Netherlands - Nature reserve services

Description

The scope of this overall project is to conduct a field test for an ecosystem approach controlling crayfish based on van Kleef et al, 2022. In a compartment of over 2 ha (figure will be carried out a system approach as complete as possible. And in the entire Molenpolder Nature Reserve compartment (50 ha), ecosystem approach measures will be implemented that are feasible and affordable on this larger scale. In this way we can compare intensive and less intensive approaches. The project team wants to remain in control and is therefore dividing the project into plots. Part of the work will be carried out by Waternet, part of the work will fall under the plot arrangement and will be realized by a privately selected market party. A detailed description of the Assignment per lot is given in the relevant Schedule of Requirements for a lot.
Direct award, see section II.2.14.This lot concerns the isolation of a compartment of more than 2 ha by the construction of two fish screens to create a compartment within which the most complete possible practical test for the ecosystem approach can be carried out. A permeable and passable fish and lobster barrier will be constructed at two locations. The fish screens are intended to minimize the exchange (between the compartment and the environment) of larger fish and lobsters. Water must be exchanged in order to monitor the maintenance of the surface water level in the compartment. A maximum mesh size of 10x3 mm is maintained. The experience of ATKB (Jouke Kampen) is that it is very difficult to make a fish barrier that does not have or get a 'leak'. ATKB will therefore be involved in the design.The barrier will be constructed with beams with H-profile, sheet steel and wooden fitting beams to secure the sheet steel in the H-profile.The width of the barrier is approximately 9 m in the wet profile and extends 2 m into the bank.The height of the barrier is approximately 1.2 m.Preconditions of the fish barriers:- Take into account a flexible water level management of -0.90 to -1.15 m NAP at the inlet and outlet. Locally, the level may go higher or lower because of the large distance between the inlet and outlet. So when setting the height of fish barriers, be sure to allow for level variations between -0.80 and -1.25 m NAP.- It is very important that the barriers are not passable by fish and lobster through the water. - A good connection to the bank so that no short circuit can occur and fish or lobster can pass behind. - Sticking the beams with H profile and sheet steel deep into the ground so that no fish can pass underneath. - Exchange of water so that no level difference occurs. Water exchange is done by placing a slotted panel of stainless steel with slots of 3 by 10 mm. The slots are placed vertically so that they can be easily wiped clean.- A gangway above the grating for the purpose of wiping clean the slot panels.- Navigability through an insert 0.5 m high and 2.5 m wide, which can be easily removed. - The navigability should also not allow fish to pass through. I.e. the boat passing through must push out the permeable section and close it again immediately after passage.- The work in constructing the fish barriers must not harm existing N2000 habitats and Habitat species.- The fish barriers must be completed by March 15, 2023. This plot deals with the construction of 30 structures, "nest rafts," in the water on which grebes can build a nest. Grebes prey on lobster but are rare in the Mill Polder. The number of breeding pairs of grebes in the Molenpolder (50 ha) in recent years is estimated at about 6, or 1 pair in over 8 ha. A territory of 1 ha or smaller is often sufficient. There is a lot of landscape structure in the Molenpolder and more grebes could breed in the Molenpolder.The hypothesis is that the limiting factor for more breeding pairs of grebes is the nesting opportunity due to the near absence of preferred substrate. Therefore, we provide more nesting opportunities to attract grebes.The intended net rafts will be made of natural material, (willow) branches combined with bundles of reeds. Using willow branches creates water roots that provide shelter for young pike, which is a beneficial side effect. The design should be able to support a weight of 1.5 kg for an extended period of time and last for several seasons.The structures for nesting support will not be in locations with N2000 Habitats. If a grebe nest is placed it should not shade a significant portion of the habitat. In addition, care must be taken to ensure that nest construction activities do not damage existing habitat. In sub-compartment 2, a pilot is being conducted for the establishment of emersal vegetation. In this pilot, 209 m2 of emergent vegetation will be established. The emersed zone with helophytes, such as reeds, is especially important for pike, predator of lobster which we want to stimulate.In the pilot we want to create water reeds in the compartment 2 on approximately 268 m2 (2 plots 209 and 59 m2). There is hardly any shallow water in the Molenpolder. The hard water bottom is almost everywhere deeper than 1 meter, mostly around 1.2 m. I.e., creating a reed zone without deepening is not possible. In the Molenpolder, it is not dug in because it would be too deep. Instead, soil is added to reach a depth acceptable to reed for planting and expansion. With 350 blocks, 700 m2 can be realized instantaneously but not all of this is necessary because if reed takes root well it expands quickly. To achieve the intended 2 m wide reed zone, 1 reed block of 1x2 m per 5 m bank length is placed at 0.5 m from the bank and surrounded with replenished soil. Thus, with 2 m2 of reed beds, 10 m2 of reed