Small Artificial Lake Research Articles

A Sponge Village Flood Response Method Based on GIS and RS Analysis Formation—A Case Study of Jiangou Village

This study was conducted in response to the Beijing–Tianjin–Hebei mega heavy rainfall event at the end of July 2023, and the severely affected and representative Jiangou village in Beijing was selected as the study area. A variety of methods were used to synthesize and analyze the situation and propose an adaptive response to heavy rainfall and flooding in the village. Based on multi-source remote sensing (RS) data, a comprehensive topographic and hydrological characterization was carried out, and the precipitation before and after the disaster was analyzed; the flood inundation area was extracted using the improved normalized water body index (MNDWI) and OTSU thresholding methods, and the changes of water bodies during the flooding period were quantitatively analyzed; and an improved convolutional-neural-network-based building identification and extraction model was constructed to extract the research distribution of buildings in the area. The sponge city construction (SPCC) method was improved to obtain a method that can mitigate flood risk and adapt to villages by constructing small artificial lakes and local topographic buffers to improve the water storage and drainage capacity of villages. The study shows that these methods are innovative in flood hazard analysis and mitigation but still need further improvement in data accuracy, simulation depth, and system evaluation.

Winter mortality and growth of juvenile noble crayfish (Astacus astacus) under realistic environmental conditions – Implications for conservation management

Noble crayfish (Astacus astacus) are endangered in many parts of Europe. Conservation efforts, including stocking measures, are widely conducted to safeguard the species and associated ecosystem functions. Due to limited availabilities of adult crayfish, juvenile noble crayfish are frequently released into lakes and rivers during autumn, usually without information on their fate and growth during the following winter. To investigate size- and density dependence of winter mortality and growth of newly stocked noble crayfish we conducted a mesocosm experiment in a small artificial lake in northern Germany. The experiment was carried out at water temperatures between 0.7 °C and 9.1 °C from mid-December until mid-March and simulated stocking densities of 20, 60, and 120 crayfish per square meter with unlimited food availability. Winter mortality rates were generally low and strongly size dependent. Specifically, a winter mortality rate of 9.2% was observed and crayfish with a total length (TL) above 34 mm all survived. The relative risk of mortality in dependence of TL increased by 41–94% (95% CI) with every decreasing centimetre of TL at the onset of winter. Increasing density had no effect on winter survival, but tended to reduce growth. Our work indicates that stocking measures of noble crayfish for conservation reasons can decrease costs and increase prospects of success if juveniles larger than 30 mm TL are used as stocking material.

Geological Factor Causing Water Decrease of the Baturagung Reservoir, Based on ERT Geoelectric Application

The Baturagung reservoir, a small artificial lake is located in the Gedangrejo village, Karangmojo district, Gunungkidul regency, Yogyakarta Special Region, Indonesia. Initially, the reservoir was built on hilly geomorphology with volcanic sandstone lithology intended to meet the agricultural water needs of the people in the surrounding area, and as a tourist spot as well. Since 2019, there has been a decrease in the volume of reservoir water so that the reservoir is never fully filled with water. Due to the decrease in reservoir water volume, residents' water needs are not being met, and visitors to this place are reduced. Therefore, it is important to accomplish a study with the purpose to identify the factors that cause reservoir water depletion, such as the conditions of geomorphology, lithological variations, geological structures, and hydrogeology of the area. The methodologies used in this study are field surveys, surface mapping, and the application of the electric resistivity tomography method. The results show that there is a weak zone with a resistivity ranges 4.24– 45.9 Ωm, northeast-southwest trend, interpreted as a fault crossing the study area. It is deduced that the fault is active, causing the tearing of the geomembrane underlying the reservoir, initiating water leakage from the reservoir to the southwest direction.

