THE EFFECTS OF CLIMATE CHANGE ON STREAM INVERTEBRATES IN THEIR ROLE AS BIOLOGICAL INDICATORS AND RESPONDERS TO DISTURBANCE

Global climate models provide estimates of future changes in air temperature and precipitation patterns, drought, flooding, sea-level rise, and increases in the frequency, duration, and intensity of extreme heat and storm events. These climate changes will affect stream invertebrate communities directly, indirectly, and through interactions with other stressors, resulting in a range of biological responses, including species range shifts, losses and replacements, novel community compositions, and altered ecosystem functions and services. Effects will vary regionally and present heretofore unaccounted influences on biomonitoring, which water-quality agencies use to assess the status and health of ecosystems as required by the Clean Water Act. Biomonitoring uses biological indicators and metrics to assess ecosystem condition, and is anchored in comparison of test sites to regionally established reference benchmarks of ecological condition. Climate change will affect responses and interpretation of these indicators and metrics at both reference and non-reference sites and, therefore, has the potential to confound the diagnosis of ecological condition if reference and non-reference sites do not change in parallel. This dissertation analyzes four regionally distributed state biomonitoring data sets to inform on 1) how biological indicators respond to the effects of climate change, 2) what climate-specific indicators may be available to detect effects, 3) how well current sampling detects climate-driven changes, and 4) how program designs can continue to detect impairment. In addition, responses were examined of stream invertebrates to a particular extreme event, wildfire, which is expected to increase in the future with climate change. In general, we found that temperature trait groups (cold- and warm-water preference taxa), as well as several taxonomically-defined invertebrate metrics and indicator groups, show responses consistent with expectation to long-term increases in temperature, although the climate responsiveness of these trait groups varied among states and ecoregions. Temperature sensitivity of taxa and their sensitivity to organic pollution were moderately but significantly correlated. Therefore, metrics selected for condition assessments because taxa are sensitive to disturbance or to conventional pollutants also were sensitive to changes in temperature. We explored the feasibility of modifying metrics by partitioning components based on temperature sensitivity to reduce the likelihood that responses to climate change would confound the interpretation of responses to impairment from other causes and to facilitate tracking of climate-change-related taxon losses and replacements. Difficulties arise in categorizing unique indicators of global changes, because of similarities in some of the temperature and hydrologic effects resulting from climate change, land use changes, and water removal. Nevertheless, the utilization of climate-sensitive traits to modify traditional biomonitoring metrics is promising in the context of using a weight-of-evidence approach for interpreting bioassessment results. Observed invertebrate responses to climate change also impair the condition of reference stations. Combined with our projection that encroachment of developed land uses over time will negatively impact up to a third or more of currently established reference sites by the end of the century, these responses suggest the importance of accounting for reference condition drift through implementation of an objective scale for condition characterization, as well as the need for reference station protection. These results can be used to identify methods that assist with detecting climate-related effects and highlight steps that can be taken to ensure that programs continue to meet resource protection goals. However, we also must recognize that many aspects of global changes are not tractable at the local to regional scales at which bioassessment is applied in support of water quality management, suggesting the need for a shift in the scale of approach from a narrow focus in the process of water resource quality protection and restoration to one that encompasses broader adaption strategies to address and manage global change impacts. Overall, we found the response of stream benthic invertebrates to a major wildfire were not devastating, with minimal responses found in total abundance or taxa richness. However, numerous taxa responded to post-fire flow and water quality disturbances either positively, negatively, negatively with recovery, or neutrally, with responses well captured by selected habit and feeding type traits. Post-fire benthic responses reflected three categories, vulnerability, resistance, and resilience, with different groups of organisms and different trait characteristics comprising each. Vulnerability was observed to both direct physical disturbance, mediated by the flow pulses that followed the fire; and to trophic impacts, themselves a response to loss of food resources due to those same flow pulses and associated water quality effects. Resistance to the post-fire physical disturbance of the stream environment was exhibited by a subset of invertebrates with habit traits that conferred the ability to withstand dislodgement and displacement that would otherwise be expected from the post-fire flow pulses. Resilience, or ability to recover in the short term following cessation of the most prominent post-fire flow events, was conferred mainly by opportunistic life-history traits. This suite of responses suggest the mechanisms through which benthic communities may be altered in the long-term, through suppression of some vulnerable taxa, partial if not temporary (short-term) suppression of some trophic resources, and possibly incomplete recovery (relative to pre-fire conditions) based on the reproductive life-history characteristics of component taxa.U.S. EPA, Global Change Research Program, and New Mexico EPSCORBiologyDoctoralUniversity of New Mexico. Biology Dept.Dahm, CliffordBixby, RebeccaCollins, ScottCrossey, LauraJacobi, GeraldBernard, Sweene