Alanna J. Rebelo

Anthropogenically induced climate change is expected to increase the intensity and frequency of natural disturbances like floods and droughts, with serious potential consequences for wetlands. While there have been some studies that have investigated the impact of hurricanes (tropical cyclones) on coastal wetlands, there are gaps in spatially quantifying the impacts of other extreme meteorological events on inland wetlands. We addressed this gap by studying the impacts of severe flooding, caused by a deep cut-off low system in September 2023, on wetlands in southern Africa. This study aimed to spatially quantify biogeomorphic changes in the wetlands following the flood event, using freely available remote sensing data from before and after the event, and to establish the best method for this analysis. Three methods were applied to detect changes, namely digitization, index analysis and change detection. For the index analysis, the effectiveness of the Normalized Difference Vegetation Index (NDVI) and Bare Soil Index (BSI) was explored. From the results of all methods, we found that bare ground increased significantly (t=-6.35, df = 8, p < 0.01) by a mean of 70 000 m ² (8%) per wetland, while greenness significantly decreased (t = 5.61, df = 8, p < 0.01) with a mean loss of vegetation of 40 000 m ² following the floods. The most accurate of the automated approaches to mapping post-flood impact on palmiet wetland systems was change detection (89%). Leveraging applications in remote sensing using freely available imagery presents a critical opportunity to study and interrogate tipping points in wetlands in data-constrained regions.

Societal Impact Statement: Ecosystems are rapidly being transformed, pushing us towards irreversible losses and even extinctions. The Kunming‐Montreal Global Biodiversity Framework aims to curb biodiversity decline. An intriguing solution lies in seed banks—where plants store seeds in the soil. Restoration efforts can revive lost ecosystems by leveraging these seed banks. In the fynbos of South Africa, this study found that it is possible to bring back ecosystems that were lost as long ago as 100 years if conditions are right. Managers can achieve best results by applying a dry season prescribed burn following removal of the driver of degradation (e.g. pine plantations or invasions).Summary: Soil‐stored seed banks are a critical evolutionary strategy for plants as they can stabilize population dynamics in response to environmental fluctuations such as droughts and natural disturbances such as fires, thus improving ecosystem resilience. This study aimed to assess resilience during the first restoration cycle of endangered Sand Fynbos following pine harvesting and a prescribed burn in South Africa. We compared above ground populations and soil‐stored seed bank composition and focused on six perennial fynbos focal species in five 1 m² plots. All six species are obligate reseeders with soil‐stored seed banks but represent a variety of important fynbos growth forms and seed types. We found that native soil‐seed bank density following over a century of plantation forestry and 10 years after the first fynbos restoration burn was comparable to, or exceeded, densities measured in other fynbos studies, especially seed banks of alien‐invaded fynbos ecosystems. The early years following pine harvesting and a restoration burn likely provide a pest‐ and predator‐free window of opportunity in which plants may re‐establish and flourish. Our results show that even for old forestry plantation areas, ecological restoration to the historic vegetation community is feasible, where there is retained seed bank resilience, through a combination of passive and active restoration methods. Ecological restoration in cases where soil seed banks persist is therefore a viable and critically important method to attain 30% conservation of terrestrial land in ecosystems with less than 30% remaining, as part of the Kunming‐Montreal Global Biodiversity Framework.

