Evaluating Tidal Marsh Sustainability in the Face of Sea-Level Rise: A Hybrid Modeling Approach Applied to San Francisco Bay

Background Tidal marshes will be threatened by increasing rates of sea-level rise (SLR) over the next century. Managers seek guidance on whether existing and restored marshes will be resilient under a range of potential future conditions, and on prioritizing marsh restoration and conservation activities. Methodology Building upon established models, we developed a hybrid approach that involves a mechanistic treatment of marsh accretion dynamics and incorporates spatial variation at a scale relevant for conservation and restoration decision-making. We applied this model to San Francisco Bay, using best-available elevation data and estimates of sediment supply and organic matter accumulation developed for 15 Bay subregions. Accretion models were run over 100 years for 70 combinations of starting elevation, mineral sediment, organic matter, and SLR assumptions. Results were applied spatially to evaluate eight Bay-wide climate change scenarios. Principal Findings Model results indicated that under a high rate of SLR (1.65 m/century), short-term restoration of diked subtidal baylands to mid marsh elevations (−0.2 m MHHW) could be achieved over the next century with sediment concentrations greater than 200 mg/L. However, suspended sediment concentrations greater than 300 mg/L would be required for 100-year mid marsh sustainability (i.e., no elevation loss). Organic matter accumulation had minimal impacts on this threshold. Bay-wide projections of marsh habitat area varied substantially, depending primarily on SLR and sediment assumptions. Across all scenarios, however, the model projected a shift in the mix of intertidal habitats, with a loss of high marsh and gains in low marsh and mudflats. Conclusions/Significance Results suggest a bleak prognosis for long-term natural tidal marsh sustainability under a high-SLR scenario. To minimize marsh loss, we recommend conserving adjacent uplands for marsh migration, redistributing dredged sediment to raise elevations, and concentrating restoration efforts in sediment-rich areas. To assist land managers, we developed a web-based decision support tool (www.prbo.org/sfbayslr).

[1]  N. Ganju,et al.  Summary of suspended-sediment concentration data, San Francisco Bay, California, Water Year 2003 , 2005 .

[2]  R. O'Neill,et al.  The value of the world's ecosystem services and natural capital , 1997, Nature.

[3]  R. Krone.  A Method for Simulating Historic Marsh Elevations , 1987 .

[4]  P. Buchanan,et al.  Summary of suspended-sediment concentration data, San Francisco Bay, California, water year 2008 , 2011 .

[5]  John Robert Lawrence Allen,et al.  Morphodynamics of Holocene salt marshes: a review sketch from the Atlantic and Southern North Sea coasts of Europe , 2000 .

[6]  Steven D. Gaines,et al.  Marine community ecology , 2001 .

[7]  R. R. Cave,et al.  Biogeochemical value of managed realignment, Humber estuary, UK. , 2006, The Science of the total environment.

[8]  J. Zedler,et al.  Wetland resources : Status, trends, ecosystem services, and restorability , 2005 .

[9]  Sfei.  2007 Pulse of the Estuary: Monitoring and Managing Water Quality in the San Francisco Estuary , 2007 .

[10]  J. Callaway,et al.  Surface Elevation Models , 2009 .

[11]  S. Luoma,et al.  Historical trends of metals in the sediments of San Francisco Bay, California , 1999 .

[12]  T. Conomos.  Properties and circulation of San Francisco Bay waters , 1979 .

[13]  M. Kearney,et al.  Sedimentation and erosion in a Chesapeake Bay brackish marsh system , 1985 .

[14]  J. Allen.  Salt-marsh growth and stratification: A numerical model with special reference to the Severn Estuary, southwest Britain☆ , 1990 .

[15]  Steven J. Phillips,et al.  Optimizing wetland restoration and management for avian communities using a mixed integer programming approach , 2009 .

[16]  Corinne Le Quéré,et al.  Climate Change 2013: The Physical Science Basis , 2013 .

[17]  D. Schoellhamer,et al.  Spatial and Temporal Variability of Suspended-sediment Concentration in a Shallow Estuarine Environment , 2004 .

[18]  R. Jones,et al.  Global Climate Change and Sea Level Rise: Potential Losses of Intertidal Habitat for Shorebirds , 2002 .

[19]  S. Pennings,et al.  Salt Marsh Communities , 2008 .

[20]  S. Rahmstorf,et al.  Global sea level linked to global temperature , 2009, Proceedings of the National Academy of Sciences.

[21]  P. Faber.  DESIGN GUIDELINES FOR TIDAL WETLAND RESTORATION IN SAN FRANCISCO BAY , 2004 .

