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The Slikken van Flakkee, a former tidal wetland in the Grevelingen, the Netherlands, has been changing under freshening conditions since 1971; in that year, the salty Grevelingen estuary was closed from the North Sea as part of the Dutch Delta Works. Our research aimed to analyse vegetation development over 1972–2016 and relates succession to quantified ecohydrogeochemical processes in the Slikken van Flakkee. We analysed succession and physico-chemical conditions at 63 monitoring locations. Based on extensive fieldwork in 2016 and 2017, we quantified the identified geochemical processes via inverse modelling and applied Canonical Correspondence Analysis (CCA) to search for interrelations with vegetation. Nine per cent of the 229 observed plant species are rare and threatened or vulnerable, according to the Dutch Red List. Succession series showed a development from saline pioneer communities towards grassland and shrub vegetation dependent on management measures (grazing and mowing versus spontaneous development), desalinisation and geochemical processes, of which dissolution of carbonates appeared to be the dominant one. During desalinisation, the water-type shifted from NaCl towards CaHCO3. The CCA confirmed the impact of geochemical and texture variables, elevation and management on vegetation. Grazing and mowing led to species-rich grasslands and forb vegetation harbouring twice as many species than the spontaneously developed area after 50 years, demonstrating the importance of active nature management. We argue that hydrological-geochemical modelling is necessary to support policy-making before deciding on the partial re-establishment of the tide in Lake Grevelingen.

Agroecological practices have been shown to control erosion, increase soil fertility, carbon stocks, pollination and biodiversity. As a consequence, these ecosystem services can contribute to a better farm economic resilience on the long-term; however, empirical evidence is scarce. In this study we aim to understand the economic performance of agroecological practices in almond orchards and the relevance of different economic and policy scenarios to incentivise the upscaling of agroecological practices. We investigated the development of the net present value (NPV) of several agroecological practices (no tillage (NT), green manure (GM) and compost (CM)) as compared to conventional tillage (CT), as well as the effect of internalising externalities through payments for soil carbon sequestration and by costs of erosion. Finally, we explored the effects of price premiums and public greening payments, on farm NPV. We found that all management regimes were profitable and that CM had a 17.2% higher NPV than CT, while both GM and NT had lower NPV than CT (69% for GM and 90.1% for NT). We found that despite NT and GM have higher soil organic carbon stocks, these provided a negligible additional income via carbon markets. CT had the highest externality costs of erosion but still its NPV was higher than NT and GM, despite the strong reductions in costs of erosion in NT and GM conferred by vegetation covers. We found that a price premium of 45% was necessary to make NT's economic performance comparable to that of CT, while a 27% price premium would be needed to make GM comparable to CT. Compensation through public greening payments would be in the order of €644 ha−1 y−1 for NT and €387 ha−1 y−1 for GM to have a similar NPV as CT. Our results suggest a trade-off between income from yield and costs from unaccounted externalities. We also find that private and public policy incentives could reverse this outcome, but requiring a large investment. Of the analysed agroecological practices, compost application appears the most promising to be scaled-up to improve both economic and environmental performance, and further research is needed to determine the outcomes of a combination of compost and vegetation covers.

In 2012 presenteerde Natuurmonumenten een plan om eilanden van slib te bouwen in het Markermeer en daarmee een waterrijk landschap bestaande uit slikken, lagunes, wadden, rietvelden en stranden te creëren. Het moest een vogelparadijs worden dat zeldzame vogelsoorten moeiteloos zouden vinden. Verspreid over een gebied van ongeveer 1.000 hectare liggen inmiddels de eerste vijf eilanden in het noordelijke deel van het Markermeer: de Marker Wadden. Op 9 november promoveerde Rémon Saaltink aan de Universiteit Utrecht als eerste Nederlandse promovendus op de Marker Wadden. Dit artikel beschrijft de uitkomsten van zijn promotieonderzoek.

This study investigates the potential of bioturbating Tubificidae to alter biogeochemical processes by sediment aeration in order to enhance ecosystem development in eco-engineering projects. We introduced Tubificidae in three different densities in clay-rich sediment from lake Markermeer . Redox potential, nutrients and major elements were measured from the water column and porewater at different depths. Mineral phase and redox transfers were chemically modelled and oxygen concentrations in bioturbated sediments for each density were mathematically predicted. The measured results of this experiment showed that Tubificidae oxygenated the upper 15 mm of the sediment. This resulted in decomposition of sedimentary organic matter with an associated sixfold increase in NH4 and NOx concentrations in the porewater and the water column. However, phosphorus concentrations were declining in the upper 16 mm, likely as a result of immobilization by pyrite oxidation and production of iron oxides. These bioturbation effects were highest in the treatment with an intermediate density of Tubificidae as aeration effects in the treatment with the highest density of Tubificidae was impeded by high respiration rates. Furthermore, with a two dimensional diffusion model, simulated effects of respiration and aeration on the oxygen concentration in the sediment suggest that the bioturbation effect is strongest at a density of 12,000 worms m−2. In ecological engineering projects where fast ecosystem development is important, introducing Tubificidae to aquatic sediments to optimal densities might enhance initial ecosystem development due to improved availability of nitrogen as nutrient. © 2018, Springer Nature Switzerland AG.