Seasonal Variation and Vertical Distribution of Inorganic Nutrients in a Small Artificial Lake, Lake Bulan, in Mongolia

This is the first seasonal observation study on nutrient dynamics undertaken in a small freshwater lake with eutrophication in Mongolia. The vertical profile and seasonal fluctuation of nutrients are crucial to understanding the biogeochemical cycles in aquatic systems. In this study, field research was carried out at a small and shallow lake, Lake Bulan, in the lower Kharaa River basin. The area has been receiving increased nutrient loads from the water catchment area for the last 20 years. Water samples were collected seasonally from the lake from 2019–2022 and analyzed for nutrients, major cations, trace metals, and dissolved organic carbon. The average concentration of dissolved inorganic nitrogen (DIN) in the surface lake water had a wide seasonal variation from 0.26 ± 0.11 mg N/L in August to 1.44 ± 0.08 mg N/L in January. Seasonal differences were also observed in the vertical profiles. Concentrations were relatively similar at the various water depths in April and September at turnover time. Thermal stratification was observed when the lake was covered in ice, with the maximum concentrations being observed in the bottom layer in the months of January and August. The phosphate concentration showed a similar variation trend. These results indicate that both the summer and winter stratifications are important for regeneration of nutrients in the bottom layer, biochemical cycling, and mitigating impacts of global warming on small and shallow lakes in Mongolia.

Diel variation of CH4 emission fluxes in a small artificial lake: Toward more accurate methods of observation

Lakes are significant sources in global methane (CH4) budgets. However, estimations of the magnitude of global CH4 emissions from lakes may be highly biased owing to the uncertainties in data originating from observation times, methods, and parameterizations of the gas transfer velocity (k). Here, we conducted continuous 48-hour measurements of CH4 fluxes using the floating chamber method seasonally at Lake Baihua, a small reservoir in southwestern China, and compared the results with estimates derived from boundary layer models. Results showed that there was a weak dependency of k on wind speed, indicating that wind speed was not the major factor regulating gas exchange in such small lakes. It is thus concluded that the wind speed-dependent boundary layer model method is not suitable for CH4 flux observations in small and medium-sized lake, and that the floating chamber method is recommended for use instead. The measured CH4 fluxes displayed remarkably diurnal patterns, therefore the use of single observations to represent daily average values comes with unacceptably large uncertainties. A reasonable alternative is averaging observations made at sunrise and at sunset to represent daily values, which has a much smaller uncertainty (ranging from 0.8% to 13.6%). The coincident peaks of CH4 and chlorophyll concentrations in the subsurface indicate that CH4 originated mainly from aerobic methanogenesis. Solar radiation is likely one of the major factors regulating CH4 production and emissions in the lake through enhancing CH4 production, inhibiting CH4 oxidation, and probably changing hydrodynamics conditions. Therefore, irradiation should be taken into consideration as a key factor in observing CH4 fluxes in lakes. As sampling times are limited, observations during both sunny and cloudy weather should be proportionally included. This is the first time, to the best of our knowledge, that solar radiation has been proposed as a key driver of CH4 emissions from lakes.

Ecosystem maturity modulates greenhouse gases fluxes from artificial lakes

Lentic ecosystems play a major role in the global carbon cycling but the understanding of the environmental determinants of lake metabolism is still limited, notably in small artificial lakes. Here the effects of environmental conditions on lake metabolism and CO2 and CH4 emissions were quantified in 11 small artificial gravel pit lakes covering a gradient of ecosystem maturity, ranging from young oligotrophic to older, hypereutrophic lakes. The diffusive fluxes of CO2 and CH4 ranged from −30.10 to 37.78 mmol m−2 d−1 and from 3.05 to 25.45 mmol m−2 d−1 across gravel pit lakes, respectively. Nutrients and chlorophyll a concentrations were negatively correlated with CO2 concentrations and emissions but positively correlated with CH4 concentrations and emissions from lakes. These findings indicate that, as they mature, gravel pit lakes switch from heterotrophic to autotrophic-based metabolism and hence turn into CO2-sinks. In contrast, the emission of CH4 increased along the maturity gradient. As a result, eutrophication occurring during ecosystem maturity increased net emissions in terms of climate impact (CO2 equivalent) due to the higher contribution of CH4 emissions. Overall, mean CO2equivalent emission was 7.9 g m−2 d−1, a value 3.7 and 4.7 times higher than values previously reported in temperate lakes and reservoirs, respectively. While previous studies reported that lakes represent emitters of C to the atmosphere, this study highlights that eutrophication may reverse lake contribution to global C budgets. However, this finding is to be balanced with the fact that eutrophication also increased CH4 emissions and hence, enhanced the potential impact of these ecosystems on climate. Implementing mitigation strategies for maintaining intermediate levels of maturity is therefore needed to limit the impacts of small artificial waterbodies on climate. This could be facilitated by their small size and should be planned at the earliest stages of artificial lake construction.

