Atmospheric River Storm Flooding Influences Tidal Marsh Elevation Building Processes

Abstract

Disturbances are a key component of ecological processes in coastal ecosystems. Investigating factors that affect tidal marsh accretion and elevation change is important, largely due to accelerating sea‐level rise and the ecological and economic value of wetlands. Sediment accumulation rates, elevation change, and flooding were examined at five marshes along a riverine‐tidal gradient in the northern San Francisco Bay‐Delta, California, USA during an Atmospheric River storm event in 2017 using Surface Elevation Tables (SETs), feldspar marker horizons (MH), and continuous water‐level sensors. Our results showed that localized marsh flooding increased during the storm event, but not evenly across sites. Marsh surface elevation increased the most at the tidal freshwater marsh site in response to the storms, with an average surface elevation gain of 45.6 ± 13.1 mm, and the least at a tidal saline marsh with an average surface elevation gain of 4.0 ± 1.2 mm. A marsh located on the large embayment did not exhibit an immediate response to the storm but had a surface elevation gain of 21.5 ± 13.7 mm 6 months after the storm. During the storm period, marsh distance to the bay was the strongest predictor of elevation change, followed by SET‐MH elevations. Conversely, during non‐storm periods, SET‐MH elevation was a relatively strong predictor of elevation change. Atmospheric Rivers appear to be a major factor affecting short‐term spatial and temporal variability in flooding and sedimentation rates in tidal marsh systems. Incorporating information about storms into monitoring could increase our understanding of how episodic storms can impact marshes.

Phenotypic trait differences betweenIris pseudacorusin native and introduced ranges support greater capacity of invasive populations to withstand sea level rise

“…Extreme meteorological events, such as torrential rains, droughts and heat waves, are more frequent now in the actual scenario of climate change (Payne et al, 2020). The water depths we recorded in the introduced range reflected the atmospheric river storm flooding that occurred in SFE in 2017 (Thorne et al, 2022). Even though the year was atypical, if we exclude analysis of the above average data from 2017, maximum inundation depth was still considerably higher in the introduced range when compared to the native range.…”

An assessment of future tidal marsh resilience in the San Francisco Estuary through modeling and quantifiable metrics of sustainability

“…Because vertical accretion in the San Francisco Estuary is also influenced by major storms/atmospheric rivers (Thorne et al, 2022), additional model runs were added to incorporate such episodic disturbance. Inputs for episodic disturbance were determined as follows.…”

“…The median frequency of large atmospheric rivers in the Delta region (categories 3-5), which increase sediment availability, was found to be approximately 3 years, based on data between 1953-2017 from Gershunov et al (2017). Next, a range of surficial deposits was chosen to be 2 mm, Frontiers in Environmental Science frontiersin.org 3 mm, and a maximum of 6 mm, which was close to the mean surficial deposit (6.5 mm) measured at Browns Island in the Delta after a Category five atmospheric river (Thorne et al, 2022). The permutations resulted in 3D response surfaces where the response variables were the metric of interest, and the independent variables were the IRE and CSLR.…”

“…Major storms known as atmospheric rivers increase discharge rates and suspended sediment concentrations in rivers, resulting in episodic increases in mineral sediment deposition on marshes (Thorne et al, 2022). This was simulated by assuming triennial surface deposits of 2, 3, or 6 mm (Table 3 and Table 4).…”

“…The baseline simulations did not allow for episodic inputs of sediment such as those generated by atmospheric rivers (Thorne et al, 2022), so we added episodic inputs ranging up to 6 mm of sediment triennially (Table 3 and Table 4). Episodic inputs of sediment increased the proportion of simulations ending in a stable state.…”