Coastal and riverine wetlands, vital for flood protection and carbon storage in the Netherlands, are under increasing threat from salt intrusion, which is being amplified by climate change, according to new research from Eleonora Saccon at the NIOZ branch in Zeeland.
Saccon master study investigated nature-based solutions to keep these crucial ecosystems effective, even as seawater flows further inland during storm surges and prolonged droughts.
Black Alder Proves More Salt-Tolerant Than Willow
Saccon investigated the salt tolerance of two tree species commonly found in Dutch floodplain wetlands: the black alder and the white willow. Willows have historically been planted to reinforce dikes, replacing the common black alders that predate the 14th century.
In controlled container experiments, Saccon tested the effect of salt concentration, duration, and seasonality on the trees. The key findings revealed a major difference in resilience:
• Winter Intrusion: Temporary salt intrusion in winter was not a problem for either species.
• Prolonged Exposure: After a prolonged period of salt water, the black alders merely sprouted again once conditions returned to normal, while the willows were left in poor condition.
• Spring/Summer Intrusion: Willows suffered and died after temporary salt intrusion in spring and summer, whereas alders resprouted and showed greater resistance.
Saccon cautioned against planting a monoculture of black alders, stressing that a variety of trees, grasses, and shrubs is needed to create a resilient system protected against diseases or single-species die-offs.
Natural Creek Systems Outperform Straight Channels
In addition to plant hardiness, Saccon examined the role of landscape structure in quickly refreshing freshwater wetlands after a salt intrusion event. Using computer simulations, she compared the water-flow dynamics of managed landscapes such as flat areas with straight channels against naturally developed marshes featuring “fractal shapes” of meandering creeks.
The study concluded that the naturally developed marsh landscape was the most effective, demonstrating the shortest duration of salt intrusion. The branching, fractal creek system allows salt water to flow in quickly but also enables it to flow back out rapidly, preventing lasting damage to the plants.
However, Saccon noted the practical constraints: creating such an optimal, unyielding creek landscape is difficult and consumes considerable space, which is often unavailable in densely utilized European areas. The ultimate solution, she concluded, is to combat salinization at the source by slowing down climate change and raising the groundwater level.