Silting up of ponds prevented by cutting with mowing boat

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Silting up of ponds prevented by cutting with mowing boat

Published on
September 20, 2019

In the ponds on campus reeds and bulrushes continue to spread further into the water. On 21 September these would be mowed with a mowing boat. However, this mowing session could not continue on this date due to the low water level. Mowing at this water level would cloud the water, possibly resulting in the death of many fish. Mowing is now done from the banks and later in the year with the mowing boat.

Management

The banks and reed beds of the ponds on campus are managed to prevent siltation. This means that the gradual transition from dry to wet is maintained. A large variety of different plants and animals find a refuge in this sloping area. 

Management of these areas consists of mowing the banks and removing the plants that encroach into the pond. Over time organic material accumulates, which means that slowly but surely the ponds silt up. The banks are mown every other year. By mowing one half the first year and the other half the second year, a large part of the bank vegetation always remains available for animals that live at the transition from wet to dry. Maintenance in the water is also necessary now and then. This means that part of the plants and the silt is removed. The frequency with which this is carried out depends on how quickly the vegetation in the ponds grows. 

Mowing on 21 September

On 21 September the plants in the pond will be mown to 10 cm above the pond floor. The cuttings will be placed high up on the edges so that the bank-side vegetation is not stifled or damaged, and then collected later. By doing this in September, the water is still warm enough for e.g. amphibians to find a good refuge, while the reeds do not have enough time to regrow before the winter. It is possible that in a few years’ time a more rigorous approach will be necessary that involves removing the silt too.

Preventing 'victims'

Unfortunately, the work may result in ‘victims’ among the water animals. We try to prevent this as much as possible. But if we do not mow, the banks will deteriorate and no longer provide a suitable living environment for these animals. The phased mowing policy of the banks and water vegetation slows down the siltation process and large parts of the ponds are always available for flora and fauna that live in more open water. By leaving some of the reeds, the plants and animals dependent on them will still have somewhere to live.

The work will be combined with the second round of mowing the flower meadows.