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| 2. |
- Bishop, Kevin, et al.
(författare)
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The Effects of Forestry on Hg Bioaccumulation in Nemoral/Boreal Waters and Recommendations for Good Silvicultural Practice
- 2009
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Ingår i: Ambio. - : Royal Swedish Academy of Sciences. - 0044-7447 .- 1654-7209. ; 38:7, s. 373-380
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Tidskriftsartikel (refereegranskat)abstract
- Mercury (Hg) levels are alarmingly high in fish from lakes across Fennoscandia and northern North America. The few published studies on the ways in which silviculture practices influence this problem indicate that forest operations increase Hg in downstream aquatic ecosystems. From these studies, we estimate that between one-tenth and one-quarter of the Hg in the fish of high-latitude, managed forest landscapes can be attributed to harvesting. Forestry, however, did not create the elevated Hg levels in the soils, and waterborne Hg/MeHg concentrations downstream from harvested areas are similar to those from wetlands. Given the current understanding of the way in which silviculture impacts Hg cycling, most of the recommendations for good forest practice in Sweden appear to be appropriate for high-latitude regions, e.g., leaving riparian buffer zones, as well as reducing disturbance at stream crossings and in moist areas. The recommendation to restore wetlands and reduce drainage, however, will likely increase Hg/MeHg loadings to aquatic ecosystems
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| 3. |
- Eklöf, Karin, et al.
(författare)
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Forestry Influence by Stump Harvest and Site Preparation on Methylmercury, Total Mercury and Other Stream Water Chemistry Parameters Across a Boreal Landscape
- 2012
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Ingår i: Ecosystems (New York. Print). - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 15:8, s. 1308-1320
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Tidskriftsartikel (refereegranskat)abstract
- Forestry has been reported to cause elevated mercury (Hg) concentrations in runoff water. However, the degree to which forestry operations influence Hg in runoff varies among sites. A synoptic study, covering 54 catchments distributed all over Sweden, subjected to either stump harvest (SH), site preparation (SP) or no treatment (Ref), was undertaken to reveal the degree of forestry impact and causes of eventual variation. All streams were sampled twice, in autumn 2009 and summer 2010. There were no significant differences in total mercury (THg) and methylmercury (MeHg) concentrations between the three treatments in either 2009 or 2010. However, when pooling the treated catchments (that is, SH and SP) and taking catchment properties such as latitude into account, the treatment had a significant influence on the THg and MeHg concentrations. Although the treatment effect on THg and MeHg did not differ between SH and SP, the study did reveal significant forestry effects on potassium (K) and total nitrogen (TN) that were greater in the SH catchments and lower in the SP catchments. Partial least square (PLS) regressions indicated that organic matter was the most important variable influencing both the THg and MeHg concentrations. There were no significant differences between the treatment groups when comparing the ratios of THg/total organic carbon (TOC) and MeHg/TOC, suggesting that the high concentrations of THg and MeHg observed at some of the treated catchments are associated with increased concentrations of TOC rather than new methylation or increased mobilization caused by factors other than TOC.
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| 4. |
- Eklöf, Karin, et al.
(författare)
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Impact of Forestry on Total and Methyl-Mercury in Surface Waters : Distinguishing Effects of Logging and Site Preparation
- 2014
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 48:9, s. 4690-4698
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Tidskriftsartikel (refereegranskat)abstract
- Forestry operations can increase the export of mercury (both total and methyl) to surface waters. However, little is known about the relative contribution of different forestry practices. We address this question using a paired-catchment study that distinguishes the effects of site preparation from the antecedent logging. Runoff water from three catchments, two harvested and one untreated control, was sampled biweekly during one year prior to logging, two years after logging, and three years after site preparation. The logging alone did not significantly increase the concentrations of either total or methyl-mercury in runoff, but export increased by 50-70% in one of the harvested catchments as a consequence of increased runoff volume. The combined effects of logging and site preparation increased total and methyl-mercury concentrations by 30-50% relative to preharvest conditions in both treated catchments. The more pronounced concentration effect after site preparation compared to logging could be related to site preparation being conducted during summer. This caused more soil disturbance than logging, which was done during winter with snow covering the ground. The results suggest that the cumulative impact of forest harvest on catchment mercury outputs depends on when and how forestry operations are implemented.
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| 5. |
- Eklöf, Karin, et al.
