Search

Contains fulltext : 306578.pdf (Publisher’s version ) (Open Access)

Contains fulltext : 305310.pdf (Publisher’s version ) (Open Access)

09 september 2022, Contains fulltext : 286473.pdf (Publisher’s version ) (Open Access)

Radboud University, 26 mei 2023, Promotores : Lamers, L.P.M., Welte, C.U. Co-promotor : Veraart, A.J., Contains fulltext : 292806.pdf (Publisher’s version ) (Open Access), Methane is the second most important greenhouse gas and is responsible for around 20 percent of global warming. Unlike carbon dioxide (CO2), most methane comes from natural systems, and more specifically from shallow lakes. Yet as a society we have a huge impact on this, because nutrients from agriculture production and increases in temperature that are caused by climate change increase methane emissions. However, why this is so, and whether this process can be reversed, is not yet clear. This PhD thesis therefore focused on the methane cycle in lakes, and the way in which this is influenced by warming, nutrients and carbon. Evidence showed that warming causes a different type of methane-consuming bacteria in lake beds, which resulted in less methane being consumed. Extra nutrients increased methane consumption, but only at low concentrations. Methane production is therefore likely to increase at high concentrations, which would cause a greater emission of methane. Extra carbon increased methane production but did not affect methane consumption. It was ultimately found that methane emissions from shallow lakes can be cut down by control measures that reduce nutrients in shallow lakes. Although global warming is a universal problem, increases in nutrients and carbon are mostly caused by local factors. As a result, it is vital that their availability in shallow lakes is locally reduced in order to cut methane emissions and combat climate change.

Coastal ecosystems are generally controlled by the combination of bottom-up (resource-driven) and top-down (consumer-driven) trophic, and non-trophic interactions. Anthropogenic disruption of these interactions, for example, through eutrophication or overfishing, leads to loss of the foundation species composing these ecosystems. Within degraded ecosystems, new interactions may become dominant, hampering restoration of the foundation species.We demonstrate this concept in saltwater Lake Grevelingen, where seagrass restoration was seriously hampered by a newly discovered non-trophic interaction between the seagrass Zostera marina and the ragworm Platynereis dumerilii. Platynereis constructs dwelling tubes between seagrass leaves by glueing and entangling them, leading to loss of biomass and increased epiphyte cover. To test the roles of epiphyte grazing (top-down) and eutrophication (bottom-up) on this new-found interaction, we executed a field experiment introducing the snail Littorina littorea under natural nutrient concentrations and Platynereis densities and performed a full factorial mesocosm experiment applying Littorina, Platynereis and nutrient treatments.Our field results show that survival of reintroduced Zostera in Lake Grevelingen is seriously hampered by Platynereis, which can be suppressed by grazer addition.In our mesocosm experiment, we demonstrate that top-down control by Littorina protects seagrass through two pathways: (1) mitigating bottom-up regulated epiphyte growth by trophic top-down forcing and (2) hampering the non-trophic interaction between Zostera and Platynereis by grazing epiphytes and dwelling tubes.Synthesis and applications. With coastal ecosystems globally under pressure, our study emphasises the importance of understanding ecosystem-specific trophic and non-trophic key interactions when considering restoration. We show how negative interspecific int

Reef-forming species form integral aspects of coastal ecosystems, but are rapidly degrading world-wide. To mitigate these declines, nature managers increasingly rely on the restoration of habitat-structuring, reef-forming species by, for example, introducing artificial reefs that may directly function as complex reef habitat. Since the use of biodegradable structures to restore biogenic reefs is becoming a popular technique, its effectiveness as reef habitat must be assessed. Therefore, we examine the trophic complexity on experimental large-scale biodegradable artificial reefs using food web network analysis. We placed biodegradable artificial reefs on soft-sediment intertidal flats in the Dutch Wadden Sea in a large-scale (~650 m) and 2.5-year-long experiment. We compared food web networks and biodiversity indicators between biodegradable reefs and bare controls and quantified species composition inside and near the artificial reef community to assess the expansion of the reef community. During 2.5 years, we observed that artificial reefs changed food web networks compared to bare controls: in species richness (+76%), link density (the number of interactions per species; +15%) and the fraction of basal species (species of lowest trophic level; +40%), but lowered the connectance: the realized fraction of all possible links between species (−33%). Their effects on food web networks increased over time with a higher species richness (+22%) and more complex food web (link density +13%) on the artificial reef 2.5 years after deployment compared to 1.5 years. However, the effects of the reefs did not extend beyond the reef structures; the species composition and biodiversity of macrozoobenthos near the reefs were comparable to the control. Synthesis and applications. This study shows that biodegradable artificial reefs offer an effective tool for the restoration of food web complexity and biodiversity of inter

Despite active seagrass restoration gaining traction as a tool to halt and reverse worldwide seagrass losses, overall success remains limited. Restoration strategies, through seeding or transplantation, face different environmental bottlenecks that limit success. Choosing the most appropriate strategy of the two for a specific location, however, is hampered by lack of direct practical comparisons between strategies within a single system. To investigate potential life stage dependent bottlenecks, we compared seed-based and transplant-based restoration of Zostera marina in the subtidal saltwater Lake Grevelingen. Our results demonstrate that seedling recruitment was negatively impacted by bioturbation from the lugworm Arenicola marina and sediment movement due to hydrodynamic exposure. Transplant-based restoration was clearly more successful butsurprisingly best predicted by leaf gluing by the ragworm Platynereis dumerilii. This previously undescribed interaction caused seagrass leaves to clump and reduce effective photosynthetic surface and leaf movement. We suggest that the observed behavior of these worms may result from a lack of foodweb interactions, illustrating the importance of trophic control for seagrass restoration. Thus, in addition to recognizing life stage dependent environmental bottlenecks for restoration strategy selection, seagrass restoration may also require the active recovery of their associated food webs.

