Annual Water Level Fluctuations Research Articles

Assessment of water level fluctuation impacts along River Nile, Egypt

ABSTRACT This paper aims to develop a computational model to assess and evaluate the annual water level fluctuation (WLF) impacts and their trends along any open channel (river, canal or lake) and provide reliable information that may help handle their implications. The impacts are related to water recession, flood plain areas, uncovered river bars and islands, locations of navigation bottle necks, and dredging works. The model is developed using Excel Spreadsheet VBA Coding. It computes the horizontal and inclined recession distances that govern water in take construction. It also computes the uncovered flood plain areas along the river reach to avoid encroachments and human interventions. In addition, it identifies the number of bar sand islands that emerge at low water levels to protect them against infringements. It also determines the locations of navigation bottle necks and computes the dredge volumes required. It can handle long river reaches quickly. Moreover, it is open-accessed where no hard locks or license renewals are required. It is run on Microsoft Excel which is an available and familiar environment to engineers. Therefore, the model can be a quick and powerful tool to support the decision-making process for projects related to such impacts, especially at the prefeasibility study stages. Reach '1' of River Nile in Egypt was taken as a case study to apply the model and show its capabilities in assessing the WLF impacts. This could help compute and analyze the size of the impacts and conceive their trends. Finally, the model could provide information about the impacts in concrete figures which can support decision making in coping properly with the impacts.

Wrack line formation and composition on shores of a large Alpine lake: The role of littoral topography and wave exposure.

Wrack lines are a key formation along shorelines that provide organic matter and bring ecological diversity to the local environment. Although wrack line formation has been extensively studied along marine beaches and estuaries, in contrast, knowledge about the environmental variables that promote wrack line formation within inland lakes is widely lacking. In one of the first studies to focus on wrack line formation on lakesides, we analysed the dimensions, volume, elevation and particulate composition of 36 wrack lines across 20 shore sections of a large, oligotrophic Alpine lake with natural water level fluctuations (Lake Constance-Obersee). Using multivariate partial least squares (PLS) regression, we identified the key environmental variables that drive wrack accumulation in lakeside areas. Our results demonstrate that wrack line volume increased with (1) the width of the eulittoral zone as an indicator of the swash conditions (up-rush vs. down-wash), (2) high exposure to wind waves as indicated by the total effective fetch, (3) high exposure to ship waves (catamaran ferry), and (4) the width of the sublittoral zone as an indicator of the availability of source material (Chara spp.) and of the wave energy dissipation rate of the incoming deep water waves. Sediment texture played only a minor role. Wide eulittoral zones and high ship wave exposure favoured high proportions of lake-borne components (Chara remains, mollusc shells), while the reverse was true for land-based components. Anthropogenic wastes were only present in small proportions. We discuss four main factor groups influencing the amount of wrack in marine beaches and on lakeshores considering similarities (waves, breakers, swash, dissipation, relief) and differences (tides vs. annual water level fluctuations) of the two systems, and point out research gaps. We demonstrate that wrack line formation is also important in large inland lakes and can be analysed using basic ideas from relevant marine studies.

Application of spectral analysis to the reservoir-triggered earthquakes in Three Gorges reservoir region, China

In the Three Gorges reservoir region, central China, seismic activity increased substantially after the reservoir impoundment in 2003 which continues till date. Previous studies show that these are reservoir-triggered earthquakes and various factors are responsible for the increase in seismic activity after the reservoir impoundment. However, these studies do not provide a comprehensive assessment of influence of reservoir water level variations on spatiotemporal distribution of earthquakes. In this study, we statistically analyze the influence of the water level variations on the increased seismic activity in the reservoir region for the period from May 2003 to April 2020, using the power spectrum and singular spectrum techniques. Our statistical analyses confirm the influence of long-term variations in the water level time series on the occurrence of earthquakes after the reservoir impoundment. The analysis also indicates a positive role of annual reservoir water level fluctuations in the total seismicity of the region. Depending on the cluster patterns and relationship with faults, the earthquakes of the Three Gorges reservoir region are divided into three seismic zones (A, B, and C). For zone C, both the power spectrum and singular spectrum analyses confirm the strong periodic influence of reservoir water level variations on the earthquakes. Increase in seismicity of zone B is only in the initial period but not in the later stages of water impoundment and our statistical analyses indicate that the seismicity of this zone is not directly related to the annual reservoir water level variations. This confirms the conjecture in the earlier studies that the seismicity of this zone is related to the collapse of coal mines present in the area in the initial stages of reservoir impoundment. For zone A, our statistical analyses do not show strong influence of the annual reservoir water level variations on the occurrence of earthquakes. We suggest that this is due to the contribution of various other factors along with reservoir impoundment in the occurrence of earthquakes in this zone, as also opined in some earlier studies.

