The Role of Low-Molecular-Weight Organic Carbons in Facilitating the Mobilization and Biotransformation of As(V)/Fe(III) from a Realgar Tailing Mine Soil

Several low-molecular-weight organic carbon (LMWOC) compounds (acetate, propionate, butyrate, lactate, and glucose) were added to flooded arsenic-rich tailing mine soil to investigate their effect to the mobilization of As/Fe and potential shift of microbial community. A promoting effect to the mobilization and biotransformation of As(V)/Fe(III) in the soils resulting from the supplementation with LMWOCs substrate was indicated compared to the biotic microcosm amended with deionized water alone. During 38-day biotic incubation, more than 2100 μg/L of As(III) and 4.2 mg/L of Fe(II) levels were released from the soils amended with LMWOCs substrates, compared to the levels of As(III) and Fe(II) (less 35 μg/L and 1.82 mg/L) derived from the biotic supplementation with deionized water alone. PCR-DGGE indicated that several LMWOCs-responded bacteria were mostly related to Firmicutes and Proteobacteria. Moreover, a negligible impact on the abundance of Fe(III)-reducing family Geobacteraceae was indicated in the LMWOCs-amended soils. However, an increased abundance of sulfate-reducing bacteria but a decreased abundance of arsenate-respiring bacteria were indicated upon the soils supplemented with acetate alone, compared with other LMWOC amendments. DNA-stable isotope probing analysis demonstrated that the dual roles of acetate was not only served as an electron donor for biotransformation of As(V)/Fe(III) in soil, but also assimilated as a powerful energy source to promote the growth of sulfate-reducing bacteria. The findings suggest that there are specific bacteria that preferentially respond to the additions of LMWOC for controlling the biochemical cycle process of As/Fe in soils.     

Zooplankton (Cladocera) in assessments of biologic integrity and reference conditions: application of sedimentary assemblages from shallow boreal lakes

Zooplankton are potentially powerful proxies for the assessments of biologic integrity. The paleolimnological perspective and use of fossil Cladocera also provide the means to reconstruct reference conditions and natural long-term community dynamics. Unfortunately, the use of zooplankton in lake quality assessments is currently underexploited. We studied a surface sediment dataset of 41 lakes in Finland to examine the relationship between Cladocera remains and environmental variables. Of the examined environmental variables, total phosphorus availability was found to be the most important variable in explaining the Cladocera community composition. Following the tests on species environment relations, we selected a lake trophic typology as the most suitable environmental variable for developing a new tool for limnoecological quality assessments. A test of the model on a modern and historic sample from a eutrophied lake showed that the test lake has proceeded from “mesotrophic/poor” to “eutrophic/bad” limnoecological state in agreement with previous independent evidence. The model developed here showed favorable performance that can be used to provide reliable estimates of ecological and environmental state of lakes.     

Role of essential fatty acids in trophometabolic interactions in the freshwater ecosystems (a review)

Polyunsaturated fatty acids (PUFA) of omega3 family are of crucial physiological importance for the most animals and they are an essential and deficient component of human nutrition. These compounds are most effectively synthesized by some groups of algae, hence, aquatic ecosystems are considered to be the main source of these PUFA for human nutrition. Factors controlling the content and distribution of omega3 PUFA in freshwater organisms of basic trophic levels and determined PUFA final production in freshwater ecosystems are considered in the review. PUFA biosynthesis is known to be tightly related to basic fatty acid metabolic pathways. Hence, fatty composition and the PUFA content of major freshwater hydrobiont groups, including bacteria, algae, invertebrates and vertebrates, and environmental and population age effects are described. The peculiarities of PUFA transfer between organisms of various trophic levels are discussed. The essential omega3 PUFA is one of the important parameter of food quality of aquatic consumers and they can determine the rate of energy and matter transfer between producers and primary consumers and, as a result, in a whole freshwater food chain. Analysis of PUFA content and its regulation in biomass of various fish populations indicates that freshwater ecosystems are of the same value in respect of PUFA sources as marine ecosystems. Despite the great practical importance, the studies focused on production and whole pools of omega3 PUFA in different freshwater ecosystems are still scarce and need to be continued.     

