Amplitude Of Water Level Fluctuations Research Articles

HYDROLOGICAL REGIME OF THE IKVA RIVER (SOUTHERN BUG BASIN)

This article reveals the issue of a detailed study of the hydrological regime of small plain rivers in the presence of data from regular observations. The Ikva River, the object of our study, belongs to the Southern Bug basin and is its small tributary, on which a hydrological indicators monitoring station has been operating since 1939. Since 1955, a continuous series of observations has been available, which allowed us to carry out a detailed analysis and description of the main hydrological characteristics – levels (H, cm) and water flows (Q, m3/s), to evaluate their fluctuations in time, cyclicity and the relationship Q= f(H). The construction of the corresponding graphs confirmed that the Ikva River is characterized by cyclic flow fluctuations, and since 1965 we have already observed two complete cycles of fluctuations in water level lasting about 30 years. At the moment (2022), the flow indicators record the minimum of the low-water phase of the second cycle, so we can expect an increase in the flow in the near future and the transition to a new cycle. We have also determined that the amplitude of water level fluctuations of the Ikva River at the post in the village of Stara Sinyava over many years is 60 cm, and varies from a minimum of 75 cm (1957) to 135 cm (1981), that is, a little more than 0.5 meters in total. This agrees quite well with the literature data and estimates of other authors, considering the plain nature and small size of this object. The long-term course of the water levels of the Ikva River is characterized by a slight increase, while the long-term fluctuations of the average water flow at this station also do not have a large amplitude: from 0.66 m3/s (2020) to 3.64 m3/s (1979) i.e. 2.98 m3/s. At the same time, the general trend line for multi-year cost fluctuations shows, on the contrary, a tendency to decrease them. Therefore, we can state that the graphs of multi-year costs and levels are not synchronous, which is evidence of the manifestation of vertical channel deformations in the area of the post. As the water level increases, the decrease in water consumption is a direct sign of siltation of the riverbed in this area and the raising of the bottom level due to accumulative processes over a long period. The largest amplitudes are characterized by the parameters of the maximum runoff, that is, the amplitudes of the maximum levels (∆Нmax = 168 cm) and maximum flows (∆Qmax = 92.9 m3/s), which is not surprising, because we are talking about the characteristics of the period of floods and inundations, which are always marked by significant fluctuations in time. An interesting fact, identified for us for the first time, is that the characteristics of the minimum flow of the closed period of the channel are characterized by higher amplitudes than the characteristics of the open period. Therefore, the summer low water is more pronounced than the winter low water, which means that in the warm period (summer), the lack of precipitation more clearly provokes a decrease in water levels and flows in the channel system than during the winter period. The reason can be both winter thaws and the specifics of the groundwater regime. Key words: hydrological regime; water level; water flows; hydrological cycle; low water phase; high water phase; relationship Q=f(H).

Synoptic results on the potential impacts of the Lake Maggiore water management strategy on freshwater littoral ecosystems and invertebrate biocoenosis (NW, Italy)

The first results of the application of the integrated multidisciplinary protocol to study the effects of water level management on the Lake Maggiore littoral habitats and biocoenosis are presented. The "Parchi Verbano Ticino" project (2019-2021, ID: 481668) was the driving force to fine-tune the monitoring and management system of multidisciplinary information (chemistry, hydro-morphology, macro- and meio-fauna monitoring). The study reveals that water level fluctuations in Lake Maggiore, sometimes characterized by measurable changes in water levels, have remarkable effects on littoral habitats and on the structure and function of macro- and meiofaunal assemblages living there. Overall, this study provides insights into the potential impacts of Lake Maggiore water management strategy on freshwater littoral ecosystems during late spring-early summer, and emphasizes the need for a comprehensive understanding of the lake ecosystem dynamics. Thanks to the results achieved, publicly endorsed water management rules will be stated, for the late spring-early summer period, considering frequency and amplitude of water level fluctuations as crucial factors in management plans to mitigate their impacts. The endorsed rules turn out to be a negotiated compromise between the maintenance of ecosystem services and the protection of littoral life below water.

