A time‐dependent budget model for nutrients in the Baltic Sea

Abstract

Overall budgets for nutrient and humus are described for the Baltic Sea as well as for the subsystems, i.e., the Baltic proper, the Bothnian Bay and the Bothnian Sea. The residence times for total phosphorus, total nitrogen, silicate and humus are 13.3, 5.5, 11.2 and 9.6 years respectively, compared to 21.8 years for a conservative substance (salt). About 90% of the nutrient losses are due to biogeochemical sinks within the Baltic Sea. Thus only about 10% is exported to external areas (the Kattegat/Belt Sea). For humus the corresponding figures are about 75 and 25%, respectively. This means that the Baltic Sea to a large extent can be regarded as a closed system and perturbations in the water exchange with the North Sea should have little effect on the nutrient budgets. The sinks are parameterized by an expression borrowed from limnology where the net nutrient loss is a function of the winter surface concentration. A budget model is run in a prognostic, hindcast mode with the assumed time‐dependent phosphorus and nitrogen loading of the Baltic proper. The computed development of the winter surface concentrations of total P and total N for the period 1950‐1988 appears quite realistic. The possibility of having variable sinks which are functions of the surface winter concentrations of nitrogen and phosphorus is described using calculations based on data from the different Baltic subareas. Such sinks should significantly decrease the winter N:P ratio in the surface water when the nutrient loading increases with time. With better descriptions of in particular the pools of nutrients in the sediment, it would be possible to model future changes of nutrient concentrations in the water column in relation to loading.

Nutrient transports in the Baltic Sea – results from a 30-year physical–biogeochemical reanalysis

“…The in-and outflows of phosphorus between the subbasins, except the Gulf of Riga and Gulf of Finland, simulated in REANA are smaller than the results by Wulff and Stigebrandt (1989), Savchuk (2005), and Savchuk and Wulff (2007). However, the net transports of phosphorus are similar between our results and these earlier studies in subbasins except Kattegat and Danish Straits.…”

Key processes in the coupled carbon, nitrogen, and phosphorus cycling of the Baltic Sea

“…As noted by Wulff and Stigebrandt (1989) in their early estimates of nutrient budgets for the Baltic Sea, budget calculations cannot be considered complete if only the water column is included and not the benthic compartment. By including the active sediment layer in our budget calculations, we have obtained a complete coverage of the C, N, and P cycling on a system-scale.…”

“…Thus, DIC pools are replenished through a net uptake of atmospheric CO 2 . Wulff and Stigebrandt (1989) estimated the pelagic residence times to 5.5 and 13.3 years for TN and TP respectively by dividing pool sizes (based on winter values in the period [1977][1978][1979][1980] by the sum of advective and biogeochemical sinks. On the other hand, Wulff et al (2001) and Savchuk (2005) calculated the pelagic residence times of TN and TP by dividing pool sizes by external loads: Wulff et al …”

Pyrosequencing reveals contrasting seasonal dynamics of taxa within Baltic Sea bacterioplankton communities

“…Typical estuarine environments, such as river outlets, are mixing zones between fresh and marine waters, in which short retention times limit the possibilities for autochthonous communities to establish (Crump et al, 2004). In contrast, the central Baltic Sea has a long retention time (45 years (Wulff and Stigebrandt, 1989)) and is conceivably dominated by microbes that have adapted to this specific environment. In the Baltic Sea proper (B6 PSU), Riemann et al (2008) found that surface bacterioplankton communities seemed to be strongly influenced by typical freshwater bacterial groups within Actinobacteria, Verrucomicrobia and Betaproteobacteria, whereas many typical marine taxa appeared to be missing.…”