Development of the benthic macrofauna community after tidal restoration at Rammegors : Progress report 1

The managed realignment project Rammegors aims at re-establishing estuarine nature in a formerly freshwater wetland. For this purpose, a tidal inlet was constructed in the Krabbekreekdam to generate a reduced tidal influence that should allow the development of salt marsh area, tidal flat area and low energetic shallow sub-tidal. A central question of the Rammegors tidal restoration project is how the flora and fauna will develop in the area. To understand the biotic and abiotic processes related to the tidal restoration in Rammegors, a monitoring programme is being executed by the Centre of Expertise Delta Technology. The monitoring focuses on the main biotic and abiotic developments in the area. This progress report only focuses on the early colonization of macrobenthic invertebrates in Rammegors. Benthic macrofauna and sediment sampling took place in spring and autumn 2017 at twenty stations along 4 transects with varying distances to the outlet. A fast colonization of the benthic macrofauna was observed in Rammegors. Twenty and twenty-eight taxa were observed in the area in spring and autumn 2017 respectively. The communities significantly differed between spring and autumn. In spring densities reached high values, especially for the brackish mud shrimp Manocorophium insidiosum and mosquito larvae Chironomidae. In autumn these brackish species almost disappeared from the area. Their presence in autumn, even in low numbers, as well as the observation of the brackish cockle Cerastoderma glaucum indicate that, after the tidal restoration, parts of Rammegors are still under influence of brackish water. A relation was found between elevation and the benthic macrofauna development. Species richness showed an optimum around +0.4m NAP with lower values at both lower and higher elevations. Total density significantly increased with elevation, with highest total density at the higher elevations and a gradient in ecological richness was observed with higher richness further from the inlet. As the spring community significantly differs from the autumn community, we will continue sampling in both seasons in 201

Experimental study on a breaking-enforcing floating breakwater

Floating breakwaters are moored structures that attenuate wave energy through a combination of reflection and dissipation. Studies into floating breakwaters have been generally restricted to optimising the attenuation performance. This study presents a novel floating breakwater type that was developed to have good attenuation performance while keeping wave drift loads as small as possible. The floating breakwater was designed as a submerged parabolic beach that enforces wave energy dissipation through breaking. The design was tested in a 3D shallow-water wave basin in captive and moored setups for regular and irregular wave conditions. Results are presented in terms of attenuation performance, motions, and (mooring) loads. The results show that the breaking of waves improves the attenuation performance of the floater in captive setup. However, in moored setup, the attenuation performance was dominated by diffraction and radiation of the wave field, with breaking being of secondary importance. This shows that breaking-enforcing floating breakwaters have potential, but require a high vertical hydrostatic and/or mooring stiffness in order to enforce intense breaking. Mean wave drift loads on the object showed significant difference between breaking and non-breaking waves in both setups, with breaking waves leading to lower normalized loads. This is attributed to breaking-induced set-up and set-down of the water level. As a result, the new breakwater design has a more favourable balance between wave attenuation and drift loads than common (i.e., box-, pontoon-, or mat-type) floating breakwater designs. Tests with varying surface roughness showed that floating breakwaters may benefit from dual-use functions that naturally increase the roughness (e.g., shellfish, vegetation), which have a marginal effect on the attenuation performance, but increase the added mass and hydrodynamic damping and as such, reduce mooring line loads

Thermal stress affects bioturbators' burrowing behavior:A mesocosm experiment on common cockles (<i>Cerastoderma edule</i>)

