Present and Past‐Millennial Eutrophication in the Gulf of Gdańsk (Southern Baltic Sea)

Abstract

Eutrophication is manifested by increased primary production leading to oxygen depletion in near‐bottom water and toxic cyanobacteria blooms. This is an important contemporary problem of the Baltic Sea and many other coastal waters. The present eutrophication is mainly ascribed to anthropogenic activity. To compare the present trophic state with that during past millennia, two sediment cores (50 cm long and ~400 cm long covering ca. 5,500 years) were taken from the Gulf of Gdańsk (southern Baltic Sea). The core subsamples were analyzed for phytoplankton pigments (chlorophylls and their derivatives, and carotenoids). In addition, carbon (Ctot, Corg, and δ13C), 14C dating, grain size, diatoms, and selected metals in the cores were analyzed to determine conditions in the depositional environment. The results indicated that there were high primary production periods in the past, during the Littorina Sea and the Roman Climatic Optimum, accompanied by oxygen deficiency in the near‐bottom water, most probably caused by climate warming. The ratio of 132,173‐cyclopheophorbide‐a enol, a labile degradation product of chlorophyll‐a, to the sum of other chloropigments‐a (CPPB‐aE/ΣChlns‐a) is proposed as a new paleoredox proxy. Heterocystous cyanobacteria blooms of an intensity similar to or even greater than at present also occurred in past millennia and were connected with climate warming. Hence, eutrophication must have occurred in the past, which means that natural factors have a substantial influence on it.

Stable isotope analysis in food web research: Systematic review and a vision for the future for the Baltic Sea macro-region

“…Archeological research also addressed fish trading and commercialization in the Baltic and North Sea regions (Barrett et al 2008 , 2011 ; Orton et al 2011 ), and provided δ 13 C and δ 15 N values of cod bone samples from geographically diverse medieval settlements, thereby providing information on spatial isotopic variability. Finally, BSIA of cyanobacterial pigments (Bianchi et al 2000 ; Borgendahl and Westman 2006 ; Szymczak‐Żyła et al 2019 ) and cladoceran fossils (Struck et al 1998 ) in sediment cores were used to investigate the role of cyanobacteria-produced nitrogen over the last century and during the Baltic Sea formation in the Holocene. The historic perspective (decades to millenia) provided by these studies represents a unique counterpart to the more recent (years to decades) perspective of contemporary SIA studies.…”

Distribution and characterization of organic matter within the sea surface microlayer in the Gulf of Gdańsk

“…The study area included a transect in the southern Baltic Sea, more specifically in the Gulf of Gda ńsk, starting at the Vistula River mouth and extending about 47 km toward the open sea ( Figure 1 , Table S1). The brackish Baltic Sea is characterised by a high water residence time due to poor exchange with the North Sea through the Danish Straits ( Szymczak-Żyła et al, 2019 ). This and its large catchment area make it vulnerable to eutrophication, anoxia, and the impacts of pollutants ( P ȩ dzi ński andWitak, 2019 , Szymczak-Żyła et al, 2019 ).…”

“…The brackish Baltic Sea is characterised by a high water residence time due to poor exchange with the North Sea through the Danish Straits ( Szymczak-Żyła et al, 2019 ). This and its large catchment area make it vulnerable to eutrophication, anoxia, and the impacts of pollutants ( P ȩ dzi ński andWitak, 2019 , Szymczak-Żyła et al, 2019 ). Between the early and late 20 th century intensive inputs of nitrogen and phosphorus increased fourfold and eightfold, respectively ( Glasby and Szefer, 1998 ;Larsson et al, 1985 ), promoting eutrophication, reducing water transparency, and causing a shift from macrophyteto phytoplankton-dominated systems in some areas of the Baltic Sea ( Andrén, 1999 ).…”

Reconstructing N<sub>2</sub>-fixing cyanobacterial blooms in the Baltic Sea beyond observations using 6- and 7-methylheptadecane in sediments as specific biomarkers

“…While cyanobacterial blooms have occurred in the Baltic Sea for thousands of years (Bianchi et al, 2000;Poutanen and Nikkilä, 2001;Jilbert et al, 2015;Funkey et al, 2014;Sollai et al, 2017;Szymczak-Żyła et al, 2019), it is often assumed that their frequency and intensity have increased due to anthropogenic impact. Long-term monitoring programs indicate that the frequency and abundance of diazotrophic cyanobacteria have increased since the early 1900s and even more significantly since the 1970s (Kahru et al, 1994), due to the massive anthropogenic loading of nutrients (in particular phosphorus) to the Baltic Sea (Finni et al, 2001;Poutanen and Nikkilä, 2001;Stal et al, 2003;Vahtera et al, 2007).…”

“…Biomarkers considered to be characteristic for cyanobacteria in modern and past ecosystems include some carotenoid pigments (zeaxanthin and echinenone; Lotocka, 1998;Bianchi et al, 2000;Poutanen and Nikkilä, 2001;Funkey et al, 2014;Jilbert et al, 2015;Szymczak-Żyła et al, 2019). However, zeaxanthin and echinenone are not entirely specific to cyanobacteria and are certainly not limited to nitrogenfixing cyanobacteria (Bianchi, 2007;Sollai et al, 2017).…”