Ecological assessment of human disturbance to stream ecosystems using algae

Algal attributes responded to land use and environmental variables related to low-level human disturbance in streams of glaciated northern Michigan, USA. Diatom species composition and dominant species changed with a human disturbance gradient (HDG), which was defined by covariation among nutrient concentrations and land uses. The percentage of native diatom species was negatively correlated with the HDG. Simpson dominance index and diversity indices were not correlated with the HDG. Average diatom biovolume was positively correlated with the HDG. Relative abundance of species sensitive to trophic status decreased and % trophic tolerant species increased with the HDG, Cl −, and conductivity, but did not correlate with nutrient concentrations. Thus changes in diatom assemblages due to nutrient enrichment could be detected, but not related to the narrow range in nutrient concentrations.; Of the three major benthic algal habitats in streams, diatoms on plants were the most sensitive assemblages to the human disturbance. Epiphytes also had the smallest beta diversity and fastest species turnover along an HDG, while epipelon and epilithon had about the same beta diversity and species turnover rate. Epiphytes had the most variance in species composition and species-environment relations explained by CCA. Epiphyton was more sensitive than epilithon and epipelon based on changes in trophic status indicators along the HDG. Species composition of epipelon was distinctly different from the epilithon and epiphyton. Heterogeneity in species composition among habitats did not decrease along the HDG.; A regional pattern in nutrient limitation of periphyton was not observed with experiments in 16 streams despite very low P concentrations. However, species composition did respond to experimental nutrient enrichment. Further examination showed that nutrient enrichments did not change species composition in experiments in the same way that composition varied among streams with different nutrient concentrations. Diatom assemblages from treatment and control clay pots at the same site were more similar than assemblages from the same treatments between sites. Therefore, extrapolation of experimental results from small-scale experiments to large regional scales may be constrained by the local species pools.; A diatom-based Index of Biotic Integrity (IBI) for the Interior Plateau Ecoregion (IPE) of the US was developed using data collected by the Kentucky Division of Water. Diatom attributes at reference and impacted sites were selected for the IBI based on significant differences between site groups, high separation power, and low CV. Seven metrics were selected from a list of 59 attributes to form a diatom IBI, which successfully distinguished reference and impaired sites in both development and test datasets. The IBI scores were significantly related to measures of human disturbance in watersheds. This IBI had more separation power than the other diatom IBIs.