Emerging investigator series: geochemistry of trace elements associated with Fe and Mn nodules in the sediment of limed boreal lakes.

Thousands of boreal lakes were limed for decades in Scandinavia to counteract the effect of anthropogenic acidification. We measured the concentrations of alkali earth metals (Ca, Mg, Ba), metals (Mn, Fe, Al, Co, Cd, Pb, Zn), metalloids (As, Mo) and phosphorus (P) in 165 surface sediment samples from 17 limed lakes, as well as the sediment column and porewater of two lakes chosen from this set. We report that formation of ferromanganese nodules is widespread in limed lakes, and that those nodules are enriched in trace elements, reaching for example 11 500, 908 and 40 µg g-1 for Ba, Mo and As, respectively. Nodules are more abundant between the littoral and the profundal zones. Intense redox cycling of Fe and Mn at the sediment-water interface has redistributed trace elements in the sediment column. Ba, Co, Mo, Pb and Zn partitioned with Mn (oxy)hydroxides and As and P with Fe (oxy)hydroxides. Fe, Mo, Co and As remobilized to the porewater also diffused downward and were likely sequestrated with sulfides. We conclude that the diagenetic redistribution and partitioning of trace elements onto Fe-Mn nodules, rather than direct inputs from liming, is the cause of the elevated trace element burden in surface sediments.

Seasonal and year-to-year variation of mercury concentration in perch (Perca fluviatilis) in boreal lakes.

The authors examined the seasonal and year-to-year variations of mercury (Hg) concentrations in populations of perch (Perca fluviatilis) from 2 boreal freshwater lakes in southeast Norway. Fish Hg concentrations were determined seasonally (spring, summer, and autumn) over 3 yr (2010, 2011, and 2012) to test the hypothesis that there are substantial changes in fish Hg concentrations during the year (seasonal variation) as well as annually. Concentrations were significantly (p < 0.0001) different in the 2 study lakes, with mean seasonal concentrations varying from 0.24 mg/kg to 0.36 mg/kg and from 0.29 mg/kg to 0.37 mg/kg, respectively. The Hg concentrations of both perch populations showed significant year-to-year (p < 0.0001) and seasonal variation (p < 0.01). The changing fish Hg concentrations were 25% and 28% (2010-2011) and 17% and 0% (2011-2012) in the 2 lakes over the 3 yr, respectively. The results demonstrate how the significant year-to-year increase is, among other variables, related to changes in trophic position, shown through stable nitrogen (δ(15)N) isotope data. The seasonal variation is related to summer growth dilution. The results highlight the clear need for yearly studies of fish Hg concentrations, rather than the 3-yr cycle suggested by current European policy through the Water Framework Directive. The lack of yearly sampling may result in erroneous conclusions regarding fish Hg concentration time trends.

Environmental factors influencing mercury speciation in Subarctic and Boreal lakes.

Environmental drivers of total mercury (TotHg) concentrations, methylmercury (MeHg) concentrations, and MeHg fractions (a proxy for methylation potential, expressed as %MeHg) were assessed in a synoptic study of 51 lakes in southeast (Boreal) and northeast (Subarctic) Norway. Concentrations of TotHg and MeHg ranged between 0.5-6.6 ng/L and <0.02-0.70 ng/L, respectively. The lakes span wide ranges of explanatory environmental variables, including water chemistry, catchment characteristics, climate conditions, and atmospheric deposition of Hg, sulphur and nitrogen (N). Dissolved organic matter (DOM), measured as total organic carbon (TOC), was the variable most strongly correlated with TotHg (r(2)=0.76) and MeHg (r(2)=0.64) concentrations. Lakes in the Subarctic region had significantly lower TotHg and MeHg concentrations, and %MeHg than lakes in the Boreal region (p<0.01), implying a lower aquatic food web exposure of aqueous Hg species in Subarctic Norway than in the Boreal lakes. Statistical modelling (partial least squares) using data from the Boreal lakes produced models explaining 82%, 75% and 50% of the spatial variation of TotHg and MeHg concentrations and %MeHg, respectively. After TOC, the most significant explanatory variables were N availability, base cation status, and lake and catchment size. We conclude that a key process driving TotHg concentrations is DOM as a transport vector, while the role of DOM for MeHg and %MeHg is likely related to a combination of transport and DOM as a substrate for methylation. Also, negative correlations between MeHg, and catchment and lake size are consistent with in-lake and in-stream de-methylation processes. The statistical relationship suggests that N availability exerts a positive contribution on concentrations of MeHg and %MeHg.

