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Biological nitrogen fixation (BNF) is an important source of bioavailable nitrogen in the aquatic environment that supports primary production. However, little is known about its occurrence and potential in eutrophic freshwater habitats. This study investigated the diazotrophic diversity and seasonal variation of nitrogenase activity (NA) in the sediments of a cyanobacterial bloom‐occurring bay of a freshwater lake. Sequencing analysis of the nifH gene revealed that diazotrophs in Clusters I and III constituted the dominant components of the diazotrophic community in Meiliang Bay. Both nifH and 16S rRNA gene sequencing indicated that the microbes in sediments have different community structures during the winter than during other seasons. The concentrations of dissolved sulfide, sulfate, and nitrate in pore water were significantly correlated with NA in sediments; however, the Mantel test indicated that dissolved sulfide had a more significant effect on the structure of the diazotrophic community than did other environmental factors. Laboratory culture experiments under different redox conditions further confirmed the inhibitory effect of dissolved sulfide on BNF in sediments. This study revealed that the BNF in sediments of Meiliang Bay was closely linked to variations in dissolved sulfide concentration, which has broadened our understanding of BNF in freshwater lakes. Plain Language Summary: The hypoxic environment formed by cyanobacterial blooms in eutrophic lakes and the rapid decomposition of dead cyanobacteria provide conditions for heterotrophic nitrogen fixation in sediments. Benthic biological nitrogen fixation can theoretically replenish nitrogen to the blooms in the water column. However, our understanding of the diversity of nitrogen‐fixing bacteria and the nitrogen‐fixing potential in freshwater lake sediments is very limited. Here, we explored the community structure and nitrogenase activity of nitrogen‐fixing bacteria in the sediments of a typical eutrophic lake. Our results showed that the nitrogen‐fixing microorganisms in the sediments were mainly heterotrophic Proteobacteria, and active nitrogen fixation occurred during the winter. The diazotrophic community structure and nitrogenase activity were significantly correlated with dissolved sulfide in pore water, and the high concentrations of sulfide during the summer may inhibit nitrogenase activity in sediments. Key Points: High diazotrophic diversity occurred in the sediments of a cyanobacterial bloom area in Lake TaihuThe diazotrophic community and nitrogenase activity were correlated with dissolved sulfide in sedimentsActive sediment nitrogen fixation occurred in winter, nearly seven times as much as in summer [ABSTRACT FROM AUTHOR]

The Hula Valley in northern Israel was partly covered by swamps and a shallow lake. The entire valley was drained and converted for agricultural cultivation. Later, an additional soil reclamation operation was implemented, including eco-tourism. From the early 1990s, winter migratory cranes have attracted visitors, thus supporting the hydrological management of the entire valley that protects the downstream Lake Kinneret. It was documented that these birds have a minor impact on phosphorus pollution, but severely damaged agricultural crops are protected by mild deportation and daily, short, periodical corn seed feeding. [ABSTRACT FROM AUTHOR]

In the semiarid environment of the Fuegian steppe (Argentina), shallow lakes were intensively exploited by hunter-gatherers throughout the Holocene. The archaeological record concentrated along their shoreline frequently reports the first stages of the lithic reduction sequence. In this article, we consider rock availability at different coastal sectors in Lake Amalia. The data focus on the size and weight of the cobbles used as raw material (in Lake Amalia and nearby locations), aiming to compare transported material and that which is spatially located. We analyze information regarding the role played by shallow lakes in the exploitation of steppe environments and their importance in hunter-gatherers' mobility. We suggest that raw material frequency, size, and spatial distribution have conditioned space-use patterns in the Fuegian steppe. The Amalia locality study case sheds light on recurrent visits to specific places in these landscapes. [ABSTRACT FROM AUTHOR]

We carried out geochemical analyses on a sediment core from Lake Harris, Florida (USA) to identify sources of organic matter to the sediment throughout the Holocene, and relate changes in those sources to shifts in past climate and environmental conditions. We hypothesized that the sources of organic matter changed in response to regional hydrologic shifts following de-glaciation, and to human population expansion in the state during the 20th century. Hydroclimate shifts in Florida were related to: 1) a steady rise in relative sea level and the fresh water table that began in the early Holocene, 2) wetland formation and expansion ca. 5,000 cal yrs BP, and 3) the onset of the modern El Niño (ENSO) cycle ~3,000 cal yrs BP. Stratigraphic changes in sediment variables from Lake Harris reflect each of these hydroclimate periods. Early in the Holocene, Lake Harris was a marsh-like system in a relatively dry, open-prairie environment. Organic sediments deposited at that time were derived largely from terrestrial sources, as inferred from high TOC/TN ratios, a dominance of longer-chain of n-alkanes (n-C29-31), relatively negative organic carbon isotope values (δ13CTOC), and low biogenic silica concentrations. In the middle Holocene, a positive shift in δ13CTOC coincided with the onset of wetter conditions in Florida. Submerged macrophyte biomarkers (n-C21-23) dominated, and during that period bulk organic carbon isotope values were most similar to δ13C values of mid-chain-length n-alkanes. In the late Holocene, δ13CTOC values declined, CaCO3 levels decreased to trace amounts, organic carbon concentrations increased and diatom biogenic silica concentrations increased from 10 to 120 mg g-1. Around 2,900 cal yrs BP, the effects of ENSO intensified and many Florida lakes deepened to their current limnetic state. Concentrations of algal and cyanobacterial biomarkers in the Lake Harris core increased by orders of magnitude after about AD 1940, in response to human-induced eutrophication, an inference supported by values of δ15N that fluctuate around zero. [ABSTRACT FROM AUTHOR]

