irradiance at the water surface, and light attenuation coefficients for the lake. In areas shallower than LCD, there is no light limitation for the growth of S. pectinata. The LCD ranged from 0.23 to 0.54 m and well explained the growth range of S. pectinata in Te Waihora during the 2016–2017 ecological survey. The estimated LCD also suggests low turbidity levels in early spring are critical for the growth of S. pectinata with the current water level fluctuation regimes. LCD is a useful parameter for understanding the growth of submerged macrophytes in shallow turbid lakes from the perspective of light availability.

Metabolism in a deep hypertrophic aquatic ecosystem with high water-level fluctuations: a decade of records confirms sustained net heterotrophy.

Long-term and seasonal changes in production and respiration were surveyed in the Valle de Bravo reservoir, Mexico, in a period during which high water-level fluctuations occurred (2006–2015). We assessed the community metabolism through oxygen dynamics in this monomictic water-body affected by strong diurnal winds. The multiple-year data series allowed relationships with some environmental drivers to be identified, revealing that water level-fluctuations strongly influenced gross primary production and respiratory rates. Production and respiration changed mainly vertically, clearly in relation to light availability. Gross primary production ranged from 0.15 to 1.26 gO2 m−2 h−1, respiration rate from −0.13 to −0.83 gO2 m−2 h−1 and net primary production from −0.36 to 0.66 gO2 m−2 h −1 within the production layer, which had a mean depth of 5.9 m during the stratification periods and of 6.8 m during the circulations. The greater depth of the mixing layer allowed the consumption of oxygen below the production layer even during the stratifications, when it averaged 10.1 m. Respiration below the production layer ranged from −0.23 to −1.38 gO2 m−2 h−1. Vertically integrated metabolic rates (per unit area) showed their greatest variations at the intra-annual scale (stratification-circulation). Gross primary production and Secchi depth decreased as the mean water level decreased between stratification periods. VB is a highly productive ecosystem; its gross primary production averaged 3.60 gC m−2 d−1 during the 10 years sampled, a rate similar to that of hypertrophic systems. About 45% of this production, an annual average net carbon production of 599 g C m−2 year−1, was exported to the hypolimnion, but on the average 58% of this net production was recycled through respiration below the production layer. Overall, only 19% of the carbon fixed in VB is buried in the sediments. Total ecosystem respiration rates averaged −6.89 gC m−2 d−1 during 2006–2015, doubling the gross production rates. The reservoir as a whole exhibited a net heterotrophic balance continuously during the decade sampled, which means it has likely been a net carbon source, potentially releasing an average of 3.29 gC m−2 d−1 to the atmosphere. These results are in accordance with recent findings that tropical eutrophic aquatic ecosystems can be stronger carbon sources than would be extrapolated from temperate systems, and can help guide future reassessments on the contribution of tropical lakes and reservoirs to carbon cycles at the global scale. Respiration was positively correlated with temperature both for the stratification periods and among the circulations, suggesting that the contribution of C to the atmosphere may increase as the reservoirs and lakes warm up owing to climate change and as their water level is reduced through intensification of their use as water sources.

On the morphological evolution of restored banks: Case study of the Meuse river

In recent years, many riverbanks in Europe had their protections removed to reactivate natural erosion processes and improve riparian habitats. Yet, other river functions may be affected, such as navigation and flood conveyance. The quantification and prediction of erosion rates and volumes is then relevant to manage and control the integrity of all river functions. This work studies the morphological evolution of riverbanks along two restored reaches of the Meuse River in the Netherlands, which are taken as case studies. This river is an important navigation route and for this its water level is strongly regulated with weirs. Through aerial photographs and two airborne LIDAR surveys, we analysed the evolution over nine years of restoration and reconstructed the topography along 2.2 km. of banks. An extraordinary low-water level after a ship accident provided the opportunity to observe and measure the bank toe. The banks show a terrace of erosion close to the normally regulated water level, highly irregular erosion rates up to 7 m/year, embayments evolving with upstream and downstream shifts, and sub-reaches with uniform erosion. Probable causes of erosion include ship-waves, high water flows and water level fluctuations. Distinct patterns might be explained by the presence of riparian trees and soil strata of different compositions. These intriguing case studies will continue to be studied to disentangle the role of different erosion drivers, predict erosion magnitudes and establish whether bank erosion will stop or continue in the future.

