INFLUENCES OF WATERSHED, RIPARIAN‐CORRIDOR, AND REACH‐SCALE CHARACTERISTICS ON AQUATIC BIOTA IN AGRICULTURAL WATERSHEDS¹

Abstract

Multivariate analyses and correlations revealed strong relations between watershed and riparian‐corridor land cover, and reach‐scale habitat versus fish and macroinvertebrate assemblages in 38 warmwater streams in eastern Wisconsin. Watersheds were dominated by agricultural use, and ranged in size from 9 to 71 km2 Watershed land cover was summarized from satellite‐derived data for the area outside a 30‐m buffer. Riparian land cover was interpreted from digital orthophotos within 10‐, 10‐to 20‐, and 20‐to 30‐m buffers. Reach‐scale habitat, fish, and macroinvertebrates were collected in 1998 and biotic indices calculated. Correlations between land cover, habitat, and stream‐quality indicators revealed significant relations at the watershed, riparian‐corridor, and reach scales. At the watershed scale, fish diversity, intolerant fish and EPT species increased, and Hilsenhoff biotic index (HBI) decreased as percent forest increased. At the riparian‐corridor scale, EPT species decreased and HBI increased as riparian vegetation became more fragmented. For the reach, EPT species decreased with embeddedness. Multivariate analyses further indicated that riparian (percent agriculture, grassland, urban and forest, and fragmentation of vegetation), watershed (percent forest) and reach‐scale characteristics (embeddedness) were the most important variables influencing fish (IBI, density, diversity, number, and percent tolerant and insectivorous species) and macroinvertebrate (HBI and EPT) communities.

Benefits of riparian forest for the aquatic ecosystem assessed at a large geographic scale

“…From a regional-scale river network nutrient modelling study in the ecoregion HER9, a significant diminution of nutrient load was attributed to riparian forest cover (Curie et al, 2011). The observed responses are also in line with records for other parts of the world (Storey and Cowley, 1997;Stewart et al, 2001;Meador and Goldstein, 2003;Arnaiz et al, 2011). Although no process-based experimental set up is used, and no site-specific information of forest cover to the biotic measurements is included, the data presented here over a large geographical scale yields consistent proof for the stated hypotheses of this functional benefit of riparian forests at the terrestrial-aquatic 06p11…”

“…For smaller agricultural watersheds in North Carolina, 73% of the variance in fish and macroinvertebrate communities was explained by watershed and local riparian corridor characteristics (Stewart et al, 2001;Wilson et al, 2008;Arnaiz et al, 2011), whereas riparian forest as a single predictor explained 63% of the fish species assemblages in smaller headwater streams of agriculturally dominated catchments of a northern Great Plains ecoregion (Wilson et al, 2008). In our multi-stressor context, only up to 22% of the variance for nutrients (Table II) and 5% for biotic integrity metrics (Table V) are explained by riparian forest cover.…”

“…Such benefits may include the following: addition of organic matter, diversifying the trophic conditions; thermal regulation by forest canopy cover; structuring of habitat and provision of microhabitat; and buffer for nutrients and pollutant influx to the water course (Lowrance et al, 1984;Lowrance et al, 1997;Wenger et al, 1999). These functions have been evidenced only from local studies with field measurements (Storey and Cowley, 1997;Wallace et al, 1997;Parkyn et al, 2003;Dodds and Oakes, 2006;Rios and Bailey, 2006) and from some larger scale studies in strictly agricultural watersheds (Stewart et al, 2001;Wilson et al, 2008;Arnaiz et al, 2011). The cumulative watershed impact of forested riparian zones on stream nutrient levels is also acknowledged (Newbold et al, 2010;Curie et al, 2011;Wang et al, 2011), but remains poorly understood (Weller et al, 2011).…”

Large‐scale relationships between basin and riparian land cover and the ecological status of European rivers

“…The actual influence of riparian areas on river biota, and particularly the invertebrate indices, has been evaluated mainly in meso-scale studies (Lammert & Allan, 1999;Sponseller, Benfield & Valett, 2001;Stewart et al, 2001). The PLS models used in France, Slovakia and Estonia demonstrated, at large scale, a very clear negative relationship between artificial land cover in the riparian corridors and invertebrate indices.…”

Habitat associations of fish assemblages in the Cache River, Illinois

“…As a result of processes occurring at various and interacting scales, it has long been suggested to incorporate multiple spatial and temporal scales when analyzing community assembly (Poff 1997;Ricklefs 1987;Fausch et al 2002). Given the widespread influence of human activities at the landscape scale, different land uses and covers are commonly found to be associated with fish assemblages (Lammert and Allan 1999;Roth et al 1996;Stewart et al 2001;Allan et al 1997;Pease et al 2011). Agricultural land use, specifically, can have long-term effects on fish assemblages (Harding et al 1998).…”