Fluvial systems provide natural resources (e.g., fish and clean water) as well as cultural and ecological services (e.g., transportation, energy, irrigation, recreation and waste assimilation) basic to human societies (Naiman et al., 2002). At the start of the century, large dams contributed to 20% of the world’s electricity supply and irrigation agriculture produced 40% of the world’s food (Gleick, 1998). This usage of fluvial natural resources has translated in the lost of more than 40% of their biodiversity, which will largely compromise their natural functioning (Naiman et al., 2002). In fact, water shortage and losses of freshwater ecosystem services may reach to 40% of the world’s population by 2050, given the actual predictions under global climatic change scenarios (Millenium Ecosystem Assessment, 2005).
Success in attaining sustainable water resources management is then a major challenge for engineer planning, which can only be achieved through a multi-objective, multipurpose catchment perspective (Petts, 2007). Integrated Catchment Management (ICM) is an emerging discipline and process within the Integrated assessment field, which attempts to address the demands of decision makers for management (Jakeman & Letcher, 2003). However, ICM practices lag far behind its theoretical development, because of three main reasons: (1) high complexity level of fluvial ecosystems, (2) lack of well structured biophysical data in most parts of the catchments, and (3) high uncertainty of ecological responses to environmental changes.
First, any attempt to disentangle which part of the observed variability in any of the fluvial system components is due to natural change or human activities needs to be supported by a strong theoretical catchment construct. However, this catchment construct has proven to be difficult to establish as basic environmental principles and different component interrelationships that allow fluvial systems to function and provide their services are still poorly understood (Naiman et al., 2002). Secondly, the paucity of datasets that include hydrological, river morphology, water quality and biological data constitutes a significant impediment to the understanding of biophysical relationships and to produce important advances in eco-hydrology, eco-hydraulics and environmental assessment disciplines. Finally, human activities affect fluvial systems in very diverse ways (Ormerod et al., 2010; Tockner et al., 2010). In order to evaluate their relationships, it is well needed to properly address which are the effects that each human activity might produce in a river system so that responses can be identified and isolated through a well designed field survey or through specific designed experiments. This is of special relevance when looking at the effects of land use cover on river systems, as changes on land use cover have the potential to modify many different river system processes (hydrological, morphological, water quality and biological dynamics) (Figure 1). Moreover, reversal of land use cover to a less-developed state is rarely possible, and so improvement on river condition largely depends on best management practices and improvements in landscape management and planning (Allan, 2004). Thus, one of the biggest challenges for catchment management is to provide with effective management strategies to ameliorate or reduce the effects that land use changes pose on fluvial systems. However, many uncertainties on which are the mechanisms by which river processes are impaired from land uses still remain unclear, and management practices have failed to account for effective solutions, even in clear-cut and straightforward cases (Carpenter et al., 1998; McKergow et al., 2003). Moreover, the true benefits of many river reach restoration programs have also been questioned recently (Palmer et al., 2010), as land use legacy effects, as well as the covariation, existence of thresholds and collinearity between land uses and river processes are rarely taken into account up (Allan, 2004; King et al., 2005).
Figure 1. Diagram showing the importance of catchment and river reach vegetation on key factors that determine species assemblages in river systems and, thus, river ecosystem functioning.
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