Impact of high water level fluctuations on stable isotopic signature of POM and source identification in a floodplain lake—Bang Lake (Poyang Lake)

In order to recognize impact of water levels on the sources and migration of particulate organic matter in a floodplain lake—Bang Lake (Poyang Lake), suspended particulate matters (SPM), superficial sediment organic matters (SOM) and aquatic plants were collected in and around Bang Lake from June 2012 to May 2013, and their carbon and nitrogen stable isotopic compositions (δ13C, δ15N) and organic C/N ratio were determined. The results showed that the δ13C and δ15N values of SPM obviously changed with water levels. In the flowing period, the SPM showed the most negative δ13C (−35.4 to −30.8 ‰), δ15N (+4.2 to +7.6 ‰) and C/N > 8, suggesting that SPM in the period was mainly derived from 13C-depleted land C3 plants. The highest δ13C and C/N ratios of SPM appeared in the flooding period because the lake and river were connected and the soil organic matter and the river-derived SPM were input to the lake. In the lowering period, the relatively lower δ13C and δ15N values of SPM were almost consistent with those of the decayed aquatic plants, meaning that aquatic plants were the main components of the SPM. In the lentic period, the δ13C and C/N ratios of SPM were similar to those of SOM due to the re-suspended SOM in the shallow lake. The SOM in the lentic period (δ13C: −30.4 to −25.5 ‰) mainly came from the decline of aquatic plants. With water level rising, the δ13C of SOM turned to be higher (−26.1 to 24.3 ‰), while the C/N ratios changed small. It may be the result of that fast water flow scoured and suspended the surface of sediment. The δ13C and C/N ratios of aquatic plants changed obviously with water levels, which was mainly due to the seasonal variation of photosynthesis and respiration. The δ15N values of aquatic plants were dependent on that of water-soluble N at different water levels. These results indicated that the sources of the organic matter in the lake were obviously influenced by the water levels.

Water‐level fluctuations regulate the structure and functioning of natural lakes

Summary Despite becoming one of the main pressures on aquatic ecosystems globally, understanding of the ecological impacts of altered water‐level regimes in lakes lags far behind that of other human disturbances (e.g. eutrophication, acidification). We employed a multifaceted approach to explore the potential importance of water‐level fluctuations (WLF) for the structure and functioning of littoral zones and multiple trait responses of primary producers and benthic consumers across a range of natural lakes. We found that lakes with high WLF had significantly more coarse littoral substrata with less coverage of macrophyte vegetation in the shallows than in lakes with low WLF. Lakes with high WLF also had greater proportions of motile diatom species and omnivorous benthic invertebrates in shallow waters, altered taxonomic and trophic structure of benthic consumers and more homogeneous algal and benthic invertebrate assemblages. Variation along the littoral depth gradient needs to be examined when assessing the impacts of hydrological pressures in lakes. We found that depth interacted with WLF in its effects on habitat structure and mediated the response of both producer and consumer benthic assemblages to WLF. Our results indicate that amplified WLF significantly affect both the structure and functioning of lake ecosystems. Given the growing importance of WLF as an increasingly pervasive pressure on lake ecosystems worldwide, our findings have important implications for the conservation and management of global aquatic biodiversity. Inclusion of both biological traits and sampling along a depth gradient in existing and in future monitoring programmes could improve significantly the ability to detect and predict effects of altered patterns of WLF on lake ecosystems.

Community metabolism in a deep (stratified) tropical reservoir during a period of high water-level fluctuations.