Rising anthropogenic-induced nutrient enrichment of surface waters is of great concern globally as it jeopardizes the ecological integrity and functioning of freshwater ecosystems. Floating wetlands have been successfully used to treat nutrient enriched wastewater in developing nations, and provide additional co-benefits. We aimed to quantify the nutrient removal efficiency of high-potential, endemic wetland species on floating wetlands in different conditions and to understand whether the nutrient uptake process was characterised by key plant functional traits. Two experiments were run under Mediterranean-climate conditions of the Western Cape of South Africa: (1) a closed, oligotrophic mesocosm experiment representing local conditions and (2) a real-life (in-situ) eutrophic application. The mesocosm experiment conducted under oligotrophic local conditions yielded low nitrate, phosphate and ammonium removal rates (34.8–35.2 mgNO₃-Nm^− 2.d^− 1, 10.4–10.7 mgPO₄-Pm^− 2.d^− 1 and 3.6–3.8 mgNH₄-Nm⁻2.d^− 1) in comparison to other floating wetland studies globally, yet high removal efficiencies (> 90%). However the eutrophic in-situ experiment demonstrated the potential for these same endemic plants to remove up to 312 g.m^− 2 of nitrogen and 47 g.m^− 2 of phosphorus per year– which is relatively high compared to similar global research. Cyperus textilis had the highest daily nutrient uptake and content followed by Prionium serratum and Juncus lomatophyllus, while J. lomatophyllus had the greatest nutrient uptake efficiency. Two of the three species (C. textilis and P. serratum) stored significantly more total nutrients in their shoot tissue compared to their root tissue, suggesting that the permanent removal of nutrients from the system is possible through shoot harvesting. Floating wetlands planted with endemic plant species have the potential to remove nutrients effectively and sustainably from eutrophic water and can thus be implemented as low-cost nature-based solutions to mitigate pollution of lentic systems.

Rising anthropogenic-induced nutrient enrichment of surface waters is of great concern globally as it jeopardizes the ecological integrity and functioning of freshwater ecosystems. Floating wetlands have been successfully used to treat nutrient enriched wastewater in developing nations, and provide additional co-benefits. We aimed to quantify the nutrient removal efficiency of high-potential, locally endemic wetland species on floating wetlands in different conditions and to understand whether the nutrient uptake process was characterised by key plant functional traits. Two experiments were run under Mediterranean-climate conditions of the Western Cape of South Africa: (1) a closed, oligotrophic mesocosm experiment representing local conditions and (2) a real-life (in-situ) eutrophic application. The mesocosm experiment conducted under oligotrophic local conditions yielded low nitrate, phosphate and ammonium removal rates (34.8-35.2 mgNO₃-Nm^-2.d^-1, 10.4-10.7 mgPO₄-Pm^-2.d^-1 and 3.6-3.8 mgNH₄-Nm^-2.d^-1) in comparison to other floating wetland studies globally, yet high removal efficiencies (>90%). However the eutrophic in-situ experiment demonstrated the potential for these same locally endemic plants to remove up to 312 g.m^-2 of nitrogen and 47 g.m^-2 of phosphorus per year– which is relatively high compared to similar global research. Cyperus textilis had the highest daily nutrient uptake and content followed by Prionium serratum and Juncus lomatophyllus, while J. lomatophyllus had the greatest nutrient uptake efficiency. Two of the three species (C. textilis and P. serratum) stored significantly more total nutrients in their shoot tissue compared to their root tissue, suggesting that the permanent removal of nutrients from the system is possible through shoot harvesting. Floating wetlands planted with endemic plant species have the potential to remove nutrients effectively and sustainably from eutrophic water and can thus be implemented as low-cost nature-based solutions to mitigate pollution of lentic systems.

The term nature-based solutions (NBS) has gained traction in recent years and has been applied in many settings. There are few comprehensive assessment frameworks available that can guide NBS planning and implementation while at the same time capturing the short- and long-term impacts and benefits of the NBS. Here a recently presented framework, which builds on the theory of change and was developed to assess NBS at different phases of the project cycle, was applied to seven diverse case studies. The case studies addressed water quality and quantity issues in peri-urban areas across the global north and south. Framework indicators covering the sustainability dimensions (environmental, social and economic) were assessed at three stages of the framework: context, process and results. The work sought to investigate the following research objectives: (1) Can this framework be robust and yet flexible enough to be applied across a diverse selection of NBS projects that are at different phases of the project cycle and address different kinds of water challenges within varied ecological, social and economic contexts? (2) Is it possible to draw generalisations from a comparative analysis of the application of the framework to the case studies? Results showed that the framework was able to be applied to the case studies; however, their diversity showed that NBS projects designed in one context, for a specific purpose in a specific location, can not necessarily be transferred easily to another location. There were several process-based indicators that were universally significant for the case studies, including expertise, skills and knowledge of the involved actors, roles and responsibilities of involved actors and political support. The result-based indicators were case study-specific when environmental indicators were case study-specific, and important social indicators were environmental identity and recreational values. Overall, the use of the framework benefits the recognition of the implementation’s advances, such as the change in context, the processes in place and the results obtained.