Combined stable‐isotope and fatty‐acid analyses demonstrate that large wood increases the autochthonous trophic base of a macroinvertebrate assemblage

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Influence of timing of fishing on trophic levels and diets of typical fish and invertebrate species in the Bohai Strait over a single year based on carbon and nitrogen isotope analysis

Fishing is the most widespread human exploitation of marine resources, which has an annual cyclical influence on aquatic species in Chinese offshore waters. This study used carbon and nitrogen isotopic ratios as tracers to reveal the changes in trophic level and dietary composition of offshore organisms during four cruises in March, June, August and November 2014. The results indicated that the trophic levels of fishes declined during two fishing periods, from March (average trophic level = 3.36) to June (3.01), and from August (2.99) to November (2.57), while most invertebrates did not show this trend. The self-restoring ability of this ecosystem was reflected in the trophic level changes after the closed fishing season (from June 1 to September 1). The trophic levels of fishes remained stable, and some species even recovered such as Enchelyopus elongates (trophic level increased from 2.84 in June to 2.86 in August), Cryptocentrus filifer (from 3.10 to 3.12), and Ernogrammus hexagrammus (from 2.91 to 2.96). According to the trophic results, we selected the invertebrates Octopus minor and Asterias amurensis from the top trophic levels for dietary composition analysis. The composition of their diets changed significantly after fishing periods, and the proportions of some smaller and “non-commercial” species increased, such as Notoacmea schrenckii and Chlorostoma rustica. After the closed fishing season, the larger and “commercial” species contributed a greater proportion to their diet composition. These results indicated that the closed fishing season should be prolonged to give the ecosystem enough time to restore itself and further halt the trend of this fishery towards environment deterioration.     

Resilience to changes in lake trophic state: Nutrient allocation into Daphnia resting eggs

During past decades, many lakes underwent drastic human‐caused changes in trophic state with strong implications for population dynamics and food web processes. We investigated the influence of trophic state on nutrient allocation into Daphnia resting eggs. The production of resting eggs is an important survival strategy, allowing Daphnia to cope with unfavorable environmental conditions. Allocation of essential nutrients into resting eggs may crucially influence embryonic development and offspring survival and thus is of great ecological and evolutionary interest. The capacity of Daphnia to adjust the allocation of nutrients into resting eggs may depend on the dietary nutrient supply, which may vary with trophic state‐related changes in the phytoplankton community composition. Resting eggs were isolated from sediment cores taken from Lake Constance, a large prealpine lake with a distinct eutrophication and reoligotrophication history, and analyzed for elemental (carbon, nitrogen, and phosphorus) and biochemical (sterols and fatty acids) nutrients. Carbon allocation into Daphnia resting eggs continuously decreased over time, irrespective of changes in trophic state. The allocation of nitrogen into Daphnia resting eggs followed the changes in trophic state, that is, nitrogen concentrations in resting eggs increased with eutrophication and decreased again with reoligotrophication. The allocation of phosphorus, sterols and long‐chain polyunsaturated fatty acids, such as eicosapentaenoic acid, into Daphnia resting eggs did not change significantly over time. Changes in trophic state strikingly influenced all trophic levels in Lake Constance. However, nutrient allocation into Daphnia resting eggs was mostly resilient to changes in lake trophic state.     

