Citation Boon P, Willby N, Gilvear D & Pryce D (2016) The regional hyporheic fauna of gravel-bed rivers and environmental controls on its distribution. Fundamental and Applied Limnology, 187 (3), pp. 223-239. https://doi.org/10.1127/fal/2016/0705
Abstract The hyporheic zone (HZ) of rivers is important for functional processes and a critical habitat for a specialist biota (the hyporheos). Knowledge of the hyporheos and its variability within and between rivers, however, remains limited at all scales. This paper describes an extensive survey of the invertebrate fauna and the physico-chemical characteristics of the HZ, through sampling 25 geographically dispersed Scottish rivers. Invertebrates were collected using two techniques for comparison of depth of sampling and effectiveness of invertebrate retrieval: Bou–Rouch pumping using standpipes inserted to 0.5 m depth and Karaman–Chappuis pit sampling. The faunal assemblage was dominated by Oligochaeta, cyclopoid Copepoda, Nematoda and Diptera, which accounted for almost 80% of individuals. The fauna of pits and standpipes was influenced by different but related variables; distance to source and source altitude were strong predictors of pit faunal composition, compared with site altitude and longitude in standpipes. These factors suggest a general biogeographical component to the composition of the hyporheos. Pit assemblages were also influenced by conductivity, and standpipes by total alkalinity, implying a secondary influence of water chemistry or productivity. Explained variation in faunal composition in standpipes was significantly greater than for pits suggesting a higher degree of environmental determinism and associated specialization within the deeper hyporheos. Faunal richness was positively correlated with dissolved oxygen saturation in pit and pipe samples highlighting potential sensitivity to temperature-related effects, siltation and eutrophication. Inclusion of hyporheic sampling in biological assessments might result in greater nature conservation significance being attributed to the hyporheos, thus supporting a call for greater recognition of the HZ and its associated services in environmental protection.