A comparison of riparian condition and aquatic invertebrate community indices in central Nevada

The importance of maintaining healthy riparian communities to sustain natur al stream processes and function is well documented. Land management agenci es in the West are currently developing methods to assess and monitor ripar ian community condition to adapt land use practices that would better prote ct rangeland ecosystems. To determine whether these methods also provide an indication of abiotic and biotic stream condition, we compared the classif ication system of riparian communities developed by the U.S. Forest Service (USFS) to physical parameters of stream condition and to aquatic invertebr ate community assemblages. Thirty-three sites in 19 different streams of th e Toiyabe Range in central Nevada were measured for water quality substrate characteristics, and fish abundance and diversity, We sampled aquatic inve rtebrates and calculated community indices based on environmental tolerance levels. taxonomic diversity; and abundance of sensitive taxa. USFS personn el classified these sites by dominant riparian plant community type (meadow , willow, or aspen) and ecological status (low, moderate, or high) using pl ant abundance data, rooting depth, and soil infiltration to determine simil arities to potential natural communities. Riparian condition indices as well as community diversity were significantl y correlated to proportions of fine and small-diameter substrate in streamb eds. Accumulation of silt was significantly related to plant community type , with meadow sites expressing highest proportions. Further examinations in dicated that 2 of 6 invertebrate community indices were significantly relat ed to ecological status, with highest diversity levels occurring mainly in willow- and aspen-dominated sites in moderate ecological condition. Neverth eless, we show that several other environmental variables, including substr ate characteristics, dissolved oxygen, water temperature, and species richn ess of fish communities, were more strongly and consistently related to inv ertebrate assemblage patterns. Our results demonstrate that information on aquatic invertebrates and stream condition could augment the existing ripar ian classification system and provide useful monitoring tools to more thoro ughly examine ecosystem health in rangelands.