A.M. Michalak and C.B. Field
There is no resource more central to life on Earth than water, and its role in shaping the arc of human history cannot be overstated. Whether through its presence or absence, water has both fueled the growth of the world's great societies and hastened their demise. Humanity's need for water is inextricably linked to its need for security, energy, food, and community. At the same time, climate change, population growth, and economic development are currently placing unprecedented demands on this limited resource, as well as increasing the uncertainty associated with future demands and availability. As with all limited resources, both challenges and opportunities emerge as resources become scarcer; it is how societies and ecosystems respond to such "stresses" that determines their fate. The collection of essays in this special issue frame current issues within the context of the decisions that we face and the opportunities that emerge as we are confronted with increasing demands on this limited resource.
Figure: The Mississippi River draining into the Gulf of Mexico in 1999. The Mississippi river drains the heart of the North American continent, carrying vast quantities of nutrients that flow off of agricultural lands. These nutrients act as fertilizer for the phytoplankton in the Gulf waters. When the phytoplankton die, the process of their decomposition absorbs oxygen dissolved in the water, creating annual “dead zones” that are harmful to the Gulf ecosystem. Eutrophication, i.e. the delivery of excessive nutrients to surface waters, is occurring throughout the world in areas with intensive agriculture or with large human populations, and causing impacts including dead zones and harmful algae blooms.