Effect of sediment geochemistry on the nutrient release rates in Cootes Paradise Marsh, Ontario, Canada

Although there has been reduction in nutrient loadings from external sources, high nutrient levels and a prolific algal growth remain major stresses, affecting the water quality in Cootes Paradise, a coastal wetland at the western tip of Lake Ontario. It has been documented that internal loading, resulting from sediment P release, may be a significant contributor of the total P input to some lakes. To assess the importance of internal loadings from sediments to Cootes Paradise, nutrient fluxes from sediments at three locations were estimated. The investigated sites were representative of different sedimentary environments, including sites receiving effluents from a sewage treatment plant and combined sewer overflows. An unaffected site in the main body of the marsh was included for comparison. The results derived from the Fickian diffusion model indicate that sites receiving outfalls from the sewage treatment plant and combined sewer overflow had the highest nutrient fluxes. These two sites had also the highest ammonia-nitrogen fluxes. The lowest flux was estimated at the unimpacted site located in the main body of Cootes Paradise. The differences in nutrient fluxes appear to be attributable to spatial heterogeneity of bottom sediments. Sites which had the highest sediment phosphorus concentrations had the steepest porewater nutrient gradients and the highest fluxes. The results suggest that sediment phosphorus geochemistry is important in regulating the phosphorus concentrations in porewater, which consequently, governs the phosphorus fluxes from sediments. The data suggest that sediment may be an important source of nutrients in areas containing nutrient contaminated sediments and release of nutrients from these sediments may delay the recovery of the marsh even after the reduction of the external phosphorus loading.

Keywords:

• coastal wetlands
• sediments
• nutrient fluxes
• phosphorus
• internal loadings
• porewater

Acknowledgments

The authors gratefully acknowledge the dedicated assistance of Aaron Lawrence and the capable field assistance of Mike Mawhinney and Ken Hill. The field equipment was prepared and calibrated by Sergio Krickler and Bob Rowsell. The efforts of Graphic Arts Unit in production of final figures and the logistical support of the Royal Botanical Gardens staff, namely, Tÿs Theÿsmeÿer is greatly appreciated. Professor Peter Lee of the Lakehead University in Thunder Bay kindly shared the information with us and provided access to sediment data. We also thank Scott Brown, Jim Maguire and the anonymous reviewers for valuable comments and constructive criticism. The financial support of the Regional Municipality of Hamilton Wentworth is greatly appreciated.

Notes

^*Depth and temperature were measured only at the time of peeper retrieval; Conductivity and pH are means from two sampling events (peeper deployment and retrieval).

^*Peeper deployment.

^**Peeper retrieval.