Lake sediment cores contain useful archives of severe past climate events (e.g. droughts, hurricanes, dust storms) and patterns of global climate change. Most such records come from higher latitudes in the Northern Hemisphere. Here we present sediment core data from shallow, equatorial Lake La Tembladera on the southern coast of Ecuador, which contains a > 100-year record of flooding events. We used geochemical properties of a Pb-dated sediment core to identify two distinct sedimentary facies. Facies one represents lake-derived deposits and is characterized by sediments with relatively higher organic matter and nitrogen content. Facies two represents flood events and is characterized by sediments with greater concentrations of inorganic carbon and terrigenous elements Al and Ti. Pollen from introduced Pinus sp. and Hg associated with recent gold mining provided independent time-markers in the sediment to validate the Pb chronology. The comparisons of the geochemical signal with the ENSO reconstructions revealed that the sediments contain a poor signal of ENSO from AD 1930-1965. The weak ENSO signal may result from minimal climate sensitivity in the lake or early water control efforts (e.g. rudimentary damming). However, from AD 1965, the climate signal is totally masked by recent and documented anthropogenic works such as dams and canals. This record shows how anthropogenic efforts to minimize societal impacts of ENSO floods have masked the natural climate signal and nicely mirrored recent trends between climate and anthropogenic activities in tropical latitudes. [ABSTRACT FROM AUTHOR]

We analyzed the interplay between neutral and deterministic processes in maintaining contrasting alternative bacterioplankton communities through time in highly productive shallow lakes and evaluated the relevance of these processes when a regime shift from a clear to a turbid state occurred. We observed that local assembly is ruled primary deterministically, via local habitat filtering, with a secondary role of stochastic processes. We also found a hierarchy in the environmental sorting: while an unusual Verrucomicrobia dominance characterizes the three systems, local conditions limit within-bacterial community membership to closely phylogenetically related and ecologically similar taxa. These results indicate that bacterial abilities to establish in these lakes are strongly determined by their traits, and point toward special physiological adaptations to persist when these systems undergo a regime shift. Altogether, these results hint to a divergence in function among these alternative communities, mediated by major shifts in bacterial community trait structure, particularly regarding carbon use. [ABSTRACT FROM AUTHOR]

Animal vectors are essential for the movement of invertebrate resting eggs between water bodies. However, differences in habitat preferences and feeding behaviour between bird species may result in variations in the dispersal of invertebrates via these birds, even if the different bird species live in the same lake. To test such effects, faecal samples from Anas platyrhynchos (collected in autumn and spring) and Tadorna tadorna (collected in spring) were cultured in water at 20° C and 12 L: 12 D conditions in order to quantify the resting eggs which could be internally transported by these birds. One half of each faecal sample was initially cultured at a conductivity of 0.6 mS cm −1 and the other half at 6 mS cm −1 . 1054 invertebrates hatched from a total of 60 faecal samples, including cladocerans, copepods, ostracods, rotifers and ciliates, with a wide variability among faeces. Autumn yielded a low proportion of samples with hatchlings (12.5%) compared to spring (90%). Significant differences were observed between birds, but not between conductivity treatments. Thus, our results imply different hatching dynamics affected by disperser and season, but most species transported as resting eggs by birds seem to have a wide tolerance to hatch under variable salinity conditions. These differences may largery influence the metacommunity dynamics of lake networks, and could be a key factor to consider in wetland conservation planning. [ABSTRACT FROM AUTHOR]

