Limnetic Ecosystems Research Articles

Resolving spatially complex interactions between hydrodynamics and biogeochemical processing in a large reservoir with metalimnetic oxygen deficits

Deoxygenation in the deep water of stratified lakes and reservoirs due to climate warming and human activities poses a threat to crucial limnetic ecosystem services. Metalimnetic oxygen minima (MOM) typically occurs during the mid to late stages of limnetic stratification. To investigate the mechanism of MOM during stably stratified periods in the Panjiakou Reservoir, northern China, four years of in-situ monitoring was conducted in parallel with longitudinal-vertical 2D modeling. The model simulated the hydrodynamic, water quality, algal, and DO processes in 2017 and 2020, and was calibrated and verified by the measurements. Three scenarios were designed to test the impact of hydrological processes and the high oxygen-consuming sedimentation zones (HOCSZ). We concluded that the stratification and the corresponding advection generated in the metalimnion are the driving forces of MOM in the reservoir, and the limnetic eutrophication-related benthic HOCSZ are the seedbeds of the metalimnetic hypoxia. This unique spatial setting driving the biogeochemical processing and MOM dynamics required a new generation of modelling, incorporating spatial inhomogeneities of sediment characteristics and a sophisticated resolution of hydrodynamics. Metalimnetic horizontal advection, hypolimnetic upwelling currents, sedimentation hot spots and the formation of high oxygen consumption zones became the major initiation processes leading to MOM. The numerical modeling not only represented the occurrence, development, and extinction of MOM but also comprehensively explained the spatial differences in the vertical morphology of MOM and its inter-annual variations. Our studies help to identify management strategies to mitigate the impacts of MOM on aquatic ecological security and drinking water quality, thus supporting the optimization of reservoir regulations.

Limnological factors that affect waterbird assemblages in semi-arid reservoirs of Tigray National Regional State, northern Ethiopia

Published accounts of the conservation of biodiversity indicate that understanding patterns of species distribution and richness is crucial. However, what drives patterns of species composition in a landscape remains debatable. I examined the relationship between limnological characteristics of reservoirs, morpho-edaphic variables, biological variables, and patterns of bird species richness and distribution. Six limnological, three morpho-edaphic variables, and biological variables were recorded for 35 reservoirs and analyzed by multivariate statistical techniques. To investigate the most important explanatory factors influencing avian species richness and their distribution, redundancy analysis (RDA) was used. A total of 85 bird species from 54 genera, with a mean species richness 14.23 ± 6.72 (mean ± standard deviation) per reservoir, were recorded. The RDA analysis identified two significant RDA axes, and 34.4% of the variation in species richness is explained by environmental variation (R2adj = 0.34375; P < 0.001). Bird species richness was positively correlated with the surface area of reservoirs. I showed here that reservoir size and environmental heterogeneity were the important features that affect bird species richness, thus providing an important insight into the ecological relationship between waterbird species richness and the limnological characteristics of reservoirs. The strong positive correlation between species richness and both size and environmental variables underscores the importance of these reservoir features in the management of wildlife conservation. Large, environmentally heterogeneous reservoirs can support more species than small, environmentally homogeneous reservoirs because large, environmentally heterogeneous limnetic ecosystems can provide different resources for nesting, foraging, and roosting habitats for a diversified bird species. The result here also plays a role towards strengthening our knowledge of aquatic bird ecology and the natural history of African-Eurasian Migratory waterbirds.

