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With the retreat of glaciers, new ponds and lakes are often formed. These are gradually colonised and become more productive as vegetation develops in their catchments, creating more complex food webs. Near the Jakobshavn Isbræ in West Greenland, we studied trophic structure and food web complexity using stable isotopes in 26 lakes belonging to two different age groups (19 new lakes and 7 nearby older (> 150 years) ones). The older lakes had significantly higher total nitrogen and pelagic chlorophyll-a concentrations, as well as a higher organic matter content in the surface sediment. The biomass and richness of cladocerans, copepods and rotifers were higher in the older lakes and so was the zooplankton:phytoplankton biomass ratio. Multivariate analyses showed a marked difference between the zooplankton communities of new and older lakes. Layman food web metrics indicated higher food chain length and width of invertebrates (zooplankton and benthic macroinvertebrates) in the older lakes, being significantly higher in lakes with fish. Our findings highlight a potential sequence of succession occurring in lakes created by glacial retreat in the Arctic, implying an increase in food web complexity and higher taxonomic (and likely also functional) diversity following ageing and increased nutrient state. [ABSTRACT FROM AUTHOR]

Zooplankton grazing at similar nutrient levels is generally regarded as lower in brackish than in freshwater lakes, but experimental evidence of this is lacking. Accordingly, we conducted short-term zooplankton grazing experiments in bottles with water from 12 Danish brackish lakes covering a large gradient in salinity (0.3–17.4‰) and nutrient concentrations as well as with water from 24 mesocosms established in the same area with various salinities (0.5–12‰), two nutrient levels and low fish density. Grazing was low in 11 of the 12 lakes, even when they were dominated by edible phytoplankton and nutrient addition led to a major increase in phytoplankton biomass. By contrast, grazing was significant in most of the mesocosms, particularly at high nutrient levels and salinities of 8‰ or below where Daphnia dominated. Moreover, grazing decreased the biomass of most phytoplankton taxa, except for a few (e.g. Ankyra at 0.5–2‰ and Ochromonas and Chaetoceros at 8‰). Our results provide experimental support for potentially significant grazing by zooplankton on phytoplankton in brackish lakes up to a salinity of 8‰ at low fish density; however, grazing in summer was generally low in the majority of the lakes, which we attribute to high predation on zooplankton. [ABSTRACT FROM AUTHOR]

Many northwest European lake systems are suffering from the effects of eutrophication due to continued loading and/or poor, ineffective management strategies. Coastal brackish lakes are particularly difficult to manage due to complex nitrogen, phosphorus, and salinity dynamics that may exert varying influence on lake biological communities, but long-term data on how these important and often biodiverse systems respond to change are rare. In this study, palaeolimnological data (including sedimentary parameters, diatoms, and plant macrofossils) and environmental monitoring data (for the last ~40 years) have been used to assess environmental change over the last 100 years in Kilen, a brackish lake in northwest Jutland, Denmark. Kilen has been regularly monitored for salinity (since 1972), TP (from 1975), TN (from 1976), and since 1989 for biological data (phytoplankton, zooplankton, and macrophytes), which allows a robust comparison of contemporary and paleolimnological data at high temporal resolution. The palaeolimnological data indicate that the lake has been nutrient rich for the last 100 years, with eutrophication peaking from the mid-1980s to the late 1990s. Reduced nutrient concentrations have occurred since the late 1990s, though this is not reflected in the sediment core diatom assemblage, highlighting that caution must be taken when using quantitative data from biological transfer functions in paleolimnology. Lake recovery over the last 20 years has been driven by a reduction in TN and TP loading from the catchment and shows improvements in the lake water clarity and, recently, in macrophyte cover. Reduced salinity after 2004 has also changed the composition of the dominant macrophyte community within the lake. The low N:P ratio indicates that in summer, the lake is predominately N-limited, likely explaining why previous management, mainly focusing on TP reduction measures, had a modest effect on the water quality of the lake. Despite a slight recovery, the lake is still nutrient-rich, and future management of this system must continue to reduce the nutrient loads of both TN and TP to ensure sustained recovery. This study provides an exceptional opportunity to validate the palaeolimnological record with monitoring data and demonstrates the power of using this combined approach in understanding environmental change in these key aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Body size is usually considered a good indicator of trophic position in fish communities. Indeed, the proverbial wisdom that "Big Fish Eat Little Fish" is consistent with observations from marine systems where systematic removal of the largest individuals has occurred, with cascading effect in the ecosystems. Trophic cascades are also well documented in temperate lakes but may not be as pronounced in (sub)tropical lakes due to higher degree of fish omnivory. We analysed fish communities along a climatic gradient and showed the classical correlation between body size and relative trophic position disappears in warmer climates where large fish appear to be feeding systematically on the lowest trophic levels. This concurs with experimental findings demonstrating that omnivorous fish tend to include more plant and less animal matter in their diet at higher temperatures. Accordingly, the community-wide trophic web indicators, calculated based on stable isotopes (δ13C and δ15N), showed that the average degree of trophic diversity declined from cold to warm lakes and that the trophic webs become more truncated towards warmer climates. This has implications for lake restoration approaches in warmer climates and in temperate lakes within the context of global warming. [ABSTRACT FROM AUTHOR]

