Evaluating relationships between sediment chemistry and anoxic phosphorus and iron release across three different water bodies

Abstract

This study evaluated phosphorus (P) and iron (Fe) release from anoxic sediment cores in 3 different water bodies, Lake Winnipeg in Manitoba and Lake Simcoe and Hamilton Harbour in Ontario, and developed empirical models to predict P and Fe release rates as functions of sediment and water chemistry. Maximum P and Fe sediment release rates, which occurred shortly after sulfate (SO4) was depleted in most cores, showed unique positive linear relationships for each lake. High P release rates only occurred from Lake Simcoe and Lake Winnipeg sediments with molar ratios =8.1 of NaOH-extractable aluminum (Al) to reducible Fe (Fe extractable with bicarbonate-dithionite [BD]). High Fe release rates only occurred in Lake Winnipeg sediments, perhaps due to low SO4 reduction rates (<115 mg m-2 d-1). Three approaches were used to develop linear regression models for maximum P and Fe release rates using data from all lakes: only Lake Winnipeg, only Lake Simcoe, and low (=8.1) and high molar ratios (>20) of NaOH-extractable Al to BD-extractable Fe. Regression models differed depending on the study sites used, and only 3 of the 5 significant regression models for P release had high predictive value (R2 > 0.7). Four of the 5 significant Fe release models had R2 > 0.7, but we were unable to find a significant Fe model for Lake Simcoe. These results are important because they delineate the limitations of this approach to modeling release using operationally defined fractions.