Geochemical characterization of an urban lake in the centre of Rome (Lake Bullicante, Italy)

Urban lakes have become increasingly important in the planning of urban ecology, green infrastructure and green areas in European cities. This paper describes the chemical, isotope and microbial features of Lake Bullicante, a small artificial lake located within the urban area of the city of Rome. It has an anthropogenic origin due to excavation works that intercepted the underlying aquifer, giving rise to a water body. The lake area is 7.000 m2, with a maximum depth of 7 m and located on the distal deposits of the Alban Hills Volcanic District in an area named Acqua Bullicante (i.e. Bubbling Water), where degassing phenomena were historically recorded. The proximity of this volcanic district motivated the study on Lake Bullicante as a potential open-air laboratory to trace possible degassing phenomena in a highly urbanized area. A preliminary geochemical and microbial sampling survey was carried out in winter 2018. Samples were collected along a vertical profile of the lake from the surface to the maximum depth. Major, minor, trace elements, dissolved gases and stable isotopes (δD-H2O, δ18O- H2O, δ13C-CO2) were analyzed, along with the analysis of 87Sr/86Sr ratio. The microbial community characteristics were analysed by epifluorescence microscopy (CARD-FISH) and flow cytometry. The chemical composition and water isotopes suggest that lake water has a meteoric origin and is related to a Ca-HCO3 shallow aquifer hosted in volcanic rocks. This is confirmed by both the 87Sr/86Sr ratio of lake water, which falls in the range of values of Alban Hills volcanites, and the chemical-isotopic composition of neighboring wells. A relatively high concentration of dissolved CO2, its isotopic signature (δ^13C-CO2 20‰ V-PDB), and the high content in organic matter (DOC 10-30 mg/L) suggest for the lake a eutrophication state with denitrification also occurring. Considering the relatively high concentrations of dissolved CO2, an external input of carbon dioxide cannot be completely excluded and as a consequence, not even the hypothesis of mixing processes between biotic and inorganic CO2. This makes further investigations necessary especially during the summer, when the lake is stratified. A summer survey could be also useful to better understand the microbial processes into the lake, its eutrophication evolution and health status, and to plan eventual proper remediation strategies, providing important tools to the local administration and stakeholders to improve, protect and preserve this ecological niche.

Performance of IPAG60 for the treatment of turbid water from Lake Cibuntu, Cibinong

Water is the main need of all beings. People need water to fulfil their daily needs such as drinking, bathing, washing and other sanitation activities. The more population, the more activities that require water, so the greater the need for clean and or drinking water. Indonesian people require an average of 144 L/day/person of water. The level of clean water services in various regions in Indonesia is still relatively low, 45.85% in average, especially in the marginal area. Most of the water treatment plant in marginal areas cannot produce viable clean/drinking water, both in quality and quantity. Lake Cibuntu is a small artificial lake located in the Cibinong Science Center, Cibinong. It used as raw water for Peat Water Treatment Plant (IPAG60) and whose all measured parameters close to the required standard of the Regulation of Ministry of Health No 492/2010. This study aims to determine the performance of IPAG60 in treating water from Lake Cibuntu into clean water based on physical, chemical and biological parameters. Results showed that the quality of producing water meets the standards. The performance of efficiency achieved is 95% and can be maintained for 3 months of operations. Comparative studies between producing water from IPAG60 and local water company (PDAM) showed that the production water of IPAG60 has better quality. In case of water color, produced water from IPAG60 has a color level of 4 NTU, while tap water from PDAM has a color level of 11 NTU.

