Very high-resolution satellite imagery (≤5 m resolution) has become available on a spatial and temporal scale appropriate for dynamic wetland management and conservation across large areas. Estuarine wetlands have the potential to be mapped at a detailed habitat scale with a frequency that allows immediate monitoring after storms, in response to human disturbances, and in the face of sea-level rise. Yet mapping requires significant fieldwork to run modern classification algorithms and estuarine environments can be difficult to access and are environmentally sensitive. Recent advances in unoccupied aircraft systems (UAS, or drones), coupled with their increased availability, present a solution. UAS can cover a study site with ultra-high resolution (<5 cm) imagery allowing visual validation. In this study we used UAS imagery to assist training a Support Vector Machine to classify WorldView-3 and RapidEye satellite imagery of the Rachel Carson Reserve in North Carolina, USA. UAS and field-based accuracy assessments were employed for comparison across validation methods. We created and examined an array of indices and layers including texture, NDVI, and a LiDAR DEM. Our results demonstrate classification accuracy on par with previous extensive fieldwork campaigns (93% UAS and 93% field for WorldView-3; 92% UAS and 87% field for RapidEye). Examining change between 2004 and 2017, we found drastic shoreline change but general stability of emergent wetlands. Both WorldView-3 and RapidEye were found to be valuable sources of imagery for habitat classification with the main tradeoff being WorldView’s fine spatial resolution versus RapidEye’s temporal frequency. We conclude that UAS can be highly effective in training and validating satellite imagery.

https://www.mdpi.com/2072-4292/10/8/1257/pdf

Integrating Drone Imagery into High Resolution Satellite Remote Sensing Assessments of Estuarine Environments

Valuation of ecosystem services can play an important role in guiding decision-making concerning the restoration of natural ecosystems which is particularly important in tropical coastal wetlands due to their widespread deterioration. This study investigates the environmental status and provision of key ecosystem services of the Ashtamudi lake Ramsar site in Kerala, India, and explores the feasibility of wetland restoration scenarios through a multi-year program involving stakeholder workshops, primary market data collection, and stated preference non-market valuation. Relying on the input of local stakeholders, we apply a choice experiment to estimate the willingness to pay for wetland restoration scenarios with a focus on water quality, mangrove conservation and sustainable fisheries. Results indicate that local stakeholders attribute the greatest value to mangrove conservation, followed by water quality and sustainably managed fisheries. Furthermore, we show that the local residents’ willingness to pay for modest and moderate wetland improvement scenarios may outweigh the potential cost of the restoration projects, especially for modest restoration objectives and even under conservative assumptions regarding the benefits and costs of restoration. We discuss how such results can inform local policy in the development of sustainable management practices and act as a benchmark for the extensive network of wetlands in Kerala.

Economic appraisal of ecosystem services and restoration scenarios in a tropical coastal Ramsar wetland in India

Earlier declines in marine resources, combined with current fishing pressures and devastating coral mortality in 2015, have resulted in a degraded coral reef ecosystem state at Puakō in West Hawaiʹi. Changes to resource management are needed to facilitate recovery of ecosystem functions and services.
We developed a customised ecosystem model to evaluate the performance of alternative management scenarios at Puakō in the provisioning of ecosystem services to human users (marine tourists, recreational fishers) and enhancing the reef's ability to recover from pressures (resilience).
Outcomes of the continuation of current management plus five alternative management scenarios were compared under both high and low coral-bleaching related mortality over a 15-year time span.
Current management is not adequate to prevent further declines in marine resources. Fishing effort is already above the multispecies sustainable yield, and, at its current level, will likely lead to a shift to algal-dominated reefs and greater abundance of undesirable fish species. Scenarios banning all gears other than line fishing, or prohibiting take of herbivorous fishes, were most effective at enhancing reef structure and resilience, dive tourism, and the recreational fishery. Allowing only line fishing generated the most balanced trade-off between stakeholders, with positive gains in both ecosystem resilience and dive tourism, while only moderately decreasing fishery value within the area.
Synthesis and applications. Our customised ecosystem model projects the impacts of multiple, simultaneous pressures on a reef ecosystem. Trade-offs of alternative approaches identified by local managers were quantified based on indicators for different ecosystem services (e.g. ecosystem resilience, recreation, food). This approach informs managers of potential conflicts among stakeholders and provides guidance on approaches that better balance conservation objectives and stakeholders’ interests. Our results indicate that a combination of reducing land-based pollution and allowing only line fishing generated the most balanced trade-off between stakeholders and will enhance reef recovery from the detrimental effects of coral bleaching events that are expected over the next 15 years.

