18 research outputs found
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A hierarchical stream habitat classification system: development and demonstration
Classification of Streams and stream habitats is useful for research involving establishment of monitoring stations, determining local impacts of land use practices, generalization from site-specific data, and assessment of basin-wide, cumulative impacts of human activities on streams and their biota. This thesis presents a framework for a hierarchical classification system, entailing an organized view of spatial and temporal variation between and within
stream systems. Stream habitat systems, defined and classified on several spatio-temporal scales, are associated with watershed geomorphic features and events. Variables selected for classification define relative long-term capacities of systems, not simply short-term states. Streams and their watershed environments are classified within the context of a regional biogeoclimatic classification. The framework is a perspective that should allow more systematic
interpretation and description of watershed/stream relationships. The classification system was used to assess changes in stream habitat caused by logging and debris removal in a fourth-order
stream in the High Cascades of Oregon. Habitat organization, trout density, and habitat use were compared in logged (clear-cut, 1962) and forested stream sections in the same stream segment. The
hierarchical classification system allowed pool/riffle habitats to he related to the geomorphic history of different stream reaches. Due to the presence of large debris dams and abundant woody debris, forested reaches varied in morphology and encompassed a wide array of pool/riffle habitats, including debris-created pools and side channels. Clear-cut reaches were relatively homogeneous, and were dominated by boulder-formed habitats. Although trout density was highly reach-specific, total density of the forested section was 40% greater than that of the clear-cut section. The smallest size class was absent and large (>14 cm) individuals were uncommon in clear-cut reaches. A regression model showed that most of the variation among reaches in trout density was related to the relative area comprised of six key pool/riffle types. The habitat classification system proved useful in demonstrating that the forested stream section, because of
its diversity of pool/riffle types, may best provide the range of habitats required by all size classes through changing streamflow conditions
A General Protocol for Restoration of Regulated Rivers
Large catchment basins may be viewed as ecosystems in which natural and cultural attributes interact. Contemporary river ecology emphasizes the four-dimensional nature of the river continuum and the propensity for riverine biodiversity and bioproduction to be largely controlled by habitat maintenance processes, such as cut and fill alluviation mediated by catchment water yield. Stream regulation reduces annual flow amplitude, increases baseflow variation and changes temperature, mass transport and other important biophysical patterns and attributes. As a result, ecological connectivity between upstream and downstream reaches and between channels, ground waters and floodplains may be severed. Native biodiversity and bioproduction usually are reduced or changed and non-native biota proliferate.Regulated rivers regain normative attributes as distance from the dam increases and in relation to the mode of dam operation. Therefore, dam operations can be used to restructure altered temperature and flow regimes which, coupled with pollution abatement and management of non-native biota, enables natural processes to restore damaged habitats along the river’s course. The expectation is recovery of depressed populations of native species. The protocol requires: restoring peak flows needed to reconnect and periodically reconfigure channel and floodplain habitats; stabilizing baseflows to revitalize food-webs in shallow water habitats; reconstituting seasonal temperature patterns (e.g. by construction of depth selective withdrawal systems on storage dams); maximizing dam passage to allow recovery of fish metapopulation structure; instituting a management belief system that relies upon natural habitat restoration and maintenance, as opposed to artificial propagation, installation of artificial in-stream structures (river engineering) and predator control; and, practising adaptive ecosystem management.Our restoration protocol should be viewed as an hypothesis derived from the principles of river ecology. Although restoration to aboriginal state is not expected, nor necessarily desired, recovering some large portion of the lost capacity to sustain native biodiversity and bioproduction is possible by management for processes that maintain normative habitat conditions. The cost may be less than expected because the river can do most of the work