What happens to Oregon s tidal wetlands with sea level rise? Laura Brophy Estuary Technical Group Institute for Applied Ecology Corvallis, OR Laura@appliedeco.org
Project maps future tidal wetlands, predicts losses Funding: Oregon Watershed Enhancement Board, USFWS Coastal Program Contractor: Estuary Technical Group (Laura Brophy, Michael Ewald) Conducted for the MidCoast Watersheds Council Project Manager: Fran Recht, PSMFC
Project provides tools for conservation and restoration planning This project: - Maps future tidal wetlands for 6 sea level rise ( SLR ) scenarios - Covers all 23 Oregon estuaries S of the Columbia - Provides tools to help local groups prioritize the mapped areas for action planning - Reaches out to coastal watershed councils and other interested groups
What estuaries are covered by the maps? Alsea Bay Beaver Creek Chetco River Coos Bay Coquille River Elk River Necanicum River Nehalem River Nestucca Bay Netarts Bay New River Pistol River Rogue River Salmon River Sand Lake Siletz Bay Siuslaw River Sixes River Tillamook Bay Umpqua River Winchuck River Yachats River Yaquina Bay
What is a tidal wetland?
a wetland that is flooded by the tides (at least once a year, usually daily to monthly) Our project maps tidal marsh and tidal swamp (shrub/forested), but not mud flats
Tidal wetland types I. Tidal marsh Low marsh High marsh
Tidal wetland types II. Tidal swamp Forested Shrub
How will sea level rise affect tidal wetlands? And why should we care?
Tidal wetlands support many creatures Salmon Birds Mammals Other fish & shellfish
What else can tidal wetlands do for us? Store carbon in the soil, helping to reduce global warming Reduce flooding Provide scenic beauty and recreation Filter and clean water
Yaquina Estuary normal high tide
Yaquina Estuary King Tide Future normal high tide?
So how can our tidal wetlands survive into the future?
They ll remain in place if possible otherwise move upslope if they can Tidal wetlands may keep pace with sea level rise, if there s enough accretion (deposited sediment and organic matter). If not, then tidal wetland vegetation won t survive in its current location, and wetlands will need to migrate upslope. We call the area they ll move to, the Landward Migration Zone or LMZ.
First step in determining where future tidal wetlands may be: We need to know where they are now!
Tidal wetlands aren t always easy to identify
But this recent project in Oregon gives us accurate maps of current tidal wetlands: Updating Oregon's estuarine wetland habitat maps: Modernizing the foundation for coastal resource management Products released Oct. 2014: http:///www.coastalatlas.net/cmecs Andy Lanier 1, Laura Brophy 2, Tanya Haddad 1, Laura Mattison 1 1 Oregon Coastal Management Program, Department of Land Conservation and Development, Salem, OR 2 Estuary Technical Group, Institute for Applied Ecology, Corvallis, OR
What s new about the 2014 Oregon estuary habitat maps? All current and former tidal wetlands, including diked; this helps identify restoration opportunities and vulnerable areas All the way to head of tide, including freshwater tidal Based on land elevations and NOAA water level models Much greater accuracy than past maps A very good starting point for mapping future tidal wetlands
Tidal wetlands form in a narrow elevation range This is the Landward Migration Zone or LMZ
Elevation-based mapping - example Tillamook estuary tidal floodplain 12 miles upstream
Elevation-based mapping Where are the current and former tidal wetlands?
Elevation-based mapping
We use the same elevation-based method to map future tidal wetlands Current areas within tidal wetland elevation range (blue & green) This low ground just above current tide range is the Landward Migration Zone or LMZ : Potential future tidal wetland
Source of projected sea level rise data: National Academy of Sciences 2012 West Coast SLR study
SLR scenarios For Newport, high end of 2030 range = 9 (23 cm) High end of 2050 range = 1.6 ft (48 cm) We also added an intermediate scenario: 2.5 ft (75 cm) and two higher scenarios: 8.2 and 11.5 ft (~2130, 2160) High end of 2100 range = 4.7 ft (142 cm)
Wetlands are shifting into the LMZ
Many diked ag lands (former tidal marsh) are water or mudflat at 4.7 ft SLR
Wetlands are shifting further into the LMZ
LMZ area (ac) Results... By the numbers These bar charts show acres of potential future tidal wetlands at each SLR scenario. 1400 1200 1000 800 Alsea Bay Estuary Impervious Not impervious Green color shows areas that are not developed -- better potential for future tidal wetlands. 600 400 200 0 0.0 0.8 1.6 2.5 4.7 8.2 11.5 Orange means developed (impervious) areas. SLR (ft)
