Effects Of Water Level Fluctuations Research Articles

MACROPHYTIC COMMUNITY AS BIOLOGICAL INDICATORS OF POLLUTION IN ANCHAR LAKE OF KASHMIR

The most significant biotic constituent in a lake ecosystem is represented by macrophytes in their diverse forms. Macrophytes, because of their capacity to integrate environmental changes over periods of a few years, and reflect the cumulative effects of successive disturbances, are considered excellent indicators of the ecological state of water bodies Macrophytes are by far the most investigated group used for exploring the effects of water level fluctuation on biological organisms in aquatic ecosystems . In lake ecosystems, Overall 31 species of aquatic macrophytes were reported from Anchar Lake with different morphology, which consisted of emergent (14), rooted floating leaf type (08), submerged (06) and free floating (03). The efforts mainly focus on the relationships between water level fluctuation and the presence, species richness, distribution and cover of macrophytes.

Spatiotemporal dynamics of coupled dissolved silica and bicarbonate in a dam-induced urban lake system in the Three Gorges Reservoir Area

Dissolved silica (DSi) and bicarbonate (HCO3–) stoichiometric coupling is collectively regulated by chemical weathering and algal activity, and potentially indicates the aquatic silicon retention and carbon emission in aquatic systems. Damming markedly remodels the hydrological conditions and aquatic biological activity, however, its effects on the spatiotemporal dynamics of coupled DSi and HCO3– remain poorly understood. Here we deciphered a 2-year hydrological and water quality dataset collected at multiple sites within an urban lake, namely Hanfeng Lake, the largest pre-dam of the Three Gorges Reservoir, to unravel the spatiotemporal dynamics of DSi and HCO3– and selected hydrological and water quality variables using cluster analysis, and to explore the best predictors for DSi:HCO3– using partial least squares regression. The changes of DSi, HCO3– and selected water variables could be characterized by spatial east and west zones, and further by temporal periods 1, 2 and 3 corresponding respectively to fluctuation stage, fluvial stage and lacustrine stage in each zone based on the hydrographic features of Hanfeng Lake. Wet season presented higher flow velocity, permanganate index, concentrations of DSi, HCO3–, nitrate-nitrogen and total suspended solids, and lower water level, secchi depth and chlorophyll-a, but equal DSi:HCO3– relative to dry season. DSi was overall negatively correlated with HCO3–, highlighting the dominant role of chemical weathering rather algal activity. DSi:HCO3– exhibited significant relationships with various variables, but was the best predictable using water level, permanganate index and nitrogen-based variables, suggesting the strong effects of water level fluctuation and pollution discharge on the coupling of silicon and carbon. Our results have great significance for understanding and modeling the biogeochemical cycles of silicon and carbon in the dam-induced lake ecosystems worldwide.

Effect of water-level fluctuations on methane and carbon dioxide dynamics in a shallow lake of Northern China: Implications for wetland restoration

Shallow lakes are characterized by strong hydrological fluctuations, affecting their biochemistry and carbon (C) balance. This study explored carbon dioxide (CO2) and methane (CH4) flux under strong water-level fluctuations in a shallow lake while also addressing its implications regarding wetland restoration. The DeNitrification-DeComposition (DNDC) model, a process-based biogeochemical model, was used to simulate CO2 and CH4 flux under intensive water-level fluctuations in Lake Baiyangdian (BYD), Northern China. Results showed that: (i) the DNDC model was able to reasonably capture CO2 and CH4 dynamics, which were determined to be extremely sensitive to water-depth fluctuations at a −10 cm to 10 cm range; (ii) the lowest CO2 flux was observed at a 40-day duration, while the trend in annual CH4 flux was to increase as inundation time increased, changing from −2.27 kg C/ha/y to 1.57 kg C/ha/y; and (iii) CO2 and CH4 flux increased under higher fluctuation frequencies, wherein CO2 flux was lowest in January and February and CH4 flux increased from December to March under certain frequencies. Our results indicate that water-level fluctuations (e.g., water depth, duration, frequency, and timing) affected both CO2 and CH4 flux. As it pertains to water diversion projects used for shallow lake restoration initiatives, the optimum approach, pertinent to water yields, diversion time, and duration, should first be considered carefully. Results from this study provide useful information for assisting policymakers with respect to reducing gaseous C emissions during ecological water transfer project regulations in shallow lakes.

