| Eutrophication of fresh waters caused by phosphorus (P) is not a new environmental problem, coming to the forefront in the 1960s, most notably in the Great Lakes region. In central Idaho, Cascade Reservoir is affected by eutrophication, exhibiting many undesirable traits, including excessive growth of algae and other aquatic plants. Agriculture P inputs are considered one of the main causes of fresh water eutrophication, as much as 25% of the total P loading that enters the Cascade Reservoir. Agricultural P loading varies spatially with land use and temporally with seasonal variations. Few studies have focused specifically on the seasonal variability in P loading and P dynamics.; The overall objective of this dissertation research was to assess agricultural P loading by considering the seasonal variations of hydrological pathways, biochemical mechanisms, and temperature. This was achieved through a field and laboratory component. The field component was a three-year study performed in the Cascade Reservoir watershed in an agricultural setting. The laboratory component assessed water flow paths on P release using flumes, and the evaluation of biochemical mechanisms on P release was evaluated using soil columns.; Results from the field study indicated that the highest P loading occurred in Spring 1999, after a prolonged soil saturation period followed by a rising temperature and intense flooding. The laboratory studies each illustrated mechanisms, which alone can influence P release. The flume study illustrated that a flow path that traverses the surface soil enriched with P (the mixing layer) transported the most SRP and the column study showed that the combination of a long saturation plus a rising temperature exacerbated SRP releases. It appears that a combination of these effects occurred in Spring 1999. |