LMZ area (ac) Results... By the numbers Summed across all 23 estuaries, the model shows little change in potential tidal wetland area until >3 ft SLR 45000 40000 35000 30000 25000 20000 15000 10000 5000 0 All 23 estuaries Impervious Not impervious 0.0 0.8 1.6 2.5 4.7 8.2 11.5 SLR (ft) -21% But potential tidal wetland area drops sharply after 4.7 ft SLR: -41% -60%
LMZ area (ac) Most estuaries show a pattern of slightly increased tidal wetland area during early SLR scenarios. Tillamook Bay Estuary Followed by sharp decreases in tidal wetland area when SLR is >3 ft 7000 6000 5000 4000 3000 2000 1000 0 Impervious Not impervious 0.0 0.8 1.6 2.5 4.7 8.2 11.5 SLR (ft)
LMZ area (ac) Tillamook Bay Estuary 7000 6000 5000 4000 3000 2000 1000 Impervious Not impervious The proportion of LMZs in developed areas (impervious surfaces) increases as SLR pushes up into populated areas 0 0.0 0.8 1.6 2.5 4.7 8.2 11.5 SLR (ft)
LMZ area (ac) LMZ area (ac) LMZ area (ac) LMZ area (ac) Here are more estuaries with the typical pattern of early, slight increases in LMZs, followed by sharp declines after SLR >3 ft Alsea Bay Estuary Umpqua River Estuary 1400 1200 1000 800 600 400 Impervious Not impervious 6000 5000 4000 3000 2000 Impervious Not impervious 200 1000 0 0.0 0.8 1.6 2.5 4.7 8.2 11.5 0 0.0 0.8 1.6 2.5 4.7 8.2 11.5 SLR (ft) SLR (ft) 450 400 350 300 250 200 150 100 50 0 Netarts Bay Estuary Impervious Not impervious 0.0 0.8 1.6 2.5 4.7 8.2 11.5 SLR (ft) 800 700 600 500 400 300 200 100 0 Beaver Creek Estuary Impervious Not impervious 0.0 0.8 1.6 2.5 4.7 8.2 11.5 SLR (ft)
LMZ area (ac) LMZ area (ac) Two major estuaries lacking broad river valleys (Coos and Yaquina) show steadily decreasing LMZs. In both, substantial portions of LMZs are on developed land. Coos Bay Estuary 8000 7000 6000 5000 4000 3000 2000 1000 0 Impervious Not impervious 0.0 0.8 1.6 2.5 4.7 8.2 11.5 2500 2000 1500 Yaquina River Estuary Impervious Not impervious SLR (ft) 1000 500 0 0.0 0.8 1.6 2.5 4.7 8.2 11.5 SLR (ft)
LMZ area (ac) LMZ area (ac) The New River and Necanicum show increases in LMZs up to 8 or 10 ft SLR but for the Necanicum, nearly half is on developed land. 2500 2000 1500 New River Area Estuary Impervious Not impervious 1000 500 0 0.0 0.8 1.6 2.5 4.7 8.2 11.5 SLR (ft) 2500 2000 Necanicum River Estuary Impervious Not impervious 1500 1000 500 0 0.0 0.8 1.6 2.5 4.7 8.2 11.5 SLR (ft)
Alsea Bay Beaver Creek Chetco River Coos Bay Coquille River Elk River Necanicum River Nehalem River Nestucca Bay Netarts Bay New River Area Pistol River Rogue River Salmon River Sand Lake Siletz Bay Siuslaw River Sixes River Tillamook Bay Umpqua River Winchuck River Yachats River Yaquina Bay LMZ area (ac) 9000 8000 7000 6000 5000 4000 3000 2000 1000 Results for all 23 estuaries show the overall pattern: The largest estuaries show sharp losses at higher SLR scenarios. Increases for some smaller estuaries can t make up for these losses. LMZ area by estuary and SLR scenario 0 0 ft 0.8 ft 1.6 ft 2.5 ft 4.7 ft 8.2 ft 11.5 ft
LMZs are not in the same places as current tidal wetlands Bar charts don t show how the locations of future tidal wetlands differ from current tidal wetlands At 4.7 ft SLR, 2/3 of potential tidal wetlands are in different places from current tidal wetlands At 8.2 and 11.5 ft SLR, there is no overlap between locations of future and current tidal wetlands.
Summary of results Most estuaries show a sharp decline in potential tidal wetland area after 3 to 5 ft SLR Although some estuaries show LMZ gains, these tend to be small in acreage Maps show locations of LMZs, for action planning Maintaining tidal wetland functions will require landscapescale thinking At 4.7 ft SLR, 2/3 of potential tidal wetlands are in different locations from current tidal wetlands
So... What should we do? The landscape is big; funds are small Strategic focus is vital Working to help groups with their action planning
Setting priorities: some criteria Data are available for 5 factors that affect importance and feasibility of conserving & restoring LMZs. We scored each of these 5 factors: Future tidal wetland area (hectares) at 4.7 ft SLR (more = higher) Area of even higher LMZs (8.2 and 11.5 ft SLR) Current land use zoning (non-developed = higher) Land ownership (public = higher) Development status (undeveloped = higher)
Nestucca River estuary Black areas indicate developed (impervious) land We added the 5 scores to calculate a total score
Nestucca River estuary This scoring- and the underlying data - may help local groups make decisions about how to work towards solutions.
