Aquatic-to-terrestrial contaminant flux in the Scioto River basin, Ohio, USA THESIS Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By Jeremy M. Alberts Graduate Program in Environment and Natural Resources The Ohio State University 2012 Committee: Dr. Mažeika S.P. Sullivan, Advisor Dr. Amanda D. Rodewald Dr. Stanley D. Gehrt Copyrighted by Jeremy M. Alberts 2012 Abstract Aquatic emergent insects provide important prey subsidies to riparian consumers. These aquatic-to-terrestrial feeding relationships provide a pathway through which aquatic contaminants are “reterrestrialized” into riparian food webs. However, influences of land use and land cover (LULC) on the magnitude of aquatic-to-terrestrial contaminant transfers remain largely unexplored. To that end, I investigated aquatic-to-terrestrial contaminant fluxes at 11 study reaches in the Olentangy and Scioto Rivers (OH, USA), representing urban, agricultural, and mixed land uses. At nine study reaches, I collected benthic sediment, aquatic emergent insects, ants (Formica subsericea), spiders of the family Tetragnathidae, riparian vegetation, and periphyton. At eight of these reaches, as well as additional four reaches where I erected nest-boxes, I sampled riparian swallows including: bank (Riparia riparia), northern rough-winged (Stelgidopteryx serripennis), tree (Tachycineta bicolor), and cliff (Petrochelidon pyrrhonota) swallows. Subsequently, all biological samples were analyzed for δ13C and δ15N. Sediment, ants, spiders, and swallows were tested for a suite of toxic elements including arsenic (As), selenium (Se), lead (Pb), and mercury (Hg). Two-source (δ13C and δ15N) mixing models indicated that Tetragnathidae were highly reliant on aquatic insects ( ̅= 76.9%, SD = 8.9%), whereas ant dependence was ii less but with greater variability ( ̅ = 27.8%, SD = 25.1%). Characteristics of shoreline habitat including standing dead trees and % overhanging vegetation explained 70 and 42% of the variation in the contribution of aquatic prey to F. subsericea and Tetragnathidae, respectively. Spider density was positively related to land-cover characteristics associated with urbanization (% impervious surfaces, % invasive shrubs, population density) and nearshore habitat. Shoreline habitat also was strongly related to the overall flux (i.e., contaminant load assimilated into consumer tissue) of Se (R2 = 0.58) and As (R2 = 0.51) to the tetragnathid spider assemblage, and Pb flux to spiders was higher in urban and agricultural reaches than in mixed reaches (F = 6.10, P = 0.025). F. subsericea density exhibited a positive relationship with urbanization (R2 = 0.83). As and Se flux to F. subsericea assemblages was positively related to urbanization (R2 = 0.70) as well as shoreline habitat, and Pb flux was higher in urban reaches than other land use types (F = 8.68, P = 0.017). For swallows, Hg concentrations were significantly higher at rural reaches than at urban reaches (t = -2.96, P = 0.003, df = 24), and Hg concentrations in swallows were positively related to Hg concentrations in sediment (R2 = 0.23, P = 0.030), though no relationships were evident for Se in swallows. We found that swallow Hg concentrations were significantly higher in rural than urban reaches (t = -2.96, P = 0.003, df = 24), and marginally so for Se (t = -1.54, P = 0.068, df = 24). To an extent, these relationships iii appear to be mediated by swallow reliance on aquatic emergent insect prey. For example, swallows that exhibited a higher proportion of aquatic prey in their diet and fed at a higher trophic level also exhibited elevated Se levels. I also found that both Se and Hg concentrations in adult swallows were significantly higher than those observed in juveniles (Se: t = -3.47, P = 0.013, df = 4; Hg: t = -4.35, P = 0.006, df = 4). Collectively, my results indicate that LULC mediates aquatic contaminant flux to terrestrial consumers via regulation of aquatic resource utilization. For riparian arthropods, differences in density associated with landscape variability can result in a significant discrepancy between the magnitude of contaminant export by aquatic emergent insects and the realized contaminant flux to riparian food webs. At a broader spatial scale, riparian swallows may represent a useful assessment tool for contaminant exposure in linked aquatic-terrestrial systems. iv Dedication I dedicate this thesis to Jennifer. Without her endless patience and support, this never would have been possible. For everything you’ve done for me, and for all of the time spent away with which you’ve had to deal, I thank you from the bottom of my heart. I couldn’t have done it without you. I would also like to thank my parents, who have been more encouraging and supportive than any person has the right to expect. Thank you both very much, for everything. v Acknowledgments I would like to thank the funding sources for this project, The Ohio State University School of Environment and Natural Resources, The Ohio Agricultural Research and Development Center SEEDS program, and the United States Forest Service. I would also like to thank my committee, Dr. Stan Gehrt and Dr. Amanda Rodewald, for their valued assistance and direction throughout the course of this project. I also extend my gratitude to the array of undergraduates, lab mates, faculty, and staff that helped me in various ways. There is not enough space here to thank every individual, but know that your assistance was greatly appreciated. Finally, I would like to give special thanks to my advisor, Dr. Mažeika Sullivan, for his patience and guidance with all aspects of this research project. This would have been a nearly impossible task without his assistance and support. vi Vita June 1997 .......................................................Wheeling Park High School 2001................................................................B.S. Biology, Muskingum College 2010 to present ..............................................Graduate Teaching Associate, School of Environment and Natural Resources, The Ohio State University Field of Study Major Field: Environment and Natural Resources vii Table of Contents Abstract ............................................................................................................................... ii Acknowledgments............................................................................................................. vii Vita .................................................................................................................................... vii Table of Contents ............................................................................................................. viii List of Tables ................................................................................................................... ixx List of Figures………………………………………………………………………….…xi Chapter 1: Background and Literature Review ................................................................. 1 Chapter 2: Land use mediates aquatic-to-terrestrial contaminant flux ........................... 31 Chapter 3: Riparian swallows as integrators of landscape change in a multiuse river system: implications for aquatic-to-terrestrial transfers of contaminants ......................... 76 References ....................................................................................................................... 113 Appendix A: Study Reach Description .......................................................................... 134 Appendix B: Arthropod Contaminant Concentrations ................................................... 135 Appendix C: Arthropod Density .................................................................................... 137 Appendix D: Swallow Contaminant Concentrations ...................................................... 138 viii List of Tables Table 1.1. Common aquatic contaminants, their impacts on humans and wildlife, and major pathways through which they enter aquatic systems. ............................................... 3 Table 1.2. Estimated mass of contaminants exported from aquatic to terrestrial systems by aquatic emergent insects. ............................................................................................. 12 Table 2.1. Biomass and contaminant concentrations of aquatic emergent insects of the families Chironomidae and Hydropsychidae and contaminant export estimates from nine study reaches in the Scioto River basin, Ohio, USA. Note: Hydropsychidae was only collected from one urban reach. ........................................................................................ 62 Table 2.2. Contribution of aquatic prey to riparian arthropod consumer diet for study reaches in the Scioto River basin, Ohio (calculated using IsoError v 1.04; Phillips and Greg 2001). ....................................................................................................................... 63 Table 2.3. Adjacent (500 m on each side of river) land-use and land-cover (LULC) principal component analysis: eigenvalues and the percent variance captured by the principal components (eigenvalues > 1), along with each principal component’s loadings and the proportion of the variance (r2) each variable shared with the PCA axes. Bold type indicates those axes used as successful predictor variables in regression models. ........... 64 ix Table 2.4. Estimated flux (aquatic contaminants uptaken by riparian consumers)