Biodiversity, Water Chemistry, Physical Characteristics, and Anthropogenic Disturbance Gradients of Sandstone Springs on the Colorado Plateau

Springs located on the Colorado Plateau are highly threatened and represent a small percentage of the landscape; yet they are disproportionately important to diverse native flora and fauna. The relationships between anthropogenic disturbance, aquatic macroinvertebrate species composition, and environmental variables at these springs have received little study. We selectively visited 40 sandstone springs in southeastern Utah and southwestern Colorado to span a range of impacts. We classified the springs into impact categories based on a spring impact score, and we measured biodiversity (aquatic macroinvertebrates), water chemistry (nutrients, dissolved O2, pH, specific conductivity, temperature, turbidity, coliform bacteria [Escherichia coli]), physical characters (solar radiation, substrate, vegetation cover, bank stability, discharge), and presence of anthropogenic disturbance. Escherichia coli abundance was higher in high impact categories, and turbidity increased with increasing disturbance. No differences in total N, total P, specific conductivity, flow, dissolved O2, pH, or substrate were found among the impact categories. Vegetation cover was higher in low impact categories than in moderate and high impact categories, while potential annual and growing-season solar radiation was lower in low impact categories than in high impact categories. Global and subsequent multiple response permutation procedure (MRPP) comparisons suggested strong differences in aquatic macroinvertebrates between low and high impact springs and no difference at moderate impact springs. Mean taxa richness (α-diversity), total taxa richness (γ-diversity), and percent of taxa richness composed of shredders peaked at moderate disturbance levels. The percentage of non-insect taxa richness was reduced in high impact categories, and Odonata (dragonflies and damselflies) were higher in low impact categories than in high impact categories. All high impact springs had both livestock use and vehicle use (roads or off-highway vehicles), and our data suggest that disturbances caused by one or both of these uses alter the aquatic macroinvertebrate assemblage. We suggest that disturbance may increase macroinvertebrate richness, where a mix of tolerant and intolerant species co-occur, until macroinvertebrate richness reaches a threshold; after surpassing this threshold, macroinvertebrate diversity decreases.