Copepods as environmental indicator in lakes: special focus on changes in the proportion of calanoids along nutrient and pH gradients

Copepods are important contributors to the zooplankton community in lakes. Being “sandwiched” between predators and resources, they are sensitive to changes in the environment. It has been proposed that the proportion of calanoids of total copepod abundance or biomass could be a valuable indicator of eutrophication. We investigated relationships between environmental factors and the abundance, biomass and size of calanoid and cyclopoid copepods as well as their proportions in summer in 68 Danish freshwater lakes (587 lake years) with contrasting nutrient levels and pH. When lake pH was?<?6.0, mean lake depth and trophic state were the most important factors and calanoids completely dominated the copepod community. In shallow lakes with a mean depth?<?2.5 m and with pH?>?6.0, the proportion of calanoids in terms of biomass decreased substantially with increasing phosphorus and chlorophyll a concentrations but stayed around 50% at?>?2.5 m depth irrespective of nutrient level. Time series of the lakes, recovering from eutrophication, confirmed this multi-lake pattern although the trajectory varied from lake to lake. We conclude that the proportion of calanoids in terms of biomass might be a valuable indicator of trophic state in shallow but not deep lakes and only when pH?>?6.

     

Spectroscopic characterization of plastocyanin from hornwort

Plastocyanin isolated from an aquatic higher plant, Ceratophyllum demersum L. (hornwort), has been characterized by electronic absorption, circular dichroism (CD), and electron paramagnetic resonance (EPR) spectroscopies. The visible absorption, CD, and EPR spectra of hornwort plastocyanin indicated a complete similarity of blue copper center to those of terrestrial higher plants and algae. However, the ultraviolet absorption spectrum of hornwort plastocyanin exhibited a lower tyrosine (Tyr) and a higher phenylalanine (Phe) content of the protein comparing with other plastocyanins. The ratio of Phe/Tyr residues was estimated to be 9 by amino acid analysis. The hornwort plastocyanin resembles in amino acid composition terrestrial higher plant plastocyanins rather than alga plastocyanins but is peculiar in the content of Phe and Tyr residues.     

Quantifying Ecological Stability: From Community to the Lake Ecosystem

We performed a methodological study aimed at extending our previously developed approach to quantify the ecological stability of biotic communities and an entire ecosystem, using Lake Kinneret as a case study. The ecological stability of the biotic communities (phytoplankton and zooplankton) of Lake Kinneret was estimated using two different aggregating schemes. The first scheme used the combined stability index, based on the combined indices of the individual phytoplankton (SI[Comb]_P) and zooplankton (SI[Comb]_Z) taxonomic groups. The total community stability index was calculated based on the total abundances of these communities. The stability of the entire ecosystem was estimated for two sets of ecosystem state variables, a lake “trophic state” set and a “water quality” set, which provided considerably different estimates of the lake ecosystem stability. Good agreement between the results of this study and qualitative estimates of Lake Kinneret stability validates the suitability of this approach to estimate the stability of different ecological units.     

Spatio-temporal patterns along a primary succession on alluvial sediments

Dynamic alluvial landscapes offer many possibilities to study primary succession processes on newly developed habitats. However, within the Central European environmental conditions, where watercourses and their riparian spaces are under severe anthropogenic pressures — water regulation, deforestation, lowering of groundwater — natural processes are limited. We studied primary succession on alluvial stream deposits in an artificial lake, where we aimed to follow the terrestrialisation rate and habitat turnover, along with plant species richness and composition across successional stages. In 30 years, a pristine white-willow riparian forest developed. One half of the initially aquatic habitat became terrestrial. The frequency of change, studied on 11250 quadrats 10×10 m each (on a scale from “no change” to 8 changes) and the mean of change per habitat type (most of the habitats changed 2 to 3 times) revealed only one successional trajectory. The percentage flow chart showed a deterministic pathway of succession. The “time since formation” of a terrestrial habitat shows that more than 20% of the lake was terrestrialised within in the first ten years. We studied species richness and composition along three composed transects, following successional stages. We found that the newly assembled riparian white willow woodland has a surprisingly low colonisation rate of plant species.     

