New species for delta research discovered in Botanical Gardens
Researchers from the Botanical Gardens and the Faculty of Geosciences have discovered several plant species that are interesting for studying the creation of river landscapes around the world. The researchers used plant seeds for the experiments, but so far they only had access to a single species: Lucerne, also known as alfalfa. But hortulanus Gerard van Buiten thought they were completely unsuitable for that purpose. The researchers explain their findings in a publication in the journal Earth Surface Processes and Landforms.
River landscapes and deltas are created as rivers meander from the mountains to the sea carrying sand, silt and organic material. To replicate that process, researchers use a metronome: a 20-meter long basin filled with water and sand that constantly tilts back and forth, causing the water to flow in and out and create natural sand banks and bays.
To replicate the vegetation along the banks, researchers around the world use Lucerne seeds, better known as alfalfa. “It’s easy to get, cheap, and it germinates fast. But alfalfa is a plant from dry grasslands, so it won’t make a representative root system in wet sand. So the research group leader Maarten Kleinhans asked if I knew of any better candidates”, explains hortulanus Gerard van Buiten, co-author of the publication.
Special layout
In order to find suitable species, the researchers experimented with around 25 different plants in the Botanical Gardens. “We came up with a special layout in the garden to measure germination capacity, growth speed, and development of plants and roots. After conducting experiments in the greenhouses for one season, we had five good candidates, all plants native to wetlands or riverbanks.” They published their findings in the scientific journal Earth Surface Processes and Landforms.
Practical knowledge of plants can provide some great ideas for research
Three species have already been tested in the metronome: water dock, beccabunga, and big treefoil. “These species have seeds with very different sizes and shapes, so they wash up on sand banks at different depths. The roots penetrate perfectly into the wet sand and hold the sand in place, so they influence the formation of sand banks. That makes them the perfect candidates for this type of research”, says Van Buiten. “Practical knowledge of plants can provide some great ideas for research.”
Meandering
The species discovered through the experiments have the same effect in miniature as the natural vegetation in the river deltas, explains final author Maarten Kleinhans. “They create current resistance, catch sediment and hold sand in place.” The researchers discovered that one of the seedling species creates meandering rivers, because the seedlings hold back the current along the banks and the flood plains. “That explains why the Rhine was still a broad, shallow river during the last ice age, but rivers in today’s warm climate have started to meander, with the Ijssel as an ideal example”, says Kleinhans.
The main question now is what effect plants have on a full-scale landscape. “How fast do they help sediment deposition to form new land? Do they also change river mouths? And what effect do small plants have?”, asks Kleinhans. “That knowledge is vital for all low-lying areas on earth, now that sea levels are rising and water discharge from the rivers is changing. Perhaps nature can help us to stay ahead of rising water through ‘land level rise’.”
Publication:
Species selection and assessment of eco‐engineering effects of seedlings for biogeomorphological landscape experiments. Earth Surface Processes and Landforms, 17 July 2019. Ivar R. Lokhorst, Sjoukje I. de Lange, Gerard van Buiten, Sanja Selaković and Maarten G. Kleinhans. All authors are affiliated with Utrecht University.