Responses of lakeshore herbaceous plant guilds to altered water level fluctuations in Yangtze floodplain lakes, China

River–lake disconnection has led to alterations in natural water level fluctuations (WLFs) in lakes along the middle and lower reaches of the Yangtze River to various extents. To predict the effects of altered WLFs on lakeshore vegetation, lakeshore herbaceous plant guilds (LPGs) in six Yangtze floodplain lakes were classified in this study. The lakeshore herbaceous plant distribution pattern, main influencing factors, and responses of different LPGs to altered WLFs were analyzed. A total of 130 plant species were identified from the six lakes. With the increase in the amplitude of WLFs, the total species number in the six lakes showed a hump–shaped trend, whereas the lakeshore herbaceous plant coverage showed a positive correlation. The Qili Lake with the largest WLFs had the lowest species number and highest plant coverage. The species numbers, average biomass, and coverage of lakeshore herbaceous plants in all the six lakes were obviously higher in spring than in autumn. The lakeshore herbaceous plants in the six lakes were classified into eight guilds. Small differences in pH, organic matter, total nitrogen, and total phosphorus were detected in the substrate among the eight LPGs, but obvious differences in soil moisture content and duration and depth of submergence were observed. The canonical correspondence analysis showed that the main environmental factors affecting the distribution of different LPGs in the six lakes in spring and autumn were the amplitude of WLFs and duration of submergence. The regression analyses showed that the biomass of perennial mesophyte with erect stem guild and perennial hygrophyte with well–developed rhizome guild responded sensitively to alterations in the amplitude of WLFs and duration of submergence, and the guilds could be considered as indicator groups at a regional scale. Morphological parameters such as plant height, stem diameter, leaf thickness, and specific leaf area of the eight LPGs showed no significant linear relationships with the increase in WLFs. The use of these parameters in the evaluations of alterations in WLFs needs to be further analyzed.

Experimental and Simulation Research on the Process of Nitrogen Migration and Transformation in the Fluctuation Zone of Groundwater Level

The fluctuation of groundwater causes a change in the groundwater environment and then affects the migration and transformation of pollutants. To study the influence of water level fluctuations on nitrogen migration and transformation, physical experiments on the nitrogen migration and transformation process in the groundwater level fluctuation zone were carried out. A numerical model of nitrogen migration in the Vadose zone and the saturated zone was constructed by using the software HydrUS-1D. The correlation coefficient and the root mean square error of the model show that the model fits well. The numerical model is used to predict nitrogen migration and transformation in different water level fluctuation scenarios. The results show that, compared with the fluctuating physical experiment scenario, when the fluctuation range of the water level increases by 5 cm, the fluctuation range of the nitrogen concentration in the coarse sand, medium sand and fine sand media increases by 37.52%, 31.40% and 21.14%, respectively. Additionally, when the fluctuation range of the water level decreases by 5 cm, the fluctuation range of the nitrogen concentration in the coarse sand, medium sand and fine sand media decreases by 36.74%, 14.70% and 9.39%, respectively. The fluctuation of nitrogen concentration varies most significantly with the amplitude of water level fluctuations in coarse sand; the change in water level has the most significant impact on the flux of nitrate nitrogen and has little effect on the change in nitrite nitrogen and ammonium nitrogen, and the difference in fine sand is the most obvious, followed by medium sand, and the difference in coarse sand is not great.

