Phosphorus Loss from Soil to Water in the Lee Catchment – a Spatial Analysis
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Department of Civil and Environmental Engineering University College Cork Phosphorus loss from soil to water in the Lee catchment – A spatial analysis By Julien Gillet A Thesis submitted for the Degree of Master of Engineering Science October 2006 Acknowledgements I would like to express my thanks to the following people: Prof. Gerard Kiely, my supervisor, for his guidance and his encouragement. Prof. J.P.J. O’Kane, for the use of the facilities of the Department of Civil and Environmental Engineering, UCC. Dr. Michael Creed, for his administrative support. Cecile Delolme, for help and encouragement to come to Ireland Mr Gerard Morgan , Mr Stuart Warner and Dr Xie Quishi of the Aquatic Services Unit for data collection and laboratory analysis as well as for their advices and suggestions. Paul Guero for his support and friendship all along this year. The students and staff of the Civil and Environmental Engineering Department, Anna Laine, Paul Leahy, Matteo Sottocornola, Ken Byrne, Anne Brune, Sylvia Palumbo, Micheal Fenton, James Eaton and Adrian Birkby for their help and friendship. ii Abstract In most fresh water systems, phosphorus is considered to be the key limiting nutrient and excessive introduction of phosphorus into surface waters is likely to lead to eutrophication. In Ireland, where eutrophication is the main threat in terms of water quality, it is believed that over 70% of phosphorus reaching inland waters emanates from agricultural sources. With the improved control of farmyard losses, most of the phosphorus is now considered to originate from diffuse field sources. The River Lee catchment, 1135 km² in area, was monitored through a network of 56 stream water quality sites that were sampled 8 times over 2 years, during base and storm flow conditions. The 56 subcatchments draining to the sampling sites are representative of different land uses, different soil types and different climate conditions occurring in the catchment. In this mostly rural study area, land is almost entirely dedicated to agriculture and natural areas. This ensured that most of the phosphorus was coming from diffuse sources and not from point sources. A large part of the work consisted in collecting and processing the data describing the study area: land use, agricultural management practices, soil type and precipitation. Intense use of GIS tools was made at this stage to extract and manage the information. Great attention was given to explain the sources and the transformations applied to these data. A lack of available data is actually often reported when dealing with phosphorus loss studies at such a large scale. To investigate the relationships between the different variables and the SRP concentrations in the rivers, simple and multiple regression analyses were carried out. The proportion of land dedicated to agriculture was identified to be the best predictor of the log-transformed Soluble Reactive Phosphorus (SRP) concentrations during storm flow (R²=0.89). Phosphorus losses also appear to increase with stocking density, fertiliser P and Soil P levels. In terms of land use, cultivated land is the main contributor to the P transfers followed by grassland. In contrast, phosphorus levels appeared to decrease with the increasing proportion of forestry and peat land. Réalta, the Irish phosphorus model, was also used and evaluated for the Lee catchment. iii Table of Contents Acknowledgements....................................................................................................................ii Abstract.....................................................................................................................................iii Table of Contents ..................................................................................................................... iv Chapter 1 Introduction ............................................................................................................1 1.1 Definition of Problem...................................................................................................2 1.2 Background: phosphorus basics.................................................................................3 1.2.1 The Phosphorus Cycle..........................................................................................4 1.2.2 Phosphorus in soil ................................................................................................5 1.2.3 Phosphorus in water .............................................................................................6 1.3 Literature Review: P loss to water .............................................................................7 1.4 Phosphorus: Policy context .........................................................................................9 1.5 Previous research projects ........................................................................................10 1.6 Objectives and Methodology.....................................................................................11 1.7 Layout of the thesis ....................................................................................................11 Chapter 2 Study Area Description.........................................................................................12 2.1 Catchment location ....................................................................................................13 2.2 Catchment description...............................................................................................13 2.2.1 Topography ........................................................................................................13 2.2.2 Climate ...............................................................................................................14 2.2.3 Soil .....................................................................................................................16 2.2.4 Land Use ............................................................................................................17 2.3 River System...............................................................................................................19 2.4 Sampling Sites ............................................................................................................19 2.5 General Water Quality ..............................................................................................23 2.6 Environmental Pressures ..........................................................................................26 2.6.1 Point Sources......................................................................................................26 2.6.2 Diffuse Sources ..................................................................................................29 Chapter 3 Data Presentation .................................................................................................30 3.1 GIS Background.........................................................................................................31 3.1.1 Basic concepts....................................................................................................31 iv 3.1.2 Methods..............................................................................................................32 3.2 DATA 1- Catchment’s characteristics .....................................................................33 3.2.1 Land Cover.........................................................................................................33 3.2.1.1 Presentation of CORINE database ............................................................33 3.2.1.2 Classes.......................................................................................................33 3.2.1.3 Data processing .........................................................................................35 3.2.2 Soil & Subsoil ....................................................................................................37 3.2.2.1 Soil.............................................................................................................37 3.2.2.2 Subsoil.......................................................................................................38 3.2.2.3 Data ...........................................................................................................39 3.2.3 Slope...................................................................................................................41 3.3 DATA 2- Agriculture.................................................................................................42 3.3.1 Census of Agriculture ........................................................................................42 3.3.2 Livestock............................................................................................................42 3.3.3 Fertiliser .............................................................................................................44 3.4 DATA 3- Hydrology...................................................................................................48 3.4.1 Flow....................................................................................................................48 3.4.2 Precipitation .......................................................................................................51 3.4.2.1 Rain gauges data........................................................................................51 3.4.2.2 Radar data..................................................................................................52