LONGITUDINAL PATTERNS IN STREAM CHANNEL GEOMORPHOLOGY AND AQUATIC HABITAT IN THE LUQUILLO MOUNTAINS OF PUERTO RICO Andrew Stephen Pike A DISSERTATION in Earth and Environmental Science Presented to the faculties of the University of Pennsylvania in partial fulfillment of the requirements for the degree of Doctor of Philosophy 2008 ___________________________________ Supervisor of Dissertation – Dr. Frederick N. Scatena ___________________________________ Graduate Group Chairperson – Dr. Gomaa Omar ACKNOWLEDGEMENTS This dissertation would not have been possible with the help and support of numerous mentors, colleagues, and friends, all of whom deserve recognition here. First and foremost, I would like to thank my advisor, Fred Scatena. Although his expectations were high and his demands were challenging, his perpetual guidance from the field to the office has been unparalleled. With his iron drive to help me succeed, and his deep breadth of knowledge of the natural world, it has truly been an honor to have studied under Fred. Second, I would like to thank each member of my graduate committee. I extend special thanks to Art Johnson, for first launching me onto the scientific research course, and for his continued mentorship throughout the years; I most certainly would not have made it this far without him. I thank Todd Crowl for arranging for me to spend an enjoyable and beneficial semester in his laboratory at Utah State University. I thank Dana Tomlin for his lucid intellect and always enlightening discussions. Lastly, I am deeply appreciative of Gomaa Omar not only for his support in handling logistical issues, but also for sharing his unique talent of bringing out the buried spiritual essence in scientific work. The field work required to survey tropical mountain rainforest streams was inherently enjoyable, but it was not without its challenges. Yet I had the pleasure of working with people who knew how to get a difficult job done, and have a good time doing it. The assistance from the following people made four summers of stream surveys possible, and all the more pleasant: Erik Drew, Tamara Heartsill-Scalley, Emmanuelle Humblet, Kris Johnson, Kunal Mandal, José Marcial, Amanda Moyer, Pablo Piña, and of course, Jennifer Schiffner. ii Housing and logistical support while in the field was made possible by the El Verde Field Station (University of Puerto Rico), the Sabana Research Center (United States Forest Service), and the International Institute for Tropical Forestry (IITF). My colleagues on the Biocomplexity project were critical in the formulation of this dissertation. I especially thank Katie Hein for her hard work collecting ecological data, her insight throughout the project, and for two excellent field seasons that made this collaborative project work. I also thank Drs. Ellen Wohl, Jorge Ramirez, Alan Covich, Felipe Blanco, and all others involved with the project for their intellectual contributions. I would like to thank numerous people around the department of Earth and Environmental Science at Penn. A special thanks for Karen Taylor for her support in all matters of life. Also, thanks to all the fellow grad students for their camaraderie, and to all the faculty who I’ve studied with and learned from over the past years. Funding for this dissertation was provided from the National Science Foundation Biocomplexity Grant (NSF #030414) —Rivers, Roads, and People: Complex Interactions of Overlapping Networks in Watersheds. Additional support was provided by the University of Pennsylvania, and the Long-Term Ecological Research (LTER) Network. iii ABSTRACT LONGITUDINAL PATTERNS IN STREAM CHANNEL GEOMORPHOLOGY AND AQUATIC HABITAT IN THE LUQUILLO MOUNTAINS OF PUERTO RICO Andrew S. Pike Frederick N. Scatena The hydrologic, geomorphic, and ecological dynamics of tropical montane streams are poorly understood in comparison to many temperate and/or alluvial rivers. Yet as the threat to tropical freshwater environments increases, information on the dynamics of relatively pristine streams is important for understanding landscape evolution, managing and conserving natural resources, and implementing stream restoration. This dissertation characterizes the geomorphology and hydrology of five adjacent watersheds draining the Luquillo Experimental Forest (LEF) in northeastern Puerto Rico, and discusses implications on aquatic habitat. I performed several interrelated studies, including: 1) formulating a geographic information systems (GIS) framework to estimate hydrologic parameters from topographic information and hydrologic records, 2) developing a method to determine active stream channel boundaries (“bankfull” stage) that allows for comparison of channel geometry on the basis of flow-frequency, 3) decoupling the relative influences of lithologic and hydraulic controls on channel morphology using an extensive field-based stream survey and analysis of stream profiles, channel geometry, and sediment dynamics, 4) linking network- and pool-scale geofluvial dynamics to