As long as lakes and reservoirs are an important component of the global carbon cycle, monitoring of their metabolism is required, especially in the tropics. In particular, the response of deep reservoirs to water-level fluctuations (WLF) is an understudied field. Here, we study community metabolism through oxygen dynamics in a deep monomictic reservoir where high WLF (~10 m) have recently occurred. Simultaneous monitoring of environmental variables and zooplankton dynamics was used to assess the effects of WLF on the metabolism of the eutrophic Valle de Bravo (VB) reservoir, where cyanobacteria blooms are frequent. Mean gross primary production (P g) was high (2.2 g C m−2 day−1), but temporal variation of P g was low except for a drastic reduction during circulation attributed to zooplankton grazing. The trophogenic layer showed net autotrophy on an annual basis, but turned to net heterotrophy during mixing, and furthermore when the whole water-column oxygen balance was calculated, considering the aphotic respiration (R aphotic). The high total respiration resulting (3.1 g C m−2 day−1) is considered to be partly due to mixing enhanced by WLF. Net ecosystem production was equivalent to a net export of 3.4 mg CO2 m−2 day−1 to the atmosphere. Low water levels are posed to intensify boundary-mixing events driven by the wind during the stratification in VB. Long-term monitoring showed changes in the planktonic community and a strong silicon decrease that matched with low water-level periods. The effects of low water-level on metabolism and planktonic community in VB suggest that water-level manipulation could be a useful management tool to promote phytoplankton groups other than cyanobacteria.

Differential effects of reduced water potential on the germination of floodplain grassland species indicative of wet and dry habitats

AbstractFloodplain meadow ecosystems are characterized by high water level fluctuations and highly variable soil water potentials. Additionally, climate change scenarios indicate an increasing risk for summer drought along the northern Upper Rhine and the Middle Elbe River, Germany. While adult plants often persist even after strong changes in water availability, early life phases, such as seed germination and seedling establishment, might be more vulnerable. Therefore we tested whether reduced soil water potentials will affect the germination of meadow species and whether the response varies between (1) forbs indicative of wet and dry habitats and (2) seeds originating from sites along the rivers Elbe and Rhine. We exposed seeds of 20 floodplain meadow species with different moisture requirements from five plant families to a water potential gradient ranging from 0 to − 1.5 MPa. While across species germination percentage and synchrony decreased, germination time increased at reduced water potentials. Germination of the species indicative of dry habitats decreased more strongly, was slower and less synchronous at reduced water potentials than that of species indicative of wet habitats. Seeds from sites along the rivers Elbe and Rhine did not differ in their germination characteristics. We propose that species of wet sites follow an all-or-nothing-strategy with fast and synchronous germination to maximize competitive advantages, betting on a high probability of moist conditions for establishment (optimists). In contrast, species from dry sites appear to follow a bet-hedging strategy with a moisture-sensing mechanism for unsuitable conditions (pessimists), resulting in a slower and less synchronous germination.

Growth response of the submerged macrophyte Myriophyllum spicatum to sediment nutrient levels and water-level fluctuations

Sediment nutrient levels and water-level fluctuations are important factors that affect the development and growth of submerged macrophytes; however, little is known about the adaptive responses of macrophytes to these factors. We conducted an experiment using the submerged macrophyte Myriophyllum spicatum L. grown under 2 sediment nutrient levels (high: 2.7 mg g−1 total nitrogen, TN; 1.5 mg g−1 total phosphorus, TP; low: 1.45 mg g−1 TN and 0.70 mg g−1 TP) and 3 amplitudes of water-level fluctuation (static, ±50 cm, ±100 cm) in outdoor ponds. We hypothesized that increased nutrient supply would promote the growth of M. spicatum, which can acclimate to the negative effects of moderate water-level fluctuations. After 112 d of growth under high-nutrient conditions, the plants produced a greater shoot biomass (higher branch number and length), resulting in greater accumulation of total biomass. However, plant growth was inhibited by increasing the amplitude of the water-level fluctuations: at ±100 cm, the plants allocated more biomass to the roots and produced fewer and longer branches. Conversely, plant growth was promoted in the high-nutrient sediments at ±50 cm amplitude. The production of auto-fragments was increased in the high-nutrient sediment but was significantly decreased by high water-level fluctuations. Thus, sediment nutrient levels and water-level fluctuations have strong interactive effects on the growth and reproduction of M. spicatum, and increased sediment nutrients in combination with moderate water level fluctuations facilitate nutrient acquisition, plant growth, and reproduction. Our study implies that moderate water-level fluctuations benefit the restoration of submerged macrophyte communities, particularly in high-nutrient habitats.

