The importance of catchment vegetation alkalinity, phosphorus burial and macrophytes as revealed by a recent paleolimnological study in a soft water lake

The land use within a catchment maymarkedly affect the environmental conditions in a lake and the storage capability
of its sediments. This study investigated howchanges in the dominant catchment vegetation (fromlocal stands
of deciduous trees over extensive heathland with some agriculture tomainly coniferous forest) occurring during the
last ca. 200 years were reflected in the sediments of a soft water lake and how these changes influenced the lake
ecosystem. Pollen, macrofossils, metals, different phosphorus (P) forms, organic matter, carbon and nitrogen contents
were determined in short sediment cores. This novel combination of proxies revealed that 1) the reduction
of deciduous trees in thewatershed seemingly reduced the calcium(Ca) supply to the lake and thereby its buffering
capacity. This development was accompanied by decreased abundances of Ca-dependent species and subsequent
increases in acidophilic species. 2) The sedimentary contents of organic matter, non-reactive P and humic-bound
P were evidently higher in sediments deposited during the time when deciduous trees were abundant, which is
probably linked to a stabilising effect by Ca. 3) An erosion event clearly reduced the amounts of macrofossils of
isoetid species and characeans, indicating a reduction in their maximum distribution depth because of lower
water transparency. Overall, the results of our paleolimnological study are of importance within lake management
by convincingly showing how land use changes may (irreversibly) affect environmental conditions and species
composition in soft water lakes and the storage of organic matter and P in their sediments.