K. Moritz

Trends in deposition and canopy leaching of mineral elements as indicated by bulk deposition and throughfall measurements

In the past three decades, numerous studies on the biogeochemistry of forested ecosystems in Europe and North America have shown that the deposition of mineral elements from the atmosphere strongly influences their functioning. Acidification of soils, surface- and groundwaters, N saturation and forest decline are key processes that change with rates of deposition of mineral elements (Ulrich 1994; Fenn et al. 1998; Evans et al. 2001). As an example of ecosystem functioning, the losses of elements from the ecosystem by seepage and runoff can be considered. On a European-wide, scale the deposition of S and N was shown to determine the Al losses from seepage and runoff in acid forest soils (Dise et al. 2001), the N deposition to determine the NO3 losses (MacDonald et al. 2002) and the Mg deposition to largely determine the Mg losses (Armbruster et al. 2002).

Investigating soil and groundwater quality at different scales in a forested catchment: the Waldstein case study

The impact of anthropogenic depositions on soil and groundwater quality has been the subject of numerous studies in the last two decades. However, the problem of linking results and models at different scales remains to be solved. A case study has been performed in the Fichtelgebirge region in South-East Germany. Data from this case study has been used to analyse scale dependences of spatial variance, autocorrelation lengths, and the interdependence of soil hydrological and soil chemical parameters. For soil suction, spatial variability increases stepwise with scale. Three different sources of variation could be identified, predominating at different ranges of scale, making a deterministic mapping feasible. Local SO4 deposition explained much of the spatial pattern of SO4 concentration in soil solution and in catchment runoff observed at different scales. This is mainly due to the fact that the sorption capacity of the soils in this region has been exceeded. Decreasing SO4 deposition in the long term run is likely to enhance the influence of the soil, and reduces the correlation between deposition and soil solution concentration. NO3 showed minimum variation at the county scale. This seems to be a reasonable representative elementary area for mapping regional NO3 concentration patterns. For protons and Cl, neither observed spatial patterns nor the scale dependence of spatial heterogeneity could be explained adequately.

Dynamics of Runoff and Runoff Chemistry at the Lehstenbach and Steinkreuz Catchment

Many functional biogeochemical aspects of terrestrial ecosystems are intimately linked to water transport processes. Most of the transport of subsurface matter occurs in the liquid phase. In addition, water fluxes exert a major control on, e.g., plant and microbial activity, which in turn has a major impact on matter fluxes and solute turnover in the subsoil.

Factors Controlling Total Concentration and Aqueous Speciation of Aluminium in an Acidic Headwater Stream of the Bavarian Forest National Park: a Modelling Approach

The purpose of the present paper is to analyse factors controlling total concentration and aqueous speciation of aluminium in the Grose Ohe River, using a thermodynamic equilibrium model and a mixing approach. A model compound for humic substances is derived on the basis of the relation between anion deficit and the organic carbon content in the river as well as literature data. An equilibrium speciation model for aluminium is set up, considering this model compound and relevant inorganic solutes. Although the model cannot be verified directly, its results may be viewed as qualitatively correct. Applying the model to measured stream water samples highlights that aqueous speciation of aluminium is mainly controlled by the pH value and discharge and that free aluminium concentrations reach clearly toxic levels during acidic episodes. Comparing measured concentrations of sulfate and H+ and calculated concentrations of Al3+ with solubility curves of gibbsite like minerals and jurbanite clearly shows that total aluminium concentrations are not controlled by equilibria with these mineral phases alone. The observed relationship can be better explained from a mixture of two distinct waters, representing lowflow and highflow chemistry, and the resulting equilibrium concentrations. This indicates that total aluminium concentration, in particular during high discharge events, is mainly controlled by the mixture of waters with differing chemistry and flowpaths. Kontrollfaktoren fur die Gesamtkonzentration und die wassrige Speziierung von Aluminium in einem sauren Quellfluss im Nationalpark Bayerischer Wald: Ein Modellansatz Ein Gleichgewichtsmodell und ein Mischungsansatz werden verwendet, um die Kontrollmechanismen fur die Speziierung und die Gesamtkonzentration von gelostem Aluminium in der Grosen Ohe zu analysieren. Auf Grundlage von Literaturdaten und der Beziehung zwischen Anionendefizit und organisch gebundenem Kohlenstoff wird eine Modellsubstanz fur die im Wasser enthaltenen Huminstoffe abgeleitet und zusammen mit relevanten anorganischen Spezies ein Modell fur die Aluminiumspeziierung aufgestellt. Wenngleich dieses nicht direkt verifiziert werden kann, sind auf seiner Grundlage qualitative Aussagen moglich. Die Anwendung des Modells auf im Bachwasser gemessene Konzentrationen verdeutlicht, dass die Speziierung von Aluminium durch das Abflussgeschehen gesteuert wird und wahrend Versauerungsschuben offenkundig toxische Konzentrationen freien Aluminiums auftreten. Aus dem Vergleich der gemessenen Sulfat- und H+- und der berechneten Al3+-Konzentrationen mit den Loslichkeitskurven von Gibbsit und Jurbanit wird deutlich, dass die Aluminiumkonzentration nicht ausschlieslich durch Gleichgewichte mit diesen Mineralphasen gesteuert wird. Die beobachteten Konzentrationsbeziehungen lassen sich besser aus der Mischung zweier Wasser (Basis- bzw. Hochwasserabfluss) und den sich hieraus ergebenden Gleichgewichtskonzentrationen erklaren. Insbesondere bei Hochwasser wird die Aluminiumkonzentration offenbar durch die Mischung von Wassern mit unterschiedlichen Abflussbildungsprozessen und Chemismen gesteuert.

Trends in the Input-Output Relations: The Catchment Budgets

One important focus of biogeochemical ecosystem studies is that of identifying sinks and sources of various substances in the system. These might be either finite or transient sinks or sources. A quantification of element budgets within catchments is of crucial importance for the identification of critical ecosystem states such as nutrient loss, acidification and contamination of waters and deterioration of soils (Ulrich 1994). However, sinks might turn into sources and vice versa over time. Thus, long-term monitoring is important when interpreting element fluxes and budgets. The latter especially holds true because element budgets and fluxes are subject to high spatial and temporal variability, causing large errors in their estimation, as has been shown previously for the Lehstenbach catchment (Manderscheid and Matzner 1995; Manderscheid et al. 2000a; Alewell et al. 2004).