Morphometry of Juodis and Lydekinis lakes

Bathymetric surveys of Juodis and Lydekinis Lakes (located in outskirts of Vilnius city, Lithuania) were carried out on April 28 and May 1, 2020, from a boat with attached Lowrance HDI SKIMMER XDCR transducer (200 kHz), Simrad GO5 chartplotter and Lowrance Point-1 GPS/Glonass receiver. Average distance between profiles was ~10 m and depth measurement accuracy up to 2–5 cm. Accuracy of water surface elevation measurement using GNSS receiver Topcon Hiper SR up to 1–2 cm. Later, detailed (0.5x0.5 m) digital lake bottom models (DEM) were developed, bathymetric plans of the lakes were created, the main morphometric features were calculated, the boundaries and area of the lake catchments were defined, and the physical-geographical characteristics of the lakes were described based on field observations and various data. Juodis and Lydekinis are small shallow lakes of glaciokarst origin, located in Tapeliai glacial tunnel valley. Juodis Lake is considerably elongated while shape of Lydekinis Lake is close to the circle. According to survey data, the surface area of Juodis Lake is 9.2 ha, water surface elevation 135.8 m a.s.l., maximum depth 3.7 m, mean depth 1.2 m, volume 114.9 thousands m3, catchment area 344 ha. The surface area of Lydekinis Lake is 1.7 ha, water surface elevation 138.2 m a.s.l., maximum depth 4.9 m, mean depth 2.2 m, volume 36.3 thousands m3, catchment area 71 ha. During the observation period (from June of 2018 to April of 2022), the annual amplitude of water level fluctuations in Juodis Lake reached up to 0.16 m. Water level fluctuations in Lydekinis lake were very large due to the reconstruction of the dam and the installation of new culverts. Currently, the water level in Lydekinis Lake is significantly raised, most of the lake shore and the surrounding wetland are flooded. Keywords: Juodis, Lydekinis, glaciokarst, lake, bathymetric chart, morphometry, Lithuania

Morphometry of Gelionys and Žaliasis Lakes

Bathymetric surveys of Gelionys and Žaliasis Lakes (located in the Baltic Uplands, Aukštadvaris Regional Park, Lithuania) were carried out on April 21, 2020, from a boat with attached Lowrance HDI SKIMMER XDCR transducer (200 kHz), Simrad GO5 chartplotter and Lowrance Point-1 GPS/Glonass receiver. At the same time, the shorelines of the lakes were revised. Average distance between profiles was ~10 m and depth measurement accuracy up to 2–5 cm. Accuracy of water surface elevation measurement using GNSS receiver Topcon Hiper SR up to 1–2 cm. Later, detailed (0.5 × 0.5 m) digital lake bottom models (DEM) were developed, bathymetric plans of the lakes were created, the main morphometric features were calculated, the boundaries and area of the lake catchments were defined, and the physical-geographical characteristics of the lakes were described based on field observations and various data. Gelionys and Žaliasis are small lakes of glaciokarst origin. Gelionys Lake is oval-shaped while shape of Žaliasis Lake is closer to the circle. Despite small surface area the lakes are quite deep. According to survey data, the surface area of Gelionys Lake is 4.79 ha, water surface elevation 216.1 m a.s.l., maximum depth 19.8 m, mean depth 6.0 m, volume 288.3 thousands m3, catchment area 71 ha. The surface area of Žaliasis Lake is 2.14 ha, water surface elevation 120.9 m a.s.l., maximum depth 15.84 m, mean depth 5.7 m, volume 122.2 thousands m3, catchment area 60 ha. During the observation period (from May of 2018 to September of 2020), the annual amplitude of water level fluctuations in Gelionys Lake reached up to 0.47 m, and in Žaliasis Lake up to 0.33 m. Keywords: Gelionys, Žaliasis, glaciokarst, lake, bathymetric chart, morphometry, Lithuania, Aukštadvaris Regional Park.

Moderate hydrological disturbance and high nutrient substrate enhance the performance of Myriophyllum aquaticum