In environmental risk assessments of nuclear waste, there is need to estimate the potential risks of a large number of radionuclides over a long time period during which the environment is likely to change. Usually concentration ratios (CRs) are used to calculate the activity concentrations in organisms. However, CRs are not available for all radionuclides and they are not easily scalable to the varying environment. Here, an ecosystem transport model of elements, which estimates concentrations in organisms using carbon flows and food transfer instead of CR is presented. It is a stochastic compartment model developed for Lake Eckarfjärden at Forsmark in Sweden. The model was based on available data on carbon circulation, physical and biological processes from the site and identifies 11 functional groups of organisms. The ecosystem model was used to estimate the environmental transfer of 13 elements (Al, Ca, Cd, Cl, Cs, I, Ni, Nb, Pb, Se, Sr, Th, U) to various aquatic organisms, using element-specific distribution coefficients for suspended particles (K d PM ) and upper sediment (K d sed ), and subsequent transfer in the foodweb. The modelled CRs for different organism groups were compared with measured CRs from the lake and literature data, and showed good agreement for many elements and organisms, particularly for lower trophic levels. The model is, therefore, proposed as an alternative to measured CR, though it is suggested to further explore active uptake, assimilation and elimination processes to get better correspondence for some of the elements. The benthic organisms (i.e. bacteria, microphytobenthos and macroalgae) were identified as more important than pelagic organisms for transfer of elements to top predators. The element transfer model revealed that most of the radionuclides were channelled through the microbial loop, despite the fact that macroalgae dominated the carbon fluxes in this lake. Thus, element-specific adsorption of elements to the surface of aquatic species, that may be food sources for organisms at higher trophic levels, needs to be considered in combination with generic processes described by carbon fluxes. [ABSTRACT FROM AUTHOR]

Life-history traits like dominance of certain reproductive modes (e.g. vegetative, specialized, unspecialized or sexual propagules) and overwintering strategies (evergreen or re-sprouting) determine the success and timing of the ability of aquatic plants to colonize new areas. In the present experiment the distribution of these reproductive modes was examined in-situ, where new gaps were experimentally formed and establishment of new vegetation observed on a monthly bases in ten plots. During a period of 126 days, altogether 73% of all established plants (n = 1822) colonized by rhizomatic growth and 11% by rooting of vegetative fragments. Myriophyllum spicatum was observed to use mostly fragment rooting (81%), while Potamogeton perfoliatus followed a more mixed strategy combining re-rooting fragments and rhizomatic growth (31% and 41%, respectively). Stuckenia pectinata also preferred colonisation by rhizomes (84%). No colonisation by specialized vegetative units (tubers or turions) was observed during the study period The importance of surrounding vegetation was shown by comparing colonisation on inner and marginal sections of the plots (30% vs.70%). Three different patterns of timing of peak colonisation intensities were observed, related to species’ life-history traits. While several experimental works have been done on the regeneration and colonisation abilities of different species under laboratory conditions, information on the in-situ application of the different strategies is scarce. Insights on the modes by which plants succeed in colonising gaps helps us understand how (re)establishment of aquatic vegetation might function in lake ecosystems recovering after eutrophication. [ABSTRACT FROM AUTHOR]

Phytoplankton and benthic algae coexist in shallow lakes and the outcome of the competition between these two photoautotrophs can markedly influence water clarity. It is well established that exposed artificial substrate in eutrophic waters can remove nutrients and fine particles from the water column via the attached periphyton canopy. However, the effects of the introduction of artificial substrate on the competition between planktonic and benthic primary producers remain to be elucidated. We conducted a short-term outdoor mesocosm experiment to test the hypothesis that the nutrient and light changes induced by exposed artificial substrate (polythene nets) would benefit the benthic algae. Artificial substrate significantly reduced total nitrogen and phosphorus concentrations and water clarity improved, the latter due to the substrate-induced reduction of both organic and inorganic suspended solids. Consequently, as judged from changes in chlorophyll a (Chl-a) concentrations in water and sediment, respectively, exposed artificial substrate significantly reduced the phytoplankton biomass, while benthic algae biomass increased. Our results thus indicate that exposed artificial substrate may be used as a tool to re-establish benthic primary production in eutrophic shallow lakes after an external nutrient loading reduction, paving the way for a benthic- or a macrophyte-dominated system. Longer term and larger scale experiments are, however, needed before any firm conclusions can be drawn on this. [ABSTRACT FROM AUTHOR]

Lake margin sedimentary systems have been the subject of only limited study. The cyclic Middle Devonian lacustrine succession of Northern Scotland contains repeated developments of shore zone sandstones and thus provides an ideal location for the study of these units. The cycles comprise deep lake, shallow lake, playa and shore zone facies. Detailed field observations are presented alongside ground penetrating radar data which has aided large-scale and three-dimensional characterization of the shore zone sand bodies. Loading and discrete channel forms are recognized in thin-bedded sandstones within the lower portion of the lake shore zone successions. Up-section, the sandstone beds appear to become amalgamated, forming subtle low angle accretionary bar complexes. Where imaged on the radar profiles, the repeated development of shoreward migrating features succeeded by more shallow angled lakeward accreting surfaces is recognized; these are ascribed to washover and swash-backwash processes, respectively. The orientation of these features is similar to palaeocurrent measurements from oscillation ripples, suggesting an alignment of the shore zone bars perpendicular to the prevailing wind direction. Further loaded sandstone beds and sand-filled shallow channel features overlie the bar forms. The context of the shore zone facies allows the controls on its formation to be examined. The shore zone sandstones overlie playa facies which contain abundant desiccation horizons, reflecting the most arid phase in the climatically controlled lacustrine cycle. As climatic conditions ameliorated, the rejuvenation of fluvial systems resulted in the transport of sand out into the basin. Initial deposition was limited to intermittent events where sediment was laid down on a water-saturated substrate. High resolution fluctuations in lake level resulted in periodic short-lived reworking events along the lake margins which produced amalgamated sands, forming low relief bars. Shore zone reworking is likely to have occurred over a wide area as the lake margin migrated back and forth, and gradually transgressed. [ABSTRACT FROM AUTHOR]

