4.7 Article

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

Journal

SCIENCE OF THE TOTAL ENVIRONMENT
Volume 725, Issue -, Pages -

Publisher

ELSEVIER
DOI: 10.1016/j.scitotenv.2020.138279

Keywords

Eutrophication; Lake restoration; Phosphorus fractions; Phosphorus release; Sediment removal

Funding

  1. Doctoral Programme in Sustainable Use of Renewable Natural Resources (AGFOREE) of the University of Helsinki
  2. Suomen Kulttuurirahasto (Finnish Cultural Foundation
  3. Finland) [00180511, 34F70268]
  4. Niemi-saatio (Niemi Foundation
  5. Finland) [20170072]
  6. Center for Environmental Investments SA (Estonia) [15149]

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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 froma 1-ha highly eutrophic lake. Wemeasured 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 Pwas 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, porewater SRP, and near-bottomwater total P and SRP concentrationswhich 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 lakewater quality remain only short-termunless there is an adequate control on external loading to the lake. (C) 2020 The Authors. Published by Elsevier B.V.

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