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Response of eutrophication in the eastern Gulf of Finland to nutrient load reduction scenarios
Authors:
O. P. Savchuk, T. R. Eremina, A. V. Isaev andI. A. Neelov.
Source:
Hydrobiologia (2009) 629:225—237
DOI 10.1007/s10750-009-9776-y, online: 23.04.2009
Abstract:
The trophic status of the eastern Gulf of Finland, where the largest Baltic metropolis St.Petersburg sits at the mouth of the largest Baltic river Neva, is elevated but existing recommendations on water protection measures are controversial. In this study, the effects of nutrient load reductions on this ecosystem were estimated with the aid of a three dimensional coupled hydrodynamic- biogeochemical model. As a reference, the contemporary seasonal dynamics were simulated with nutrient inputs corresponding to the recent estimates of point and riverine sources. In order to eliminate the effects of natural inter-annual variations, the computations were run under recurrent annual forcing for 3 years, until quasi steady-state seasonal dynamics were reached. Reasonable comparability of simulated concentrations and biogeochemical fluxes to available field estimates provides credibility to scenario simulations. These simulations show that substantial reductions of nutrient point sources in St.Petersburg would affect only the Neva Bay as the immediate receptor of treated sewage waters, where primary production could decrease by up to 20%. Eutrophication in the other parts of the Neva Estuary and in the entire eastern Gulf of Finland would change insignificantly owing to increased nutrient import from the offshore waters. Therefore, more significant changes can occur only via a reduction in nutrient pools in the open Gulf of Finland and the Baltic Proper, which would require a longer time.
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