A dataset of carbon dioxide flux observation of the <italic>Miscanthus sacchariflorus</italic> ecosystem of Dongting Lake Wetland from 2014 to 2016

With considerable carbon sequestration potential, lakes are active channels of terrestrial carbon cycle. As the second largest freshwater lake in China, Dongting Lake has huge annual water level fluctuations (12–14 m), and the unique hydrological situation is a major challenge and of significance to the study of the carbon and water cycle processes at Dongting Lake, the control mechanism and its response to environmental changes. Miscanthus sacchariflorus is widely distributed at Dongting Lake and is a perennial tall bamboo-like herb with well-developed rhizomes and high carbon sequestration potential. Targeting the Miscanthus sacchariflorus ecosystem of Dongting Lake as the research object, we used the eddy-correlation (EC) system in the study to conduct long-term localized observations of carbon fluxes in the Miscanthus sacchariflorus ecosystem. As the first Dongting Lake ecosystem research station in China, National Field Scientific Observation and Research Station of Dongting Lake Wetland Ecosystem in Hunan Province (Dongting Lake National Station) collated the fluxes and conventional meteorological data of the Dongting Lake Miscanthus sacchariflorus ecosystem from June 2014 to December 2016 based on the data processing system of the China Flux Observation and Research Network (ChinaFLUX). The dataset includes the data files of net ecosystem carbon exchange, ecosystem respiration, ecosystem carbon exchange, latent heat flux, sensible heat flux, air temperature, relative air humidity, water vapor pressure, net radiation, and soil temperature at half-hourly, daily, monthly, and yearly scales. It can provide a strong data base for scientific understanding of the spatial and temporal dynamics of carbon, water and heat in the Miscanthus sacchariflorus ecosystem, material and energy cycles, estimation of global carbon sequestration potential, as well as response and adaptation to global climate change.

How far are groundwater resource assessments in India reliable?

AbstractThe article critically reviews the methodology adopted by the Central Ground Water Board (CGWB) for the assessment of groundwater resources in India. The authors developed a water balance equation that simulates the changes in annual and seasonal groundwater storages of an agricultural region, using a water accounting framework; they solved the developed equation using the data of annual and seasonal water level fluctuations for a wet year for Ludhiana district of Punjab to estimate different components of the water balance. The estimated values are used to test the robustness of the CGWB methodology for monsoon recharge. The annual groundwater storage change obtained from solving the water balance equation was compared with the observed change in annual groundwater storage and was found to closely tally. As per the water balance equation, the CGWB estimates of rainfall recharge conform to the annual water level fluctuations recorded by the agency and therefore are not reliable. Hence, we could infer that our methodology is superior to that of CGWB for estimating monsoon recharge. The validated equation was also used to estimate the recharge from rainfall during a dry year. Using these outputs in a simple groundwater balance equation, irrigation return flows were estimated for the wet and dry years. The equation was then extended to the Ahmednagar district of Maharashtra, a hard rock area, for estimating the surface water import during a wet year, the key unknown in the region's water balance. Hence, our methodology can be employed to estimate rainfall recharge for dry years using annual changes in groundwater storage and estimated consumptive uses of water, when the “WLF approach,” used by CGWB, fails, owing to the presence of an additional variable, that is, monsoon draft. For wet years, it can be used to arrive at the consumptive use of water for various purposes.

