Brook Water Quality and Background Leaching from Unmanaged Forested Catchments in Finland

The water chemistry of 21 outlet brooks in undisturbed, forested catchments (0.074–38 km²) in Finland was monitored during three years (1997–1999) in order to estimate the background levels and leaching of total organic carbon (TOC), iron, nitrogen and phosphorus, and examine the relationships between catchment characteristics and brook water quality in pristine forested areas. The studied catchments are located throughout Finland except the northernmost parts of the country. The concentrations of TOC were relatively high, on average 20 mg L^-1. Annual leaching of TOC ranged from 3000 to 10 000 kg km^-2. The average total nitrogen concentration and annual leaching were 430 μg L^-1 and 140 kg km^-2, respectively. The average total phosphorus concentration and annual leaching were 15 μg L^-1 and 5.4 kg km^-2, respectively. On a national level temperature and discharge conditions were the most important variables for predicting total phosphorus, total nitrogen and TOC concentrations. Both total nitrogen and total phosphorus concentrationsdisplayed positive correlation with temperature, and thus the concentrations were higher in the south than in the north. Nitrogen was mainly organic and showed strong correlation with TOC. On the catchment level, both TOC and total nitrogen concentrations and export had a strongpositive correlation with the abundance of Norway spruce (Piceaabies Karsten) and a strong negative correlation with the abundance of Scots pine (Pinus sylvestris L.). Nitrate concentrations and leaching were related to average site type. The more fertile the average site type was in the catchment, the higher the nitrate concentrations and export were.     

Acid neutralizing capacity of solutions containing organic acids isolated from Finnish lakes

Organic vs. bicarbonate contribution to Gran alkalinity was studied using empirical measurements. Distilled water with various amounts of bicarbonate and organic acids was equilibrated with synthetic air during Gran titrations. Natural organic acids isolated from Finnish lakes were used as a carbon source for these solutions. The experimental design corresponded to computer simulations made by Cantrell et al. (1990). The results indicate that the discrepancy between the Gran ANC and the ANC calculated from anion deficit can be explained partly by the organic acids, which remain unprotonated in the titration. The unprotonated fraction of organic acids was on average 5.5 and 6.2 eq per mg of dissolved organic carbon (DOC), when pH ranges of 3.0–4.0 and 3.5–4.5 for Gran plot regression were used, respectively. The acid neutralizing capacity provided by organic acids varied from 18 to 75 eq/L, depending on the initial pH and DOC concentration and the pH range of the Gran plot regression. The results of empirical Gran titrations agree with the theoretical calculations made by Cantrell et al. (1990).