INVASION OF THE THIARID SNAIL Melanoides tuberculata (MOLLUSCA) IN A CONSERVATION AREA OF THE SEMIARID REGION OF BRAZIL

This paper records the invasive gastropod Melanoides tuberculata in a limnetic ecosystem located in integral protection area in the semiarid region of the state of Paraíba in northeast Brazil. Live individuals were collected and photographed along shallow margins of the Piranhas Reservoir associated with different types of substrates. Photographic quadrants were used to calculate the number of living individuals and empty shells on different substrates. Individuals of M. tuberculata were found at five sampling sites in the littoral zone on different types of substrates with densities ranging of 13 ind.(m2)-1 to 22 ind.(m2)-1. The average density of individuals was: 18 ind.(m2)-1 on thin sediment, 15 ind.(m2)-1 on gravel and 20 ind.(m2)-1 on rocks. Empty shells were extremely abundant in the terrestrial zone of the reservoir. We did not observe native species of freshwater molluscs in the marginal areas of the reservoir in which the specimens of M. tuberculata were found. Knowledge about the distribution, establishment and impact caused of M. tuberculata in limnetic ecosystems of the Brazilian semi-arid region needs to be better studied in order to ascertain the degree of impact on native species and environmental modifications that reflect negatively on ecosystems.

Arsenic and uranium contamination of Orog Lake in the Valley of Gobi Lakes, Mongolia: Field evidence of conservative accumulation of U in an alkaline, closed-basin lake during evaporation

The shrinkage of inland, alkaline, and saline lakes has caused the elevation of arsenic and uranium concentrations in lake water. However, the chemical reactions associated with these enrichments remain unclear. We conducted a five-year study of the water chemistry of Orog Lake (Mongolia) and the chemical and spectroscopic characteristics of the sediment to determine the geochemical behavior of arsenic and uranium during evaporation. The arsenic and uranium concentrations increased as evaporation caused the lake to shrink. The maximum concentrations of arsenic and uranium exceeded 200 µg/L and 600 µg/L, respectively, when the lake area was the smallest. Comparisons of the monitoring results with predictions of geochemical modeling suggested that some arsenic was removed from the lake water under highly desiccated conditions. Sequential extraction and X-ray absorption near-edge structure analyses showed that ferrihydrite can take up As(V). The accumulation of uranium could be reproduced by considering only evaporation. The conservative behavior of uranium can be explained by the low affinity of U(VI) for carbonate and ferrihydrite at pH > 9 and high dissolved inorganic carbon concentrations. The ubiquitous formation of extremely soluble U-bearing salts after the complete desiccation of inland lakes may thus become a serious threat to limnetic ecosystems.

Fishery Status and Rebuilding of Major Economic Fishes in the Largest Freshwater Lake in China Based on Limited Data

Poyang Lake, the largest freshwater lake in China, possesses abundant fishery resources, but its fish stock status is still unclear. In this work, the stock status of and fishing efforts of nine major economic fishes in the Poyang Lake were estimated from 2000 to 2019 with a catch-based maximum sustainable yield (CMSY) model based on catch and resilience data. It was further predicted whether the biomass of those fishes could be restored to support maximum sustainable yield (Bmsy) under the policy of “Ten years fishing moratorium in the Yangtze River”. The results showed that goldfish Carassius auratus, grass carp Ctenopharyngodon idella, and black carp Mylopharyngodon piceus suffered from higher fishing efforts and low biomass in the past 20 years; bighead carp Hypophthalmichthys nobilis, yellow catfish Tachysurus fulvidraco, and common carp Cyprinus carpio responded differently to their fishing efforts; silver carp Hypophthalmichthys molitrix, Amur catfish Silurus asotus, and mandarin fish Siniperca chuatsi were underexploited. Six species were overfished in 2019, and their biomass would be expected to recover for sustainable exploitation during the fishing moratorium, except for M. piceus. This study provided a case study of feasible freshwater fishery evaluation in limnetic ecosystems.

Aquatic Insects Diversity and Water Quality Assessment of a Tropical Freshwater Pond in Benin City, Nigeria

