Hydrochemistry and hydrology of forest riparian wetlands

Forest stream riparian wetlands have a number of important features. This investigation treats one aspect, the nitrogen retention after upland clear-cutting which leads to elevated nitrate leaching, and the importance of the flow pathways in this connection. The runoff occurs mainly via the upper permeable section of the peat while the lower peat act as an aquitard, restricting the flow from the underlying till. The till groundwater is progressively artesian towards the discharging stream. Water analyses from piezometers show that the water chemistry in the peat is rather variable, indicating the presence of channelling. Channelling is also indicated by spring discharges from the peat that have elevated nitrate contents pointing to bypass flow. Redox bars indicating sulphate reduction display the same picture of irregular distribution. However, a general observation is that volumes with sulphate reduction increase towards the stream and that sulphate reduction occurs preferably in the surface peat, indicating the importance of a degradable substrate for the sulphate reducers. Nitrate reduction during the growth season occurs predominantly close to the upland till areas. The riparian tree stand is dominated by spruces which are likely to be disfavoured by the rising groundwater level after clear-cutting. The riparian tree stand does not extend far enough towards the upland to be benefited by the elevated nitrate flux. Buffer stands should be broader, extending into the till upland where they can utilise the leached nitrate and, more important, thanks to their deeper rooting depth protect the peatland trees against wind felling. (C) 2004 Elsevier B.V. All rights reserved.