Phenotypic plasticity can determine the performance of exotic plants in environmental disturbance. Aquatic plants can adapt to the stress caused by water level fluctuations in the water level, water depth, or substrate nutrients through phenotypic plasticity. The high-potential invasiveness of Myriophyllum aquaticum in riparian wetlands may be associated with its growth and phenotypic plasticity. The interactive effects of fluctuations in the water level, water depth, and substrate nutrients on the growth performance of M. aquaticum were evaluated. We performed two two-factorial experiments to evaluate the effects of (i) frequency and amplitude of water level fluctuations and (ii) water depth and substrate nutrients on the performance of M. aquaticum. The results indicated that in the first experiment, low fluctuation frequency with a ± 20 cm amplitude significantly increased the value of all growth traits (except for total length of lateral branches). Regardless of fluctuation frequency, relative to a ± 60 cm amplitude and a static water level, the maximum values of total biomass, plant height, relative growth rate, and total length of lateral branches existed in moderate fluctuation amplitudes (± 20 cm, ± 40 cm). In the second experiment, the growth performance of M. aquaticum decreased with increasing water depth from 25 cm to 75 cm. High nutrient substrate significantly increased all growth traits (except for chlorophyll content) in water depths of 25 and 50 cm. Above all, M. aquaticum has optimal growth performance in response to low fluctuation frequency, moderate fluctuation amplitudes (± 20 cm, ± 40 cm), and high nutrient substrate in shallow water (water depth lower than 75 cm). These results indicate that M. aquaticum has a high-potential invasiveness in shallow water and with low disturbance of freshwater habitats.

Škilietų ir Tabaliukų ežerų morfometrija / Morphometry of Škilietai and Tabaliukai Lakes

Depth measurements of Škilietai and Tabaliukai Lakes (located in the Baltic Uplands, Aukštadvaris regional park, Lithuania) were taken in January and February of 2019. At the same time, the shorelines of the lakes were revised. Measurements were made from ice; measurement density varies from 34 to 46 spots per hectare. Depth measurement accuracy up to 0,05 m in Tabaliukai Lakes and Lake Škilietai I, up to 0,1 m in Lake Škilietai II. Accuracy of spot coordinates and water surface elevation measurement using GNSS receiver Topcon Hiper SR up to 1–2 cm. Later, detailed (0.50 x 5 m) digital lake bottom models (DEM) were developed, bathymetric plans of the lakes were created, the main morphometric features were calculated, the boundaries and area of the lake catchments were defined, and the physical-geographical characteristics of the lakes were described based on field observations and various data. Škilietai and Tabaliukai are small and closed groups of lakes (each group consists of 2 lakes) of glaciokarst origin. Despite small surface area (1.7–5.3 ha) the lakes are quite deep (9.8–18.5 m). Differences in the surface area and volume (77.8–436.3 thousand m3) of lakes are due to large differences in catchment areas. The shape of the lakes is remarkably regular, close to the circle. Tabaliukai Lakes usually are connected through bog lag and share the same water level, meanwhile, the water level in Škilietai Lakes differs on average by ~0.20 m. During the observation period (from spring of 2018 to May of 2020), the amplitude of water level fluctuations in Škilietai Lakes reached 0,41–0,48 m, and in Tabaliukai Lakes 0,67 m. The differences in the area and volume of the studied lakes are mainly due to the very different area of the lake catchments. Keywords: Škilietai, Tabaliukai, glaciokarst, lakes, bathymetric chart, morphometry, Lithuania, Aukštadvaris Regional Park.

The effects of flooding regimes and soil nutrients on lakeshore plant diversity in a pristine lake and a human managed lake in subtropical China

The hydrological regimes of many freshwater lakes have been dramatically changed by human activity. Nevertheless, few studies have reported the effects of human water management on the formation mechanisms of lakeshore plant communities. In this study, we investigated the effects of flooding and soil nutrients on the plant diversity of lakeshore Carex communities fringing a pristine lake (Poyang Lake) and a human managed lake (Shengjin Lake), two adjacent floodplain lakes in the middle and lower reaches of the Yangtze River. Over time, the Carex meadow at Shengjin Lake experienced a lower flooding frequency and a smaller amplitude of water level fluctuations in comparison with those obtained at Poyang Lake, but similar flooding durations were found for both sites. Soil total nitrogen (TN), total phosphorus (TP) and the ratio of TN to TP in study plots at Shengjin Lake tended to be higher than those in the plots at Poyang Lake at the 0–100 cm soil depth except for soil TP at the 0–10 cm soil depth. A total of 23 plant species were recorded in the Carex communities at the two lakes. Artificial water management increased plant diversity but had no effect on plant biomass in the Carex community. The primary factor in determining plant diversity changed from the flooding regime to the concentrations of soil nutrients as the water regime underwent management. Flooding regimes had strong direct impacts on the plant communities, while imposing few indirect effects on plants by changing soil nutrients in the pristine lake. Our results represent essential information for enhancing the robustness of management efforts for these large and important freshwater lakes.

