Causes and consequences of variation in UV transparency for freshwater ecosystems

This dissertation consists of four independent yet interrelated research chapters, each of which addresses a topic under the umbrella of understanding the patterns, causes, and consequences of changes in ultraviolet (UV) transparency in freshwater ecosystems.;Chapter 1: Differences in UV transparency and thermal structure between alpine and subalpine lakes: implications for organisms. This chapter addresses the important role of water temperature and UV transparency in structuring alpine lake ecosystems and the consequences of these forces for aquatic organisms that inhabit them. This chapter includes data I collected on a suite of alpine and subalpine lakes throughout graduate school as well as longer term data on these lakes. This chapter was published in Photochemistry and Photobiological Sciences in 2009 (Rose et al. 2009).;Chapter 2: Patterns of spatial and temporal variability of UV transparency in Lake Tahoe, California-Nevada. This chapter examines how UV transparency varies relative to longer wavelength photosynthetically active radiation (PAR, 400--700nm) along inshore-offshore transects in the lake and vertically within the water column as well as temporally throughout 2007. This chapter was published in Journal Geophysical Research, Biogeosciences in 2009 (Rose et al. 2009b).;Chapter 3: Allochthony Indicators in Freshwaters: Separating the Signals. This chapter compares the utility of several traditional and novel indicators of allochthony including DOC:Chl a, a440:Chl a, stable hydrogen isotopes of seston, measurements of the fluorescence index, the spectral slope region S350--400nm and the ratio of diffuse attenuation coefficients (Kds) at 320:380nm UV. We found significant relationships between most indicators and evidence to support S350--400nm and 320:380nm UV K d ratios as indicators across a broad gradient of lakes. This chapter is currently in preparation for submission to Limnology and Oceanography .;Chapter 4: The Role of UV and Fish in Regulating the Vertical Distribution of Daphnia. This chapter tests the relative importance UV and planktivorous fish in regulating the vertical distribution of Daphnia in the water column of Lake Giles, Pennsylvania using a large scale mesocosm experiment. We found clear evidence of UV effects, but much more limited evidence of fish effects. This chapter is currently in preparation for submission to Limnology and Oceanography.