[22]  J. Day,et al.  Soil Accretionary Dynamics, Sea-Level Rise and the Survival of Wetlands in Venice Lagoon: A Field and Modelling Approach , 1999 .

[23]  Norman L. Miller,et al.  POTENTIAL IMPACTS OF CLIMATE CHANGE ON CALIFORNIA HYDROLOGY 1 , 2003 .

[24]  L. Schile,et al.  EMERGING ISSUES FOR THE RESTORATION OF TIDAL MARSH ECOSYSTEMS IN THE CONTEXT OF PREDICTED CLIMATE CHANGE , 2007 .

[25]  S. Droege,et al.  Tidal Marshes: A Global Perspective on the Evolution and Conservation of Their Terrestrial Vertebrates , 2006 .

[26]  A. Cazenave,et al.  Sea-Level Rise and Its Impact on Coastal Zones , 2010, Science.

[27]  S. Temmerman,et al.  Coastal marsh response to historical and future sea-level acceleration , 2009 .

[28]  J. D. Fretwell,et al.  National water summary on wetland resources , 1996 .

[29]  S. Luoma,et al.  The impact of human activities on sediments of San Francisco Bay, California: an overview , 1999 .

[30]  Denise J. Reed,et al.  The impact of sea-level rise on coastal salt marshes , 1990 .

[31]  R. Delaune,et al.  Wetland soil formation in the rapidly subsiding Mississippi River Deltaic Plain: mineral and organic matter relationships. , 1990 .

[32]  B. Dawson,et al.  INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE (IPCC) , 2008 .

[33]  Makiko Sato,et al.  Paleoclimate Implications for Human-Made Climate Change , 2011, 1105.0968.

[34]  R. Delaune,et al.  Marsh vertical accretion via vegetative growth , 2006 .

[35]  L. Schile,et al.  Tidal Wetland Vegetation in the San Francisco Bay-Delta Estuary , 2012 .

[36]  R. Grossinger,et al.  Baylands Ecosystem Habitat Goals , 1999 .

[37]  R. Fairbanks.  A 17,000-year glacio-eustatic sea level record: influence of glacial melting rates on the Younger Dryas event and deep-ocean circulation , 1989, Nature.

[38]  Daniel R. Cayan,et al.  Potential effects of global warming on the Sacramento/San Joaquin watershed and the San Francisco estuary , 2002 .

[39]  J. Hunt,et al.  Relationships between sediment contamination and toxicity in San Francisco Bay , 1999 .

[40]  M. Josselyn.  The Ecology of San Francisco Bay Tidal Marshes: A Community Profile, , 1983 .

[41]  Melvin J. Dubnick.  Army Corps of Engineers , 1998 .

[42]  P. Williams,et al.  Will Restored Tidal Marshes Be Sustainable , 2003 .

[43]  T. Conomos.  San Francisco Bay - the urbanized estuary , 1982 .

[44]  David H. Schoellhamer,et al.  Trends in the Sediment Yield of the Sacramento River, California, 1957 - 2001 , 2004 .

[45]  Michael D. Dettinger,et al.  Projected Evolution of California's San Francisco Bay-Delta-River System in a Century of Climate Change , 2011, PloS one.

[46]  Philip B. Williams,et al.  Physical Evolution of Restored Breached Levee Salt Marshes in the San Francisco Bay Estuary , 2002 .

[47]  J. Pethick,et al.  Development of a coastal vulnerability index: a geomorphological perspective , 2000, Environmental Conservation.

[48]  M. Fenster,et al.  Coastal Impacts Due to Sea-Level Rise , 2008 .

[49]  S. Dasgupta,et al.  The impact of sea level rise on developing countries: a comparative analysis , 2007 .

[50]  M. Kearney,et al.  Island Land Loss and Marsh Vertical Accretion Rate Evidence for Historical Sea-Level Changes in Chesapeake Bay , 1991 .

[51]  Maggi Kelly,et al.  Mapping changes in tidal wetland vegetation composition and pattern across a salinity gradient using high spatial resolution imagery , 2011, Wetlands Ecology and Management.

[52]  D. Cahoon,et al.  Coastal Wetlands , 2019, Beaches and Coasts.

[53]  Michael D. Dettinger,et al.  CLIMATE CHANGE SCENARIOS AND SEA LEVEL RISE ESTIMATES FOR THE CALIFORNIA 2008 CLIMATE CHANGE SCENARIOS ASSESSMENT , 2009 .

[54]  M. B. Machmuller,et al.  Forecasting the effects of accelerated sea‐level rise on tidal marsh ecosystem services , 2009 .

