Periphyton responses to surfactants: Community structure and mat architecture

Experiments investigating algal periphyton community responses to surfactants were conducted in artificial stream mesocosms housed in Procter and Gamble's Experimental Stream Facility (ESF). Algal periphyton are sensitive to various environmental stressors and when exposed to them, typically respond through the loss of sensitive species, replacing them with tolerant species. Experiments involved investigations of surfactant influence on periphyton community structure. Other influences (e.g. light, oxygen distribution, and substratum heterogeneity) were also considered.; Chapter 1 validated whether the diel, vertical migration rhythm, characteristic of some epipelic algae in natural aquatic ecosystems, also existed in Gyrosigma attenuatum, the algal species dominating sediments in ESF “artificial” streams, and determined whether the rhythm was influenced by surfactant exposure. Results indicated cells did undergo this diel rhythm, which was apparently driven by light and not influenced by surfactant exposure. In Chapter 2, it was hypothesized that Gyrosigma attenuatum would adopt an upright growth form when provided a light stimulus, independent of surfactant exposure. Another hypothesis was that a cell's orientation angle could be predicted by its depth in the sediment. Results indicated that cells exhibited no greater inclination toward the upright orientation when presented a light source than when not. During light conditions, cells oriented more horizontally near the sediment surface where grazers were likely present. Chi-square tests demonstrated a weak correlation between depth and orientation angle. It appears that susceptibility to surface grazers, not surfactant exposure, may regulate the upright orientation at the sediment surface. In Chapter 3, light and oxygen profiles in sediments were obtained with microelectrodes during dark and light periods. Epipelic algal distribution was analyzed via scanning electron microscopy. These techniques were used jointly to assess spatial heterogeneity of light and oxygen and the biological structure of sediment communities.; Substrate heterogeneity had a major influence on periphyton community structure, as reported in Chapter 4. Similarity between communities developing on artificial substrata that varied in surface texture was low. Chemical effects on community structure were negligible, except at highest concentrations. Results showed that surface texture could compensate for loss of some sensitive species due to chemical exposure.