Phosphorus Retention and Transformation in Floodplain Forests of the Southeastern United States
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Graduate Theses, Dissertations, and Problem Reports 2013 Phosphorus Retention and Transformation in Floodplain Forests of the Southeastern United States John A. Navaratnam West Virginia University Follow this and additional works at: https://researchrepository.wvu.edu/etd Recommended Citation Navaratnam, John A., "Phosphorus Retention and Transformation in Floodplain Forests of the Southeastern United States" (2013). Graduate Theses, Dissertations, and Problem Reports. 666. https://researchrepository.wvu.edu/etd/666 This Dissertation is protected by copyright and/or related rights. It has been brought to you by the The Research Repository @ WVU with permission from the rights-holder(s). You are free to use this Dissertation in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you must obtain permission from the rights-holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/ or on the work itself. This Dissertation has been accepted for inclusion in WVU Graduate Theses, Dissertations, and Problem Reports collection by an authorized administrator of The Research Repository @ WVU. For more information, please contact [email protected]. Phosphorus Retention and Transformation in Floodplain Forests of the Southeastern United States John A. Navaratnam Dissertation submitted to the Eberly College of Arts and Sciences at West Virginia University in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Biology Richard B. Thomas, Ph.D., Chair Mark R. Walbridge, Ph.D. William T. Peterjohn, Ph.D. Kevin C. Daly, Ph.D. R. Kelman Wieder, Ph.D. Department of Biology Morgantown, WV Keywords: Phosphorus Biogeochemistry, Wetland, Floodplain Forest, Alluvial, Blackwater, River, Soil, DNA, Bacteria, Fungi, Isotope, 31P-NMR Copyright 2013 John A. Navaratnam ABSTRACT Phosphorus Retention and Transformation in Floodplain Forests of the Southeastern United States John A. Navaratnam Phosphorus (P) commonly limits productivity in freshwater ecosystems; thus, increased P loading, either in dissolved (DP) or particulate (PP) form, can lead to eutrophication. In riverine ecosystems, floodplain forests (FFs) provide an important ecosystem service, that of improved water quality downstream, by either removing P from these incident floodwaters (retention) or by transforming P prior to export. The central goal of my dissertation research is to understand these biogeochemical mechanisms of P retention and transformation in rivers and streams and their associated FFs in the Atlantic Coastal Plain of the southeastern US (VA, NC, SC, GA). To assess the nature of P removal during flooding events, I conducted a detailed study of DP and PP forms (inorganic, Pi and organic, Po) in waters from alluvial (AL) and blackwater (BW) FFs. At each FF site, floodwaters were collected both from the river inflow point (RI), from within the floodplain (FP) near the outflow point, and analyzed P forms by 31P nuclear magnetic resonance (NMR) spectroscopy. In both AL and BW samples, total DP and dissolved orthophosphate (DPi) declined significantly from RI to FP, while dissolved pyrophosphate (complex DPi) and total DPo were significantly higher in FP than in RI waters. Orthophosphate monoesters comprised the majority of the DPo pool and were significantly higher in FP floodwaters in both AL and BW systems. This suggests that in both AL and BW systems, DPi was converted to DPo form during flooding events, reducing its bioavailability and potential to cause the eutrophication of downstream waters. 32 In a second study, I added Pi dissolved in river water to soil cores collected AL and BW FFs to identify specific mechanisms of P retention and transformation during flooding. As much 32 32 as 77 % of added Pi was transformed to Po within 2 h of addition in BW river waters, while 32 in AL river waters, all added Pi remained in inorganic form. However, when labeled river waters were added to soil cores, upon contact with the soil surface, additional transformation was 32 observed resulting in an increase in the proportion of Po in headwaters, averaging 68 and 80 % of total 32P recovered in AL and BW cores, respectively. Across all soil cores, average 12 and 0.5 % of the total 32P added was recovered from head- and drain-waters, respectively. The remaining 87.5 % of added 32P was recovered in soils, distributed within the soil fractions (73 32 32 %), microbial biomass (9 %) and roots (6 %). The proportion of Pi and Po in cores averaged 69 and 31 % in AL compared to 53 and 47 % of total 32P recovered in BW cores. These result suggest that floodplain soils act as a second line of defense protecting water quality, by retaining