Aquatic insects are species of significant importance to water bodies because they serve various purposes including nutrient cycling, vectors of pathogens and bioindicators of water quality. Analyzing their community structure is a veritable tool in studies of biodiversity and quality of limnetic ecosystems. Therefore, we investigaTed the health status of a pond in Benin City, Nigeria using insect’s abundance, composition, distribution and physicochemical parameters of the waterbody. Insects were sampled using sweep nets and identified to the species level while water samples were collected and analyzed using in-situ and ex-situ methods to determine the physicochemical properties in three sampling stations. The results of the physicochemical assessment of the water indicated that conditions did not differ widely between sites (P &gt; 0.05) except for total alkalinity, and the recorded values were well within the ambient FMEnv permissible limits for surface water except for dissolved oxygen,turbidity and phosphate. A total of 10 insect taxa, comprising of 103 individuals in 2 orders were recorded in the study and among the orders, Hemiptera comprised of 7 species and Coleoptera comprised of 3 species. Majority of the insect fauna found in this study are typically found in similar water bodies in the tropics. However, the obsereved insect community structure revealed a relatively low taxa richness with a dominance of pollution-resistant species which suggests a moderately polluted condition of the waterbody. &#x0D; Keywords: Aquatic insects, bioindicators, biodiversity, water quality, pond.

A Comparative Analysis of the Mouthpart Structures of Two Epischura Species (Copepoda, Calanoida) from Lakes Differing in their Trophic Status

Planktonic copepods, being a connecting link between primary production and higher order consumers, are often a key component of the food net in limnetic ecosystems. Many studies indicate a strong relationship between feeding mode and the structure of the mouthparts of copepods. Early studies attributed members of the genus Epischura to different groups according to their feeding mode and assumed that the species inhabiting the territory of Asia were only adapted to feeding on phytoplankton. We compared the fine morphology of the mouthparts of the Asian species, Epischura baikalensis and E. chankensis, living in different environments. The measurements were made using electron and light microscopy. The mesh sizes of the food capture net formed by the setae and setules ranged between 3.2 μm for E. chankensis and 9.1 μm for E. baikalensis. The area presumably covered by the first maxillae was 13215 μm2 and 66470 μm2, respectively. The resistance force of one seta is ten times higher for E. baikalensis than for E. chankensis. According to the results of calculations of hydrodynamic characteristics based on Reynolds number, these species are unable to filter food particles, but they capture them by drawing them into the mouth. The significant difference in the length of the oral appendages indicates that E. baikalensis is better adapted to living in an oligotrophic lake. For feeding on small particles at low concentrations, it is more beneficial to have long oral appendages even at high energy costs

Establishment of a high-sensitivity reporter system in mammalian cells for detecting juvenoids using juvenile hormone receptors of Daphnia pulex.

Environmental waters are polluted by various chemicals originating from human activities. Recently, the environmental risk of juvenile hormones (JHs) to aquatic microcrustaceans has been recognized by risk assessors and researchers. JH is a major arthropod hormone that regulates molting and reproduction and has analogs that have been used as insect growth regulators. JHs are known to disturb the sex determination system of Daphnia, which is a keystone animal in limnetic ecosystems and is not the target of extermination. To assess the risk of contaminant chemicals and to protect biodiversity, reliable methods for detecting such chemicals are essential. In this study, we attempted to establish a practical in vitro reporter assay system for detecting chemicals with JH activity. Using a newly constructed reporter vector (modified from the JH response element of Tribolium castaneum Krüppel homolog 1, which is a major JH responsive gene in insects), strong JH-dependent transcriptional activity (>40-fold activation) was found in Chinese hamster ovary cells that express JH receptors of Daphnia pulex. Dose-response analysis conducted on several JH and non-JH chemicals revealed that the established reporter assay system has strict specificity to JH chemicals, and the half maximum effective concentration (EC50 ) was between 10-7 and 10-9 m. These results suggest that the new system is a rapid and economical method for assessing the environmental risk of JH-active chemicals.