Influence of hydraulic retention time and amplitude of water level fluctuations on water quality in irrigation reservoirs of the Kala Oya river basin, Sri Lanka

Management of reservoir water quality is a global challenge due to the natural process of eutrophication and anthropogenic aggravation. In Sri Lanka, irrigation reservoirs support several secondary uses such as fish production, livestock farming, and many communal uses including drinking water supply. In the present study, basic limnological parameters of ten irrigation reservoirs of Sri Lanka were investigated from June 2013 to February 2016, with a view to identifying influence of hydrological regimes on reservoir water quality. Spatio-temporal similarities of water quality parameters were studied employing the self-organizing map (SOM) routine of the artificial neural network application. The sample vectors, classified on the SOM lattice, indicated 6 clusters at 50% similarity level. When reservoir that were categorized according to hydraulic retention time (HRT) and relative reservoir level fluctuation (RRWL; defined as the ratio of the mean reservoir level amplitude to mean depth), were compared with dominant water quality parameters in SOM lattice, it was evident that some productivity-related water quality parameters were influenced HRT and RRWL. The results of the study revealed that HRT and RRWL can essentially be controlled through management of hydrological regimes in irrigation reservoirs, thus, close dialogue between irrigation authorities and other users of reservoir water resources are needed to ensure desired water quality of the reservoirs.

Pump Hydro Energy Storage systems (PHES) in groundwater flooded quarries

Pump storage hydroelectricity is an efficient way to temporarily store energy. This technique requires to store temporarily a large volume of water in an upper reservoir, and to release it through turbines to the lower reservoir, to produce electricity. Recently, the idea of using old flooded quarries as a lower reservoir has been evoked. However, these flooded quarries are generally connected to unconfined aquifers. Consequently, pumping or injecting large volumes of water, within short time intervals, will have an impact on the adjacent aquifers. Conversely, water exchanges between the quarry and the aquifer may also influence the water level fluctuations in the lower reservoir. Using numerical modelling, this study investigates the interactions between generic flooded open pit quarries and adjacent unconfined aquifers, during various pump-storage cyclic stresses. The propagation of sinusoidal stresses in the adjacent porous media and the amplitude of water level fluctuations in the quarry are studied. Homogeneous rock media and the presence of fractures in the vicinity of the quarry are considered. Results show that hydrological quarry – rock interactions must be considered with caution, when implementing pump – storage systems. For rock media characterized by high hydraulic conductivity and porosity values, water volumes exchanges during cycles may affect significantly the amplitude of the water level fluctuations in the quarry, and as a consequence, the instantaneous electricity production. Regarding the impact of the pump – storage cyclic stresses on the surrounding environment, the distance of influence is potentially high under specific conditions, and is enhanced with the occurrence of rock heterogeneities, such as fractures. The impact around the quarry used as a lower reservoir thus appears as an important constraining factor regarding the feasibility of pump – storage systems, to be assessed carefully if groundwater level fluctuations around the quarry are expected to bring up adverse effects. Results highlight opportunities and challenges to be faced, to implement pump – storage hydroelectricity systems in old flooded open pit quarries.

