Fast and Living Ring-Opening Polymerization of l-Lactide Initiated with In-situ–Generated Calcium Alkoxides

The ring-opening polymerization of l-lactide with calcium alkoxides generated in-situ from bis(tetrahydrofuran)calcium bis[bis(trimethylsilyl)amide] and 2-propanol are presented. The polymerization in THF at room temperature proceeds rapidly and in a living manner, giving poly(l-lactide)s of controlled molecular weight, low polydispersity, and tailored end-functionalities. Kinetic studies show the absence of an induction period and a pseudo-first order rate constant of 6.41 L mol^–1 min^–1, which is significantly higher than for related Y₅(-O)(O ⁱ Pr)_13– or aluminum alkoxide-initiated polymerizations. The initiation involves a two-step process: (1) alcoholysis of bis(tetrahydrofuran)calcium bis[bis(trimethylsilyl)amide] to give the corresponding calcium alkoxide and (2) ring-opening of l-lactide via acyl-oxygen cleavage and insertion into the calcium-alkoxide bond. In the presence of excess alcohol, fast and reversible exchange between free alcohol molecules and coordinated alkoxide ligands takes place. This allows tuning of the poly(l-lactide) molecular weight over a wide range.     

Growth and trace metal accumulation of two Salix clones on sediment-derived soils with increasing contamination levels

The growth and metal uptake of two willow clones (Salix fragilis 'Belgisch Rood' and Salix viminalis 'Aage') was evaluated in a greenhouse pot experiment with six sediment-derived soils with increasing field Cd levels (0.9-41.4 mg kg-1). Metal concentrations of eight elements were measured in roots, stems and leaves and correlated to total and soil water metal concentrations. Dry weight root biomass, number of leaves and shoot length were measured to identify eventual negative responses of the trees. No growth inhibition was observed for both clones for any of the treatments (max. 41.4 mg kg-1 Cd, 1914 mg kg-1 Cr, 2422 mg kg-1 Zn, 655 mg kg-1 Pb), allowing their use for phytoextraction on a broad range of contaminated sediments. However, dry weight root biomass and total shoot length were significantly lower for S. viminalis compared to S. fragilis for all treatments. Willow foliar Cd concentrations were strongly correlated with soil and soil water Cd concentrations. Both clones exhibited high accumulation levels of Cd and Zn in aboveground plant parts, making them suitable subjects for phytoextraction research. Cu, Cr, Pb, Fe, Mn and Ni were found mainly in the roots. Bioconcentration factors of Cd and Zn in the leaves were highest for the treatments with the lowest soil Cd and Zn concentration.     

Lessons learned from applying adaptation pathways in flood risk management and challenges for the further development of this approach

Worldwide, an increase in flood damage is observed. Governments are looking for effective ways to protect lives, buildings, and infrastructure. At the same time, a large investment gap seems to exist—a big difference between what should necessarily be done to curb the increase in damage and what is actually being done. Decision-makers involved in climate adaptation are facing fundamental (so-called deep) uncertainties. In the course of time, the scientific community has developed a wide range of different approaches for dealing with these uncertainties. One of these approaches, adaptation pathways, is gaining traction as a way of framing and informing climate adaptation. But research shows that “very little work has been done to evaluate the current use of adaptation pathways and its utility to practitioners and decision makers” (Lin et al. 2017, p. 387). With this paper, the authors, as action researchers and practitioners involved in two of the world’s largest real-life applications of this approach in flood risk management, aim to contribute to filling in that gap. Analysis of the experience in the United Kingdom and the Netherlands in long-term planning in flood risk management shows that the adaptation pathways approach is effective in keeping decision processes going forward, to the final approval of a long-term plan, and helps increase awareness about uncertainties. It contributes to political support for keeping long-term options open and motivates decision-makers to modify their plans to better accommodate future conditions. When it comes to implementing the plans, there are still some major challenges, yet to be addressed, amongst others: the timely detection of tipping points in situations with large natural variability, the inclusion of measures that prepare for a switch to transformational strategies, and the retention of commitment of regional and local authorities, non government organizations, and the private sector, to climate adaptation as national policies move from blueprint planning to adaptive plans. In delivering this feedback, the authors hope to motivate the scientific community to take on these challenges.     