Preliminary Observations on the Nature,Taxonomic Composition,Distribution, Behaviour and Nutrient Requirements of the “Unusual” Algal “Jellies” of Oguta Lake in Southeastern Nigeria

Preliminary observations were made between October 1982 and May 1983 on the nature, taxonomic composition, spatial distribution, buoyancy behaviour and nutrient requirements of some unusual planktonic algal “jellies” in Oguta Lake in Southeastern Nigeria. These “jellies” are macroscopic, blue-green algal masses whose excessive mucilage of high consistency acts as substrata for other epiphytic components viz. diatoms and green algae. They are more abundant in the lentic areas of the lake, undergo diurnal vertical movements and have their growth enhanced by spikes of nitrogen and phosphorus salts into their aquatic medium. The effects of these “jellies” on the ecology and general water use of the lake are discussed. Speculations on the reasons for their occurrence are given and possible control measures outlined.     

Operational Effect Variables and Functional Ecosystem Classifications – a Review on Empirical Models for Aquatic Systems along a Salinity Gradient

This paper presents a comparative study based on a very comprehensive set of empirical data from many international data bases including fresh water systems, coastal brackish water areas and marine coastal areas. We present a general trophic level classification system (oligotrophic, mesotrophic, eutrophic and hypertrophic categories) for sites/areas characterised by a wide range of salinities. This classification system targets on the following operational effect variables (bioindicators), which are meant to reflect key structural and functional aspects of aquatic ecosystems and characteristic (median) values for entire defined areas (the ecosystem scale) for the growing season: Secchi depth (as a standard measure of water clarity), chlorophyll‐a concentrations (a measure of primary phytoplankton biomass), the oxygen saturation in the deep‐water zone (an indicator reflecting sedimentation, oxygen consumption, oxygen concentrations and the habitat conditions for zoobenthos, an important functional group) and the macrophyte cover (an important variable for the bioproduction potential, including fish production, and the “biological value” of aquatic systems). For a wide range of systems, these bioindicators can be predicted using practically useful models, i.e., models based on variables that can be accessed from standard monitoring programs and maps. These bioindicators are regulated by a set of abiotic factors, such as salinity, suspended particulate matter (SPM), nutrient concentrations (N and P), morphometry and water exchange. Empirical data ultimately form the basis for most ecological/environmental studies and this work uses maybe the most comprehensive data set ever related to trophic level conditions. It also gives compilations of empirically‐based (statistical) models quantifying how the variables are interrelated and how they reflect fundamental aspects of aquatic ecosystems. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Zooplankton and environmental factors of a recovering eutrophic lake (Lysimachia Lake, Western Greece)

The present study investigates the zooplankton community dynamics and the abiotic environment in the eutrophic Lake Lysimachia (western Greece). The lake is considered to be recovering from eutrophication after the termination of an urban sewage inflow in 2000, and its waters are replenished constantly from the nearby oligotrophic Lake Trichonis. The results show that, although a decrease in nutrient concentrations was observed compared to the past, the lake still has eutrophic characteristics. This was reflected in the zooplankton community which is typical of those found in eutrophic lakes where rotifers prevail. Similarities among this lake and other nearby lakes were found considering the zooplankton community composition and seasonal variation. However, Lake Lysimachia is inhabited also by a number of different and even unique species (e.g., Moina micrura), suggesting that this ecosystem may be an important biodiversity refuge. Most of the zooplankton species were correlated with water temperature and, to a lesser extent, eutrophication key-water quality variables. Although there are few available data on the zooplankton of the lake, the abundance and composition of the community presenting characteristics indicative of intermediate trophic conditions and suggesting that the lake is probably under a kind of “biological” recovery.     