Occurrence and depositional history of organochlorine pesticides in the sediments of the Zayandehrud River in the arid region of Central Iran

In this study, surface sediments along the Zayandehrud River (14 samples), and two dated core sediments (46 samples) from small artificial urban lakes at the middle section of the Zayandehrud River in the Gavkhooni basin in the central arid regions of Iran were analyzed for residual levels of 20 organochlorine pesticide (OCP) compounds. Total OCP concentrations ranged from 0.1 to 50.1 ng g-1 dry weight and from 1.9 to 51.5 ng g-1 dry weight in surface and core sediments, respectively. Dichlorodiphenyldichloroethylene (DDE) and dichlorodiphenyldichloroethane (DDD) were found to be the predominant OCPs in these sediments. The calculated metabolic and isomeric ratios confirmed the aged nature of residual dichlorodiphenyltrichloroethane (DDT) in sediments. Moreover, the isomeric ratios indicated the aged nature of technical HCH (hexachlorocyclohexane), while the contribution of γ- HCH (lindane) as a main source has increased, especially in the last two decades. Past usage, as well as current usage of endosulfan technical mixture in the Gavkhooni basin, has been found in the last four decades. Analyses of sedimentary cores, as natural archives, have shown the successful ban on the use of organochlorine pesticides (especially DDT) in the Gavkhooni basin, and to some extent, in the central plateau of Iran. In general, it can be concluded that natural factors (i.e., floods and wet years) lead to soil leachate and play an essential role in remobilization and transfer of residual OCPs from soil to inland aquatic ecosystems in the Gavkhooni basin, which is an arid region.

Modeling the interaction of light and nutrients as factors driving lake eutrophication

Eutrophication is a major problem in the field of water environments at present, and its main driving factors are light and nutrients. In this paper, the process of eutrophication in small artificial lake is studied, according to the principle of water optics and conservation of mass, the light and the nitrogen and phosphorus in water nutrients were selected as influencing factors, and 16 different scenarios of light-nutrients interaction conditions were designed by orthogonal experiment. Then water eutrophication model was used to analyze the process of eutrophication under different light-nutrient scenarios. According to the comparison of simulation results, if the concentration of nutrients is increased under low light conditions, the growth of algae will be inhibited; And if the light condition is set to a fixed value, the simulation results under different nitrogen and phosphorus concentrations in the water show that the effect of phosphorus on algae growth is greater than that of nitrogen; In addition, comparing the growth of algae under different light and phosphorus scenarios, it can be seen that the light-driven effect is more significant than that of phosphorus. By simulating all the design scenarios and analyzing the results, it can be found that the algae growth rate reaches a maximum when the light intensity and the nitrogen and phosphorus concentration increase to a certain range; while continuing to increase the light and nutrient concentration exceeds a certain threshold range, the rate of algae growth will be inhibited.

Phytophilous Fauna of a Small and Artificial Urban Lake

Abstract Phytophilous community on Myriophyllum spicatum was studied in a small artificial urban lake in the city of Osijek (eastern Croatia), during the spring and summer season in 2010. In the eutrophic conditions, macrophyte stands were well developed and in the formed periphyton representatives of the following invertebrate taxa were found: Hydrozoa, Nematoda, Gastropoda, Cladocera, Copepoda, Insecta larvae - including families Chironomidae and Coleoptera. They displayed differences in temporal abundance patterns. Two separate phases in macrophyte colonization with differences in invertebrate composition and abundance were recorded. Insect larvae, particularly Chironomidae, were most abundant in the first phase, through the spring period, and Hydra oligactis (brown hydra) was most abundant in the second phase, i.e. summer period. Concurrently, microcrustacean abundance declined towards the end of the summer. Results of the analyses indicated that water temperature and perihyton biomass were the variables exerting the main influence on the invertebrate assemblage, while interestingly, macrophyte size and biomass were negatively correlated with most of the fauna abundance. On the other hand, brown hydra was negatively correlated with all other invertebrate taxa, except gastropods. Larger surface of submersed macrophytes is the main parameter supporting the increase of invertebrate abundance due to providing protection from predators and growth for periphyton, an important food source for these phytophilous organisms. Macrophyte length was positively correlated with Hydra abundance, while Chironomids were more influenced by periphyton biomass. These organisms can indicate water quality conditions and a potential increase in primary and secondary production.