Early diverging lineages within Cryptomycota and Chytridiomycota dominate the fungal communities in ice-covered lakes of the McMurdo Dry Valleys, Antarctica

Antarctic ice-covered lakes are exceptional sites for studying the ecology of aquatic fungi under conditions of minimal human disturbance. In this study, we explored the diversity and community composition of fungi in five permanently covered lake basins located in the Taylor and Miers Valleys of Antarctica. Based on analysis of the 18S rRNA sequences, we showed that fungal taxa represented between 0.93% and 60.32% of the eukaryotic sequences. Cryptomycota and Chytridiomycota dominated the fungal communities in all lakes; however, members of Ascomycota, Basidiomycota, Zygomycota, and Blastocladiomycota were also present. Of the 1313 fungal OTUs identified, the two most abundant, belonging to LKM11 and Chytridiaceae, comprised 74% of the sequences. Significant differences in the community structure were determined among lakes, water depths, habitat features (i.e., brackish vs. freshwaters), and nucleic acids (DNA vs. RNA), suggesting niche differentiation. Network analysis suggested the existence of strong relationships among specific fungal phylotypes as well as between fungi and other eukaryotes. This study sheds light on the biology and ecology of basal fungi in aquatic systems. To our knowledge, this is the first report showing the predominance of early diverging lineages of fungi in pristine limnetic ecosystems, particularly of the enigmatic phylum Cryptomycota.

Pollution Assessment of Toxic Metals in Representative Limnetic Ecosystem Sediments in the Southeastern Black Sea, Turkey

In this study, the natural and anthropogenic toxic metal pollution, and the general characteristics of lake sediments are investigated spatially and temporally. Three lakes are chosen in 2014 according to their origin from the Southeastern Black Sea‐Sera Lake, Uzungol Lake, and Borçka Dam Lake. Four sampling campaigns are conducted during the four seasons: spring, autumn, winter, and summer. The elements lead (Pb), copper (Cu), zinc (Zn), nickel (Ni), and arsenic (As) are selected for investigation. The highest average toxic concentrations of Cu (498.46 μg g−1), Pb (185.60 μg g−1), and As (18.74 μg g−1) were found in Borçka Dam Lake; however, those of Zn (435.00 μg g−1) and Ni (143.42 μg g−1) are found in Sera Lake. The highest metal concentrations are observed in autumn. Metal concentrations are determined by inductively coupled plasma mass spectrometry. The potential ecological risk index (RI) and geoaccumulation index (IGEO) values are calculated for assessing sediment pollution. The assessment of sediments according to their potential ecological risk to the aquatic environment reveal that Cu contamination is a moderate risk in Borçka Dam Lake. According to IGEO classifications, the highest IGEO values are found in Borçka Dam Lake in autumn. Accordingly, the study area is determined to be highly contaminated with Cu and Pb. Cu and Pb can be considered as major contributors to ecological risk in these Southeastern Black Sea lakes.

Heterotrophic activity of bacterioplankton along the gradients of the chlorophyll a concentration and water temperature in marine and limnetic ecosystems

The dependence of the heterotrophic activity of bacterioplankton (V, μg C L–1 h–1) on the concentration of chlorophyll a (Chl, μg L–1) and the water temperature (T) was examined for lakes (37°29′–80°36′ N) and marine polar waters (69°16′–80°36′ N). It was shown that ~76% of the V variations was related to changes in Chl and T.

Growth response to surface mine reclamation in West Virginia

Surface mining in West Virginia has a long history of erasing or damaging arboreal and limnetic ecosystems in the state. In addition to altering the topography of the land, runoff from surface mines causes a host of long term effects on the environment even years after mining activities have ceased. Acid mine drainage (AMD) is caused by weathering sulfide minerals such as pyrite that have been exposed to the elements from mining activity. AMD lowers the pH of soil and water and introduces dissolved heavy metals that are harmful to life and the environment. These metals include aluminum that is known to especially harmful to plant root development and subsequent growth. Trees growing in AMD contaminated watersheds have been shown to suffer decreased growth and species richness compared to those growing in uncontaminated systems. Sites suffering from AMD are often subjected to remediation efforts by environmental agencies such as the DEP, though the efficacy of some common remediation practices is not well understood.We cored trees growing in proximity to old surface mines reclaimed by the DEP at different times over the past 20 years to establish a chronology of growth through stages of contamination and remediation. Five mines were chosen for the study. Two of them had not experienced any remediation efforts, while the other three completed abatement in 1996, 1997, and 2010. Results did not show an improvement in tree growth post remediation, suggesting that DEP abatement practices are ineffective long-term in terms of impacts on vegetation health.

