The Pennsylvania State University The Graduate School College of Engineering HYDROLOGIC CONTROLS OF NUTRIENT FLUXES IN GLACIAL MELTWATER STREAMS AT INTER-ANNUAL, SEASONAL, AND DAILY TIMESCALES IN THE MCMURDO DRY VALLEYS, ANTARCTICA A Thesis in Civil Engineering by Mitchell R. Weaver Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science May 2011 The thesis of Mitchell R. Weaver was reviewed and approved* by the following: Michael N. Gooseff Assistant Professor of Civil Engineering Thesis Advisor Christopher J. Duffy Professor of Civil Engineering Peggy A. Johnson Professor of Civil Engineering Head of the Department of Civil Engineering *Signatures are on file in the Graduate School iii ABSTRACT In the McMurdo Dry Valleys of Antarctica, glaciers are hydrologically linked to closed- basin lakes at the valley floor by glacial meltwater streams. Streams flow through porous, well- defined channels with extensive chemically active hyporheic zones. Temporally varying dynamics of meltwater generation and sub-stream thaw depth are thought to control the potential for the hyporheic zone and benthic communities to influence transport of nutrients and dissolved ions downstream. Using the McMurdo LTER database, patterns in stream discharge, electrical conductivity (both with 15-minute sampling intervals), and solute chemistry (weekly sampling intervals) were examined on eight MDV streams from 1990-2008. Discharge and electrical conductivity values were highly variable among streams. Discharge values were highly dependent upon glacial source area, but meteorological and topographical complexities create large variability at all time scales. The longer streams were found to have much higher electrical conductivity values than the shorter streams, suggesting that there are more opportunities for hyporheic weathering reactions along longer stream reaches. Weekly sampled water solutes from each stream‟s entire record were plotted against the discharge recorded at the time when the sample was taken. Silicate concentrations displayed a decreasing logarithmic relationship, while nutrient concentrations had no apparent relationship. This suggests that with the exception to bioreactive solutes, the majority of hyporheic interactions could possibly be characterized by electrical conductivity and discharge. To attain information on in-stream nutrient dynamics and nutrient fluxes, glacial source water at the upper reach of Green Creek and stream outlet water at the lower reach of Green Creek were sampled hourly for two separate diel periods during the 2008-09 austral summer. Both dates were in late January under two distinct flow conditions (~0.5 L/s and ~10 L/s). Under low flow conditions, nutrient cycling was found to be uptake dominated. High flow conditions showed both uptake and regeneration with much higher nutrient loads, but as in the low flow conditions, no apparent temporal trends were found. Nutrient concentrations could not be predicted using the two parameters of discharge and electrical conductivity with in-stream nutrient dynamics likely too complicated at the sub-daily scale. iv TABLE OF CONTENTS LIST OF FIGURES ................................................................................................................. v LIST OF TABLES ................................................................................................................... vi ACKNOWLEDGEMENTS ..................................................................................................... vii Chapter 1 Introduction to Study .............................................................................................. 1 1.1 McMurdo Dry Valley Background ............................................................................ 1 1.2 Hydrologic Cycle: a McMurdo Dry Valley Perspective ............................................ 5 1.2.1 Glaciers and Snowfields .................................................................................. 6 1.2.2 Streams ............................................................................................................ 7 1.2.3 Lakes ............................................................................................................... 7 1.3 Chemical Origin and Transport .................................................................................. 8 1.3.1 Chemical Weathering ...................................................................................... 8 1.3.2 Nutrient Cycling .............................................................................................. 10 1.4 Discharge and Solute Concentration Relationships ................................................... 10 1.5 Thesis Approach ........................................................................................................ 11 Chapter 2 Inter-annual Timescale ........................................................................................... 12 2.1 Site Selection .............................................................................................................. 13 2.2 Background ................................................................................................................ 17 2.3 Methods ...................................................................................................................... 17 2.3.1 Field Data Collection ...................................................................................... 17 2.3.2 Seasonal Summaries ........................................................................................ 18 2.3.3 Daily Probability of Flow and Mean Daily Statistics ...................................... 18 2.3.4 Flow/EC Duration Curves ............................................................................... 19 2.3.5 Chemistry Statistics ......................................................................................... 20 2.4 Results ....................................................................................................................... 21 2.4.1 Hydrology........................................................................................................ 21 2.4.1.1 Seasonal Summaries ............................................................................. 21 2.4.1.2 Probability of Flow ............................................................................... 24 2.4.1.3 Flow Duration Curves .......................................................................... 25 2.4.2 Electrical Conductivity .................................................................................... 31 2.4.3 Chemistty ........................................................................................................ 31 2.5 Discussion .................................................................................................................. 34 Chapter 3 Seasonal Timescale ................................................................................................ 36 3.1 Methods ...................................................................................................................... 37 3.1.1 Daily Statistics................................................................................................. 37 3.1.2 Discharge and Concentration Relationships with Time .................................. 37 3.1.3 Chemistry ........................................................................................................ 39 3.2 Results ........................................................................................................................ 39 3.3 Discussion .................................................................................................................. 46 v Chapter 4 Daily Timescale ...................................................................................................... 47 4.1 Methods ...................................................................................................................... 49 4.1.1 Experiment ...................................................................................................... 49 4.1.2 Quantifying Hyporheic Influence .................................................................... 50 4.1.3 Nutrients .......................................................................................................... 50 4.2 Results ........................................................................................................................ 54 4.2.1 Streamflow and Conductivity .......................................................................... 54 4.2.2 Hyporheic Influence ........................................................................................ 54 4.2.3 Hysteresis ........................................................................................................ 55 4.2.4 Nutrient Fluxes ................................................................................................ 55 4.2.5 Discharge and Nutrient Relationships ............................................................. 55 4.3 Discussion .................................................................................................................. 62 Chapter 5 Synthesis and Implications of Study ...................................................................... 64 References ................................................................................................................................ 67 vi LIST OF FIGURES Figure 1-1: Maps of the Antarctic continent