Print PageStreams and the biota that inhabit them are threatened by anthropogenic landuse via changes in hydrological dynamics, water chemistry, temperature, and substrate composition. To address stream degradation, stream conservation and restoration strategies focus on preserving extant riparian forest and reestablishing lost riparian habitat. However, these conservation efforts are often patchy, and the long maturation time for restored buffers has made the effectiveness of restoration efforts difficult to quantify. To better understand the relative effects of whole watershed land use and patchy riparian buffers on stream habitat, we assessed communities of benthic macroinvertebrates sampled from12 streams. Watersheds for these streams were dominated by cultivation, urban/suburban development, grassland (pasture, lawn, golf courses), or forest. For each stream, we assessed reaches characterized by presence or absence of riparian forest. To quantify stream biological condition, we used the percent of individuals from intolerant insect Orders Ephemeroptera (minus Baetidae), Plecoptera, and Trichoptera (%EPT). Physicochemical characteristics were measured to assess potential mechanistic links between changes in landscape and biota.
Results/Conclusions
Invertebrate communities revealed distinct patterns between watershed types. Intolerant invertebrates were more abundant in watersheds that most resembled historical, less-altered habitat. Forested watersheds averaged the highest %EPT (23.8) followed by grassland (16.1), cultivated (1.96), and developed (0.31). Percent EPT was significantly higher in cultivated watersheds than in developed. Despite having wide forest buffers, forested reaches were similar to non-forested reaches in %EPT, except in grassland watersheds, where %EPT was 24.8% higher in reaches that were forested. Differences in riparian buffer type had no effect in developed or cultivated watersheds, which is where riparian restoration is often directed. Not surprisingly, high values of %EPT were associated with cobbly substrate, high dissolved oxygen, low nutrients, and low conductivity. However, generally good abiotic conditions were not associated with high %EPT in developed watersheds, potentially suggesting other sources of degradation. Neither nutrient concentrations nor sediment toxicity improved the relationship. Nutrient concentrations were significantly higher in cultivated watersheds for all nutrients measured. There were no discernable patterns in sediment toxicity. These results confirm that intensive land use can significantly degrade biological communities in streams, and that limited forested riparian corridors alone may be insufficient to mitigate this degradation.