Meteorological forcing and hydrological connectivity together control the thermal regime of Xiangxi Bay, a tributary of the Three Gorges Reservoir

Thermal conditions, such as stratification and mixing characteristics, are important for water quality and ecology in lakes and reservoirs. The prevailing strong stratification is a major factor contributing to global algal blooms, underscoring the need to understand the thermal regime and driving mechanisms. The thermal conditions of riverine/canyon-type reservoirs and tributaries are distinct from those of other districts, and hydrological connectivity and meteorological forcing play an important role in stratification and mixing. To test this concept and analyse how hydrological and meteorological conditions affect the thermal regime of Xiangxi Bay (XXB), one of the largest tributaries at the head of the Three Gorges Reservoir (TGR) in China, we conducted approximately one year of field monitoring. The results indicate that XXB is a typical subtropical continuous warm polymictic water body. Affected by the regulation of the TGR, the water level of XXB fluctuated up to 30 m. The stratification started in March and reached its maximum during the flood season; with reservoir storage in September, the stratified structure gradually collapsed. The combination of lower water level, increased shortwave radiation (SW) and warmer air temperature (AT) enhanced the stratification intensity (N). Vertical mixing produced by meteorological forcing was limited, turbulent mixing in the near-surface was dominated by the convection velocity (w∗) rather than the frictional velocity (u∗w), and high wind speeds enhanced the convection effect. During the heating period, the peak u∗w lagged behind w∗ by approximately 3 h, and near-surface stratification suppressed wind-induced turbulence. In addition, no temporal heterogeneity was observed during the cooling period. The heat budget was mainly controlled by the intrusive discharge of the mainstream of the TGR, and the annual water level fluctuation was the main factor affecting the heat imbalance (ΔQT-ΔQM). However, in the near-surface of the water column, heat distribution (indicator: mld) was mainly dominated by the water–air heat flux, Qnet (r = -0.833, p < 0.01, n = 323), and the difference in the cooling rate between the mainstream of the TGR and XXB induced a diurnal heat imbalance. The results of this study, the first long-term, muti-parameter field monitoring effort in XXB, provide new insights into the thermal regime of riverine reservoirs and their influencing factors while offering a thermodynamic perspective on eutrophication and algal blooms in reservoir tributaries.

Effects of hydrological forcing on short- and long-term water level fluctuations in Lake Huron-Michigan: A continuous wavelet analysis

Understanding water level fluctuation patterns in the Great Lakes is one of the pillars for designing adaptive management practices that can mitigate the impacts of extreme water levels on shoreline infrastructure and associated economic activities. The present study uses continuous wavelet transformation to conduct a two-dimensional frequency-scale spectral analysis on monthly water levels in Lake Huron-Michigan. Consistent with past work, we detected 1-, 8-, 12-, and 36-year quasi-state periodicities in water level records during the 1860–2015 period. The wavelet analysis revealed diminishing, re-emergent, and/or intermodulation patterns in the long-term periodicities, but the 1-year cycle has persisted throughout the temporal domain studied. While the features of the dominant frequencies are consistent with previous findings, the consideration of wavelet ridges with the continuous wavelet transformation yielded a complete picture of evolution in time–frequency domain that is impossible to achieve with the same accuracy using conventional signal processing methods. Continuous wavelet transformation and analysis of wavelet coherence between hydrological and water level changes signified the role of runoff and evaporation as the primary drivers of water level fluctuations in Lake Huron-Michigan. Evaporation strongly influences the annual water level fluctuations, whereas runoff and precipitation covary with the water levels in both intraannual and interannual cycles. Specifically, analysis of phase differences indicated that runoff leads water level change by π/4 rad from 2-month up to 1.5-year cycles, then runoff starts to become nearly in-phase (with small intermittent lags) up to the 12-year cycle, two main recurring cycles of 0.5- and 1-year. Finally, we conducted a comprehensive assessment of 16,809 regression models, which highlighted the effects of runoff-minus-evaporation in modulating the extreme high or low water levels, which in turn could inundate the areas close to the shoreline or reduce the navigability in shallow parts of Lake Huron-Michigan.

