Effects Of Water Level Changes Research Articles

Leveraging Bayesian network to reveal the importance of water level in a shallow lake ecosystem: A study based on Paleo-diatom and fish community

Lake ecological processes and nutrient patterns are increasingly affected by water level variation around the world. Still, the long-term effects of water level change on lake ecosystems and their implications for suitable lake level management have rarely been studied. Here, we studied the ecosystem dynamics of a mesotrophic lake located in the cold and arid region of northern China based on long-term paleo-diatom and fishery records. Utilizing a novel Copula-Bayesian Network model, possible hydrological-driven ecosystem evolution was discussed. Results show that increased nutrient concentration caused by the first water level drop in the early 1980s incurred a transition of sedimental diatoms towards pollution-resistant species, and the following water level rise in the mid-1980s brought about considerable external loading, which attributed to eutrophication and caused the miniaturization of fishery structure. In the 21st century, a continuous water level plummet further reduced the sediment diatom biomass and the fish biomass by altering nutrient concentration. However, with the implementation of the water diversion project in 2011, oligotrophic species increased, and the ecosystem developed for the better. From the perspective of water quality protection requirements and the ecological well-being of Lake Hulun, the appropriate water level should be around 542.42–544.15 m. In summary, our study highlights the coupling effect of water level and water quality on Lake Hulun ecosystem and gives shed to lake water level operation and management under future climate change and human activities.

Reservoir Drawdown Highlights the Emergent Effects of Water Level Change on Reservoir Physics, Chemistry, and Biology

AbstractWater level drawdowns are increasingly common in lakes and reservoirs worldwide as a result of both climate change and water management. Drawdowns can have direct effects on physical properties of a waterbody (e.g., by altering stratification and light dynamics), which can interact to modify the waterbody's biology and chemistry. However, the ecosystem‐level effects of drawdown remain poorly characterized in small, thermally stratified reservoirs, which are common in many regions of the world. Here, we intensively monitored a small eutrophic reservoir for 2 years, including before, during, and after a month‐long drawdown that reduced total reservoir volume by 36%. During drawdown, stratification strength (maximum buoyancy frequency) and surface phosphate concentrations both increased, contributing to a substantial surface phytoplankton bloom. The peak in phytoplankton biomass was followed by cascading changes in surface water chemistry associated with bloom degradation, with sequential peaks in dissolved organic carbon, dissolved carbon dioxide, and ammonium concentrations that were up to an order of magnitude higher than the previous year. Dissolved oxygen concentrations substantially decreased in surface waters during drawdown (to 41% saturation), which was associated with increased total iron and manganese concentrations. Combined, our results illustrate how changes in water level can have cascading effects on coupled physical, chemical, and biological processes. As climate change and water management continue to increase the frequency of drawdowns in lakes worldwide, our results highlight the importance of characterizing how water level variability can alter complex in‐lake ecosystem processes, thereby affecting water quality.

The effect of water level changes on the density of newly hatched European whitefish (Coregonus lavaretus (L.)) larvae in unregulated and regulated lakes

The effect of the water levels during the period from spawning to hatching of whitefish (Coregonus lavaretus (L.)) on the density of newly hatched larvae was examined from a 23-year time series. The density of larvae was estimated in four lakes with contrasting water level regulation regimes in Central Finland using depth zone stratified bongo and tube net sampling in 2000–2022 and 2008–2022. In the regulated Tehinselkä, larval density was also modeled as a function of the whitefish spawning stock, vendace stock indices, and water levels. Larger water level maximum drops during winter were observed in three regulated lakes (41–68 cm) than in the unregulated lake (35 cm). The average larval densities were highest in the unregulated Lake Southern Konnevesi and regulated Tehinselkä, with densities >20 individuals ha−1. The regulated lakes Ruotsalainen and Puula had lower average densities, <10 individuals ha−1. Significant synchrony in the inter-annual variation in the density time series was observed between Tehinselkä and S. Konnevesi as well as Tehinselkä and Ruotsalainen. None of studied water level variables were associated with larval density in any lake. Thus, the small-scale regulation in these Finnish lakes did not show any direct effects on the production of whitefish larvae. Our analysis did not provide information on the potential effects of water level regulation on later life. For example, it did not cover the impact on whitefish food resources or the abundance of competitors and predators regulating whitefish growth and mortality in the juvenile stage.

