Influence of wetlands on nutrients in headwaters of agricultural catchments

We investigated the influence of land cover on nutrient concentrations (295 samples) in headwater streams over a 2-year period in 10 agriculture-dominated subcatchments (163-8373 ha) in southern Ontario Canada. In this region, monitoring and research on nutrient dynamics in headwater wetlands is sparse. Our results indicated a significant positive correlation (Pearson coefficient ? = 0.320) between soluble reactive phosphorus (SRP) in the headwater streams and the percentage of wetlands in these agriculture-dominated catchments. This result suggests that headwater wetlands, and other wet riparian zones, are key sources of SRP in the headwater streams. Nitrate concentrations were positively correlated with % agricultural land cover (? = 0.316), consistent with previous studies, while SRP concentrations were negatively correlated with % agricultural land cover (? = -0.325). There was a significant positive correlation between SRP concentrations and discharge in some of the streams. Seasonal SRP trends appear to be closely related to temperature-dependent seasonal changes in redox conditions, including levels of dissolved O-2. Surficial geology had some influence on nitrate concentrations in the streams, which tended to be higher in catchments dominated by glacial till (till terrain), compared to catchments with extensive areas of outwash sand, in addition to till terrain.