Export of DOM from Boreal Catchments: Impacts of Land Use Cover and Climate

Abstract

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 km 2 , 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 = À0.83, r = À0.82 and r = À0.61, respectively). The higher the upstream lake percentage, the lower the export indicating organic matter retention in lakes.

Dissolved organic carbon in New Zealand peatlands

“…Collier et al (1989) and Moore & Jackson (1989) examined DoC concentrations and fluxes in Westland (South Island) catchments containing Pakihi poorly drained soils, noting high DoC concentrations and export (30 to 38 mg litre -1 and 31 to 44 g m -2 yr -1 , respectively) and an increase in export with catchment drainage for forestry, in contrast to export of 8 to 21 g m -2 yr -1 in nearby upland forested and harvested sites (Moore 1989). in the Northern Hemisphere, several studies have recorded high DoC concentrations within peat porewaters and the concentration in streams is often closely related to the proportion of peatland within the catchment (e.g., eckhardt & Moore 1990;Mattson et al 2005).…”

Predicting the export and concentrations of organic carbon, nitrogen and phosphorus in boreal lakes by catchment characteristics and land use: A practical approach

“…The DON predictions, in turn, were only satisfactory. The catchments with the highest peatland proportion had the highest TOC, DON and DOP export loads and modelled and measured concentrations, which is a typical observation in boreal and temperate regions (Dillon and Molot 1997;Pellerin et al 2004;Mattsson et al 2005;Williams et al 2005;Kortelainen et al 2006). DOM exports are large because peatlands are in close hydrological contact with receiving watercourses, peat C storage is large, organic matter decomposition is incomplete due to the anaerobic conditions, and the peat contains few compounds that can retain C such as iron and aluminium (Domisch et al 2000;Kalbitz et al 2000;Freeman et al 2001).…”

“…In addition to low peatland percentage, the catchments of the lakes 9-12 also contained agricultural land (3.5-17 % of the area). The C:N ratio of leached organic matter is typically lower in agricultural than peatland dominated catchments (Mattsson et al 2005), which may also increase the decomposition of organic matter and result in lower TOC, DON and DOP concentrations. Furthermore, it has been found that TOC, DON and DOP concentrations and export decrease with increasing percentage of lakes in the catchment areas (Mattsson et al 2005).…”

“…The C:N ratio of leached organic matter is typically lower in agricultural than peatland dominated catchments (Mattsson et al 2005), which may also increase the decomposition of organic matter and result in lower TOC, DON and DOP concentrations. Furthermore, it has been found that TOC, DON and DOP concentrations and export decrease with increasing percentage of lakes in the catchment areas (Mattsson et al 2005). The catchments of lakes 9-12 had high water percentage (17-32 % of the catchment area), and the overestimation of TOC, DON and DOP concentrations may be due to that part of the organic matter is retained in the upstream lakes (Mattsson et al 2005).…”

“…Furthermore, it has been found that TOC, DON and DOP concentrations and export decrease with increasing percentage of lakes in the catchment areas (Mattsson et al 2005). The catchments of lakes 9-12 had high water percentage (17-32 % of the catchment area), and the overestimation of TOC, DON and DOP concentrations may be due to that part of the organic matter is retained in the upstream lakes (Mattsson et al 2005). The clear-water lakes 9-12 were rather large and deeper than the other lakes (Table 1).…”