the abundance of migratory fish and iv shrimp through a collaborative analysis combining geomorphic surveys and aquatic faunal sampling. This research indicates that these streams have some properties resembling both temperate montane and alluvial rivers. Similar to low-gradient rivers where floodplains mark channel boundaries, the active channel stage in these streams is defined by the incipient presence of woody vegetation and soil development. Systematic basin-scale geomorphic patterns are well-developed despite apparent non-fluvial and lithologic control on local channel morphology. This implies that strong fluvial forces are sufficient to override channel boundary resistance; a feature common in self-forming “threshold” alluvial channels. Migratory aquatic fauna abundances are influenced by a variety of geomorphic factors such as barrier waterfalls and suitable headwater habitat, and are consequently highly variable and patchy. These results stand in contrast to the notion that aquatic communities mirror systematic geomorphic gradients, but rather acknowledges the influences of multiscale geomorphic processes. Ultimately, this research provides baseline information on physical and biological processes in relatively unaltered tropical streams and can be used to inform further studies that document human interactions with stream networks. v TABLE OF CONTENTS ACKNOWLEDGEMENTS ii ABSTRACT iv LIST OF TABLES x LIST OF FIGURES xii CHAPTER 1: General Introduction Introduction 1 Chapter Outlines 6 References 9 CHAPTER 2: Application of Digital Terrain Analysis to Model Surface Water Flow in the Luquillo Mountains of Northeastern Puerto Rico Abstract 15 Introduction 16 Study Area 17 Digital Elevation Model (DEM) Construction 18 Stream Network Extraction 22 Rainfall, Runoff, and Discharge 24 Conclusion 27 Acknowledgements 27 References 28 CHAPTER 3: Defining a Bankfull Analog for Tropical Montane Streams Using Riparian Features Abstract 31 vi Introduction 33 Study Area 38 Northeastern Puerto Rico 38 Regional Stream Gages 41 Riparian Vegetation 42 Methods 50 Field Surveys 50 Estimation of Flow-Frequency 51 Multivariate Regression Trees 55 Effective Discharge 56 Results 60 Riparian Vegetation 60 Bankfull Discharge and Effective Discharge 61 Multivariate Regression Trees 61 Discussion 70 Riparian Features 70 Bankfull and Effective Discharge 73 Applicability to other stream systems 76 Conclusion 77 Acknowledgements 78 References 79 CHAPTER 4: Longitudinal Patterns in Stream Channel Geomorphology in the Tropical Mountain Streams of the Luquillo Mountains, Puerto Rico vii Abstract 88 Introduction 89 Study Area 97 Methods 105 Results 109 Longitudinal Profiles 109 Hydraulic Geometry 113 Grain Size 116 Stream Power 127 Discussion 130 Conclusion 136 Acknowledgements 137 References 138 CHAPTER 5: Multiscale Linkages Between Geomorphology and Aquatic Habitat in a Tropical Montane Stream Network, Puerto Rico Abstract 149 Introduction 151 Study Area 156 Stream Community 161 Methods 164 Field Methods 164 Pool Length and Spacing 168 Statistical Analyses 168 viii Principal Components Analysis 168 Non-Parametric Multiplicative Regression 169 Stepwise Multiple Linear Regression 171 Results 171 Species Distribution in Geomorphic Space 171 Longitudinal Trends of Species 183 Influence of Reach and Pool-Scale Geomorphology 192 Pool Size and Spacing 195 Discussion 195 Landscape Scale Patterns 195 Reach and Pool-Scale Patterns 201 Conclusion 204 References 205 CHAPTER 6: Conclusions and Future Research Summary and Conclusions 216 Future Research 218 APPENDIX 222 Site Information 227 Baseflow Channel Geometry 234 Active Channel Geometry 241 Grain Size and Pebble Count Data 248 Additional Biocomplexity Pool Information 255 INDEX 259 ix LIST OF TABLES Table 3.1 Physiographic site information for the selected study gages. 44 Table 3.2 Riparian features (vegetation, substrate, and soil 52 characteristics) that were recorded at each survey point. Table 3.3 For each study USGS gage, the time span of the discharge 54 record, flow parameters, and at station width and depth hydraulic geometry coefficients and exponents. Table 3.4 The median height above water table, unit discharge, flow 68 frequency, and recurrence interval of zones defined by the multivariate regression tree analysis. Table 3.5 The discharge, unit discharge, flow frequency, and 69 recurrence interval associated with the bankfull stage, the effective discharge, and the bankfull analog at each study stream gage. Table 4.1 Downstream hydraulic geometry coefficients and exponents 115 divided by watershed. Table 5.1 Species identified during trapping and electrofish sampling. 166 Table 5.2 Principal component eigenvalues for 58 geomorphic 173-174 variables, using data from 113 pools throughout the study basins. Table 5.3 Principal component eigenvalues for 20 geomorphic 181 variables measured for pools in the Quebrada Prieta. Table 5.4 Landscape scale variables used to predict species 184 presence/absence using a NPMR 2-parameter model. x