[55]  S. Schladow,et al.  Tidal oscillation of sediment between a river and a bay: A conceptual model , 2004 .

[56]  P. V. Sundareshwar,et al.  RESPONSES OF COASTAL WETLANDS TO RISING SEA LEVEL , 2002 .

[57]  A. Southward.  San Francisco Bay: The urbanized estuary , 1980 .

[58]  Luca Carniello,et al.  Critical bifurcation of shallow microtidal landforms in tidal flats and salt marshes. , 2006, Proceedings of the National Academy of Sciences of the United States of America.

[59]  J. Grace,et al.  Elevated CO2 enhances biological contributions to elevation change in coastal wetlands by offsetting stressors associated with sea‐level rise , 2009 .

[60]  W. Landman.  Climate change 2007: the physical science basis , 2010 .

[61]  S. Temmerman,et al.  Limits on the adaptability of coastal marshes to rising sea level , 2010 .

[62]  Ian Townend,et al.  Estuarine flooding and managed retreat , 2002, Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences.

[63]  H. L. Miller,et al.  Climate Change 2007: The Physical Science Basis , 2007 .

[64]  K. Wasson,et al.  Salt Marsh-Upland Ecotones in Central California: Vulnerability to Invasions and Anthropogenic Stressors , 2011, Wetlands.

[65]  Elizabeth Burke Watson,et al.  Changing elevation, accretion, and tidal marsh plant assemblages in a South San Francisco Bay tidal marsh , 2004 .

[66]  L. Ward,et al.  VERTICAL ACCRETION IN MARSHES WITH VARYING RATES OF SEA LEVEL RISE , 1986 .

[67]  R. Delaune,et al.  Sedimentation, accretion, and subsidence in marshes of Barataria Basin, Louisiana1 , 1983 .

[68]  M. Bertness,et al.  Experimental warming causes rapid loss of plant diversity in New England salt marshes. , 2009, Ecology letters.

[69]  R. Delaune,et al.  Subsidence. accretion. and sea level rise in south San Francisco Bay marshes , 1990 .

[70]  Robert J. Nicholls,et al.  Increasing flood risk and wetland losses due to global sea-level rise: regional and global analyses , 1999 .

[71]  P. Gleick,et al.  THE IMPACTS OF SEA-LEVEL RISE ON THE CALIFORNIA COAST , 2009 .

[72]  Harry H. Roberts,et al.  Drowning of the Mississippi Delta due to insufficient sediment supply and global sea-level rise , 2009 .

[73]  D. Cahoon,et al.  Elevated CO2 stimulates marsh elevation gain, counterbalancing sea-level rise , 2009, Proceedings of the National Academy of Sciences.

[74]  Philip B. Duffy,et al.  Uncertainty in projections of streamflow changes due to climate change in California , 2005 .

[75]  Bruce E. Jaffe,et al.  Anthropogenic influence on sedimentation and intertidal mudflat change in San Pablo Bay, California: 1856–1983 , 2007 .

[76]  M. Barbour,et al.  Terrestrial Vegetation of California, 3rd Edition , 2007 .

[77]  M. Kirwan,et al.  A coupled geomorphic and ecological model of tidal marsh evolution , 2007, Proceedings of the National Academy of Sciences.

[78]  D. Cahoon,et al.  Caribbean mangroves adjust to rising sea level through biotic controls on change in soil elevation , 2007 .

[79]  J. French,et al.  Numerical simulation of vertical marsh growth and adjustment to accelerated sea‐level rise, North Norfolk, U.K. , 1993 .

[80]  J. Pethick,et al.  Long-term Accretion Rates on Tidal Salt Marshes , 1981 .

[81]  N. Miller,et al.  CLIMATE CHANGE IMPACTS UNCERTAINTY FOR WATER RESOURCES IN THE SAN JOAQUIN RIVER BASIN, CALIFORNIA 1 , 2004 .

[82]  B. Ingram,et al.  Holocene Environmental History and Evolution of a Tidal Salt Marsh in San Francisco Bay, California , 2008 .

[83]  B. F. Atwater,et al.  History, landforms, and vegetation of the estuary's tidal marshes , 1979 .

[84]  D. Schoellhamer.  Sudden Clearing of Estuarine Waters upon Crossing the Threshold from Transport to Supply Regulation of Sediment Transport as an Erodible Sediment Pool is Depleted: San Francisco Bay, 1999 , 2011 .

[85]  Dan Laffoley,et al.  Mitigating climate change through restoration and management of coastal wetlands and near-shore marine ecosystems : challenges and opportunities , 2011 .