Long-term Development of Inorganic Nutrients and Chlorophyllαin the Open Northern Baltic Sea

Abstract

Eutrophication is an ongoing process in most parts of the Baltic Sea. This article reports on the changes during recent decades of several eutrophication-related variables in the open sea areas surrounding Finland (wintertime nutrient concentrations, wintertime nutrient ratios, and summer time chlorophyll alpha concentrations at the surface). The sum of nitrate- and nitrite-nitrogen ([NO3+NO2]-N) was observed to increase nearly fourfold in the Northern Baltic Proper and the Gulf of Finland and almost double in the Bothnian Sea from the 1960s until the 1980s or 1990s. The increase was followed by a decrease, which was modest in the two former subregions. Phosphate-phosphorus (PO4-P) concentrations followed a similar pattern in the Northern Baltic Proper (threefold increase and subsequent slight decrease) and Bothnian Sea (30% increase and subsequent decrease), but increased throughout the study in the Gulf of Finland, with the present concentration being threefold to the measurements made in the early 1970s. The PO4-P concentration decreased throughout the study in the Bothnian Bay. Silicate-silicon (SiO4-Si) concentrations decreased 30-50% from the early 1970s to the late 1990s and increased 20-40% thereafter in the Northern Baltic Proper, the Gulf of Finland, and the Bothnian Sea. Chlorophyll alpha showed an increase of over 150% in the Northern Baltic Proper and the Gulf of Finland from the 1970s until the early 2000s. In the Bothnian Sea the chlorophyll alpha concentration increased more than 180% from the late 1970s until the late 1990s, and decreased thereafter. According to these long-term observations, the Gulf of Finland and Northern Baltic Proper show clear signs of eutrophication, which may be emphasized by hydrographical changes affecting the phytoplankton communities and thus the algal biomass.

Determination of Metals in Sea Water of the Baltic Sea in Międzyzdroje

“…It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands [73][74][75][76][77]. It drains into the Kattegat by way of the Øresund, the Great Belt and the Little Belt.…”

“…It drains into the Kattegat by way of the Øresund, the Great Belt and the Little Belt. The Kattegat continues through Skagerrak into the North Sea and the Atlantic Ocean [73][74][75]. The Baltic Sea is connected by artificial waterways to the White Sea via the White Sea Canal, and to the North Sea via the Kiel Canal.…”

“…The Baltic Sea might be considered to be bordered on its northern edge by the Gulf of Bothnia, on its northeastern edge by the Gulf of Finland, and on its eastern edge by the Gulf of Riga. These various gulfs can also be considered part of the Baltic Sea [73][74][75][76][77]. …”

Development of tools for ecological quality assessment in polish marine areas according to the Water Framework Directive. Part III — Secchi depth

“…Therefore water transparency, as determined by the visibility of Secchi disc (the Secchi depth) has been identified by HELCOM as an indicator of eutrophication (HELCOM 2006); it being considered a secondary effect or response indicator. Secchi depth is a parameter for which data sets are available over long time periods (Sandén&Håkanson 1996, Aarup 2002, Fleming-Lehtinen et al 2006. Technically the measurement is simple, cheap and easy, and the method has remained practically unchanged over the years.…”

“…Decrease in sea water transparency during the vegetation season has been observed in all Baltic Sea sub-regions over the last hundred years (Trzosińska 1992, Fleming-Lehtinen et al 2006). In the southern Baltic Proper these changes have not been as marked as in northern regions, and here this decreasing trend has ceased in the last 10 to 15 years (Łysiak-Pastuszak&Piątkowska 2004).…”