Phosphorus recycling in sediments of the Central Baltic Sea
2012 (English)In: Biogeosciences Discussions, ISSN 1810-6277, E-ISSN 1810-6285, Vol. 9, 15459-15500 p.Article in journal (Refereed) Published
Benthic fluxes of dissolved inorganic phosphorus (DIP) were measured in situ in the Eastern Gotland Basin (EGB), Central Baltic Sea, using benthic landers. A total of 40 flux measurements on 13 stations at water depths ranging from 30–210 m and under different oxygen regimes were carried out on three cruises during three consecutive years (2008–2010) in August–September. Our study is the first to report in situ DIP fluxes in the Baltic Proper, and it provides the most comprehensive data set of benthic DIP fluxes in the Baltic Proper existing to date. DIP fluxes increased with increasing water depth and with decreasing bottom water oxygen concentration. Average fluxes were calculated for oxic bottom water conditions (−0.003 ± 0.040 mmol m−2 d−1), hypoxic conditions (0.027 ± 0.067 mmol m−2 d−1) and anoxic conditions (0.376 ± 0.214 mmol m−2 d−1). The mean flux on anoxic bottoms was ca. 5–10 times higher than previous estimates based on ex situ measurements, but agreed well with previous flux estimations from changes in the basin water DIP pool. The DIP flux was positively correlated with the organic carbon inventory of sediment and the benthic flux of dissolved inorganic carbon (DIC) on anoxic stations, but these variables were uncorrelated on oxic stations. The positive correlation between DIP and DIC fluxes suggests that the benthic DIP flux on anoxic bottoms in the Baltic Proper is mainly controlled by rates of deposition and degradation of organic matter. The flux from anoxic sediment was very P rich in relation to both C and N, and the average C:P ratio in fluxes on anoxic accumulation bottoms was 69 ± 15, which is well below the Redfield C:P ratio of 106:1. On oxic stations, however, the C:P flux ratio was much higher than the Redfield ratio, consistent with well-known P retention mechanisms associated with iron and bacteria in oxidized sediment. Using a benthic mass balance approach, a burial efficiency of 4% was calculated for the anoxic part of the EGB, which suggests that anoxic Baltic sediments are very efficient in recycling deposited P. Based on the measured fluxes and recent estimates of the areal extent of anoxic and hypoxic bottoms, an internal load of 146 kton yr−1 was calculated. This is 7–12 times higher than recent estimates of the external load and clearly highlights the dominance of anoxic sediments as a P source in the Baltic Sea.
Place, publisher, year, edition, pages
2012. Vol. 9, 15459-15500 p.
Research subject Marine Ecology
IdentifiersURN: urn:nbn:se:su:diva-114985DOI: 10.5194/bgd-9-15459-2012OAI: oai:DiVA.org:su-114985DiVA: diva2:795345