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  Nutrient inputs  
  Nutrient concentrations, ratios and limitation  
  Phytoplankton and harmful algal blooms  
  Oxygen depletion  
  Degradation of organic matter in eustuarine sediments  
  Submerged aquatic vegetation  
  Softbottom macrobenthos  
  Fish kills  

Figure 2.1
Annual runoff from Denmark to the Kattegat – Belt Sea area 1975-2001.

Figure 2.2
Annual mean air temperature measured at Sprogø/Risø 1978-2001. (Data from Sund og Bælt Holding and Wind Energy Department, Risø National Laboratory).

Figure 2.3
Mean summer (May-Aug.) solar radiation measured at Højbakkegård/Risø. (Data from Laboratory for Agrohydrology and Bioclimatology, Department of Agricultural Sciences, The Royal Veterinary and Agricultural University, and Wind Energy Department, Risø National Laboratory).

Figure 2.4
Chlorophyll a + Carbon-biomass


The Danish marine waters are continuously affected by short term variations in freshwater runoff, air temperature, wind forcing and solar radiation, governing the nutrient load, water temperature, water exchange and stratification as well as irradiance available for primary production. Large inter annual variations are also present in these driving forces, especially concerning runoff. However, no general trend is detected in the time series over the last 25 years.

The climatic driving forces are used in later chapters in an attempt to correct the chemical and biological indicators for natural climatic induced variations.

Freshwater runoff from Denmark to the Kattegat and Belt Sea varied between a minimum of 4.84 km3 in 1976 to a maximum of 12.52 km3 in 1994. Runoff was generally low in the mid 1970s, high during the 1980s, 1994–95 and 1998–2000, and very low in 1976, 1989 and 1996–97 (Figure 2.1).

The annual mean air temperature at Sprogø in the middle of the Great Belt varied from 5.8°C in 1987 to 8.3°C in 1990 (Figure 2.2). The mean summer (May–Aug.) solar radiation measured close to Copenhagen varied from 175 to 244 W m-2 in 1987 and 1976, respectively (Figure 2.3).

The mean annual wind speed measured 70 m above sea level at Sprogø in the Great Belt varied from 6.3 m s-1 in 1985 to 7.1 m s-1 in 1994 (Figure 2.4).

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Danish Environmental Protection Agency & National Environmental Research Institute • updated: