ELECTRICAL RESISTANCE SENSOR ARRAYS AS A MEANS TO QUANTIFY LONGITUDINAL CONNECTIVITY OF RIVERS

Electrical resistance sensors are used as a novel approach to quantify streamflow continuity (continuous through time) and longitudinal connectivity (continuous through space) across watersheds in south-eastern Arizona, USA. We demonstrate this approach by reporting on a spatial array of 21 sensors installed in streams supporting naturally perennial, intermittent and ephemeral flow on the US Army Garrison, Fort Huachuca. Continuity and connectivity were quantified based on a strict interpretation of continuous flow at an individual sensor (strict continuity) or simultaneous streamflow at multiple sensors (strict connectivity). In addition, we evaluated continuity and connectivity to include periods (<48?h) when in-channel refuges may exist between streamflow events (refuge-maintained continuity and connectivity). Continuous streamflow in intermittent reaches accounted for 34% of the 121-day monitoring period (15 April13 August 2010) and 28% of the summer monsoon period (1 July13 August 2010). Streamflow in ephemeral reaches accounted for 1.5% and 2.3% of the entire monitoring and monsoon period, respectively. Canyon-wide longitudinal connectivity was rare (<1%); however, substantial longitudinal connection occurred along extensive portions of individual canyons. The refuge-maintained criteria increased continuity 28%, with less influence on connectivity (e.g. <3% increase in only some portions of canyons). Despite this result, the refuge-maintained concept remains important because of its broad applicability to refuge persistence across aquatic species and hydro-climatic regimes. The approach presented in this study supports the growing scientific research on the influence of longitudinal hydrologic connectivity on population dynamics and ecological processes in dendritic river networks. Copyright (c) 2011 John Wiley & Sons, Ltd.