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Finnish rivers exported annually on average 1.2 M t carbon, and total organic carbon (TOC) comprised the major share (nearly 80 %) of this export. The mean area specific carbon export was 4.5 g C m year. The highest organic carbon export originated from peat dominated catchments, whereas rivers draining agricultural catchments had the highest area-specific inorganic carbon fluxes. Between 1975 and 2014 total inorganic carbon (TIC) concentrations rose more steadily than the respective TOC concentrations. There was an overall decrease in TOC concentrations between 1975 and the mid-1990s. Decreased point source loading contributed to this pattern, although decreases were also detected in rivers without any major pollution sources. From the mid-1990s TOC concentrations started to rise and the increase was even more pronounced than the earlier decrease. The upward trend was ubiquitous, both in time and space, and it was not possible to link the changes to any specific catchment characteristics or another single driver. Warming climate, changes in hydrology and decreases in acidic deposition were the major driving factors although their contribution varied geographically. At the same time both TOC and TIC export increased slightly, but the strong upward trends in TOC concentrations were not reflected as clearly in TOC export trends. This was because changes in water flow had a dominant influence on TOC export to the sea and any changes in concentrations were masked behind the variation in flow. [ABSTRACT FROM AUTHOR]

Large-scale forestry operations, like clear-cutting, may impair surface water quality if not done with environmental considerations in mind. Catchment and country level estimates of nutrient loads from forestry are generally based on specific export values, i.e., changes in annual exports due to the implemented forestry operations expressed in kg ha. We introduce here a specific concentration approach as a method to estimate the impact of clear-cutting on nutrient concentrations and export in headwater streams. This new method is potentially a more dynamic and flexible tool to estimate nutrient loads caused by forestry, because variation in annual runoff can be taken into account in load assessments. We combined water quality data from eight boreal headwater catchment pairs located in Finland and Sweden, where the effect of clear-cutting on stream water quality has been studied experimentally. Statistically significant specific concentration values could be produced for total nitrogen, nitrate, ammonium, and phosphate. The significant increases in the concentrations of these nutrients occurred between 2 and 6 years after clear-cutting. Significant specific concentration values could not be produced for total phosphorus and total organic carbon with the whole dataset, although in some single studies significant increases in their concentrations after clear-cutting were observed. The presented method enables taking into account variation in runoff, temporal dynamics of effects, and the proportional size of the treated area in load calculations. The number of existing studies considering large site-specific variation in responses to clear-cutting is small, and therefore further empirical studies are needed to improve predictive capabilities of the specific concentration values. [ABSTRACT FROM AUTHOR]

The long-term impacts of current forest management methods on surface water quality in Fennoscandia are largely unexplored. We studied the long-term effects of clear-cutting and site preparation on runoff and the export of total nitrogen (total N), total organic nitrogen (TON), ammonium (NH-N), nitrate (NO-N), total phosphorus (total P), phosphate (PO-P), total organic carbon, and suspended solids (SS) in three paired-catchments in Eastern Finland. Clear-cutting and soil preparation were carried out on 34 % (C34), 11 % (C11), and 8 % (C8) of the area of the treated catchments and wide buffer zones were left along the streams. Clear-cutting and soil preparation increased annual runoff and total N, TON, NO-N, PO-P, and SS loads, except for SS, only in C34. Runoff increased by 16 % and the annual exports of total N, TON, NO-N, and PO-P by 18, 12, 270, and 12 %, respectively, during the 14-year period after clear-cutting. SS export increased by 291 % in C34, 134 % in C11, and 16 % in C8 during the 14, 6, and 11-year periods after clear-cutting. In the C11 catchment, NO-N export decreased by 12 %. The results indicate that while current forest management practices can increase the export of N, P and SS from boreal catchments for many years (>10 years), the increases are only significant when the area of clear cutting exceeds 30 % of catchment area. [ABSTRACT FROM AUTHOR]