The impact of water level changes on the growth and physiology of Arundo donax var. versicolor

In order to investigate the effects of water level changes on the growth and physiology of Arundo donax var. versicolor and to understand its adaptive mechanisms to water level fluctuations, this study was conducted. A. donax var. versicolor was selected as the experimental species, and a dual-pot method was employed to simulate both rising and falling water level conditions. The study analyzed morphological characteristics (plant height, stem diameter, leaf traits, root traits), biomass, and photosynthetic features (chlorophyll a, chlorophyll b, chlorophyll a + b, carotenoids) of A. donax var. versicolor under these two water level conditions. The results revealed that (1) under the condition of rising water level, the morphological characteristics and chlorophyll content showed an overall trend of increasing initially and then decreasing with the increase of the rate. The growth rate of 0.2–0.4 cm/d groups were better, while exceeding its tolerance range led to a decrease in photosynthetic pigment content and even cell inactivation. (2) falling water level were more complex, with plant height, stem diameter, leaf length, leaf width, and leaf area being higher in the 0.8–1 cm/d groups, but values for leaf number and root characteristics were lower. This suggests that moderate stress can promote the growth of A. donax var. versicolor, but in the later stages, it can lead to leaf yellowing, root shrinkage, and even death.

Effects of water level changes in reservoir basin on coastal erosion

In this article, the Chimkurgan reservoir built in the Kashkadarya basin, located in the Qamashi district of the Kashkadarya region, is selected. Considering the change in the water level of the Chimkurgan reservoir, the level of erosion of the shores in the zone of 14 m of water level change on the left bank of the reservoir was considered. Over time, the forces induced by water weaken the soil aggregates, negatively affecting the soil's stability. The density composition of the reservoir coastal soils was determined at the specified heights. The degree of erosion of the reservoir’s banks, depending on the soil type, was also considered. To the bottom of the reservoir, the degree of erosion of coastal soils was determined in the water level change zone at heights of 9 m, 11 m, 13 m, 15 m, 17 m, and 19 m, 22 m, 23 m. It was found that the types of soils obtained from the elevations in the specified place differ from each other. It was determined that the type of soil at these heights is clay, soft soil, and sand, and to a certain extent, the erosion of the banks differs depending on the type of soil.

The study on the comparative responses of aquatic vegetation to the interannual water level variation in different hydrologically connected sub‐lakes based on GEE technology

AbstractWater level variation is considered as a main controlling environment factor affecting the growth of aquatic vegetation in Poyang Lake, the largest freshwater lake in China. It is significant to study the influences of water level change on aquatic vegetation under various hydrological conditions. Taking the free connected sub‐lake Bang Lake and partially controlled sub‐lake Dahuchi Lake of Poyang Lake as research objects and based on the cloud computing platform of remote sensing of Google Earth Engine (GEE), the pixel binary model method was used to estimate the aquatic vegetation cover from 2000 to 2019, and the spatial and temporal variation characteristics were discovered first. Meanwhile, the combined method of Sen + M‐K (Theil–Sen Median method and Mann‐Kendall trend test) was conducted to simulate the trends of water fluctuation. Second, the hydrological parameters indicating water level fluctuation were established, and the relationship between these parameters and the area covered by aquatic vegetation in different sub‐lakes was explored. The results were as follows. (1) The aquatic vegetation cover of the freely connected sub‐lake Bang Lake was more susceptible to water level changes, while the partially controlled sub‐lake Dahuchi Lake was relatively stable underwater level change. (2) The aquatic vegetation was patchily and sporadically distributed in years with low vegetation cover, while in the years with high vegetation cover, it was distributed in a ringlike pattern, spreading from the centre of the lake to the shore. (3) The aquatic vegetation cover of the freely connected sub‐lake Bang Lake was more likely to be influenced by the water level fluctuation (WLF), while the aquatic vegetation cover of the partially controlled sub‐lake Dahuchi Lake was more likely to be influenced by the flooding duration of 17 m water level (L17). The flooding duration of 19 m water level (L19) had a strong negative correlation with the predicted aquatic vegetation cover of both Bang Lake and Dahuchi Lake. It suggests that there was a certain degree of time lag in the effect of water level changes on the free connected sub‐lakes, but there was no obvious time lag on the partially controlled sub‐lakes. (4) The aquatic vegetation of the freely connected sub‐lake Bang Lake were dominated by stabilization and slight improvement, while aquatic vegetation in the partially controlled sub‐lake Dahuchi Lake were dominated by stabilization and significant degradation. This study can help to further understand the vegetation changes in hydro‐ecological system with different hydrological connectivity and will provide a reference for lake management and conservation.

