Primary distinguishing features of freshwater ecoregion onservation
Connectivity 1 is essential to maintaining freshwater biodiversity. This includes connectivity between and within aquatic habitats, connectivity with the riparian zone and floodplains, and connectivity with subterranean systems. Loss of connectivity will fundamentally alter ecosystem processes and negatively affect species.
Because aquatic habitats are linked to each other, focusing solely on the protection of discrete sites will be an incomplete solution to developing a biodiversity vision, except perhaps in systems characterized by isolated, hydrologically unconnected habitats.
The recovery of disturbed habitats normally is dependent on the presence of adjacent or connected undisturbed habitats —called spatial refugia —that can serve as sources of recolonization. Among the most effective spatial refugia may be ecologically intact catchments, if they remain.
Within a catchment, the effects of land-based activities are propagated downhill and downstream, so an assessment must look beyond target freshwater habitats and consider land uses within the larger catchment. Although we know that land use affects aquatic habitats, we generally do not know the degree or extent of effects for different land uses, which complicates the analysis and design of a vision.
Downstream impacts can also propagate upstream, especially in systems characterized by migratory species. For coastal areas, a vision may need to extend to the marine environment.
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Physical processes may be the most important ecosystem components to protect, particularly for large river systems with active floodplains. One of the primary challenges for freshwater ecoregion conservation is developing approaches to protect hydrologic processes operating over large spatial scales. In altered systems this may include restoration of the natural hydrograph.
For most freshwater species, we are currently unable to identify minimum population sizes or minimum critical area requirements. This, in turn, constrains our ability to identify the minimum amount of intact aquatic habitat that must be conserved. Furthermore, minimum habitat requirements may be linear versus areal, and a species ’habitat needs may vary according to life stage or season.
Exotic species pose one of the most serious threats to freshwater biodiversity, and the establishment of exotics is often irreversible. When humans introduce new species, either intentionally or accidentally ,native species confined to water have limited escape routes. Exotics may also invade habitats when natural dispersal barriers are breached, such as through interbasin water transfers.
Because humans depend on water sources and often manipulate them,and because virtually all changes to the terrestrial landscape affect aquatic systems,very few freshwater ecoregions remain intact.For this reason,restoration may be a large component of freshwater ecoregion conservation.
Terrestrial ecoregion boundaries rarely correspond to catchments. When working within a terrestrial ecoregion, boundary issues may complicate an assessment of freshwater biodiversity features. Extending the region of analysis for the freshwater assessment to include whole catchments, if possible, is often the best solution.
Subsurface freshwater habitats (e.g., groundwater-fed systems such as caves, hyporheic zones2 ), which often contain important but poorly known biodiversity elements, are connected to each other and to surface water habitats in ways that do not necessarily correspond to catchments. In ecoregions containing distinct subterranean biotas, or where groundwater acts as a major input to surface water habitats, mapping groundwater may be required. This task adds an extra layer of complexity to the ecoregion effort ,Similarly, wetland habitats may straddle catchments.
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Most non-vertebrate freshwater taxa are poorly known, and for a given ecoregion there may be only one or two experts for groups such as molluscs, crustaceans, aquatic insects, and aquatic plants. Consequently, freshwater visioning workshops will generally have fewer taxonomic groups represented by fewer experts than for comparable terrestrial analyses or workshops. A smaller group creates both opportunities and constraints, and the workshop structure should take these into account.
At present, widely available remote sensing technology cannot detect most aquatic habitat characteristics, and high-resolution imagery is necessary to identify the generally finer zonation of riparian vegetation.