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Climate Change

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Refuge Response to Climate Change and Sea Level Rise

Climate change has put a new face on conservation. After decades of following established paradigms, conservationists are being forced to reexamine some of the basic tenets of our field. Like coastal locations around the country and world, the Humboldt Bay area is and will continue to be impacted by effects of climate change, especially sea level rise (SLR).  Models and predictions vary geographically but for the state of California, the conservative SLR estimate is 6” by 2030, 12” by 2050, and 36” by 2100.  The CA Coastal Commission requires projects to assess impacts from a minimum SLR of 3’ and a maximum of 6’ by 2100, the rest of the California Resource Agencies use 55” by 2100.  But on Humboldt Bay the north Spit station record gives us a relative SLR of 18.6” per century, due to subsidence.  Based on a recently completed vulnerability assessment a SLR of 2’ to 3’ will be a significant tipping point on Humboldt Bay.
Sea level rise will have obvious and significant impacts within the coastal zone and to refuge habitats and infrastructure.  Given this level of uncertainty, the practice of adaptive management is critical. Adaptive management can be summarized as “learning by doing and adapting based on what’s learned.” Research and monitoring are essential pieces of adaptive management. Management actions are closely monitored so that outcomes can be assessed and modified as needed.  

Wetland Habitats

Refuge wetlands that were historically salt marsh were significantly changed by past human actions such as diking, filling, and conversion to pasture.  This dramatically changed the topography, bathymetry, hydrology, complexity and value of these wetlands to fish and wildlife.  Refuge efforts over the last 20 years have been to try and restore these areas to more functional wetlands to the extent possible.  These efforts have included removing dikes (where possible), modification of tidegates to allow more estuarine influence and fish passage in muted systems, use of water control structures to manage seasonal wetlands, excavation of historic channels which were filled, placement of large wood to increase habitat complexity in wetlands, and in some cases filling areas that have subsided so that vegetated wetlands can re-establish.  This last technique may become more necessary and commonplace as water levels rise.
Questions about how coastal wetlands and associated resources will respond to SLR are ultimately tied to human responses, for most wetlands of coastal California, including Humboldt Bay, are “hemmed in” by infrastructure and/or development or agriculture.  As sea level rises, habitats like salt marsh would migrate inland.  However, levee create an abrupt edge that will prevent this from happening.

Dune Ecosystems

In some ways, coastal dunes are one of the more resilient ecosystems with respect to climate change. Located at the boundary zone between marine and terrestrial ecosystems, they are dynamic systems that have historically undergone constant, albeit gradual change in response to climate and related sea level changes. From this long history of change, we know that dunes have the capacity to migrate and equilibrate with new sea levels. However, there are many unknowns given the unprecedented rate of change we are beginning to experience. And although these ecosystems have the benefit of physical adaptation, the fact that dunes tend to be geographically isolated means that the migration of species endemic to dunes may be limited. Adaptive management has been ongoing at the Lanphere Dunes since the 1970’s, and has led to much of the research and collaboration carried out on the dunes and estuary. With the challenge of extreme uncertainty about climate change, we are implementing a new emphasis on understanding abiotic processes in our dunes, funded through the Fish and Wildlife Service’s newly established Inventory and Monitoring Program.
Our “Abiotic Monitoring Program” actually addresses both physical processes and their interaction with dune vegetation. In collaboration with Patrick Hesp, an international expert in coastal dune geomorphology, we designed a project to determine the status of the sediment budget, monitor long-term changes in dune topography (as well as short-term responses to extreme events), and discern responses in vegetation. With the help of  the USFWS Coastal Program we are using RTK GPS (an extremely precise tool for measuring elevation) to measure elevation at one-meter intervals along 14 transects placed parallel with prevailing winds. Transect placement allows for comparison of changes in foredunes with different dominant vegetation and degrees of stability. Transects are run at two seasonal extremes of vegetation and topographic variation (January and July). Vegetation plots are placed at regular intervals along the transects. Transects extend from the beach (approximately Mean High Water) inland between 156 and 256 meters.
Coastal foredunes are essentially sand-sharing systems that accumulate sediment in the summer and release it to offshore bars in the winter. The degree of accumulation can vary depending on the amount of sediment delivered alongshore and onto beaches, the vegetation present in the foredune, and the occurrence of extreme erosional events. Data collected from this program extends along a 3-km stretch of dunes that is characterized by differences in these variables. Our data will allow us to characterize responses under these different conditions. Results can then be incorporated into models that will allow us to predict how the dunes will change as sea levels rise, and how vegetation may respond to these changes. At the same time, this monitoring design will allow us to track changes in rear dunes that result from climatic changes in temperature, precipitation, fog and other variables. 
Coastal dunes encompass a high degree of biodiversity, and are inherently resilient to rising sea levels and extreme events. Our new monitoring program will result in increased understanding of our dune systems that will allow us develop specific management strategies in keeping with these basic guidelines.  
Despite the many uncertainties associated with climate change, there is consensus among conservation science experts regarding some basic guidelines to steer us through this period of rapid change. These include the need to preserve the variety of ecological settings that will continue to support California’s biodiversity as they shift in response to a changing climate; the importance of developing strategies that enhance the persistence of coastal ecosystems as sea levels rise and the need to manage ecosystems for resilience in the face of extreme events.

Page Photo Credits — © Andrea Pickart
Last Updated: Mar 06, 2013
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