University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 2007 Energy Flow in a Floodplain Aquifer Ecosystem Brian Reid The University of Montana Follow this and additional works at: https://scholarworks.umt.edu/etd Let us know how access to this document benefits ou.y Recommended Citation Reid, Brian, "Energy Flow in a Floodplain Aquifer Ecosystem" (2007). Graduate Student Theses, Dissertations, & Professional Papers. 372. https://scholarworks.umt.edu/etd/372 This Dissertation is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. ENERGY FLOW IN A FLOODPLAIN AQUIFER ECOSYSTEM By Brian LeGare Reid BS, Cornell University, 1990 Dissertation presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Biology The University of Montana Missoula, MT May 2007 Approved by: Dr. David A. Strobel, Dean Graduate School Dr. F. Richard Hauer, Chair Flathead Lake Biological Station Division of Biological Sciences Dr. Ray Callaway Division of Biological Sciences Dr. James Gannon Division of Biological Sciences Dr. Mark Lorang Flathead Lake Biological Station Division of Biological Sciences Dr. Jack Stanford Flathead Lake Biological Station Division of Biological Sciences Dr. William Woessner Geology Department © COPYRIGHT by Brian LeGare Reid 2007 All Rights Reserved ii Reid, Brian, PhD, May 2007 Biology Energy Flow in a Floodplain Groundwater Ecosystem Chairperson: Dr. F. Richard Hauer ABSTRACT We developed an energy budget to identify energy sources for the invertebrate community of a large 20 km2 floodplain aquifer, based on biomass distributions, organismal respirometry, in situ community respiration, mesocosm and microcosm experiments, stable isotopes and invertebrate gut contents. The invertebrate respiration scaling exponent was 0.474 (+/- 0.068, 95% CI) across six orders in body mass, which is significantly lower than the ¾ power scaling predicted by metabolic theory. Invertebrate production was dominated by copepods (Diacyclops, Acanthocyclops, Bryocamptus), Stygobromus amphipods, and amphibiont stoneflies, and ranged from 26.9 to 4200 mg C/m3 sediment/year. Production and density showed a U-shaped response to dissolved oxygen (high production at both low and high oxygen concentrations). Production declined exponentially with depth for most sites, but at sites with orthograde oxygen profiles there was an exponential increase at the oxycline. Aerobic microbial community production ranged from 1210 to 2020 mg C/m3 sediment/year, also showing a U-shaped response to oxygen. System respiratory quotient (RQ) ranged from ≈ 0 to 9.5, indicating a significant contribution of anaerobic production to system energy flow. We documented multiple lines of evidence for DOC (soil, river) and buried POM carbon sources, however POM was by far the largest carbon reservoir in the aquifer at ≈ 108 (to 1010) mg C/ m3 sediment. Energy from POM breakdown was the only source sufficient to explain microbial and invertebrate production. Carbon stable isotope signatures showed strong levels of depletion for invertebrates (δ13C -25‰ to -70‰). These results suggest a significant anaerobic subsidy of aerobic food webs in the subsurface, and a potential methane subsidy of 10% to 99% of invertebrate energy flow. Oxygen showed high, non- random, spatial and temporal variation across the aquifer, with a large scale decline in oxygen along the axis of the floodplain, and distinct hotspots of low oxygen. Low oxygen hotspots corresponded with migration of stonefly nymphs 100’s of meters into the aquifer. The U-shaped responses and biogeochemical trends suggest a major threshold at bulk oxygen concentrations of 3-5 mg/l. Collectively, these findings indicate the role of dissolved oxygen as a key variable in groundwater ecosystems. iii ACKNOWLEDGEMENTS I would like to thank Dr. Jack Stanford for providing the opportunity to work on one of the most interesting and least explored ecosystems in the world. I thank my advisor Dr. F. Richard Hauer, and my committee, Drs. Ray Callaway, Mark Lorang, Matthias Rillig, Jack Stanford and William Woessner. Dr. James Gannon offered abundant advice, and thanks also to Dr. William Holben and Dr. Emily Bernhardt. Dr. Charlie Hall provided a simple insight that set everything in motion. I would particularly like to thank the Dalimata family, especially John, Ruth, Chris and Steve, for pulling my truck out of the mud, ideas, friendship, the most amazing field site in the world, the new amphipod Stygobromus presleyii, the smartest dog I’ve ever had, and pulling my truck out of the mud again. Every graduate student would benefit from