Benthic nutrient fluxes in the Eastern Gotland Basin (Baltic Sea) with particular focus on microbial mat ecosystems
DOI | 10.1016/j.jmarsys.2016.01.007 |
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Aasta | 2016 |
Ajakiri | Journal of Marine Systems |
Köide | 158 |
Leheküljed | 1-12 |
Tüüp | artikkel ajakirjas |
Keel | inglise |
Id | 49056 |
Abstrakt
Benthic fluxes and water column distributions of dissolved inorganic nitrogen (DIN) and total dissolved phosphate (PO4 3−) were measured in situ at 7 sites across a redox gradient from oxic to anoxic bottom waters in the Eastern Gotland Basin (Baltic Sea). The study area was divided into the oxic zone (60 to ca. 80 m water depth, O2 N 30 μM), the hypoxic transition zone (HTZ, ca. 80 to 120 m, O2 b 30 μM) and the deep anoxic and sulfidic basin (Nca. 120 m). Sediments in the HTZ were covered by mats of vacuolated sulfur bacteria. Ammonium (NH4 +) fluxes in the deep basin and the HTZ were elevated at 0.6 mmol m−2 d−1 and 1 mmol m−2 d−1 , respectively. Nitrate (NO3 −) fluxes were directed into the sediment at all stations in the HTZ and were zero in the deep basin. PO4 3− release was highest in the HTZ at 0.23 mmol m−2 d−1 , with a further release of 0.2 mmol m−2 d−1 in the deep basin. Up-scaling the benthic fluxes to the Baltic Proper equals 109 kt yr−1 of PO4 3− and 266 kt yr−1 of DIN. This is eight- and two-fold higher than the total external load of P (14 kt yr−1 ) and DIN (140 kt yr−1 ) in 2006 (HELCOM 2009b). The HTZ makes an important contribution to the internal nutrient loading in the Baltic Proper, releasing 70% of P (76 kt yr−1 ) and 75% of DIN (200 kt yr−1 ) despite covering only 51% of area.