Survival of salmonid eggs in a degraded gravel bed stream: the role of groundwater – surface water interactions

The effect of hyporheic water quality on developing salmonids was assessed between spawning and hatch. Results from a low-lying degraded agricultural catchment (Newmills Burn) were compared with those from a near-pristine upland spawning stream (Gimock Burn), providing a set of comparisons beyond the range of hyporheic conditions present in the Newmills Burn. It was demonstrated that hyporheic water quality in the Newmills Burn varied temporally and spatially as a consequence of variable fluxes of chemically reduced groundwater through heterogeneous drift deposits. Mortality rates from samplers located within artificial redds ranged from 0 to 100% and showed a clear negative relationship with mean dissolved oxygen (DO) concentrations (r(2) = 0.85, P < 0.01). Where embryo mortality was less than 100%, low DO appeared to affect rates of embryo development. Embryos exposed to lower DO concentrations were observed to have a higher percentage mass of yolk sac than those developing in more favourable conditions. The chemical characteristics of hyporheic water in the stream were indicative of the mixing of longer residence regional groundwater with local surface water at shallow depths. The hyporheic water of the Gimock Burn approximated closely to that of surface water suggesting a local origin. Hyporheic water quality affects egg survival and may limit recruitment when egg deposition is marginal or inadequate. A consideration of hyporheic dynamics and groundwater-stream interactions should form part of channel modification or restoration works in salmonid spawning streams. Copyright (C) 2003 John Wiley & Sons, Ltd.