The effects of atmospheric deposition and acidification are generally more significant in the northern boreal part of the Baltic Sea catchment than in the southern cultivated areas, because of the lower buffer capacity of the surface waters and soils. Atmospheric deposition of acids, metals and nutrients peaked in the 1970s and 1980s with the notorious acidification effects observed in lakes and streams of Sweden and Finland (Weyhenmeyer 2008).
17.2.3.1 Human DriversĪtmospheric deposition. In most other watersheds around the Baltic Sea, freshwater biogeochemistry is affected by following human drivers: atmospheric deposition, forestry and wetland management, eutrophication, and damming and other types of hydrological alteration. 2008) and in unmanaged headwater catchments (Mattsson et al. 2004), in the Simojoki river basin (Lepisto et al. Relatively natural unperturbed conditions can be found in the well-studied River Kalixälven (Ingri et al. However, the occurrence of sedimentary bedrock in cultivated watersheds and the higher temperatures that increase weathering reactions lead to a higher ionic strength and higher alkalinity. Background loads and concentrations in the cultivated watersheds are difficult to estimate because humans have influenced these landscapes over many centuries. However, the bedrock dominated by acid volcanic and plutonic acid rocks as well as the occurrence of coniferous forests and wetlands storing huge amounts of organic C leads to freshwaters in boreal watersheds characterised by low ionic strength, low alkalinity and high concentrations of humic and fulvic acids that form the major pool of dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP). 2007) and older stored soil organic C (Vonk et al. Nitrogen enters the system through biological N fixation, and organic C stems from recently produced biomass (mainly litter and root exudates) (Froberg et al. Generally, weathering reactions charge rainwater with basic cations and anions including dissolved inorganic carbon (DIC), orthophosphate and silicic acid when infiltrating natural soils (Drever 1997).
#Atmos b2 basic digital atmosphere controller drivers
17.2.3 Drivers of Change in Sources, Transformation and Export of Biogenic Elements to the Baltic Seaįreshwater biogeochemistry in relatively unperturbed aquatic systems within the Baltic Sea catchment and the background load of the biogenic elements C, N, P and Si is the result of its weathering regime, which characterises total ionic strength, acidity (pH) and alkalinity as well as vegetation cover and vegetation type. 2006, 2008a) are compounding factors affecting freshwater biogeochemistry, especially in the boreal watersheds. 2007 Weyhenmeyer 2008), management of forestry and wetlands as well as damming and other types of hydrological alteration (Dynesius and Nilsson 1994 Nilsson et al. However, additional drivers such as atmospheric deposition (Monteith et al. Winter and spring mean monthly discharge increased at most observation sites, and the spring peak has become earlier at a third of sites (Korhonen and Kuusisto 2010). To date, observations on the discharge regime of major Finnish boreal rivers reveal no changes in mean annual flow during the period 1912–2004 (Korhonen and Kuusisto 2010), but the seasonal distribution of streamflow has changed (see also Chap. 2010) and the projected changes in temperature and precipitation are expected to result in fundamental changes within the Baltic Sea catchment (Graham 1999 Graham and Bergstrom 2001 Weyhenmeyer and Karlsson 2009). These changes could be potentially more significant than the variations in riverine fluxes observed over the past 35 years (HELCOM 2004), since changes in lifestyle translate directly into anthropogenic nutrient emissions and riverine fluxes (Howarth et al. Two major drivers-human lifestyles and global warming -which strongly influence agricultural practices and eutrophication and hydrological patterns for example, could significantly alter the transport of biogenic elements to the Baltic Sea over the near term (Arheimer et al.
In the central parts of the Baltic Sea, a mean salinity of 7 corresponds to about 80 % freshwater and 20 % marine water from the Atlantic.
The Baltic Sea is an estuarine system with water residence times of around 30 years and is highly susceptible to changes in riverine loads of biogenic elements (carbon, C nitrogen, N phosphorus, P silicon, Si) (Wulff et al. Landcover in the Baltic Sea drainage basin 17.2.2 Changes Shaping the Baltic Sea