Summary

Description

Executive Summary Southern California tidal marshes have been affected by coastal development and urbanization.Over the past 150 years, dredging and filling operations have resulted in the loss of 42 of SanDiego Bays historic shallow subtidal habitat, 84 of its intertidal mudflat habitat, and 70 of itssalt marsh habitat San Diego Bay NWR CCP 2006. The San Diego National Wildlife RefugeComplex, administered by the U.S. Fish Wildlife Service, was established in 1972 with the goalof protecting rare birds, migratory species and marsh dependent species of southern California. Our study follows a bottomup approach to evaluating local sealevel rise effects on tidal marshes.The study was conducted at the parcel scale while being relevant for landscape scalemanagement. The objectives of this study were to: 1 develop high resolution digital elevationmodels DEMs for the salt marshes of the San Diego Refuge Complex, 2 monitor water levelsand tidal cycles to assess parcel level inundation patterns and capture extreme water events, 3inventory vegetation species composition and relationship to elevation and tidal ranges, and 4develop sealevel rise marsh response models for Tijuana Slough marsh. This report contains baseline elevation, tidal range, and plant community results for the San DiegoBay National Wildlife Refuge Complex: Tijuana Slough National Wildlife Refuge Tijuana,Sweetwater marsh unit Sweetwater, South San Diego Bay unit South Bay, and Seal BeachNational Wildlife Refuge Seal Beach. A total of 12,013 elevation points were measured across all sites between September andDecember 2011 with a Real Time Kinematic RTK GPS 2.5 cm vertical accuracy. 11,470elevation data points were used to create digital elevation models DEMs for the marsh platforms.Elevation for all sites fell within a large range of 1.4 m NAVD88 with 84 between 1.2 and 2.6 m.Across all sites mean elevation was 0.46 m SD 0.65 above mean high water MHW. Vegetation was sampled in 0.25m2 quadrats at 2,855 locations across all sites. Distinct zonationin plant communities was observed in relation to elevation and tidal datum MHW, because plantsare typically restricted by their inundation tolerance and soil salinities. Batis maritima andSarcocornia pacifica were the two most common species across all site; B. maritima occurred at65 of the sampled quadrats, and S. pacifica occurred at 63 of all surveyed quadrats. Water level loggers were deployed at all sites n8 starting in September 2011. Water level datafrom September 2011 to January 2013 are presented in this report. Peak tide levels for this timeperiod were averaged for each site to produce sitespecific tidal datums for mean tide level MTL,mean high water MHW, and mean higher high water MHHW. We used the Marsh Equilibrium Model MEM to project initial estimates of marsh elevation changeunder sealevel rise SLR scenarios to 2100 for Tijuana marsh. Results from the SLR responsemodeling for the north arm of the Tijuana marsh indicated that relative elevation will decreasethrough 2100 under mid 93 cm and high 166 cm SLR scenarios, but it will maintain elevationunder the low 44 cm SLR scenario. MEM results were categorized by low, mid, and high marsh habitat types. Results showed that lowmarsh will decrease dramatically after 2030 under low SLR rates, whereas under mid SLR, lowmarsh will increase through 2090 before beginning to decrease. Under high SLR rates, low marshincreases to 2060 and then decreases until it disappears in 2090. Mid and high marsh will remainconstant under low SLR rates. However, mid marsh decreases after 2060 and disappears after2100 under mid SLR rates. Under high SLR rates, mid marsh decreases after 2030 and disappearsafter 2080. High marsh disappears after 2070 under mid SLR, and disappears after 2050 with highSLR. Ongoing work is underway to improve SLR marsh response modeling at Tijuana, Seal Beach andSweetwater. This w