Sizeable net export of base cations from a Carpathian flysch catchment indicates their geogenic origin while the 26Mg/24Mg, 44Ca/40Ca and 87Sr/86Sr isotope ratios in runoff are indistinguishable from atmospheric input.

Nutrient imbalances may negatively affect the health status of forests exposed to multiple stress factors, including drought and bark beetle calamities. We studied the origin of base cations in runoff from a small Carpathian catchment underlain by base-poor flysch turbidites using magnesium (Mg), calcium (Ca) and strontium (Sr) isotope composition of 10 ecosystem compartments. Our objective was to constrain conclusions drawn from long-term hydrochemical monitoring of inputs and outputs. Annual export of Mg, Ca and Sr exceeds 5-to-15 times their atmospheric input. Mass budgets per se thus indicate sizeable net leaching of Mg, Ca and Sr from bedrock sandstones and claystones. Surprisingly, δ26Mg, δ44Ca and 87Sr/86Sr isotope ratios of runoff were practically identical to those of atmospheric deposition and soil water but significantly different from bedrock isotope ratios. We did not find any carbonates in the studied area as a hypothetical, easily dissolvable source of base cations whose isotope composition might corroborate the predominance of geogenic base cations in the runoff. Marine carbonates typically have lower δ26 Mg and 87Sr/86Sr ratios, and silicate sediments often have higher δ26Mg and 87Sr/86Sr ratios than runoff at the study site. Mixing of these two sources, if confirmed, could reconcile the flux and isotope data.

Controls on δ26Mg variability in three Central European headwater catchments characterized by contrasting bedrock chemistry and contrasting inputs of atmospheric pollutants.

Magnesium isotope ratios (26Mg/24Mg) can provide insights into the origin of Mg pools and fluxes in catchments where Mg sources have distinct isotope compositions, and the direction and magnitude of Mg isotope fractionations are known. Variability in Mg isotope compositions was investigated in three small, spruce-forested catchments in the Czech Republic (Central Europe) situated along an industrial pollution gradient. The following combinations of catchment characteristics were selected for the study: low-Mg bedrock + low Mg deposition (site LYS, underlain by leucogranite); high-Mg bedrock + low Mg deposition (site PLB, underlain by serpentinite), and low-Mg bedrock + high Mg deposition (site UDL, underlain by orthogneiss). UDL, affected by spruce die-back due to acid rain, was the only investigated site where dolomite was applied to mitigate forest decline. The δ26Mg values of 10 catchment compartments were determined on pooled subsamples. At LYS, a wide range of δ26Mg values was observed across the compartments, from -3.38 ‰ (bedrock) to -2.88 ‰ (soil), -1.48% (open-area precipitation), -1.34 ‰ (throughfall), -1.19 ‰ (soil water), -0.99 ‰ (xylem), -0.95 ‰ (needles), -0.82 ‰ (bark), -0.76 ‰ (fine roots), and -0.76 ‰ (runoff). The δ26Mg values at UDL spanned 1.32 ‰ and were thus less variable, compared to LYS. Magnesium at PLB was isotopically relatively homogeneous. The δ26Mg systematics was consistent with geogenic control of runoff Mg at PLB. Mainly atmospheric/biological control of runoff Mg was indicated at UDL, and possibly also at LYS. Our sites did not exhibit the combination of low-δ26Mg runoff and high-δ26Mg weathering products (secondary clay minerals) reported from several previously studied sites. Six years after the end of liming at UDL, Mg derived from dolomite was isotopically undetectable in runoff.

The fate of atmospherically derived Pb in Central European catchments: insights from spatial and temporal pollution gradients and Pb isotope ratios.

Soils in polluted regions are generally regarded as a delayed, long-lasting source for Pb contamination of aquatic systems. Lead deposited on topsoil is slowly transported downward with particulate and colloidal organic matter, driven by infiltrating precipitation. Then, Pb is tightly retained in mineral soil. Lead export from catchments is extremely low and decoupled from the atmospheric input. We tested this hypothesis in 11 small catchments, differing in pollution levels. Input/ouput Pb fluxes were monitored for 14-15 years in an era of decreasing industrial Pb emission rates. Between 1996/1997 and 2010, Pb deposition fluxes decreased significantly, on average by 80%. At the beginning of the monitoring, Pb export constituted 2 to 58% of Pb input. At the end of the monitoring, Pb export constituted 2 to 95% of Pb input. Highly polluted sites in the northeast exported significantly more Pb than less polluted sites further south. The (206)Pb/(207)Pb isotope ratios of runoff (1.16) were identical to those of topsoil and present-day deposition, and different from mineral soil and bedrock. Lead isotope systematics and between-site flux comparisons indicated that a portion of the incoming Pb had a relatively short residence time in the catchments, on the order of decades.

Behaviour of arsenic in forested catchments following a high-pollution period.

