Environmental Impacts—Marine Biogeochemistry

Abstract

Marine biogeochemistry deals with the budgets and transformations of biogeochemically reactive elements such as carbon, nitrogen and phosphorus. Inorganic nitrogen and phosphorus compounds are the major nutrients and control organic matter (biomass) production in the surface water. Due to various anthropogenic activities, the input of these nutrients into the Baltic Sea has increased drastically during the last century and has enhanced the net organic matter production by a factor of 2-4 (eutrophication). This has led to detrimental oxygen depletion and hydrogen sulphide production in the deep basins of the Baltic Sea. Model simulations based on the Baltic Sea Action Plan (BSAP) indicate that current eutrophication and thus extension of oxygen-depleted areas cannot be reversed within the next hundred years by the proposed nutrient reduction measures. Another environmental problem is related to decreasing pH (acidification) that is caused by dissolution of the rising atmospheric CO 2 . Estimates indicate a decrease in pH by about 0.15 during the last 1-2 centuries, and continuation of this trend may have serious ecological consequences. However, the concurrent increase in the alkalinity of the Baltic Sea may have significantly counteracted acidification.

Long-term alkalinity trends in the Baltic Sea and their implications for CO2 -induced acidification

“…Pelagic primary production can however contribute to surface water A T , when the organic matter is exported. With respect to alkalinity trends in the Baltic Sea surface water, it is reasonable to assume that nitrate based primary production and thus the A T contribution increased along with nutrient inputs that peaked around 1980 (Gustafsson et al ; Schneider et al ). However, recent modelling studies suggest that the previously increasing nitrogen uptake by phytoplankton levelled off around 1990 (Gustafsson et al ).…”

“…This implies that a reliable acidification estimate cannot solely be based on the atmospheric pCO 2 evolution. Previous studies indeed suggested that the alkalinity in the eastern Gotland Sea increased by around 100 µmol kg −1 (∼6%) from 1930 to 2010 (Schneider et al ). Extensive A T measurements were performed in the Baltic Sea region with investigations dating back to the early 20 th century (Buch ; Hjalmarsson et al ).…”

Model simulation of seasonal growth of Fucus vesiculosus in its benthic community

“…All treatments were superimposed on the natural fluctuations of all environmental variables. The elevated levels of both factors were chosen according to climate change predictions for shallow coastal Baltic habitats over the next 100 years (Elken et al ; Schneider et al ).…”

Seasonal Photophysiological Performance of Adult Western Baltic Fucus vesiculosus (Phaeophyceae) Under Ocean Warming and Acidification

“…Due to anthropogenic global change, ocean warming and acidification may singly or interactively affect photophysiological performance of Fucus during the different seasons. Fucus was exposed to single and combined treatments of elevated seawater temperature ( + 5 • C) and pCO 2 (1100 ppm) in all four seasons as predicted for shallow coastal Baltic habitats for the year 2100 (Elken et al, 2015;Schneider et al, 2015;Müller et al, 2016). These scenarios, including natural fluctuations forced by diurnal and seasonal changes, atmospheric and hydrographic conditions, were simulated using benthic mesocosms [Kiel Outdoor Benthocosms (KOBs), Wahl et al, 2015a].…”