Interannual Water-level Fluctuations and the Vegetation of Prairie Potholes: Potential Impacts of Climate Change

Mean water depth and range of interannual water-level fluctuations over wet-dry cycles in precipitation are major drivers of vegetation zone formation in North American prairie potholes. We used harmonic hydrological models, which require only mean interannual water depth and amplitude of water-level fluctuations over a wet–dry cycle, to examine how the vegetation zones in a pothole would respond to small changes in water depth and/or amplitude of water-level fluctuations. Field data from wetlands in Saskatchewan, North Dakota, and South Dakota were used to parameterize harmonic models for four pothole classes. Six scenarios in which small negative or positive changes in either mean water depth, amplitude of interannual fluctuations, or both, were modeled to predict if they would affect the number of zones in each wetland class. The results indicated that, in some cases, even small changes in mean water depth when coupled with a small change in amplitude of water-level fluctuations can shift a prairie pothole wetland from one class to another. Our results suggest that climate change could alter the relative proportion of different wetland classes in the prairie pothole region.

Coseismic response of water level in Changping well, China, to the Mw 9.0 Tohoku earthquake

Summary A water-level meter installed in Changping well, China, recorded coseismic fluctuations and a step change induced by the M w 9.0 Tohoku earthquake of 11 March 2011. Here we analyse the correlation between water level in the well and vertical ground motions recorded at a nearby surface site, and we examine the relationship between the characteristics of these two datasets and the well-aquifer system parameters. During the arrival period of P- and S-waves, the water level provides information about the intensification of high-frequency ground motions. During the arrival period of the surface waves, the amplitude of water-level fluctuations was closely related to the velocity of vertical-component surface motions. The fluctuation periods of these two parameters are in the range 15–35 s, and the period of oscillation displays a large-to-small characteristic behaviour. The amplification effect on the water level in Changping well, driven by the pressure fluctuation induced by the surface wave, was relatively small, but a low-to-high characteristic is apparent during the coseismic period, related to the gradual enhancement of aquifer permeability due to the action of seismic waves. The coseismic step increase in water level was related to the enhancement of aquifer permeability under the action of seismic waves, and the results of an inversion of water-level tidal-response characteristics show that permeability increased by ∼6.56 × 10 −14 m 2 in the vicinity of Changping well in response to the action of seismic waves emanating from the Tohoku earthquake.

Effects of Inter-Annual Water Level Fluctuations on Vegetation Evolution in Typical Wetlands of Poyang Lake, China

The frequency and amplitude of water level fluctuations were major driving forces for wetland vegetation evolution in the Poyang Lake Deltas. This study examined changes in wetland vegetation evolution of two deltas, namely Ganjiang Main-branch Delta wetland (GMD) and Ganjiang Southern-branch Delta wetland (GSD), in autumns from 1973 to 2009. Wetland vegetation evolution monitoring using Landsat remotely sensed imageries was related to changes in hydrology stemming including the annual peak, lowest water levels and number of flooded days at four characteristic water levels (10, 13, 15 and 17 m) from natural climatic variations. Results showed that the annual peak water level of GMD (Xingzi station) decreased by 5.78 m and the annual lowest water level decreased by 2.27 m; while the annual peak water level of GSD (Tangyin station) decreased by 6.41 m and the annual lowest water level decreased by 2.53 m. The number of flooded days at water levels 15 and 17 m indicated a consistent trend while flooded days at water levels 10 and 13 m were significantly different. Vegetation coverage of both deltas showed trends of increasing and expanded fan-shaped towards the middle of the lake area. The annual peak and lowest water levels had negative correlation with the vegetation coverage areas for both deltas. The flooded days at water level 13 m had the greatest effect on the vegetation coverage area at GMD; while the flooded days at water level 17 m had the greatest effect on the vegetation coverage area at GSD.

The Impact of Available Nitrogen Deficiency on Long-Term Changes in the Lake Kinneret Ecosystem

Lake Kinneret Ecosystem structure has undergone significant modification since early 1990s. Scientists have indicated several causative factors for those long-term changes. The sharp decline of Peridinium and the upset of Cyanobacteria are the major changes. Several options were suggested as the reason for those changes. Among others are the followings: high amplitude of water level fluctuations, global warming, fisheries management, salts diversion, onset and offset of beach vegetation, anthropogenic operations in the drainage basin, allelopathic trait of algal competition, etc. It was suggested that the reduction of ammonia supply from the Hula Valley resulted in the conversion of the land from lake and swamps covered to agriculture followed by elimination of treated domestic sewage and fishponds effluents enhanced deficiency of available N in Lake Kinneret. This paper evaluates the impact of available Nitrogen decline which enhanced Kinneret ecosystem modifications.