Evaluation of the WRF-Lake Model in the Large Dimictic Reservoir: Comparisons with Field Data and Another Water Temperature Model

Abstract The WRF-lake, as a one-dimensional (1D) lake model popularly used for coupling with the Weather Research and Forecasting (WRF) system and modeling lake–atmosphere interactions, does not consider the heat exchange caused by inflow–outflow, which is an important characteristic of large reservoirs and can affect the energy budget and reservoir–atmosphere interactions. We evaluated the WRF-lake model by applying it at a large dimictic reservoir, Miyun Reservoir, in northern China. The results show that the WRF-lake model, though ignoring inflow–outflow, yields good surface water temperature simulation through reasonable parameterization. The Minlake model, as a better physically based model in reservoirs, was used to test the effect of inflow–outflow, including heat carried by inflow–outflow water exchange and water level change on the 1D model’s performance. The effect of heat carried by inflow–outflow is mainly in summer, negatively correlated with hydraulic residence time and positively correlated with temperature difference between inflow and outflow. For a reservoir with hydraulic residence time of 3 years and temperature difference between inflow and outflow about 10°C in summer, the heat carried by inflow–outflow is far less than the heat exchange through the surface (<2%) and therefore has little influence on total energy balance. The effect of water level change is mainly on latent heat and sensible heat in unit area, rather than outgoing longwave radiation. Though influencing the temperature in deep layers, the water level change does not have a significant impact on the surface temperature. Significance Statement The purpose of this study is to evaluate the applicability of WRF-lake, an important submodule of the Weather Research and Forecasting (WRF) system, in the large dimictic reservoir. This is important because WRF-lake does not consider the effect of inflow–outflow and water level change, which are important characteristics of large reservoirs and can affect the heat budget and reservoir–atmosphere interactions. The applicability of WRF-lake in large reservoirs with frequent inflow–outflow and water level change is widely concerned but has never been discussed in previous studies. Our research explored the applicability of WRF-lake in the large dimictic reservoir and discussed the effect of inflow–outflow and water level change quantitively.

Effects of water level changes on the morphological and physiology of the submerged macrophyte Vallisneria natans

To study the response of the Vallisneria natans morphological and physiology to water level change, seedlings were placed in a submerged condition at depths ranging from 50 cm to 135 cm and set the rising and declining water levels respectively (0.2 cm/d, 0.5 cm/d, 0.8 cm/d, 1.1 cm/d, 1.4 cm/d, 1.7 cm/d). After 50 days of simulation experiment, we observed the effects on plant height, the number of blades, root activity, biomass, chlorophyll a (Chl a), chlorophyll b (Chl b), chlorophyll (a + b) (Chl a + b), carotenoid (Car), soluble protein (SP) and soluble sugar (SS) of V. natans under different water level change rates. The results showed that (1) plant height and the number of blades showed an overall upward trend under the condition of high-rate water level change, while the low-rate change of water level showed a trend of first rising and then decreasing. (2) the root activity of 0.5–1.7 cm/d groups increased with the test time at rising water level, and the declining water level showed a trend of increasing and then decreasing. The total biomass showed an upward trend with the extension of the test time. (3) Chl a, Chl b, Chl (a + b), and Car showed a multi-peak downward trend with the extension of the test time. (4) the response of SP and SS to the test time showed a trend of first increase and then decrease with water level changes. In conclusion, our study demonstrates that the morphological and physiology of V. natans could adapt to water level changes, but it could be stressed if the water level exceeded the suitable range.