Regularities in Primary Production,Secchi Depth and Fish Yield and a New System to Define Trophic and Humic State Indices for Lake Ecosystems

General relationships between phytoplankton production, chlorophyll, total, dissolved and particulate phosphorus, Secchi depth, humic level, trophic level, fish production and latitude are described by regression equations using an extensive “Soviet” data base covering a wide domain of lake characteristics and a European data base. New systems for defining lake trophic and humic status are presented. The results may be used for more precise estimates of fundamental lake properties and for many practical issues of lake management, e.g., predictions of fish catch. We have used strict chlorophyll‐a concentrations for every trophic class and we have omitted Secchi depth from the trophic classes, since Secchi depth and other variables strongly related to water clarity (like suspended particulate matter and particulate organic carbon) depend on autochthonous production, allochthonous influences and resuspension. We have used the Secchi depth as a simple operational measure of the effective depth of the photic zone. It has also been shown that among these lakes there exist a very strong relationship between primary production and latitude. In fact, 74% of the variability among the lakes in mean summer primary production can be statistically related to variations in latitude. These data also show a strong relationship between primary production and fish yield, which can be used to address many fundamental issues in lake management, like “normal and abnormal fish production”.     

Eutrophication as a driver of microbial community structure in lake sediments

Lake sediments are globally important carbon sinks. Although the fate of organic carbon in lake sediments depends significantly on microorganisms, only few studies have investigated controls on lake sedimentary microbial communities. Here we investigate the impact of anthropogenic eutrophication, which affects redox chemistry and organic matter (OM) sources in sediments, on microbial communities across five lakes in central Switzerland. Lipid biomarkers and distributions of microbial respiration reactions indicate strong increases in aquatic OM contributions and microbial activity with increasing trophic state. Across all lakes, 16S rRNA genes analyses indicate similar depth-dependent zonations at the phylum- and class-level that follow vertical distributions of OM sources and respiration reactions. Yet, there are notable differences, such as higher abundances of nitrifying Bacteria and Archaea in an oligotrophic lake. Furthermore, analyses at the order-level and below suggest that changes in OM sources due to eutrophication cause permanent changes in bacterial community structure. By contrast, archaeal communities are differentiated according to trophic state in recently deposited layers, but converge in older sediments deposited under different trophic regimes. Our study indicates an important role for trophic state in driving lacustrine sediment microbial communities and reveals fundamental differences in the temporal responses of sediment Bacteria and Archaea to eutrophication.     

Diatom community succession in the recent history of a eutrophic Yunnan Plateau lake, Lake Dianchi, in subtropical China

Fish introduction, eutrophication and disappearance of aquatic vegetation are important disturbances of aquatic ecosystems, especially in plateau lakes, which are generally considered to be very vulnerable. Fish were introduced to Lake Dianchi, a eutrophic plateau lake in southwest China, in the late 1950s and 1970s. After the introduction, invasive fish became the dominant species, and the total fish yield increased. Meanwhile, the trophic level of Lake Dianchi had a tendency to increase in the past decades because of the increases in human activities in the watershed area. In addition, the area of aquatic vegetation decreased from more than 90 to 1.8% of the lake area from the 1950s to 2000. This study investigated the effects of fish introduction, eutrophication and aquatic vegetation on the diatom community of Lake Dianchi by examining the changes of microfossil diatom assemblage and abundance. Results showed that the absolute abundance and diatom assemblages changed after fish were introduced. The endemic species, Cyclotella rohomboideo-elliptica, disappeared with the introduction of fish and increasing trophic levels after 1958. Fragilaria crotonensis entered into the lake with the introduction of fish and gradually thrived in the lake after 1958. Diatom species numbers also decreased gradually from 21 to 9 from the past to present. Epiphytic diatoms disappeared with the decrease of aquatic vegetation after 1985. Our study indicated that eutrophication was the most important process determining diatom abundance, and fish introduction was a secondary process determining diatom abundance, while aquatic vegetation had a more important role in structuring the diatom community in this eutrophic plateau lake.     

