The goal of restoring ecological integrity in rivers is frequently accompanied by an assumption that a comparative reference reach can be identified to represent minimally impaired conditions. However, in many regulated rivers, no credible historical, morphological or process-based reference reach exists. Resilient restoration designs should instead be framed around naturalization, using multiple analytical references derived from empirically-calibrated field- and model-based techniques to develop an integrated ecological reference condition. This requires baseline data which are rarely collected despite increasing evidence for systematic deficiencies in restoration practice. We illustrate the utility of baseline data collection in restoration planning for the highly fragmented and regulated lower Merced River, California, USA. The restoration design was developed using various baseline data surveys, monitoring, and modeling within an adaptive management framework. Baseline data assisted in transforming conceptual models of ecosystem function into specific restoration challenges, defining analytical references of the expected relationships among ecological parameters required for restoration, and specifying performance criteria for post-project monitoring and evaluation. In this way the study is an example of process-based morphological restoration designed to prompt recovery of ecosystem processes and resilience. For the Merced River, we illustrate that project-specific baseline data collection is a necessary precursor in developing performance-based restoration designs and addressing scale-related uncertainties, such as whether periodic gravel augmentation will sustain bed recovery and whether piecemeal efforts will improve ecological integrity. Given the numerous impediments to full, historical, restoration in many river systems, it seems apparent that projects of naturalization are a critical step in reducing the deleterious impacts of fragmented rivers worldwide.
Tidal marsh restoration largely depends on natural seed rain to revegetate restored sites, but often little is known about the abundance and composition of the seed rain, or how it is influenced by individual species' dispersal or recruitment limitations. We monitored vegetation, seed rain, seed bank, and physical conditions at three restored and one reference tidal marsh to evaluate the seed rain's ability to revegetate restored sites, and the relative role of seed dispersal in revegetation patterns. The vegetation at the reference site is significantly more species-rich than the restored sites, while the composition of their seed rain is similar. Species absent from the vegetation at restored sites are missing from the seed rain at all sites, suggesting that these species are dispersal limited. This does not preclude recruitment limitations for these species, however, as several key physical conditions differ between restored sites and the reference site, which experiences less time inundated and higher summer soil salinity. Although a large amount of the seed rain is washed out of the marsh before becoming incorporated into the seed bank, total seed input is high at restored sites, suggesting that the natural seed supply is adequate to fully revegetate restored marshes, although with lower species richness than reference sites. The strongest influences on a species abundance in the seed rain are its frequency in the vegetation and seed production, suggesting that fecund species that colonize a site early will continue to dominate the seed rain and vegetation development in restored sites.
Setting instream flows to protect aquatic resources is required by California state law, but this task is not straightforward for an intermittent river that is naturally dry six or more months of every year. The Santa Maria River, 200 km northwest of the Los Angeles metropolitan area, lies within the northern range of the federally endangered southern California steelhead (Oncorhynchus mykiss) and is a logical candidate for instream flow protection: the watershed historically supported the anadromous life history of this species, but fish must navigate the lowermost 39 km of the commonly dry mainstem river to move between the ocean and freshwater habitats in the upper watershed. Mainstem flows are partly controlled by Twitchell Dam, constructed across one of the Santa Maria River's two main tributaries in 1962. The dam is operated to maximize groundwater recharge through the bed of the mainstem Santa Maria River, thus minimizing discharge to the Pacific Ocean and so reducing already limited steelhead passage opportunities. Conventional criteria for determining suitable instream flows for steelhead passage are ill‐suited to intermittent, Mediterranean‐type rivers because they ignore the dynamic channel morphology and critical importance of headwater flows in providing cues that once presaged passage‐adequate mainstem discharges but no longer do so. Hydrologic analysis of pre‐dam flows, coupled with established criteria for successful O. mykiss migration, provides an objective basis for evaluating alternative dam‐management scenarios for enhancing steelhead passage, although their implementation would redirect some water that for the past half‐century has exclusively supported irrigated agriculture and municipal water supplies. Copyright © 2013 John Wiley & Sons, Ltd.
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