Leaching of Nutrients,Organic Carbon and Iron from Finnish Forestry Land

This study provides an assessment of the spatial variability of the long-term leaching of nutrients, total organic carbon (TOC) and iron (Fetot) from 22 forested catchments (0.69-56 km2), distributed across all but the northenmost areas of Finland. The natural, unmanaged Kruunuoja catchment is located in a national park, while the other catchments represent Finnish forestry land. The average leaching of Ptot (4.2 kg km-2 yr^-1) from the Kruunuoja catchment was small compared to the catchments representing forestry land (on average 10 kg km-2 yr^-1). Moreover, P fertilization was the most important predictor for the spatial variation in Ptot leaching (r2=0.45). Leaching of TOC, Fetot and N compounds was not closely related to forestry practices. Median C/N ratio in the study streams was high (range 34-66). The average inorganic N proportion and leaching of P_tot were lowest in the Kruunuoja catchment (7.3 % and 2.8 kg km-2 yr^-1, respectively) and highest in the southernmost Teeressuonoja catchment (54 % and 100 kg km-2 yr^-1, respectively) located in the highest N deposition area. The most important forestry practices since the 1960's have affected about 2.4 % of the area of study sites per year (cf. 2% in the entire country in 1991). Moreover, the mean annual runoff from the catchments (230-430 mm yr^-1) agrees with the mean annual runoff from Finland (301 mm yr^-1). Consequently, the results of the study catchments can be used to estimate average total annual leaching from Finnish forestry land: 2,700 t of Ptot, 48,000 t of Ntot, 110,000 t of Fetot and 1.5 million t of TOC.     

Organic vs. minerogenic acidity in headwater streams in Finland

This study provides an assessment of the transport of organic carbon and organic acids from typical Finnish forested catchments since the 1960's. The 21 study catchments (0.69–56 km²) are located over Finland excluding the northernmost regions. The mean annual total organic carbon (TOC) load from the catchments ranges from 2 600 to 8 800 kg/km²/a. Using a total acidity of 9.7 eq/mg DOC this would represent organic acid load of about 25–85 keq/km²/a which is higher than the mean annual deposition of strong acids in the highest deposition areas in southern Finland. The study demonstrates that organic acids dominate stream water acidity over large regions in Finland. In southern Finland minerogenic acidity is, however, more important. Organic acids exceeded mineral acids not only in autumn but also during spring snowmelt in 18 catchments. Moreover, the lowest pH values (25th percentile) were dominated by organic acids in 20 catchments. In most catchments TOC better explained pH than non-marine sulphate. In stepwise multiple regression base cations and TOC explained 67–83 % of the variation in pH for catchments divided into six groups according to season, deposition and peatland percentage; non-marine sulphate had minor contribution.