There is a strong interest in developing a capacity to predict the occurrence of cyanobacteria blooms in lakes and to identify the measures to be taken to reduce water quality problems associated with the occurrence of potentially harmful taxa. Here we conducted a weekly to bi-weekly monitoring program on five shallow eutrophic lakes during two years, with the aim of gathering data on total cyanobacterial abundance, as estimated from marker pigments determined by HPLC analysis of phytoplankton extracts. We also determined bloom composition and measured weather and limnological variables. The most frequently identified taxa were Aphanizomenon flos-aquae , Microcystis aeruginosa , Planktothrix agardhii and Anabaena spp. We used the data base composed of a total of 306 observations and an adaptive regression trees method, the boosted regression tree (BRT), to develop predictive models of bloom occurrence and composition, based on environmental conditions. Data processing with BRT enabled the design of satisfactory prediction models of cyanobacterial abundance and of the occurrence of the main taxa. Phosphorus (total and soluble reactive phosphate), dissolved inorganic nitrogen, epilimnion temperature, photoperiod and euphotic depth were among the best predictive variables, contributing for at least 10% in the models, and their relative contribution varied in accordance with the ecological traits of the taxa considered. Meteorological factors (wind, rainfall, surface irradiance) had a significant role in species selection. Such results may contribute to designing measures for bloom management in shallow lakes. [ABSTRACT FROM AUTHOR]

Biological communities in shallow lakes are often subject to the combined effects of eutrophication and wind-wave disturbance. However, their relative importance in regulating macrozoobenthic community assembly has not been well addressed. In the present study, a monthly sampling of macrozoobenthos and environmental parameters was conducted at ten sites from December 2012 to November 2013 in Lake Hongze, the fourth largest freshwater lake in China, which has undergone serious water quality deterioration over the past few decades. A total of 30 taxa were recorded during the 12 sampling occasions, including 6 chironomids, 6 bivalves, 4 gastropods, 4 oligochaetes, 4 polychaetes, 4 crustaceans and 2 other aquatic insects. The mean abundance and biomass of total macrozoobenthos varied greatly among the ten sites and presented distinctive taxonomic composition between the protected bays and the offshore zone. Three eutrophication parameters (including permanganate index (COD Mn ), chlorophyll a, and total phosphorus in surficial sediments) and three wind-wave variables (including Secchi depth, turbidity, and mean effective fetch) were highly related to spatial variation of macrozoobenthic assemblages. When eutrophication variables were controlled, there was a significant correlation between community similarity and wind-wave disturbance condition, and vice versa . Variation partitioning showed that wind wave disturbance explained 15.9% of the variation in benthic community composition, slightly lower than that explained by eutrophication (17.9%). These results indicate that wind-wave disturbance is as important as eutrophication in regulating benthic community structure in this large shallow lake. Wind-wave disturbance imposed opposite effects on benthic community relative to eutrophication, and were more prominent in the offshore zone weakening the role of eutrophication. [ABSTRACT FROM AUTHOR]

Drained peatlands often act as carbon dioxide (CO2) hotspots. Raising the groundwater table is expected to reduce their CO2 contribution to the atmosphere and revitalise their function as carbon (C) sink in the long term. Without strict water management rewetting often results in partial flooding and the formation of spatially heterogeneous, nutrient-rich shallow lakes. Uncertainties remain as to when the intended effect of rewetting is achieved, as this specific ecosystem type has hardly been investigated in terms of greenhouse gas (GHG) exchange. In most cases of rewetting, methane (CH4) emissions increase under anoxic conditions due to a higher water table and in terms of global warming potential (GWP) outperform the shift towards CO2 uptake, at least in the short term. Based on eddy covariance measurements we studied the ecosystem-atmosphere exchange of CH4 and CO2 at a shallow lake situated on a former fen grassland in northeastern Germany. The lake evolved shortly after flooding, 9 years previous to our investigation period. The ecosystem consists of two main surface types: open water (inhabited by submerged and floating vegetation) and emergent vegetation (particularly including the eulittoral zone of the lake, dominated by Typha latifolia). To determine the individual contribution of the two main surface types to the net CO2 and CH4 exchange of the whole lake ecosystem, we combined footprint analysis with CH4 modelling and net ecosystem exchange partitioning. The CH4 and CO2 dynamics were strikingly different between open water and emergent vegetation. Net CH4 emissions from the open water area were around 4-fold higher than from emergent vegetation stands, accounting for 53 and 13 gCH4 m-2 a-1 respectively. In addition, both surface types were net CO2 sources with 158 and 750 gCO2 m-2 a-1 respectively. Unusual meteorological conditions in terms of a warm and dry summer and a mild winter might have facilitated high respiration rates. In sum, even after 9 years of rewetting the lake ecosystem exhibited a considerable C loss and global warming impact, the latter mainly driven by high CH4 emissions. We assume the eutrophic conditions in combination with permanent high inundation as major reasons for the unfavourable GHG balance. [ABSTRACT FROM AUTHOR]

