Climate-driven tradeoffs between landscape connectivity and the maintenance of the coastal carbon sink

Abstract

Ecosystem connectivity tends to increase the resilience and function of ecosystems responding to stressors. Coastal ecosystems sequester disproportionately large amounts of carbon, but rapid exchange of water, nutrients, and sediment makes them vulnerable to sea level rise and coastal erosion. Individual components of the coastal landscape (i.e., marsh, forest, bay) have contrasting responses to sea level rise, making it difficult to forecast the response of the integrated coastal carbon sink. Here we couple a spatially-explicit geomorphic model with a point-based carbon accumulation model, and show that landscape connectivity, in-situ carbon accumulation rates, and the size of the landscape-scale coastal carbon stock all peak at intermediate sea level rise rates despite divergent responses of individual components. Progressive loss of forest biomass under increasing sea level rise leads to a shift from a system dominated by forest biomass carbon towards one dominated by marsh soil carbon that is maintained by substantial recycling of organic carbon between marshes and bays. These results suggest that climate change strengthens connectivity between adjacent coastal ecosystems, but with tradeoffs that include a shift towards more labile carbon, smaller marsh and forest extents, and the accumulation of carbon in portions of the landscape more vulnerable to sea level rise and erosion.

Upland forest retreat lags behind sea‐level rise in the mid‐Atlantic coast

“…Climate‐driven landscape reorganization, manifested in coastal ecosystems as the migration of marshes into adjacent uplands via sea‐level rise, is affecting large sections of the global coast (Kirwan & Gedan, 2019; McDowell et al., 2022; Osland et al., 2022). This phenomenon is considered one of the major processes that will fundamentally modify the feedbacks of coastal ecosystems to global climate (Chen & Kirwan, 2022a; Smart et al., 2020; Smith & Kirwan, 2021; Valentine et al., 2023; Warnell et al., 2022) and potentially incur large socioeconomic repercussions (Bhattachan et al., 2018; Kirwan & Megonigal, 2013). However, predictions of coastal ecosystem transformations remain limited by an incomplete understanding of how the impacts of relative sea‐level rise rate (RSLRR) are potentially mediated by spatially variable environmental drivers.…”

Sediment Exchange Across Coastal Barrier Landscapes Alters Ecosystem Extents

“…BarrierBMFT (Figure 1) is an exploratory model framework that couples Barrier3D (I. R. B. Reeves et al, 2021), a spatially-explicit model of barrier evolution, with the Coastal Landscape Transect model (CoLT; Valentine et al, 2023), which integrates carbon cycling dynamics into the Bay-Marsh-Forest Transect Model (BMFT) of Kirwan et al (2016). See Text S1 in Supporting Information S1 for a detailed description of the model framework, boundary conditions, and its components.…”

Shoreface erosion counters blue carbon accumulation in transgressive barrier-island systems

“…The coastal landscape is widely recognized for its ability to store organic matter in blue carbon ecosystems, such as salt marshes and seagrass beds, that bury carbon (C) in soils and sediments at rates orders of magnitude greater than terrestrial systems 1 . Sea-level rise (SLR) is thought to augment the coastal C sink 2 , especially in marshes that are building soils vertically at rates similar to those of relative SLR 3 – 5 . A direct coupling between SLR and soil C accumulation can result in increases in C stocks even where marshes are eroding 2 , 6 .…”

“…Sea-level rise (SLR) is thought to augment the coastal C sink 2 , especially in marshes that are building soils vertically at rates similar to those of relative SLR 3 – 5 . A direct coupling between SLR and soil C accumulation can result in increases in C stocks even where marshes are eroding 2 , 6 . However, the capacity of the coastal zone to store blue carbon over centuries to millennia under rapid rates of SLR remains uncertain.…”