Biomonitoring of Selected Freshwater Bodies Using Diatoms as Ecological Indicators

Lakes supply water for irrigation, drinking, fisheries, etc. and thus have significant economic and recreational value. In order to determine impacts of human activities on aquatic ecosystem it is important to distinguish anthropogenic impact and natural variation. In limnetic ecosystem, water quality is influenced by physical, chemical, and biological factors. Freshwater communities are very much sensitive to environmental variables. The algal flora constitutes a vital link in the food chain and its productivity depends on water quality at a given time. Diatoms in particular are of utmost importance, as potential indicators of water quality due to their sensitivity and strong response to many physical, chemical and biological changes. Occurrence of diatom communities in selected fresh water bodies of Goa along with physico-chemical parameters have been studied for a period of two consecutive years and the data has been used in biomonitoring. Using OMNIDIA GB 5.3 software, Louis Leclercq IDSE/5 index is derived and the level of degradation due to organic and anthropogenic pollution has been found out. Findings showed seasonal variations in physico-chemical parameters and diatom population. The diversity of diatoms was considerably high in Syngenta, Lotus and Curtorim lakes compared to Khandola Pond. Gomphonema parabolum, Navicula halophila, Navicula microcephala, Navicula mutica indicates organic pollution in the water bodies. Amphora ovalis, Stauroneis phoenicenteron, Synedra ulna indicates anthropogenic pollution in Syngenta, Lotus and Curtorim lakes while Navicula rhynococephala indicate anthropogenic pollution in Khandola Pond. Biomonitoring has been proven to be necessary and hence the importance of diatoms as ecological indicators of water quality has been stressed.

Phosphorus characteristics, distribution, and relationship with environmental factors in surface sediments of river systems in Eastern China.

Phosphorus (P) is an essential nutrient for aquatic organisms. However, too much P discharged into limnetic ecosystems can induce eutrophication. The concentration of P in freshwater ecosystems has escalated in Eastern China due to overuse of fertilizer and excess emission of sewage, which is the result of the development of industry and agriculture in this area. However, little is known about the P characteristics and its environmental factors in river systems. Here, we present the results of P characterization and its relationships with environmental factors in Eastern China by applying SMT and (31)P-NMR methods. The results showed that the concentrations of P in surface sediments varied with the river system, and more than 50% of the samples had P concentrations exceeding 500mgkg(-1). HCl-Pi was the dominant Pi in surface sediments, with the highest percentage (96.5%) in the Yellow River System. Mono-P was the dominant Po in river sediments, followed by DNA-P. The PCA approach indicated that NaOH-Pi and ortho-P clustered in one group, with a second group including mono-P, diesters-P, and HCl-Pi. Phon-P and pyro-P belonged to different groups. On a regional scale, NaOH-Pi and Po showed a negative relationship with pH in sediments. Continuous eutrophication was induced by the presence of dams, and oxygen-consuming pollutants, such as NH3-N and CODcr, even when external P input was cut in heavily polluted rivers. The research revealed the characteristics of P in different river systems and proposed a conceptual model of P biogeochemical cycles in heavily polluted rivers. Results from this study may provide insight into P characteristics in Eastern China and would set a scientific basis for effective P management in developing countries.

Characteristics and Distribution of Phosphorus in Surface Sediments of Limnetic Ecosystem in Eastern China.

