Miranda, L.E., Raines, C.D. 2019. Reservoir diel water quality patterns relative to riparian shade. Lake and Reservoir Management 35:148–155. https://www.tandfonline.com/doi/abs/10.1080/10402381.2019.1570573
Investigations into the effects of riparian shade on water quality have focused on streams, with less emphasis on natural lakes, and almost no attention given to reservoirs. In view of this deficit, our objective was to assess diel water quality patterns in the nearshore zone of a reservoir and test whether diel patterns differed relative to the presence or absence of riparian shade. Light intensity, temperature, dissolved oxygen, turbidity, oxidation-reduction potential, and specific conductance were greater in unshaded sites (p < 0.05), whereas concentrations of phosphate and nitrate were greater in shaded sites, and pH values were similar in shaded and unshaded sites. Most variables exhibited distinct diel cycles, except specific conductance, turbidity, phosphate, and nitrate. Other than light intensity (average 66% lower in shade), differences in water quality patterns between shaded and unshaded sites seemed small (average <5%) and within the range of tolerances of aquatic biotic communities. In most lacustrine systems the nearshore shaded band is small relative to the unshaded open water, and the large open-water volume tends to neutralize effects of shading on water physicochemistry. As a result, riparian shade may not have a large influence on water temperature and chemistry of lacustrine systems, and its biggest effect may be a reduction in light intensity in the nearshore band. The observed decrease in light intensity in shaded sites has the potential to influence biotic assemblages through competitive mechanisms associated with finding food, avoiding predation, and other aspects associated with rather than through physiologic effects via water quality.