(författare)
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Impact of stump harvest on run-off concentrations of total mercury and methylmercury
- 2013
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 290, s. 83-94
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Tidskriftsartikel (refereegranskat)abstract
- Forest harvesting operations have been reported to increase the levels of both total mercury (THg) and methylmercury (MeHg) in runoff water and downstream biota. Mobilization of such harmful substances by logging may pose ecological risks that may be influenced further by site preparation and stump harvest. Stump harvest is currently being explored as a method to increase the supply of biofuels. In this catchment study we investigated the effects of stump harvest, in comparison with ordinary site-preparation, on the runoff concentrations of THg and MeHg as well as several other chemistry parameters. Both treatments were also compared with unharvested reference catchments. Water samples from watercourses draining these catchments were analyzed for various variables including THg, MeHg, total organic carbon, absorbance and total suspended solids. One year of pre-treatment data, starting when the treated areas were just logged, and 2 years of post-treatment data, after stump harvest or site-preparation, were collected with a sample frequency of twice a month. The concentrations of THg and MeHg in the treated areas were decreasing after both stump harvest and site preparation relative to the reference catchment. Further, our results indicate that stump harvest has not caused increased concentrations of any of the studied parameters in relation to traditional site preparation. Two factors are proposed to be responsible for the lack of response to stump harvest and site preparation; (1) the areas are still undergoing recovery from the former logging which may have led to greater Hg export and/or (2) there is variability among sites in how they respond to forestry operations, depending on the biogeochemical and hydrological status of the area. Although no forestry response caused by stump harvest or site preparation was found, we noted that the concentrations of both THg and especially MeHg were high (median THg: 4.5-10.4 ng L-1, median MeHg: 0.7-2.1 ng L-1) in all catchments both before and after treatment, compared to other studies. Variables indicating the organic carbon content were the ones most strongly correlated to the variation of both THg and MeHg in the PLS models based on the dataset from the whole sampling period and all catchments. The relatively high concentrations of THg and MeHg during the study period appeared to be more influenced by organic carbon, but also hydrology and temperature as well as possibly the initial logging rather than by the soil disturbance caused by either stump harvest or site preparation.
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| 6. |
- Eklöf, Karin, et al.
(författare)
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Parsimonious Model for Simulating Total Mercury and Methylmercury in Boreal Streams Based on Riparian Flow Paths and Seasonality
- 2015
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 49:13, s. 7851-7859
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Tidskriftsartikel (refereegranskat)abstract
- The complexity of mercury (Hg) biogeochemistry has made it difficult to model surface water concentrations of both total Hg (THg) and especially methylmercury (MeHg), the species of Hg having the highest potential for bioaccumulation. To simulate THg and MeHg variation in low-order streams, we have adapted a conceptual modeling framework where a continuum of lateral flows through riparian soils determines streamflow concentrations. The model was applied to seven forest catchments located in two boreal regions in Sweden spanning a range of climatic, soil, and forest management conditions. Discharge, and simulated riparian soil water concentrations profiles, represented by two calibrated parameters, were able to explain much of the variability of THg and MeHg concentrations in the streams issuing from the catchments (Nash Sutcliffe (NS) up to 0.54 for THg and 0.58 for MeHg). Model performance for all catchments was improved (NS up to 0.76 for THg and 0.85 for MeHg) by adding two to four parameters to represent seasonality in riparian soil water THg and MeHg concentrations profiles. These results are consistent with the hypothesis that riparian flow-pathways and seasonality in riparian soil concentrations are the major controls on temporal variation of THg and MeHg concentrations in low-order streams.
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| 7. |
- Gantner, Nikolaus, et al.
(författare)
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MERCURY CONCENTRATIONS IN LANDLOCKED ARCTIC CHAR (SALVELINUS ALPINUS) FROM THE CANADIAN ARCTIC. PART I : INSIGHTS FROM TROPHIC RELATIONSHIPS IN 18 LAKES
- 2010
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Ingår i: Environmental Toxicology and Chemistry. - : Wiley. - 0730-7268 .- 1552-8618. ; 29:3, s. 621-632
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Tidskriftsartikel (refereegranskat)abstract
- Concentrations of mercury (Hg) have increased slowly in landlocked Arctic char over a 10- to 15-year period in the Arctic. Fluxes of Hg to sediments also show increases in most Arctic lakes. Correlation of Hg with trophic level (TL) was used to investigate and compare biomagnification of Hg in food webs from lakes in the Canadian Arctic sampled from 2002 to 2007. Concentrations of Hg (total Hg and methylmercury [MeHg]) in food webs were compared across longitudinal and latitudinal gradients in relation to delta C-13 and delta N-15 in periphyton, zooplankton, benthic invertebrates, and Arctic char of varying size-classes. Trophic magnification factors (TMFs) were calculated for the food web in each lake and related to available physical and chemical characteristics of the lakes. The relative content of MeHg increased with trophic level from 4.3 to 12.2% in periphyton, 41 to 79% in zooplankton, 59 to 72% in insects, and 74 to 100% in juvenile and adult char. The delta C-13 signatures of adult char indicated coupling with benthic invertebrates. Cannibalism among char lengthened the food chain. Biomagnification was confirmed in all 18 lakes, with TMFs ranging from 3.5 +/- 1.1 to 64.3 +/- 0.8. Results indicate that TMFs and food chain length (FCL) are key factors in explaining interlake variability in biomagnification of [Hg] among different lakes. Environ. Toxicol. Chem. 2010; 29: 621-632. (C) 2009 SETAC
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| 8. |
- Gantner, Nikolaus, et al.
