New Research Opportunities in the Earth Sciences - New Research Opportunities in the Earth Sciences - page 64

COUPLED HYDROGEOMORPHIC-ECOSYSTEM RESPONSE TO
NATURAL AND ANTHROPOGENIC CHANGE
The ways in which ecosystems and landscapes have co-evolved through time
and the nature of their coupled responses to human activity and climate change
present tremendous new opportunities for advancing our understanding of Earth
surface processes as well as providing critical scientific input to managers tasked with
finding solutions to problems associated with environmental change. This research
opportunity differs from the later section on biogeochemical cycles in that its roots
are more in geomorphology and materials cycling than geochemistry.
Coupled Landscape and Ecosystem Dynamics
Recognition of the magnitude of influence that hydro-geomorphological
processes exert on ecological systems and ecological systems' influence on landscape
processes and dynamics has opened up exciting new areas in the emerging fields of
ecohydrology, ecogeomorphology, and geobiology. It is now widely documented that
living systems influence the style and pace of surface processes and biogeochemical
cycling and that disturbance regimes influence ecosystem trajectories and dynamics.
The full scope and breadth of these linkages, however, are only beginning to be
understood, in part because of the bi-directional nature of such feedbacks.
Over relatively short timescales, understanding the response of landscapes and
ecosystems to disturbance requires explicit consideration of their interactions.
Landslides, overgrazing, and flooding are just a few examples of disturbances in
which geomorphic, hydrological, and ecological processes are inextricably coupled.
Consider, for example, flooding. Vegetation on hill slopes and stream banks plays an
important role in regulating the delivery of water and sediment to stream channels at
the same time that overbank transport of water and sediment regulates the soil and
nutrient conditions for vegetation in riparian zones and floodplains. While natural
disturbances have always been an important driver of landscape and ecosystem co-
evolution, humans have, in many cases, altered the frequency, intensity, and impact
of disturbances. Returning to the example of flooding, through activities such as
deforestation, agriculture, installation of dams and levees, and increasing nutrient and
contaminant loads in runoff and streamflow, humans have modified stream and
floodplain morphology, hydrology, and ecology, often in ways never anticipated and
often with the effect of exacerbating the magnitude, frequency, and damage
associated with floods. In a time when humans are rapidly becoming the dominant
change agent, human-environmental interactions can no longer be ignored in the
quest for a unified model of the Earth surface system.
A similar coupling of landscapes and ecosystems is evident on the longer
timescales of climate change, particularly in rapidly changing, marginal environments
like wetlands, permafrost, and desert margins. Salt marshes, for example, can become
unstable when they are flooded too frequently, a potential consequence of sea-level
rise. The existence of salt marshes is dependent on an adequate sediment supply and
the presence of intertidal vegetation, such as Spartina alterniflora on western Atlantic