Lead (Pb) pollution in and around Ulaanbaatar is of national concern, given that the Mongolian capital is home to nearly half of the country's entire population. By comparison, Mongolian countryside is a pristine environment because of its sparse population and low industrial activity. The concentration of Pb in urban soils (average of 39.1 mg kg) was twice the values found (average 18.6 mg kg) in background territories (i.e., Mongolian rural sites). Furthermore, Pb contamination was examined by using Pb stable isotopic composition, and covariance of Pb isotopic ratios showed two groups between rural and urban soils as pristine and disturbed sites. The Pb/Pb ratio, the most prominent fingerprint for Pb pollution, was 1.163-1.185 for the urban whereas values for rural soils (1.186-1.207) were analogue to the regional Pb isotopic signatures. Local coal sources and their combustion products, one of the potential Pb pollution sources in Ulaanbaatar, have significant radiogenic properties in terms of Pb isotopic composition and revealed an average of 1.25 for Pb/Pb and 19.551 for Pb/Pb ratios. Thus, contributions from coal firing activity to Pb pollution lower than it was assumed, and smaller range of these values measured in urban soils may be attributed to the mixing of less radiogenic Pb as a constituent of the leaded gasolines. [ABSTRACT FROM AUTHOR]

The concentration of natural radionuclides and the feasibility of recovery of uranium from browncoal ash of a Mongolian cogeneration plant were investigated. The concentrations of the elements were determined by instrumental gamma-activation (IGAA) and X-ray fluorescence (XRF) analysis. Uranium from brown-coal ash was leached with an 8 M HNO + HF (10%) mixture. The extraction of uranium from the solution and its purification for the removal of accompanying elements were carried out on an anion exchanger. An ash sample after leaching contains neither natural radioactive elements (U and Th) nor their decay products, thereby allowing for the use of the ash as a building material. [ABSTRACT FROM AUTHOR]

Cross-latitude studies on lakes have a potential to predict how global warming may cause major changes in phytoplankton biomass and composition, e.g., the development of favourable conditions for cyanobacteria dominance. However, results from these studies may be influenced by biogeographical factors, and the conclusions may, therefore, not hold when considering local response patterns. We used monthly monitoring data from 504 lakes in Denmark—a small and homogeneous geographical region—to establish empirical relationships between key phytoplankton groups and a set of explanatory variables including total phosphorus (TP), total nitrogen (TN), lake mean depth (DEP) and water temperature (TEMP). All variables had strong effects on phytoplankton biomass and composition, but their contributions varied over the seasons, with TEMP being particularly important in June–October. We found dominance of cyanobacteria in terms of biomass and also an increase in dinophytes biomass at higher TEMP, while diatoms and chlorophytes became less important. In May, however, the TEMP effect on total phytoplankton biomass was negative, likely reflecting intensified zooplankton grazing. Our results suggest that biogeographical effects are of minor importance for the response patterns of phytoplankton to temperature and that substantial concentration reductions of TN and TP are needed in eutrophic lakes to counteract the effect of the climate change-induced increase in TEMP. [ABSTRACT FROM AUTHOR]

Sorption of U(VI) with soil from the region of location of the radioactive waste repository was studied. The radionuclide 237U produced by the photonuclear reaction 238U( γ, n)237U on an electron accelerator, MT-25 microtron (FLNR, JINR), was used as tracer. The U(VI) speciation in solution at various U concentrations was calculated in the range pH 1–7 using the Speciation program. [ABSTRACT FROM AUTHOR]