Biogeochemistry of a cirque-lake landscape: An interdisciplinary study in a catchment of the northern Black Forest, Germany

Abstract

The pedological analysis of the soil continuum in a catchment can yield substantial insight in flow paths, transport processes, and possible linkages between terrestrial and aquatic ecosystems. In an interdisciplinary study we investigated precipitation, lake tributaries, and soils of three sandstone-dominated subcatchments of a dystrophic cirque lake during 1989 and 1990. The chemistry of tributary 1 is characterized by relatively higher pH values, positive alkalinity at base flow, higher concentrations of Ca, Mg, and K and lower dissolved Organic carbon (DOC). It does not fit to the chemistry of the very acid leached podzolized soils in its subcatchment (weak linkage). The dominance of base flow and lower intra-annual variations in discharge and temperature further confirm the conclusion of a dominating vertical flow path of soil water into the regolith and bedrock zone with substantial buffering in that zone (groundwater flow). Tributary 2 shows the lowest pH values and the highest concentrations of DOC, Fe, Al, and P, which fits very well the chemistry of the very acid, leached, permanently wet soils of its catchment (strong linkage). The dominance of storm flow water with high intra-annual variations in discharge corresponds with the high soil moisture and prevalent lateral flow path of water in the soil cover (lateral subsurface flow). Tributary 'mix' behaves intermediate between tributaries 1 and 2 but is more similar to that of tributary 1. This is due to the dominance of podzolized over reductomorphic soils in the subcatchment. Lateral transport of matter can be inferred from the soil pattern in all catchments, but its relevance for lake inlet chemistry depends on the existence of downslope immobilization zones.