Tools we provide For each estuary: Future tidal wetland maps (online; for 6 SLR scenarios) Map of prioritization rankings Tables and bar charts of potential tidal wetland area now, and in the future Report describing potential ways to use the data, and the limitations of the data
How can the results be used? Plan in 4 dimensions for resilience look upslope Use maps to understand vulnerability Talk with upslope landowners Consider easements, restoration activities, other tools to conserve LMZs Recognize that gradients and connectivity are important, regardless of sea level rise
Discussion: How do results compare to other models? SLAMM and WARMER are two widely-used models
SLAMM Sea-level affecting marshes model Applied at several Pacific Northwest Wildlife Refuges in 2010 Model primarily uses elevation to determine future wetland locations and types Models at OR sites used accretion data from Salmon R. Estuary We used SLAMM model results from Bandon Marsh and Siletz Bay NWRs
WARMER Wetland accretion Rate Model of Ecosystem Resilience USGS team applied the model at 14 PNW sites OR Sites: Bandon Marsh and Siletz Bay NWRs; Bull Island (Coos Bay) For model inputs, USGS team measured local accretion and organic matter accumulation, and estimated plant productivity 2015 report (Thorne et al.) provides detailed data on model and results
How do LMZ results compare to SLAMM and WARMER? We compared results for Bandon Marsh and Siletz Bay, where all 3 models were run Results were compared within a defined area (the WARMER model boundary) for comparability Areas compared do not have dikes, so we are directly comparing elevation-based model results
How do LMZ results compare to SLAMM and WARMER? Vegetated tidal wetland area (ac) 250 200 150 Bandon Marsh Unit, Bandon Marsh NWR, Coquille River Estuary LMZ WARMER SLAMM 100 50 Results from all 3 models are very similar at Bandon. 0 0 1 2 3 4 5 Sea level rise (ft)
Vegetated tidal wetland area (ac) How do LMZ results compare to SLAMM and WARMER? Siletz Bay NWR, Siletz Bay Estuary 180 160 140 120 100 80 60 40 20 0 LMZ WARMER SLAMM 0 1 2 3 4 5 Sea level rise (ft) For Siletz, at 4.7 ft SLR, WARMER shows much less tidal wetland (much more conversion to mudflat)
Vegetated tidal wetland area (ac) How do LMZ results compare to SLAMM and WARMER? Siletz Bay NWR, Siletz Bay Estuary 180 160 140 120 100 80 60 40 20 LMZ WARMER SLAMM This difference is likely due to WARMER s method for calculating mudflat conversion, combined with local topography at Siletz Bay. 0 0 1 2 3 4 5 Sea level rise (ft)
0 ft SLR 2.5 ft SLR 4.7 ft SLR WARMER LMZ 0 ft SLR 2.5 ft SLR 4.7 ft SLR
0 ft SLR 2.5 ft SLR 4.7 ft SLR SLAMM LMZ 0 ft SLR 2.5 ft SLR 4.7 ft SLR
0 ft SLR 2.5 ft SLR 4.7 ft SLR WARMER 0 ft SLR 2.5 ft SLR 4.7 ft SLR LMZ
0 ft SLR 2.5 ft SLR 4.7 ft SLR SLAMM 0 ft SLR 2.5 ft SLR 4.7 ft SLR LMZ
Conclusions: How do LMZ results compare to SLAMM and WARMER? All 3 model results were similar at Bandon SLAMM and LMZ were similar at Siletz WARMER results were different at higher SLRs at Siletz, due to site characteristics and differences in methods Across broader landscapes, interpretation using local knowledge is critical WARMER does not model diked lands SLAMM has model options for handling diked lands, but interpretation is challenging Understanding vulnerability of diked lands will be critical to SLR adaptation planning
Discussion Why do we have limited LMZs? Coastal geology: Steep watersheds Limited coastal plain Drowned river mouth estuaries
The lower course of the river valley has been drowned by rising sea levels since the end of the last Ice Age. What s a drowned river mouth estuary? Sediments have filled in much of the former valley. Their height Is limited mostly by tide heights in the lowest part of the bay. Illustration courtesy of J. Good, OSU Extension Service
Discussion What about accretion rates? Accretion (and OM accumulation) can definitely keep up with limited, historic SLR. Can they keep pace with rapid, accelerated SLR? We are not using an accretion model That s why we have shown the year with a question mark (e.g. 2050?) SLR will continue; date may vary but sea level will ultimately reach the level shown
Discussion What about land uplift rates/ tectonics? Tectonics & different land uplift rates: Could lead to slightly different RSLR rates Effect is smaller than the error in models Literature doesn t support adjustments to LMZs based on tectonics
Discussion What about earthquakes? A major subduction zone earthquake: Would have a huge effect on tidal wetland distribution across the landscape Immediate post-seismic subsidence could be over a meter Accretion would gradually fill in the subsided area, as it did after the 1700 earthquake Rate of recovery is unknown
Questions? Laura Brophy Laura@appliedeco.org Estuary Technical Group Institute for Applied Ecology, Corvallis, OR