Accretion and Elevation Change Monitoring in a Remediated Tidal Marsh Brian Walker Abstract In response to years of pollution from a neighboring chemical company, The University of California is currently managing a remediation project at the UC Richmond Field Station Tidal Marsh. The recently excavated, cleaned, and re-graded soil on tidal marsh is being replanted. In the long term, restoration biologists hope that this area will be home to the endangered species, the California Clapper Rail and the Salt Marsh Harvest Mouse. This study will help planners to determine where to plant elevation sensitive plants by attempting to answer the following questions: 1) What is the rate of elevation change of the UC Richmond tidal marsh in the month following initial exposure to the tidal influence of the San Francisco Bay? 2) Is there a correlation between sediment accretion and the elevation change of the marsh? The change in elevation is detected at four points along six transects in the marsh using poles as reference points. Accretion is measured using small plates placed next to each pole, such that sediment captured weekly by the plate is considered to be accretion in the transect area. No significant relationship could be found between accretion and elevation change, while accretion varied significantly according to the relative elevation of the marsh. Rainfall events are shown to correlate significantly with accretion events and should be considered closely by restoration biologists.Introduction In the San Francisco Bay, the presence of functional tidal marsh has consistently diminished since the late 1800’s, when it accounted for nearly 400,000 acres bordering the bay. Today, scientists estimate that only 8,000 acres of this tidal marsh remain (The Bay Institute 2003). The importance of tidal marsh is well-documented as a habitat for endangered species such as the California Clapper Rail and the Salt Marsh Harvest Mouse, as well as thousands of migratory birds each year (Gutstein 1989). Tidal marsh plants can also function as bioremediation tools by incorporating low levels of pollutants into their biomass and out of the soil (Cheng et al. 2002). In response to years of pollution from a neighboring chemical company, the University of California is currently managing a remediation project at the UC Richmond Field Station, in an effort to comply with state requirements. Potential tidal marsh areas, such as those owned by the University of California, were contaminated with toxic pollutants such as mercury and arsenic by Stauffer Chemical, a company that no longer operates in the area. As part of the remediation project at the UC Richmond Field Station, contaminated soils have been moved to a toxic chemical land fill in Bakersfield and replaced with clean fill. The land has now been graded to exchange bay and marsh water through a bay inlet, and tidal marsh plants will be planted to create the area’s desired habitat and restore animal life to the area (URS Corporation 2002). In order to continue with the restoration project, the marsh’s change in elevation will be evaluated due to its importance in establishing a vegetated tidal marsh habitat. The rate of accretion, defined for this paper as accumulation of sediment over time, was monitored and compared to the elevation change, to determine if a relationship can be found between accretion rate and elevation change at this site. Previous studies have shown that elevation change does not occur in direct correspondence with sediment accretion; however, compaction commonly causes marshes that have net accumulation to lower in elevation. Because the quantity of accretion in San Francisco Bay Estuaries is thought to decrease with the age of the marsh (Reed 2002), studying the newly restored and relatively vegetation-free UC Richmond site is of particular interest. The marsh’s geologic age is difficult to place because new fill has been added, and its lack of vegetation indicates that it is biologically very young. Previous studies of tidal marsh land have examined the relationship between different shoreline properties and the rate of accretion or erosion that occurs in shoreline areas. A numberof predictive formulas have been established from controlled wave pool and field experiments, that consider such factors as mean sediment size, wave energy, and shoreline slope. One study predicts accretion will occur when wave heights are smaller, and also specifically warns against using predictive formulas that can lead to misrepresentations of coastal systems (Jackson 1999). Other studies have found that greater amounts of vegetation tend to decrease erosion rates, sometimes to the point of accretion (Van Eerdt 1985). Researchers have also considered the effects of storm events on accretion in salt marshes and found that greater rainfall correlates with higher rates of accretion (Fonjweng and Pfefferkorn 2001). However, most of these studies are very site specific and are not reliable predictors of accretion on all shorelines. Similarly, the relationship between accretion and elevation change in marshland has been studied in the San Francisco Bay Estuary as well as the Mississippi Delta. In both instances it was found that accretion rates exceeded the rate of elevation rise, indicating that soil sediments are being compacted (Cahoon 1995 and Reed 2002). Because rates of accretion, erosion, and elevation change experience large variation from site to site (Gibb 1978), it is important to conduct a study specific to the UC Richmond Field Station Tidal Marsh if the UC intends to successfully remediate the marsh. Because the University of California intends to develop a planting plan as a portion of the restoration project that will be completed at the UC Richmond Field Station, it is important to gather information that will promote such a planting plan: each species in the planting plan will flourish under specific environmental conditions that change based on the height of the marsh (Gutstein 1989), thus elevation change is a crucial factor in determining the success of the vegetation planted in the tidal marsh area. As a result of the demands posed by the restoration project, the primary research question that will be addressed in this study is: What is the elevation change of the UC Richmond Field Station tidal marshland? In addition, this study will consider the relationship between marsh sediment accretion