The influence of low-intensity watershed development on the hydrology, geomorphology, physicochemistry and macroinvertebrate diversity of small coastal plains streams

Coastal areas are under increasing pressures from human population growth and expansion, resulting in widespread conversion of forested and agricultural lands to low-density residential development. We investigated stream response to urban land use in 13 small coastal watersheds with low-levels of impervious surface cover (IS, 1.5 − 10.9%). Specifically, we examined putative mechanistic relationships between pre-selected land-cover categories (riparian forest, agriculture and IS) and stream hydrology, geomorphology, and water-chemistries. We further examined relationships between commonly used benthic macroinvertebrate response metrics, land-cover variables and potential environmental stressors. We used partial least squares (PLS) regression, which has been shown to perform well for model selection and parameter estimation in small sample and collinear situations. Physicochemical variables total phosphorus (TP), total suspended solids (TSS), specific conductivity (SPC), pH and median water temperature were significantly associated with both% riparian forest buffer (FB) and% IS. Storm-event frequency and a baseflow index were associated with% IS alone; in contrast, % FB and IS were significantly associated with hydrologic flashiness and bankfull width. Benthic macroinvertebrate density was associated with% IS and associated hydro-geomorphic stressors, benthic diversity (richness, H', evenness) and taxa sensitivity/tolerance metrics (% EPT, NCBI) were more strongly associated with maximum water temperatures, gradients of organic matter and flow permanence in these streams than anthropogenic land-cover or associated stressors.