Design of climate-resilient marsh restoration projects using a novel multiscale biogeomorphic model

Abstract:

Coastal marsh ecosystems have been degraded due to human land occupation, but are nowadays restored in many places around to world for their valuable ecosystem services. Such restoration projects must be resilient to future consequences of climate change, such as accelerating sea level rise, which may lead to marsh submergence. Yet, an important question that remains open is whether such climate resilience can be steered by pre-designing the initial landscape.

To answer that question, we developed a novel multiscale biogeomorphic model, allowing for the coupled simulation of vegetation and landform development through feedbacks between vegetation dynamics (colonization, expansion, die-back), hydrodynamics (tides) and geomorphodynamics (erosion, sedimentation, channel formation). Complementary to previous approaches, our model can run on large domains of several km², while at the same time accounting for vegetation dynamics at sub-meter resolution, and simulating several decades of landscape evolution. Novel techniques have been specifically developed to make this multiscale approach possible.

Here we present results for a real-life large-scale (about 5 km²) multi-inlet tidal marsh restoration project in the Scheldt estuary (Netherlands & Belgium). We evaluate our new modeling approach by comparing predicted rates of vegetation colonization and marsh sediment accretion, as well as predicted channel formation patterns, to observed data from nearby existing marshes. We also use our model to demonstrate that spatial patterns of vegetation development and sediment accretion rates can be steered by pre-designing the initial landscape conditions. In particular, in the specific context of this multi-inlet system, we show that inlet size does not necessarily positively correlate with sediment accretion rates on the vegetated platforms, contrary to what is generally thought.

The ability to steer the landscape development is highly relevant as, for instance, sedimentation rates determine whether coastal marshes are able to keep up with future scenarios of sea level rise. With this study, we illustrate how our novel modeling approach can provide a useful tool for designing large-scale marsh restoration projects that facilitate the development of climate-resilient marsh ecosystems.