Fluxes and budgets of Cd, Zn, Cu, Cr and Ni in a remote forested catchment in Germany

The input of heavy metals by atmospheric deposition to forested watersheds substantially decreased during the last decades in many areas. The goal of our study was to identify the present sinks and sources of metals and factors influencing metal mobility at the catchment and soil profile scale. We determined concentrations and fluxes of Cd, Zn, Cu, Cr and Ni in precipitation, litterfall, soil solutions (Oi, Oe, Oa horizon percolates, 20 and 90cm soil depth) and runoff in a forest ecosystem in NE-Bavaria, Germany for 1year. The metal concentrations in solutions were mostly <10μgl−1 beside Zn (<1200μgl−1). The present total deposition was estimated at 1.0, 560, 30, 1.2 and 10.4gha−1year−1 for Cd, Zn, Cu, Cr and Ni, respectively. The mass balance (total deposition minus runoff) at the catchment scale indicated actual retention of Zn, Cu and Ni, but an almost balanced budget for Cr and Cd. Considering the soil profile scale, the Oi horizon still acted as a sink, whereas the Oe and Oa horizons were presently sources for all metals. The solid-solution partitioning coefficients indicated higher mobility of Cd and Zn than of Cu, Cr and Ni in forest soils. In the mineral soil horizons, Kd values derived from field measurements were substantially larger than those predicted with empirical regression equations from Sauvé et al. (Environ Sci Technol 34:1125-1131, 2000; Environ Sci Technol 37:5191-5196, 2003). The mineral soil acted as a sink for all metals beside Cd. Dissolved organic C and pH influenced the metal mobility, as indicated by significant correlations to metal concentrations in Oa percolates and runoff. The solid-solution partitioning coefficients indicated higher mobility of Cd and Zn than of Cu, Cr and Ni in forest soils. Overall, the decreased deposition rates have obviously induced a source function of the Oe and Oa horizon for metals. Consequently, mobilization of metals from forest floor during heavy rain events and near surface flow conditions may lead to elevated concentrations in runof

Biogeochemistry of organotin compounds and tin in a forested catchment in Germany

Organotin compounds (OTC) are highly toxic pollutants that have been shown to affect many aquatic ecosystems. Little is known about the input and fate of OTC in terrestrial ecosystems. Here, soil pools, concentrations and fluxes in bulk precipitation, throughfall, fog, litterfall and runoff of OTC and Sntotal were investigated in a forested ecosystem (Picea abies, Karst.) in NE Bavaria, Germany. The concentrations of OTC and Sntotal were generally in the order fog>throughfall>bulk precipitation. Average concentrations of OTCtotal ranged from 57 ng Sn l−1 in fog to 5.8 ng Sn l−1 in bulk precipitation. Concentrations of Sntotal were in the same order but between 490 ng Sn l−1 in fog and 140 ng Sn l−1 in bulk precipitation, on average. Average OTCtotal concentrations in litterfall were 12.9 ng Sn g−1 and those of Sntotal in litterfall 38 ng Sn g−1. All OTC concentrations in runoff were lower than in bulk precipitation, while those of Sntotal were similar to the concentrations in bulk precipitation. Monobutyltin was the dominating OTC in bulk precipitation, throughfall, fog and litterfall, but was seldom detected in the runoff. The annual total deposition of OTCtotal (calculated as throughfall+litterfall) was 172 mg Sn ha−1 year−1, with 45 mg Sn ha−1 year−1 represented by litterfall. The annual runoff from the catchment of OTCtotal amounted to 25 mg Sn ha−1 year−1. The total deposition of Sntotal was 4.9 g Sn ha−1 year−1, of which 0.2 g Sn ha−1 year−1 was litterfall. The annual runoff of Sntotal was 2.4 g Sn ha−1 year−1. The mass balance showed a high retention of OTC and Sntotal in the catchment. The forest soils act as a strong sink for OTC and Sntotal. Only small amounts of deposited OTC are released to runoff. The ratio of soil pools to annual accumulation for total OTC (46 years) indicates that OTC inputs have been occurring already for many decades or have been substantially higher in the past than today

Dynamics of organic and inorganic arsenic in the solution phase of an acidic fen in Germany

