A river has physical integrity when river process and form are actively connected under the current hydrologic and sediment regime. One component of ecological or physical integrity is sustainability. Sustainability

is most effectively defined within a specified time interval, but implies the ability to maintain existing conditions during that time interval. Another component of integrity is resilience, which refers to the ability learn more of a system to recover following disturbance. A resilient ecosystem recovers the abundance and diversity of organisms and species following a drought or a tropical cyclone, for example, and a resilient river recovers channel geometry and sediment fluxes following a large flood. Drawing on concepts of ecological and physical integrity, a composite definition for critical

zone integrity and sustainability might be a region in which critical zone processes respond to fluxes of matter and energy in a manner that sustains a landscape and an ecosystem with at least minimum levels of diversity. selleckchem The core concept of this definition is that biotic and non-biotic processes can respond to fluctuations in matter and energy through time and space, rather than being rigidly confined to a static condition. In other words, hillslopes have the ability to fail in landslides during intense precipitation, rather than being shored up by rock bolts and retaining walls, and fish populations

have the ability to migrate to different portions of a river network in response to flooding or Farnesyltransferase drought, rather than being partitioned into sub-populations by impassable barriers such as dams or culverts. Layers of vagueness are built into this definition, however. Over what time span must the landscape and ecosystem be sustained? What constitutes an acceptable minimum level of physical or biological diversity? These are not simple questions to answer, but in addressing these questions for specific situations, geomorphologists can make vital and needed contributions to ongoing dialogs about how to preserve vitally important ecosystem services and biodiversity. Focusing on these questions can also force geomorphologists to explicitly include biota in understanding surface processes and landforms. The stabilization of hillslopes or the partitioning of rivers does not really matter in a purely physical context. Although geomorphologists may be interested to know that hillslopes cannot adjust because of stabilization or rivers cannot continue to move sediment downstream because of dams, these issues become critically important only in the context of increased hazards for humans in the hillslope example, or loss of ecosystem services for biotic communities in the dam example. The issues raised above are complex and difficult to address.