Phosphorus (P) is an essential nutrient for aquatic organisms; however, excessive P inflow to limnetic ecosystems can induce eutrophication. P concentrations in the rivers, wetlands and lakes of Eastern China have been amplified by fertilizer and sewage inputs associated with the development of industry and agriculture. Yet, knowledge of the distribution and speciation of P is lacking at the regional scale. We determined the distribution and speciation of P in limnetic ecosystems in Eastern China using Standards, Measurements and Testing (SMT) and phosphorus nuclear magnetic resonance (31P-NMR). The results indicate that P pollution in surface sediments was serious. Inorganic P (Pi) was the primary drive of variation in total P (TP) among different river systems, and Pi accounted for 71% to 90% of TP in surface sediment in Eastern China. Also, the concentrations of TP and Pi varied among watersheds and Pi primarily drove the variation in TP in different watersheds. Sediments less than 10-cm deep served as the main P reservoir. Environmental factors affect the speciation and origin of P. NaOH-Pi, HCl-Pi and organic P (Po) were related to pH accordingly at the regional scale. The physicochemical properties of sediments from different limnetic ecosystems affect the P speciation. HCl-Pi was higher in wetland sediments than in riverine and lake sediments in Eastern China. Conversely, NaOH-Pi was lowest in wetland sediments. Total Po concentration was lower in riverine sediments than in other sediments, but Mono-P was higher, with an average concentration of 48 mg kg−1. Diesters-P was highest in lake sediments. By revealing the regional distribution of TP, Pi and Po, this study will support eutrophication management in Eastern China.

Use of MODIS satellite images for detailed lake morphometry: Application to basins with large water level fluctuations

Lake morphometry is essential for managing water resources and limnetic ecosystems. For reservoirs that receive high sediment loads, frequent morphometric mapping is necessary to define both the effective life of the reservoir and its water storage capacity for irrigation, power generation, flood control and domestic water supply. The current study presents a methodology for updating the digital depth model (DDM) of lakes and reservoirs with wide intra and interannual fluctuations of water levels using satellite remote sensing. A time series of Terra MODIS satellite images was used to map shorelines formed during the annual water level change cycle, and were validated with concurrent Landsat ETM+ satellite images. The shorelines were connected with in-situ observation of water levels and were treated as elevation contours to produce the DDM using spatial interpolation. The accuracy of the digitized shorelines is within the mapping accuracy of the satellite images, while the resulting DDM is validated using in-situ elevation measurements. Two versions of the DDM were produced to assess the influence of seasonal water fluctuation. Finally, the methodology was applied to Lake Kerkini (Greece) to produce an updated DDM, which was compared with the last available bathymetric survey (1991) and revealed changes in sediment distribution within the lake.

Pigments and plastic in limnetic ecosystems: A qualitative and quantitative study on microparticles of different size classes

Recently, macroplastic (>5 mm) and especially microplastic (<5 mm) particles have been reported as emerging contaminants in marine and limnetic ecosystems. Their coloration is gained by the addition of pigments to the polymer blend which is the major component of the respective product. However, color is also a feature of paint and coatings whereby the pigment is the major component. Once abraded from a surface, paint particles may enter the environment via similar pathways as microplastic particles.So far no detailed studies of microplastic particles (pigmented and non-pigmented) as well as paint particles have been performed focusing on very small microparticles (1–50 μm), in either marine or limnetic ecosystems. Using Raman microspectroscopy with a spatial resolution down to 1 μm, we report a remarkable increase in the occurrence of (pigmented) microplastic particles below 500 μm. Among those, most particles were found at a size of ∼130 μm in a freshwater ecosystem (subalpine Lake Garda, Italy). Moreover, our qualitative and quantitative analyses revealed that the number of paint microparticles significantly increased below the size range of 50 μm due to their brittleness (the smallest detected paint particle had a size of 4 μm). Inductively coupled plasma mass spectrometry measurements showed that both colored particles found in nature as well as virgin particles contain a high variety of metals such as cadmium, lead and copper. These additives may elicit adverse effects in biota ingesting these microparticles, thus paints and associated compounds may act as formerly overlooked contaminants in freshwater ecosystems.

Heavy metal contamination in the surface sediments of representative limnetic ecosystems in eastern China.

