The rate of and controls upon DOC loss in a peat catchment

This study uses detailed monitoring of a peat catchment to estimate the amount of DOC loss within a stream. The study compares DOC concentrations and specific absorbances (absorbance at 400 nm per concentration of DOC) of shallow and deep soil waters with those at the catchment outlet. The mass balance between source and outlet is assessed by two methods: a simple method based upon a conservative tracer, and one based upon a principal component analysis using multiple tracers. The single tracer method suggests an average removal of 20% while the principal component approach suggests 32% removal. The rate of removal varies between 0.03 and 23 mg C/day. On an annual basis the removal amounts to between 45.8 and 85 ton C/year, equivalent to an areal loss of between 4 and 7.4 g C/m2/year. The change in specific absorbance, at 400 nm, shows that the DOC is sourced from shallow soil water (10 cm) and not from the deep soil water (50 cm). There is consistent increase in specific absorbance through the catchment. The rate of removal is zero-order with respect to DOC concentration but shows significant decrease with increasing specific absorbance and stream residence time. The study shows that by accounting for the loss of DOC within the streams of the catchment, the catchment is close to balance with respect to carbon and is a smaller carbon sink than previously estimated.