Johnson Wilson H, Douglas Marlis R, Lewis Jeffrey A, Stuecker Tara N, Carbonero Franck G, Austin Bradley J, Evans-White Michelle A, Entrekin Sally A, Douglas Michael E
Department of Biological Sciences, University of Arkansas, Fayetteville, AR, USA.
Department of Food Sciences, University of Arkansas, Fayetteville, AR, USA.
BMC Microbiol. 2017 Feb 3;17(1):29. doi: 10.1186/s12866-017-0926-5.
Unconventional natural gas (UNG) extraction (fracking) is ongoing in 29 North American shale basins (20 states), with ~6000 wells found within the Fayetteville shale (north-central Arkansas). If the chemical signature of fracking is detectable in streams, it can be employed to bookmark potential impacts. We evaluated benthic biofilm community composition as a proxy for stream chemistry so as to segregate anthropogenic signatures in eight Arkansas River catchments. In doing so, we tested the hypothesis that fracking characteristics in study streams are statistically distinguishable from those produced by agriculture or urbanization.
Four tributary catchments had UNG-wells significantly more dense and near to our sampling sites and were grouped as 'potentially-impacted catchment zones' (PICZ). Four others were characterized by significantly larger forested area with greater slope and elevation but reduced pasture, and were classified as 'minimally-impacted' (MICZ). Overall, 46 bacterial phyla/141 classes were identified, with 24 phyla (52%) and 54 classes (38%) across all samples. PICZ-sites were ecologically more variable than MICZ-sites, with significantly greater nutrient levels (total nitrogen, total phosphorous), and elevated Cyanobacteria as bioindicators that tracked these conditions. PICZ-sites also exhibited elevated conductance (a correlate of increased ion concentration) and depressed salt-intolerant Spartobacteria, suggesting the presence of brine as a fracking effect. Biofilm communities at PICZ-sites were significantly less variable than those at MICZ-sites.
Study streams differed by Group according to morphology, land use, and water chemistry but not in biofilm community structure. Those at PICZ-sites covaried according to anthropogenic impact, and were qualitatively similar to communities found at sites disturbed by fracking. The hypothesis that fracking signatures in study streams are distinguishable from those produced by other anthropogenic effects was statistically rejected. Instead, alterations in biofilm community composition, as induced by fracking, may be less specific than initially predicted, and thus more easily confounded by agriculture and urbanization effects (among others). Study streams must be carefully categorized with regard to the magnitude and extent of anthropogenic impacts. They must also be segregated with statistical confidence (as herein) before fracking impacts are monitored.
北美29个页岩盆地（分布于20个州）正在进行非常规天然气（UNG）开采（水力压裂法），在费耶特维尔页岩（阿肯色州中北部）内发现了约6000口井。如果能在溪流中检测到水力压裂的化学特征，就可以用来标记潜在影响。我们评估了底栖生物膜群落组成，以此作为溪流化学特征的替代指标，以便区分阿肯色河八个集水区中的人为特征。在此过程中，我们检验了以下假设：研究溪流中的水力压裂特征在统计学上与农业或城市化产生的特征有明显区别。
四个支流集水区的非常规天然气井密度显著更高且离我们的采样点更近，被归为“潜在影响集水区”（PICZ）。另外四个集水区的特点是森林面积显著更大，坡度和海拔更高，但牧场面积较小，被归类为“轻度影响集水区”（MICZ）。总体而言，共鉴定出46个细菌门/141个纲，所有样本中有24个门（52%）和54个纲（38%）。PICZ区域的生态比MICZ区域更具变化性，营养水平（总氮、总磷）显著更高，作为生物指示物的蓝细菌数量增加，以追踪这些情况。PICZ区域还表现出电导率升高（与离子浓度增加相关）以及耐盐性差的斯巴达细菌数量减少，表明存在作为水力压裂效应的盐水。PICZ区域的生物膜群落比MICZ区域的生物膜群落变化明显更小。
研究溪流根据形态、土地利用和水化学特征在组间存在差异，但在生物膜群落结构上没有差异。PICZ区域的溪流根据人为影响而共同变化，并且在质量上与受水力压裂干扰的区域发现的群落相似。研究溪流中的水力压裂特征与其他人为影响产生的特征有明显区别这一假设在统计学上被否定。相反，水力压裂引起的生物膜群落组成变化可能不如最初预测的那么具体，因此更容易与农业和城市化影响（以及其他影响）混淆。必须根据人为影响的程度和范围对研究溪流进行仔细分类。在监测水力压裂影响之前，还必须以统计学置信度（如本文所述）将它们区分开来。