Wetland soils play a key role for the transformation of heavy metals in forested watersheds, influencing their mobility, and ecotoxicity. Our goal was to investigate the mechanisms of release from solid to solution phase, the mobility, and the transformation of arsenic species in a fen soil. In methanol–water extracts, monomethylarsonic acid, dimethylarsinic acid, trimethylarsine oxide, arsenobetaine, and two unknown organic arsenic species were found with concentrations up to 14 ng As g−1 at the surface horizon. Arsenate is the dominant species at the 0–30 cm depth, whereas arsenite predominated at the 30–70 cm depth. Only up to 2.2% of total arsenic in fen was extractable with methanol–water. In porewaters, depth gradient spatial variation of arsenic species, pH, redox potentials, and the other chemical parameters along the profile was observed in June together with high proportion of organic arsenic species (up to 1.2 μg As L−1, 70% of total arsenic). Tetramethylarsonium ion and an unknown organic arsenic species were additionally detected in porewaters at deeper horizons. In comparison, the arsenic speciation in porewaters in April was homogeneous with depth and no organic arsenic species were found. Thus, the occurrence of microbial methylation of arsenic in fen was demonstrated for the first time. The 10 times elevated total arsenic concentrations in porewaters in June compared to April were accompanied by elevated concentrations of total iron, lower concentrations of sulfate and the presence of ammonium and phosphate. The low proportion of methanol–water extractable total arsenic suggests a generally low mobility of arsenic in fen soils. The release of arsenic from solid to solution phases in fen is dominantly controlled by dissolution of iron oxides, redox transformation, and methylation of arsenic, driven by microbial activity in the growing season. As a result, increased concentrations of total arsenic and potentially toxic arsenic species in fen porewaters were found in the growing season, suggesting an enhancing risk of arsenic transport of ground- and surface-waters under these conditions

Biogeochemistry of trimethyllead and lead in a forested ecosystem in Germany

Lead compounds, especially ionic organolead compounds (OLC), are highly toxic and mobile pollutants strongly affecting many ecosystems. Soil pools and fluxes with precipitation, litterfall and runoff of trimethyllead (TML), one of the dominant ionic OLC in the environment, and Pb-total were investigated in a forested ecosystem in NE-Bavaria, Germany. In addition, ad/desorption of TML to soils was studied in batch experiments and its degradation in soils was investigated using long term incubations. Total soil storage in the catchment was 11.56 mg Pb ha(-1) for TML and 222 kg Pb ha(-1) for Pb-total. More than 90% of the soil storage of TML was found in the wetland soils of the catchment representing only 30% of the area. Most Pb-total (>90%) was found in die upland soils. In upland soils. TML was only detectable in the forest floor. The annual total deposition from the atmosphere. estimated as throughfall + litterfall fluxes, amounted to 3.7 mg Pb ha(-1) year(-1) for TML and 52 g Pb ha(-1) year(-1) for Pb-total. The contribution of litterfall was 1.5 and 32%, respectively. The concentrations of TML and Pb-total in wet precipitation were: fog > throughfall > bulk precipitation. The annual fluxes with runoff from the catchment was 0.5 mg Pb ha(-1) year(-1) for TML and 2.8 g Pb ha(-1) year(-1) for Pb-total. TML degraded rapidly in the forest floor (Oa horizon) with a half-life (t(1/2)) of 33.5 days. The degradation of TML in Fen (t(1/2) = 421 days) and in the mineral soil (Bw-C horizon, t(1/2) = 612 days) was much slower. Emission of tetramethyllead front wetland soils was not observed during the I year incubation. The adsorption affinity of TML to different soils was Fen > Oa > A greater than or equal to Bw-C The ratio of total soil storages to the present annual input were 3.6 years for TML. TML and Pb-total are still deposited in remote areas even after the use of tetraalkyllead as additives has been terminated for years. The rates of deposition are, however, much lower than in the past. Forest soils act as a sink for deposited TML and Pb-total. TML is accumulated mostly in wetland soils and seems to be stable under anoxic conditions for along time. In upland soils, TML decomposes rapidly Only small amounts of TML are transferred from soils into runoff

Mobile arsenic species in unpolluted and polluted soils

The fate and behaviour of total arsenic (As) and of As species in soils is of concern for the quality of drinking water. To estimate the relevance of organic As species and the mobility of different As species, we evaluated the vertical distribution of organic and inorganic As species in two uncontaminated and two contaminated upland soils. Dimethylarsinic acid (up to 6 ng As g− 1), trimethylarsine oxide (up to 1.5 ng As g− 1), 4 unidentified organic As species (up to 3 ng As g− 1) and arsenobetaine (up to 15 ng As g− 1), were detected in the forest soils. Arsenobetaine was the dominant organic As species in both unpolluted and polluted forest soils. No organic As species were detected in the contaminated grassland soil. The organic As species may account for up to 30% of the mobile fraction in the unpolluted forest floor, but never exceed 9% in the unpolluted mineral soil. Highest concentrations of organic As species were found in the forest floors. The concentrations of extractable arsenite were highest in the surface horizons of all soils and may represent up to 36% of total extractable As. The concentrations of extractable arsenate were also highest in the Oa layers in the forest soils and decreased steeply in the mineral soil. In conclusion, the investigated forest soils contain a number of organic As species. The organic As species in forest soils seem to result from throughfall and litterfall and are retained mostly in the forest floor. The relative high concentrations of extractable arsenite, one of the most toxic As species, and arsenate in the forest floor point to the risk of their transfer to surface water by superficial flow under heavy rain events

