Academic journal article The American Midland Naturalist

Land-Use Impacts on Watershed Health and Integrity in Indiana Warmwater Streams

Academic journal article The American Midland Naturalist

Land-Use Impacts on Watershed Health and Integrity in Indiana Warmwater Streams

Article excerpt

ABSTRACT.

Many warmwater streams in the midwestern United States have been negatively influenced by human land-use practices. From Jun. through Aug. 2002 and 2003, tributaries (n = 50) of the upper Wabash River basin, Indiana, were sampled to investigate ecosystem health and integrity. Stream fish and macroinvertebrates were sampled along with in-stream habitat according to National Water-Quality Assessment Program protocols to examine relationships among fish community structure, benthic macroinvertebrate assemblages, physical-habitat complexity and water chemistry under varying land-use practices. Stream fish abundance was best explained by in-stream habitat quality (QHEI), watershed area and the amount of forested land use upstream of each sampling site. Overall index of biotic integrity (IBI) scores were low (mean = 35.58; range, 20 to 52), and varied predictably by riparian land-use type. The abundance of benthic macroinvertebrate taxa was best explained by the substrate QHEI metric (λ = 0.24; P = 0.005). Macroinvertebrate community index (ICI) scores showed more variability than IBI scores (mean = 20.40; range, 0 to 36). In-stream habitat quality (QHEI) was directly related to riparian land-use practices. Forested sites had higher QHEI scores than fallow field and agricultural sites due to increased habitat heterogeneity, large-woody debris loading and larger substrate sizes. The best model for predicting IBI scores incorporated both watershed and reach-scale variables combining slope and erosion power with maximum depth, percent canopy closure, percent fine substrates, degree of channelization and LWDI (r^sup 2^ = 0.24; adjr^sup 2^ = 0.19). Reach-scale variables (i.e., QHEI score, stream width, the proportion of unstable banks and percent fine substrates) best predicted ICI scores (r^sup 2^ = 0.69; adjr^sup 2^ = 0.66). Based on these results, we recommend that resource managers incorporate both biotic and abiotic factors at various temporal and spatial scales to predict the effects of land-use practices on community health in agriculturally dominated, warmwater streams.

INTRODUCTION

Throughout the midwestern United States, activities such as row-crop agriculture and urban development have negatively impacted aquatic habitats and associated stream fish and macroinvertebrate communities (Wang et al, 1997). Increased nutrient and sediment inputs from large-scale farming and ranching operations have been shown to degrade water quality (Cunjak, 1996; Wang et al, 1997; Walser and Bart, 1999). Likewise, stream channelization and loss of riparian buffer zones increase current velocity and water temperature (Walser and Bart, 1999; Talmage et al, 2002) and reduce coarse woody debris loading (Cunjak, 1996; Talmage et al, 2002). Similar studies have also examined the influence of watershed land-use practices and their role in defining stream ecosystems (Allan et al, 1997; Rhodes et al, 2001). Although land-use influences can be observed at various spatial scales, effects in agriculturally dominated systems are inconsistent because system health and integrity are highly variable (Wang et al, 1997, 2003; Richards, 2003). As a result, several methods for assessing stream health and system integrity have been developed to account for this variation.

Stream health indices integrate data collected on fish and macroinvertebrate communities, physical habitat and water quality. This more holistic approach relies on relationships between key biotic and abiotic factors such as species composition, habitat complexity and water chemistry to predict the biotic integrity of stream systems (Karr et al, 1987; Shields et al, 1995; Lyons, 1996). Understanding these relationships and how they vary under different land-use scenarios is important for resource managers working with riparian landowners.

Both spatial and temporal scales are important factors that explain the effects of land-use practices on stream ecosystems (Karr et al, 1987; Osborne and Wiley, 1992; Allan et al, 1997; Wang et al, 1997, 2003; Smogor and Angermeier, 2001; Sponseller et al. …

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