having a farmer on their committee. Access to field sites was also provided by the Wheeler and Pouliat families. Vincent and Neil Dalimata (who coined the term “hyperactive weaselcosm”), helped with some of the most abusive field work I could come up with, all for a few lousy sandwiches. Curtis and Dave from Rocky Boys (supported by project TRAIN) made possible the well oxygen sampling that ended up tying the whole story together. Jason and Mark from Salish Kootenai College helped drive wells and dig several enormous holes that kept filling back in, which is a great metaphor too. Big thanks to fellow field slave, lab mate, statistics coach and best friend Michelle Anderson. Scott Relyea: we should have died in that canoe. Kristin Olsen: beware the sound of breaking glassware. Mark Potter and Eric Anderson for all the help in the shop. All the staff at FLBS. Sherrie at DBS for supporting the “sleeping bags for science” campaign. And the list of people who helped in the field: Sandra Adams, Jake Chaffin, Cain Diehl, Nathan Gordon, Adam Johnson, Mike Machura, Bonnie McGill, Phil Mattson, Mike Morris, Chris Platt, Phillip Ramsey, Jessica Schultz, Audrey Thompson. Thanks, List! Thanks in advance to taxonomic gurus Euyalem Abebe (nematodes), Bob Newell (insects), Janet Reid (copepods), Rhithron Associates (chironomids) and Howard Taylor (rotifers). And finally to my friend Jessica Schultz and my grandmother Sunny, who encouraged me to hang in there. And my dad Walter Reid, the engineering brains. This project was supported in part by a two-year fellowship from the Inland Northwest Research Alliance (INRA) Subsurface Science Research Initiative (SSRI). Additional research support was from NSF Biocomplexity in the Environment grant # 0120523, and material support by an NSF Dissertation Improvement Grant and INRA. iv TABLE OF CONTENTS Abstract ……………………………………………………………………………...….iii Acknowledgments ……………………………………………………………………....iv Table of Contents …………………………………………………....…………………..v List of Figures ……………………………………………………………..…………….ix List of Tables ………………………………………………………..………………….xii Introduction…………………………………………..…………………………………..1 Chapter 1: Oxygen Dynamics and Community Respiration in a Montane Floodplain Aquifer Abstract …………………………………………………………………….…………7 Introduction……………………………………………………………………………8 Methods Study site …………………………………………………………….…………..12 Well Grid Installation and Design……………………………………………….13 Well and Surface Water Sampling……………………………………………….15 Oxygen Contouring ……………………………………………………………...16 Flowpath Oxygen and Community Respiration…………………………………17 Community Respiration………………………………………………..………...17 Respiration Model………………………………………………………………..21 Results Seasonal and Spatial Patterns in Dissolved Oxygen……………………………..22 Flowpath Oxygen and Cumulative Respiration Patterns………………………...24 Mesocosm Community Respiration……………………………………………...30 Respiration Model ……………………………………………………………….35 Discussion Sources of Energy: Rivers, Soils, or Buried Organic Matter?…………………...36 Limitations, Assumptions and Future Directions………………………………..41 Ecosystem Resistance?..........................................................................................46 Flowpaths to Progress? ………………………………………………………….47 Conclusions…………………………………………………………………………..47 References……………………………………………………………………………49 Chapter 2: Distribution and Isotopic Composition of Buried Organic Matter in Sediments of a Floodplain Aquifer Abstract………………………………………………………………………………54 Introduction ………………………………………………………………….………55 Methods Sediment Collection……………………………………………………………...58 Particulate (Detrital) Organic Matter Processing………………………………...58 Strongly Associated Particulate Organic Matter Processing.……………………60 v Results and Discussion SAPOM: Sonication Trials and Mass Balance of Carbon Fractions.……………62 POM: Distribution and Relationship to SAPOM………………………………..66 Stable Isotopes of POM and SAPOM ……………………………...……………69 Variation in Organic Matter Properties with Depth…………………...…………71 Contribution to Aquifer Organic Matter Budget ……………………….……….72 Organic Matter in Aquifer Food Webs…………………………………………..74 References…………………………………………………………….……………...75 Chapter 3: Large Scale Invertebrate Dynamics in Response to Oxygen Gradients in a Floodplain Aquifer Abstract ………………………………………………………………………….…..79 Introduction …………………………………………………………………….........80 Methods Study Site ………………………………………………………………………..84 Well Grid Design and Installation…………………………………………….....85 Well and Surface Water Sampling ………………………………………………87 Sampling Efficiency……………………………………………………………..89 Invertebrate Sample Processing……………………………………………….....90