The global biodiversity crisis has invigorated the search for generalized patterns in most disciplines within the natural sciences. Studies based on organismal functional traits attempt to broaden implications of results by identifying the response of functional traits, instead of taxonomic units, to environmental variables. Determining the functional trait responses enables more direct comparisons with, or predictions for, communities of different taxonomic composition. The North American freshwater fish fauna is both diverse and increasingly imperiled through human mediated disturbances, including climate change. The Tennessee River, USA, contains one of the most diverse assemblages of freshwater fish in North America and has more imperiled species than other rivers, but there has been no trait-based study of community structure in the system. We identified 211 localities in the upper Tennessee River that were sampled by the Tennessee Valley Authority between 2009 and 2011 and compiled fish functional traits for the observed species and environmental variables for each locality. Using fourth corner analysis, we identified significant correlations between many fish functional traits and environmental variables. Functional traits associated with an opportunistic life history strategy were correlated with localities subject to greater land use disturbance and less flow regulation, while functional traits associated with a periodic life history strategy were correlated with localities subject to regular disturbance and regulated flow. These are patterns observed at the continental scale, highlighting the generalizability of trait-based methods. Contrary to studies that found no community structure differences when considering riparian buffer zones, we found that fish functional traits were correlated with different environmental variables between analyses with buffer zones vs. entire catchment area land cover proportions. Using existing databases and fourth corner analysis, our results support the broad application potential for trait-based methods and indicate trait-based methods can detect environmental filtering by riparian zone land cover.
In the Ozark Highlands of Missouri, unstable river reaches that display rapid planform change are described as active reaches. While active reaches can be part of the natural morphodynamic regime, accelerated gravel bar deposition and bank erosion have been linked to historical and recent anthropogenic activities. Relationships between geomorphic controls and specific forms of channel instability are poorly understood in the Ozarks. The objectives of this research were to (1) develop an active reach classification scheme that provides an objective means of identifying and evaluating longitudinal patterns of instability in this and other Ozark rivers, (2) identify active reaches and different forms of instability along 80 km of the Finley River in southwest Missouri, and (3) investigate physical controls on active reaches. Historical aerial photographs and geographic information system (GIS) analysis showed that active reaches occur along 21% of the length of the main stem, preferentially in valleys with confinement ratios between 10 and 30 and near major tributary confluences. Four active reach forms were identified with proportion of length as follows: extension (8%), megabar (6%), cutoff (5%), and translation (2%). Depositional megabar-type active reaches tended to form directly downstream of erosional extensiontype active reaches, probably due to excess gravel supply by reworking of historical floodplain deposits. The lack of a dominant active reach form, along with a stable main stem sinuosity over time, suggests that the Finley River is a semi-stable, self-organized system in balance with watershed inputs since at least 1955, the date of the earliest photo series.
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