Naslov
Benthic fluxes of nutrients at the sediment/water interface in the peloid mud of Marikina Bay (Croatia)

Autori
Lojen, Sanja ; Ogrinc, Nives ; Dolenec, Tadej ; Mihelčić, Goran ; Branica, Marko

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Book of abstracts / - Peking : International Association for Semident Water Science, 1999

Skup
V: Eighth International Symposium The Interactions between Sediments and Water

Mjesto i datum
Peking, Kina, 13.09.1999. - 17.09.1999

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Sažetak
Makirina Bay is a small, shallow (0.2-1 m deep) lagoon in Central Dalmatia, Croatia. The carbonate bottom is covered by an up to 2 m thick layer of clayey silt with typical characteristics of peloid mud, covered by sea grasses and algae. Terrigenous non-carbonate minerals represent as much as 60% of the total inorganic fraction of the sediment. The presence of framboidal pyrite indicates the existence of micro-environments with strongly reducing conditions even in the uppermost part of the sediment column, in spite of intensive bioturbation and irrigation due to macrobenthic organisms. Organic carbon represents up to 5wt.% of the total sediment and the C/N ratio is between 5.7 and 9, which is relatively low for marine sediments. An in-situ incubation experiment was performed during 10 days in July 1997 at two sampling sites in order to estimate the benthic fluxes of nutrients at the sediment/water interface. Benthic fluxes were compared to diffusive fluxes at the same sites, calculated from pore water depth profiles. The fluxes of dissolved inorganic carbon - DIC, NO3-, NH4+, PO43-, SO42-, Fe, and Mn - across the sediment/water interface in the benthic chambers were evaluated from linear regressions of solute concentrations vs. time. At a site close to the riverine inflow, benthic fluxes of NO3-, NH4+, PO43-, Fe and SO42- were negative, i.e. solute was transferred into the sediment or interstitial solution (-0.4, -1.87, -0.004, -0.16 and –33.5 mmol m-2 day-1, respectively), while the flux of DIC was positive (18.5 mmol m-2 day-1). In the middle of the bay, positive fluxes of Mn (0.08), Fe (0.04), DIC (12.67) and PO43- (0.002 mmol m-2 day-1) were observed throughout the 250hour experiment, whereas the SO42- flux was negative (-22.2 mmol m-2 day-1). NO3- and NH4+ behaved differently in the first 70 hours and subsequently. In the first period, the NO3- flux was negative but later on it changed to positive (-0.15 to 0.62 mmol m-2 day-1). The NH4+ flux decreased from –2.03 to –0.92 mmol m-2 day-1 in the second period. Diffusive fluxes of NO3- and NH4+ at the sediment/water interface measured at the same time were both negative, so nitrogen or ammonia fixation by plants and methanogenic bacteria is assumed to take place within the sediment. The high benthic flux of DIC is easily explained by decomposition of sedimentary organic matter, followed by an increase in (delta)13C of released DIC, which is typical of the increasing influence of organic-derived DIC. Sulphate is consumed through bacterial sulphate reduction producing sulphide, which is then precipitated in the form of pyrite. The ammonia released during the mineralisation of sedimentary organic matter may undergo nitrification, if oxic conditions prevail. In anoxic conditions, nitrate can be denitrified to ammonia or molecular nitrogen, which can be then consumed by assimilation. However, more investigation is needed to explain the peculiar behaviour if dissolved nitrogen species.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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