ABSTRACT EFFECTS OF WILDFIRE ON WATER QUALITY AND BENTHIC MACROINVERTEBRATE COMMUNITIES OF A CHIHUAHUAN DESERT SPRING SYSTEM by Tara Jo Haan Wildfire disturbances affect resource availability and alter community composition in arid environments. Traditionally, fire effects on arid-land aquatic ecosystems are under-studied compared to terrestrial ecosystems. Chihuahuan Desert spring systems offer a unique opportunity to study such effects on macroinvertebrate community resistance and resilience. I took advantage of a rare opportunity to employ a BACI design to observe changes in water quality and macroinvertebrate communities to wildfire in a spring system on Bitter Lake National Wildlife Refuge, New Mexico. The results suggest significant water quality and species-specific response to wildfire. I observed an increase in an endangered snail, Juturnia kosteri, but there were no significant community-based changes. These results suggest that arid-land aquatic communities can be resistant to abiotic/biotic changes caused by wildland fire. With climate change predicted to increase the frequency and intensity of arid-land fires, aquatic communities may be more vulnerable to severe events in the future. EFFECTS OF WILDFIRE ON WATER QUALITY AND BENTHIC MACROINVERTEBRATE COMMUNITIES OF A CHIHUAHUAN DESERT SPRING SYSTEM A Thesis Submitted to the Faculty of Miami University in partial fulfillment of the requirements for the degree of Master of Science Department of Zoology by Tara Jo Haan Miami University Oxford, OH 2012 Advisor _______________________ Dr. David J. Berg Reader _______________________ Dr. Craig Williamson Reader _______________________ Dr. Ann L. Rypstra TABLE OF CONTENTS List of tables iii List of figures iv List of appendices v Acknowledgements vi 1. Introduction 1 2. Study area and Sandhill wildfire 5 3. Objective 7 4. Methods 9 4.1 Sample collection 9 4.2 Water quality analysis 9 4.3 Macroinvertebrate community analysis 10 5. Results 12 5.1 Water quality 12 5.2 Macroinvertebrate communities 13 6. Discussion 18 7. Conclusions, implications, and future directions 28 8. Bibliography 31 ii LIST OF TABLES Table 1: Water depth and velocity at Bitter Creek and Sago Spring Table 2: Summary statistics for water quality variables Table 3: Results of ARIMA analyses on water quality variables Table 4: Average within-season Sorensen’s Similarity Index at Bitter Creek and Sago Spring Table 5: Average among-season Sorensen’s Similarity Index at Bitter Creek and Sago Spring iii LIST OF FIGURES Figure 1: The Chihuahuan Desert of North America Figure 2. Bitter Creek and Sago Spring study areas within Bitter Lake National Wildlife Refuge Figure 3. Map of Sandhill fire perimeter Figure 4. Seasonal time series of temperature at Bitter Creek Figure 5. Seasonal time series of dissolved oxygen at Bitter Creek Figure 6. Seasonal time series of pH at Bitter Creek Figure 7. Seasonal time series of salinity at Bitter Creek Figure 8. Seasonal time series of specific conductance at Bitter Creek Figure 9. Seasonal time series of total dissolved solids at Bitter Creek Figure 10. Taxa richness and Simpson’s Index of Diversity at Bitter Creek Figure 11. Taxa richness and Simpson’s Index of Diversity at Sago Spring Figure 12. Total macroinvertebrate density at Bitter Creek and Sago Spring Figure 13. Density of three endangered macroinvertebrates at Bitter Creek Figure 14. Density of three endangered macroinvertebrates at Sago Spring Figure 15. Density of all functional feeding groups at Bitter Creek and Sago Spring Figure 16. Density of functional feeding groups with scrapers removed at Bitter Creek and Sago Spring Figure 17. Density and richness of insects at Bitter Creek and Sago Spring Figure 18. Density and richness of detritivores at Bitter Creek and Sago Spring Figure 19. Sorensen’s Similarity Index between Bitter Creek and Sago Spring iv LIST OF APPENDICES Appendix 1. Seasonal effects of hydrochemical variables. Appendix 2. Raw macroinvertebrate data from Bitter Creek pre- and post-fire Appendix 3. Raw macroinvertebrate data from Sago Spring pre- and post-fire Appendix 4. α-, β-, and γ-diversity at Bitter Creek and Sago Spring v ACKNOWLEDGEMENTS I would like to extend my sincere gratitude to my advisor, Dr. Dave Berg, for his constant patience and guidance throughout my time at Miami University. I would also like to thank my committee members, Dr. Ann Rypstra and Dr. Craig Williamson, for their suggestions, comments, and support. In addition, I would like to thank Dr. Jon Patten for his help and expertise in time series analysis and Mike Hughes of the Miami Statistical Consulting Center for assistance in ANCOVA models. Special thanks to Brian Lang of the New Mexico Department of Game and Fish for the collection of samples and his