Numerical modeling of the influence of tides on cross-shore sediment dynamics of dissipative beaches under moderate wave conditions

The influence of tides on cross-shore sediment dynamics of a longshore-uniform beach is studied by means of a 1D numerical model (XBeach). The model is modified to include longshore tidal currents induced by water level gradients. The effect of tides on cross-shore sediment dynamics is quantified by analyzing the change in suspended sediment concentration, sediment advection velocity, and sediment transport. The effect of tides is decoupled into its two main components, i.e., water level fluctuations and tidal currents. Water level fluctuations modulate wave orbital velocities, wave-averaged currents and sediment advection velocity, therefore affecting both resuspension of sediments and cross-shore sediment transport. Tidal currents favor tidally-averaged sediment resuspension due to the increase in applied shear stress on the bed. The effects of water level fluctuations and tidal currents on sediment dynamics vary in the cross-shore direction: tidal currents increase sediment resuspension in deeper water depth, while water level fluctuations control the changes observed in shallow waters. In shallow waters, tidal amplitude is a good indicator of the influence of longshore propagating tides on the cross-shore sediment dynamics of a uniform beach, while in deeper waters, tidal wavelength also plays an important role. The model predictions are able to capture the trends observed in field measurements.

Effect of water-level fluctuation on the removal of benzene from soil by SVE

In areas that experience frequent fluctuations in groundwater levels, changes in soil void space caused by fluctuations in groundwater levels directly affect the efficacy of soil vapor extraction (SVE). Most studies of SVE technology of oil-contaminated soil remediation do not consider fluctuations in groundwater levels. Here, we constructed an experimental device to study the removal of benzene by SVE under fluctuating groundwater levels. Key parameters affecting the remediation effect of SVE, such as the extraction flow, extraction time, extraction method, initial soil moisture content and initial pollutant content, were studied to characterize their effects on the efficacy of benzene removal by SVE under stable and fluctuating groundwater levels. The removal rate of benzene by SVE was approximately 10% higher under fluctuating water levels than under stable water levels. Extraction flow can directly change the removal rate under fluctuating groundwater levels. Under fluctuating groundwater levels, the removal effect of SVE on benzene in different soils of the “stabilization zone - fluctuation zone - saturation zone” also significantly differed; specifically, the removal effect of SVE in the fluctuation zone and stabilization zone was superior to that in the saturation zone. Given the fluctuation in groundwater levels at the study site, the remediation.

Geoinformation technologies for studying the effects of water level fluctuation of Lake Baikal: the case of Angarsky Sor

Lake Baikal is the world’s deepest lake and declared a UNESCO World Heritage Site. The most severe environmental problem facing the lake is the impact of water level regime fluctuation related to natural and human-caused factors. A core region under study is selected a territory of the Angarsky Sor – a shallow bay located in the Northeast of the lake. The research into a changing water content of the territory is based on imaginary provided by the Landsat-8 satellite. The study is focused on photographs taken in the high-water summer 2014 and in the law water level year 2015. The outcome of performed calculations is that an area of marshy and excessively wet regions has decreased more than 1.5 times, whereas there is a slight increase in the area of droughty waterless zones. Principal changes have been detected in the northern and north-eastern part of the Sor territory. Geoinformation technologies and remote sensing methods are considered to be efficient for the monitoring water level fluctuations, changes in the water surface area and vegetation mantle state of land ecosystems in the Sor region, what is essential for the preserving unique wetlands of the Angarsky Sor.

