Jakub Hruška

The biogeochemistry of basic cations in two forest catchments with contrasting lithology in the Czech Republic

The biogeochemistry of Ca, Mg, K, and Nawere investigated in two forested catchments in theCzech Republic, one underlain by leucogranite, theother by serpentinite. High weathering rates at theserpentinite site at Pluhův Bor resultedin Mg2+ as the dominant cation on the soilexchange complex and in drainage water. Other basiccations (Ca2+, K+, Na+) showedrelatively low concentrations and outflow instreamwater. The catchment exhibited high basesaturation in mineral soils (>70%), and nearneutral soil and stream pH, despite elevated inputsof acidic deposition. Slow growth of Norway spruceat Pluhův Bor may be caused by K deficiency, Mgoversupply and/or Ni toxicity. In contrast, thegranitic site at Lysina showed low concentrations ofbasic cations on the soil exchange complex and instreamwater. Soil and drainage water at Lysina werehighly impacted by acidic deposition. Soil pH wasextremely acidic (<4.5) throughout the soilprofile, and the base saturation of the mineral soilwas very low (<5%). Supplies of basic cationsfrom atmospheric deposition and soil processes wereless than inputs of SO2-4 on anequivalence basis, resulting in low pH and highconcentrations of total Al in drainage water. Needle yellowing in Norway spruce was possibly theresult of Mg deficiency at Lysina. Because of theirextremely different lithologies, these catchmentsserve as valuable end-members of ecosystemsensitivity to elevated levels of acidicdeposition.

Acid/base character of organic acids in a boreal stream during snowmelt

In northern regions, spring snowmelt generally results in an episodic decline of surface water pH. Natural organic acids may be an important factor in this type of pH change. We studied the variations in the acid/base character of aquatic organic acids during spring snowmelt in 1997 at Svartberget, a stream rich in total organic carbon (TOC) that is located in the boreal zone of northern Sweden. Snowmelt at Svartberget was accompanied by a drop in stream pH of up to 1.8 pH units, as well as the dilution of base cation and strong acid anion concentrations. Aluminum and TOC increased or decreased during snowmelt, depending on the sampling site within the 50-ha catchment. Although there were distinct differences in pH, TOC, and major inorganic ions in the runoff from three subcatchments, there was very little variation in the acid/base character of TOC. Thus organic acids in the Svartberget catchment share a common set of acid/base properties despite markedly different subcatchment drainage patterns, vegetation, and soils. The dissociation behavior of organic acids at Svartberget could be described with high precision (R2 = 0.91, p < 0.001, and n = 115) by a triprotic acid analog model (pKa1 = 2.5, pKa2 = 4.0, and pKa3 = 5.8), together with the measured site density of organic acids (8.6±0.8 μeq (mg TOC)−1). A Gaussian pKa distribution (μ = 4.20 and σ = 1.43) predicted organic acid dissociation with similar precision (R2 = 0.91, p < 0.001, and n = 94). Variations in site density among the tributary streams could largely be explained by aluminum complexation. Sites with lower measured site densities had greater concentrations of organically bound Al. Thus Al binding reduces the potential release or neutralization of H+ by organic acids.

Isotopic evidence for processes of sulfur retention/release in 13 forested catchments spanning a strong pollution gradient (Czech Republic, central Europe)

Sulfur isotope systematics were studied in 13 small catchments in the Czech Republic, similar in topography (V-shaped valley) and vegetation (Norway spruce). The sites differed in elevation, rainfall, bedrock, soil type and S pollution. Across the sites, δ 34 5 values decreased in the order: bulk deposition > runoff > spruce throughfall > C-horizon soil > A/B-horizon soil > 0-horizon soil > bedrock (means of 5.5, 4.8, 4.7, 4.6, 4.2, 3.1 and 1.5%o, respectively). Some of the sites had a net export of S, while others accumulated S. Sites exporting S were located in the polluted north where atmospheric S input started to decrease in 1987. Sites retaining S were located in the relatively unpolluted south. Sulfur isotope composition of runoff depended on whether the catchment accumulated or released S. Sites releasing S had runoff δ 34 S values lower than deposition. In contrast, sites retaining S had runoff δ 34 S values higher than deposition. Across the sites, the δ 34 5 values of runoff were not correlated with δ 34 S values of bedrock, indicating that the contribution of bedrock to S in runoff was negligible. The δ 34 S values of runoff were strongly positively correlated with the δ 34 S values of soil. Sulfur present in the C-horizon of soils was mainly derived from atmospheric deposition, not bedrock. Sulfur isotope mass balances were constructed for each catchment, making it possible to quantify the difference between δ 34 S values of the within-catchment source/sink of S and runoff S. Sulfur isotope mass balances indicated that the sink for the retained S at unpolluted sites and the source of the released S at polluted sites were isotopically fractionated by the same amount relative to runoff S. Inorganic and organic processes were considered as possible causes for this observation. Biological S cycling involves a variety of reactions, some of which fractionate S isotopes. In contrast, adsorption/desorption of inorganic sulfate in soil and weathering of S-containing minerals do not fractionate S isotopes. Therefore the within-catchment source/sink of S must be largely a result of biological S cycling. Organic S cycling played an important role over a wide range of atmospheric S inputs from 13 to 130 kg S ha -1 yr -1 .

