Appraising riparian management effects on benthic macroinvertebrates in the Wye River system

Abstract

Agriculture, urbanization or forestry in river catchments can influence river organisms through diffuse effects on hydrology and hydrochemistry, or local effects on habitat character, bank erosion and sediment delivery. Riparian buffer zones are sometimes established to mitigate undesirable effects on salmonids, but consequences for organisms such as macroinvertebrates are less well known. Riparian fencing and tree coppicing were carried out on upland tributaries of the Welsh River Wye (UK) from 1997 onwards with the aim of enhancing conditions for salmonid fish. The present study used routine, agency monitoring data to compare assemblages in three recently managed streams and five adjacent control streams. Data between 1995 and 2004 were used to assess treatment effects through time. Post-treatment (2000-2004) assemblages were richer in recently managed streams than in controls, mostly due to apparent gains of taxa typical of channel margins and lowland, warmer conditions. However, results were equivocal because invertebrate families typical of lowland, more eutrophic conditions increased in occurrence in all reaches irrespective of treatment, while overall richness declined. This study illustrates how routine monitoring data can reveal some effects of riparian land-use and management on stream biota. However, improved experimental design, ideally using a before-after control-intervention approach, would have allowed more effective assessment in this case study where confounding trends were so marked. We advocate using such approaches in future restoration studies to allow stronger inference and greater statistical power. The recent general decline in the richness of typical headwater organisms in the Wye system requires investigation. Copyright © 2010 John Wiley & Sons, Ltd.