Zooplankton species richness and abiotic conditions in Thirlmere Lakes, New South Wales, Australia, with reference to water-level fluctuations

ABSTRACT Water-level fluctuations can have significant effects on lake biological communities. Thirlmere Lakes are a group of five interconnected lakes located near Sydney. Water levels in Thirlmere Lakes have fluctuated over time, but there has been a recent decline that is of significant concern. In this study, we examined over one year the species composition and richness of zooplankton (Rotifera, Cladocera and Copepoda) and abiotic conditions in Lakes Nerrigorang and Werri Berri, two of the five Thirlmere lakes, with reference to lake water level. We recorded a total of 66 taxa of zooplankton, with the first report of the rotifer Notommata saccigera from Australia, and the first report of the rotifers Keratella javana, Lecane rhytida and Rousseletia corniculata from New South Wales. There was a marked difference in abiotic conditions between the two lakes, with more variable conditions in Lake Nerrigorang. There was a significant positive correlation between zooplankton species richness and lake water level but only for Lake Nerrigorang. Although the two lakes are closely situated and thought to be potentially connected at high water levels, they show distinct ecological characters and the effect of water-level fluctuations on zooplankton species richness seems to differ between the lakes.

Seasonal Water Level Fluctuation and Concomitant Change of Nutrients Shift Microeukaryotic Communities in a Shallow Lake

Seasonal water level fluctuations (WLFs) impose dramatic influences on lake ecosystems. The influences of WLFs have been well studied for many lake biotas but the microeukaryotic community remains one of the least-explored features. This study employed high-throughput 18S rRNA gene sequencing to investigate the spatiotemporal patterns of microeukaryotic communities in the dry and wet seasons with concomitant change of nutrients in Poyang Lake, which experiences huge seasonal WLFs. The results showed that the dry season and wet season had distinct microeukaryotic community compositions and structures. In the dry season, Ciliophora (13.86–40.98%) and Cryptomonas (3.69–18.64%) were the dominant taxa, and the relative abundance of these taxa were significant higher in the dry season than wet season. Ochrophyta (6.88–45.67%) and Chlorophyta (6.31–22.10%) was the dominant taxa of microeukaryotic communities in the wet season. The seasonal variation of microeukaryotic communities was strongly correlated to seasonal nutrient variations. Microeukaryotic communities responded significantly to dissolved organic carbon, total nitrogen, nitrate, and soluble reactive phosphorus in the dry season, and correlated to nitrate and total phosphorus in the wet season. The microeukaryotic community showed different modular structures in two seasons, and nutrient variations were the key factors influencing seasonal variations of the modular structures. Moreover, microeukaryotic community networks based on different seasons indicated that the microeukaryotic community co-occurrence patterns were not constant but varied largely associating with the nitrogen and phosphorus variations under the effects of WLFs. Our results are important for understanding how microeukaryotic communities respond to nutrient variation under seasonal water level fluctuation.

Microbial community structure and functional properties in permanently and seasonally flooded areas in Poyang Lake

Water level fluctuations are an inherent feature regulating the ecological structures and functions of lakes. It is vital to understand the effects of water level fluctuations on bacterial communities and metabolic characteristics in freshwater lakes in a changing world. However, information on the microbial community structure and functional properties in permanently and seasonally flooded areas are lacking. Poyang Lake is a typical seasonal lake linked to the Yangtze River and is significantly affected by water level fluctuations. Bottom water was collected from 12 sampling sites: seven inundated for the whole year (inundated areas) and five drained during the dry season (emerged areas). High-throughput 16S rRNA gene sequencing was used to identify the bacterial communities. The results showed that the taxonomic structure and potential functions of the bacterial communities were significantly different between the inundated and emerged areas. Cyanobacteria was dominant in both areas, but the relative abundance of Cyanobacteria was much higher in the emerged areas than in the inundated areas. Bacterial communities were taxonomically sensitive in the inundated areas and functionally sensitive in the emerged areas. Nitrogen, phosphorus, and dissolved organic carbon concentrations and their ratios, as well as dissolved oxygen, played important roles in promoting the bacterial taxonomic and functional compositional patterns in both areas. According to the metabolic predictions based on 16S rRNA gene sequences, the relative abundance of functional genes related to assimilatory nitrate reduction in the emerged areas was higher than in the inundated areas, and the relative abundance of functional genes related to dissimilatory nitrate reduction in the inundated areas was higher. These differences might have been caused by the nitrogen differences between the permanently and seasonally flooded areas caused by intra-annual water level fluctuations. The relative abundance of functional genes associated with denitrification was not significantly different in the inundated and emerged areas. This study improved our knowledge of bacterial community structure and nitrogen metabolic processes in permanently and seasonally flooded areas caused by water level fluctuations in a seasonal lake.

