Location of Thesis Examination

Room 4185 Support Services Building

Degree

Doctor of Philosophy

Program

Geology

Supervisor

Irena Creed

Delay of Publication

1

Abstract

This dissertation explored topographic controls on spatial and temporal patterns in water yield and nutrient (carbon, nitrogen and phosphorus) export from forested headwater catchments in the Turkey Lakes Watershed in central Ontario, where other factors contributing to differences in water yield and nutrient export, including climate, geology, forest, and soils, are relatively constant. Topographic characteristics, including (a) hydrological flushing potential (expansion of water table into nitrate-N producing areas); (b) hydrological storage potential (area of wetlands, which can alternatively allow water and nutrients to bypass wetlands when storage capacity is filled with water or to trap them when not filled); and (c) hydrological loading potential (differences in precipitation caused by elevation), were considered in deconstructing non-stationary (linear trends) and stationary (oscillating cycles) patterns in water yield and nutrient export data. Topography explained the majority of differences in water yield and nutrient export. For spatial variation, topographic metrics representing hydrologic flushing potential predicted the majority of the spatial variation in nitrate-N export. In contrast, topographic metrics representing hydrologic storage potential explained the majority of the observed spatial variation in dissolved organic carbon, dissolved organic nitrogen and total dissolved phosphorus export. For temporal variation, catchments with low hydrologic loading potential were generally more sensitive to trends and cycles for water and nutrient export. Among these catchments, hydrological storage potential had no significant effect on water export trends, but had a significant effect on water export cycles; namely, the water export range was larger in the catchments with higher hydrological storage potential, even though the water export average was the same as catchments with lower hydrological storage potential. For nutrient export, the non-stationary signals were not consistent among the nutrients, but the amplitude of stationary signals in nutrient export in catchments with high hydrological storage potential compared to those with low hydrological storage potential was higher for organic nutrients and lower for nitrate-nitrogen. Despite many similarities in these headwater catchments, topography influenced the absolute and relative magnitude of hydrological and biogeochemical export from these catchments, which will have implications on the productivity and biodiversity of downstream aquatic systems.