Effect of changes in water salinity on ammonium, calcium, dissolved inorganic carbon and influence on water/sediment dynamics |
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Authors: | P Lpez |
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Institution: | Department of Ecology, University of Barcelona, Avda Diagonal 645, E-08028, Barcelona, Spain |
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Abstract: | The effect of a sudden increase in salinity from 10 to 37 in porewater concentration and the benthic fluxes of ammonium, calcium and dissolved inorganic carbon were studied in sediments of a small coastal lagoon, the Albufera d'Es Grau (Minorca Island, Spain). The temporal effects of the changes in salinity were examined over 17 days using a single diffusion-reaction model and a mass-balance approach. After the salinity change, NH4+-flux to the water and Ca-flux toward sediments increased (NH4+-flux: 5000–3000 μmol m−2 d−1 in seawater and 600/250 μmol m−2 d−1 in brackish water; Ca-flux: −40/−76 meq m−2 d−1 at S=37 and −13/−10 meq m−2 d−1 at S=10); however, later NH4+-flux decreased in seawater, reaching values lower than in brackish water. In contrast, Ca-flux presented similar values in both conditions. The fluxes of dissolved inorganic carbon, which were constant at S=10 (55/45 mmol m−2 d−1), increased during the experiment at S=37 (from 30 mmol m−2 d−1 immediately after salinity increase to 60 mmol m−2 d−1 after 17 days).In brackish conditions, NH4+ and Ca2+ fluxes were consistent with a single diffusion-reaction model that assumes a zero-order reaction for NH4+ production and a first-order reaction for Ca2+ production. In seawater, this model explained the Ca-flux observed, but did not account for the high initial flux of NH4+.The mass balance for 17 days indicated a higher retention of NH4+ in porewater in the littoral station in seawater conditions (9.5 mmol m−2 at S=37 and 1.6 mmol m−2 at S=10) and a significant reduction in the water consumption at both sites (5 mmol m−2 at S=37; 35/23 mmol m−2 at S=10). In contrast, accumulation of dissolved inorganic carbon in porewater was lower in seawater incubations (−10/−1 meq m−2 at S=37; 50/90 meq m−2 at S=10) and was linked to a higher efflux of CO2 to the atmosphere, because of calcium carbonate precipitation in water (675/500 meq m−2). These results indicate that increased salinity in shallow coastal waters could play a major role in the global carbon cycle. |
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Keywords: | benthic fluxes coastal lagoons porewater diffusion-reaction model carbon balance ammonium balance |
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