Detecting the effect of water level fluctuations on water quality impacting endangered fish in a shallow, hypereutrophic lake using long-term monitoring data

Water level fluctuations (WLFs) affect phytoplankton dynamics, water quality, and fish populations in lakes and reservoirs around the world. However, such effects are system-specific and vary due to interactions with other external factors such as solar radiation, air temperature, wind, and external phosphorus loading. Utilizing data from a long-term monitoring program (1990–2016), we developed an approach using cross-tabulation contour and conditional probability analyses to detect the effects of WLFs on the frequency of poor water quality impacting native fish in a large, shallow, hypereutrophic lake. Through the incorporation of long-term inter-annual and seasonal variability in climatic factors and cyanobacterial bloom periodicity, our approach detected non-linear WLF effects whereby both high and low-lake levels were associated with higher probabilities of poor water quality conditions stressful to fish including high pH, high un-ionized ammonia, and low dissolved oxygen. Although lake level management may not prevent poor water quality in any given year due to other external factors such as temperature or wind, we determined that seasonally based intermediate lake levels bracketing the long-term median afforded the best water quality conditions for endangered fish during the summer period when poor water quality is most common.

Probabilistic stability analysis of earth dam slope under transient seepage using multivariate adaptive regression splines

Earth dams are widespread throughout the world and their safety has gained increasing concern from geotechnical engineering societies. Although probabilistic stability analysis approach has been widely applied to the safety assessment of geotechnical structures, few studies have been performed to investigate the effects of water level fluctuations on earth dam slope stability considering uncertainties of soil parameters. This study proposes an efficient probabilistic stability analysis approach by integrating a soft computing algorithm of multivariate adaptive regression splines (MARS). The calibration of a MARS model generally requires a large number of training samples, which are obtained from repeated runs of deterministic seepage and slope stability analyses using the GeoStudio software. Based on the established MARS model, the earth dam slope failure probability can be conveniently evaluated. As an illustration, the proposed approach is applied to the probabilistic stability analysis of Ashigong earth dam under transient seepage. The effects of the uncertainties of soil parameters and water level fluctuation velocity on the earth dam slope failure probability are explored systematically. Results show that the MARS-based probabilistic stability analysis approach evaluates the earth slope failure probability with satisfactory accuracy and efficiency. The earth dam slope failure probability is significantly affected by the water level fluctuation velocity and the coefficient of variation of the effective friction angle.

River-floodplain restoration and hydrological effects on GHG emissions: Biogeochemical dynamics in the parafluvial zone.

The parafluvial zone is frequently exposed to drying-rewetting cycles with critical consequences for the biogeochemistry of soil and sediment in river-floodplain landscapes. Upon restoration of the hydrological connectivity, substantial changes in biogeochemical processes are expected. The effects of water fluctuation on the magnitude of GHG emissions were investigated in the parafluvial zone of a restored river floodplain in Austria. Sediment composition, DOM quality and N2O, CO2, CH4 fluxes were quantified during distinct hydrological periods (intermittent, desiccation and post flood) and along a hydrological gradient. The hydrological gradient ranged from non-flooded plots in the floodplain soil (used as reference plots after restoration), to rarely-flooded and frequently flooded sediment plots in the parafluvial zone. Enhanced biogeochemical turnover rates were identified during the intermittent period, when N2O and CO2 emissions peaked. In particular, the frequently flooded plots showed significantly higher CO2 and CH4 emissions compared to non-flooded and rarely-flooded plots. This indicates a strong effect of water level fluctuation on GHG emissions, with higher emissions occurring during transitional stages of drying and rewetting. Strong positive relationships were found between individual GHG fluxes, suggesting a tight link between C and N cycles. Both the C and N cycles are dependent on similar substrate characteristics that are governed by the quality of the DOM pool. Interestingly, drier sediments in the rarely-flooded plots were also active areas for emissions. This highlights the importance to include dry phases and sites in the overall C and N emission estimates of riverine landscapes. From the restoration point of view, N2O emissions in the parafluvial zone did not differ significantly from the emissions in the reference plots, whereas CO2 and CH4 fluxes did. When making management decisions to restore connectivity, one needs to carefully consider the interplay between nutrient removal from water versus GHG emissions, to reach maximum environmental benefits.

