EXCHANGE OF PHOSPHORUS FROM SHALLOW SEDIMENTS AT 9 ALBERTA LAKES

Potential exchange of P between sediments and lakewater and particulate sediments and porewater was evaluated in nine eutrophic lakes in Alberta. Lakewater above the sediments, porewater, and sediments were collected from shallow depths during May to August 1986. Lakewater soluble-reactive P concentrations ([SRP]) were positively correlated with porewater [SRP] (p < 0.01) and negatively with the Fe/P molar ratio in porewater (p < 0.001). Potential release of SRP from sediments to lakewater (by molecular diffusion) was positively correlated with particulate P fractions that are known to exchange P with water (p < 0.01). In porewater, [SRP] was positively correlated with Fe2+ concentration and weakly correlated with pH (p < 0.001 and 0.05, respictively). These results indicate (i) potential transport of P from sediments to lakewater when Fe is not abundant, (ii) common sources and similar mobilities of Fe and P, and (iii) importance of pH in regulation of P exchange between particulate sediments and porewater. No significant relationships (p > 0.05) were found between porewater [SRP] and pariculate P fractions. In this study, correlation coefficients were generally low, which suggests (i) the chemical fractionation of particulate sediments failed to isolate the exchangeable P fraction and (ii) partitioning of P within sediments and the release of P from sediments to lakewater are complex processes, only partially regulated by pH and Fe2+ in porewater. To gain better understanding of P release from shallow sediments, future studies should include possible interactions between P and redox potential, Al, Mn, Ca, and S.