Assessment of Passive and Active Macroinvertebrate Collection Methods in Adjacent Reaches on the Upper Main Stem of the Susquehanna River

Macroinvertebrates are functional indicators of stream health based upon their sensitivity to pollution. Our study utilized different passive and active benthic macroinvertebrate collection methods (D-net, Surber sampler, rock baskets, and Hester-Dendy multiplate samplers) during the summer and fall of 2012 and 2013. Collections were taken on both sides of the west channel in the west channel of the upper main stem of the Susquehanna River near Shamokin Dam, PA. Sampling sites each included seven locations, one for passive sampling and six longitudinal locations for active sampling. Overall, we collected 50 taxa of macroinvertebrates identified to family-level, which allowed us to calculate pollution tolerance values and other comparative metrics. The Proportional Bray-Curtis Similarity Index analysis describes a very low to moderate overlap between benthic macroinvertebrate communities collected by active and passive methods (2% - 43%). Furthermore, other metrics including the Shannon Diversity and Hilsenhoff Biotic Indices reflected the variability in occurrence of pollution intolerant taxa according to method and location. The greatest variation occurred in percent EPT which showed a range of 0% to 56% in a single sample period using different methods. Passive sampling methods selectively collected colonizers and omitted other taxa (e.g. burrowers and mollusks) illustrating their bias in sampling. Overall, the metrics did not support the use of one technique over another. Rather, they supported the practice of using both passive and active collection methods in order to use macroinvertebrate community estimates to assess water quality in large rivers that have a wetted channel of cobble, silt, and sand like the upper main stem of the Susquehanna River. Based on our results we concluded that active samplers which target different habitats together with passive samplers which allow comparisons from one site to another would be the most appropriate methods to use in the upper main stem of the Susquehanna River.