Reservoir diel water quality patterns relative to riparian shade

Abstract

Miranda LE, Raines CD. 2019. Reservoir diel water quality patterns relative to riparian shade. Lake Reserv Manage. 35:148–155.

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 gap, 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, pH, and oxidation–reduction potential were higher in unshaded sites (P < 0.05), whereas phosphate levels were higher in shaded sites. Levels of nitrate, turbidity, and specific conductance were similar in shaded and unshaded sites. Most variables exhibited distinct diel cycles. Light intensity in shaded and unshaded sites peaked simultaneously near mid-day; most other variables peaked several hours later in the afternoon and evening, but 1–2 h earlier in shaded sites. Unlike in streams, in most large lacustrine ecosystems the nearshore shaded band is small relative to the unshaded open water, and consequently is not expected to have an extensive influence on whole-lake water quality. Nevertheless, because of the diversity of microhabitats available in nearshore areas, including those created by the effects of shade on water quality, the nearshore zone plays a disproportionate role in maintaining integrity of a lake or reservoir ecosystem. Existing guidelines inform shade management in lakes and reservoirs only indirectly and in generalities; additional research is needed to develop best management practices that address shade more comprehensively.

Keywords:

• Diel
• lacustrine
• light intensity
• reservoirs
• riparian
• shade
• water quality

Acknowledgments

We thank J. Boxrucker of the Reservoir Fish Habitat Partnership for assistance. A. Omer and H. Schramm provided helpful reviews. The Mississippi Cooperative Fish and Wildlife Research Unit is a cooperative effort of the Mississippi Department of Wildlife, Fisheries and Parks; Mississippi State University; and U.S. Geological Survey. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. government.

Additional information

Funding

Funding was provided by the U.S. Fish and Wildlife Service through the Reservoir Fish Habitat Partnership.