Contains fulltext : 240937.pdf (Publisher’s version ) (Open Access)

Wetlands provide vital services on which human societies depend. As they have been rapidly degrading due to anthropogenic impacts worldwide, wetland restoration is increasingly applied. When a return to the original state of a wetland is constrained, forward-looking restoration can provide a new way to enhance an ecosystem's ecological integrity. However, the direction in which new ecosystems will develop is strongly coupled to the initial environmental conditions and may benefit from active decisions on (future) management. To improve the natural values of a degrading freshwater lake in the Netherlands, a forward-looking restoration project was initiated in lake Markermeer in 2016, involving the construction of a 700-ha archipelago called the “Marker Wadden”. This archipelago should provide new habitat to higher trophic levels in the lake's food web through the development of currently missing Common reed ( Phragmites australis ) dominated marshlands with gradual land-water transitions. However, the restoration project faces strong

Biogeomorphic wetlands cover 1% of Earth’s surface but store 20% of ecosystem organic carbon. This disproportional share is fueled by high carbon sequestration rates and effective storage in peatlands, mangroves, salt marshes, and seagrass meadows, which greatly exceed those of oceanic and forest ecosystems. Here, we review how feedbacks between geomorphology and landscape-building vegetation underlie these qualities and how feedback disruption can switch wetlands from carbon sinks into sources. Currently, human activities are driving rapid declines in the area of major carbon-storing wetlands (1% annually). Our findings highlight the urgency to stop through conservation ongoing losses and to reestablish landscape-forming feedbacks through restoration innovations that recover the role of biogeomorphic wetlands as the world’s biotic carbon hotspots.

Contains fulltext : 285505.pdf (Publisher’s version ) (Open Access)

Radboud University, 02 november 2022, Promotores : Leuven, R.S.E.W., Lamers, L.P.M. Co-promotor : Kleef, H.H. van, Contains fulltext : 283337.pdf (Publisher’s version ) (Open Access)

25 mei 2022, Contains fulltext : 252385.pdf (Publisher’s version ) (Open Access)

Contains fulltext : 286286.pdf (Publisher’s version ) (Open Access)

21 augustus 2022, Item does not contain fulltext

Greenhouse gas (GHG) emissions from small inland waters are disproportionately large. Climate warming is expected to enhance their emissions and favour dominance of algae and free-floating plants at the expense of submerged plants. The different impacts these functional plant types have on their environment may have far-reaching consequences for freshwater GHG emissions. Here, we show that dominance of different functional plant types strongly controls the effect of experimental warming on GHG fluxes, mainly by modulating methane ebullition, an often-dominant GHG emission pathway. Specifically, we demonstrate that the response to experimental warming was strongest for free-floating and lowest for submerged plant-dominated systems. Importantly, our results suggest that anticipated shifts in plant type may increase total GHG emissions from shallow waters. This, together with the stronger warming-induced emission response, represents a so far overlooked positive climate feedback. Management strategies aimed at favouring submerged plant dominance may substantially mitigate GHG emissions.

Contains fulltext : 245804.pdf (Publisher’s version ) (Closed access)

Contains fulltext : 240379.pdf (Publisher’s version ) (Open Access)

27 mei 2021, Contains fulltext : 240225.pdf (Publisher’s version ) (Open Access)

01 juni 2021, Contains fulltext : 235953.pdf (Publisher’s version ) (Open Access)

Contains fulltext : 231578pre.pdf (preprint version ) (Open Access)

17 mei 2021, Contains fulltext : 239385.pdf (Publisher’s version ) (Open Access)

Contains fulltext : 234157.pdf (Publisher’s version ) (Open Access)

Contains fulltext : 235580.pdf (Publisher’s version ) (Open Access)

Contains fulltext : 239376.pdf (Publisher’s version ) (Open Access)

Contains fulltext : 235852.pdf (Publisher’s version ) (Open Access)

Wetlands die worden gedomineerd door planten, zoals kwelderplanten, zeegrassen en veenmossen, leveren belangrijke leefgebieden met een hoge biodiversiteit en veel belangrijke ecosysteemdiensten. Wereldwijd is het oppervlak van deze systemen afgelopen eeuw echter gehalveerd door menselijke activiteiten zoals veranderd landgebruik, drainage of overexploitatie. Herstel is extra lastig omdat deze ecosystemen afhankelijk zijn van biobouwers die langzaam hun omgeving veranderen, waardoor deze geschikter wordt voor hun vestiging en overleving. In een vierjarig onderzoek bekeken we de mogelijkheid om vestiging van biobouwers met biologisch afbreekbare matrixstructuren te vergroten en versnellen en zo natuurherstel een kickstart te geven.