Saturday, May 18, 2024

Stronger storms free more nutrients from mud flats

EcologyStronger storms free more nutrients from mud flats


If storms become stronger in the future due to climate change, more nitrogen may be released from the bottom of coastal seas. This is shown by research of marine biogeochemist Dunia Rios-Yunes at NIOZ in Yerseke. Rios-Yunes will defend her PhD-thesis today at the University of Utrecht. “The dynamics of nutrients in deltas and estuaries have been a bit of a blind spot for marine science, so far,” she says.

Inflatable couch

For her experiments, Rios-Yunes spent many hours on an inflatable couch on the dry bottom of the Wester- and the Oosterschelde. “I mimicked a storm on the mud, using a bucket without a bottom and a big blender, stirring up the mud and measuring the release or the uptake of nitrogen and phosphorus. But, since I needed to do this for six hours in a row, I rapidly found out that I needed a little bit of comfort, sitting on the mud. The inflatable couch was my life saver during the field work,” she jokingly says.

More N, less P

Rios-Yunes found out that considerable amounts of nitrogen are released when her experimental storm stirs the bottom. “In just a couple of hours, the amount of nitrogen that is normally released in weeks, may come out of the mud during one storm. This means that much more nutrients become available in the water column, and these could be used algae to grow.” Phosphorus, on the other hand, was taken up during the ‘storm’ in the Oosterschelde but released in the Westerschelde. “This may be because of the differences in chemical composition of the mud between an estuary and a tidal bay.”

Ecosystem services

Storage of nutrients like nitrogen and phosphorus, but also of many trace elements, are considered a crucial ecosystem service of places like the Wester- and the Oosterschelde. This ecosystem service is under increasing pressure, Rios-Yunes explains. For example, the Oosterschelde coast is relatively important for storage of nutrients, compared to the subtidal sea bottom. But due to the Oosterschelde storm surge barrier and also with rising sea levels in the future, the coast of the Oosterschelde is ‘eaten by the currents’. “Therefore, relatively large amounts of nutrients may become available for algae and other organisms.”

Equilibria

Temperature and salinity, as well as benthic animals also influence the chemistry of the tidal sea floor. “But these phenomena have not been studied a lot, so far,” Rios-Yunes says. “For fundamental research into the dynamics of nutrients and other equilibria in tidal areas, it is very important to understand the role of temperature, salinity, benthic animals and also turmoil by storms.”

Coastal squeeze

Polici makers and keepers of natural areas like the Oosterschelde should also understand the dynamics of nutrients in a changing world, Rios-Yunes says. “My research stresses the importance to keep the coast of these tidal areas in a good condition, and thus avoid losing the valuable ecosystem services they provide.”

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