Evaluations of nutrient diffusing substrates and the primary importance of light in controlling periphyton

Abstract

Eutrophication is an increasingly recognized threat to the health of streams and rivers in the United States. This thesis presents two studies aimed at increasing the utility of periphyton analysis as a tool for water resource managers to address eutrophication. In the first study, artificial channels were used to investigate the response of periphyton to different nutrient delivery mechanisms. In two channels, nutrients were delivered via diffusion to periphyton growth surfaces using modified Matlock Periphytometers. In two additional channels, nutrients were delivered by dosing water in the channel. The data showed that nutrient delivery via diffusion elicits a significantly greater periphyton response. The use of diffusing substrates for periphyton studies remains a viable tool for some objectives, but results should be extrapolated to natural conditions with caution. In the second study, modified Matlock Periphytometers and inexpensive light meters were used to investigate the relationship between periphyton growth and light availability in two fourth-order Texas streams. The data indicate that light availability explains 91.9 percent of the variability of observed periphyton growth under control conditions, and 99.7 percent under nutrient-enriched conditions. The strong correlation suggests that efforts to address eutrophication should recognize the importance of riparian shade. Equations to predict chlorophyll-a as a function of relative light intensity are also presented.