A comprehensive analysis of heavy metal pollution was conducted in the representative limnetic ecosystems of eastern China, which are subject to rapid economic development and population growth. The results demonstrated that the average contents with standard deviations of Cd, Cr, Cu, Ni, Pb and Zn in the surface sediments were 0.925 ± 0.936, 142 ± 46.8, 54.7 ± 29.1, 60.5 ± 21.6, 61.9 ± 36.0 and 192 ± 120 mg/kg dry wt., respectively, and that higher values were mainly observed in the southern portion of the study area, especially in the basins of Southeast Coastal Rivers (SCRB) and the Zhu River (ZRB). The six heavy metals in the surface sediments all had anthropogenic origins. In addition, the limnetic ecosystems, especially in the southern portion of the study area were found to be polluted by heavy metals, especially Cd. Overall, two hotspots of heavy metal pollution in the limnetic ecosystems of eastern China were found, one that consisted of the heavy pollution regions, SCRB and ZRB, and another composed of Cd pollution. These results indicate that heavy metal contamination, especially Cd, should be taken into account during development of management strategies to protect the aquatic environment in the limnetic ecosystems of eastern China, especially in the two aforementioned basins.

Occurrence of arsenic in two large shallow freshwater lakes in China and a comparison to other lakes around the world

Elevated levels of arsenic (As) have been found in lakes and rivers due to intensive anthropogenic activities. However, information on the occurrence of As in large freshwater lakes has scarcely been available. This study aimed at integrated exploration of the occurrence of As in multiple media of the limnetic ecosystems, mainly waters, sediments, macrophytes, invertebrates and fish in two large freshwater lakes (Taihu and Dianchi) during 2009–2010. The dissolved As concentrations in lake water for Lake Dianchi (3.08–10.48 μg L− 1) were significantly higher than the dissolved As concentrations in Lake Taihu (1.39–5.65 μg L− 1). The As concentrations in sediments by dry weight in Lake Dianchi (12.49–169.25 mg kg− 1) were also significantly higher than the As concentrations in Lake Taihu sediments (4.66–10.85 mg kg− 1). The highest As concentration observed for invertebrates was registered in a mussel species (Novaculina chinensis) at 25.0 mg kg− 1, and the lowest As concentration was observed in shrimp (Exopalaemon modestus) at 1.2 mg kg− 1 in Lake Taihu. Although different macrophyte species were sampled in the two lakes, a common pattern was observed for the As concentrations in the plants. Submerged plants had higher levels of As than floating plants. Arsenic concentrations in Lake Taihu Ceratophyllum demersum L. could be 12.0 mg kg− 1; in contrast, in Nymphoides peltatum, the As concentration was 1.4 mg kg− 1. Six common fish species were collected in Lakes Taihu and Dianchi. No significant differences in As concentrations in fish muscles from the two lakes were found, although As bioaccumulation factors (BAFs) for fish muscles in Lake Taihu were much higher than the BAFs observed in Dianchi. This difference suggests that fish in Taihu and Dianchi have a balancing mechanism for As through metabolism, which might regulate As concentration in muscle tissues at relatively low levels. Overall, the occurrence of As in the two large shallow freshwater lakes in China is relatively lower in concentration than As levels in other lakes around the world, but human health risks from As contamination exist.

Projecting impacts of climate change on surface water temperatures of a large subalpine lake: Lake Tahoe, USA

Predicted increases in atmospheric CO2 concentration are expected to cause increases in air temperatures in many regions around the world, and this will likely lead to increases in the surface water temperatures of aquatic ecosystems in these regions. Using daily air and littoral water temperature data collected from Lake Tahoe, a large sub-alpine lake located in the Sierra Nevada mountains (USA), we developed and tested an empirical approach for constructing models designed to estimate site-specific daily surface water temperatures from daily air temperature projections generated from a regional climate model. We used cluster analysis to identify thermally distinct groups among sampled sites within the lake and then developed and independently validated a set of linked regression models designed to estimate daily water temperatures for each spatially distinct thermal group using daily air temperature data. When daily air temperatures projections, generated for 2080-2099 by a regional climate model, were used as input to these group models, projected increases in summer surface water temperatures of as much as 3 °C were projected. This study demonstrates an empirical approach for generating models capable of using daily air temperature projections from established climate models to project site specific impacts on littoral surface waters within large limnetic ecosystems.