EXPLORATION OF HELOPHYTE GROWTH DYNAMICS IN THE PSKOVSKOE LAKE LITTORAL ZONE USING REMOTE SENSING DATA

The article presents the results of an assessment of the spatio-temporal dynamics of the Pskovskoe Lake littoral zone overgrowing with helophytes in the period from 1989 to 2019. Lake Pskovskoe is a shallow body of water with a high trophic status, annual water level fluctuations, and an extensive littoral zone (about 15 % of the water surface area). The said factors, coupled with global warming, create favorable conditions for the expansion of higher aquatic vegetation. A detailed analysis of the history of research of the lake water area is provided. The types of the lake overgrowing in different years with indication of the prevalent ecological groups and dominant species are suggested. Lake Pskovskoe is characterized by the helophytic – “fragmentary-belt” type of overgrowing. Data from the literature and own field data were analyzed; multispectral satellite images taken in different years were thematically processed. The process of littoral overgrowing in this period has been fluctuating, with a positive trend component. In low-water years, the occurrence of helophytic plants increased. The expansion of helophytes in relation to the averaged shoreline configuration ranged from 26.56 to 641.9 ha, i. e. 0.04–0.9 % of the lake total area. The largest helophyte expansion was noted at Talabsk station, where the overgrown area gained 7.5 hectares in the period from 2007 to 2017. Amongyear changes of the main structural parameters of the southern reed (Phragmites australis (Cav.) Trin. Et Steud., 1840), the species playing the key role in the overgrowing of Lake Pskovskoe, are analyzed. The density and biomass of the reed stands have increased over the period of observations.

Distribution, sources and risk assessment of PAHs in soil from the water level fluctuation zone of Xiangxi Bay, Three Gorges Reservoir.

Information on PAH distribution in the water level fluctuation zone (WLFZ) of Three Gorges Reservoir is limited. In this study, we investigated PAH distribution and sources and assessed PAH risks, over one annual water level fluctuation cycle (June 2017-June 2018) at four elevations spanning the WLFZ (145m, 155m, 165m and 175m) at seven locations in the water level fluctuation zone along Xiangxi River. The mean total PAH concentration in June 2018 (953ngg-1) was significantly higher than in June 2017 (494ngg-1), and the horizontal and vertical distributions of PAHs changed significantly. The changes in distribution patterns provided evidence for the cause of increased PAH levels, which were attributed to construction of the Xiangxi River Bridge. Thus, this study of PAH dynamics in the WLFZ soils of Xiangxi Bay also provided valuable information on the impact of bridge construction on WLFZ soils. The change in PAH levels among stations implicated sediment disturbance resulting from bridge construction as the major contributor to the increased PAH levels. Source characterization, based on the ratios of certain PAHs, indicates that PAHs are mainly from the combustion of petroleum fuels, biomass and coal. These ratios indicated that the proportion of PAHs from fuel combustion increased from 2017 to 2018, implicating the heavy equipment used during bridge construction as another source of the increased PAH levels. The incremental lifetime cancer risk (ILCR) model was used to assess the health risk of the PAHs and the range among all age groups (10-5-10-4) indicates a potential health risk. The mean effects range-median quotient (M-ERM-Q) was used to assess the ecological risk of PAHs and the range (0.1-0.5) indicates low to medium risk. The increase in PAH levels from 2017 to 2018 increased the risk to public health and the environment. The results of this investigation provide a reference for ecological restoration of the WLFZ and support development of effective policies for environmental and public health. Further, the results provide information on the impact of bridge construction on WLFZ soils and identify research needed to more fully understand PAH dynamics in WLFZ soils.

Responses of an emergent macrophyte, Zizania latifolia, to water-level changes in lakes with contrasting hydrological management

Twenty-four lakes associated with the Yangtze floodplain and Huaihe basin, China, with different degrees of disconnection from the river systems, exhibited managed hydrologies ranging from minimally fluctuating reservoir-like lakes, through intermittently fluctuating lakes to those with large, quasi-natural fluctuations in level. We hypothesized that annual water-level fluctuations limit growth and survival of the emergent macrophyte Zizania latifolia. We investigated adaptations to submergence and sought to define the tolerances of Z. latifolia to the amplitude and timing of water-level fluctuations in these types of lake, at different stages in its phenology and life cycle. Shoots from rhizome buds emerged in early spring and reached maximum extension with high water levels in summer. Z. latifolia did not occur in lakes with the highest amplitude (>5 m) of fluctuation. Height growth in lakes with low amplitude (reservoir-like) was smaller than in lakes with greater amplitude (intermittent to quasi-natural fluctuations), giving the appearance of ‘short’ and ‘tall’ phenotypes. Across all lakes, however, maximum height was linearly related to water depth in June and to annual amplitude of water level, indicating a continuous phenotypic response. Peak biomass was weakly affected by these environmental drivers. Field experiments showed that seedlings tolerated water depths of c. twice their height (0.6 m), and submergence rates similar to their maximum extension growth rate (2 cm.d−1). Sprouting of rhizome buds was unaffected by submergence to a depth of 0.4 m, but then declined with depth. This study reveals the effects of large-scale hydrological engineering on an emergent macrophyte of economic and conservation importance and informs the management of its populations under seasonally fluctuating water-level regimes.

