Capturing past eutrophication in coastal sediments – Towards water-quality goals. (31st May 2019)

• Record Type: Journal Article
• Authors: Rydin, Emil; Kumblad, Linda
• Is Part Of: Estuarine, coastal and shelf science. Volume 221(2019)
• Page Start: 184
• Page End: 188
• Publication Date: 2019-05-31
• Subjects: Baltic sea -- Sediment -- Phosphorus (P) -- Aluminium (Al) -- Internal load -- Brackish water; Estuarine oceanography -- Periodicals; Coasts -- Periodicals; Estuarine biology -- Periodicals; Seashore biology -- Periodicals; Coasts; Estuarine biology; Estuarine oceanography; Seashore biology; Periodicals; 551.461805
• DOI: 10.1016/j.ecss.2019.02.046
• Languages: English
• ISSNs: 0272-7714

Abstract

Abstract: Björnöfjärden is a semi-enclosed brackish bay located in the Stockholm archipelago (Baltic Sea, Sweden). Anthropogenic phosphorus (P) loading to the bay over the past century has overwhelmed the largely unchanged natural supply of elements and compounds that permanently sequester P in sediments. At the same time, eutrophication has shifted surface sediments from oxic to anoxic conditions and reduced their P-retention capacity. Consequently, the release of P from anoxic sediments has become the main P source to the water column. Here we report on a long-term remediation program to reverse eutrophication in Björnöfjärden. After the implementation of measures that reduced the land-based external load to the bay, sediment-P retention was increased by mixing a solution of aluminum (Al) chloride into the anoxic and azoic sediments (>6 m water depth) at a dose of 50 g Al/m 2, a first in a brackish environment. As a result, P accumulation in the surface sediment reached 2.0 g P/m 2 after 3.4 years, corresponding to 1.6 mg P/m 2 -day. This is the first time that the P accumulation rate has been determined in aquatic sediments following the addition of P-sequestering material, such as Al. The P that accumulated was dissolved P that mainly migrated from below the layer of P accumulation. The aim of the Al-addition was to sequester legacy P that had accumulated during the past century and to return Björnöfjärden to a low productivity regime, which would allow the surface sediment to become oxic and enable natural P binding by iron. Graphical abstract: Image 1 Highlights: Limited sediment-P burial delays recovery from eutrophication. Al addition increased the sediment-P burial in anoxic, brackish coastal sediment. Mobilized sediment P was trapped by added Al. Additional post-eutrophication sediment-P binding to oxidized Fe is estimated. Conceptual model of sediment-P distribution for the entire eutrophication cycle is presented.