Assessing the ecological effects of hydromorphological pressures on European lakes

ABSTRACT In European countries, hydromorphological (HyMo) pressures are the second most commonly occurring types of pressures on aquatic ecosystems (after eutrophication). HyMo pressures (i.e., man-made alterations to the hydrology and morphometry of aquatic ecosystems) impact the functioning of lakes and rivers in multiple ways. Initially, they have profound effects on littoral communities, such as macrophytes, benthic invertebrates, and fish. Ultimately, they result in pervasive alteration of whole-lake ecosystems. Extensive efforts have been devoted to the development of ecological assessment methods and management measures focusing mainly on eutrophication, whereas HyMo alterations are less understood and not properly addressed. We attempted to clarify the conceptual background, to highlight achievements in method development, including pressure–response relationships and metrics used in assessment, and to underscore issues requiring urgent attention. We concluded that the currently used biological methods do not reliably address HyMo alterations. The need to develop specifically responding biological and HyMo assessment methods and to measure the necessary variables in routine monitoring programs is urgent. This review paper also serves as an introductory article to a small special series of papers on the ecological impacts of water level fluctuations. Papers in this series include an updated literature review on the ecological effects of water level fluctuations on lake macroinvertebrates, a review article specifically devoted to water level fluctuations indicators in the littoral of natural and artificial lakes, and a paper addressing the relationships between water level fluctuation alteration and spatial and temporal patterns of cladoceran communities in a dammed lake.

Nitrous Oxide and Methane Dynamics in Woodchip Bioreactors: Effects of Water Level Fluctuations on Partitioning into Trapped Gas Phases.

Woodchip bioreactors (WBRs) are low-cost, passive systems for nonpoint source nitrogen removal at terrestrial-aquatic interfaces. The greenhouse gases nitrous oxide (N2O) and methane (CH4) can be produced within WBRs, and efforts to reduce N2O and CH4 emissions from WBR systems require improved understanding of the biogeochemical and physical-chemical mechanisms regulating their production, transport, and release. This study evaluates the impact of trapped gas-filled void volumes as sinks of dissolved gases from water and as sources of episodic fluxes when water levels fall. Dissolved gas tracer experiments in a laboratory bioreactor were used to parameterize nonequilibrium advection-dispersion-gas transfer models and quantify trapping of gas-filled voids as a function of antecedent hydrological conditions. Experiments following a water-level rise revealed that up to 24% of the WBR pore volume was occupied by trapped gas phases, which were primarily located in pore spaces inside woodchips. This finding was confirmed with X-ray-computed microtomography. N2O (3.3-10%) and CH4 (4.3-14%) injected into the reactor following a water table rise partitioned into gas-filled voids and were released when water tables fell. In the case of N2O, partitioning into trapped gas phases makes N2O unavailable for enzymatic reduction, potentially enhancing N2O fluxes under fluctuating water levels.

