Flow alterations in rivers due to unconventional oil and gas development in the Ohio River basin.

Unconventional oil and gas (UOG) exploration and development in the Ohio River basin has been a controversial issue for the past decade. The process of extracting gas and oil from shale formations utilizes significant amounts of water with little to no recycling in the region. The environmental risks to date have largely focused on air and water quality, with some attention paid to noise pollution. This study examines the risk for excessive water withdrawals and potential for negative impacts of low streamflow, which have largely not been addressed, as basin-wide studies have indicated that UOG will not significantly alter flow at large scales. The smallest watersheds, however, are often not monitored and therefore no historical record of flow is present. Using modelled estimates of historic flow, the impacts of UOG-related water withdrawals in HUC12 watersheds (approximately 1st to 3rd order streams) across the eastern Ohio River basin were estimated. Modelling of the effect of well operations showed that >10 % and >20 % reductions in streamflow occurred at least episodically in 53 % and 42 % of the HUC12 watersheds analyzed, respectively, amounting to 8.8 % and 2.4 % of active days. Although such severe reductions were usually infrequent in a particular stream, they could have lasting negative impacts on the stream biota. These flow reductions have the potential to affect downstream users, including regionally-endangered species. The legal framework surrounding water withdrawal permitting should have a substantial impact on flow reduction, but a lack of sufficient monitoring and clear reporting of water withdrawal sources hinders effective monitoring and protection of stream and riparian habitats.

Modelling dimethylsulfide diffusion in the algal external boundary layer: implications for mutualistic and signalling roles.

Dimethylsulfide (DMS), a dominant organic sulfur species in the surface ocean, may act as a signalling molecule and contribute to mutualistic interactions between bacteria and marine algae. These proposed functions depend on the DMS concentration in the vicinity of microorganisms. Here, we modelled the DMS enrichment at the surface of DMS-releasing marine algal cells as a function of DMS production rate, algal cell radius and turbulence. Our results show that the DMS concentration at the surface of unstressed phytoplankton with low DMS production rates can be enriched by <1 nM, whereas for mechanically stressed algae with high activities of the enzyme DMSP-lyase (a coccolithophore and a dinoflagellate) DMS cell surface enrichments can reach ~10 nM, and could potentially reach µM levels in large cells. These DMS enrichments are much higher than the median DMS concentration in the surface ocean (1.9 nM), and thus may attract and support the growth of bacteria living in the phycosphere. The bacteria in turn may provide photoactive iron chelators (siderophores) that enhance algal iron uptake and provide algal growth factors such as auxins and vitamins. The present study highlights new insights on the extent and impact of microscale DMS enrichments at algal surfaces, thereby contributing to our understanding of the potential chemoattractant and mutualistic roles of DMS in marine microorganisms.