In Puget Sound’s Stillaguamish estuary, tidal marshes exhibit evidence of multiple stressors that affect their vulnerability and provide insight into adaptive management opportunities to enhance their resilience. Despite high accretion rates, some marsh areas have receded by 10m/yr since 1964. Sources of stress include overgrazing by snow geese, high soil salinities, insect attacks, and changes in flow and inundation patterns. These interact with winter vegetation structure, sediment composition, and wave exposure to result in spatially variable marsh resilience. Some marshes are receding quickly, some slowly, and others are minimally affected. In the context of climate change, with potentially substantial near-term salinity changes due to summer low flow projections, and likely changes in sediment dynamics, it is critical to identify how marshes will respond, and develop adaptive management actions to increase resilience. Geese consume the rhizomes of four dominant bulrushes, and loosen the soil during winter storm season. Each bulrush species has different winter structural characteristics that affect grazing vulnerability, and the ability to trap sediment and attenuate erosive wave energy. Coarser sediments affect grazing intensity, being more difficult for geese bills to probe. Sediment and soil salinity affect plant density and height. During summer 2015, a harbinger for coming decades, twice-normal soil salinities resulted in stunted marsh that failed to flower. Finally, small differences in winter wave exposure affect marsh susceptibility to erosion after heavy grazing. With spatially variable marsh resilience to stress, potential adaptive management responses should similarly vary. Responses could include, among others, restoration to improve freshwater connectivity, sediment addition in restored areas to shift them above erosion thresholds or to target grazing-resistant bulrush species, snow goose population management or behavior modification, manipulation of soil particle size with sediment addition, and strategic use of logjams and sediment addition to reduce wave energy
