Nutrient variations in boreal and subarctic Swedish rivers: Landscape control of land‐ sea fluxes

Abstract

We examined the hypothesis that the extent of vegetation cover governs the fluxes of nutrients from boreal and subarctic river catchments to the sea. Fluxes of total organic carbon (TOC) and dissolved inorganic nitrogen, phosphorus, and dissolved silicate (DIN, DIP, and DSi, respectively) are described from 19 river catchments and subcatchments (ranging in size from 34 to 40,000 km2) in northern Sweden with a detailed analysis of the rivers Luleälven and Kalix%lven. Fluxes of TOC, DIP, and DSi increase by an order of magnitude with increasing proportion of forest and wetland area, whereas DIN did not follow this pattern but remained constantly low. Principal component analysis on landscape variables showed the importance of almost all land cover and soil type variables associated with vegetation, periglacial environment, soil and bedrock with slow weathering rates, boundary of upper tree line, and percentage of lake area. A cluster analysis of the principal components showed that the river systems could be separated into mountainous headwaters and forest and wetland catchments. This clustering was also valid in relation to river chemistry (TOC, DIP, and DSi) and was confirmed with a redundancy analysis, including river chemistry and principal components as environmental variables. The first axis explains 89% of the variance in river chemistry and almost 100% of the variance in the relation between river chemistry and landscape variables. These results suggest that vegetation change during interglacial periods is likely to have had a major effect on inputs of TOC, DIP, and DSi into the past ocean.

Riverine transport of biogenic elements to the Baltic Sea – past and possible future perspectives

“…Temperature increases above the global average have been predicted at high latitudes in the northern hemisphere and increases in temperature and water discharge have already been recorded in the largest Eurasian rivers (Peterson et al, 2002). Similar trends were also foreseen for the boreal and subarctic part of the Baltic Sea catchment (Graham, 2004) and the unperturbed boreal rivers of the Baltic region can be regarded as model systems for the large Siberian rivers since biogeochemical characteristics of the watersheds are similar (Humborg et al, 2004;Smedberg et al, 2006). More recently, work has focused on the role of hydrological interactions with the C budget of entire landscapes.…”

The relationship between subsurface hydrology and dissolved carbon fluxes for a sub-arctic catchment

“…To do this, we develop a simple twocomponent hydrograph separation (Sklash and Farvolden, 1979;Buttle and McDonnell, 2004) using long-term monthly samplings of stream water alkalinity. As alkalinity is added to surface water via the deeper pathways in this system (Humborg et al, 2004), we can use the monthly average alkalinity values to separate the observed total streamflow into water coming from the deeper versus shallow flow domain. This assumes that stream flow is primarily derived from the deeper flow domain during winter since the shallow flow domain freezes, and that alkalinity levels thus provide a tracer of water from the deep flow domain.…”

Light limitation of primary production in high latitude reservoirs

“…In the headwaters of the River Luleälven, gross primary production in the dominating reservoir, Akkajaure (67 o N) is low (~ 4-5 g C m 2 a 1 ) despite an excess of DIN (dissolved inorganic nitrogen) and TOC (total organic carbon) (Humborg et al, 2004). The early summer concentrations of DIN and DSi are about 2.5 and 13.3 mM respectively but only 0.01 mM for DIP (dissolved inorganic phosphorus).…”