Understanding how the hydrological regime in relation to sediment type interferes with ecosystem development is important when wetlands are created with soft muddy material. Especially when plants are used as ecological engineers to promote crest stability and soil formation. We carried out a two-year mesocosm experiment with sediments derived from the Dutch lake Markermeer to identify the effects of the hydrological regime and sediment type on ecosystem functioning in terms of nutrient availability. We measured plant productivity, plant nutrient stoichiometry, and concentrations of N, P, and K in shoots and roots of Phragmites australis and Rumex maritimus and monitored how the clay-rich sediment from lake Markermeer changed into a wetland soil. Plants grown on Markermeer sediments tend to be N limited when periodically inundated and P limited when not inundated at all. The P availability was determined by the hydrological regime, while the N availability was determined by both the hydrological regime and the sediment type. Ecosystem development on created wetlands can be manipulated by adequate management of the hydrological regime, as plant species respond differently to changes in nutrient availability. This should be considered in eco-engineering projects where plants are used as ecological engineers to fasten ecosystem development on wetlands that are to be created from clay-rich material.

This study investigates the potential of bioturbating Tubificidae to alter biogeochemical processes by sediment aeration in order to enhance ecosystem development in eco-engineering projects. We introduced Tubificidae in three different densities (5000, 15,000, and 30,000 individuals m−2) in clay-rich sediment from lake Markermeer (The Netherlands). Redox potential, nutrients and major elements were measured from the water column and porewater at different depths. Mineral phase and redox transfers were chemically modelled and oxygen concentrations in bioturbated sediments for each density were mathematically predicted. The measured results of this experiment showed that Tubificidae oxygenated the upper 15 mm of the sediment. This resulted in decomposition of sedimentary organic matter with an associated sixfold increase in NH4and NOx concentrations in the porewater and the water column. However, phosphorus concentrations were declining in the upper 16 mm, likely as a result of immobilization by pyrite oxidation and production of iron oxides. These bioturbation effects were highest in the treatment with an intermediate density of Tubificidae (15,000 worms m−2) as aeration effects in the treatment with the highest density of Tubificidae (30,000 worms m−2) was impeded by high respiration rates. Furthermore, with a two dimensional diffusion model, simulated effects of respiration and aeration on the oxygen concentration in the sediment suggest that the bioturbation effect is strongest at a density of 12,000 worms m−2. In ecological engineering projects where fast ecosystem development is important, introducing Tubificidae to aquatic sediments to optimal densities might enhance initial ecosystem development due to improved availability of nitrogen as nutrient.

Artificial sand replenishments are globally used as innovative coastal protection measures. In these replenishments elevated porewater concentrations of trace elements are found. The present study investigated possible ecotoxicological risks at 2 intertidal depositional sites, the Sand Engine as a recent innovative Dutch coastal management project and a semiartificial tidal flat. Using the sediment quality triad approach, we considered 3 major lines of evidence: geochemical characterization, toxicity characterization using bioassays with the estuarine amphipod Corophium volutator, and ecological field survey. In both depositional areas C. volutator is at risk: moderate (Sand Engine) and low (tidal flat). For tidal flat, the bioavailability of trace elements differs between the field site and the laboratory. Contamination from arsenic and copper is present, but the low survival rate of C. volutator from the bioassay suggests the presence of additional contaminations. The highly morphological dynamic environment of Sand Engine creates a less favorable habitat for C. volutator, where local spots with stagnant water can temporarily create hypoxic conditions and sulfate becomes reduced. The dynamic system mobilizes especially arsenic, triggering adverse ecotoxic effects at low original sediment concentrations. To conclude, the sediment quality triad approach shows that a semiartificial tidal flat is preferred over a highly dynamic coastal management project like the Sand Engine. The Sand Engine concept does not provide suitable conditions for macrobenthos species like C. volutator; therefore, limiting the nature development goal set together with the coastal protection goal. Assessing each line of evidence from the approach together with additional measurements established more precise and realistic conclusions, showing that evaluating the contributions of this method is necessary to understand the causes of risk in a site-specific manner. Environ Toxicol Chem 2018;37:2933-2946. © 2018 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