Macrohabitat studies in large Brazilian floodplains to support sustainable development in the face of climate change

Large floodplains are complex ecosystems at the land–water boundary. Because of rainy and dry seasons, most tropical floodplains are subjected to annual water-level fluctuations. During typical low-water periods, extensive areas of the floodplains are dry. However, relatively small geomorphological differences within the boundaries of the floodplains result in comparatively large differences in the length and depth of inundation and, in turn, the establishment of distinct plant communities, called macrohabitats. The specific ecological conditions of these macrohabitats have to be taken into consideration in the development of sustainable management methods and protection measures. Extreme floods and droughts have very strong effects on flora and fauna. The low hydrological buffer capacity of floodplains makes them vulnerable to anthropogenic changes in hydrology and to the impacts of global climate change. This study presents a macrohabitat classification system that has been applied to three large Brazilian floodplains: the forested Amazonian várzeas and igapós, and the savanna floodplains of the upper Paraguai River (Pantanal of Mato Grosso). Examples are provided to demonstrate the applicability of this system in comparative inter- and intra-wetland studies and therefore its utility in assessing environmental changes, including those arising from global climate change. Our approach can also be used to guide the implementation of sustainable management methods and as a focal point for the development of environmental legislation.

Relationship among physicochemical conditions, chlorophyll-a concentration, and water level in a tropical river–floodplain system

The free-flowing Usumacinta River maintains an average annual water-level fluctuation of 6.7 m. This study evaluated relationships between 14 physicochemical and biological variables and key factors in four water-level conditions in a river–floodplain system. The analysis incorporated intra-annual variation in all variables, with each selected in accordance with multiple statistical and physicochemical criteria. Possible correlations were examined as a function of various physicochemical and biological factors at each water level. Within the study area, defined by a temporal gradient in principal component 1, the yearly river overflow above the bankfull stage is characterized by water with a low level of total suspended solids. Data on riverine wetlands suggest that seasonal changes are key to determining intra- and inter-annual chlorophyll-a levels and water clarity. However, opposite trends are observed for high and low water-level conditions. Nutrient enrichment cannot be taken as the key physicochemical factor of water level, under either water-level conditions, due to the lack of a temporal gradient in principal component 2 and the high biochemical variability of nitrate and orthophosphate levels. In conclusion, the hypothesis was accepted for the production of phytoplankton biomass and light attenuation at low and high water levels, as both were dependent on intra-annual changes. The increases in chlorophyll-a related to the minimal variability at the lowest water level open the opportunity to gauge this relationship as a possible environmental predictor for river–floodplain systems.

Mobility and potential risk of sediment-associated heavy metal fractions under continuous drought-rewetting cycles

Ecological decline in the water level fluctuating (WLF) zone of the Three Gorges Reservoir (TGR) has been well established over the past decades. However, the effect of heavy metal fractions present in the sediment and their potential ecological risk under the anti-seasonal hydrological regime are still unclear. The Pengxi River is a tributary of the Yangtze River and it has a typical annual water level fluctuation ranging from 145 to 175m above sea level. The current study examined heavy metal fractions in sediments containing Cr, Cd, Cu, Pb and Mn collected along the WLF zone using the Tessier sequential extraction scheme. The total organic carbon (TC), total nitrogen (TN), carbon/nitrogen ratio (C/N), pH, particle size composition and content of nitrate (NO3−-N), and ammonium (NH4+-N) differed dramatically among the sampled altitudes and depths and was significantly correlated with the flooding time of the WLF zone. At lower altitudes of the WLF zone, the amounts of the exchangeable (EXC), carbonate-bound (CA) and total heavy metal contents of the surface sediment were much higher compared to those of higher altitudes of the WLF zone. The risk assessment code (RAC) for Cd and Mn showed an opposite trend to that of Cr, Cu, and Pb and mainly depended on the organic matter-bound fraction (OM). The modified RAC (mRAC) indicated a very high potential adverse effect for the whole WLF zone, although the risk value was much lower at the lower altitudes and upper depths of the WLF zone. Our results showed that the positive response of the loosely bound fractions (LOS) of heavy metals to the drought-rewetting (DRW) process minimizes the risk of heavy metals in the WLF zone sediment.

