Evaluating regional resiliency of coastal wetlands to sea level rise through hypsometry‐based modeling

Abstract

Sea level rise (SLR) threatens coastal wetlands worldwide, yet the fate of individual wetlands will vary based on local topography, wetland morphology, sediment dynamics, hydrologic processes, and plant‐mediated feedbacks. Local variability in these factors makes it difficult to predict SLR effects across wetlands or to develop a holistic regional perspective on SLR response for a diversity of wetland types. To improve regional predictions of SLR impacts to coastal wetlands, we developed a model that addresses the scale‐dependent factors controlling SLR response and accommodates different levels of data availability. The model quantifies SLR‐driven habitat conversion within wetlands across a region by predicting changes in individual wetland hypsometry. This standardized approach can be applied to all wetlands in a region regardless of data availability, making it ideal for modeling SLR response across a range of scales. Our model was applied to 105 wetlands in southern California that spanned a broad range of typology and data availability. Our findings suggest that if wetlands are confined to their current extents, the region will lose 12% of marsh habitats (vegetated marsh and unvegetated flats) with 0.6 m of SLR (projected for 2050) and 48% with 1.7 m of SLR (projected for 2100). Habitat conversion was more drastic in wetlands with larger proportions of marsh habitats relative to subtidal habitats and occurred more rapidly in small lagoons relative to larger sites. Our assessment can inform management of coastal wetland vulnerability, improve understanding of the SLR drivers relevant to individual wetlands, and highlight significant data gaps that impede SLR response modeling across spatial scales. This approach augments regional SLR assessments by considering spatial variability in SLR response drivers, addressing data gaps, and accommodating wetland diversity, which will provide greater insights into regional SLR response that are relevant to coastal management and restoration efforts.

Short-term impact of sediment addition on plants and invertebrates in a southern California salt marsh

“…Urbanized estuaries with marshes around the world are at risk of submergence from SLR due to sediment starvation, human development, and the interaction of these complex processes [27,72]. Without management actions, many of these marshes may be converted to mudflat and subtidal habitats as SLR rates outpace accretion (e.g.…”

Advancing the Science of Environmental Flow Management for Protection of Temporarily Closed Estuaries and Coastal Lagoons

“…Scanes et al [104] found that the changes to estuaries as a result of climate change are occurring an order of magnitude faster than global models predict, with systems that have a limited connection to the ocean, such as temporarily closed estuaries, most affected. Doughty et al [105] found that small intermittently closing estuaries along the southern California (USA) coast will be almost entirely lost with 1.7 m of sea level rise. The quantity and timing of freshwater inflows into estuaries is likely to change, although the direction and magnitude of changes will vary from place to place.…”

“…However, in New Zealand, the mean change is not a good proxy for the effect on flow variability. In addition, predicted sea level rise varies globally and may exacerbate the effect of reduced inflows into some estuaries, changing the morphology of the estuary and hence many of the physical processes [105]. In addition to changes in sea level, Australian estuaries are warming and acidifying faster than predicted by global climate modeling, with lagoons and rivers most affected [104].…”

Assessing the spatial–temporal response of groundwater‐fed anchialine ecosystems to sea‐level rise for coastal zone management

“…To be useful for planners and land managers, models of ecosystem risk from SLR must be applicable to relevant geographic scales and must incorporate enough detail to reflect local conditions adequately (Thorne et al, 2018). Numerous models have been developed to examine how coastal ecosystems will change with SLR, including predictions for wetlands and salt marshes (Borchert et al, 2018; Craft et al, 2009; Doughty et al, 2019; Thorne et al, 2018; Traill et al, 2011), sandy beach and dune ecosystems (Keijsers et al, 2016; Le Cozannet et al, 2019), mangroves (Gilman et al, 2008; McKee et al, 2007), and coastal freshwater forests (Doyle et al, 2010). In these studies, factors such as topography, hydrology, sedimentation, erosion, regional oceanographic conditions, and the response of dominant plant species to changing conditions were found to be key considerations in predicting the location and condition of future ecosystems.…”