Anthropogenic and climatic impacts on a coastal environment in the Baltic Sea over the last 1000 years

Abstract

Coastal environments have experienced large ecological changes as a result of human activities over the last 100−200 years. To understand the severity and potential consequences of such changes, paleoenvironmental records provide important contextual information. The Baltic Sea coastal zone is naturally a vulnerable system and subject to significant human-induced impacts. To put the recent environmental degradation in the Baltic coastal zone into a long-term perspective, and to assess the natural and anthropogenic drivers of environmental change, we present sedimentary records covering the last 1000 years obtained from a coastal inlet (Gåsfjärden) and a nearby lake (Lake Storsjön) in Sweden. We investigate the links between a pollen-based land cover reconstruction from Lake Storsjön and paleoenvironmental variables from Gåsfjärden itself, including diatom assemblages, organic carbon (C) and nitrogen (N) contents, stable C and N isotopic ratios, and biogenic silica contents. The Lake Storsjön record shows that regional land use was characterized by small-scale agricultural activity between 900 and 1400 CE, which slightly intensified between 1400 and 1800 CE. Substantial expansion of cropland was observed between 1800 and 1950 CE, before afforestation between 1950 and 2010 CE. From the Gåsfjärden record, prior to 1800 CE, relatively minor changes in the diatom and geochemical proxies were found. The onset of cultural eutrophication in Gåsfjärden can be traced to the 1800s and intensified land use is identified as the main driver. Anthropogenic activities in the 20th century have caused unprecedented ecosystem changes in the coastal inlet, as reflected in the diatom composition and geochemical proxies.

Quantitative landscape reconstruction and erosion history during the past 1,100 years in the Skogaryd Research Catchment, southern Sweden

“…These changes are consistent with the general land-use changes in Sweden in the 20th century, where the traditional agricultural system with large areas for grazing and mowing was transformed into a landscape sharply divided into commercial forest and intensive crop cultivation (e.g. Björkman 2001;Åkesson et al 2015;Mazier et al 2015;Ning et al 2018). A weak recovery of shade-tolerant deciduous species is observed (Fig.…”

Middle to Late Holocene Variations in Salinity and Primary Productivity in the Central Baltic Sea: A Multiproxy Study From the Landsort Deep

“…Zillén and Conley (2010) suggest that anthropogenic forcing through increased nutrient input from the drainage area might have influenced the primary productivity in the Baltic Sea during these times. Recent studies from the Finnish and Swedish coast find no evidence of anthropogenic forcing during the MCA (Jokinen et al, 2018;Ning et al, 2018).…”

Holocene Hydrographic Variations From the Baltic‐North Sea Transitional Area (IODP Site M0059)

“…It has occurred intermittently, in particular in the deepest basins, in the Baltic Sea throughout the Holocene (Jilbert & Slomp, 2013;Kabel et al, 2012;van Wirdum et al, 2019), and the area of hypoxia has expanded sixfold from 1950 to 2000 CE (Carstensen et al, 2014). Baltic Sea hypoxic events have been steadily increasing with time and affect nutrient biogeochemical processes, ecosystem services, coastal habitats (Conley et al, 2009Ning et al, 2018), and fisheries (Breitburg, 2002). The Danish Straits hydrographically represent the transitional area between the Baltic Proper and the North Sea, and the salinity of these narrow straits is determined by the balance between the brackish water outflows and the intermittent saline water inflows from the North Sea through the Kattegat and Skagerrak (Figure 1; .…”