Macroinvertebrate diversity and food web dynamics of seepage spring habitats in the Washington D.C. area

Seepage springs are a commonly found freshwater habitat in the Washington D.C. area that are home to a variety of invertebrates including Stygobromus hayi, the only endangered species in Washington D.C. and the state amphipod, but little remains about the community structure of these habitats. We analyzed the community structure and general food web dynamics of 4 seepage springs, 1 spring, and 2 streams in the Washington D.C. area. We identified 11975 organisms of 50 unique taxa, 35 insect taxa and 15 non-insect taxa, with varying degrees of abundances from 63 samples over three seasons: Winter, Spring, and Summer. Using Jaccard’s index, it was seen that the community structure of the seepage spring environments in Great Falls, MD was similar to each other and similar over the three seasons, with an average coefficient of 0.41. While the sites were similar based on presence or absence they were each dominated by different organisms, most being either Lumbriculidae or Caecidotea kenki. Biodiversity indices of the study sites showed little to no patterns with regard to seasonal shifts or amphipod specificity. Using dual abundance stable isotope analysis of δ^13 C and δ^15 N we were able to discern the trophic positions of Lumbriculidae, C. kenki, Stygobromus tenuis, and Crangonyx shoemakeri, with estimates to the trophic positions of Tipula, Pseudolimnophila, and Platyhelminthes. It is still unclear exactly what S. tenuis was obtaining its energy from.