The Effects of Water Level Fluctuation on Zooplankton Communities in Shahu Lake Based on DNA Metabarcoding and Morphological Methods.

Simple SummaryThe water level in Shahu Lake varies greatly during an annual cycle: ~4 m deep to nearly dry. Over the course of one year we studied the relationship between zooplankton diversity and the water level in Shahu Lake using DNA metabarcoding. The morphology method was compared with the DNA metabarcoding method to see whether the results were replicable. The results were highly consistent for α-diversity and the community composition of zooplankton using both methods; both methods also showed a significant relationship between the zooplankton community composition and water level. Our research contributes to the application of the DNA metabarcoding method and aquatic ecological investigations.Background: The water level of Poyang Lake (China) fluctuates seasonally. Shahu Lake, a smaller body of water connected to Poyang Lake during the wet season, is separated in the dry season. Due to a special fishing method termed ‘lake enclosed in autumn’, the water level is lowered and reaches its lowest point in January, which is <0.5 m deep in the middle of the lake. Our research investigated the effect of water level changes on the zooplankton community composition in Shahu Lake. Methods: We used both DNA metabarcoding method (MBC) (18S rRNA gene V4 region) and morphological method (MOI) to track the zooplankton community structure over four seasons in Shahu Lake (China). Results: Totals of 90 and 98 species of zooplankton were detected by MOI and MBC, respectively, with rotifers being the main zooplankton component. The α-diversity index of both methods increased from spring to summer and decreased from summer to autumn, reaching the lowest value in winter. NMDS and a cluster analysis showed that all zooplankton communities detected by MOI and MBC were significantly separated by season. The zooplankton community in winter was separated from that of the other three seasons, but the summer and autumn communities were more similar. Conclusions: Changes in the water level had significant effects on the zooplankton community composition. We found that MBC was more able to detect the differences in the zooplankton composition than MOI. MBC also had more advantages in copepod recognition. In our study, 37 species of copepods were detected by MBC, but only 11 species were detected by MOI. We concluded that MBC should be used to research the seasonal variations of zooplankton.

The decomposition process and nutrient release of invasive plant litter regulated by nutrient enrichment and water level change.

Wetlands are vulnerable to plant invasions and the decomposition of invasive plant litter could make impacts on the ecosystem services of wetlands including nutrient cycle and carbon sequestration. However, few studies have explored the effects of nutrient enrichment and water level change on the decomposition of invasive plant litter. In this study, we conducted a control experiment using the litterbag method to compare the decomposition rates and nutrient release in the litter of an invasive plant Alternanthera philoxeroides in three water levels and two nutrient enrichment treatments. This study found that the water level change and nutrient enrichment showed significant effects on the litter decomposition and nutrient dynamic of A. philoxeroides. The increase of water level significantly reduced the decomposition rate and nutrient release of litter in the nutrient control treatment, whereas no clear relationship was observed in the nutrient enrichment treatment, indicating that the effect of water level change on litter decomposition might be affected by nutrient enrichment. At the late stage of decomposition, the increase of phosphorus (P) concentration and the decrease of the ratio of carbon to P suggested that the decomposition of invasive plant litter was limited by P. Our results suggest that controlling P enrichment in water bodies is essential for the management of invasive plant and carbon sequestration of wetlands. In addition, the new index we proposed could provide a basis for quantifying the impact of invasive plant litter decomposition on carbon cycle in wetlands.

Slope stability of underwater fill embankment in mountainous area

During construction of underwater embankment in mountainous area, there will be a weak layer between the embankment and the original mountain, which leads to the slope stability problem, because it is impossible to clear the surface and repair the slope of the original mountain below the water level. Based on the section of the Qianhuang expressway in the bay area of Zhejiang province, we carry out the numerical simulation of underwater embankment by using the finite element software GeoStudio and analyze the influence of the weak layer between submerged embankment and mountain as well as the variation of water level on the embankment slope stability. The results show that the changes of the thickness, the mechanical parameters, the relative position of the weak layer and the variation of water level have a certain impact on the stability of the embankment slope. With increase of the thickness of weak layer, the stability of the embankment slope decreases. With the continuous upward movement of the position of the weak layer, the stability coefficient of the embankment slope firstly decreases rapidly and then slows down. When there is a weak layer inside the embankment, the seepage force has a more obvious influence on the stability of the embankment slope. And the effect of water level change on the overall stability in the presence of weak layer is significantly different from that in the absence of weak layer.

