Modelling the effects of climate on long-term patterns of dissolved organic carbon concentrations in the surface waters of a boreal catchment

Abstract

Abstract. Dissolved organic carbon concentrations ([DOC])in surface waters are increasing in many regions of Europe and North America. These increases are likely driven by a combination of changing climate, recovery from acidification and change in severity of winter storms in coastal areas. INCA-C, a process-based model of climate effects on surface water [DOC], was used to explore the mechanisms by which changing climate controls seasonal to inter-annual patterns of [DOC] in the lake and outflow stream of a small Finnish catchment between 1990 and 2003. Both production in the catchment and mineralization in the lake controlled [DOC] in the lake. Concentrations in the catchment outflow were controlled by rates of DOC production in the surrounding organic soils. The INCA-C simulation results were compared to those obtained using artificial neural networks (ANN). In general, "black box" ANN models provide better fits to observed data but process-based models can identify the mechanism responsible for the observed pattern. A statistically significant increase was observed in both INCA-C modelled and measured annual average [DOC] in the lake. This suggests that some of the observed increase in surface water [DOC] is caused by climate-related processes operating in the lake and catchment. However, a full understanding of surface water [DOC] dynamics can only come from catchment-scale process-based models linking the effects of changing climate and deposition on aquatic and terrestrial environments.

Almost 50 years of monitoring shows that climate, not forestry, controls long‐term organic carbon fluxes in a large boreal watershed

“…There are a number of possible reasons for this: (i) an inappropriate model structure; (ii) problems with the calibration strategy or (iii) data quality issues. INCA‐C has been used to simulate high and variable TOC concentrations (Futter et al ., , ), suggesting that the model structure is appropriate. The calibration strategy used here based on NS statistics derived from the whole set of observations is not good at capturing rare events.…”

“…() who report that in 1991 over 30% of watershed (i.e., about 60% of the peatlands and peatland forests) had been drained. INCA‐C model parameterization was based on values for forests and peatlands from the Valkea‐Kotinen reference catchment in southern Finland (Futter et al ., , ). The effects of forest harvest on soil temperature were simulated by adjusting the thermal conductivity parameters of the soil‐temperature submodel in INCA‐C (Rankinen et al ., ) so that the simulated soil warming matched that observed by Schelker et al .…”

“…Process‐based and conceptual models are often used to check whether we understand the controls on surface water DOC dynamics (Futter et al ., ; Ledesma et al ., ; Oni et al ., ). The Integrated Catchments model for Carbon (INCA‐C) has been applied to headwater catchments in Fennoscandia (Futter & de Wit, ; Futter et al ., , , ) and to larger, temperate catchments in Sweden (Ledesma et al ., ) and Canada (Oni et al ., ).…”

Generality of Hydrologic Transport Limitation of Watershed Organic Carbon Flux Across Ecoregions of the United States

“…Despite the clear need for models capable of simulating DOC production and transport at spatiotemporal scales compatible with Earth system models, developing models with both predictive power and realistic hydrology and biology has been elusive (Abbott, Jones, et al, 2016;Kicklighter et al, 2013). Models of terrestrial DOC routing and export exist, but they are typically constrained in terms of parameterization needs and functionality across a range of spatiotemporal scales (Abbott, Baranov, et al, 2016;Futter et al, 2008;Schelker et al, 2011). In particular, these models of DOC transport are not yet capable of coupling the rapid shifts in hydrologic and biogeochemical processes that occur during flow event time scales (hours to days), when DOC export is greatest in most watersheds.…”

Long-term energy flux measurements and energy balance over a small boreal lake using eddy covariance technique

“…The mean and maximum depths are 2.5 and 6.5 m, respectively, whereas the average volume is 7.7 × 10 4 m 3 . The catchment area is small, 0.30 km 2 in size, and consists mainly of an old pristine forest and a small area of peatland [Futter et al, 2008]. Valkea-Kotinen is the uppermost lake in a lake chain and receives water from its drainage basin by surface and groundwater runoff, whereas there is a small outlet in the southern end of the lake.…”