Stability of macroinvertebrate communities in a newly formed large reservoir with recurrent impoundment events

Limited knowledge was known about the stability of newly formed large reservoirs for laking long-time datasets. We used a decade-long monitoring dataset to examine the stability of macroinvertebrate community in the Three Gorges Reservoir and the impacts of water level fluctuations caused by recurrent impoundment events. We found that the macroinvertebrate community experienced a weak directional change over the ten years. More specifically, the directional change only happened during the initial impoundment stages and the community became relatively stable since the third impoundment stage. The communities were significantly different among the three impoundment stages when the annual water level fluctuation increased consecutively. The temporal variation of the community in the former phase was on account of the increasing water level fluctuation and the intrinsic succession process. The species richness, evenness and production all showed slight increase trends since the third impoundment stage, which implied the stabilization of the community. Nevertheless, influenced by the huge annual water level fluctuations (30 m) and vagaries seasonal floods, the community experienced high stochastic year-to-year variation. Our study suggests that the macroinvertebrate community in the Three Gorges Reservoir has become relatively stable and will keep the stability with high stochastic variation for a long time.

Water quality characteristics of Poyang Lake, China, in response to changes in the water level

As one of the few remaining lakes that are freely connected with the Yangtze River, Poyang Lake exhibits large annual water level (WL) fluctuations. In this study, weekly samples were collected at the north end of Poyang Lake from September 2011 to December 2012, and we investigated the mechanism of limnological responses to fluctuations in the WL. The study covers three seasons that were associated with WL fluctuations ranging from 8 to 19 m. Spearman's rank correlations and multivariate non-metric multidimensional scaling analyses indicated that low and high WL periods differed in a number of water quality characteristics. The low WL period coincided with the non-growing season and was associated with the peak concentrations of nitrogen, the highest turbidity (Turb), and the lowest water temperature. The high WL period was mainly characterized by enhanced chlorophyll a concentration. Spearman's rank correlations revealed positive relationships between the WL and the concentrations of NO3-N and PO4-P and negative relationships between the WL and the Turb, total nitrogen, total phosphorus, NO2-N, and NH4-N concentrations. All results support the conclusion that the large WL fluctuations are the principal drivers for physicochemical variables in this floodplain lake ecosystem.

Analysis of the impact of water level fluctuations on macrophytes in Miyun Reservoir after receiving water transferred by the South-to-North Water Diversion Project

As the main primary producers in aquatic ecosystems, macrophytes affect the structure and function of aquatic ecosystems, and their distribution is controlled by water depth. Miyun Reservoir in Beijing will have to experience substantial changes in water level and surface area as it begins to receive water transferred by the South-to-North Water Diversion Project, which will have an adverse impact on the macrophytes growing there. In this study, a hydrodynamic model was constructed with MIKE21 and then used in a simulation in three scenarios: dry year, normal year and wet year. The results suggest that during water diversion, the annual and interannual water level fluctuations will be too significant for them to adapt and as a result, the original macrophytes in the reservoir tend to die and disappear completely. The area of the zone suitable for macrophyte growth, or suitable growth zone (SGZ), fluctuated. Restricted by the main dam and auxiliary dam to its south, the overall suitable growth zone moved toward the northeast and northwest of the reservoir, with a northeastward movement of its centroid. The distance and path of movement varied between scenarios. After the water diversion was completed, the suitable growth zone shrunk in the three scenarios. It is predicted that the macrophyte species diversity and richness of the reservoir can recover to the levels recorded before water diversion only in dry year. These results suggest that manual interventions should be implemented after water diversion to speed up the natural recovery of aquatic plant communities in Miyun Reservoir and thereby maintain the stability of the aquatic ecosystem.

