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Benthic Phosphorus Dynamics in the Gulf of Finland, Baltic Sea |
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| Authors: | Lena Viktorsson Elin Almroth-Rosell Anders Tengberg Roman Vankevich Ivan Neelov Alexey Isaev Victor Kravtsov Per O J Hall |
| Institution: | 1. Department of Earth Sciences, University of Gothenburg, BOX 460, S-405 30, Gothenburg, Sweden 2. Department of Chemistry, Marine Chemistry, University of Gothenburg, SE-412 96, Gothenburg, Sweden 3. SPb Scientific Research Center for Environmental Safety, Korpusnaya 18, Saint-Petersburg, Russia 4. Russian State Hydrometeorological University, Maloohtinskiy 98, Saint-Petersburg, Russia 5. Atlantic Branch of P.P Shirshov Institute of Oceanology, Russian Academy of Science (ABIORAS), Prospect Mira 1, Kaliningrad, 236022-RU, Russia |
| Abstract: | Benthic fluxes of soluble reactive phosphorus (SRP) and dissolved inorganic carbon (DIC) were measured in situ using autonomous landers in the Gulf of Finland in the Baltic Sea, on four expeditions between 2002 and 2005. These measurements together with model estimates of bottom water oxygen conditions were used to compute the magnitude of the yearly integrated benthic SRP flux (also called internal phosphorus load). The yearly integrated benthic SRP flux was found to be almost 10 times larger than the external (river and land sources) phosphorus load. The average SRP flux was 1.25?±?0.56?mmol?m?2?d?1 on anoxic bottoms, and ?0.01?±?0.08?mmol?m?2?d?1 on oxic bottoms. The bottom water oxygen conditions determined whether the SRP flux was in a high or low regime, and degradation of organic matter (as estimated from benthic DIC fluxes) correlated positively with SRP fluxes on anoxic bottoms. From this correlation, we estimated a potential increase in phosphorus flux of 0.69?±?0.26?mmol?m?2?d?1 from presently oxic bottoms, if they would turn anoxic. An almost full annual data set of in situ bottom water oxygen measurements showed high variability of oxygen concentration. Because of this, an estimate of the time which the sediments were exposed to oxygenated overlying bottom water was computed using a coupled thermohydrodynamic ocean?Csea and ecosystem model. Total phosphorus burial rates were calculated from vertical profiles of total phosphorus in sediment and sediment accumulation rates. Recycling and burial efficiencies for phosphorus of 97 and 3%, respectively, were estimated for anoxic accumulation bottoms from a benthic mass balance, which was based on the measured effluxes and burial rates. |
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