33 research outputs found
WETMETH 1.0: A New Wetland Methane Model for Implementation in Earth System Models
Wetlands are the single largest natural source of methane (CH4), a powerful greenhouse gas affecting the global climate. In turn, wetland CH4 emissions are sensitive to changes in climate conditions such as temperature and precipitation shifts. However, biogeochemical processes regulating wetland CH4 emissions (namely microbial production and oxidation of CH4) are not routinely included in fully coupled Earth system models that simulate feedbacks between the physical climate, the carbon cycle, and other biogeochemical cycles. This paper introduces a process-based wetland CH4 model (WETMETH) developed for implementation in Earth system models and currently embedded in an Earth system model of intermediate complexity. Here, we (i) describe the wetland CH4 model, (ii) evaluate the model performance against available datasets and estimates from the literature, and (iii) analyze the model sensitivity to perturbations of poorly constrained parameters. Historical simulations show that WETMETH is capable of reproducing mean annual emissions consistent with present-day estimates across spatial scales. For the 2008–2017 decade, the model simulates global mean wetland emissions of 158.6 Tg CH4 yr−1, of which 33.1 Tg CH4 yr−1 is from wetlands north of 45∘ N. WETMETH is highly sensitive to parameters for the microbial oxidation of CH4, which is the least constrained process in the literature
Mercury Export to the Arctic Ocean from the Mackenzie River, Canada
Circumpolar rivers, including the
Mackenzie River in Canada, are
sources of the contaminant mercury (Hg) to the Arctic Ocean, but few
Hg export studies exist for these rivers. During the 2007–2010
freshet and open water seasons, we collected river water upstream
and downstream of the Mackenzie River delta to quantify total mercury
(THg) and methylmercury (MeHg) concentrations and export. Upstream
of the delta, flow-weighted mean concentrations of bulk THg and MeHg
were 14.6 ± 6.2 ng L<sup>–1</sup> and 0.081 ± 0.045
ng L<sup>–1</sup>, respectively. Only 11–13% and 44–51%
of bulk THg and MeHg export was in the dissolved form. Using concentration–discharge
relationships, we calculated bulk THg and MeHg export into the delta
of 2300–4200 kg yr<sup>–1</sup> and 15–23 kg
yr<sup>–1</sup> over the course of the study. Discharge is
not presently known in channels exiting the delta, so we assessed
differences in river Hg concentrations upstream and downstream of
the delta to estimate its influence on Hg export to the ocean. Bulk
THg and MeHg concentrations decreased 19% and 11% through the delta,
likely because of particle settling and other processes in the floodplain.
These results suggest that northern deltas may be important accumulators
of river Hg in their floodplains before export to the Arctic Ocean