Dynamics of dissolved organic carbon in a coastal ecosystem

Abstract

In the Bothnian Sea, there was a marked seasonal variation of dissolved organic C (DOC) in 1990-1992, with a large increase in DOC concentrations in summer at two stations. The accumulation of DOC at the coastal station persisted for 5 months, reaching peak values 24-3 1% above the mean winter value (288 PM). At the offshore station DOC concentrations were elevated throughout the water column in July, reaching 14% above the mean winter value (29 1 PM). The DOC concentration at the coastal station was significantly correlated to water flow in an adjacent river, suggesting that the source of the summer DOC increase was largely explained by riverine input. Bioassays indicated that a large portion (22-99%) of the introduced DOC was degradable by bacteria after inorganic nutrients were added. A negative correlation between DOC and phosphate concentration was also found, suggesting that the system was P deficient in summer. The accumulation of DOC in summer was thus possibly caused by slow bacterial degradation due to phosphate deficiency and transient accumulation of refractory DOC. An annual C.balance at the coastal station indicated .an insufficient supply of C from phytoplankton production to support the C demand of the system; at the offshore station the budget was close to balanced. The results suggest that riverine DOC had a major impact on coastal DOC dynamics and that it was partly used in the microbial food web in the bay.

Bioavailability of riverine dissolved organic matter in three Baltic Sea estuaries and the effect of catchment land use

“…The insignificant effect of inorganic nutrient addition on biodegradable DOC and DON amounts suggests that the DOM degradation in the experiments was not limited by inorganic nitrogen or phosphorus availability. This is in contrast to a commonly observed stimulation of heterotrophic DOC utilization by addition of inorganic nutrients (e.g., Kuparinen and Heinänen, 1993;Zweifel et al, 1995). Neither did the addition of salt result in any significant changes in any of the study parameters.…”

Bacterial growth and DOC consumption in a tropical coastal lagoon

“…Zweifel et al (1995) observed a net doc accumulation in the Bothnian sea coastal areas, where bacterial community growth was limited by the phosphorus supply. in addition, doc may accumulate if bacterial growth rates remain low due to competition with algae for inorganic nutrients (thingstad et al, 1997).…”

Effects of inorganic nutrients, glucose and solar radiation on bacterial growth and exploitation of dissolved organic carbon and nitrogen in the northern Baltic Sea

“…The concentration of dissolved organic matter (DOM) in seawater exceeds by 1 to 2 orders of magnitude that of particulate organic matter, including living organisms and detritus (Williams 1995, Zweifel et al 1995. Thus, the DOM pool is potentially important in nutrition of pelagic osmotrophs, like bacteria and algae, which are capable of exploiting dissolved organic substrates.…”

“…Lignell 1990, Azam 1998, Ward & Bronk 2001, Berman & Bronk 2003. It has been suggested that accumulation of LDOC and LDON in the productive surface layer depends on temperature or nutrient availability, which control bacterial growth rates, or the semi-labile nature of freshly produced DOM (Williams 1995, Zweifel et al 1995, Thingstad & Lignell 1997, Søndergaard et al 2000. A broader scenario has also been suggested for labile DOM accumulation that would include a combination of grazing control of bacterial biomass by heterotrophic nanoflagellates and simultaneous limitation of bacterial production by either temperature (Zweifel 1999) or low mineral nutrient availability caused in turn by algal-bacterial competition for nutrients (Thingstad & Lignell 1997.…”

“…Thus, the DOM pool is potentially important in nutrition of pelagic osmotrophs, like bacteria and algae, which are capable of exploiting dissolved organic substrates. Investigations of annual DOM dynamics have shown that both dissolved organic carbon (DOC) and nitrogen (DON) tend to accumulate in surface waters during periods of phytoplankton growth (Williams 1995, Zweifel et al 1995. A review of studies on various aquatic environments suggested that on average, 14 to 19% of the total DOC pool is labile (LDOC) or easily degraded by bacteria (Sønder-gaard & Middelboe 1995), and similar labile shares of total DON (LDON) have, for example, been recorded in the Baltic Sea (Jørgensen et al 1999, Vähätalo & Zepp 2005; for a review, see Berman & Bronk 2003).…”