Riparian plant species composition alternates between species from standing and flowing water bodies – Results of field studies upstream and downstream of weirs along the German rivers Lahn and Fulda

Regulation measures like the installation of weirs led to distinct shifts in riparian plant communities and to a decline of typical riparian plant species occurring along the river shoreline, which is naturally poor in woody plants. These regulation measures include also run-of-river impoundments or weirs that cause distinct differences in hydrodynamic conditions in their direct proximity upstream and downstream. In the course of the year, the downstream reaches are exposed to significantly higher water level fluctuations than upstream. Thus, these reaches are assumed to provide also suitable habitat for riparian plant species of habitats being exposed to frequent disturbance by alternating water levels.We investigated the riparian vegetation in direct proximity upstream and downstream of nine weirs along the two regulated rivers Lahn and Fulda. Sampling was conducted in the transition zone from water to land directly above the actual water level during the summers 2016 and 2017. Differences in species composition were analyzed by means of NMS and indicator species analysis. Results of the indicator species analysis were used for further analyses regarding species’ functional traits and species’ habitat origin.A grouping of the relevés in accordance to the weir reach, dissimilarities in site conditions, significant indicator species for each weir reach and common indicator species upstream along both rivers point towards differences in species composition upstream and downstream. Due to rather constant water levels, upstream species composition consisted mainly of perennial species from reeds of still waters, swamp and alluvial forests and terrestrial habitats that were mainly competitors. By contrast, species from reeds of flowing waters, flooded meadows and grasslands and typical riparian plant communities (Bidention tripartitae, Chenopodion rubri) occurred more frequently downstream. Species downstream exhibited also less competitive power and short life cycles as a result of higher water level fluctuations.Upstream and downstream species composition clearly reflect the observed hydrodynamic conditions, restricting continuity to the area within two weirs. This distinctly differs from natural conditions, which leads to the establishment of novel riparian plant communities. As downstream reaches in direct proximity to weirs are related to higher water level fluctuations in the course of the year, these areas are of essential meaning as refuge for typical riparian species. Against this background, we recommend to decrease bank steepness downstream to increase the effect of water level fluctuations, which would lead to the establishment of suitable habitats for typical riparian plant species.

Responses of two macrophytes of the genus Polygonum to water level fluctuations and interspecific competition

We assessed the zonation of two emergent macrophytes, Polygonum ferrugineum and Polygonum acuminatum, and experimentally tested the effects of water level fluctuations and competition on the growth of these two species. We modelled the abundance of both species as a function of depth using a Bayesian approach based on a 16-year dataset from a subtropical floodplain. Then, we designed a factorial experiment in which species were planted in monocultures and mixtures and subjected to three water level treatments (low, high and variable) for 30 days. All response variables and relative yields were analysed with a two-way ANOVA. The modelled data showed that the two species colonize different depths, with P. acuminatum colonizing shallower areas than P. ferrugineum. Biomass accumulation did not differ between species in monocultures, but P. acuminatum showed significantly higher shoot and internode lengths when it grew submerged, indicating different survival strategies between the two species. P. acuminatum resisted inundation through an escape strategy, elongating above the water surface, while P. ferrugineum did not show this strategy. In mixtures, P. acuminatum showed a significantly higher competitive ability than P. ferrugineum, indicating that the former species has advantages over the latter during the colonization phase. These results are consistent with our observational results because they show that P. acuminatum can dominate in shallower areas by having morphological adaptations to intermittent fluctuations in water level and a competitive advantage over P. ferrugineum.

Effects of water level fluctuation on thermal stratification in a typical tributary bay of Three Gorges Reservoir, China.

Xiangxi River is a typical tributary of Three Gorges Reservoir (TGR) in China. Based on field observations in 2010, thermal stratification was significant in most months of the year. Through field data analysis and numerical simulations, the seasonal and spatial variation of thermal stratification as related to the impact of the operation of TGR were investigated. Thermal stratification was most pronounced from April to September in the Xiangxi River tributary. Air temperature (AT) and water level (WL) were the two dominant variables impacting thermal stratification. AT affected the surface water temperature promoting the formation of thermal stratification, and high WLs in TGR deepened the thermocline depth and thermocline bottom depth. These results provide a preliminary description of the seasonal variation and spatial distribution of thermal stratification, which is important for better understanding how thermal stratification affects algae blooms in Xiangxi River.