Wind-driven sediment resuspension affects the physical and biological environment of the water column in shallow estuarine lakes. This study investigated the relationship between wind-driven waves and suspended sediment concentration (SSC) using the 33 km 2 South Lake basin of Lake St Lucia, South Africa as a case study. Five wave poles measuring significant wave height and turbidity were deployed over an aggregate period of twenty days at distributed locations where sediment substrate compositions varied from muddy to sandy and depths ranged from 0.7 m to 2.1 m. The resulting turbidity dynamics were used to test a simple depth-averaged model of suspended sediment concentrations. The model performed best in the muddy regions of the lake and was able to simulate the resuspension dynamics more accurately than the settling dynamics. Peak suspended sediment concentration levels were best captured for the deeper muddy locations. The model provides a means to make spatially explicit predictions of suspended sediment concentrations that can be used to understand the forcing mechanisms for primary producer growth and distribution or to improve sediment budget calculations. [ABSTRACT FROM AUTHOR]

In this study we investigate how climate fluctuation in the Late Glacial period influenced the development of a lake and its catchment located in the East European Plain. We analyzed the sediments of the lake for pollen, subfossil Cladocera, macrofossils and chemical composition. We aimed at disentangling: (1) the climate changes and their limno-ecological responses, (2) temperature dynamics with the use of Cladocera-based transfer function (MJT) and macrofossil-based reconstruction of mean minimum July temperature (MMJT), (3) timing of the response of different proxies to environmental changes. The results of multiproxy analyses explicitly suggest that the main driver for changes in aquatic and terrestrial ecosystems as well as geomorphological processes in the catchment was climate. Reconstructed temperatures generally follow the known trends showing the increase at the beginning of the Allerød and decrease at the beginning of the Younger Dryas. However, there are some discrepancies between the two reconstructions as well as between the generally accepted temperature trends in Late Glacial. The timing of the proxy response to climate change differs, the aquatic proxies responding first. [ABSTRACT FROM AUTHOR]

Highlights: [•] Wind-induced current in shallow lake was simulated by a special equipment. [•] Acorus calamus had larger inhibitory effects on sediment resuspension. [•] Acorus calamus inhibited TP release better especially under moderate and rapid wind. [•] PP release mechanism with vegetation was mainly relevant to bed shear stress and SSC. [•] DTP release mechanism was different between plant species. [ABSTRACT FROM AUTHOR]

Lake-catchment relationships were presented with reference to each part of the subsystem. Ionic loads reflected the potential of the catchment areas and displayed the following pattern: Lake Rotcze < Lake Sumin < Lake Syczyńskie; with respect to every ion, except nitrogen. The highest specific load of ions in Lake Syczynskie and the strong hydrochemical influence of the lake inlets facilitated the growth of water blooms of cyanobacteria, with a dominance of toxic filamentous P. agardhii. It resulted in a poor ecological status of the lake (Q index = 0.8) and its hypertrophy (TSIchl-a = 78). The specific load of ions in the Lake Rotcze catchment (0.23 kg/yr.km² of P-PO4) contributed to the good ecological status (Q = 3.2) and mesotrophic character (TSIChl-a = 50) of the lake. Lake Sumin has a moderate catchment influence (2.41 kg/yr km² of P-PO4), which facilitated moderate ecological (Q = 2.1) and trophic (eutrophy; TSIchl-a = 63) status. [ABSTRACT FROM AUTHOR]

