Stream macroinvertebrate indicators response to land use and marcellus shale gas development in the Susquehanna Basin of northeastern Pennsylvania
Unconventional shale gas development may impact surface water quality due to potential effects of construction and contamination by hydrofracking and flowback fluids. To that end, in 2012 we examined water quality and macroinvertebrate indicators as a function of drilling and pipeline construction in 12-15 streams (sub-watersheds) throughout northeastern Pennsylvania – largely within the eastern extent of the Marcellus Shale development region. Most were in the North Branch drainage of the Susquehanna River (PA) in which development is allowed, though two reference watersheds were in the Delaware Basin that has a moratorium on development. Our study sites for this synoptic survey included second and third order streams with drainage areas ranging from 2.2 to 38.0 square miles, representing watersheds with no, low, medium, and high natural gas activities. Using GIS and land use classifications derived from National Land Cover Data (2006), we quantified number of wells, pipeline length, land use/land cover, area, and stream classifications, on a watershed basis for each sub-watershed and stream buffer zone (100m) in the study area.
Bivariate and multivariate regression analyses indicated that macroinvertebrate indicators showed marked seasonal variation in response to land use and shale gas development. In the spring, indicators such as EPT, Beck’s Index, and a synthetic Index for Biological Integrity (IBI) were significantly correlated with density of drilled, fracked, and producing wellpads per sub-watershed, number of violations, and pipeline density. The density of incidents emerged as a top variable for EPT Richness, Beck’s Index, and IBI, based on multivariate analysis. In contrast, macroinvertebrate indicators were not significantly correlated with land use / land cover parameters such as % agriculture, % urbanized, or % forest cover in the spring. In the summer and fall, macroinvertebrate indicators were poorly correlated with gas development parameters, except pipeline length in the stream buffer was significantly correlated with IBI in the fall. Instead, agricultural land use, and developed lands explained more variability in these indicators during summer and fall. Thus, evidence of shale gas development on stream health was found in spring, but that evidence was weaker or nonexistent in summer and fall. Additional research is needed to determine whether observed patterns occur in other years, or whether stream health would benefit from improved industry practice.