Nutrient Cycles

Nutrient Cycles

Human activities have fundamentally altered the natural flow of water and biologically essential elements through natural cycles. For example, humans now appropriate over half the usable fresh water on the planet and fix more atmospheric nitrogen into a biologically available form than all natural terrestrial sources.

These profound alterations of natural hydrological and biogeochemical cycles may change the types of organisms that a given region supports, fundamentally transforming the ecosystems upon which we depend for goods and services. The human impact on mass flows comes from direct inputs through agricultural/industrial/sewage activities, by changes in runoff and river discharge, by damming, by alterations in the ability of wetlands to take up or release nutrients, and by diffuse input from the atmosphere.

Effects of human disturbance become integrated at the watershed level, and are transferred to the coastal zone, which often suffers disproportionate impact (such as toxic blooms, anoxic dead zones, and fishery declines). The resilience of ecosystem function to these large-scale disturbances may largely depend upon the ability of bacteria and other microbes to recycle and transfer limiting resources, but very little is known about microbial diversity and feedbacks between human activities, biogeochemical cycles, and ecosystem function.

For example, how do socioeconomic variables, development, and land-use affect water quality, hydrology, and biogeochemical cycles? How can we trace the impact of a disturbance in biogeochemical cycling through an ecosystem? What are the impacts of industrial and residential wastewater discharges, storm runoff, eutrophication and anoxia on aquatic and coastal communities? What are the consequences of these impacts for fisheries and for coastal ecosystem services? Progress toward answering these questions requires multidisciplinary expertise.