No abstract

Microdistributional patterns of attached algal communities on Cladophora and glass slides were compared under varying disturbance regimes in the Upper Mississippi River, using light and scanning electron microscopy. Localized physical disturbance, induced by boat traffic and wind‐generated wave action in the main channel, inhibited development of complex attached algal communities and maintained an adnate flora with two‐dimensional architecture. In contrast, communities protected from disturbance developed a more complex, three‐dimensional architecture. A high degree of architectural similarity was observed between communities on Cladophora and glass substrates exposed to similar levels of disturbance. Communities exposed to severe disturbance resembled ones in early stages of colonization and development, whereas less disturbed communities were similar to ones in advanced stages of development. These results demonstrated that turbulence strongly influences the community structure of periphyton on both micro and macro scale levels.

The ecological health and integrity of watersheds throughout the world are being threatened by a variety of stressors. Often, restoration practices focus on single problems whereas comprehensive, multidisciplinary approaches are needed to address both the symptoms and underlying causes of impairment. A comprehensive assessment of a small, urbanized watershed in west Michigan, USA was conducted to evaluate the major stressors in the system. This assessment approach for the Mona Lake watershed included analyses of land use/land cover change, water quality in both the major surface inflows and the receiving water body, and toxic inputs into a major inflow. Because these issues are common to many watersheds, we developed a conceptual model that spatially links these stressors and predicted impacts, allowing us to assess them in a comprehensive manner. Based on our results, we generated a set of recommendations targeted for specific source or problem areas. This approach can be applied to other watersheds.

We examined the effect of nitrogen:phosphorus (N:P) ratios and nutrient concentrations on periphyton when nutrients (N and P) are provided in excess. A gradient of seven N:P ratios ranging from 7.5:1 to 1:7.5 and each at three absolute concentrations, was established using nutrient-releasing substrata placed in a meso-oligotrophic lake. Differences in total algal biovolume among nutrient ratios were significant (analysis of covariance [ANCOVA]) when P concentration was entered as the co-variate. In addition, total algal biovolume was significantly correlated with N concentration but not P. To further evaluate the relationship between nutrient ratios and biovolume, we analyzed (using four 1-way analysis of variances [ANOVAs]) four subsets of data defined as a series of treatments where one nutrient concentration remained relatively constant as the other changed creating different N:P ratios. Ratios of data subsets ranged from 1:1 to 7.5:1 and 1:1 to 1:7.5 with low and high concentrations of both series. Only diatom biovolume varied with ratio but these differences are most likely related to increased green algal abundance. Species richness and diversity differed among N:P ratios (ANCOVA) when P concentration was used as the co-variate. Stigeoclonium tenue (Ag.) Gomont, which generally accounted for the increase in green algal abundance, varied with nutrient ratio (ANCOVA) when P was the co-variate. Based on the ANCOVAs, correlations, and one-way ANOVAs, periphyton in this system appears to be affected by N concentration but not by N:P treatment ratios under nutrient-rich conditions. When compared with previous studies, these data also suggest that the response of periphyton to in situ treatments constructed with nutrient-releasing substrata vary between years.