First record of an introduced population of the southern lineage of white-clawed crayfish (Austropotamobius ‘italicus’) north of the Alps

Elucidating the status of populations of endangered species of unclear origin may have important implications for conservation management. In September 2013, a population of white-clawed crayfish was discovered outside of the native range in a small artificial lake in the River Neckar catchment in southwestern Germany. White-clawed crayfish comprise two distinct lineages of yet unresolved taxonomic status, of which only the western lineage (Austropotamobius pallipes s. str.) is native to Germany. To clarify the taxonomic identity and origin of the newly discovered population, we evaluated diagnostic morphological characters and sequences of two mitochondrial genes (for 16S rRNA and cytochrome c oxidase subunit I) from two crayfish specimens. Both analyses concordantly assigned the crayfish to the southern lineage (A. ‘italicus ’), with the closest matching haplotypes originating from northwestern Italy, southeastern Switzerland, and Lake Plansee in Austria, where an abundant introduced population of this lineage is present. The artificial lake in Germany was reportedly stocked with freshwater mussels from this Austrian lake. It thus appears likely that A. ‘italicus ’ was introduced intentionally or accidentally during the process. Austropotamobius ‘italicus ’ does not naturally occur north of the Alps and thus represents a non-native taxon for Germany, a fact to be considered in its management.

No differences between littoral fish community structure of small natural and gravel pit lakes in the northern German lowlands

Habitat loss has been identified as a major contributor to declining freshwater biodiversity, resulting in a high threat level among European fishes. Non-natural ecosystems such as pit lakes may compensate habitat loss by providing new habitat for aquatic organisms. We compared the structure of the littoral fish communities of 18 natural and 19 gravel pit lakes located in the northern German lowlands to evaluate whether artificial lakes managed by angling clubs host similar communities as typically observed in natural lakes. The fish community structure was analyzed between the lake types and along gradients of lake morphometry, productivity and littoral complexity. Although the gravel pit lakes differed in morphology (characterized by steeper littoral slopes and less structured littoral habitat), differences in fish community structure between the natural and gravel pit lakes were weak and mainly related to differences in the abundance of the dominant species perch, roach and rudd. Both lake types had similar species richness, community diversity and hosted several small-bodied and endangered species. To conclude, fish communities characteristic of small natural lakes may serve as reference for the development of gravel pit lakes. Moreover, our study reveals that recreational-fisheries management of gravel pit lakes does not result in artificial communities that deviate strongly from the communities present in natural lakes. Therefore, nature conservation and fisheries management goals can be reconciled in relation to fish in small artificial lakes managed by angling clubs.

Side-boat tow to test the influence of flaps in a 2-meter planing craft model

A small craft is considered in the planing regime when its Froude number is higher than 1.2, and under that condition its weight is mainly supported by hydrodynamic pressure acting on the bottom of the hull. It is also known that installing stern flaps at a certain angle from the bottom line will alter the trim angle and, as a consequence, the resistance exerted by the water. In this work, using the classical work from Savitsky, the resistance on a planing craft is estimated, including the effect of flaps, and then the influence of those appendages on the hydrodynamic behavior of a craft of local design was experimentally verified. The wooden model was 2.0 meters long and was side towed from an outboard powered boat, with a 3.2-m arm, in a small artificial lake. The tests were run between 5 and 12 knots, with uneven intervals due to the outboard control; the model was towed without and with flaps at 5 and 10°. Finally, experimental and empirical results for towing force and trim angle were plotted. In some of the experimental curves the presence of humps may be identified, but less pronounced than with the theoretical results. Experimental resistance values are lower than those obtained from Savistky’s formulation for no flaps; in the case of flaps at 5°, the agreement in trim angle was very good. Finally, the benefit of flaps on the performance of the planing model was corroborated, but it should be emphasized that this improvement is only valid for a certain velocity range.

