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The Pennsylvania State University the Graduate School College Of The Pennsylvania State University The Graduate School College of Agricultural Sciences BIOGEOCHEMICAL CYCLING OF NITROGEN THROUGH A LANDSCAPE RICH IN LEGACY SEDIMENTS A Thesis in Soil Science by Julie N. Weitzman © 2011 Julie N. Weitzman Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science May 2011 The thesis of Julie N. Weitzman was reviewed and approved* by the following: Jason P. Kaye Assistant Professor of Soil Biogeochemistry Thesis Adviser Michael N. Gooseff Assistant Professor of Civil Engineering Richard C. Stehouwer Associate Professor of Environmental Soil Science David M. Sylvia Professor of Soil Microbiology Head of the Department of Crop and Soil Sciences *Signatures are on file in the Graduate School. ii ABSTRACT Sedimentation rates, anoxic conditions, and eutrophication have all increased in the Chesapeake Bay since the time of European settlement. Legacy sediments, deposited during the historic, post-settlement period marked by deforestation, land clearing, and plowing of uplands and valley slopes, act as a significant non-point source of nitrogen to the Bay. At Big Spring Run in Lancaster, Pennsylvania, these legacy sediments now overlay a buried hydric soil, which affects the contemporary transfer of nitrogen from uplands to streams. Recent research suggests that nitrogen transfer to streams is also affected by soil drying and rewetting. Climate change models predict that the variability and magnitude of precipitation events will increase over time. Such changes could lead to extended periods of droughts, followed by increased precipitation. These dry-rewet cycles can alter the structure and activity of soil microbial communities, impacting nutrient retention and release. This project was undertaken to increase the understanding of nitrogen processing and movement in legacy sediments along a landscape gradient before and after soil drying. Short-term incubations were carried out on field-moist soil as well as on soil that was air- dried, then rewetted prior to incubation. Samples were from three landscape positions (non- legacy uplands, legacy zone, and stream bank) and three layers (top 20 cm, midlayer, and bottom layer) . Respiration rates, net ammonification rates, and net nitrification rates were determined in laboratory incubations. A community-level physiological profile and extracellular enzymes were assayed to determine microbial activity levels. Four key discoveries were found from this work: net nitrification was greatest in the surface soils away from the stream bank; drought induced nitrate pulses were unexpectedly absent; buried hydric soils appeared to have low iii biological activity and low nitrification potential; and the low activity in the buried layer may have been due to a lack of labile carbon. Given their prevalence in Pennsylvania there was a critical need to understand how nitrogen flows through legacy sediments to improve predictions and management of nitrogen transport from uplands to streams. Future measurements are needed to explore how different hydrological flowpaths impact microbial communities and contaminant pulses in, and between, soil layers, and how such interactions change after the removal of legacy sediments. My data suggest that flowpaths through the buried hydric layer will not have strong nitrogen immobilization, despite high C in that layer. iv TABLE OF CONTENTS List of Figures ............................................................................................................................. viii List of Tables ..................................................................................................................................x Acknowledgements ...................................................................................................................... xi CHAPTER 1. Introduction and Objectives .................................................................................1 Introduction ..........................................................................................................................1 Objectives ............................................................................................................................4 CHAPTER 2. Background ............................................................................................................6 Human Impacts on the Land and the Damming of Streams ................................................6 Dams, Ponds, and Reservoir Sediments ..................................................................6 Sediment Sources, Sinks, and Transport..................................................................8 Consequences of Dam Removal ..............................................................................8 Big Spring Run Study Site ...................................................................................................9 Geologic History of Legacy Sediment Deposition ..................................................9 Study Site: Geologic and Geographic Setting .......................................................11 Rationale and Significance ....................................................................................13 Nitrogen Cycling ................................................................................................................14 Biogeochemical Cycling of Nitrogen ....................................................................14 Denitrification in Riparian Zones and Wetlands ...................................................15 v Role of Microbes....................................................................................................17 - Nitrate (NO3 ) Flushing ..........................................................................................19 Eutrophication of the Chesapeake Bay ..................................................................21 Linking Nitrogen and Legacy Sediments ..............................................................22 CHAPTER 3. Materials and Methods .......................................................................................23 Study Site ...............................................................................................................23 Basic Soil Characteristics ......................................................................................23 Second Sampling ...................................................................................................26 Microbial Analyses ................................................................................................26 Statistical Analysis and Data Treatment ................................................................29 CHAPTER 4. Results ..................................................................................................................31 Soil Carbon and Nitrogen ......................................................................................31 Soil Ammonium and Nitrate ..................................................................................32 Potential Net Nitrification ......................................................................................33 Potential Net Ammonification ...............................................................................34 Potential C Mineralization .....................................................................................35 Community Level Physiological Profile ................................................................36 Extracellular Enzymatic Activity ...........................................................................38 Pulse Data Following Rewetting of a Dry Soil ......................................................39 Correlations ............................................................................................................42 vi CHAPTER 5. Discussion .............................................................................................................44 Surface Soils ..........................................................................................................46 Midlayer Soils ........................................................................................................46 Hydric Soils ...........................................................................................................47 External Controls on Nitrification .........................................................................49 CHAPTER 6. Conclusions ..........................................................................................................52 APPENDIX: Methods, Materials, and Analytical Techniques ...............................................56 LITERATURE CITED ...............................................................................................................89 vii LIST OF FIGURES Figure 3-1: GIS converted DEM map of Big Spring Run sampling sites taken in April 2010. Each dot and number grouping represents a core location. The dashed lines around the stream depict the estimated area over which legacy sediments were deposited. Any cores collected within the borders of the two dashed lines were classified as legacy zone soils. All cores taken outside the dashed lines, away from Big Spring Run, were classified as non-legacy upland soils. Stream bank samples were collected in September 2010 and made up the third classified landscape position – stream bank.. ................................................................................................24 Figure 4-1: Total soil carbon
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