Impacts of water level fluctuations on substrate environments of lakeshore zone of the lakes in the middle and lower reaches of the Yangtze River

以长江中下游湖泊为对象,研究了水位波动对湖滨带底质环境的影响.结果表明,底质环境参数沿高程梯度变化明显.底质含水率沿高程梯度增加而减小,pH值沿高程梯度变化不大,有机质、总氮和总磷沿高程梯度呈先增大后减小的趋势.底质环境参数的季节变化也较大.分析表明,水位波动幅度、淹没深度、高水位持续时间等对湖滨带底质环境有较大影响.在中等波动幅度下,底质参数沿高程的变异系数最大,表明此时湖滨带底质异质性较高.夏季湖滨带淹没时间越长、淹没深度越大,底质养分流失越快.高水位持续时间越长,底质pH值变化就越大、营养盐流失越快.本研究结果可为湖滨带生态修复及管理提供依据.;The present paper dealt with the impacts of water level fluctuations on the lakeshore substrate environments of the shallow lakes in the middle and lower reaches of the Yangtze River. The results showed that substrate environments changed greatly with the elevation gradients. Moisture contents of substrate decreased as the elevation increased, and pH value changed little, while contents of organic matter, total nitrogen and total phosphorus in substrate increased at first and then decreased. Also, substrate environments showed clear seasonal dynamics. Analyses showed that the amplitude of water level fluctuations, submergence depth, and duration of high water level had great impacts on the substrates. The coefficients of variation of substrate parameters were the largest in the medium amplitude, indicating that the highest heterogeneity of substrate occurred under such a condition. Substrate nutrients would be lost at an increasing pace with the increase of time and depth submerged during summer. If the duration of high water level was long, the pH values would be changed greater and the nutrients would be lost faster. Our results offered a scientific foundation for ecological restoration and management of the lakeshore.

Ecological impacts of excessive water level fluctuations in stratified freshwater lakes

Water levels of lakes fluctuate naturally in response to climatic and hydrological forcing. Human over-exploitation of water resources leads to increased annual and interannual fluctuations of water levels, at times far beyond natural amplitudes and/or at altered time schedules. Climate change models predict increased occurrence of extreme events (flooding, extended droughts), which will further magnify the seasonal and multiannual amplitude of water level fluctuations in lakes. A relatively wide literature base already exists for shallow lakes, demonstrating that excessive water level fluctuations impair ecosystem functioning, ultimately leading to shifts between clear-water and turbid states. Evidence is gradually building in the published literature demonstrating that deep (stratified) freshwater lakes also respond adversely to excessive water level fluctuations. Analysis of existing data suggests that at moderate disturbance levels littoral habitats are affected, and hence their biota is also impacted. At further disturbance levels, ecosystem destabilization symptoms are observed, including weakening of keystone species, proliferation of nuisance and invasive species, loss of biodiversity, and increased internal nutrient loading. Ultimately, eutrophication symptoms are manifested, especially large and more frequent cyanobacterial blooms, without increased external nutrient loading. Examples from a range of subtropic and temperate freshwater lakes and reservoirs demonstrate that both top-down and bottom-up processes promote those symptoms. The response of aquatic ecosystems, particularly deep lakes, to water level fluctuations is an under-studied field of crucial importance to the management of water resources, where limnologists have a leading role to play in the near future.

