Effects of Channel Restoration on Water Velocity, Transient Storage, and Nutrient Uptake in a Channelized Stream

Abstract

Channel design is an important component of stream restoration, but little is known of the interplay between hydrogeomorphic features and ecosystem processes within designed channels. Water velocity, transient storage, and nutrient uptake were measured in channelized (prerestoration) and naturalized (postrestoration) reaches of a 1-km segment of Wilson Creek (KY) to assess the effects of restoration on mechanisms of nutrient retention. Stream restoration decreased flow velocity and reduced the downstream transport of nutrients. Median travel time was 50% greater in the restored channel due to lower reach-scale water velocity and the longer length of the meandering channel. Transient storage and the influence of transient storage on travel time were largely unaffected except in segments where backwater areas were created. First-order uptake rate coefficients for N and P were 30- and 3-fold higher (respectively) within the restored channel relative to its channelized state. Changes in uptake velocities were comparatively small, suggesting that restoration had little effect on biochemical demand. Results from this study suggest that channel naturalization enhances nutrient uptake by slowing water velocity. Solute injection experiments revealed differences in the functional properties of channelized, restored, and reference streams and provided a means for quantifying benefits associated with restoration of ecosystem services.

Nutrient Retention in Restored Streams and Rivers: A Global Review and Synthesis

“…Plants, fungi, and certain bacteria in the stream and riparian zone can temporarily assimilate inorganic N and P into biomass [27,28]. Assimilation rates increase with retention time and the availability of sunlight and nutrients [29][30][31]. NH 4 + and SRP are readily assimilated forms of inorganic N and P [32].…”

“…Stream restoration and floodplain reconnection have been used in an attempt to influence water quality by slowing stream flow by altering channel/floodplain morphology and riparian vegetation [29,40,41,58,59]. The objective of this review and synthesis was to evaluate the effectiveness of stream restoration and floodplain reconnection practices for restoring ecosystem functions such as N and P retention.…”

“…Nutrient uptake was measured by 19% of the studies reviewed here. All of the studies that measured nutrient uptake took place within the channel of a restored stream (except for Bukaveckas 2007, which occurred in a backwater oxbow of a remnant channel). Nutrient spiraling is a term that describes the cycling of nutrients as they are assimilated from the water column into benthic biomass, temporarily retained, and mineralized back into the water column [70].…”

Phosphorus and Nitrogen Dynamics in Riverine Systems: Human Impacts and Management Options

“…For example, the creation of riffles, cross vanes, and step pools within a restored stream shortened NH 4 -N uptake lengths from 200 to 70 m (Hines and Hershey 2011). Bukaveckas (2007) observed reductions in P and N uptake lengths from 1370 to 380 m and from 20 km to 620 m, respectively, after channel reconstruction and reconnection with the floodplain, while Roberts et al (2007) measured reductions in NH 4 -N uptake lengths of about 50-70% after addition of woody debris in stream channels.…”

“…Channel reconfiguration, such as channel widening and remeandering, and the restoration of structural complexity via the addition of flow obstructions (e.g., debris dams, side pools, and diversification of bed materials) may enhance nutrient uptake by increasing water residence time, promoting contact between the water and the sediment surface, and enhancing the hyporheic water exchange (Bukaveckas 2007;Craig et al 2008;Hines and Hershey 2011). Woody material on the stream bed additionally increases the nutrient demand of the decomposing microorganisms due to the high C-N and C-P ratios (Roberts et al 2007).…”