HiStudy on the stability of road embankment due to the effect of water level changes on the slopes

This paper presents a study on the stability of road embankment due to the effect of water level changes on the slope. Two scenarios of the drawdown were considered. The first one is the case of the embankment with the water on one slope and the second one is for the embankment with the water on both two slopes. For the two cases, the water level on one side drops. Effects of various parameters such as the permeability of the road embankment soil, the rate of change in water level on the stability of the slope were evaluated, to found out the principle of the change of stability of the embankment. The results showed that the embankment stability reduces if there is a drawdown of the water level on the slope.

The effects of water-level changes on periphytic algal assemblages in Poyang Lake

Poyang Lake, which is the largest freshwater lake in China, has a seasonal flooding cycle that significantlychanges the water level every year. The aim of this study was to research the effects of water-level changeson periphytic algal assemblages in Poyang Lake. Dynamic shift of periphytic algal biomass were studied fromNovember 2016 to July 2019. Periphytic algal biomass and species composition were analyzed microscopically, andphysicochemical conditions were measured. There were significant seasonal variations in the community distributionof periphytic algae. The biomass of the periphyton ranged from 8 to 22,636 mg m-2. Periphytic algal biomassranged from 30 to 622 mg m-2 with the average of 204 mg m-2 in the LWL phase; periphytic algal biomass rangedfrom 8 to 21,839 mg m-2, with the average of 3,399 mg m-2 in the IWL phase. It ranged from 166 to 22,636 mgm-2, with the average 4,320 mg m-2 in the HWL phase and from 16 to 3,231 mg m-2 with the average of 585 mgm-2 in the DWL phase. There were temporal variations in periphytic algal community structure in Poyang Lake.Cryptophyceae dominated in algal periphyton from November 2016 to February 2017. Bacillariophyceae dominatedfrom March to July 2017 (increasing water-level phases). Pyrrophyceae and Euglenophyceae were dominant fromAugust and September (high-water-level phase) in 2017. Bacillariophyceae dominated through 2018 with occasionaldominance of Cryptophyceae from January to June and the occasional dominance of Chlorophyceae fromJuly to December. Chlorophyceae dominated from January to July in 2019 with occasional dominance of Bacillariophyceae.The water-level variations led to environmental heterogeneity in Poyang Lake, creating heterogeneoushabitats for algal periphyton. Our study revealed the primary importance of water level, water temperature, conductivity,total nitrogen, nitrite and total phosphorus as abiotic local factors structuring the periphytic algal communityin Poyang Lake. The water-level changes did not prevent growth of periphytic algae, but it did change the periphyticalgal community assemblages. This research provides data on the periphytic algae in Poyang Lake and will beuseful for establishing biological indicators of environmental changes and protecting Poyang Lake in the future.

Slope Stability Analysis of Levee

The stability of levees can be affected during fluctuations in the water table. It is also possible for the flood caused by the typhoon to have an influence on the position of the water table in an earth levee. This paper compares the traditional methods methodology with a combination of transient seepage and slope stability analysis for analyzing rapid drawdown scenarios. Firstly the stability of a levee was calculated by conventional methods, then considering the effect of water level changes in the seepage area, the simulated transient pore-water pressure response from a finite element SEEP / W analysis was used for levee stability simulation. The Silt Solidified Piles have a positive effect on the stability of the levee. The result s provide design basis for the projects.

Water level affects availability of optimal feeding habitats for threatened migratory waterbirds.

