Phosphorus export from Canadian Shield forest catchments: Hot moments and hot spots.

摘要

Total phosphorus (TP) concentrations and export in stream water draining forested catchments on the Precambrian Shield are highly variable both between years and among neighboring catchments possibly due to variability in "hot moments" (high-flow hydrologic events) and "hot spots" (riparian corridors and wetlands). This thesis sought to investigate the causes of substantial inter-catchment variation in TP, by (a) characterizing the response of TP and TDP (total dissolved phosphorus) to hydrologic change at 2 adjacent catchments that differ 2-fold in their long-term average TP export and determine their response to high flow and b) assess the spatial variability in TP concentrations in streams and riparian corridor characteristics to provide insight into the factors controlling TP release to surface waters.;While stream TP and riparian corridor features differed between HP3 and HP3A, they were relatively consistent spatially within each catchment (with the exception of one station in HP3A) and TP concentrations measured at the weir were generally reflective of the entire stream channel. Consistent with higher stream TP concentrations, HP3 had a significantly lower slope and higher soil P and organic content in the riparian corridor, which may explain its higher TP export compared with HP3A. Seasonal and annual correlations between TP, DOC, Fe and SO4 in stream water suggest that TP release is not governed by a single process, but a combination of redox and biologically-mediated processes.;Keywords: phosphorus, storm events, high flow, riparian corridors, sampling frequency, forests.;Event-targeted sampling showed that concentrations and export of TP were higher in HP3 than HP3A, which is consistent with long-term monitoring data (Eimers et al., 2009). During individual events, the proportion of PP (particulate phosphorus) accounting for the increase in TP was greater in HP3A than HP3, while TDP concentrations remained consistently higher in HP3, indicating that the two catchments respond differently to storm events. A comparison of high frequency and routine sampling frequencies in HP3 and HP3A, found that routine monitoring underestimated TP export by approximately 20% and TDP by approximately 10%.