Associations between catchment characteristics (altitude, slope, proportion of peatland, site fertility, total stem volume, and its distribution among the main tree species), climatic drivers (temperature sum, latitude, precipitation and runoff) and atmospheric deposition and concentrations and export of C, N, P and Fe in 21 unmanaged boreal catchments (0.07 to 14 km2) were examined in data sets spanning 3 to 32 years. In the entire data base including catchments from southernmost Finland to the Arctic Circle, N and P concentrations were associated with climatic drivers and deposition, while a catchment characteristic, peatland percentage, reflecting topography and site fertility was the best predictor for TOC (total organic carbon) and total Fe concentrations and export. In a subgroup of 18 catchments located in similar climatic conditions and low N deposition in eastern Finland (<600 kg N km–2 yr–1), peatland percentage accounted for 52–75% of the export of TOC, TN (total nitrogen), TON (total organic nitrogen), NH4-N and total Fe, while slope was the best predictor of TP (total phosphorus) export (r2 = 0.56, p < 0.001). Furthermore, among these 18 catchments TOC export accounted for as much as 95% of the variance in TON export, and 61–73% of the variance in NH4-N, total Fe and TP export. Total stem volume of the tree stands and their distribution between tree species and vegetation types were not important predictors for concentrations/export. The peatland percentage of the 21 catchments ranged widely, from 0 to 88% , with an average value of 34% as in entire Finland. Consequently, among the 21 catchments there was also a large variability both in average TOC and pH, 1.2–30 mg l–1 and 4.2–7.1, respectively. The average annual TOC export was 6,200 kg km–2 yr–1 , significantly lower values were recorded for the export of TN, TP and total Fe (130, 5 and 280 kg km–2 yr–1, respectively). N and P export was mainly in an organic form. The TIN (total inorganic N) proportion averaged 13% and elevated NO3-N export occurred only in fertile, high pH sites in southernmost Finland, where stream C/N ratio was lowest. On average, 97% of the TOC, 94% of the TN and 79% of the TP was in a dissolved form. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) is an important fraction in carbon (C) and nutrient budgets for aquatic ecosystems and can have broad effects on food webs and nutrient cycling. To look at the role land use cover and climate might play in DOM transport from the boreal region, the export of total organic carbon (TOC), total organic nitrogen (TON) and dissolved organic phosphorus (DOP) was estimated for Finnish main rivers and their sub-catchments, altogether 86 catchments, situated between latitudes 60° N and 69° N and covering 297,322 km2, 88% of the total area of Finland. On an average, 94% of the TOC, 90% of the total nitrogen (TN) and 40% of the total phosphorus (TP) in Finnish rivers was in a dissolved form. The majority of the DOM export from Finnish catchments consists of organic C. The TOC export increased with increasing peatland proportion ( r = 0.39, p = 0.003), while TON export increased with the increasing percentage of agricultural land ( r = 0.60, p <0.001). Although upstream lakes covered only on average 9% of the catchment area, they were the most important predictor for TOC, TON and DOP export ( r = −0.83, r = −0.82 and r = −0.61, respectively). The higher the upstream lake percentage, the lower the export indicating organic matter retention in lakes. [ABSTRACT FROM AUTHOR]

Long-term base cation balances (Ca, Mg and K) for forest mineral soils in Finland were calculated with mass balance methods. The aim of the study was to identify the areas in which weathering and base cation deposition do not support leaching and uptake of base cations by vegetation. The effect of stem harvesting and whole-tree harvesting on the base cation balances was studied and preliminary calculations were made about the amounts of ash needed for compensation of the potential base cation depletion. The effect of sulphur emission reduction till 2010 was also considered. The study demonstrated that there would be depletion of base cations in forest mineral soils in southern, central and northeastern Finland (40–50% of the grids) in the long term if whole-tree harvesting would be practised. Theoretical calculations showed that ash application would be most useful in those areas to compensate the base cation depletion. If stem harvesting is practised, only small areas (20%) in southwestern and southeastern Finland and northeastern Lapland would show depletion of base cations in the long term. [ABSTRACT FROM AUTHOR]

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 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. [ABSTRACT FROM AUTHOR]