https://besjournals.onlinelibrary.wiley.com/doi/epdf/10.1111/1365-2664.13105

Evaluating management strategies to optimise coral reef ecosystem services

This Special Issue of Estuarine, Coastal and Shelf Science presents contributions from ECSA 55; an international symposium organised by the Estuarine and Coastal Sciences Association (ECSA) and Elsevier on the broad theme of estuaries and coastal seas in times of intense change. The objectives of the SI are to synthesise, hypothesise and illustrate the impacts of global change on estuaries and coastal seas through learning lessons from the past, discussing the current and forecasting for the future. It is highlighted here that establishing impacts and assigning cause to the many pressures of global change is and will continue to be a formidable challenge in estuaries and coastal seas, due in part to: (1) their complexity and unbounded nature; (2) difficulties distinguishing between human-induced changes and natural variations and; (3) multiple pressures and effects. The contributing authors have explored a number of these issues over a range of disciplines. The complexity and connectivity of estuaries and coastal seas have been investigated through studies of physicochemical and ecological components, whilst the human imprint on the environment has been identified through a series of predictive, contemporary, historical and palaeo approaches. The impact of human activities has been shown to occur over a range of spatial and temporal scales, requiring the development of integrated management approaches. These 30 articles provide an important contribution to our understanding and assessment of the impacts of global change. The authors highlight methods for essential management/mitigation of the consequences of global change and provide a set of directions, ideas and observations for future work. These include the need to consider: (1) the cumulative, synergistic and antagonistic effects of multiple pressures; (2) the importance of unbounded boundaries and connectivity across the aquatic continuum; (3) the value of combining cross-disciplinary palaeo, contemporary and future modelling studies and; (4) the importance of shifting baselines on ecosystem functioning and the future provision of ecosystem services.

/pdf/unbounded-boundaries-and-shifting-baselines-estuaries-and-267njligyo.pdf

Unbounded boundaries and shifting baselines: Estuaries and coastal seas in a rapidly changing world

Seasonal morphodynamic evolution in a meandering channel of a macrotidal estuary.

From the 2013 ECSA conference ‘Estuaries and Coastal Areas in Times of Intense Change’ a theme emerged that has ended up being the focus of this Special Issue of Estuarine Coastal and Shelf Science, namely ‘Changes to processes in estuaries and coastal waters due to intense multiple pressures’. Many parts of the world are continuing to experience unprecedented rates of economic growth, and those responsible for managing coastal and estuarine areas must respond accordingly. At the same time, global climate change and sea level rise are also continuing, placing new or more intense pressures on coastal areas that must be dealt with in ways that are as far as possible managed as a result of good scientific understanding. There are other pressures too, which depend on the system concerned. This article provides an overview of the papers contained within the Special Issue and provides a discussion of how these fit within the main theme of intense multiple stressors, considering how a balance can be achieved between the needs of various different stakeholders and interest groups, and the sustainability of the system concerned. We categorise the papers in four main groupings: (1) stressors related to sea level rise; (2) stressors related to changes in fresh water inputs; (3) stressors related to anthropogenic pollution; and (4) the use of indicators as a means of assessing the effects of stressors, and reflect on the fact that despite the diversity of different challenges and geographical regions involved many of the approaches and discussions contained within the Special Issue have strong similarities, leading to a set of overarching principles that should be considered when making recommendations on management strategies.

Changes to processes in estuaries and coastal waters due to intense multiple pressures – An introduction and synthesis

We present a first interpretation of three days of measurements made in 2013 from the tidal reaches of the Kaipara River (New Zealand) under both low and high freshwater inputs and a neap tidal cycle. During the first day, we occupied two stations that were approximately 6 km apart in a tidal reach that runs for 25 km from the river mouth to the upstream limit of tidal influence. During the second day, longitudinal surveys were conducted over a distance of 6 km centred on the upstream station. The data reveal a turbidity maximum in the form of a high-concentration ‘plug’ of suspended mud that was advected downstream on the ebbing tide past the upper (HB) measurement station and which exchanged sediment with the seabed by settling at low slack water and by resuspension in the early flooding tide. The data suggest that fine sediment is transported landwards and trapped in the upper part of the tidal reach under these low-flow conditions. On the third day of measurements we repeated the experiments of the first day but later in the year, for a much higher freshwater flow. This interpretation of our data set highlights the potential contribution of a range of processes to the generation of the observed suspended-sediment signals, including resuspension of local bed sediment, advection by the tidal current, settling of suspended sediment over a long timescale compared to the advection timescale, advection of longitudinal gradients in suspended sediment, and suppression of vertical mixing by density stratification of the water column. The level of temporal and spatial detail afforded by these measurements allows a much clearer understanding of the timing and importance of vertical stratification on the transport of suspended particulate matter than is generally possible using fixed-point sensors.

/pdf/field-studies-of-estuarine-turbidity-under-different-17n37xt6g2.pdf

Field studies of estuarine turbidity under different freshwater flow conditions, Kaipara River, New Zealand

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Changes to processes in estuaries and coastal waters due to intense multiple pressures – An introduction and synthesis

Field studies of estuarine turbidity under different freshwater flow conditions, Kaipara River, New Zealand