Reference conditions for Los Alamos National Laboratory steams using benthic macroinvertebrate assessment in upper Pajarito Canyon

Abstract

• Abstract-Benthic macroinvertebrates and water samples were collected at three stations in upper Pajarito Creek and at one station in each of two first-ordertributaries to Pajarito Creek at Los Alamos National Laboratory (LANL) . A total of 63 taxa were identified from the five stations. Number of taxa per study location ranged from 25 to 35 and standing crop ranged from 2351 (no/m 2) to II ,212 (no/m 2). EPT/EPT + Chironomid ratios, a measure of community balance, ranged from 0.17 to 0.84, while another measure of community balance, the Shannon-Weaver's index of diversity, ranged from 2.48 to 3.53. The Winget and Mangum CTQd index, a measure of non-organic perturbations, ranged from 72.5 to 89.1, and the Hilsenhoff Biotic Index (HBI), a measure of the presence of organic perturbation, ranged from 4.20 to 6.92. Habitat assessments indicate that four of the five stations were comparable, whereas the station farthest downstream in Pajarito Canyon displayed effects of embeddedness, chan nel alteration, scouring and reduced flow. The HBI = 6.92, calculated for Starmer Spring station (ST 0.5), indicates fairly poor water quality with substantial organic pollution likely. The complete absence of the scraper functional feeding group, the dominance of the community by one tolerant midge, and the presence of mats of filamentous algae at Starmer Spring indicate a community structure that is tolerant of nutrient enrichment. The State of New Mexico water-quality standards for livestock watering and wildlife habitat were met at all stations, while the fisheries acute standard for aluminum (750 J-lg/L) was exceeded at the station farthest downstream in Pajarito Canyon. The II metrics used to compare sites indicate that the farthest upstream station in Pajarito Canyon (PA 9.0) is appropriate for use as the reference condition for future comparisons of streams at LANL.