Soil Carbon Dynamics in the Upper Mersey Estuarine Floodplain, Northwest England: Implications for Soil Carbon Sequestration Osim Ogar Enya Ecosystems and Environment Research Centre School of Science, Engineering and Environment University of Salford, Manchester M5 4WT Submitted in Partial Fulfilment of the Requirements of the Degree of Doctor of Philosophy July, 2019 Contents List of Figures ............................................................................................................................ vi List of Tables .............................................................................................................................. x Acknowledgements ................................................................................................................. xiii Abstract ................................................................................................................................... xiv 1. Introduction ...................................................................................................................... 15 1.1 Background and significance ..................................................................................... 15 1.2 Research gap ............................................................................................................. 17 1.3 Research aim and objectives ..................................................................................... 18 1.4 Thesis structure ......................................................................................................... 18 2. Literature Review ............................................................................................................. 20 2.1 Soil carbon dynamics ................................................................................................. 20 2.1.1 Factors affecting soil carbon dynamics .............................................................. 20 2.1.1.1 Topographic position ............................................................................................ 21 2.1.1.2 Seasonal variation ................................................................................................ 21 2.1.1.4 Land use/land cover .......................................................................................... 22 2.1.1.5 Environmental factors........................................................................................ 24 2.2 Soil organic matter distribution ................................................................................ 25 2.2.1 Transformation of soil organic matter ............................................................... 27 2.3 Soil carbon sequestration ......................................................................................... 28 2.4 Effects of chemistry and contamination ................................................................... 29 2.4.1 Inorganic contaminants ..................................................................................... 30 2.4.2 Heavy metal and organic matter complex formation ....................................... 31 2.5 Cycles of soil .............................................................................................................. 32 2.5.1 Carbon cycle ....................................................................................................... 33 2.6 Microbial biodiversity ............................................................................................... 34 2.7 Types of Estuarine floodplains .................................................................................. 36 2.7.1 Vegetation types within estuarine floodplains .................................................. 37 3. Materials and Methods .................................................................................................. 40 3.1 Introduction to the chapter ...................................................................................... 40 3.2 Selection of study area ................................................................................................... 40 3.3 The Upper Mersey Estuary ............................................................................................. 41 ii 3.3.1 Study site description .............................................................................................. 41 3.3.2 Contamination history of Mersey Estuary ......................................................... 46 3.4 Overview of data collection and analysis .................................................................. 51 3.5 Laboratory experimental design ............................................................................... 54 4. Heavy Metal Contamination Status in Soil-plant System in the Upper Mersey Estuarine Floodplain ................................................................................................................................ 55 4.1 Introduction to the chapter ...................................................................................... 55 4.2 Material and methods ............................................................................................... 55 4.2.1 Field sampling ................................................................................................... 57 4.2.2 Sample preparation .......................................................................................... 58 4.2.3 Laboratory analysis ........................................................................................... 59 4.2.3.1 Soil pH, redox potential (Eh), and electrical conductivity (EC) .......................... 59 4.2.3.2 Soil organic matter determination .................................................................... 59 4.2.3.3 Heavy metal determination by H2O extraction ................................................. 59 4.2.3.4 Heavy metal determination by 1 M HNO3 extraction ....................................... 59 4.2.3.5 Heavy metal determination by 1 M NH4Cl extraction ....................................... 60 4.2.3.6 Metals and metalloids in soils using microwave digestion ............................... 60 4.2.3.7 Heavy metals in plant tissues using microwave digestion ................................ 60 4.2.3.8 XRF method ........................................................................................................ 61 4.3 Statistical analysis/metal uptake calculation ............................................................ 61 4.4 Results ....................................................................................................................... 61 4.4.1 Soil pH, redox potential (Eh) and electrical conductivity (EC) .......................... 61 4.4.2 Bulk density ....................................................................................................... 63 4.4.3 Soil organic carbon (SOC) content .................................................................... 64 4.4.4 Heavy metal concentrations in soil ................................................................... 67 4.4.5 Percentage distribution of heavy metal distribution across the different land uses/land covers ............................................................................................................... 79 4.4.6 Heavy metal concentrations in plants and their uptake .................................. 80 4.4.7 Multivariate analysis showing interaction effects among selected parameters .. 85 4.5 Discussion .................................................................................................................. 89 4.5.1 Differences in soil pH, redox potential, electrical conductivity, and soil organic carbon across the study area ........................................................................................... 89 iii 4.5.2 Heavy metal concentrations in soil under the field condition .......................... 91 4.5.3 Heavy metal concentration in plant tissue ........................................................ 94 5. Variations in Soil Organic Carbon Storage ........................................................................ 98 5.1 Introduction to the chapter ...................................................................................... 98 5.2 Material and methods ............................................................................................... 99 5.2.1 Field monitoring ............................................................................................... 100 5.2.2 Sample preparation ........................................................................................ 101 5.2.3 Laboratory analysis ......................................................................................... 102 5.2.3.1 Bulk density ...................................................................................................... 102 5.2.3.2 Particle size distribution................................................................................... 102 5.2.3.3 Soil pH, Eh and EC ............................................................................................ 103 5.2.3.4 Soil organic carbon determination .................................................................. 104 5.3 Statistical analysis ................................................................................................ 104 5.4 Results ..................................................................................................................... 105 5.4.1 Soil morphological characteristic of Widnes Warth