Abstract
Highly dynamic hydro-geomorphic processes are known to drive exports of carbon (C) from river basins, but are not yet fully understood. Within this study, we simulated total organic carbon (TOC) exports at the outlet of Lake Simojärvi in the Gulf of Bothnia (Finland) with a parsimonious hydrological model. With thorough consideration of the dependence of erosion and sediment transport processes on seasonal precipitation rates, a satisfactory agreement was obtained between modelling and experimental observations (1962–2005). This provided confidence in the capability of the parsimonious model to represent temporal and spatial export dynamics. In the period 1860–2014, TOC export at the outlet of Lake Simojärvi was estimated to be highest on average (~5.5 Mg km−2·year−1) over 1974–2014 while the lowest TOC export (~2.5 Mg km−2·year−1) was estimated in 1860–1918 (with high levels of interannual-to-multidecadal variation). Regional simulations indicate that TOC increased in recent decades (on average, 4–5 Mg km−2·year−1 in 1974–2014 against ~3 Mg km−2·year−1 in 1940–1973) in northern Scandinavia and Finland. Warming-induced variability of TOC (which depends on precipitation patterns) may have altered the rates of C exchanges in aquatic ecosystems over recent years. TOC exports may continue to increase in boreal catchments with increasing temperatures as represented by future projections.
Highlights
Northern soils are known to store large quantities of carbon (C), though the susceptibility of C to be released as a consequence of environmental changes is uncertain
With the minimalist regression model developed in this study, we address for the effect of multiple sediment sources, while considering the system complexity and process interactions for total organic carbon (TOC) export
The values of the parameters obtained from the full set of TOC observations available (1962–2005)
Summary
Northern soils are known to store large quantities of carbon (C), though the susceptibility of C to be released as a consequence of environmental changes is uncertain. Climate and land-use changes pose a potential threat to further losses of C [1]. The importance of small streams in C cycling is highlighted in Huotari et al [1] and other studies (e.g., [2,3]). C-budget studies have incorporated surface waters in watersheds covering large areas, mostly in remote regions having limited human disturbance (e.g., [4,5]). Human induced perturbations within catchments affect C export into aquatic systems and may have large implications in regional C cycling. Peatland drainages trigger successions in C cycling and export to aquatic systems [7]
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