What-if nature-based storm buffers on mitigating coastal erosion

Creating ecosystem buffers in intertidal zones, such as seagrass meadows, has gained increasing attention as a nature-based solution for mitigating storm-driven coastal erosion. This study presents what-if scenarios using an integrated model framework to determine the effectiveness and strategies for planting seagrass to reduce coastal erosion. The framework comprises two levels of simulation packages. The first level is a regional-scale coupled hydrodynamic model that simulates the processes of a specific storm and provides boundary forces for the morphodynamic model XBeach to apply at the next level, which simulates nearshore morphological evolution. The framework is applied to the open coast of Norderney in the German Bight of the North Sea. We demonstrate that optimising the location and size of seagrass meadows is crucial to increase the efficiency of onshore sediment erosion mitigation. For a specific depth range, depending on the storm's intensity, the most significant reduction in erosion may not be achieved by starting the meadow at the depth that permits the largest meadow size. To maintain a significant coastal protection effect, seagrass density and stem height should be considered together, ensuring erosion reduction by at least 80 % compared to the unprotected coast. This study provides valuable insights for the design and implementation of seagrass transplantation as a nature-based solution, highlighting the importance of considering location, size, density, and stem height when using seagrass meadows for coastal protection.

A Digital Twin modelling framework for the assessment of seagrass Nature Based Solutions against storm surges

In this paper we demonstrate a novel framework for assessing nature-based solutions (NBSs) in coastal zones using a new suite of numerical models that provide a virtual "replica" of the natural environment. We design experiments that use a Digital Twin strategy to establish the wave, sea level and current attenuation due to seagrass NBSs. This Digital Twin modelling framework allows us to answer "what if" scenario questions such as: (i) are indigenous seagrass meadows able to reduce the energy of storm surges, and if so how? (ii) what are the best seagrass types and their landscaping for optimal wave and current attenuation? An important result of the study is to show that the landscaping of seagrasses is an important design choice and that seagrass does not directly attenuate the sea level but the current amplitudes. This framework reveals the link between seagrass NBS and the components of the disruptive potential of storm surges (waves and sea level) and opens up new avenues for future studies.

Black Sea biogeochemistry: response to decadal atmospheric variability during 1960-2000 inferred from numerical modeling

The long-term variability of the physical and biochemical structure of oxic and suboxic layers in the Black Sea was studied using a one-dimensional coupled hydrophysical and biogeochemical model. The focus was on the correlation between atmospheric forcing (2 m air temperature and dew point temperature, surface level pressure, surface wind) affected by the North Atlantic Oscillation in and the regional responses. The quality of model performance was demonstrated using observed vertical and temporal distribution of biogeochemical variables. It was shown that during 1960-2000, the long-term variability of simulated winter-mean SST in the Black Sea correlated reasonably well with the variability of 2 m air temperature. Furthermore, the thermal state of the upper ocean impacted largely on the variability of biogeochemical variables, such as oxygen, nitrate and phytoplankton concentration. The tele-connection between North Atlantic Oscillation and Black Sea biogeochemistry was manifested in a different way for the specific time-interval 1960-2000; the corresponding regime shifts were thus associated with the large scale forcing. One such extreme event occurred in 1976 leading to a pronounced shift in the oxygen and hydrogen sulfide state.