help throughout the course of my master’s research, as well as his timely responses to my many emails. Numerous undergraduate students aided in the sorting and identifications of macroinvertebrates, so I thank Keara Stanislawczyk, John Abeln, and Robert Firor for their assistance in that process. Funding for this research was provided by the National Science Foundation grant DEB-0717064 and the New Mexico Department of Game and Fish. Finally, I would like to thank my family for their endless support and encouragement throughout my education. vi 1. INTRODUCTION Disturbances are discrete events that disrupt ecosystem structure, affect availability of resources and/or substratum, and change the physical landscape of an environment (Resh et al., 1988, Gresswell, 1999, Minshall, 2003). However, disturbances are also important in maintaining biodiversity of habitats and evidence suggests that moderate disturbance intensities and frequencies often allow for maximum species richness (Hobbs and Huenneke, 1992). Disturbances may be natural, such as droughts or floods, or they may be human-caused, such as the clearing of forests or the introduction of exotic species. Wildfires are an agent of disturbance which have been shown to have powerful effects in numerous ecosystems. For many years, wildfire effects in terrestrial environments were much more studied than in aquatic ecosystems (Minshall et al., 1989, Gresswell, 1999, Minshall, 2003), and wildfire studies in arid-land aquatic environments are particularly lacking. In addition, much of the previous research focusing on fire in aquatic systems emphasized alterations in water yield and quality, rather than effects on biota (Gresswell, 1999). Wildfires are characterized by their intensity, magnitude, frequency, scale, and pattern, and are heavily influenced by an areas’ local climate, vegetation and fuels, geomorphology, hydrology, and other environmental attributes, making the specific effects of a wildfire event widely variable and difficult to predict (Dwire and Kauffman, 2003). The effects of a wildfire on a stream ecosystem can be broken down into three response periods: (1) short-term (<1 year) changes result directly from changes in water chemistry and food quality; (2) mid-term (1-10 years) and (3) long-term (>10 years) responses refer to changes resulting from the removal and later successional replacement of the terrestrial cover in a stream catchment (Minshall et al., 1997). The most powerful short-term effects likely result from increased channel erosion leading to increased overland runoff and elevated sediment loads in streams, especially following significant precipitation events. Mid- and long-term responses, including return to pre-fire conditions, closely correspond to vegetative regrowth (Minshall et al., 1995, Ryan et al., 2011). Ultimately, however, the overall responses heavily depend on both the size and intensity of the fire, as well as the physical, chemical, and biological traits of each site (Gresswell, 1999). In addition, there is generally a gradual decrease in harmful fire effects with increasing stream size (Minshall, 2003). 1 The consequences of wildfire on freshwater macroinvertebrates are due to both direct and indirect effects of fire. Direct effects include increased temperature, nutrients, charcoal, and ash. These are associated with the time from the fire to the first major precipitation and runoff event. Indirect effects of fire refer to the channel alteration, increased erosion, and sediment transport and deposition that commence with the first runoff after the fire (Minshall, 2003). The direct effects of fire on macroinvertebrates are often minor, but communities are less resistant and resilient to the indirect effects, specifically intense sedimentation after a fire (Vieira et al., 2004). Community resistance refers to the magnitude of change from the pre-disturbed state and depends on the ability of organisms to avoid mortality or displacement after the fire. Community resilience refers to the rate of recovery to the pre-disturbed state and depends on the recolonization abilities of species, as well as the occurrence of repeated post-fire disturbances such as flooding, which may reset the recovery trajectory (Vieira et al., 2004). Macroinvertebrates have often been considered good indicators of stream quality. While there is not sufficient evidence to consider any one particular macroinvertebrate species as a gauge of water quality, the community as a whole has long been used as an indicator of pollution (Goodnight, 1973). Many macroinvertebrate species have life cycles greater than a year, allowing for the integration of longer-term pollution effects, but they may also respond rapidly to habitat stressors and alterations in water