Internal phosphorus loading in a small shallow Lake: Response after sediment removal

Mina Kiani; Priit Tammeorg; Juha Niemistö; Asko Simojoki; Olga Tammeorg

doi:10.1016/j.scitotenv.2020.138279

Internal phosphorus loading in a small shallow Lake: Response after sediment removal

Sci Total Environ. 2020 Jul 10:725:138279. doi: 10.1016/j.scitotenv.2020.138279. Epub 2020 Mar 27.

Authors

Mina Kiani¹, Priit Tammeorg², Juha Niemistö³, Asko Simojoki², Olga Tammeorg⁴

Affiliations

¹ Department of Agricultural Sciences, University of Helsinki, Helsinki, Finland. Electronic address: mina.kiani@helsinki.fi.
² Department of Agricultural Sciences, University of Helsinki, Helsinki, Finland.
³ Ecosystems and Environment Research Programme, University of Helsinki, Helsinki, Finland.
⁴ Ecosystems and Environment Research Programme, University of Helsinki, Helsinki, Finland; Centre for Limnology, Estonian University of Life Sciences, 61117 Rannu, Tartumaa, Estonia.

PMID: 32305643
DOI: 10.1016/j.scitotenv.2020.138279

Abstract

Mankind is taking advantage of numerous services by small shallow lakes such as drinking water supply, irrigation, and recreational function; however, many of these lakes suffer from eutrophication. Given the key role of phosphorus (P) in eutrophication process, one of the effective restoration methods especially for small shallow lakes is removal of sediments enriched with nutrients. In our study, we used interannual, seasonal, and spatial data to examine the changes in sediment P mobility after removal of sediments in 2016 from a 1-ha highly eutrophic lake. We measured the sediment redox potential, analyzed soluble reactive P (SRP) in the pore water and P fractional composition of the surface sediments, and calculated the diffusive flux of P in three locations in two continuous years (2017 and 2018) after the excavation. Similar measurements were done before sediment removal at central site of the lake in 2015. Removing nutrient-rich sediment also removed 6400 kg of P, and thus the potential for release of P from sediments decreased on a long-term scale. However, a large pool of releasable P was rebuilt soon after the sediment removal due to high external P loading, resulting in extensive anoxia of sediment surface and associated internal P loading as high as 1450 mg m^-2 summer^-1. Moreover, the Fe-P and labile P fractions were the most important sources of P release, as evidenced by their considerable seasonal and interannual changes after the sediment removal. The sediment total Fe negatively correlated with diffusive flux of P, pore water SRP, and near-bottom water total P and SRP concentrations which indicated a strong linkage between sediment P dynamics and Fe after the restoration. Sediment removal could be a beneficial restoration approach, but the effects on lake water quality remain only short-term unless there is an adequate control on external loading to the lake.

Keywords: Eutrophication; Lake restoration; Phosphorus fractions; Phosphorus release; Sediment removal.