Freshwater macroinvertebrates of the Mid-Atlantic region

Freshwater macroinvertebrates are an extremely diverse and adaptive group of organisms that have successfully invaded virtually every type of aquatic habitat. This chapter provides a habitat-based description of Mid-Atlantic region (MAR) macroinvertebrates, beginning with a review of adaptations to differing aquatic environments, followed by a synopsis of Riparia's research regarding macroinvertebrate bioassessments in various hydrogeomorphic (HGM) wetland types. Early research revealed that the HGM classification was insufficient in controlling natural variation, making it difficult to assess community responses to anthropogenic disturbance. This prompted an effort to develop a more ecologically relevant habitat classification for MAR wetland macroinvertebrates. The remainder of the chapter presents a case study of this habitat approach applied to headwater and floodplain complexes. First, we defined the riverine hierarchy by building on existing classification schemes and adding a level, the aquatic ecological set, to differentiate between habitats structured by flow, flood, and groundwater pulses. Next, we compiled the macroinvertebrate data collected from all aquatic habitats within reference-standard floodplain reaches and did an exploratory analysis, which revealed six major habitat types: riffle, other baseflow, and flow pulse habitats in the active zone, flood pulse habitats in the floodplain, seasonal groundwater, and temporary habitats. Further comparison with impacted riverine complexes indicated these systems respond to anthropogenic disturbance primarily through changes in hydrological connectivity and hydroperiod. The end result is loss of flow pulse habitats, floodplain terrestrialization, and loss of heterogeneity in wetland habitats, the latter primarily through a shift from seasonal to either permanent or ephemeral hydroperiods.