Impact of alternating wet and dry periods on long-term seasonal phosphorus and nitrogen budgets of two shallow Mediterranean lakes

The water balance, with large seasonal and annual water level fluctuations, has a critical influence on the nitrogen and phosphorus dynamics of shallow lakes in the semi-arid climate zone. We constructed seasonal water and nutrient budgets for two connected shallow lakes, Lakes Mogan and Eymir, located in Central Anatolia, Turkey. The study period covered 20years with alternations between dry and wet years as well as restoration efforts including sewage effluent diversion and biomanipulations in Lake Eymir. Both lakes experienced a 1–2m water level drop during a drought period and a subsequent increase during the wet period, with seasonal water level fluctuations of 0.60 to 0.70m. During wet years with high water levels, small seasonal differences were observed with a nutrient peak in spring caused by external loading and nutrient loss via retention during summer. During years with low water levels, nutrient concentrations increased due to internal and external loading, exacerbated by evaporative water loss. In Lake Eymir, a shift to eutrophic conditions with turbid water occurred under low water level conditions and consequent internal loading of P from the sediment, causing high nutrient concentrations in summer. Our results indicate a threat of lakes drying out in the semi-arid climate zone if evaporation increases and precipitation decreases as anticipated from the global climate change predictions. In addition, our results show the influence of the water balance on the eutrophication of shallow lakes in the Mediterranean climate zone and highlight the ultimate consequences for lake management.

Aquifer response to recharge\u2013discharge phenomenon: inference from well hydrographs for genetic classification

The continuous groundwater level data emanating from a high-frequency automatic water level recorder installed in a purpose-built piezometer provides a true hydrograph. Analyses of such hydrographs fairly reflect the aquifer character and can be used to draw inference for genetic classification of hard rock aquifers. The signature shape of annual water level fluctuation curve (annual cycle) of a piezometer is due to the specific character of the aquifer and the way it responds to the recharge–discharge phenomenon. The pattern of annual cycle remains identical year after year, although its magnitude may vary with the annual quantum of recharge–discharge. Lithology of the aquifer does not control the shape of the curve. Based on the crest and trough shape, the hard rock aquifers of Peninsular India, where the monsoonal pattern of rainfall occurs, have been classified into genetic groups. It is also found that the nature of the aquifer can be determined by visual comparison of apparent line thickness of the hydrograph, where thin lines denote unconfined aquifer and the apparently thicker lines correspond to confining condition. The response of an aquifer to a pumping event can be identified and separated by its pattern. Thus, the aquifer classification can be automated by adopting the proposed classification scheme.

Masked Expression of Life-History Traits in a Highly Variable Environment

Differing life-history strategies may act as a constraint on reproductive expression that ultimately limits the ability of individual species to respond to changes in the magnitude or frequency of environmental variation, and potentially underlies the variation often inherent in phenotypic and evolved responses to anthropogenic change. Alternatively, if there are environmental cues that predict reproductive potential, differential expression of life-history strategies may represent differences in the adaptive capacity to optimize current reproductive value given variation in environmental conditions. We compared several aspects of walleye Sander vitreus spawning ecology at two reservoirs that differ in environmental variability (i.e., annual water-level fluctuation) to identify the capacity of phenotypic expression and the corresponding association with age. Despite significant differences in female body and liver masses between reservoirs that differ in environmental variability, we found no difference in reproductive investment measured by egg size and fecundity. Walleye in a highly variable environment appear to exhibit reproductive traits more typical of a short-lived life-history strategy, which may be resultant from the interaction of environmental and anthropogenic pressures. This finding emphasizes the need to identify the degree to which life-history expression represents physiological constraints versus ecological optimization, particularly as anthropogenic change continues to alter environmental conditions.

Quantifying Tropical Wetlands Using Field Surveys, Spatial Statistics and Remote Sensing

Tropical wetlands support high biodiversity and ecological services, but in most areas they suffer from a paucity of baseline data to support management. We demonstrate how modern technology can be used to develop ecological baseline data including, landuse/landcover, water depth, water quality, lake-level fluctuation, and normalized difference vegetation index (NDVI). For the first time we quantified and mapped these metrics for the Paya Indah Wetlands, Malaysia using the new high-spatial-resolution World View 2 imagery. Landuse/landcover classifications were validated by field visits and visual interpretation of the imagery. NDVI was extracted based on red and near infra-red 2 bands. Topo to Raster method was used for interpolation of water depths. Annual mean of a water-quality index and annual water-level fluctuation of lakes were interpolated across lakes using the inverse-distance weighting method. Qualitative and quantitative accuracy assessment of classification (75 % overall accuracy, user’s accuracies ranged from 60 % to 90 % and producer’s accuracy ranged from 60 % to 97 %) was promising and clearly illustrated that World View 2 imagery can yield fast and reasonably precise identification of ecosystem characteristics for ecological baselines.