Abiotic effects of UV on planktonic P kinetics

Abstract.

We examined the effect of ultraviolet radiation (UVR) on phosphorus availability in the surface waters of three thermally stratified Canadian shield lakes: Muskoka, Brandy, and Plastic. Study lakes were selected to encompass a range of chemical parameters (DOC, TP, pH, Fe, and NO⁻₃) that have been shown to influence aquatic photochemistry. Differences in spectral absorbance of DOM (280 – 700 nm) occurred after UVR treatment in all lakes. UVR exposed lake filtrate from Lake Muskoka had an increase in spectral absorbance throughout the UV spectrum (280 – 399 nm), but a decrease throughout the PAR spectrum (400 – 700 nm). UVR exposed lake filtrate from Brandy and Plastic Lakes had decreased spectral absorbance at all wavelengths (280 – 700 nm). Photochemical changes of UVR exposed lake filtrate (<0.2 μm) resulted in a more rapid turnover of the PO ^3–₄ pool when reintroduced to whole lake water (Muskoka). Lake filtrate from Brandy and Plastic Lake did not respond to treatment.