Spatial trends of trace-element contamination in recently deposited lake sediment around the Ni-Cu smelter at Nikel, Kola Peninsula, Russian Arctic.

A large copper-nickel smelter complex is located at the Kole Penninsula, Russia, close to the Norwegian border. Trace-element concentrations in surface sediments (0-0.5 cm) and pre-industrial sediments from 45 lakes in the region were used to uncover spatial deposition patterns and contamination factor of sediments. Elevated concentrations were found, especially for Ni and Cu, but also for Pb, Co, Hg, As, and Cd. Highest concentrations were found up to 20 km from the smelter, but the concentrations decreased exponentially with distance from the smelter. Increasing Ni, Cu, As, and Hg concentrations from sub-surface to surface sediments were found for lakes at intermediate distances (20-60 km). This may reflect recent changes in atmospheric depositions, as shown in nearby Norwegian areas. However, we cannot rule out that this also may have been caused by diagenetic processes, especially for the most redox-sensitive elements such as As.

Screening for Stockholm Convention persistent organic pollutants in the Bosna River (Bosnia and Herzogovina).

The Stockholm Convention, which aspires to manage persistent organic pollutants (POPs) at the international level, was recently ratified in Bosnia and Herzegovina (BiH). Despite this fact, there is in general a paucity of data regarding the levels of POPs in the environment in BiH. In the present study, screening for POPs was conducted in one of the country's major rivers, the Bosna. A two-pronged approach was applied using passive samplers to detect the freely dissolved and bioavailable concentrations in the water phase and sediment analysis to provide an integrated measure of historical contamination. At several places along the river, the concentrations of polycyclic aromatic hydrocarbons (PAH) were high and exhibited potential for both chronic and acute effects to biota. River water also showed elevated concentrations of PAH, up to 480 ng L(-1) near the city of Doboj, and diagnostic ratios suggested combustion sources for the contamination present in both types of sample. The levels of the other contaminants measured-polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and polybrominated diphenyl ethers--were generally low in the water phase. However, PCBs and some OCPs were present in river sediments at levels which breach the international criteria and thus suggest potential for ecological damage. Additionally, the levels of heptachlor breached these criteria in many of the sites investigated. This study presents the first screening data for some of these Stockholm Convention relevant compounds in BiH and reveals both low concentrations of some chemical groups, but significant point sources and historic contamination for others.

Levels of persistent organic pollutants in the Neretva River (Bosnia and Herzegovina) determined by deployment of semipermeable membrane devices (SPMD).

The main objective of this study was to determine levels of certain persistent organic pollutants (POPs) in Neretva River, Bosnia and Herzegovina (BiH), which is currently facing implementation of the Stockholm Convention on persistent organic pollutants (POPs) and environmental protection strategies. This is the very first report on the deployment of semipermeable membrane devices (SPMDs) in BiH. SPMDs were used for continuous 3-weeks sampling of POPs at three locations, covering 220 km long stream of the Neretva River. Water concentrations of polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs) and polybrominated diphenylethers (PBDEs) were calculated using performance reference compounds (PRCs). The total OCP concentrations ranged from 40 to 140 pg L(-1) and most of compounds were detected only in lower course of the river. Total PAH ranged from 160 to 4000 pg L(-1) and show a clear spatial variation. Dominant PAHs were phenanthrene, fluoranthene, fluorene and acenaphthene. Total PCB ranged from undetectable to 120 pg L(-1). From the group of 15 PBDE congeners investigated, only PBDE-47 and PBDE-99 were detected. Since the concentrations of broad spectrum of POPs found in the Neretva River are quite low, future actions should be focused on preservation rather than on sanitation measures. Regular monitoring should anyhow be established.