Weekly dynamics of phytoplankton functional groups under high water level fluctuations in a subtropical reservoir-bay

In reservoirs, water level fluctuations strongly influence phytoplankton development. However, studies on the response of phytoplankton in the reservoir-bay to water level fluctuations are very scarce, especially in the highly dynamic reservoir system, for instance, the Three Gorges Reservoir (TGR) on the Yangtze River in China. Therefore, we carried out weekly monitoring in a typical tributary bay-Xiangxi Bay of the TGR from March 2008 to March 2009, to analyze the dynamics of phytoplankton functional groups, as well as their response to the water level fluctuations and other environmental conditions. The phytoplankton functional groups G (short, nutrient-rich water columns with high light and without nutrient deficiency), M (dielly mixed layers of small eutrophic, low latitude with high insolation and without flushing and low total light) and Lo (summer epilimnia in mesotrophic lakes with segregated nutrients and without prolonged or deep mixing) were the most important in biomass, mainly represented by Pandorina morum and Eudorina elegans, Microcystis aeruginosa, Peridiniopsis niei and Ceratium hirundinella, respectively. The dominant functional groups had close relationships with the water level fluctuations, light and nutrient, etc. Principal components analysis and redundancy analysis indicated that phytoplankton functional groups in Xiangxi Bay were restricted by the mixing regime and other abiotic variables under the influences of the mixing regime. In Xiangxi Bay, the water level fluctuation showed significant correlations with many physicochemical variables, including the mixing depth (r = 0.97, p < 0.001) and the relative water column stability (r = -0.80, p < 0.001). The study implied that water level fluctuations had complex influence on environmental changes and selecting for phytoplankton functional groups in a highly dynamic reservoir-bay. The important characteristics of the dominant phytoplankton functional groups in Xiangxi Bay were also discussed.

A contribution to the data on tench (Tinca tinca L., Cyprinidae, pisces) distribution in Serbia

The studies on the ichthyofauna of Serbia that have been conducted so far indicate the sporadic tench (Tinca tinca L.) presence in typical habitats. The hydroenvironmental conditions necessary for the survival of this fish species are highly variable and, generally, are more favourable in the northern part of the country (the Vojvodina Province). Although the tench presence has been registered at over 30 sites, there is a tendency of a decrease in population abundance. This is due to the reduction of the surface area of the macrophyte-covered flood zones induced by the damming and regulation of rivers, high water level fluctuations, and water amount reduction in the majority of watercourses, a massive increase in the number of allochthonous phytofagous species, reservoir sediment deposition, water quality deterioration and other factors. The tench conservation status in Serbia is officially designated as Low Risk - Least Concern. It may be transferred to a higher category if the tendency towards deterioration of survival conditions for the species should continue.

Developing sustainable water management scenarios by using thorough hydrologic analysis and environmental criteria

Wetlands constitute a significant source of life since they incorporate unique habitats with endemic and migrant species. They also contribute to the preservation of high global biodiversity and they are under protection according to EU legislation. Nevertheless, during the last century, significant degradation has been observed in wetlands, mainly due to intensification of agriculture and poor water management practices. Calcareous fens habitat with the endangered species Cladium mariscus and Carex spp. is an ecologically significant wetland that undergoes great ecological stresses globally, due to the irrational use of water resources. In Trichonis lake, Western Greece, this habitat has been under deterioration during the last 50 years due to the lack of a sustainable water management plan that has caused destabilization of the hydrologic balance and high water level fluctuations. This human induced hydrologic regime has led to seasonal shifting between drought and flooding which constitute unfavorable conditions for this fen habitat and as a result significant elimination of this ecosystem extent has occurred. This study has adopted technologically advanced scientific methods such as GIS applications and remote sensing techniques to quantify the existing water resources and formulate a sustainable management scheme by considering both anthropogenic water uses and environmental protection.