Pirkko Kortelainen

Global carbon dioxide emissions from inland waters

Carbon dioxide (CO2) transfer from inland waters to the atmosphere, known as CO2 evasion, is a component of the global carbon cycle. Global estimates of CO2 evasion have been hampered, however, by the lack of a framework for estimating the inland water surface area and gas transfer velocity and by the absence of a global CO2 database. Here we report regional variations in global inland water surface area, dissolved CO2 and gas transfer velocity. We obtain global CO2 evasion rates of 1.8  petagrams of carbon (Pg C) per year from streams and rivers and 0.32  Pg C yr−1 from lakes and reservoirs, where the upper and lower limits are respectively the 5th and 95th confidence interval percentiles. The resulting global evasion rate of 2.1 Pg C yr−1 is higher than previous estimates owing to a larger stream and river evasion rate. Our analysis predicts global hotspots in stream and river evasion, with about 70 per cent of the flux occurring over just 20 per cent of the land surface. The source of inland water CO2 is still not known with certainty and new studies are needed to research the mechanisms controlling CO2 evasion globally.

Sediment organic carbon burial in agriculturally eutrophic impoundments over the last century

The OC buried in these lakes originates in both autochthonous and allochthonous production. These analyses suggest that OC sequestration in moderate to large impoundments may be double the rate assumed in previous analyses. Extrapolation suggests that they may bury 4 times as much carbon (C) as the world’s oceans. The world’s farm ponds alone may bury more OC than the oceans and 33% as much as the world’s rivers deliver to the sea.

Leaching of nitrogen from forested catchments in Finland

This study provides an assessment on the spatial variability of the long-term leaching (8-23 years) of nitrogen and organic carbon from 22 forested catchments (0.69-56 km 2 ). The catchments are located throughout Finland excluding the northernmost regions. The Kruunuoja catchment is located in a national park; the other catchments represent typical Finnish forestry land. The leaching from the 21 forestry land catchments can be considered to represent average leaching from Finnish forestry land since the most important forestry practices (ditching, clear-cutting, scarification, and fertilization) since the 1960s have affected about 2.4% of the catchment area per year (compare 2.5% in the entire country in 1980 and 2% in 1991). Moreover, the mean annual runoff from the catchments, 230-420 mm yr -1 , agree with the mean annual runoff from Finland (301 mm yr -1 from 1931 to 1990). The major part of the nitrogen transported from the catchments consisted of organic nitrogen (on average 79%). The average inorganic nitrogen proportion ((NO 3 -N + NH 4 -N)/N tot ) was lowest (7.3%) in the Kruunuoja catchment and was highest (54%) in the southernmost Teeressuonoja catchment located in the highest anthropogenic nitrogen deposition area. The median C/N ratio in the study streams was high, ranging from 34 to 66. Nitrate leaching from the catchments varied between 2.8 (Kruunuoja) and 100 kg km -2 yr -1 (Teeressuonoja) and was negatively related to C/N ratio in stream water and latitude. The stepwise multiple regression model selected C/N ratio and nitrogen deposition which together explained 72% of the variation in NO 3 -N leaching. Retention of NO 3 -N deposition (calculated as ((input-output)/input) was high in all catchments, ranging from 0.99 in Kruunuoja to 0.67 in Tceressuonoja.

Global abundance and size distribution of streams and rivers

Abstract To better integrate lotic ecosystems into global cycles and budgets, we provide approximations of the size-distribution and areal extent of streams and rivers. One approach we used was to employ stream network theory combined with data on stream width. We also used detailed stream networks on 2 continents to estimate the fraction of continental area occupied by streams worldwide and corrected remote sensing stream inventories for unresolved small streams. Our estimates of global fluvial area are 485 000 to 662 000 km2 and are +30–300% of published appraisals. Moderately sized rivers (orders 5–9) seem to comprise the greatest global area, with less area covered by low and high order streams, while global stream length, and therefore the riparian interface, is dominated by 1st order streams. Rivers and streams are likely to cover 0.30–0.56% of the land surface and make contributions to global processes and greenhouse gas emissions that may be +20–200% greater than those implied by previous estimates.

