Characterization of sedimentary phosphorus in Lake Erie and on-site quantification of internal phosphorus loading
Citation
Wang, Y.T., Zhang, T.Q., Zhao, Y.C., Ciborowski, J.H.H., Zhao, Y.M., O'Halloran, I.P., Qi, Z.M., Tan, C.S. (2021). Characterization of sedimentary phosphorus in Lake Erie and on-site quantification of internal phosphorus loading. Water Research, [online] 188 http://dx.doi.org/10.1016/j.watres.2020.116525
Plain language summary
Harmful algal blooms and hypoxia are two environmental problems that negatively impact Lake Erie socioeconomically and ecologically. Harmful algal blooms are fueled by excess phosphorus in the lake which has predominantly come from non-point sources such as agricultural runoff (i.e. external phosphorus loading). Despite effort to minimize external phosphorus loading, harmful algal blooms have increased in intensity and frequency in the last 25 years. It has been proposed that sediments in Lake Erie serve as a major reservoir of phosphorus, and so, internal phosphorus loading may be contributing to the total quantity of phosphorus delivered to the lake. Little is known about internal loading of phosphorus from sediments, which makes assessing the efficacy of current water quality mitigation and conservation measures challenging. Accordingly, this paper set out to fill the knowledge gap on sedimentary phosphorus as well as to quantify the forms of sedimentary phosphorus in Lake Erie with respect to their availability for algal growth in Lake Erie. According to the results of this paper, sedimentary phosphorus in Lake Erie may be causing and maintaining harmful algal blooms and hypoxia in the central basin and delaying the recovery of water quality despite the external phosphorus reduction measures in place. This study confirmed that sedimentary phosphorus, and its associated biogeochemical cycling, plays an important role in phosphorus release into the overlying water contributing to the eutrophic status of lakes.
Abstract
Lake Erie harmful algal blooms and hypoxia are two major environmental problems, and have severe impacts on human health, aquatic ecosystems, and the economy. However, little is known about internal loading of phosphorus (P) from sediments, which pose a challenge for assessing the efficacy of current conservation measures on the improvement of lake water quality. A modified Hedley's extraction procedure was employed to analyze representative sediment samples collected from the Lake Erie basin for assessing sedimentary P stock, potential availability for release into lake water, and internal P loading. Inorganic and organic P in the sediments were characterized by sequential extractions in H2O, 0.5 M NaHCO3, 0.1 M NaOH, and 1.0 M HCl, respectively. In the 0 – 10 cm sediment, total P stock was 172, 191, and 170 metric tons km−2 in the western, central, and eastern basins, respectively. Sedimentary P seems unlikely to contribute to internal P loading in the western basin, while in the eastern basin it can potentially contribute to an internal loading of 359 metric tons P yr−1. In the central basin, 41% of organic P, 15% of non-HCl extractable inorganic P, and 9.7% of residual P in the 0 – 10 cm sediment is potentially available for release into lake water; in the 10 – 20 cm sediment, organic P extracted by NaHCO3 and NaOH is also partially available. The central basin potentially contributes to internal P loading at a total amount of 10,599 metric tons yr−1. Internal P loading may not contribute to HABs in the western basin, but it can cause and maintain hypoxia in the central basin and delay the recovery of lake water quality for a lengthy time period in response to external P reduction measures.