Extensive ephemeral wetlands at Poyang Lake, created by dramatic seasonal changes in water level, constitute the main wintering site for migratory Anatidae in China. Reductions in wetland area during the last 15 years have led to proposals to build a Poyang Dam to retain high winter water levels within the lake. Changing the natural hydrological system will affect waterbirds dependent on water level changes for food availability and accessibility. We tracked two goose species with different feeding behaviors (greater white‐fronted geese Anser albifrons [grazing species] and swan geese Anser cygnoides [tuber‐feeding species]) during two winters with contrasting water levels (continuous recession in 2015; sustained high water in 2016, similar to those predicted post‐Poyang Dam), investigating the effects of water level change on their habitat selection based on vegetation and elevation. In 2015, white‐fronted geese extensively exploited sequentially created mudflats, feeding on short nutritious graminoid swards, while swan geese excavated substrates along the water edge for tubers. This critical dynamic ecotone successively exposes subaquatic food and supports early‐stage graminoid growth during water level recession. During sustained high water levels in 2016, both species selected mudflats, but also to a greater degree of habitats with longer established seasonal graminoid swards because access to tubers and new graminoid growth was restricted under high‐water conditions. Longer established graminoid swards offer less energetically profitable forage for both species. Substantial reduction in suitable habitat and confinement to less profitable forage by higher water levels is likely to reduce the ability of geese to accumulate sufficient fat stores for migration, with potential carryover effects on subsequent survival and reproduction. Our results suggest that high water levels in Poyang Lake should be retained during summer, but permitted to gradually recede, exposing new areas throughout winter to provide access for waterbirds from all feeding guilds.

Characteristics and Influencing Factors of Soil Microbial Biomass Carbon and Nitrogen in Drawdown Area in the Three Gorges Reservoir

Taking a typical drawdown area located in Wangjiagou of the Three Gorges Reservoir as the study object, four elevations 180,175,165 and 155 m were selected to explore the effect of water level change on soil microbial biomass carbon (SMBC) and microbial biomass nitrogen (SMBN). Wherein, 175,165 and 155 m elevations located in the fluctuating zone, manifested as short, medium and long-term flooding, respectively; 180 m was used as the control, located on the land and never flooded. Sampling depth in soil samples was 0-20 cm, collected once a week. The results indicated that, soil organic carbon (SOC) and total nitrogen (TN) contents at 180 m had no obvious seasonal changes, while they showed remarkable seasonal trends at 175m, which in spring and summer were significantly higher than in autumn and winter; SMBC and SMBN contents and their allocation ratio at four elevations were similar and had significant seasonal fluctuation, which were highest in autumn and lowest in summer at each elevation, indicating that in drawdown area the microbial activity and turnover rate of soil organic carbon and nitrogen were limited by the high-temperature and low-humidity soil environment in summer. Data analysis showed that, compared with the 180 m elevation, contents of SOC, TN, SMBC and microbial quotient, SMBN and its allocation proportion showed varying degrees of increase, while contents of these indexes were significantly lower than control except SMBN and its allocation proportion, meaning that compared with 180 m short and medium-term flooding was conducive to improve soil carbon, nitrogen and their turnover rate and microbial biomass, however, contents of soil carbon and nitrogen and microbial biomass carbon were significantly restricted at 155 m as soil was subjected to flooding stress, meanwhile the turnover rate of SOC was reduced. Correlation analysis implied that SMBC and SMBN had very significant negative correlation with temperature at 5 cm soil depth and pH, meaning that the two environmental factors had a strong effect on soil microbial biomass.

Multi-proxy palaeoecological responses to water-level fluctuations in three shallow Turkish lakes