Due to high availability of adsorption sites, forested catchments could be net sinks for pollutant arsenic both during the period of increasing and decreasing pollution. We tested this hypothesis along a north-south pollution gradient in spruce die-back affected areas of Central Europe. For two water years (2007-2008), we monitored As fluxes via spruce-canopy throughfall, open-area precipitation, and runoff in four headwater catchments (Czech Republic). Since 1980, atmospheric As inputs decreased 26 times in the north, and 13 times in the south. Arsenic export by runoff was similar to atmospheric inputs at three sites, resulting in a near-zero As mass balance. One site exhibited a net export of As (2.2 g ha(-1) yr(-1)). In contrast, the preceding period (1995-2006) showed much higher As fluxes, and higher As export. Czech catchments do not serve as net sinks of atmospheric As. A considerable proportion of old industrial arsenic is flushed out of the soil.

Increasing arsenic concentrations in runoff from 12 small forested catchments (Czech Republic, Central Europe): patterns and controls.

The 40-year long period of heavy industrialization in Central Europe (1950-1990) was accompanied by burning of arsenic-rich lignite in thermal power plants, and accumulation of anthropogenic arsenic in forest soils. There are fears that retreating acidification may lead to arsenic mobilization into drinking water, caused by competitive ligand exchange. We present monthly arsenic concentrations in surface runoff from 12 headwater catchments in the Czech Republic for a period of 13 years (1996-2008). The studied area was characterized by a north-south gradient of decreasing pollution. Acidification, caused mainly by SOx and NOx emissions from power plants, has been retreating since 1987. Between 1996 and 2003, maximum arsenic concentrations in runoff did not change, and were < 1 ppb in the rural south and < 2 ppb in the industrial north. During the subsequent two years, 2004-2005, maximum arsenic concentrations in runoff increased, reaching 60% of the drinking water limit (10 ppb). Starting in 2006, maximum arsenic concentrations returned to lower values at most sites. We discuss three possible causes of the recent arsenic concentration maximum in runoff. We rule out retreating acidification and a pulse of high industrial emission rates as possible controls. The pH of runoff has not changed since 1996, and is still too low (<6.5) at most sites for an As-OH(-) ligand exchange to become significant. Elevated arsenic concentrations in runoff in 2004-2005 may reflect climate change through changing hydrological conditions at some, but not all sites. Dry conditions may result in elevated production of DOC and sulfur oxidation in the soil. Subsequent wet conditions may be accompanied by acidification leading to faster dissolution of arsenic-bearing sulfides, dissolution of arsenic-bearing Fe-oxyhydroxides, and elevated transport of arsenic sorbed on organic matter. Anaerobic domains exist in normally well-aerated upland soils for hours-to-days following precipitation events.

Export of arsenic from forested catchments under easing atmospheric pollution.

Massive lignite burning in Central European power plants peaked in the 1980s. Dissolved arsenic in runoff from upland forest ecosystems is one of the ecotoxicological risks resulting from power plant emissions. Maxima in As concentrations in runoff from four forest catchments have increased 2-5 times between 1995 and 2006, and approach the drinking water limit (10 microg L(-1)). To assess the fate of anthropogenic As, we constructed input/output mass balances for three polluted and one relatively unpolluted forest catchment in the Czech Republic, and evaluated the pool size of soil As. The observation period was 11 years, and the sites spanned a 6-fold As pollution gradient. Two of the polluted sites exhibit large net As export via runoff solutes (mean of 4-5 g As ha(-1) yr(-1) for the 11-year period; up to 28 g As ha(-1) yr(-1) in 2005). This contrasts with previous studies which concluded that forest catchments are a net sink for atmogenic arsenic both at times of increasing and decreasing pollution. The amount of exported As is not correlated with the total As soil pool size, which is over 78% geogenic in origin, but correlates closely with water fluxes via runoff. Net arsenic release is caused by an interplay of hydrological conditions and retreating acidification which may mobilize arsenic by competitive ligand exchange. The effects of droughts and other aspects of climate change on subsequent As release from soil were not investigated. Between-site comparisons indicate that most pollutant As may be released from humus.

Processes affecting oxygen isotope ratios of atmospheric and ecosystem sulfate in two contrasting forest catchments in Central Europe.

Sulfate aerosols are harmful as respirable particles. They also play a role as cloud condensation nuclei and have radiative effects on global climate. A combination of delta18O-SO4 data with catchment sulfur mass balances was used to constrain processes affecting S cycling in the atmosphere and spruce forests of the Czech Republic. Extremely high S fluxes via spruce throughfall and runoff were measured at Jezeri (49 and 80 kg S ha(-1) yr(-1), respectively). The second catchment, Na Lizu, was 10 times less polluted. In both catchments, delta18O-SO4 decreased in the following order: open-area precipitation > throughfall > runoff. The delta18O-SO4 values of throughfall exhibited a seasonal pattern at both sites, with maxima in summer and minima in winter. This seasonal pattern paralleled delta18O-H2O values, which were offset by -18 per thousand. Sulfate in throughfall was predominantly formed by heterogeneous (aqueous) oxidation of SO2. Wet-deposited sulfate in an open area did not show systematic delta18O-SO4 trends, suggesting formation by homogeneous (gaseous) oxidation and/or transport from large distances. The percentage of incoming S that is organically cycled in soil was similar under the high and the low pollution. High-temperature 18O-rich sulfate was not detected, which contrasts with North American industrial sites.