How are the changes in earth different from humans?
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Accelerated human modification of the landscape and human-driven climate changes are fundamentally altering Earth’s surface processes and creating ecological challenges that scientists and policy makers are struggling to address. The environmental impacts of human activity are expected to increase as the climate continues to warm and as the world becomes progressively more populated, industrialized, and urbanized. Scientific research has generally succeeded in documenting the magnitude of these biophysical changes, including habitat loss and fragmentation, soil erosion, biodiversity loss, and water depletion and degradation. Yet the exact processes leading to these changes are still not adequately understood and quantified, and we still lack the best methods and techniques for detecting, measuring, and analyzing global change.
Soil erosion provides a prime example to understand what is at stake. Although a natural process, soil erosion has greatly accelerated globally due to cultivation, deforestation, and a host of other land-use practices (Montgomery, 2007a,b; Figure 1.1). Increased soil erosion generates sediment supply that often exceeds the transport capacity of stream systems, leading to vast sediment storage on channel beds, on hillslopes, and in floodplains. This historical sedimentation has already had significant impacts on channel processes, aquatic systems, and fisheries (Waters, 1995; NRC, 2004). Moreover, these legacy sediments represent a future risk because they can be remobilized and introduced into aquatic systems even following landscape amelioration (Walter and Merrits, 2008).
Anticipated climate change will heighten the human impact on the physical environment in many places. Predicting the magnitude and timing of these future impacts remains uncertain, but measurable changes have already occurred climatically (Elsner et al., 2008) and hydrologically over the past few decades, with earlier ice-out dates, reduced magnitudes of spring runoff and summer low flows, and changes in the timing of peak streamflows (Hodgkins et al., 2002, 2003; Huntington et al., 2003, 2004). Future climate change will likely bring greater hydrological and ecological shifts nationally and globally, with potentially profound impacts on water availability (Arnell, 2004; Milly et al., 2005; IPCC, 2007).
Earth surface changes, then, frequently raise resource management challenges, prompting efforts at ecological restoration, and environmental legislation often requires communities or other stakeholders to restore stream channels or wetlands. Yet it is uncertain how, and under what circumstances, most disturbed natural systems can recover, and even less is known about the baseline conditions that may potentially guide restoration efforts. Despite the development of a billion-dollar-a-year restoration industry, the science of watershed restoration is still in its infancy (Wohl et al., 2005; Walter and Merrits, 2008). Large uncertainties remain in other aspects of wetland and river restoration as well, including the ecological and economic tradeoffs of structural (“hard”) vs. nonstructural (“soft”) approaches and, more importantly, the metrics, goals, and time frames for guiding and achieving watershed restoration. These are just a few examples of the
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