Nitrogen, organic carbon and sulphur cycling in terrestrial ecosystems: linking nitrogen saturation to carbon limitation of soil microbial processes

Elevated and chronic nitrogen (N) deposition to N-limited terrestrial ecosystems can lead to ‘N saturation’, with resultant ecosystem damage and leaching of nitrate (NO3−) to surface waters. Present-day N deposition, however, is often a poor predictor of NO3− leaching, and the pathway of the ecosystem transition from N-limited to N-saturated remains incompletely understood. The dynamics of N cycling are intimately linked to the associated carbon (C) and sulphur (S) cycles. We hypothesize that N saturation is associated with shifts in the microbial community, manifest by a decrease in the fungi-to-bacteria ratio and a transition from N to C limitation. Three mechanisms could lead to lower amount of bioavailable dissolved organic C (DOC) for the microbial community and to C limitation of N-rich systems: (1) Increased abundance of N for plant uptake, causing lower C allocation to plant roots; (2) chemical suppression of DOC solubility by soil acidification; and (3) enhanced mineralisation of DOC due to increased abundance of electron acceptors in the form of

Role of Organic Solutes in the Chemistry Of Acid‐Impacted Bog Waters of the Western Czech Republic

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Contrasting vulnerability of drained tropical and high‐latitude peatlands to fluvial loss of stored carbon

SO42− and NO3− in anoxic soil micro-sites. Here we consider each of these mechanisms, the extent to which their hypothesised impacts are consistent with observations from intensively-monitored sites, and the potential to improve biogeochemical models by incorporating mechanistic links to the C and S cycles.

Application of the forest-soil-water model (PnET-BGC/CHESS) to the Lysina catchment, Czech Republic

The concentration of chemical oxygen demand (COD), a common proxy for dissolved organic matter (DOM), was measured at seven drinking-water reservoirs and four streams between 1969 and 2006. Nine of them showed significant DOM increases (median COD change +0.08 mg L(-1) yr(-1)). Several potential drivers of these trends were considered, including air temperature, rainfall, land-use and water sulfate concentration. Temperature and precipitation influenced inter-annual variations, but not long-term trends. The long-term DOM increase was significantly associated with declines of acidic deposition, especially sulfur deposition. Surface water sulfate concentrations decreased from a median of 62 mg L(-1)-27 mg L(-1) since 1980. The magnitude of DOM increase was positively correlated with average DOM concentration (R(2) = 0.79, p < 0.001). Simultaneously, DOM concentration was positively correlated with the proportion of Histosols within the catchments (R(2) = 0.79, p < 0.001). A focus on the direct removal of DOM by water treatment procedures rather than catchment remediation is needed.

The leaching behaviour of lead metallurgical slag in high-molecular-weight (HMW) organic solutions

In many regions, naturally occurring organic acid anions can effectively buffer mineral acid inputs from atmospheric deposition, moderating their effect on surface water pH. We studied the effect of chronically high inputs of acid rain on the chemistry of three brown-water streams in the western Czech Republic. The dissolved organic acids in the streams were similar in character to those of other systems in Europe and North America. The site densities (the carboxyl group content per mass of C) were similar to values reported from Fenno-Scandia, and the relationship between the apparent pKa and pH conformed to those from two North American studies. Sulfate and organic acid anions (OA−) were the dominant anions in all three streams, yet despite high dissolved organic carbon and total organic acid concentrations, OA − comprised only 21–32% of total anion charge. This pattern was due to very high sulfate concentrations and, in two of the streams, a low degree of dissociation of the organic acids, probably the results of high long-term inputs of strong acids. Stream water pH was highly correlated to sulfate concentration, but uncorrelated with OA−, suggesting that free acidity is controlled by strong mineral acids rather than organic acids. Thus future reductions in strong acid inputs should result in increased pH and a return to organic control over acid-base chemistry.