Examining effects of natural gas development on fishes of the Fayetteville Shale.

摘要

Due to advances in hydraulic fracturing and horizontal drilling making shale formations more easily accessible, natural gas development (NGD) has drastically increased in the past decade and is projected to continue rising through at least 2040. Cumulative effects of infrastructure associated with NGD (e.g. well pads, pipelines, and unpaved roads) have received relatively little attention, especially in relation to aquatic ecosystems. We looked at relationships of fish communities and populations of Etheostoma whipplei in relation to NGD at a total of 14 sites, chosen along a gradient of gas well densities, throughout the Fayetteville Shale in north-central Arkansas in Spring 2012. While community composition indices can reflect changes in catchment level land use and help link the chain of connections from exposure of ecosystems to environmental perturbation, shifts at the community level are reflections of population responses, and changes in species level variables can be detected quicker than changes at the community level. We chose 11 community metrics to compare responsiveness to NGD, of which six were significantly correlated. Species richness and percent herbivorous were positively correlated to NGD, whereas percent sensitive individuals, simple lithophilic, darters and benthic invertivores were negatively correlated to NGD. Nonparametric partial correlations were used to hold pasture constant while looking at effects of NGD. While all significant correlations were related to NGD, all community metrics besides percent top carnivores were more strongly correlated to NGD than percent pasture. Nonparametric partial correlations are robust analyses for partitioning effects of landscape disturbances which can have similar perturbations, such as expected siltation associated with NGD and pastureland used for grazing. To determine if declines noted across three consecutive years in proportional abundance of Year Class One E. whipplei in relation to increasing natural gas well density were related to reproductive investment or post-spawn mortality, we examined seven life history characteristics. Male gonadosomatic index (GSI) increased with increased NGD, whereas female GSI did not. In March, mean clutch size was significantly higher in our Control group (sites with no NGD) compared to Low and High groups (sites with various degrees of NGD within catchment). Female skewed sex ratios occurred only in the Control group, whereas there was not a significant departure from 1:1 sex ratio in either Low or High groups. While reproductive investment does not appear to decline with increased NGD, phenotypic plasticity does not appear to be compensating for negative population effects, suggesting declines in recruitment is likely related to post-spawn mortality. Due to overlap in distribution of E. whipplei with the Arkoma Shale basin, current lack of phenotypic plasticity could pose a serious threat to this species if recruitment continues to decline with persistence of NGD within its distribution. These data explore measures of demographics in relation to a landscape disturbance, as well as identify metrics and analyses sensitive to cumulative effects of NGD in the Fayetteville Shale.