Integrating aquatic and terrestrial components to construct a complete carbon budget for a north temperate lake district

Abstract

The development of complete regional carbon (C) budgets for different biomes is an integral step in the effort to predict global response and potential feedbacks to a changing climate regime. Wetland and lake contributions to regional C cycling remain relatively uncertain despite recent research highlighting their importance. Using a combination of field surveys and tower-based carbon dioxide (CO 2 ) flux measurements, modeling, and published literature, we constructed a complete C budget for the Northern Highlands Lake District in northern Wisconsin/ Michigan, a $6400 km 2 region rich in lakes and wetlands. This is one of the first regional C budgets to incorporate aquatic and terrestrial C cycling under the same framework. We divided the landscape into three major compartments (forests, wetlands, and surface waters) and quantified all major C fluxes into and out of those compartments, with a particular focus on atmospheric exchange but also including sedimentation in lakes and hydrologic fluxes. Landscape C storage was dominated by peat-containing wetlands and lake sediments, which make up only 20% and 13% of the landscape area, respectively, but contain 480% of the total fixed C pool (ca. 400 Tg). We estimated a current regional C accumulation of 1.1 AE 0.1 Tg yr À1 , and the largest regional flux was forest net ecosystem exchange (NEE) into aggrading forests for a total of 1.0 AE 0.1 Tg yr À1 . Mean wetland NEE (0.12 AE 0.06 Tg yr À1 into wetlands), lake CO 2 emissions and riverine efflux (each ca. 0.03 AE 0.01 Tg yr À1 ) were smaller but of consequence to the overall budget. Hydrologic transport from uplands/wetlands to surface waters within the region was an important vector of terrestrial C. Regional C fluxes and pools would be misrepresented without inclusion of surface waters and wetlands, and C budgets in heterogeneous landscapes open opportunities to examine the sensitivities of important fluxes to changes in climate and land use/land cover.

Regional-scale lateral carbon transport and CO<sub>2</sub> evasion in temperate stream catchments

“…Although this range of variation is most likely within the uncertainty of the various estimates, the variability across different landscapes is certainly small in comparison to the order of magnitude differences in potential controlling factors like catchment NPP, fractional water coverage as well as size and climatic zone of the study area. In lake-rich regions, evasion from inland waters was observed to be dominated by lakes (Buffam et al, 2011;Jonsson et al, 2007), which cover up to 13 % of the surface area of those regions. In the present study, as well as in other studies on catchments where lakes are virtually absent (Wallin et al, 2013) and the fractional water coverage was smaller than 0.5 % of the terrestrial surface area, an almost identical Table 3.…”

“…Only few studies have quantified C fluxes and pools including inland waters at the regional scale (10 3 -10 4 km 2 ) (Chris-tensen et al, 2007;Buffam et al, 2011;Jonsson et al, 2007;Maberly et al, 2013) or for small (1-10 km 2 ) catchments (Leach et al, 2016;Shibata et al, 2005;Billett et al, 2004). The majority of existing regional-scale studies on terrestrialaquatic C fluxes are from the boreal zone and are characterized by a relatively large fractional surface area covered by inland waters, a high abundance of lakes and high fluvial loads of dissolved organic carbon (DOC).…”

The role of waterborne carbon in the greenhouse gas balance of drained and re-wetted peatlands

“…However, much of the research on GHG emissions from peatland water bodies has been carried out within natural features such as streams, pools and lakes (e.g. Hope et al, 2001;Billett and Moore, 2008;Repo et al, 2007;Dinsmore et al, 2010;Buffam et al, 2011;Koehler et al, 2011;Juutinen et al, 2013;Wallin et al, 2013). While this has enhanced our understanding of fundamental processes, natural fluxes and measurement techniques, it has not provided direct data on GHG emissions from artificial water bodies within managed peatlands, notably drainage ditches.…”

“…Worrall et al (2014) estimated that 23% of POC in UK river systems is mineralised before reaching the estuary, but did not provide an estimate of burial rates in freshwater sediments. These burial rates are likely to be higher in lake-dominated boreal regions than in UK rivers, therefore we estimated freshwater POC burial at 20% of riverine input (range 10-30%) based on values reported by Gudasz et al (2010), Algesten et al (2003), Buffam et al (2011) and Tranvik et al (2009). For estuaries, we took the estimate of Worrall et al (2014), based on a previous analysis by Tappin et al (2003), that 45% of POC reaching estuaries is mineralised before it reaches the sea, and 4% buried in estuarine sediments.…”

“…Jonsson et al (2007) estimated that 45% of all terrestrially-derived organic carbon was mineralised and evaded as CO2 within a 3000 km 2 mixed boreal catchment, with sedimentation negligible and the remainder exported to the sea. For a 6400 km 2 lake-rich catchment in the Northern United States, Buffam et al (2011) estimated that 33% of terrestrial C inputs to the aquatic system were degassed as CO2, 2% as CH4, 26% accumulated in sediments and 40% transported downstream. For a set of 21 large Swedish boreal catchments, Algesten et al (2003) estimated that 50% of all organic carbon entering the aquatic system was removed, with CO2 degassing accounting for 90% of removal and sedimentation for 10%.…”