Trends in hydrometeorological conditions and stream water organic carbon in boreal forested catchments

Temporal trends in stream water total organic carbon (TOC) concentration and export were studied in 8 forested headwater catchments situated in eastern Finland. The Seasonal Kendall test was conducted to identify the trends and a mixed model regression analysis was used to describe how catchment characteristics and hydrometeorological variables (e.g. precipitation, air and stream water temperatures, and atmospheric deposition) related to the variation in the concentration and export of stream water TOC. The 8 catchments varied in size from 29 to 494 ha and in the proportion of peatland they contained, from 8 to 70%. Runoff and TOC concentration were monitored for 15-29 years (1979-2006). Trends and variation in TOC levels were analysed from annual and seasonal time series. Mean annual TOC concentration increased significantly in seven of the eight catchments. The trends were the strongest in spring and most apparent during the last decade of the study period. The slopes of the trends were generally smaller than the variation in TOC concentration between years and seasons and between catchments. The annual TOC export showed no clear trends and values were largely determined by the temporal variability in runoff. Annual runoff showed a decreasing trend in two of the eight catchments. Mean annual air and stream water temperatures showed increasing trends, most clearly seen in the summer and autumn series. According to our modeling results, stream water temperature, precipitation and peatland percentage were the most important variables explaining annual and most seasonal TOC concentrations. The atmospheric deposition of SO4, NH4, and NO3 decreased significantly over the study period, but no significant link with TOC concentration was found. Precipitation was the main hydrometeorological driver of the TOC export. We concluded that stream water TOC concentrations and exports are mainly driven by catchment characteristics and hydrometeorological factors rather than trends in atmospheric acid deposition.

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.

Export of dissolved organic matter in relation to land use along a European climatic gradient

The terrestrial export of dissolved organic matter (DOM) is associated with climate, vegetation and land use, and thus is under the influence of climatic variability and human interference with terrestrial ecosystems, their soils and hydrological cycles. We present a data-set including catchments from four areas covering the major climate and land use gradients within Europe: a forested boreal zone (Finland), a temperate agricultural area (Denmark), a wet and temperate mountain region in Wales, and a warm Mediterranean catchment draining into the Gulf of Lyon. In all study areas, DOC (dissolved organic carbon) was a major fraction of DOM, with much lower proportions of DON (dissolved organic nitrogen) and DOP (dissolved organic phosphorus). A south-north gradient with highest DOC concentrations and export in the northernmost catchments was recorded: DOC concentrations and loads were highest in Finland and lowest in France. These relationships indicate that DOC concentrations/export are controlled by several factors including wetland and forest cover, precipitation and hydrological processes. DON concentrations and loads were highest in the Danish catchments and lowest in the French catchments. In Wales and Finland, DON concentrations increased with the increasing proportion of agricultural land in the catchment, whereas in Denmark and France no such relationship was found. DOP concentrations and loads were low compared to DOC and DON. The highest DOP concentrations and loads were recorded in catchments with a high extent of agricultural land, large urban areas or a high population density, reflecting the influence of human impact on DOP loads.

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 NO 3 − -N 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.

Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire: an expert assessment

As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release w ...

Finnish lake survey: the role of organic and anthropogenic acidity

A lake survey consisting of 987 randomly selected lakes was conducted in Finland in autumn 1987. The survey covered the whole country, and the water quality of the lakes can be considered as representative of the approximately 56 000 lakes larger than 0.01 km2 in Finland. The median TOC concentration is 12 mg L-1 and the median pH 6.3. The proportion of lakes with TOC concentrations > 5 mg L-1 in the whole country is 91 %. Organic anion is the main anion in the full data set (median 89 μeq L-1). The high organic matter concentrations in Finnish lakes are associated with catchment areas containing large proportions of peatlands and acid organic soils under coniferous forest. The survey demonstrated that organic matter strongly affects the acidity of lakes in Finland. The decreasing effect of organic matter on the pH values was demonstrated by both regression analysis and ion balances. At current deposition levels of *SO4 the pH of humic lakes in Finland is determined to a greater extent by high TOC concentrations than by *SO4 in most areas. In lakes with pH values lower than 5.5 the average organic anion contribution is 56 % and non-marine sulfate contribution 39 %. However, in the southern parts of the country, where the acidic deposition is highest, the minerogenic acidity commonly exceeds the catchment derived organic acidity.