Dendrochronology of Atriplex portulacoides and Artemisia maritima in Wadden Sea salt marshes

The study uses a rather unusual method, dendrochronology, to investigate the growth and survival of Atriplex portulacoides L. and Artemisia maritima L. on salt marshes at two field sites on the Dutch North Sea barrier islands of Terschelling and Ameland. By providing information on longevity of these typical salt-marsh shrubs, dendrochronology offers an indirect way to investigate the influence of management regime – grazing in this case – on marsh quality and areal extent. Diminishment of salt marshes is a continuing concern in the northern Netherlands. The two shrub species studied here, A. portulacoides and A. maritima, are common to salt marshes. With their extensive roots and branches, they facilitate sedimentation and stabilize salt marshes. Using dendrochronology, this study found that annual growth rings could be identified to determine shrub age and growth. In A. portulacoides these rings took the form of a narrow band of terminal parenchyma. In A. maritima they were made up of unlignified marginal parenchyma together with higher vessel density at the beginning of the growing season. Growth rings indicated that intense grazing was clearly detrimental to the survival of A. portulacoides at the Terschelling site. However, grazing facilitated survival of A. maritima at the Ameland site by reducing light and nutrient competition from grasses. No growth trends could be found, however, as the lifespan for both species is short and many other influences on shrub growth could be identified.     

Usability of the climate-resilient nature-based sand motor pilot,The Netherlands

Coastline maintenance in the Netherlands, formally in place since 1990, aims at a sustainable preservation of coastal flood protection. Over 25 years annual assessments, comparing the actual coastline positions with the 1990 reference position of the coastline, have governed the execution of sand nourishments following an adaptive management method. This method involves yearly assessment of the coastline based on measurements, design and adoption of nourishment strategies and measures and execution of the nourishments. This management approach has enabled learning and introduction of innovations in coastline maintenance. For instance, in comparison to the early nineties, nourishments are now placed more on the foreshore and the yearly nourishment budget has doubled. The most recent innovation in coastline maintenance is the ‘Sand Motor’, a nature-based nourishment approach, which concentrates the regular nourishments in space and time, given that natural processes should redistribute the sediment over the wider coastal system. In contrast to regular nourishments, the Sand Motor combines flood protection with nature and recreational objectives and is much larger in dimensions. Five years after the construction of the Sand Motor we investigate its usability in this article. We present the results of first Sand Motor evaluation and draw conclusion on the adoption and usefulness of it for coastline management from the perspective of the adaptive management method used in coastline maintenance. Recent evaluation of the monitoring data shows that the large amount of sand used for the Sand Motor has a positive impact on coastal protection. Bridging between the Sand Motor pilot and daily nourishement practice is however not yet achieved.     

In Flanders Fields: De/politicization and Democratic Debate on a GM Potato Field Trial Controversy in News Media

In May 2011, a highly mediatized direct action in the form of a “field liberation” took place in Flanders, Belgium, against a field trial of genetically modified potatoes. This direct action and its aftermath revealed the conflictual and antagonistic nature of the genetically modified organisms debate in Flanders. Consequently, it serves as a particularly suitable case to investigate the post-political thesis with regard to environmental discourse and politics. The aim of this paper is to investigate in what ways news media in their reporting contribute to processes of depoliticization and, resultantly, impede a democratic debate on the issues at stake. This paper attempts to provide an answer to this question based on a critical discourse analysis of the reporting by Flanders’ two generalist, elite newspapers, De Standaard and De Morgen and the alternative online news site DeWereldMorgen. The findings reveal the existence of three ideological cultures, which are characterized by different degrees of de/politicization. We conclude by discussing how this study adds to our understanding of the relation between the depoliticization of environmental discourse, democratic debate and twenty-first-century news media.     