zone is created. Per 5 m, 11 m3 of additional soil is needed. Of which 7 m3 is needed for the one-sided embankment.For (after natural expansion) 100 linear meters of reed zone, it requires:- 20 reed blocks (40 m2)- 220 m3 of soil (at 30 m3 bucket is 7.3 cargo loads)With the transplantation, a root zone must be included. Then it is an advantage if large plots can be used: relatively little root zone is then broken up.The exact way in which the pilot will be carried out Waternet will figure out in the pilot together with the contractor. In summer 2021 lobster reduction started in Molenpolder - West. In winter 2021-2022 the fish stock was reduced in the entire project area, especially the bream, roach and kolblei stock was reduced. After fish reduction, it is undesirable for young bream, roach and colblei to enter the area through the pumping station. In the Molenpolder, directly behind the pumping station and valve weir is a trap. . In the summers of 2021 and 2022, this trap has frequently found quite a lot of fish of 10-15 cm in good condition indicating successful immigration. And we want to prevent catfish from the Molenpolder to swim into the Nedereindse vaart.Waternet therefore wants to build:1. a row of slats under the bridge ;To prevent fish from swimming into the pumping station bowl: to be attached (Bruijs and Vriese, 2023, chapter 4.3)2. the active self-cleaning wedgewire drum sieve at the pump pumping station (Bruijs and Vriese, 2023, chapter 4.1.43. a hinged fine grid on either side of the valve weir . (Bruijs and Vriese, Chapter 4.2)The aim is to have these modifications ready before the 2023 intake season begins.Preconditions Fish barrier:- The fish barrier should prevent fish from reaching the Molenpolder Nature Reserve via passage of the pumping station and valve weir. Effective exclusion of cyprinids, 0+ to 1+ (5 to 15 cm): especially bream, colbeli, roach; - The fish barrier must prevent released catfish from the Molenpolder from swimming into the Nedereindse vaart.- The application of the fish barrier must guarantee the required throughput of the pumping station pump and flow over the valve weir. Operative under the worst case scenario (highest flows);- Operative during periods of no flow (fish may not actively pass the system themselves);- Effective management of aquatic vegetation/drifting debris, without the need to perform manual cleaning operations;- The incorporation and application of the fish barrier must be price acceptable. This plot deals with:1. Reintroduction of submerged aquatic plants and Crabweed2. Release of pike, eel and catfish3. Release of native mussels4. Establishment of emersal vegetation5. Fencing of emersal vegetation6. Establishment of timber habitat7. Monitoring and modeling and interpretation Practical testFurther information in the program of requirements of parcel 5. Activities for dredging problems- Together with private persons and the State Forestry Administration, develop a strategy for the dredging problem. - Soil quality for - Develop strategy to mitigate the problem. Think broader than just dredging. - Develop and encourage private owners to take initiative to implement the dredging strategy together.- Organize consultation moments with the private owners and Staatsbosbeheer and develop a strategy for the dredging problem together with these owners.- Encourage the private owners to take initiative to implement the dredging strategy together.- Part of the assignment will be to test the strategy against the Nature Act.- The result will be a dredging strategy supported by the owners and set out in a report.Activities Trees in the riverbank problem1.Determine the extent of the problem and the number of trees in the riverbank that impede water quality and the development of marsh vegetation.3. Develop a strategy to mitigate the problem. Organize consultation moments with the private owners and the Forestry Commission and together with these owners develop a strategy for the trees in the riverbank problems.5. Encourage the private owners to take the initiative to implement the strategy together.6. Implementation of a pilot to implement the strategy remove trees in the bank 9. A sufficiently low phosphorus load is essential for this project. The external phosphorus load from water intake is below the critical limit. Nevertheless, the Mill Polder seems too nutrient-rich given the huge numbers of lobsters caught, especially in the extreme southeast. The cause of the excessive nutrient richness is due to internal phosphorus sources. The excess water from the southeast should flow through the rest of the Molenpolder toward the outlet at the Krom. If monitoring (plot 5) and quantifying the dredging problem (plot 6), shows that the phosphorus load from the Southeast is too high then it is necessary to eliminate this load. This could be done by releasing the excess water from the extreme Southeast on the east side of the main waterway. This would require a permeable weir and automation east outlet In this way, this phosphorus-rich water will no longer enter the clean part of the Molenpolder in the middle and west. And the main part of the Molenpolder gets more chance to recover. Another assignment to ATKB to reduce crayfish in Molenpolder East is ongoing in 2024. There is no ongoing assignment in Molenpolder West in 2024. Activities- In 2024 reduce lobsters in Molenpolder West (35 ha)- In 2025 reduce lobsters in Molenpolder East (15 ha) and Molenpolder West (35 ha).- Reduce lobsters at least from the beginning of May to the end of November, but preferably start earlier than May and longer than November. Find a method that takes fewer hours to implement.

Opportunity closing date

29 December 2023

Value of contract

£1m-5m