Fine‐scale spatial differences in humpback whale diet composition near Kodiak,Alaska

On the North Pacific feeding grounds, humpback whales (Megaptera novaeangliae) are recovering from commercial whaling at a rapid rate (6.8%). The potential effect that this recovery will have on trophic dynamics involving these predators is currently unknown. To better elucidate complex trophic dynamics, variability in diet composition of apex predators on their respective feeding grounds needs to be understood. Thus, we explored the diet composition of two defined subaggregations of humpback whales of the Kodiak Archipelago population (“North,” “South”) using stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope ratios of humpback whale skin and regional prey samples in Bayesian dietary mixing models. Humpback whales in the “North” region consumed proportionally more fish, dominated by capelin (Mallotus villosus), whereas, whales in the “South” region consumed predominantly krill. The difference in diet composition appears to reflect regional differences in prey availability. Thus, regional variability in diet composition by humpback whales may have disproportionate impacts on prey resources of sympatric predators depending on available prey biomass. As a result, we suggest fine‐scale studies of apex predator diets are needed to better model trophic dynamics with accuracy.     

Cladocera and geochemical evidence from sediment cores show trophic changes in Polish dystrophic lakes

Change in the trophic state of lakes is a topic of primary interest for limnologists and paleolimnologists, but also for governments in many countries. These changes can be the result of the natural evolution of lake ecosystems, but nowadays are most often connected with human activity influencing water bodies. In this article, we reconstruct changes in the lake productivity and trophic state in three dystrophic (humic) lakes located in Northern Poland. Sediments from these lakes, which are part of a national park, were submitted to Cladocera and chemical composition analyses. Currently, the trophic state of these lakes has been described based on the water's chemical composition, and they have been classified as undisturbed ecosystems with a stable trophic state. The main objective of this study was to evaluate whether these lakes have been stable and undisturbed ecosystems during the past centuries and therefore whether they can be classified as natural and pristine. The results of subfossil Cladocera analysis and sedimentary geochemical analysis confirmed the specific nature of studied lakes. However, our results were surprising and showed that during the last 200 years two of the three lakes have undergone distinct trophic changes, while one of them has barely changed at all.     

Evidence of dramatic biodiversity loss in a wet biotope calls for urgent conservation strategies

Abstract

The small lake “Lago di Corree”, located in the middle Volturno plain (Campania Region, Italy), is a biotope belonging to the Roccamonfina–foce Garigliano Regional Park. It is a “habitat island” in a landscape matrix characterised by intensive agriculture. In the present investigation, plant biodiversity loss, assessed by means of historical and recent field floristic surveys, is related to the lake dynamics and landscape transformation inferred using remote sensing (photointerpretation). A dramatic reduction of plant diversity, and the regional-scale local extinction of several aquatic species are reported     

Long-term zooplankton composition data reveal impacts of invasions on community composition in the Waikato lakes,New Zealand

Data collected on zooplankton community composition over longer time periods (>?10 years) are rare. We examined among-lake spatial and temporal trends of zooplankton communities from a monitoring programme undertaken in the Waikato region, New Zealand. A total of 39 lakes were sampled over a period of 12 years, between 2007 and 2019, with varying degrees of temporal effort. We focussed particularly on eight lakes, considered here as ‘long-term lakes’, where samples were collected with greater regularity (including 5 with 12 years of data). Among lakes, suspended sediment concentrations and indicators of lake trophic state were inferred to be important in determining the zooplankton distributions; as this region is dominated by shallow lakes, the relative importance of suspended sediments was high. Among the long-term lakes, the greatest dissimilarities in zooplankton community composition among years were in Lake Waahi, where the Australian Boeckella symmetrica was first detected in 2012. That is, the greatest temporal changes to zooplankton composition during the study period were due to the invasion by non-indigenous species, rather than changes in trophic state or other environmental variables; non-native species commonly dominated the individual counts of species through much of 2014 and 2015, with most samples since 2016 being again dominated by native species. Following this lake, the largest and shallowest lakes in the dataset—Whangape and Waikare—exhibited the greatest variability in community composition among years.