Drought severely affects small creatures in brooks

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Drought severely affects small creatures in brooks

Published on
July 10, 2020

The extremely dry summers experienced in the Netherlands in recent years cause the demise of an increasing number of small creatures that inhabit creeks, known as macrofauna. This is the outcome of a collaborative study conducted by several water authorities and Wageningen Environmental Research.

Between 2018 and 2019, researchers of Wageningen Environmental Research analysed the differences in macrofauna diversity in different brooks in collaboration with the water authorities. Their goal was to learn more about the resilience of the macrofauna in these brooks. Their findings were recently published on  H2O Waternetwerk (Dutch).

Type of creek and duration of drought determining

The macrofauna found in creeks have an important role in the ecosystem: they are essential to removing organic waste such as leaves and serve as food for fish and birds. Many characteristic macrofaunae in creeks have now become rare and are only found in a small number of locations in the Netherlands. If a stream dries up completely resulting in a species disappearing entirely, the chances of recolonisation are slim. The contemporary landscape is no help either. Stream valleys are often separated by open, intensively used land that flying water insects are unable to bridge.

Still, not all macrofaunae suffer from drought to the same degree. In creeks with poor water quality or breaking bulk, the composition of macrofaunae barely changes. It is primarily the creeks with a high ecological quality that suffer a loss of macrofaunae during extreme droughts. This effect is felt strongest by species that inhabit relatively fast streaming water such as caddice flies. These, however, are species characteristic to Dutch creeks.

Dead freshwater shrimps on the floor of a dried-out creek (Source: Ralf Verdonschot)
Dead freshwater shrimps on the floor of a dried-out creek (Source: Ralf Verdonschot)

The duration of the drought is relevant as well. Some species of macrofauna can survive in the deep wet potholes in the creek floor, or even under a layer of wet leaves, for months. But during a lengthy period of drought, even these spots eventually dry out, allowing only specially adapted species such as species that lay drought-resistant eggs, to persist.  Moreover, dried out creeks spread during extended periods of drought, which means the animals must bridge a larger distance to return once the stream starts flowing again.

Future perspective

So far, 2020 is unusually dry, and climate models predict an increasing occurrence of drought. To protect our valuable stream inhabitants from these conditions, their resilience must be fortified. A good start is more variation in the creeks and leaving fallen trees and branches where they lie. This allows for the formation of deeper potholes where the creatures can seek shelter when the water level drops. These potholes remain humid for longer, even after the water has completely evaporated. Increasing the shade near creeks can also help prevent them from drying out.

On a larger scale, it is important to alter water management, preferably in the entire stream area. Water should not be drained but rather retained, for example, in the stream valley. This will allow the groundwater to resupply the creek with water for a longer time. Additionally, less water should be claimed for purposes such as watering crops, producing drinking water and industrial processes. This will relieve the pressure on the remaining populations in the lowland creeks and ensure the ecological quality is preserved.

Where possible, the creek should be given room, allowing the water to sink into the sediments gradually, replenishing the groundwater, such as here, along the Leuvenumse beek (Credit: Ralf Verdonschot)
Where possible, the creek should be given room, allowing the water to sink into the sediments gradually, replenishing the groundwater, such as here, along the Leuvenumse beek (Credit: Ralf Verdonschot)