Global Warming, Sea Level Rise, and Coastal Wetland Sustainability John Rybczyk Huxley College of the Environment Western Washington University

Predicted Contributions to Sea Level Rise Over the Next 100 years Thermal Expansion of the Oceans Melting of Alpine Glaciers Melting of Greenland Ice Sheet Antarctic Ice Sheet Contributions (+ or - ?) Current rate of ESLR = 0.15 cm yr -1

“Even if the ice melted, there would be no rise in ocean levels. After all, if you have a glass of water with ice cubes in it, as the ice melts, it simply turns to liquid and the water level in the glass remains the same.” (Rush Limbaugh)

Can coastal wetlands persist given predicted increases in the rate of ESLR?

Factors Affecting Wetland Elevation Relative to Sea Level O.M. Production (above and belowground) Allogenic Sediment Deposition Eustatic Sea Level Rise Deep Subsidence Shallow Subsidence (Primary Compaction and Decomposition)

Deltaic systems as models for future trends

Factors Affecting Wetland Elevation Relative to Sea Level O.M. Production (above and belowground) Allogenic Sediment Deposition Eustatic Sea Level Rise Deep Subsidence Shallow Subsidence (Primary Compaction and Decomposition)

modern delta( yrs BP) ( yrs PB)

Factors Affecting Wetland Elevation Relative to Sea Level O.M. Production (above and belowground) Allogenic Sediment Deposition Eustatic Sea Level Rise Deep Subsidence Shallow Subsidence (Primary Compaction and Decomposition) Tide Gauge

Factors Affecting Wetland Elevation Relative to Sea Level O.M. Production (above and belowground) Allogenic Sediment Deposition Eustatic Sea Level Rise Deep Subsidence Shallow Subsidence (Primary Compaction and Decomposition) Horizon Markers

Factors Affecting Wetland Elevation Relative to Sea Level O.M. Production (above and belowground) Allogenic Sediment Deposition Eustatic Sea Level Rise Deep Subsidence Shallow Subsidence (Primary Compaction and Decomposition) SET and Horizon Markers

Old Oyster Bayou ( ) O.M. Production Allogenic Sediment Deposition Eustatic Sea Level Rise…………… cm/year Deep Subsidence…………………… 0.70 cm/year Shallow Subsidence………………… 0.12 cm/year 0.48 cm/year Elevation Deficit = 0.49 cm/year

Problems with Direct Measurements

Pulsing Events

Storm delivers 2 cm thick sediment layer 16,500 grams of mineral matter/m : 9 storms with winds over 100 mph Return rate of once every 12 years

Decomposition Primary Production Sediments Wetland Elevation

Decomposition Primary Production Sediments Wetland Elevation Feedback

A combined field and modeling approach

Some Recent Model Applications Effect of SLR on coastal wetlands in NW Mediterranean deltas The importance of pulsing event for maintaining wetland elevation relative to sea level Modeling sediment collapse in a Honduran mangrove forest following Hurricane Mitch The effect of wastewater effluent on sediment dynamics in coastal wetlands.

Eight Year Field Study in Old Oyster Bayou

Old Oyster Bayou ( ) O.M. Production Allogenic Sediment Deposition Eustatic Sea Level Rise…………… cm/year Deep Subsidence…………………… 0.70 cm/year Shallow Subsidence………………… 0.12 cm/year 0.48 cm/year Elevation Deficit = 0.49 cm/year

Elevation at Old Oyster Bayou (Relative to Sea-Level)

Britch and Dunbar (1996). Land Loss is coastal Louisiana

A. ESLR 15.6 cm/100 yrs D.S. = 0.35 cm/yr B. ESLR 15.6 cm/100 yrs D.S. = 0.7 cm/yr C. ESLR 48 cm/100 yrs D.S. = 0.35 cm/yr D. ESLR 48 cm/100 yrs D.S. = 0.7 cm/yr

: 9 storms with winds over 100 mph Return rate of once every 12 years

Ebro Delta Wetland Site Year

Ebro Delta Wetland

Chioggia Wetland: Po Delta, Italy

Some General Conclusions Few site could keep pace with predicted increases in ESLR. Maintenance or restoration of pulsing functions are critical. Wetland elevation is most sensitive to rates of deep subsidence, a forcing function in the model, mineral inputs, and below ground production. Wetland elevation was least sensitive to rates of decomposition. Action before the “point of no return” due to positive feedback loops.

Future Directions More mechanistic algorithms to describe below ground processes, soil compaction, and mineral inputs. Spatilization and links to hydrodynamic models Develop better links between elevation and primary production

Pore Volume (%) Total weight above core cohort (g) 100% 50% 75% k Maximum Reduction Maximum Reduction/2 Minimum Reduction compaction i = total weight i /(k + total weight i )