Transport and degradation of pesticides in a biopurification system under variable flux Part II: A macrocosm study

Transport of bentazone, isoproturon, linuron, metamitron and metalaxyl were studied under three different flows in macrocosms. The aim was to verify the observations from Part I of the accompanying paper, with an increase in column volume and decrease in chemical and hydraulic load. Very limited breakthrough occurred in the macrocosms for all pesticides, except bentazone, at all flows.From batch degradation experiments, it was observed that the lag time of metamitron and linuron decreased drastically in time for all flows, indicating a growth in the pesticide degrading population. This in contrast to isoproturon and metalaxyl, where an increase in lag time could be observed in time for all flows. From the batch degradation experiments, it could be concluded that the influence of flow on the lag time was minimal and that the inoculation of the pesticide-primed soil had a little surplus value on degradation.     

An attempt to electrically enhance phytoremediation of arsenic contaminated water

Water polluted with arsenic presents a challenge for remediation. A combination of phyto- and electro-remediation was attempted in this study. Four tanks were setup in order to assess the arsenic removal ability of the two methods separately and in combination. Lemna minor was chosen for As remediation and collected from a ditch in Utrecht, The Netherlands. The tanks were filled with surface water without any pre-cleaning, therefore containing various elements including metals as Mn (2.9 mg L(-1)), Cu (0.05 mg L(-1)), Fe (1.39 mg L(-1)), and Ba (0.13 mg L(-1)). This water was then spiked with As and allocated to a feed container, guaranteeing a continuous flow of 0.12 mL s(-1) to each tank. Two experiments were performed: Exp. 1 with 3 consecutive stages with rising applied voltage and Exp. 2, with a constant voltage over a period of 6 d. Measurements of pH and temperature were taken every working day, as well as water samples from outlets of all tanks including feed container for control. From the present study, there was no evidence that As had been taken up by the plants, but a strong depletion of As was observed in the tanks where current was applied. Preliminary results clearly showed that applying voltage to the electrodes caused 90% removal of As from the spiked surface water.     

Sorption kinetics and its effects on retention and leaching.

Sorption of pesticides to substrates used in biopurification systems is important as it controls the system's efficiency. Ideally, pesticide sorption should occur fast so that leaching of the pesticide in the biopurification system is minimized. Although modeling of pesticide transport commonly assumes equilibrium, this may not always be true in practice. Sorption kinetics have to be taken into account. This study investigated the batch sorption kinetics of linuron, isoproturon, metalaxyl, isoxaben and lenacil on substrates commonly used in a biopurification system, i.e. cow manure, straw, willow chopping, sandy loam soil, coconut chips, garden waste compost and peat mix. The first-order sorption kinetics model was fitted to the observed pesticide concentrations versus time resulting in an estimated kinetic rate constant alpha. Sorption appeared to be fast for the pesticides linuron and isoxaben, pesticides which were classified as immobile, while less mobile pesticides displayed an overall slower sorption. However, the substrate does not seem to be the main parameter influencing the sorption kinetics. Coconut chips, which is a substrate with a high organic matter content showed slow sorption for most of the pesticides. The effect of different estimated alpha values on the breakthrough of pesticides through a biopurification system was evaluated using the HYDRUS 1D model. Significant differences in leaching behavior were observed as a result of the obtained differences in sorption kinetics.     

Characterizing pesticide sorption and degradation in macro scale biopurification systems using column displacement experiments

The efficiency of biopurification systems to treat pesticide-contaminated water was previously studied in microcosms. To validate the obtained results, macrocosm systems were set-up. Four pesticides (linuron, isoproturon, bentazone, and metalaxyl) were continuously applied to ten different organic substrate mixes. Retention of the pesticides was similar and in some cases slightly lower in the macrocosms compared to the microcosms. Differences in retention between the different mixes were however minimal. Moreover, the classification of the retention strength of the pesticides was identical to that observed in microcosms: linuron > isoproturon > metalaxyl > bentazone. Monod kinetics were used to describe delayed degradation, which occurred for isoproturon, metalaxyl and bentazone. No breakthrough of linuron was observed, thus, this pesticide was appointed as the most retained and/or degraded pesticide, followed by isoproturon, metalaxyl and bentazone. Finally, most of the matrix mixes efficient in degrading or retaining pesticides were mixes containing dried cow manure.