Effects of natural gas recovery on Arkansas streams

Background/Question/Methods

Advances in natural gas drilling and extraction have resulted in rapid expansion of wells in shale basins.  The rate of gas well installation in the Fayetteville shale is 774 wells/ year since 2005 with thousands more planned. The Fayetteville shale covers 23,000 km² although gas well development is concentrated within 8,000 km². Rapid and concentrated activity and wells placed close to streams increases potential for negative effects on surface waters. We quantified turbidity and suspended sediment from April 2009-December 2011 during eight storms in 10 stream catchments with a gradient of gas well densities. We also collected aquatic invertebrates from the same 10 streams in spring 2010 and 2011. We predicted catchments with faster well installation rates and greater well densities to have higher turbidity and suspended sediments and lower invertebrate diversity and density.  

Results/Conclusions

Turbidity was positively related to gas well density during four and negatively related to gas well density during one storm (p<0.05). Turbidity from three storms was related to road density, drainage area, or woody/herbaceous land.  Inorganic sediment concentration was also positively related to well density during three storms, while in other storms it was positively related to woody/herbaceous land or road density. Aquatic invertebrate diversity was not related to gas well activity in 2010, but diversity declined with increasing well density in 2011 (p=0.04, R²=0.43). Aquatic invertebrate density increased with increased gas activity in both years (p<0.01, R²=0.72; p=0.04, R²=0.42), while density of longer-lived taxa declined with increased sediment transport in 2011 (p=0.03, R²=0.47). Expanding gas activity in small stream catchments was related to episodic increases in suspended sediments that can promote more small bodied invertebrate taxa and reduce longer lived taxa. Our data suggest that proximity of well development to small streams and consistent and enforced implementation of regional best management practices should be considered to reduce sedimentation into surface waters during gas well recovery.