Carbon uptake by mature Amazon forests has mitigated Amazon nations’ carbon emissions

Background

Several independent lines of evidence suggest that Amazon forests have provided a significant carbon sink service, and also that the Amazon carbon sink in intact, mature forests may now be threatened as a result of different processes. There has however been no work done to quantify non-land-use-change forest carbon fluxes on a national basis within Amazonia, or to place these national fluxes and their possible changes in the context of the major anthropogenic carbon fluxes in the region. Here we present a first attempt to interpret results from ground-based monitoring of mature forest carbon fluxes in a biogeographically, politically, and temporally differentiated way. Specifically, using results from a large long-term network of forest plots, we estimate the Amazon biomass carbon balance over the last three decades for the different regions and nine nations of Amazonia, and evaluate the magnitude and trajectory of these differentiated balances in relation to major national anthropogenic carbon emissions.

Results

The sink of carbon into mature forests has been remarkably geographically ubiquitous across Amazonia, being substantial and persistent in each of the five biogeographic regions within Amazonia. Between 1980 and 2010, it has more than mitigated the fossil fuel emissions of every single national economy, except that of Venezuela. For most nations (Bolivia, Colombia, Ecuador, French Guiana, Guyana, Peru, Suriname) the sink has probably additionally mitigated all anthropogenic carbon emissions due to Amazon deforestation and other land use change. While the sink has weakened in some regions since 2000, our analysis suggests that Amazon nations which are able to conserve large areas of natural and semi-natural landscape still contribute globally-significant carbon sequestration.

Conclusions

Mature forests across all of Amazonia have contributed significantly to mitigating climate change for decades. Yet Amazon nations have not directly benefited from providing this global scale ecosystem service. We suggest that better monitoring and reporting of the carbon fluxes within mature forests, and understanding the drivers of changes in their balance, must become national, as well as international, priorities.

     

Impacts of saline water irrigation and shrimp pond discharges on the surrounding waters of a coastal district in the Mekong delta of Vietnam

This study discusses impacts of saline water irrigation and shrimp pond discharges on the surrounding waters in the coastal Cai Nuoc district, Mekong delta of Vietnam where the landscape was re-shaped by shrimp aquaculture since 2000. Sampling took place at the end of the wet season of 2009 in the district (as aquaculture sites) and a nearby freshwater-dominated reference site. The aquaculture sites showed significantly higher salinities and organic loadings (biochemical oxygen demand, chemical oxygen demand) but lower dissolved nutrients (NO₃–N, NO₂–N, and PO₄–P), total iron, and phytoplankton diversity compared to the reference site. Irrigation of saline waters has exacerbated salinization, leading to significant biological changes in the surrounding waters. Impacts of shrimp pond discharges on the surrounding waters were not very dramatic in terms of organic loadings and nutrients. The increase in organic loadings in the surrounding waters was mostly due to contribution from other pollution sources, such as domestic/industrial discharges and runoff. Enhanced salinization and changes in nutrients resulted in a decline in species richness and diversity, and a change in the evenness of the phytoplankton community. Besides, the composition of zooplankton and zoobenthos were also restructured. The mild impacts of shrimp pond discharges on the surrounding waters were primarily due to the limited inputs for shrimp aquaculture in this area.