(författare)
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MERCURY CONCENTRATIONS IN LANDLOCKED ARCTIC CHAR (SALVELINUS ALPINUS) FROM THE CANADIAN ARCTIC. PART II : INFLUENCE OF LAKE BIOTIC AND ABIOTIC CHARACTERISTICS ON GEOGRAPHIC TRENDS IN 27 POPULATIONS
- 2010
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Ingår i: Environmental Toxicology and Chemistry. - : Wiley. - 0730-7268 .- 1552-8618. ; 29:3, s. 633-643
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Tidskriftsartikel (refereegranskat)abstract
- Among-lake variation in mercury (Hg) concentrations in landlocked Arctic char was examined in 27 char populations from remote lakes across the Canadian Arctic. A total of 520 landlocked Arctic char were collected from 27 lakes, as well as sediments and surface water from a subset of lakes in 1999, 2002, and 2005 to 2007. Size, length, age, and trophic position (delta N-15) of individual char were determined and relationships with total Hg (THg) concentrations investigated, to identify a common covariate for adjustment using analysis of covariance (ANCOVA). A subset of 216 char from 24 populations was used for spatial comparison, after length-adjustment. The influence of trophic position and food web length and abiotic characteristics such as location, geomorphology, lake area, catchment area, catchment-to-lake area ratio of the lakes on adjusted THg concentrations in char muscle tissue were then evaluated. Arctic char from Amituk Lake (Cornwallis Island) had the highest Hg concentrations (1.31 mu g/g wet wt), while Tessisoak Lake (Labrador, 0.07 mu g/g wet wt) had the lowest. Concentrations of THg were positively correlated with size, delta N-15, and age, respectively, in 88, 71, and 58% of 24 char populations. Length and delta N-15 were correlated in 67% of 24 char populations. Food chain length did not explain the differences in length-adjusted THg concentrations in char. No relationships between adjusted THg concentrations in char and latitude or longitude were found, however, THg concentrations in char showed a positive correlation with catchment-to-lake area ratio. Furthermore, we conclude that inputs from the surrounding environment may influence THg concentrations, and will ultimately affect THg concentrations in char as a result of predicted climate-driven changes that may occur in Arctic lake watersheds. Environ. Toxicol. Chem. 2010; 29: 633-643.
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| 9. |
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| 10. |
- Guimarães, Jean R.D., et al.
(författare)
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Simultaneous radioassays of bacterial production and mercury methylation in the periphyton of a tropical and a temperate wetland
- 2006
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Ingår i: Journal of Environmental Management. - : Elsevier BV. - 0301-4797 .- 1095-8630. ; 81:2, s. 95-100
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Tidskriftsartikel (refereegranskat)abstract
- Laboratory radioassays were made to study mercury (Hg) methylation together with bacterial production in the periphyton of two aquatic macrophytes, the submerged Myriophyllum spicatum, from a constructed wetland in Sweden and the floating Eichhornia crassipes, from a eutrophied tropical lake in Brazil. Time course incubations were made by addition of 203HgCl2 and the methylmercury formed was extracted at pre-defined time intervals. Bacterial production (14C-leucine incorporation) was measured at the same time intervals, with plants removed from parallel incubations made with and without addition of cold HgCl2. For E. crassipes, higher methylmercury production was observed at elevated bacterial production, whereas for M. spicatum, the bacterial production was significantly lower, and Hg methylation was below the detection limit. The combined results confirm the importance of microbial processes for Hg methylation, although other factors are known to influence this process in complex ways. The addition of Hg did not significantly influence bacterial production, while the incubation temperatures used (25 and 35 1C) resulted in different methylation rates. Radiotracer techniques for measurements of bacterial production such as 14C-leucine uptake can provide useful insights into the Hg cycle in aquatic environments, and our data suggest that they may be used as a proxy of mercury methylation potentials.
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