Showing papers by "Karsten Kalbitz published in 2004"

Dissolved organic matter in small streams along a gradient from discontinuous to continuous permafrost

Abstract: The Yenisei river passes every type of permafrost regime, from south to north, being characterized by increasing continuity of the permafrost and by decreasing thickness of the active layer. We used that situation to test the hypothesis that amounts and properties of dissolved organic matter (DOM) in small streams draining forested catchments respond to different permafrost regimes. Water samples were taken from eight tributaries along the Yenisei between 67130 0 N and 65149 0 N latitude. The samples were analysed for dissolved organic carbon (DOC) and nitrogen (DON) and DOM was characterized by its chemical composition (XAD-8 fractionation, sugars, lignin phenols, amino acids, protein, UV and fluorescence spectroscopy), and its biodegradability. Most properties of the tributary waters varied depending on latitude. The higher the latitude, the higher were DOC, DON and the proportion of the hydrophobic fraction of DOC. The contribution of hexoses and pentoses to DOC were higher in southern tributaries; on the other hand, phenolic compounds were more abundant in northern tributaries. Mineralizable DOC ranged between 4% and 28% of total DOC. DOM in northern tributaries was significantly (Po0.05) less biodegradable than that in southern tributaries reflecting the differences in the chemical properties of DOM. Our results suggest that the differences in DOM properties are mainly attributed to differences of permafrost regime, affecting depth of active layer, soil organic matter accumulation and vegetation. Soil organic matter and vegetation determine the amount and composition of DOM produced in the catchments while the depth of the active layer likely controls the quantity and quality of DOM exported to streams. Sorptive interactions of DOM with the soil mineral phase typically increase with depth. The results imply that a northern shift of discontinuous permafrost likely will change in the long term the input of DOM into the Yenisei and thus probably into the Kara Sea.

The Lehstenbach and Steinkreuz catchments in NE Bavaria, Germany

Abstract: The arched, densely forested Fichtelgebirge (ca. 1,000 km2) lies in the northeastern part of Bavaria (district of Oberfranken; near the frontier to the Czech Republic; Fig. 2.1) at the confluence of three Palaeozoic, Variscian mountain ridges of central Europe: the Franconian forest, Ore Mountains, and Bohemian forest. The Fichtelgebirge comprises a large granitic pluton surrounded by metamorphic rock series as gneiss, mica schists, and phyllites. The summits of the Fichtelgebirge, Schneeberg (1,053 m), and Ochsenkopf (1,023 m) do not reach the timberline. The mountain ridge acts as a main European catchment between the Atlantic North Sea and the Danubian Black Sea.

Clear-cutting of a Norway spruce stand : implications for controls on the dynamics of dissolved organic matter in the forest floor

Abstract: Summary Clear-cutting of forest provides a unique opportunity to study the response of dynamic controls on dissolved organic matter. We examined differences in concentrations, fluxes and properties of dissolved organic matter from a control and a clear-cut stand to reveal controlling factors on its dynamics. We measured dissolved organic C and N concentrations and fluxes in the Oi, Oe and Oa horizons of a Norway spruce stand and an adjacent clear-cutting over 3 years. Aromaticity and complexity of organic molecules were determined by UV and fluorescence spectroscopy, and we measured δ13C ratios over 1 year. Annual fluxes of dissolved organic C and N remained unchanged in the thin Oi horizon (∼ 260 kg C ha−1, ∼ 8.5 kg N ha−1), despite the large reduction in fresh organic matter inputs after clear-cutting. We conclude that production of dissolved organic matter is not limited by lack of resource. Gross fluxes of dissolved organic C and N increased by about 60% in the Oe and 40% in the Oa horizon upon clear-cutting. Increasing organic C and N concentrations and increasing water fluxes resulted in 380 kg C ha−1 year−1 and 10.5 kg N ha−1 year−1 entering the mineral soil of the clear-cut plots. We found numerous indications that the greater microbial activity induced by an increased temperature of 1.5°C in the forest floor is the major factor controlling the enhanced production of dissolved organic matter. Increasing aromaticity and complexity of organic molecules and depletion of 13C pointed to an accelerated processing of more strongly decomposed parts of the forest floor resulting in increased release of lignin-derived molecules after clear-cutting. The largest net fluxes of dissolved organic C and N were in the Oi horizon, yet dissolved organic matter sampled in the Oa horizon did not originate mainly from the Oi horizon. Largest gross fluxes in the Oa horizon (control 282 kg C ha−1) and increased aromaticity and complexity of the molecules with increasing depth suggested that dissolved organic matter was derived mainly from decomposition, transformation and leaching of more decomposed material of the forest floor. Our results imply that clear-cutting releases additional dissolved organic matter which is sequestered in the mineral soil where it has greater resistance to microbial decay.

Environmental Controls on Concentrations and Fluxes of Dissolved Organic Matter in the Forest Floor and in Soil Solution

Abstract: Dissolved organic matter (DOM) in soils plays an important role in many ecosystem processes. For example, DOM affects the transport of nutrients and pollutants and the weathering of soil minerals (Temminghoff et al. 1997; Raulund-Ramussen et al. 1998; Kalbitz et al. 2000). It also has great implications for the below-ground C and N cycle, because the leaching loss of DOM can account for a substantial portion of the annual litterfall C and N (McDowell and Likens 1988; Quails et al. 1991; Hongve et al. 2000).