Fluvial lakes affect on phosphorus and potassium concentrations in the Samica Stęszewska River

Fluvial lakes affect on phosphorus and potassium concentrations in the Samica Stęszewska River The aim of the study was to evaluate the effect of shallow lakes on reactive, total phosphorus and potassium concentrations in the river water and analyse the effect of changes in water retention in lake on nutrient concentrations in river waters. The study was carried out in the Samica Steszewska River. This is lowland river, which flows through two polymictic lakes. The study site is located in the Wielkopolska Lowland, Central-west Poland. Water samples were collected at depths of 0.5 m below the water surface. Reactive, total phosphorus and potassium were analysed monthly by standard methods. The study was carried out from January to December 1999-2002 (period with high water retention), 2005-2008 (period with low water retention), at four control points. Sites were located at the inflow and outflow of the Samica Stęszewska River into and out of Niepruszewskie and Tomickie Lakes. From 1974 to 2002, Lake Niepruszewskie was regulated at its outlet by a weir. In 2002, the water level was reduced. Changes of water retention in Niepruszewskie Lake influenced water discharge of the Samica Stęszewska River. The results indicate that changes in water retention have significantly influenced water quality in the river, particularly total and reactive phosphorus concentrations; however, this influence was not observed in respect to potassium concentrations. Nutrient concentrations in river strongly depend on water quality of the lake ecosystem and their buffering capacity. Additionally, by improving water quality, increased oxygen concentrations, and decreasing dissolved nutrient concentrations, as well as increased amplitude of water level fluctuations in lakes may increase P-fixation rates in outlet streams.

Aboveground biomass and nutrient limitation in relation to river connectivity in montane floodplain marshes

Abstract Riverine floodwater pulses provide water, nutrients, and sediments to floodplain wetlands, but flood pulses also act as a natural disturbance by removing biomass, scouring sediments, and delivering turbid waters. We investigated nearly pristine montane floodplain wetlands with varying degrees of river connectivity in Jasper National Park, Canada: three fully connected riverine marshes, three partially connected beaver-impounded marshes, and three completely disconnected railway-impounded marshes. Our objectives were to determine how river connectivity affects plant biomass and water and sediment chemistry, estimate impacts of nutrient limitations on plant biomass, and compare natural variations in river flooding on plant biomass and nutrients. The amplitude of water level fluctuations, a measure of flood disturbance and river connectivity, was highest in flood years and in riverine marshes. Sites with river connectivity had significantly higher plant biomass than sites without river connectivity ...

The influence of water level fluctuations on the potential for convective flow in the emergent macrophytes Typha domingensis and Phragmites australis

This paper examines the influence of the amplitude of water level fluctuations and elevation on the gas space anatomy and potential for convective flow in the emergent macrophytes Typha domingensis Pers. and Phragmites australis (Cav.) Trin. ex Steud. Plants were grown under a range of amplitudes of cyclic water level fluctuations: static, ±15, ±30 and ±45 cm. The water level of each treatment fluctuated around an initial and average depth of 60 cm. Within each amplitude treatment, plants were grown at three elevations: sediment surface 20, 40 and 60 cm above the base of the pond. The gas space anatomy of T. domingensis showed a range of modifications in response to experimental treatments. Lacunal cross-sectional area of the leaves increased with decreasing elevation as a product of changes in both fractional porosity and total cross-sectional area. Lacunal cross-sectional area of leaves was maintained across the gradient in amplitude through changes in fractional porosity despite decreasing total cross-sectional area. As a result of these adaptations in gas space anatomy, specific resistance in T. domingensis decreased with decreasing elevation but was unaffected by amplitude. In contrast, no unequivocal anatomical modifications were detected in P. australis and the specific resistance was constant across treatments. Estimates of the total resistance to convection in the above-ground parts of the plant suggests the adaptations in the gas space anatomy by T. domingensis largely compensated for increases in the pathlength of convection due to decreasing elevation. Total resistance increased significantly with increasing amplitude. P. australis had a low specific resistance which minimised the effect of increasing amplitude on total resistance but, lacking the ability to adapt gas space anatomy, the total resistance was strongly affected by elevation. The differential impact of elevation and amplitude suggests the two species have contrasting aptitudes for aeration across gradients in elevation and amplitude. T. domingensis is better suited to tolerate a range of static water depths whereas P. australis is better suited to fluctuating water levels especially when growing at high elevations.