Potential for deliberate management of element interactions to address major environmental issues.

Human activities often decouple elements from their natural stoichiometry through the selective release and mobilization of elements such as C, N, S, and P from their long-term stores (Austin et al., Chapter 2, this volume). Many environmental problems arise from these biogeochemical changes, including rising atmospheric CO2 and the degradation of the quality of land, air, and water. A mechanistic understanding of elemental interactions provides an opportunity for deliberate manipulations of elements in order to mitigate environmental problems. In this chapter we demonstrate that recoupling of elements can be a successful strategy for minimizing or alleviating the harmful effects of human activities and for restoring degraded ecosystems. There are two fundamentally different pathways by which elemental interactions can be manipulated to achieve environmental goals. The first is to limit the source of the excess elemental inputs (limiting primary forcing). Examples include decreasing the emissions of pollutants or greenhouse gases or minimizing the applications of fertilizers or other chemicals. A second approach is to minimize the effects of excess elements by introducing another change to counteract the undesirable effects of the primary forcing. Examples of enhanced secondary forcing would be liming of acidified lakes and soils in order to mitigate acidification or enhancing carbon sequestration by fertilizing terrestrial systems with nitrogen and oceans with iron.