Natural or human-induced water-level fluctuations influence the structure and function of shallow lakes, especially in semi-arid to arid climate regions. In order to reliably interpret the effect of water-level changes from sedimentary remains in the absence of historical data, it is crucial to understand the variation in sedimentary proxies in relation to water level measurements. Here, we took advantage of existing water surface elevation data on three large shallow lakes in Turkey to elucidate the impact of lake-level changes on benthic-pelagic primary production over the last 50–100years. Sub-fossil cladocerans, diatoms, plant remains and pigments were investigated as biological variables; X-ray fluorescence (XRF) and loss on ignition (LOI) analyses were conducted as geochemical-physical variables on a set of 210Pb and 137Cs dated cores. Dating of the cores were robust, with the exception of uncertainties in Lake Marmara littoral core due to low unsupported 210Pb activities and high counting errors. Results indicated that Lake Marmara was dominated by benthic species throughout the sediment record, while Lakes Beyşehir and Uluabat shifted from a littoral-dominated system to one with increased pelagic species abundance. In all cores there was a stronger response to longer-term (decadal) and pronounced water-level changes than to short-term (annual-biennial) and subtle changes. It was also noted that degree of alteration in proxies differed between lakes, through time and among pelagic-littoral areas, likely emphasising differences in depositional environments and/or resolution of sampling and effects of other stressors such as eutrophication. Our results highlight lake-specific changes associated with water-level fluctuations, difficulties of conducting studies at required resolution in lakes with rather mixed sediment records and complexity of palaeolimnological studies covering recent periods where multiple drivers are in force. They further emphasise the need to include instrumental records when interpreting effects of recent water-level changes from sediment core data in large shallow lakes.

Floods decrease zooplankton beta diversity and environmental heterogeneity in an Amazonian floodplain system

Floods are major determinants of ecological patterns and processes in river-floodplain systems. Although some general predictions of the effects of water level changes on ecological attributes have been identified, specific tests using the flood pulse concept are scarce, mainly in tropical areas, where large river-floodplain systems abound. We tested the hypothesis that floods decrease environmental and biological variability using data from a near-pristine floodplain in Central Amazon (Brazil). We recorded nine limnological variables and the zooplankton community structure at eleven sites during one low and one high water period. During the low water period, when the levels of hydrological connectivity were low, asynchronous processes (e.g., sediment disturbance by biota, decomposition, and predation) likely determined the large environmental and biological heterogeneity in the floodplain. On the other hand, environmental variability and zooplankton beta diversity were significantly decreased by the flood. We postulate that floods act as “rubber erasers”, reducing the environmental and ecological idiosyncrasies created during low water periods. Also, we suggest that dilution effects and enhanced connectivity during the high water period, along with species sorting during the low water period, may determine zooplankton beta diversity patterns in river-floodplain systems.

Laboratory Investigations on Effects of Water Level Change on Surf-zone Processes

ABSTRACT Yoo, J.; Shin, S.; Do, K.D.; Shim, J.S.; Ha, T., and Jun, K.C., 2014. Laboratory investigations on effects of water level change on surf-zone processes. Tidal level and current often influence the rip current and the morphological changes in the macro-tidal beaches. Effects of water level change on surf zone processes were investigated through laboratory experiments conducted in a two dimensional wave flume. A movable beach was installed using a find sand in the flume starting with 1/50 slope from the offshore and ending with 1/20 slope near the shore. Irregular waves were generated by a piston type wave maker with active absorption. In the meantime, water level was changed gradually by using a pump and drain system to consider waves and tide simultaneously. Herein, three different tidal phases (i.e. flood tide, full tide and ebb tide) were conditioned with a gradual depth change of about 10 ~ 15 cm in the offshore during a period of about 30 minutes per phase except the full tide, while only one...

Water level and fish-mediated cascading effects on the microbial community in eutrophic warm shallow lakes: a mesocosm experiment

Information on the effects of water level changes on microbial planktonic communities in lakes is limited but vital for understanding ecosystem dynamics in Mediterranean lakes subjected to major intra- and inter-annual variations in water level. We performed an in situ mesocosm experiment in an eutrophic Turkish lake at two different depths crossed with presence/absence of fish in order to explore the effects of water level variations and the role of top-down regulation at contrasting depths. Strong effects of fish were found on zooplankton, weakening through the food chain to ciliates, HNF and bacterioplankton, whereas the effect of water level variations was overall modest. Presence of fish resulted in lower biomass of zooplankton and higher biomasses of phytoplankton, ciliates and total plankton. The cascading effects of fish were strongest in the shallow mesocosms as evidenced by a lower zooplankton contribution to total plankton biomass and lower zooplankton:ciliate and HNF:bacteria biomass ratios. Our results suggest that a lowering of the water level in warm shallow lakes will enhance the contribution of bacteria, HNF and ciliates to the plankton biomass, likely due to increased density of submerged macrophytes (less phytoplankton); this effect will, however, be less pronounced in the presence of fish.