Bacterial community composition of sediments from Artificial Lake Maslak, Istanbul, Turkey

Small artificial lakes are ubiquitous in various natural environments. Small impoundments increase the residence time of water, thereby increasing the potential for retention of nutrients through biological and physical processes. We examined bacterial community structure of Lake Maslak, a small freshwater impoundment located in a densely populated region. The objective of our study was to investigate bacterial communities of the lake sediment which has not been determined and to elucidate the factors controlling bacterial diversity and the biogeochemical processes within the lake. For these purposes, surface water, lake bed sediments, and one core sample were collected. Microbiological characteristic of the lake bed and core sediments was determined by denaturing gradient gel electrophoresis targeting the 16S rRNA gene. Along with the microbiological studies, physicochemical (O(2), pH, temperature) and geochemical properties of the surface (NO (3) (-) , NO (2) (-) , NH (4) (+) ,PO (4) (-) ,SO (4) (2-) , K(+), Mg(2+), Ca(2+)) and pore water (K(+), Mg(2+), Ca(2+)) were determined in addition to heavy metals contents (Co Cu, Fe, Zn, Pb, Cd). Eight lake bed and one core sediments were also collected and analyzed for heavy metals and elemental compositions. Nitrate concentration in the surface water ranges from 0.27-1.8 mg/L, and ammonium (0.0-0.83 mg/L) appears to follow nitrate concentration. Sulfate concentration in the surface water (mean 60 mg/L) is greater than those measured in the pore water (mean, 37.5 mg/L). Fe, Zn, Pb, and Cd were not determined in the surface water, whereas Co was significantly higher both in the surface and pore water. Unlike Co, Pb, Zn, and Cd were not measured in the pore water. Lakebed and core sediments show significant enrichment in Pb, Zn, and Cu, indicating anthropogenic pollution. Consistent with geochemical parameters, microbiological analysis suggests a diverse bacterial community in the lake sediments and influence of anthropogenic pollution (e.g., atmospheric emission) on bacterial community.

Carbon export and fate in carbonate catchments: A case study in the karst plateau of southwestern China

Abstract The consumption of CO 2 due to carbonate weathering is thought to be an important terrestrial sink for atmospheric CO 2 . However, the reaction and fate of weathering products may significantly affect the magnitude of the sink. Carbon mass balances were determined in Hongfeng Lake, a small artificial lake located in the carbonate plateau of SW China. This was accomplished by measuring the concentrations of DIC (dissolved inorganic C), DOC (dissolved organic C), POC (particulate organic C), and CO 2 partial pressure in lake waters, inflows and outflows, and in surrounding spring waters. Results show that maximum DIC (mainly HCO 3 - derived from carbonate weathering by CO 2 ) to DOC ratios in the catchment export load reach ∼21, implying that as much as ∼80% of the exported primary production is in the form of HCO 3 - , and, therefore, the CO 2 consumed by carbonate weathering and subsequent DIC export is a critical component of the C balance in this ecosystem. This exported HCO 3 - subsidizes C cycling of aquatic ecosystems in the catchment, and 32% (excluding carbonate-derived C) returns to the atmosphere as CO 2 evasion through the fluvial and lacustrine water–air interface and 10% is stored in lake sediment. This lake has a small CO 2 emission rate (13.2 ± 3.9 mmol m −2 d −1 , or 0.097 mol m −2 a −1 relative to catchment area) compared to mean values for many reservoirs found in temperate and tropical climatic zones. This is likely due in part to low organic C loads supplied by the karst-dominated catchment, and low lake water DOC concentrations. The estimate indicates that more C (39%) returns to the atmosphere and much less (13%) is stored in sediments, implying that the C sink of carbonate weathering may not be as significant as once thought.