As coastal lowlands are prone to sea water flooding, sea-level rise might globally increase this risk. To protect its coastline, the Netherlands adds an average of 12 million m3 of sand annually, but more is needed to cope with the expected consequences of global warming. In 2011 a novel approach for coastal protection was applied near The Hague, consisting of a mega beach nourishment of 21.5 million m3 of sand: the Sand Engine e an artificial sand spit rising to 6 m above mean sea level. It uniquely combines coastal engineering construction with environmental, ecological and social considerations. To construct the Sand Engine, material was used from the seafloor, which changed the materials environment from anaerobic to aerobic, triggering two main hydrogeochemical processes: pyrite oxidation and groundwater freshening. The objective of this study was to assess the sediment geochemistry of the Sand Engine and understand the hydrogeochemistry with respect to pyrite oxidation and freshening. When sufficient buffer capacity is lacking, the mobility of metals and metalloids originated from the mineral pyrite, can cause local impacts on ecology and environment. Geochemical and multivariate statistical analyses were performed on 174 sediment samples from the Sand Engine and from material collected from the seafloor prior to its construction, as well as on 86 samples of pore water collected from the Sand Engine. First, a cluster analysis was performed, using model-based (Mclust) and variable clustering. Second, a robust factor analyses (RFA) was used to explain the variation between the groups and discover relationships between elements and/or soil properties within the groups. We distinguished three clusters of sediment samples and two clusters of pore water samples. Sediment cluster 1 was comprised exclusively of surface samples from the Sand Engine; it was differentiated from the other two clusters by its geochemistry, sorting processes and weathering. Sediment clusters 2 consisted of shallow samples from the Sand Engine, as well as deeper autochthone material from the sand pit. Sediment cluster 3 contained deeper samples from the Sand Engine and also shallow autochthone material from the sand pit. Sediment clusters 2 and 3 show differences in carbonate content and, especially, in reactive iron, confirming that in the sand pit area a Holocene marine layer overlies Pleistocene fluvial sand. For the pore water samples, two clusters were estimated: a saline water cluster and a fresh water cluster. Thus the Sand Engine contains source material from two different geological layers, which vary in their reactive iron concentration and carbonate minerals. Pyrite oxidation is seen with depth, resulting in iron oxides and an increase in alkalinity because of calcite dissolution. With the development of the Sand Engine source material is expected to show a decrease in pyrite oxidation, because of low amount of available sulphide minerals. Carbonate dissolution due to pyrite oxidation will then decrease as well. Additional calcite dissolution is caused by freshening processes. With the amount of CaCO3 present in the sand, the Sand Engine contains calcareous-rich sand where acidic conditions are not likely to occur during its life span and therefore create no local environmental risks for acidification. At the surface of the mega beach nourishment, sorting processes are causing locally enrichment of iron oxides and associated elements, as well as a decrease in the stability of heavy minerals like rutile.

We address the development of policy by polycentric governance configurations, taking Caribbean overseas territories and their advancements on invasive alien species (IAS) policy as an example. The British, Dutch, and French islands in the Caribbean address this matter to different degrees, which we analyzed through differences in their type of polycentric governance configuration with their respective European counterpart. We employ a continuum ranging from predominantly polycentric to predominantly monocentric governance configurations to characterize the three case studies. Based on semistructured interviews with government actors, park managers, and NGO employees on Anguilla, Guadeloupe, and St. Eustatius, plus a literature study, we characterize St. Eustatius as highly polycentric and Guadeloupe as becoming increasingly polycentric. Anguilla cannot be considered either of the two, given the virtually absent involvement of the UK. Policy development on IAS showed most progress in Guadeloupe, whereas in Anguilla and St. Eustatius, IAS management is ad hoc. Within these cases, the hampering effect of dispute about the functioning of the configuration was clear. For Guadeloupe, increasing autonomy to decide on policy priorities within a coherent system where standards are set and ample resources made available appears conducive to policy development. That same balance inherent to polycentric systems between autonomy and coherence is hard to strike for St. Eustatius, and currently mainly perceived as a trade-off, hampering policy development. By discussing these three cases, this study illustrates how different polycentric configurations can affect policy development.

To enhance protection and maintain wide beaches for recreation, beaches are replenished with sand: socalled beach nourishments. We compared four sites: two traditional beach nourishments, a mega beach nourishment and a reference without beach nourishment. Two sites contain calcareous-rich sand, whereas the other two sites have calcareous-poor sand. We aimed to understand hydrogeochemical processes to indicate factors critical for the mobility of trace elements at nourishments. We therefore analysed the chemical characteristics of sediment and pore water to ascertain the main drivers that mobilise toxic trace elements. With Dutch Quality Standards for soil and groundwater, the characteristics of sediment and pore water were compared to Target Values (the values at which there is a sustainable soil quality) and Intervention Values (the threshold above which the soil's functions are at risk). The pore water characteristics revealed that Target Values were regularly exceeded, especially for the nourishment sites and mainly for Mo (78%), Ni (24%), Cr (55%), and As (21%); Intervention Values for shallow groundwater were occasionally exceeded for As (2%), Cr (2%) and Zn (2%). The sediment characteristics did not exceed the Target Values and showed that trace elements were mainly present in the fine fraction of