Environmental changes, many of them man-made, proceed at unprecedented rates at spatial scales ranging from local to global. What are the consequences for ecosystem processes? I will address this question by assessing impacts of different drivers of global change on primary production and organic matter decomposition as the two most fundamental processes in the biosphere. Specifically, I will present results from field experiments exploring how warming, sustained nutrient enrichment, and climate-induced storm events may affect biomass production and decomposition in lakes and streams. While the mechanisms underlying some of the observed impacts appear to be straightforward, others are unexpected, underscoring the need for manipulative field experiments that capture the complexity of natural ecosystems to forecast consequences of environmental change.