Factors preventing development of productive delta marsh vegetation
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- Effects of relict levees on sediment and debris deposition in delta systems
- Delta plain accretion rate among systems compared to sea level rise
- Fringing marsh resilience, wave attenuation and flood management
- Distributary configuration effects on delta sediment deposition
- Development of tidal channels following restoration
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Given adequate seed source, sites with restored tidal prism will develop vegetation that reflects elevation, salinity, and sediment texture.
Naturally occurring tidal marsh zonation has been studied extensively for over 30 years. In the presence of seed source, vegetation has repeatedly established on restoration sites in zones driven by elevation, salinity, as well as the porosity and topography that affect redox conditions. Vegetation appears to be relatively predictable and symptomatic of site conditions. Despite the extent of this scientific record, projects continue to propose extensive sampling of relative species dominance, often without stratification based on known vegetation controls, or prediction of vegetation based on site assessment.
Spatially explicit predictions provide a basis for replacing extensive field vegetation data collection, with remote sensing and verification methods that more efficiently and accurately represent patterns of whole system development, and can be related to hydrodynamic and topographic observations. Development of these methods should enable implementation and verification of remote sensing methods on multiple sites. Verification need not be annual, and if delayed, could include productivity estimates that would more strongly document recovery of vegetation processes than measures of species composition.
Delta Strategy Analysis
The uncertainties in how this topic affects delta restoration has resulted in its inclusion in the ESRP River Delta Adaptive Management Strategy. This three criteria analysis should build off the analysis above, and supports development of learning projects.
Repeated observation has affirmed the development of vegetation consistent with abiotic conditions and seed source. Elevation and texture (affecting soil redox), and salinity (of soil pore water) have been strongly linked to composition and productivity. Long term monitoring on east coast marshes has shown recovery of benthic invertebrate production with recovery of surface soil layers.
Since a general pattern of vegetation development has been established at many sites, factors that may cause exceptions to this pattern are likely to be subtle and difficult to predict using quantitative models for specific restoration settings.
At this point, isolated and poorly understood observations of weak or varied vegetation development are unlikely to change how we do restoration. Problems that develop due to poor vegetation development are most easily resolved through ‘intelligent tinkering’ than quantitative study.