The studies of differences in life history and suitability of both water temperatures and trophic levels among rotifer sibling species improve our understanding of speciation, sibling species coexistence and possible niche differentiation over space and time, and consequences for the functioning of ecosystems induced by climate change and eutrophication. We collected Brachionus calyciflorus from Lake Baixiang and Lake Kongque, two tropical shallow lakes, in Xishuangbanna city, Yunnan, China, clonally cultured them in laboratory, and found that the B. calyciflorus complex contains two sibling species named sibling species BNA13 and BNB3 by phylogenetic analysis, and investigated the life-table parameters of the two sibling species BNA13 and BNB3 at four temperatures (16, 20, 24 and 28°C) and four algal densities (0.5, 1.0, 2.0 and 4.0×106 cells.mL−1). The results showed that the responses to increasing temperature and algal density for each of the life-table parameters differed with rotifer sibling species. Sibling species, temperature, algal density and their interactions almost all significantly affected the durations of juvenile period, embryonic development, reproductive period, post-reproductive period, mean lifespan, net reproductive rate, generation time and intrinsic rate of population growth. Sibling species significantly affected the age-specific survivorship. Temperature, algal density and their interaction and the interaction of sibling species and temperature significantly affected the age-specific fecundity. Regardless of the effects of temperature and algal density, the durations of juvenile period, embryonic development, reproductive period, post-reproductive period and mean lifespan, age-specific survivorship, net reproductive rate and generation time of the B. calyciflorus sibling species BNA13 were greater than those of BNB3, but the intrinsic rate of population growth of BNA13 was lower than those of BNB3. This suggests that the two B. calyciflorus sibling species adopted variable life history strategies, low population growth and high survivorship for sibling species BNA13, and high population growth and low survivorship for sibling species BNB3. Both the intrinsic rates of population growth of BNA13 and BNB3 were the highest at 28°C and 4.0×106 cells.mL−1 algal density, indicating that some adaptations of the B. calyciflorus sibling species BNA13 and BNB3 in tropical shallow lakes to water temperatures and trophic levels were similar, and they have the potential for coexistence in single waterbody of higher temperature and higher trophic level. [ABSTRACT FROM PUBLISHER]

Recruitment dynamics of fishes can determine their abundance and subsequent effects of adult populations on ecosystem properties. Common CarpCyprinus carpiois a widespread invasive species that can exert negative density-dependent effects on aquatic food webs. However, little is known concerning processes that regulate their recruitment. We used summer-through-fall electrofishing catch rates of age-0 Common Carp to investigate the importance of biotic (stock size, prey availability, egg and juvenile predation, intraspecific competition) and abiotic (water level fluctuation, temperature, wind events) factors on recruitment and growth in 13 lakes across eastern South Dakota from 2008 to 2010. Mean relative abundance of age-0 Common Carp was highly variable spatially and temporally, ranging from 0 to 152.2 fish per hour of electrofishing. Ricker stock–recruitment models indicated that peak production of age-0 Common Carp occurred when adult Common Carp relative abundance was low. Recruitment also increased with spring–summer temperatures, decreased with wind events, and was affected by annual water level fluctuations. Age-0 Common Carp growth, estimated by mean size in August, was highly variable (mean TL = 42–165 mm) and influenced by the abundance of conspecifics and wind events, indicating that density-dependent interactions may have occurred during early life stages. Combined, our results suggest that the early life history of Common Carp is regulated by density-dependent processes and abiotic environmental conditions, which provide new insights into mechanisms regulating recruitment of this widespread invasive species. Received October 29, 2012; accepted November 21, 2012 [ABSTRACT FROM AUTHOR]

Constraints on lake communities are complex and are usually studied by using limited combinations of variables derived from measurements within or adjacent to study waters. While informative, results often provide limited insight about magnitude of simultaneous influences operating at multiple scales, such as lake- vs. watershed-scale. To formulate comparisons of such contrasting influences, we explored factors controlling the abundance of predominant aquatic invertebrates in 75 shallow lakes in western Minnesota, USA. Using robust regression techniques, we modeled relative abundance of Amphipoda, small and large cladocera, Corixidae, aquatic Diptera, and an aggregate taxon that combined Ephemeroptera-Trichoptera-Odonata (ETO) in response to lake- and watershed-scale characteristics. Predictor variables included fish and submerged plant abundance, linear distance to the nearest wetland or lake, watershed size, and proportion of the watershed in agricultural production. Among-lake variability in invertebrate abundance was more often explained by lake-scale predictors than by variables based on watershed characteristics. For example, we identified significant associations between fish presence and community type and abundance of small and large cladocera, Amphipoda, Diptera, and ETO. Abundance of Amphipoda, Diptera, and Corixidae were also positively correlated with submerged plant abundance. We observed no associations between lake-watershed variables and abundance of our invertebrate taxa. Broadly, our results seem to indicate preeminence of lake-level influences on aquatic invertebrates in shallow lakes, but historical land-use legacies may mask important relationships. [ABSTRACT FROM AUTHOR]

