Impact of natural gas wells on periphyton and metabolism in streams in north central Arkansas

Background/Question/Methods

Recovery of natural gas has increased significantly in recent years.  Construction of natural gas wells (NGWs) increases the potential for sediment erosion into streams, which could negatively influence periphyton communities.  The goal of this study was to determine if increasing NGWs within catchments negatively impact stream periphyton biomass and metabolism.  Ten streams with varying catchment densities of NGWs (0-3.2 wells/km²) were sampled during winter and spring of 2010 and 2011 to examine the effects of NGW’s on periphyton and metabolism.  Two cobbles from three riffles and three pools were collected within each stream to quantify periphyton biomass in the form of chlorophyll a (chl a) and ash-free dry mass (AFDM).  Whole stream metabolism was estimated from diel curves of dissolved oxygen at a single station, within each stream over a three day period.  In addition, dissolved nutrients, turbidity, and light transmittance were measured across sites and land use variables were quantified for each catchment using ArcMap.  We used multiple linear regressions to examine effects of NGWs, well density, land use, and water quality on periphyton and metabolism response variables.

Results/Conclusions

Chlorophyll a was positively related to the number of wells in a catchment during both winter sampling events (2010 r²=0.83, p<0.01; 2011 r²=0.39, p=0.05).  Gross primary production (GPP) was also positively related to well density during winter 2011 (r²=0.78, p=0.02), and was best explained by well density and turbidity in spring 2010 (overall model r²=0.72, p=0.02).  Nutrients and light transmittance were not positively related to chlorophyll a or GPP.  Therefore, NGW effects on additional environmental factors, such as on densities or biomass of grazing macroinvertebrates, might explain the positive effect of NGWs on stream periphyton and GPP.  Our findings suggest that increases in primary production may result from NGW development in catchments.  Periphyton and primary production metrics may be useful indicators of NGW impacts on streams.