Spatially explicit, landscape-scale modelling of GHG sources and sinks

Maria Holmberg and colleagues present an approach to collate spatially explicit estimated fluxes of GHGs (carbon dioxide, methane and nitrous oxide) for the main land use sectors in the landscape, and show how these fluxes can be aggregated to calculate net emissions of an entire region. They used INCA-C and PERSiST to estimate the flux of organic carbon from terrestrial ecosystems to lakes and rivers.

They developed and tested the approach in a large river basin in Finland, providing information from intensively studied eLTER research sites. To evaluate the full GHG balance, they included fluxes from natural ecosystems (lakes, rivers, and undrained mires) together with anthropogenic fluxes from agriculture and forestry. They quantified fluxes using an anthropogenic emissions model (FRES), a forest growth and carbon balance model (PREBAS), and literature values for emissions from lakes, rivers, undrained mires, peat extraction sites and cropland. Spatial data sources included CORINE land use data, soil map, lake and river shorelines, national forest inventory data, and statistical data on anthropogenic activities. Emission uncertainties were evaluated with Monte Carlo simulations. They summed the vertical fluxes of spatially explicit net emissions, disregarding the impact of lateral fluxes from terrestrial to aquatic ecosystems on the vertical fluxes.

Their model results showed that artificial surfaces were the most emission intensive land-cover class while lakes and rivers were about as emission intensive as arable land. Forests were the dominant land cover in the region (66%). The forest C sink decreased total emissions for the region by 72%. The region’s net emissions amounted to 4.37 ± 1.43 Tg CO2-eq yr-1, corresponding to a net emission intensity 0.16 Gg CO2-eq km-2 yr-1, and estimated per capita net emissions of 5.6 Mg CO2-eq yr-1. Using INCA-C and PERSiST, the amount of organic C leaching from mires, cropland, and forests to the watercourses was estimated to correspond to about 10% of the CO2 and CH4 emissions from land to air.

Although the landscape approach developed by Dr. Holmberg and colleagues opens opportunities to examine the sensitivities of important GHG fluxes to changes in land use and climate, management actions, and mitigation of anthropogenic emissions, there is still a need to extend the work to a fully integrated regional GHG budget, accounting for all lateral fluxes of C- and N-containing compounds.


Sediment transport to the Mekong Delta

Giamba Bussi and colleagues have published a new study of the effects that dams and climate change are having on sediment transport in the Mekong Delta. Credible predictions of sediment dynamics are essential for achieving the UN Sustainable Development Goals. The livelihoods of millions of people living in the world’s deltas are deeply interconnected with the sediment dynamics of these deltas. Sustainable inputs of fluvial sediments from upstream rivers are critical for ensuring the fertility of delta soils and for promoting sediment deposition that can offset rising sea levels. Yet, in many large river catchments this supply of sediment is being threatened by the planned construction of large dams. In this study, Dr. Bussi and colleagues apply the INCA hydrological and sediment model to the Mekong River catchment in South East Asia. Their aim was to assess the impact of several large dams (both existing and planned) on suspended sediment fluxes in the river. After calibrating to present day conditions, they forced the INCA model with future climate scenarios to assess the interplay of changing climate and sediment trapping caused by dam construction. Their results suggest that historical sediment flux declines have mostly been caused by dam construction and that sediment trapping will increase in the future if new, planed dams are constructed. If all dams that are currently planned for the next two decades are built, the model predicts a decline of suspended sediment flux of 50% (47–53% 90% confidence interval) compared to current levels (99 Mt/year at the delta apex), with potentially damaging consequences for local livelihoods and ecosystems.

New Papers

Simulating metals transport with INCA

Paul Whitehead and colleagues have published a new version of INCA. INCA-Metals, to simulate the impact of point source metal discharges (e.g., from tannery wastes or acid mine drainage) and diffuse rural runoff on riverine water quality. The model accounts for the key chemical reaction kinetic processes operating as well as sedimentation, resuspension, dilution, mixing and redistribution of pollutants in rivers downstream of discharge points. The model is dynamic and simulates the daily hydrology and behavior of eight metals, including cadmium, mercury, copper, zinc, lead, arsenic, manganese and chromium, as well as cyanide and ammonia. Like all members of the INCA family, the model is semi-distributed and can simulate catchment, tributary and instream river behavior. The apply the new model to predict impacts of the Savar tannery complex on the Dhaleshwari River system in Bangladesh on pollution levels in the river system and to evaluate a set of treatment scenarios for pollution control, particularly in the dry season. They show that the new effluent treatment plant at Savar needs to significantly improve its operation and treatment capability in order to alleviate metal pollution in the downstream Dhaleshwari River System and also protect the Meghna River System that discharges into the Bay of Bengal.