Asmeret Asefaw Berhe

The Significance of the Erosion-induced Terrestrial Carbon Sink

ABSTRACT Estimating carbon (C) balance in erosional and depositional landscapes is complicated by the effects of soil redistribution on both net primary productivity (NPP) and decomposition. Recent studies are contradictory as to whether soil erosion does or does not constitute a C sink. Here we clarify the conceptual basis for how erosion can constitute a C sink. Specifically, the criterion for an erosional C sink is that dynamic replacement of eroded C, and reduced decomposition rates in depositional sites, must together more than compensate for erosional losses. This criterion is in fact met in many erosional settings, and thus erosion and deposition can make a net positive contribution to C sequestration. We show that, in a cultivated Mississippi watershed and a coastal California watershed, the magnitude of the erosion-induced C sink is likely to be on the order of 1% of NPP and 16% of eroded C. Although soil erosion has serious environmental impacts, the annual erosion-induced C sink offsets up to 10% of the global fossil fuel emissions of carbon dioxide for 2005.

Anthropogenic Drivers of Ecosystem Change: an Overview

This paper provides an overview of what the Millennium Ecosystem Assessment (MA) call indirect and direct drivers of change in ecosystem services at a global level. The MA definition of a driver is any natural or human-induced factor that directly or indirectly causes a change in an ecosystem. A direct driver unequivocally influences ecosystem processes. An indirect driver operates more diffusely by altering one or more direct drivers. Global driving forces are categorized as demographic, economic, sociopolitical, cultural and religious, scientific and technological, and physical and biological. Drivers in all categories other than physical and biological are considered indirect. Important direct drivers include changes in climate, plant nutrient use, land conversion, and diseases and invasive species. This paper does not discuss natural drivers such as climate variability, extreme weather events, or volcanic eruptions.

Linking soil organic matter dynamics and erosion‐induced terrestrial carbon sequestration at different landform positions

[1]xa0Recently, the potential for terrestrial carbon (C) sequestration by soil erosion and deposition has received increased interest. Erosion and deposition constitute a sink for atmospheric carbon dioxide relative to a preerosional state or a noneroding scenario, if the posterosion watershed C balance is increased due to (1) partial replacement of eroded C by new photosynthate in the eroded site; and (2) preservation from decomposition of at least some eroded soil organic carbon (SOC) arriving in depositional settings. Little is known, however, about differences in C dynamics at different erosional and depositional landform positions within the same eroding system. We determined the contribution of different landform positions to erosion-induced terrestrial C sequestration by measuring rates of net primary productivity (NPP), replacement of eroded C, and decomposition of organic matter (OM) at four categorically different landform positions within a naturally eroding toposequence in northern California. We found that eroded C is replaced by NPP 15 times over in the summit of the site studied and 5 times over in the slope. Profile-averaged, long-term rate constant for SOM decomposition was 2 to 14 times slower in the depositional settings compared with that in eroding slopes. As a result, the inventory of C in the depositional settings was 2 to 3 times larger than that of the eroding positions. Owing to both C replacement at eroding sites and reduced rates of OM decomposition in depositional sites, soil erosion constitutes a C sink from the atmosphere at our study site.

Soil Erosion: Data Say C Sink

In the letter “Soil erosion: a carbon sink or source?” (R. Lal and D. Pimentel, 22 February, p. [1040][1]) and in its Response (K. Van Oost et al. , 22 February, p. 1042), the authors note that soil erosion is a serious threat to land health. Nevertheless, evidence points toward a carbon (C)

Politicizing Indiscriminate Terror: Imagining an Inclusive Framework for the Anti-Landmines Movement

Landmines are indiscriminate weapons of mass terror that detrimentally affect human beings, the ecological system they live in, the regional economy, and political stability. Despite the extensive nature of the impacts, the landmine crisis is almost exclusively advocated on the basis of human rights principles. A comprehensive framework that considers environmental degradation as a principal aftermath of the global landmine crisis is critically missing from the broader matrix of variables around which the anti-landmine movement converges. This article discusses the current humanitarian framework of the International Campaign to Ban Landmines; its shortcomings to address the interconnected impacts of landmines on the environment; and attempts to describe what an inclusive, environmentally sensitive framework would have to incorporate to address the overall landmine impacts effectively.