Response of aquatic macrophyte biomass to limnological changes under water level fluctuation in tropical reservoirs.

We evaluated the response of the biomass of aquatic macrophytes under limnological changes after water level fluctuation (WLF) of two tropical reservoirs (R1 and R2), located in northeastern Brazil. Initially we tested the hypothesis that post-WLF limnological conditions and biomass of macrophytes increase or decrease, depending on the variable or species. We monitored a 4 × 50 m permanent plot, in four expeditions per period (pre- or post-WLF), assessing species biomass and 10 limnological variables. We utilized 0.25 × 0.25 m quadrats for biomass. Once the effect of WLF in limnological variables and species biomass was confirmed, we utilized Canonical Correspondence Analysis to understand the relationship between limnological variables and species biomass. The abundant and/or dominant species in pre-WLF of R1 ( Pistia stratiotes, Eichhornia crassipes and Salvinia auriculata) and R2 (Paspalidium geminatum and S. auriculata) reduced their biomass post-WLF and were correlated with temperature, total phosphorous and nitrate. The reduced biomass of P. stratiotes, E. crassipes and S. auriculata in post-WLF widened resource availability, allowing coexistence of species. Therefore, we suggest that the change of limnological conditions in post-WLF in artificial lakes acts only as a moderator factor of the interspecific interaction (especially coexistence), without direct relation between these conditions and species biomass.

Effects of water level fluctuations on root architectural and morphological traits of plants in lakeshore areas of three subtropical floodplain lakes in China.

Plant roots in lakeshore areas can directly determine the survival of the aboveground plant parts. However, most current studies are focused on the aerial shoots, and less attention has been paid to the functions of the roots. In order to evaluate the effects of water level fluctuations (WLFs) on root architectural and morphological traits of plants in lakeshore areas, field investigations were conducted seasonally in three subtropical floodplain lakes with different types of WLFs. The results showed that both the pH and moisture contents of the soils were significantly different in all seasons among the three lakes, while the total nitrogen and total phosphorus in the soils only showed significant differences in certain seasons. Significant differences were also found in the two architectural trait parameters (root length density and root branching number) and three morphological trait parameters (root tissue density, root surface area, and root volume), all of which (except for root tissue density) were highest in the Dahuchi lake that experiences intermittent WLFs, and lowest in the Chaohu Lake with reservoir-like WLFs. With increasing lakeshore elevation gradients, we found that root length density, root branching number, root surface area, and root volume in the three lakes changed significantly, and all these root trait parameters increased first and then decreased. However, no significant differences were found for the above four root traits in the three lakes over the different seasons. Spearman correlation analyses indicated that both the hydrological and physicochemical factors were strongly correlated with the architectural and morphological root trait parameters, and the duration of submergence (duration) was the most important factor, judging from the correlation coefficients (R). The results of stepwise multiple regression further indicated the duration was the key factor affecting plant root traits. Based on the results of this study, we suggest that the WLFs in reservoir-like lakes should be changed in order to improve the ecological functions of the lakeshore.

Effect of large-scale surface water level fluctuations on earthquake recurrence interval under strike-slip faulting

While tectonic motion is seen as a primary cause of the earthquakes, the effects of water level fluctuations on geological rates of seismicity have not been studied in depth. Can fluctuations of tens to hundreds of meters significantly perturb local fault systems and modify the behaviour of their seismic cycles? Our novel theoretical modelling can explain variability in the paleoseismic rates of large earthquakes rupturing strike-slip faults, by large-scale water level fluctuations in basins overlying the faults. We demonstrate that water level increase can significantly affect effective stresses at the faults, generate immediate and delayed seismic responses, and accelerate seismic events under strike-slip faulting regime. Both, water level induced stress change and hence seismic recurrence interval, are significantly affected by an interplay between hydro-mechanical properties of the fault zone. Our modelling demonstrates that water level fluctuation of historic water bodies in the tectonic depression of the Dead Sea fault could have triggered changes in the paleo-seismic rates.