Predictions Concerning Internal Phosphorus Release in Cootes Paradise Marsh and Implications for Restoration

Abstract

To assess the relative contribution of phosphorus release from sediment in Cootes Paradise Marsh, I first examined spatial and temporal variability of laboratory-measured release rates from sediment samples collected from 12 sites within the wetland (Chapter 1 ). The microbial communities from these 12 sites were characterized on the basis of sole-carbon-source utilization using BIOLOG GN plates containing 95 substrates. Results from these experiments were entered into a principal component analysis and the release rates for all sites were regressed against corresponding PC 1 and PC2 scores (Chapter 2). Differences in microbial physiology as defined by PC 1 and PC2 scores accounted for 49% and 53%, respectively of the variation in phosphorus release rates. Using stepwise multiple regression, I concluded that the key determinants of laboratory-derived release rates from West Pond sediment (a highly eutrophic site within Cootes Paradise Marsh) are oxic state, ambient temperature and time of sediment collection (Chapter 3). Using this information I developed a multivariate model to predict release rates. This model, along with 2 alternative approaches, was used to estimate the extent of internal loading (kg d-1) in Cootes Paradise Marsh (Chapter 4). Method 1 was a highly controlled, static approach and resulted in an internal load of 11 .6 kg d-1, which was attributed to diffusion. The remaining two methods were more dynamic in nature as they took into account temporal variation, ambient temperature and the development of anoxia. Using Method 2, I estimated an internal load of 7.8 to 8.5 kgd-1, which was based on empirically-derived laboratory release rates. Method 3 consisted of the predictive model from which I estimated an internal load of 6.7 kgd-1• I attributed the release from the latter two methods to microbial mineralization processes. Based on this work and a previous estimate of internal loading in Cootes Paradise Marsh (Prescott & Tsanis 1997), I concluded that mineralization accounts for 22.3% of total phosphorus loading to the system, preceded only by urban runoff ( 41% ).