The Relationship Between Land Disturbance and Trace Elements in Streams of North-Central Arkansas

Unconventional oil and gas extraction (UOG) is an important energy source in the US and its importance is expected to increase through 2035.  UOG could deliver trace elements to streams by sediment disturbance during pad formation, spilled or leaked hydraulic fluids and produced water, and increased road traffic.  Elevated trace element concentration in streams has the potential to alter macroinvertebrate communities.  Base-flow trace elements and macroinvertebrates were collected across a gradient of UOG extraction in streams of the Fayetteville Shale in spring 2011 and 2012.  We predicted trace element concentrations in stream water would increase in catchments with more gas activity.  Principle components analysis indicated positive correlations between Al, Cl, Pb, Ni, Na, SO₄, K, and gas well density (r=0.79), paved road density (r=0.61) and % pasture (r=0.60).  Further, we predicted increased concentrations of heavy metals would result in a decline in Ephmeroptera, Plecoptera, and Trichoptera density.  Our prediction was supported by a decrease in Plecoptera (r=-0.77) and Trichoptera density (r=-0.71), and percent Ephemeroptera, Plecoptera, and Trichoptera (r=-0.63) along an increasing gradient of trace element concentrations. We will continue to examine relationships between water column and sediment trace elements and macroinvertebrate community structure.