Biogeochemistry of organic and inorganic arsenic species in a forested catchment in Germany

Little is known about the fate and behavior of diffuse inputs of arsenic (As) species in forested catchments which often are the sources of drinking water. The objective of this study was to investigate the mobility and transformation of different As species in forest ecosystems to assess the environmental risk related to the diffuse pollution of As. We determined concentrations and fluxes in precipitation, litterfall, soil solutions (Oa horizon and 20- and 90-cm depth), and runoff of organic and inorganic As species and Astotal in a forest ecosystem in NE-Bavaria, Germany. The concentrations of Astotal were mostly <1 μg As L-1 in aqueous samples and were highest in forest floor percolates (7.6 μg As L-1). In litterfall, the concentrations of As species never exceeded 0.1 μg As g-1. Arsenate and arsenite were the prevalent As species in all samples. Organic As species, comprising monomethylarsonic acid, dimethylarsinic acid, trimethylarsine oxide, arsenobetaine, and three unidentified organic As species, were mostly found in throughfall reaching up to 45% of Astotal. The total deposition of Astotal (calculated as throughfall + litterfall) was 5.6 g As ha-1 yr-1 with 16% contribution of litterfall. The annual Astotal fluxes were 30 g As ha-1 yr-1 for forest floor percolates, 8.0 g As ha-1 yr-1 at 20-cm soil depth, and 1.4 g As ha-1 yr-1 at 90-cm soil depth. The annual runoff of Astotal from the catchment amounted to 3.8 g As ha-1 yr-1. The annual fluxes of total organic As species was highest in total deposition (1.1 g As ha-1 yr-1) and decreased largely with depth in the soil profile. The annual runoff of total organic As species was only 0.08 g As ha-1 yr-1. Significant correlations in soil solutions and runoff were found between Astotal and dissolved organic C and Fe. Correlations between Astotal concentrations in runoff and water fluxes were seasonally dependent and with a steeper slope in the growing season than in the dormant season. The elevated concentrations of organic As species in throughfall indicate microbial methylation of As in the phyllosphere, but no evidence for methylation in the soil was found. The mass balance of the catchment points out the strong retention and probable degradation or oxidation of organic As species and arsenite but also to mobilizable pools of Astotal and arsenate. The forest floor is presently a source, whereas the mineral soil is a sink for Astotal and arsenate. The As concentrations in runoff seem to be controlled by As mobilization from forest floor and riparian wetland soils during heavy rain events and superficial flow. The risk for excessment of the drinking water threshold concentrations of As in runoff and soil solutions is considered low at our site

Adsorption and desorption of organotin compounds in organic and mineral soils

Organotin compounds (OTC) are deposited from the atmosphere into terrestrial ecosystems and can accumulate in soils. We studied the adsorption and desorption of methyltin and butyltin compounds in organic and mineral soils in batch experiments. The adsorption and desorption isotherms for all species and soils were linear over the concentration range of 10–100 ng Sn ml−1. The strength of OTC adsorption correlated well with the carbon content and cation exchange capacity of the soil and was in the order mono- > di- > tri-substituted OTCs and butyltin > methyltin compounds. The OTC adsorption coefficients were much larger in organic soils (Kd > 104) than in mineral soils. The adsorption and desorption showed a pronounced hysteresis. Trimethyltin adsorption was partly reversible in all soils (desorption 2–12% of the adsorbed amounts). Dimethyltin, tributyltin and dibutyltin exhibited reversible adsorption only in mineral soils (desorption 4–33% of the adsorbed amounts). Mono-substituted OTCs adsorbed almost irreversibly in all soils (desorption < 1% of adsorbed amounts). Trimethyltin was more mobile and more bioavailable in soils than other OTCs. It might therefore be leached from soils and accumulate in aquatic ecosystems. The other OTCs are scarcely mobile and are strongly retained in soils

Degradation of organotin compounds in organic and mineral forest soils

Broad industrial application of organotin compounds (OTC) leads to their release into the environment. OTC are deposited from the atmosphere into forest ecosystems and may accumulate in soils. Here, we studied the degradation of methyltin and butyltin compounds in a forest floor, a mineral, and a wetland soil with incubation experiments at 20degreesC in the dark. OTC degraded slowly in soils with half-lives estimated from 0.5 to 15 years. The first order degradation rate constants of OTC in soils ranged from 0.05 to 1.54 yr(-1). The degradation rates in soils were generally in the order mono- greater than or equal to di- > tri-substituted OTC. Stepwise dealkylation was observed in all cases of di-substituted OTC, but only in some cases of tri-substituted OTC. Decomposition rates of OTC in the forest floor were higher than in wetland and mineral soils. Tetramethyltin in the gas phase was not detected, suggesting little tin methylation in the wetland soils. Slow degradation of OTC in soils might lead to long-term storage of atmospherically deposited OTC in soils