P inputs that are not initially transformed within the water column (river- and head-waters) during flooding events. Despite our knowledge of the significant role of microorganisms in wetland soil P dynamics, little is known about the metabolic processes or taxonomic composition of the bacteria and fungi involved in the retention and transformation of P in wetlands, especially FFs. In a third study, I compare changes in microbial community composition in AL and BW FFs. Soil chemical properties reveal that total P (TP) concentrations were significantly higher in AL compared to BW soils, whereas total C (TC) was significantly higher in BW compared to AL FF soils. Similarly, the bacterial and fungal community composition was taxonomically different in AL compared BW FF soils. Detrended correspondence analyses of the microbial profiles and the subsequent fitting of environmental variables to ordination plots, revealed that TP and pH were associated with the composition of bacterial and fungal communities in AL soils, whereas, TC was strongly correlated with the microbial community profiles in BW FFs. These results indicate that differences in FF type (AL vs. BW) are associated with differences in soil TC, TP and pH, that are important predictors of microbial composition. My findings clearly indicate that FFs are indeed valuable ecosystems that have profound effects on the biogeochemical retention and transformation of excess P loadings carried with floodwaters, playing an important role in maintaining water quality in downstream aquatic ecosystems. It is forecasted that by 2025 as much as two-thirds (an estimated 5 out of the 8 billion people) of the world population will experience severe water scarcity due to climate change impacts and poor water quality resulting from the eutrophication of potable freshwater reservoirs. North America is likely to be impacted by these trends, and as such future policy decisions may be dependent on the prioritization of riparian wetlands (particularly FFs) based on their ecosystems functions and values. Despite their importance, in the southeastern US alone, bottomland hardwood forests (including FFs) continue to be lost at a rapid rate. This destruction of FF wetlands and their associated biogeochemical function is likely to add substantially to the eutrophication problem, and will continue to do so unless measures are taken to assess the sustainability of the ecosystem services they provide, and successfully replicate them through conservation, creation, and/or restoration of these wetland types. ii ACKNOWLEDGEMENTS I would like to express my gratitude to Dr. Mark R. Walbridge for his encouragement and support during the course of this dissertation. His editorial advice was essential to the completion of this document. I would also like to thank the members of my advisory committee; Dr. Richard B. Thomas, Dr. R. Kelman Wieder, Dr. Kevin C. Daly, Dr. William T. Peterjohn, and as well as Dr. Barbara J. Cade-Menun, for providing much-appreciated encouragement and support following Mark’s departure from WVU within a year of my studies. Over the years, I have been privileged to mentor several undergraduate students with research projects, and am especially indebted to the diligent efforts made by Neha A. Kumar, Joseph D. Lynch, John L. McClannahan, and Hasan Shahid. I would also like to acknowledge the faculty, administrative staff, and graduate students of our department, both past and present. Finally, I would like to thank my family and friends for their unconditional love, patience, and unyielding support, especially during some of the more difficult times over the course of this degree. iv TABLE OF CONTENTS ABSTRACT ii ACKNOWLEDGEMENTS iv TABLE OF CONTENTS v LIST OF FIGURES vii LIST OF TABLES x LIST OF APPENDICES xii Chapter 1 1 General Introduction 1 References 19 Chapter 2 37 Distribution of Phosphorus Forms during Spring Flooding Events in Alluvial and Blackwater Rivers and their Adjacent Floodplain Forests in the Southeastern US Abstract 38 Introduction 40 Methods 49 Results 52 Discussion 58 Conclusions 68 References 71 Chapter 3 108 32 3- Retention and Transformation of PO4 during Simulated Flooding of Floodplain Forest Soil Mesocosms Abstract 109 v Introduction 111 Methods 120 Results 126 Discussion 132 Conclusions 144 References 146 Chapter 4 184 Microbial Diversity and Function in Floodplain Forests of the Southeastern US Abstract 185 Introduction 187 Methods 198 Results 209 Discussion 214 Conclusions 229 References 231 Chapter 5 318 General Conclusions 318 References 324 Appendices 327 vi LIST OF FIGURES Figure 1.1: Biogeochemical transformation and retention of P in the sediment and the water column in floodplain forests (FFs) during flooding events. 35 Figure 2.1: