Management options for restoring estuarine dynamics and implications for ecosystems: a quantitative approach for the Southwest Delta in the Netherlands

The Delta Works, a series of dams and barriers constructed in the 1960's–1980's changed the estuarine landscape of the Rhine-Meuse-Scheldt delta (SW Netherlands) into more stagnant and disengaged freshwater, brackish water or saltwater lakes. The remaining tidal systems were adapted by building a storm surge barrier in the Oosterschelde and dike reinforcement works along the Westerschelde. The Delta Works brought protection against flooding, but at the same time resulted in environmental and socio-economic problems, such as degradation of ecological quality and ecosystem functioning, disruption of fish migration routes, water and sediment quality problems.In this study we explore in an integrated, quantitative way the consequences of a number of management options for the Southwest Delta and their implications for the occurrence and distribution of aquatic and estuarine habitats, considering the mutual coherence between the water basins. Five scenarios were evaluated using a 1D hydraulic, water quality and primary production numerical model and GIS habitat mapping. Scenarios vary from small-scale interventions, such as changes in day-to-day management of hydraulic infrastructures or creation of small inlets in dams, feasible in the short term, to restoration of an open delta by removing dams and barriers, as a long term potential. We evaluate the outcomes in relation to the restoration of estuarine dynamics, as this is in policy plans proposed as a generic solution for the current ecological and environmental problems. Net water flow rates show more complex patterns when connectivity between water basins is increased and when sluice management is less strict. Estuarine transition zones and fish migration routes are partly restored, but only fully develop when basins are in open connection with each other. Area of intertidal habitats, tidal flats and tidal marshes, increases in each scenario, ranging between 7 and 83%, 1–56%, and 8–100% respectively, depending on scenario. Large scale infrastructural adaptations are needed to restore estuarine dynamics at large scale.The use of a 1D numerical model allowed to quantify the effect of different management measures for all water basins simultaneously, but also has its limitations. The model does not resolve more complex processes such as vertical mixing and morphodynamic changes. This requires expert judgment and more detailed 3D modelling

The Effect of Histidine-tryptophan-ketoglutarate Solution and University of Wisconsin Solution: An Analysis of the Eurotransplant Registry

Background Both University of Wisconsin (UW) and histidine-tryptophan-ketoglutarate (HTK) solutions are currently used in the Eurotransplant region for preservation of liver allografts. Previous studies on their effect have led to a lot of discussion. This study aims to compare the effect of HTK and UW on graft survival. Methods First liver transplantations in recipients 18 years or older from January 1, 2007, until December 31, 2016, were included. Graft survival was compared for livers preserved with HTK and UW at 30 days, 1, 3, and 5 years. Multivariable analysis of risk factors was performed and outcome was adjusted for important confounders. Results Of all 10 628 first liver transplantations, 8176 (77%) and 2452 (23%) were performed with livers preserved with HTK and UW, respectively. Kaplan-Meier curves showed significant differences in graft survival between HTK and UW at 30 days (89% vs 93%, P=<0.001), 1 year (75% vs 82%, P=<0.001), 3 years (67% vs 72%, P<0.001), and at 5 years (60% vs 67%, P<0.001). No significant differences in outcome were observed in separate analyses of Germany or non-German countries. In multivariable analysis, UW was associated with a decreased risk of graft loss at 30 days (HR 0.772, P=0.002) and at 1 year (0.847 (0.757-0.947). When adjusted for risk factors, no differences in long term outcome could be detected. Conclusions Because the use of preservation fluids is clustered geographically, differences in outcome by preservation fluids are strongly affected by regional differences in donor and recipient characteristics. When adjusted for risk factors, no differences in graft survival exist between transplantations performed with livers preserved with either HTK or UW

The structure and functional roles of tidal flat meiobenthos

Meiofauna comprise the smallest multicellular and largest unicellular metazoans in benthic food webs. They are highly abundant and species-rich, yet essential aspects of the factors driving their community structure and abundance remain poorly understood. Similarly, their functional roles in benthic carbon cycling remain poorly characterized and even more poorly quantified. In the frame of two projects, we addressed questions regarding both the biotic and abiotic factors that drive meiobenthic assemblage structure, and their roles in benthic carbon cycling. Our research involved an intricate combination of manipulative laboratory experiments and field work, the latter mostly focusing on the intertidal flats bordering the Paulina salt marsh in the Scheldt estuary. The results add considerably to our understanding of the factors that drive meiobenthic assemblage structure. They clearly demonstrate that biotic interactions among different meiofauna, and between meio- and macrofauna, are extremely important and moderate the impacts of prominent abiotic drivers of assemblage structure such as granulometry and oxygen availability. From a functional point of view, we demonstrated that tidal flat meiofauna rely predominantly on carbon derived from in situ primary production by microphytobenthos. Quantification of grazing rates of meiofauna on microphytobenthos and benthic bacteria does not, however, point at an important direct contribution of meiofauna to benthic carbon cycling. The role of meiobenthic species diversity remains to be established, but laboratory experiments into the role of nematodes in OM decomposition reveal that in addition to species identity, species diversity does have a significant, yet largely unpredictable effect on OM decomposition rates

From past to present: biodiversity in a changing delta

A large-scale coastal engineering project (the ‘Delta works’) changed large-scale, dynamic estuarine nature in the southwest of the Netherlands into a diverse mosaic of ecosystems with different characteristics. This led to a suite of ecological problems, which is why plans are made to restore estuarine dynamics. Until today the effect of the Delta works on biodiversity in the subsystems is still poorly understood. We combined long-term datasets on macrobenthos, fish, birds and key species and present reliable and factual information on changes in biodiversity in the Southwest Delta in the past decennia in relation to the Delta works and other developments. Effects of the Delta works on biodiversity are highly diverse and depend on many different factors and histories specific for the different water bodies. If connections are restored, effects on species richness and biodiversity will depend on the specific characteristics of the separate basins. Because restoration of estuarine dynamics likely occurs on a reduced scale, effects on biodiversity may only be modest. However, effects on the occurrence of rare species of the brackish and intertidal transition zones may be more significant. It is recommended to study this further

Biodiversity in a changing Oosterschelde: from past to present

De biodiversiteit onder vogels in de Oosterschelde neemt significant toe van 84 soorten in 1987 tot 105 soorten in 2008. Metname de herbivore en piscivore vogels zijn verantwoordelijk voor deze toename. Broedvogels nemen toe in aantal vanaf1994. Vissen vertonen echter weinig verandering in de gemeten periode (1970-2008) en vertonen een lichte significantetoename in het aantal soorten in de periode 1996-2001. De macrofauna-gemeenschap vertoont een constant hoge ShannonWiener-index tussen de 2,5 en 3,5, maar de aantallen tussen soorten zijn erg ongelijk verdeeld doordat er veel soorten metrelatief lage aantallen zijn en een paar soorten voorkomen in relatief hoge aantallen. De aantallen individuen voor suspensie- enfilter feeders en oppervlakte deposit- en facultatieve suspensie feeders nemen significant af over de gehele gemeten periode(1993-2008). Zeehonden (twee soorten) nemen in aantallen toe. Met name Gewone zeehond (Phoca vitulina) vertoont eenforse stijging in aantallen en ook de Grijze zeehond (Halichoerus grypus), hoewel minder abundant, vertoont een stijging inaantal waargenomen individuen. Bruinvissen (Phocoena phocoena) zijn niet beschouwd in de analyse. Het areaal aan zeegrasvertoont een sterke daling in 1984-1993 van 657 tot 63, een afname van 90%. Ook het schorareaal neemt af