Surface-subsurface hydrologic exchange and nutrient dynamics in the hyporheic zone of the Tanana River Item Type Thesis Authors Clilverd, Hannah M. Download date 25/09/2021 20:38:49 Link to Item http://hdl.handle.net/11122/5557 SURFACE-SUBSURFACE HYDROLOGIC EXCHANGE AND NITROGEN DYNAMICS IN THE HYPORHEIC ZONE OF THE TANANA RIVER SURFACE-SUBSURFACE HYDROLOGIC EXCHANGE AND NUTRIENT DYNAMICS IN THE HYPORHEIC ZONE OF THE TANANA RIVER A THESIS Presented to the Faculty of the University of Alaska Fairbanks in Partial Fulfillment of the Requirements for the Degree o f MASTER OF SCIENCE By Hannah M. Clilverd, B.Sc. Fairbanks, Alaska RASMUSQN U H tM T UNIVERSITY OF ALASKA FAIRBANKS ABSTRACT The aquatic-terrestrial interface is an active site of biogeochemical transformation, regulating the flux of nutrients between ecosystems. I addressed the hydrologic controls on nitrogen biogeochemistry in the hyporheic zone of a glacially fed riyer. I measured hyporheic concentrations of solutes and gases along subsurface flowpaths on two islands. Denitrification was quantified using an in situ 6 15N 0 3 ‘ push-pull technique. Nitrate concentration was consistently greater in river than in hyporheic water. Denitrification ranged from 1.9 - 29.4 mgN kg sediment' 1 day'1. Hotspots of methane partial pressure, averaging 50,000 ppmv, were found in densely vegetated areas with low oxygen concentration (< 0.5 mg0 2 L'1). Hyporheic flow was an important source of nitrogen to microbes and vegetation, transporting on average 0.41 gNCV-N m"2 day "1 through surface sediments. Results suggest that denitrification is a major sink for river nitrate in boreal forest floodplain soils, particularly at the river-sediment interface. The stability of the river hydrograph is a key factor regulating anaerobic metabolism in the hyporheic zone. iv TABLE OF CONTENTS PAGE SIGNATURE PAGE.....................................................................................................................i TITLE PAGE.................................................................................................................................ii ABSTRACT..................................................................................................................................iii TABLE OF CONTENTS............................................................................................................iv LIST OF FIGURES.....................................................................................................................vi LIST OF TABLES.................................................................................................................... viii PREFACE.....................................................................................................................................ix CHAPTER 1: INTRODUCTION............................................................................................1 The hyporheic zone ...................................................................................................................1 Biogeochemical transformations along hyporheic flowpaths.............................................2 Nitrogen supply in riparian zones................... 5 Hydrology and biogeochemistry of the Tanana River at Bonanza Creek LTER 6 Literature cited........................................................................................................................ 10 CHAPTER 2: SURFACE-SUBSURFACE HYDROLOGIC EXCHANGE AND NUTRIENT DYNAMICS IN THE HYPORHEIC ZONE OF THE TANANA RIVER IN INTERIOR ALASKA.........................................................................................23 ABSTRACT............................................................................................................................ 23 INTRODUCTION................................................................................................................. 24 METHODS..............................................................................................................................25 Study site..............................................................................................................................25 V Study design........................................................................................................................ 27 Sampling and analytical techniques................................................................................27 In situ denitrification..........................................................................................................29 Push-pull calculations.......................................................................................................31 Data analysis......................................................................................................................32 Analysis of subsurface hydrology and capillary..................................................... rise 33 Long term patterns in climate and river hydrology.......................................................34 RESULTS................................................................................................................................35 Climate and river hydrology.............................................................................................35 Spatial patterns in hyporheic chemistry......................................................................... 35 Subsurface hydrology and nitrogen losses.....................................................................37 Temporal variation in hyporheic chemistry....................................................................38 DISCUSSION......................................................................................................................... 39 Hyporheic zone hydrology and nitrogen transformation.............................................39 Subsurface methane and carbon dioxide........................................................................ 41 Climate, river hydrology and hyporheic chemistry.......................................................42 ACKNOWLEDGEMENTS.................................................................................................. 4 3 LITERATURE CITED..........................................................................................................44 CHAPTER 3: CONCLUSIONS............................................................................................65 Literature cited........................................................................................................................ 6 6 LIST OF FIGURES PAGE CHAPTER 1: FIGURE. 1. Conceptual model of the groundwater-surface water interface from Triska etal. (1989)............................................................................................................................. 18 FIGURE. 2 . Conceptual model of metabolic processes along subsurface flowpaths.... 19 FIGURE. 3. Predicted thermodynamic equilibrium proportions of electron donors and acceptors as a function of the pH and oxygen activity (log a O2) at 15°C.......................20 FIGURE. 4. Stages of primary succession on the Tanana River floodplain in interior Alaska....................................................................................................................................... 21 FIGURE. 5. Temporal variation in Fairbanks, Alaska mean temperature and precipitation from 1930 - 2005 (panel a) and Tanana River discharge for the long term mean 1973 - 2005 (panel b)................................................................................................... 22 CHAPTER 2: FIGURE. 1. Diagram of the in situ push-pull 6 15N0 3 ~ technique..................................... 53 FIGURE. 2. Example data of the production of groundwater dilution corrected 15N2 0 and 15N2 during the incubation period using the in situ push-pull technique..................54 FIGURE. 3. Cubic regression between mean daily air temperature and mean daily river discharge from 1973 - 2005.................................................................................................. 5 5 FIGURE. 4. Longitudinal patterns of oxygen (panel a) and nitrate (panels b and c) concentrations at Island I and Island II.................................................................................56 FIGURE. 5. Longitudinal patterns in the partial pressure of carbon dioxide (panel a) and methane (panel b) at Island I and Island II....................................................................57 FIGURE. 6 . Concentrations of hyporheic oxygen and dissolved organic carbon (mean± SE; panel a), and indices of hyporheic anaerobiosis (CELiiCC^; mean ± SE ).................58 FIGURE. 7. Location of hyporheic wells ( • ) at Island II on the Tanana River 59 FIGURE. 8 . Relationship between mean water table height and mean daily river stage. 60 FIGURE. 9. Denitrification rates in hyporheic sediment.................................................. 61 FIGURE. 10. Temporal variations in hyporheic nitrate concentration (mean ± SE; panel a) and methane partial pressure (mean ± SE; panel b)........................................................62 FIGURE. 11. Predicted mean number of days from 1993 - 2005 that the water table was above the mean rooting zone (0.75m depth) for willow .............................................63 FIGURE. 12. Comparison of the calcium and magnesium concentrations in river water, hyporheic water along the well transects, and hyporheic water in the willow-alder transitional w ells......................................................................................................................64