Landscape allometry of oligohaline tidal channels of the lower Chehalis River, Washington

Abstract

The fractal geometry of landforms implies that landscapes can be viewed as systems of related rates of change between various geomorphic features of the landscape. Consequently, biological patterns and processes associated with landscape features may also be described by related rates of change, i.e., exhibit landscape-scale allometry. The goals of this dissertation were [1] to examine this hypothesis in a system of oligohaline tidal channels (sloughs) in the Chehalis River (Washington) delta; and [2] to suggest practical applications of landscape allometry in the management and restoration of estuarine sloughs to benefit juvenile Pacific salmon (Oncorhynchus spp.).The Chehalis sloughs exhibited allometric form with respect to length, perimeter, surface area, and outlet width and depth. Ebb surface flow velocity was correlated with slough size, as was exit time and export of tiny drogues used to model floating allochthonous detritus. Consequently, the percent organic matter in slough sediments depended on slough size and channel width, as did surface deposit feeder biomass.In contrast, a slough excavated to mitigate port improvements did not resemble the allometric forms of natural sloughs. This resulted in high retention of allochthonous inputs, sediment accretion, and headcutting. Additionally, intertidal sedge habitat abundance and distribution in large sloughs did not conform to the allometric patterns seen in smaller sloughs, suggesting that sedge habitat in large sloughs has been destroyed by past log storage and transportation.A model relating slough size to tidal export of riparian inputs, showed close agreement between model predictions and observed net export of spruce needles. Differences between observed and modeled aphid and chironomid export could be explained by fish predation. The model indicated that small sloughs export a greater proportion of riparian input than do large sloughs. Thus, landscape allometry supplements other theories of landform influences on tidal export.Landscape allometry has several practical implications: [1] natural allometric templates suggest restoration and mitigation design criteria, realistic goals given project constraints, and standards for measuring project success; [2] slough size becomes a covariate, allowing replication of reference sites; [3] historical disturbances can be inferred; and [4] predicted fish distributions in sloughs suggest restoration priorities.