Growth and mortality of Cichla spp. (Perciformes, Cichlidae) introduced in Volta Grande Reservoir (Grande River) and in a small artificial lake in Southeastern Brazil

The growth and mortality parameters were estimated through the analysis of length frequency distribution for species of Cichla spp. introduced into a lake in Leme (SP), and in Volta Grande reservoir (SP-MG). In Leme, Cichla kelberi presented larger frequency in the inferior classes of lengths, larger instantaneous rate of natural mortality, and smaller number of cohorts than C. kelberi and C. piquiti in Volta Grande. The values of growth performance obtained for the species were similar, corroborating the validity of the estimated growth and mortality parameters. The increase of the growth rate in small and less diverse environments occurs due to predation. The genus Cichla adapts well in locations in which it is introduced, however this adaptation shows itself to be strongly adjusted to each particular location, determining great plasticity and establishment capacity.

Evidence of Large Change in Unionid Mussel Abundance from Selective Muskrat Predation, as Inferred by Shell Remains Left on Shore

Three species of unionid mussels (Pyganodon grandis, Lampsilis siliquoidea, and Toxolasma parvus) were preyed on by muskrats (Ondatra zibethicus) that left shell remains at feeding sites (middens) along the shore of Lake LaSalle (West) in western New York State, USA. Mussels became established within five years of the construction of this small artificial lake, and individuals of all three species have grown rapidly to large size. The abundance of prey in middens in 1988–1990 and a marked decline in subsequently deposited shells indicate how dramatically muskrats had exploited this food source. They consumed > 2700 individuals of P. grandis (by far the most common prey item) through 1990, yet only 20 newly deposited shells were found in 1993. At a midden where prey depletion was directly catalogued during 1988, larger specimens of P. grandis were consumed first, suggesting size selection. L. siliquoidea has been least affected by predation, and was the mussel most often found alive in the littoral zone. No live T. parvus were ever collected, and this species is known only from middens. Complete collections of shell remains from the shoreline through 1999 suggest that the mussel population may be recovering slowly. Muskrat predation may be more important in influencing mussel population structure than previously realized, and the effects can be dramatic spatially and temporally.

Evidence of Large Change in Unionid Mussel Abundance from Selective Muskrat Predation, as Inferred by Shell Remains Left on Shore

Three species of unionid mussels (Pyganodon grandis, Lampsilis siliquoidea, and Toxolasma parvus) were preyed on by muskrats (Ondatra zibethicus) that left shell remains at feeding sites (middens) along the shore of Lake LaSalle (West) in western New York State, USA. Mussels became established within five years of the construction of this small artificial lake, and individuals of all three species have grown rapidly to large size. The abundance of prey in middens in 1988–1990 and a marked decline in subsequently deposited shells indicate how dramatically muskrats had exploited this food source. They consumed > 2700 individuals of P. grandis (by far the most common prey item) through 1990, yet only 20 newly deposited shells were found in 1993. At a midden where prey depletion was directly catalogued during 1988, larger specimens of P. grandis were consumed first, suggesting size selection. L. siliquoidea has been least affected by predation, and was the mussel most often found alive in the littoral zone. No live T. parvus were ever collected, and this species is known only from middens. Complete collections of shell remains from the shoreline through 1999 suggest that the mussel population may be recovering slowly. Muskrat predation may be more important in influencing mussel population structure than previously realized, and the effects can be dramatic spatially and temporally.

Seasonal and spatial dynamics in the phytomacrofaunal community of Lake Henley, New Zealand

The invertebrate communities associated with dense beds of exotic macrophytes were sampled monthly between June 1993 and June 1994 from three sites in Lake Henley, a small artificial lake in the Southern Wairarapa, North Island, New Zealand and from a small stream flowing into the lake. All communities were dominated by either the gastropod Potamopyrgus antipodarum or by oligochaetes. Community composition was similar at sites within the lake monoculture but changed seasonally. These changes appeared to be predominantly a result of seasonal fluctuations in the presence of filamentous algae on the macrophyte beds. Communities sampled from the stream site had a number of taxa in common with the lake communities but were quite distinctive in terms of the relative abundance of these component taxa. The diversity of the lake phytomacrofauna community, although comparable to similar studies in other New Zealand lakes, had a lower proportion of insect taxa perhaps because of the low floral diversity, the lack of depth variation, the absence of a nearby colonising source or the young age of the lake.