The influence of dissolved organic matter on the acid-base system of the Baltic Sea

作者：Kulinski Karol^*; Schneider Bernd; Hammer Karoline; Machulik Ulrike; Schulz Bull Detlef

来源：Journal of Marine Systems, 2014, 132: 106-115.

DOI：10.1016/j.jmarsys.2014.01.011

• Organic alkalinity
• Total alkalinity
• pH
• C-T
• DOC
• Carbonate system
• Ultrafiltration
• DOM acid-base properties
• DOM dissociation constant

To assess the influence of dissolved organic matter (DOM) on the acid-base system of the Baltic Sea, 19 stations along the salinity gradient from Mecklenburg Bight to the Bothnian Bay were sampled in November 2011 for total alkalinity (A(T)), total inorganic carbon concentration (C-T), partial pressure of CO2 (pCO(2)), and pH. Based on these data, an organic alkalinity contribution (A(org)) was determined, defined as the difference between measured A(T) and the inorganic alkalinity calculated from C-T and pH and/or C-T and pCO(2). A(org) was in the range of 22-58 mu mol kg(-1), corresponding to 1.5-3.5% of A(T). The method to determine Am was validated in an experiment performed on DOM-enriched river water samples collected from the mouths of the Vistula and Oder Rivers in May 2012. The A(org) increase determined in that experiment correlated directly with the increased DOC concentration caused by enrichment of the >1 kDa DOM fraction. To examine the effect of A(org) on calculations of the marine CO2 system, the pCO(2) and pH values measured in Baltic Sea water were compared with calculated values that were based on the measured alkalinity and another variable of the CO2 system, but ignored the existence of Am. Large differences between measured and calculated pCO(2) and pH were obtained when the computations were based on A(T) and C-T. The calculated pCO(2) was 27-56% lower than the measured value whereas the calculated pH was overestimated by more than 0.4 pH units. Since biogeochemical models are based on the transport and transformations of A(T) and C-T, the acid-base properties of DOM should be included in calculations of the CO2 system in DOM-rich basins like the Baltic Sea. In view of our limited knowledge about the composition and acid/base properties of DOM, this is best achieved using a bulk dissociation constant, K-DOM, that represents all weakly acidic functional groups present in DOM. Our preliminary results indicated that the bulk K-DOM in the Baltic Sea is 2.94 . 10(-8) mol kg(-1). Although this K-DOM has no thermodynamic meaning, it can be a useful tool in numerical studies as it allows an approximation of A(org) in seawater.

• 出版日期2014-4