Recent efforts to achieve social, economic, and environmental goals related to sustainability emphasize the importance of nature-based solutions (NBS), as grey infrastructure alone is insufficient to address current challenges. The majority of frameworks proposed in the literature fail to address the full potential of NBS, neglecting long-term results, unintended consequences, co-benefits, and their contribution to achieving global environmental agreements, such as the Agenda 2030, especially for water management in a peri-urban context. Here we present an innovative framework that can be applied to both NBS project planning and evaluation for several water-based challenges, giving practitioners and researchers a tool not only to evaluate ongoing projects but also to guide new ones. The framework considers three main stages of a NBS project: (1) context assessment, (2) NBS implementation and adaptation process, and (3) NBS results. This tool has the potential to be used to evaluate whether NBS projects are aligned with sustainability dimensions through a set of adaptable sustainability indicators. The framework can also highlight how the NBS targets are related to the sustainable development goals (SGD) and contribute to catalyzing the 2030 Agenda. The framework is an important tool for water management and other NBS types.

Quantifying how well Nature-based Solutions can offset anthropogenic climate change impacts is important for adaptation planning, but has rarely been done. Here we show that a widely-applied Nature-based Solution in South Africa – invasive alien tree clearing – reduces the impact of anthropogenic climate change on drought streamflow. Using a multi-model joint-attribution of climate and landscape-vegetation states during the 2015–2017 Cape Town “Day Zero” drought, we find that anthropogenic climate change reduced streamflow by 12–29% relative to a counterfactual world with anthropogenic emissions removed. This impact on streamflow was larger than corresponding reductions in rainfall (7–15%) and reference evapotranspiration (1.7–2%). Clearing invasive alien trees could have ameliorated streamflow reductions by 3–16% points for moderate invasions levels. Preventing further invasive alien tree spread avoided potential additional reductions of 10–27% points. Total clearing could not have offset the anthropogenic climate change impact completely. Invasive alien tree clearing is an important form of catchment restoration for managing changing hydroclimatic risk, but will need to be combined with other adaptation options as climate change accelerates.

Ecological restoration efforts at scale have been shown to play an important role in reducing human impact on the environment, improving climate change adaptation and halting extinctions globally. Upscaling restoration efforts needs funding, and therefore evidence of the benefits of restoration is needed. The aims of this study are firstly to improve the evidence base of the water-related benefits of restoration using a fine-scale modelling approach (with field work and remote-sensing inputs, and well-validated models), and secondly to explicitly quantify uncertainties to understand the general applicability of the principles discovered. We model the impacts of restoration (in this study the clearing of alien trees) on streamflow in four strategic water providing catchments using the fully-distributed MIKE-SHE modelling tool. We find that the benefits of clearing mature infestations of alien trees, such as pines, from naturally tree-less ecosystems increases available water resources by 15.1-29.5%. Clearing riparian invasions has a 1.7 times greater impact compared to terrestrial (non-riparian) invasions. The largest impacts of passive restoration on streamflow are in the mid to low flows, and this impact is greater in dry years relative to wet years. The findings are novel in that they shed light on the spatial uncertainties in the modelled gains. These findings have implications for leveraging investment to upscale restoration efforts in water scarce regions, as they suggest improved water security during the dry season and droughts. Upscaling efforts is essential if the degradation of ecosystems globally is to be prevented, halted and reversed, as proposed by the United Nations Decade on Ecosystem Restoration.