Purpose: We investigated the effect of growth strategy (i.e., single or mixed plant types) of two emergent plants (i.e., Phragmites australis and Typha orientalis) on the distribution of phthalic acid esters (PAEs) and their monoester metabolites (PAMs) in the sediments and roots in two adjacent shallow lakes in Tianjin, China, as well as the removal of PAEs from the sediments. Materials and methods: Dibutyl phthalate (DBP), di-2-ethylhexyl phthalate (DEHP), and their PAMs were measured in sediments and roots sampled on 18th May 2010. PAE-degrading bacteria and phospholipid fatty acid (PLFA) of the sediment samples were also analyzed. Results and discussion: The results showed that DBP, DEHP, and their PAMs were detected in nearly all of the samples, and the PAE concentrations were 1 to 2 orders of magnitude higher than those of their corresponding monoester metabolites. The PAE distribution patterns in sediments from the two lakes were different and influenced by plant growth strategy. Phytoavailability of PAEs was also affected by plant growth strategy. Conclusions: Compared with the non-rhizosphere sediments, the total organic carbon-normalized PAE concentration in the rhizosphere sediments decreased in the presence of the emergent plants. The PAE removal from the rhizosphere sediments was related not only to plant species but also to growth strategy, which was consistent with the findings of PLFA. The enhancement of PAE biodegradation in the rhizosphere was mainly the result of changes in the microbial community structure for different plant species and in microbial biomass for the same plant species. [ABSTRACT FROM AUTHOR]

Abstract: In northeastern Siberia, Russia, a 1.2m sediment core was retrieved and radiocarbon dated from a small and shallow lake located at the western side of the lower Lena River (N 69°24′, E 123°50′, 81ma.s.l.). The objective of this paper is to reconstruct the palaeoenvironmental variability and to infer major palaeoclimate trends that have occurred since ~13.3cal. kyr BP. We analysed the diatom assemblages, sedimentology (grain-size, total organic carbon (TOC), total nitrogen (TN)), and the elemental and mineralogical composition using X-ray fluorescence (XRF) and X-ray diffractometry (XRD) of the sediment core. Our results show parallel changes in the diatom species composition and sediment characteristics. Enhanced minerogenic sediment input and the occurrence of pyrite is indicative of a cold period between ~12.7 and 11.6cal. kyr BP. The diatom data enable a qualitative inference about the local ecological conditions to be made, and reveal an oligotrophic lake system with alkaline and cold conditions during the earliest Holocene. Moderately warmer climates are inferred for the period from ~9.1 to 5.7cal. kyr BP. The major shift in the diatom assemblage, from dominance of small benthic fragilarioid taxa to a more complex diatom flora with an influx of several achnanthoid and naviculoid diatom species, occurred after a transitional period of about 1400yr (7.1 to 5.7cal. kyr BP) at ~5.7cal. kyr BP, indicating a circumneutral and warmer hydrological regime during the Holocene thermal maximum (HTM). Diatom valve concentrations declined starting ~2.8cal. kyr BP, but have been rising again since ≤600cal. yr BP. This has occurred in parallel to the increased presence of acidophilous diatom taxa (e.g. Eunotia spp.) and decreased presence of small benthic fragilarioid species in the most recent sediments, which is interpreted as the result of neoglacial cooling and subsequent recent climate warming. Our findings are compared to other lake-inferred climate reconstructions along the Lena River. We conclude that the timing and spatial variability of the HTM in the lower Lena River area reveal a temporal delay from north to south. [Copyright &y& Elsevier]

Abstract: The relative abundance of the different picoplankton components (eukaryotic picophytoplankton (Peuk), picocyanobacteria (Pcy) and bacterioplankton), and their relationships with the lake conditions were studied in three types of shallow lakes from the Pampa Plain (Argentina) that differ in their optical properties: clear-vegetated, phytoplankton-turbid and inorganic-turbid. All the selected lakes, but one, are characterized by their different alternative steady state (clear-vegetated and phytoplankton-turbid water phases) following the model proposed by . Autotrophic and heterotrophic picoplankton abundances were analyzed seasonally in relation to environmental variables. All the lakes presented high concentrations of total nitrogen (TN) (>229μgL−1), total phosphorus (TP) (>46μgL−1) and dissolved organic carbon (DOC) (>13.7mgL−1). Clear-vegetated lakes were characterized by vertical diffuse PAR (photosynthetic active radiation) attenuation coefficient (kdPAR) lower than 11m−1, whereas inorganic-turbid lake always showed values higher than 21.1m−1. The euphotic zone depth (Z 1%) was wider in clear-vegetated lakes (40–140cm) and thinner in the inorganic-turbid (10–20cm). The phytoplankton-turbid lakes presented a wide range in the values of these variables (kdPAR: 5.2–35.8m−1; Z 1%: 10–90cm). Phytoplankton chlorophyll-a (Chl-a) strongly differed, ranging from 1.6 to 334.6μgL−1. Picophytoplankton was mainly represented by phycocianine-rich (PC-rich) Pcy in all cases, dominating over Peuk algae. The total and relative abundances of eukaryotic picophytoplankton, Pcy and bacterioplankton, as well as the size structure of the phytoplankton community differed among the water bodies. In general, clear-vegetated water bodies exhibited similar abiotic characteristics, picophytoplankton/bacterioplankton ratios, and phytoplankton size structure. Contrarily, no clear trend was identified for the group of turbid lakes. The contrasting results obtained for the importance of the picoplankton components in phytoplankton-turbid shallow lakes evidence that the availability of the energetical and nutrient resources cannot be solely considered to predict their relative importance in this type of shallow lake. [Copyright &y& Elsevier]

