Brookwater quality and background leaching from unmanaged forested catchments in Finland

The water chemistry of 21 outlet brooks in undisturbed, forested catchments (0.074-38 km(2)) 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 mug L-1 and 140 kg km(-2), respectively. The average total phosphorus concentration and annual leaching were 15 mug 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 concentrations displayed 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 strong positive correlation with the abundance of Norway spruce (Picea abies 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.