Benthic Macroinvertebrate Metacommunity Structure of the Guadalupe River Basin, TX
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Benthic macroinvertebrates (BMI) are widely used as bio-indicators for local in-stream quality. However, local community structure can be affected by smaller scale (local) environmental conditions and larger scale processes. I assessed the abundance and diversity of BMI and their relationship with local in-stream conditions, regional patterns of land-use/land cover (LULC), and large scale physiographic gradients across the Guadalupe River System, a large basin (3,256 km2) in Central Texas. Macroinvertebrates, water quality, and habitat conditions across 28 sites in the Guadalupe River and its main tributaries were sampled. Highest species diversity occurred near the headwaters, and decreased downstream. Pollution tolerance levels increased downstream and followed an increasing agriculture gradient. Landscape factors explained a large proportion of variation in macroinvertebrate community structure (38%), but 16% of it was spatially structured (shared with spatial factors latitude and longitude) and 4% was explained by spatial factors alone. Local environmental factors were strongly correlated with landscape factors and explained similar amount of variation as landscape factors. My study highlights the importance of incorporating physiographic gradients when examining local and regional diversity and composition of BMI communities, especially in large complex watersheds. My results will help develop more effective monitoring programs for larger river systems.