Increased chloride levels and habitat heterogeneity reduce insect diversity in Rio Grande riparian habitats

Background/Question/Methods As a result of exponential human population growth in New Mexico, the Rio Grande has become a heavily managed water resource. In an effort to meet the water demands of the growing population, seventeen dams and reservoirs have been constructed along the Rio Grande. During the summer of 2007, I sampled ground dwelling arthropods to determine the effect of river management on insect community composition in two different habitat types. Thirty-four pitfall traps filled with soapy water were established in the Sevilleta National Wildlife Refuge adjacent to the Rio Grande, and in Cibola Springs, an unmanaged artesian water system representative of headwater habitat. Results/Conclusions After an intensive two-month collection period, it was concluded that insect diversity was higher at Cibola Springs compared to the Rio Grande, but insect abundance was higher at the Rio Grande. Twenty-seven insect families were identified at Cibola Springs and twelve insect families were identified at the Rio Grande, with common insect families carabidae, formicidae, elateridae, and gryllidae populating both sites. Bromide, nitrate, and phosphate levels did not significantly differ between the two research sites. However, the build-up of organic matter in the Rio Grande, and chloride content may explain the lower species diversity in the Rio Grande riparian zone relative to Cibola Springs. Chloride content was thirty-six times higher in the Rio Grande than Cibola Springs. In addition, higher habitat heterogeneity at Cibola Springs, despite its smaller aerial extent, may have influenced insect diversity compared to the more homogenous riparian zone surrounding the Rio Grande. Results show the dramatic changes in insect populations from headwater systems to managed floodplains, and highlight the importance of small headwater areas for the conservation of biodiversity.