Print PageThis is the first phase of a study that examines how location within the stream network influences community assembly in the context of stream restoration. Metacommunity ecology examines species dispersal and interactions among communities within a region and provides a series of frameworks understanding the mechanisms driving local community assembly. Stream networks are spatially structured environments and connectivity among communities may limit dispersal leading to weak regional effects in isolated locations, such as small streams. It follows that in the context of stream restoration the strength of community response to local habitat manipulations will depend upon the position of the restoration within the network.
In the summer of 2010, macroinvertebrate communities were sampled at sixteen stream restoration sites and adjacent non-restored reaches in Baltimore County, Maryland. Additionally, we measured environmental conditions including dissolved oxygen, pH, temperature, light, depth and velocity and a rock was removed from each reach to measure algal growth. Half of the sites were first or second order and the other half were third or fourth order. Age of the restorations varied from less than one year to over 10 years, with most approximately 5-7 years old. The restoration techniques varied, but all included some type of in-stream habitat manipulation.
Results/Conclusions
Light levels were consistently higher at restored sites relative to adjacent, reflecting the removal of riparian vegetation due to heavy equipment accessing the stream, bank re-grading, and other manipulations. Other environmental parameters measured showed little change between the restored and adjacent reaches. Initial analysis of the benthic macroinvertebrate samples yielded some differences between the communities at the restored and adjacent reaches. The next step will be further analysis utilizing multivariate techniques to examine the relationship between the environmental conditions and both community composition and functional traits. We predict that grazers would be present in greater abundance in restored reaches relative to the adjacent reaches. Given the constraints imposed by river dendritic network structure, dispersal should play less of a role in shaping communities in smaller streams compared to large. That is, we expect a significant non-random, deterministic signal of assembly at restoration sites in small streams relative to large. Future work will include a field study that will manipulate shade levels and an experimental study manipulating dispersal rates and shade in artificial streams.
