Abstract
Coastal wetlands are important ecosystems for carbon storage and coastal resilience to climate change and sea-level rise. As such, changes in wetland habitat types can also impact ecosystem functions. Our goal was to quantify historical vegetation change within the Nisqually River watershed relevant to carbon storage, wildlife habitat, and wetland sustainability, and identify watershed-scale anthropogenic and hydrodynamic drivers of these changes. To achieve this, we produced time-series classifications of habitat, photosynthetic pathway functional types and species in the Nisqually River Delta for the years 1957, 1980, and 2015. Using an object-oriented approach, we performed a hierarchical classification on historical and current imagery to identify change within the watershed and wetland ecosystems. We found a 188.4 ha (79%) increase in emergent marsh wetland within the Nisqually River Delta between 1957 and 2015 as a result of restoration efforts that occurred in several phases through 2009. Despite these wetland gains, a total of 83.1 ha (35%) of marsh was lost between 1957 and 2015, particularly in areas near the Nisqually River mouth due to erosion and shifting river channels, resulting in a net wetland gain of 105.4 ha (44%). We found the trajectory of wetland recovery coincided with previous studies, demonstrating the role of remote sensing for historical wetland change detection as well as future coastal wetland monitoring.
Highlights
Coastal wetlands are ecologically and economically beneficial ecosystems, they are at significant risk of degradation and loss
Within the United States alone, the rate of coastal wetland decline between 2004 and 2009 was 324.3 km2 annually, with the majority of salt marsh loss attributed to coastal storms and land development [3]
For our first objective we developed remote sensing methods utilizing limited historical data and imagery ranging from air photo to satellite image with panchromatic and multispectral bands to map coastal wetland habitat types, photosynthetic functional types, and emergent marsh plant species for the years 1957, 1980, and 2015
Summary
Coastal wetlands are ecologically and economically beneficial ecosystems, they are at significant risk of degradation and loss. In the contiguous United States, wetlands cover 5% of total land area, of which only 5% are tidally influenced coastal wetlands [2]. These are some of the most readily declining ecosystems globally. Within the United States alone, the rate of coastal wetland decline between 2004 and 2009 was 324.3 km annually, with the majority of salt marsh loss attributed to coastal storms and land development [3]. Carbon sequestration rates for tidal saline wetlands and mangroves are globally estimated to be at 44.6 TgC/year, and the release of greenhouse gases from these wetlands are minimal [5]. There is a growing interest in including tidal salt marsh in climate mitigation strategies and policies [6]
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