Statistical analysis of freshwater parameters monitored at different temporal resolutions

HA Statistics;GE Environmental Sciences

Mohamad Hamzah, Firdaus ; Scott, Marian E.

University:University of Glasgow

Department:School of Mathematics and Statistics

关键词: Statistical Analysis, Environmental Parameters, Temporal Resolutions;   

Others  :  http://theses.gla.ac.uk/3350/1/2012hamzahphd.pdf

来源: University of Glasgow

【 摘 要 】

Nowadays, it is of great importancein ecological and environmental studies to investigate some prominent features in environmental determinants using appropriate statistical approaches. The initial motivation of this work was provided by the enthusiasm of the limnologist, biologist and statistician, interested in exploring and investigating certain features of time series data at different temporal resolutions to environmental parameters in freshwater. This thesis introduces a variety of statistical techniques which are used to provide sufficient information on the features of interest in the environmental variables in freshwater. Chapter 1 gives the background of the work, explores the details of the locations of the case studies, presents several statistical and ecological issues and outlines the aims and objectives of the thesis. Chapter 2 provides a review of some commonly usedstatistical modelling approaches to model trend and seasonality. All the modelling approaches are then applied tolow temporal resolution (monthly data) of temperature and chlorophyll measurements from 1987-2005 for the north and south basins of Loch Lomond, Scotland. An investigation into the influence of temperature and nutrients onthe variability of log chlorophyll is also carried out. Chapter 3 extendsthe modelling for temperature in Chapter 2with the use of a mixed-effects model with different error structures for temperature data at a moderate temporal resolution (1 and 3 hourly data) in the north, mid and south basins. Three approaches are proposed to estimate the positions of a sharp change in gradient of temperature (thermocline) in deeper basins,using the maximum relative rate of change, changepoint regression and derivatives of a smooth curve. Chapter 4 investigates several features in semi-continuous environmental variables (15 and 30 minutes data). The temporal pattern of temperature, pH, conductivity and barometric pressure, and the evidence of similarity of the signals of pH and conductivity is determined, using wavelets. The time taken for pH and conductivity to return to `baseline levels' (recovery period) followingextreme discharge is determined for different thresholds of `extreme discharge' for the Rivers Charr and Drumtee Burn, Scotland and models for the recovery period are proposed and fitted. Model validation is carried out for the River Charr and the occurrence of clusters of extreme discharge for both rivers is investigated using the extremal index. Chapter 5 summarises the main findings within this thesis and several potential areas for future work are suggested.