Abstract: The 2500 BP Hverfjall eruption in northern Iceland produced pyroclastic and effusive deposits of widely different characteristics along the length of the eruptive fissure. The southern half of the fissure was located in a shallow lake, whereas the northern part of the fissure extended onto dry land. This specific setting, with overlapping periods of activity at the different vents, resulted in various mingling features between fine-grained phreatomagmatic deposits and lava flows. Here we reconstruct the course of events during this eruption based on field observations and granulometric analyses of the resulting deposits. The eruption can be divided into three main phases depending on the main depositional characteristics and vent locations. The initial phase is dominated by phreatomagmatic fall deposits which are attributed to an overall high eruption rate in a shallow lacustrine setting. The second phases involved opening of two new vents on dry ground, and deposition of scoria and lava flows. The third and final phase of the eruption is associated with a lowering of the eruption rate in the southernmost vent, with a shift in the activity from continuous uprush and fall deposits to discrete explosions and emplacement of base surges. These surges display features consistent with drying up with increasing distance from the vent, suggesting that their dynamics changed during emplacement. Most wet surges were channelized within a preexisting graben structure close to the vent, but some more dilute (i.e., dry) surges were able to flow over this obstacle and continued to flow for more than 5km away from the vent and 100m uphill before stopping. [Copyright &y& Elsevier]

Abstract: Regime shifts in shallow lakes may significantly affect partitioning of sediment-bound hydrophobic organic chemicals (HOCs) such as polychlorobiphenyls (PCB) and polycyclic aromatic hydrocarbons (PAH). In replicated experimental model ecosystems mimicking the alternative stable states ‘macrophyte-dominated’ and ‘suspended solid – phytoplankton dominated’, we tested the effects of macrophytes and benthivorous fish presence on mass distribution and bioaccumulation of hexachlorobenzene, PCBs and PAHs. HOC mass distributions and lipid-normalized concentrations in sediment (Soxhlet- and 6-h Tenax-extractable), suspended solids, macrophytes, periphyton, algae, zooplankton, invertebrates and carp revealed that mobile, i.e. less hydrophobic or less aged HOCs were more susceptible to ecological changes than their sequestered native counterparts. Macrophytes were capable of depleting considerable percentages of the bioavailable, fast desorbing HOC fractions in the sediment upper (bioactive) layer, but did not have a significant diluting effect on lipid-normalized HOC concentrations in carp. Carp structured invertebrate communities through predation and stimulated partitioning of HOCs to other system compartments by resuspending the sediment. These results show that shifts in ecosystem structure have clear effects on fate, risks and natural attenuation of sediment-bound organic contaminants. [ABSTRACT FROM AUTHOR]

Abstract: The valley of the Sanaga River, notably in its lower course, experienced a marked alluvial accumulation (7–12m thick) when the Holocene sea-level and thus the base level of the river approached the present zero. This resulted in an increased height of the floor of the streambed, which facilitated the overflowing of the floods over the top of the river banks. The sediments of Lake Ossa, situated approximately 35km from the Atlantic shoreline, but the margins of which extend to 1–2km from the Sanaga River, were studied on the basis of five sediment cores. This lake basin remained isolated from the river until 6500cal. BP, from when we note the first alluvial accumulation, especially in its southern part. A more easily submersible segment of the lake shoreline about 2km long was identified. Several specific mineralogical markers of the sandy fraction and the clayey fraction allow us to distinguish autochthonous materials emanating from proximal hillsides upstream of the river, and then to follow the increase of these allochthonous particles during the second half of the Holocene. The first important introduction of alluvial materials in the lake, notably sands, was associated with an acceleration of the accumulation rate. These sedimentary processes seem to have intervened independently of the climate change of the region; they began in a dense forest wet phase and continued during a period of relative opening of the landscape corresponding to more contrasted seasons. The accumulation of coarse alluviums in the lake occurred according to an approximately south–north axis, while that of the suspended load developed with a wider fan-like geometry. These sedimentary processes are diachronous according to the distance from the Sanaga River and so lead us to reconsider partly the palaeoenvironmental meaning of the assemblages of pollen and possibly also of diatoms from previous studies. These vegetal markers were previously considered to have been deposited in the lacustrine system, in restricted isolation. [Copyright &y& Elsevier]

Reports on the decline in phosphorus and nitrogen concentrations after effluent diversion in the Shallow Lake Site, Arkansas. Association between pre diversion clear water and large-bodied daphnia magna; Evidence for importance of biological structure in determining extent of chemical resilience; Reason for high release rates of nitrogen and phosphorus.