In-stream and hyporheic water quality of the River Esk, North Yorkshire: implications for Freshwater Pearl Mussel habitats

River systems and their catchments are important for ecological, social and economic reasons. However, the increased and changing usage of these natural environments and resources for anthropogenic benefit have led to degradation in water quality, which has led to severe declines in aquatic species populations and their suitable habitats, as well as presenting health concerns with regards to drinking water standards. As a result of this, the Water Framework Directive (2000/60/EC) has been introduced, which is an EU legislation that requires “good ecological status” of freshwaters by 2015, providing a driver for management and conservation for UK river systems. One example of declines in species populations are freshwater pearl mussels (Margaritifera margaritifera), which are under extreme threat of extinction. Combining species revival with water quality improvements provides a method for testing effectiveness of implemented measures. This study analyses water quality, hydrological characteristics and hyporheic zone chemistry of the River Esk, North Yorkshire, through a variety of spatial and temporal scales. Changing water quality through storm events showed that general water quality of the Esk is of little concern, however, higher flows bring acidification to the upper part of the network, which presents a serious threat to freshwater pearl mussel survival. The hyporheic zone displayed interesting results in that chemical concentrations were far higher, whilst dissolved oxygen levels and redox potential were lower. Nitrate values were also lower, suggesting that reducing conditions were supporting oxygen demanding chemical reactions such as denitrification, creating undesirable habitats for aquatic invertebrates. This study concludes that there is a lack of vertical connectivity between the channel and zones of interaction.