The intensity of marine heatwaves is increasing due to climate change. Heatwaves may affect macroinvertebrates' bioturbating behavior in intertidal areas, thereby altering the deposition-erosion balance at tidal flats. Moreover, small-scale topographic features on tidal flats can create tidal pools during the low tide, thus changing the heat capacity of tidal flats. These pools could then potentially operate as refuge environments during marine heatwaves. We studied behavior responses to heat waves using the well-known bioturbating cockle Cerastoderma edule as a model species. Different temperature regimes (i.e., fluctuating between 20 and 40 °C) and micro-topographies (i.e., presence vs. absence of tidal water pools) were mimicked in a mesocosm experiment with regular tidal regimes. Our results demonstrate that behavioral responses to heat stress strongly depend on the site-specific morphological features. Cockles covered by shallow water pools moved up when exposed to thermal stress, while burrowing deeper into the sediment in the absence of water pools. But in both cases, their migratory behavior increased under heat stress compared to regular ambient treatments. Moreover, long-term cumulative heat stress increased cockles' respiration rates and decreased their health conditions, causing mass mortality after four weeks of gradually increasing heat exposure. Overall, the present findings provide the first insights into how bioturbating behavior on tidal flats may change in response to global warming

Promoting self-facilitating feedback processes in coastal ecosystem engineers to increase restoration success:Testing engineering measures

Coastal ecosystem engineers often depend on self‐facilitating feedbacks to ameliorate environmental stress. This makes the restoration of such coastal ecosystem engineers difficult. We question if we can increase transplantation success in highly dynamic coastal areas by engineering measures that promote the development of self‐facilitating feedback processes.Intertidal blue mussels Mytilus edulis are a typical example of ecosystem engineers that are difficult to restore. A lack of self‐facilitating feedbacks at low densities limits establishment success when young mussels are transplanted on dynamic mudflats.In a large field experiment, we investigated the possibility of increasing transplantation success by stimulating the formation of an aggregated spatial configuration in mussels, thereby reducing hydrologically induced dislodgment and the risks of predation. For this, we applied engineering measures in the form of fences that trapped wave dislodged mussels.Mussel loss rates were significantly lower when mussels were placed between both artificial fences, and in high densities (4.2 kg/m2) compared with mussels placed in areas without fences and in low densities (2.1 kg/m2). The fences induced the formation of a banded pattern with high local mussel densities, which locally reduced predation.Synthesis and applications. Our results underline the importance of actively promoting the development of self‐facilitating processes, such as aggregation into patterns, in restoration projects of ecosystem engineers. In particular, the current study shows that engineering measures can help to initiate these kinds of self‐facilitating interactions, especially in highly dynamic areas

Een natuurlijkere toekomst voor Nederland in 2120

Nederland staat voor grote opgaven: de energietransitie, verduurzaming van de landbouw, herstel van de biodiversiteit, verstedelijking en klimaatadaptatie. Al deze opgaven hebben gevolgen voor de ruimtelijke inrichting van ons land. Het is onvermijdelijk dat Nederland er over honderd jaar anders uit zal zien. Grote veranderingen zijn nodig om opgewassen te zijn tegen een stijgende zeespiegel, perioden van extreem weer, een toenemende vraag naar voedselproductie en een noodzaak om de uitstoot van broeikasgassen terug te dringen.Deze opgaven vragen om een nieuw verhaal voor Nederland. Een verhaal waarin dit dichtbevolkte land zich ontwikkelt tot een gidsland waar natuur, duurzame economie, leefbaarheid en veiligheid voorop staan. Een verhaal gebaseerd op ‘nature based solutions’ waarin opgaven voor klimaat en biodiversiteit hand in hand gaan.Wageningen University & Research heeft dit verhaal geschreven gebaseerd op expertkennis: een toekomstvisie voor Nederland in 2120, waarin natuur en natuurlijke processen een hoofdrol spelen. Een visie die bedoeld is om te inspireren. Het schetst een toekomst waarin economische ontwikkeling en een natuur-inclusieve samenleving hand in hand gaan. De toekomstvisie houdt rekening met de bijzondere kenmerken van verschillende deelgebieden in Nederland. Door middel van kaarten en doorsnedes laten we op hoofdlijnen zien wat er per gebied mogelijk is op het gebied van ruimtelijke inrichting. Dit toekomstbeeld schetst een denkrichting gebaseerd op de uitkomsten van diverse ontwerp- en discussiesessies met onderzoekers. Er is behoefte aan nadere uitwerking en onderbouwing. Samen met stakeholders gaan we deze visie verder ontwikkelen, onderbouwen en vertalen naar handelingsperspectief voor het hier en nu