Long-term trends in catchment organic carbon and nitrogen exports from three acidified catchments in Nova Scotia, Canada

摘要

We sampled two streams in southwestern Nova Scotia from 1983 to 2004 and one stream from 1992 to 2004 for total organic carbon (TOC) and nitrogen (TN) in order to investigate if changes in catchment exports could be determined over the sampling periods, and if so what were the controlling factors. We first show that early TOC measurements underestimated concentrations due to analytical shortcomings and then produce a correction to adjust values to more accurate levels. Our trend results showed that TOC concentrations decreased in the two streams with the longest record, from 1980 to 1992 when acid deposition to the area decreased most rapidly, and have remained constant since then. TOC exports only decreased at one site over the total sampling period. As expected, we also measured seasonal changes in exports, with the autumn period showing TOC and TN exports as high as during spring snowmelt. We found that only 24% of deposition N is exported from the larger catchments, most of it in organic form, while the smallest catchment exported 16%. We also show a constant increase in TN from 1994 to the present at all three sites sampled. Our results do not support the hypothesis that reductions in sulfur acidification lead to increases in catchment organic carbon mobilization to streams.