Nitrogen and Sulphur biogeochemistry in a High Arctic glacial watershed: an investigation with isotopic tracers and solute chemistry Arif Husain Ansari Department of Geography The University of Sheffield June 2012 Thesis submitted for the degree of Doctor of Philosophy Table of Contents Nitrogen and Sulphur biogeochemistry in a High Arctic glacial watershed: an investigation with isotopic tracers and solute chemistry ................................................................................... i Acknowledgements ....................................................................................................................................... 2 CHAPATER 1: INTRODUCTION .............................................................................................................. 3 1.1 Significance of this study ...................................................................................................... 3 1.2 Aim of the study .................................................................................................................... 4 1.3 Thesis outline ........................................................................................................................ 6 CHAPTER 2: NITROGEN AND SULPHUR BIOGEOCHEMICAL CYCLING IN HIGH ARCTIC: A REVIEW ....................................................................................................................................................... 7 2.1 Nitrogen Biogeochemistry .................................................................................................... 7 2.1.1 Introduction ................................................................................................................................. 7 2.1.2 Source of fixed nitrogen to the Arctic .......................................................................................... 9 2.1.2.1 Atmospheric input ..................................................................................................................... 9 2.1.2.1.1 Stratospheric input ............................................................................................................... 10 2.1.2.1.2 Tropospheric input ............................................................................................................... 12 2.1.2.2 Geological nitrogen ................................................................................................................. 13 2.2 Sulphur Biogeochemistry .................................................................................................... 16 2.2.1 Introduction ................................................................................................................................ 16 2.2.2 Source of sulphur in the Arctic .................................................................................................. 17 2.2.2.1 Atmospheric input ................................................................................................................... 17 2.2.2.1.1 Biogenic ............................................................................................................................... 17 2.2.2.1.2 Volcanic emission, sea spray and dust ................................................................................. 18 2.2.2.1.3 Anthropogenic ...................................................................................................................... 18 2.2.2.2 Geological sulphur .................................................................................................................. 19 2.3 Deposition of atmospheric nitrogen and sulphur ................................................................ 19 2.4 Post-deposition processes .................................................................................................... 22 2.5 Snow and supraglacial ice biogeochemistry ....................................................................... 24 2.6 Subglacial and Proglacial runoff biogeochemistry ............................................................. 26 2.7 Stable isotopes in biogeochemical studies .......................................................................... 30 Page | i 2.7.1 Stable isotope composition of major N and S sources in High Arctic ....................................... 31 2.7.2 Fractionation .............................................................................................................................. 34 2.7.2.1 Kinetic fractionation ............................................................................................................... 35 2.7.2.2 Equilibrium fractionation ........................................................................................................ 35 2.8 Nitrogen based biological processes responsible for isotopic fractionation ....................... 35 2.8.1 Nitrogen fixation ........................................................................................................................ 35 2.8.2 Assimilation ............................................................................................................................... 36 2.8.3 Mineralisation and Nitrification ................................................................................................. 36 2.8.4 Denitrification ............................................................................................................................ 38 2.8.5 Dissimilatory nitrate reduction to ammonia (DNRA) ................................................................ 38 2.8.6 Anammox ................................................................................................................................... 39 2.9 Sulphur based biological processes responsible for isotopic alterations........................... 39 2.9.1 Sulphide oxidation ..................................................................................................................... 39 2.9.2 Sulphate reduction...................................................................................................................... 40 CHAPTER 3: FIELD SITE AND METHODOLOGY ............................................................................... 41 3.1 Svalbard climate and its importance in research context .................................................... 41 3.2 Field Site: Glacier Midtre Lovénbreen................................................................................ 45 3.2.1 Geology ...................................................................................................................................... 47 3.2.2 Ecology ....................................................................................................................................... 49 3.2.3 Glacier structure ......................................................................................................................... 51 3.2.4 Mass Balance ............................................................................................................................. 52 3.2.5 Hydrology .................................................................................................................................. 53 3.3 Sampling.............................................................................................................................. 54 3.3.1 Sampling sites and sampling frequency ..................................................................................... 54 3.3.2 Winter deposition sampling ....................................................................................................... 57 3.3.3 Summer stream sampling ........................................................................................................... 57 3.3.4 Sample preservation ................................................................................................................... 57 3.3.5 Real time stream monitoring ...................................................................................................... 58 3.4 Chemical analysis ................................................................................................................ 60 3.4.1 Dissolved Organic Carbon (DOC) ................................................................................................ 60 3.4.2 Total dissolved nitrogen (TDN) and dissolved organic nitrogen (DON) by Thermalox analyser ............................................................................................................................................................ 61 Page | ii 3.4.3 Dissolved organic nitrogen (DON) by persulphate oxidation metheod ..................................... 62 3.4.4 Major ions .................................................................................................................................. 63 3.4.5 Dissolved silicate (SiO2) ..................................................................................................... 64 3.5 Analysis of stable isotopic tracers ....................................................................................... 65 15 18 3.5.1 Denitrifier method for δ N-NO3 and δ O-NO3 analysis using GC-IRMS ............................... 65 34 18 3.5.2 δ S-SO4 and δ O-SO4 analysis ................................................................................................. 65 18 3.5.3 δ O-H2O Analysis ..................................................................................................................... 66 3.6 Rock dissolution experiments