Tom Spencer

Climate change will have pervasive effects on the world’s coasts, but at broad scales these changes have typically proven difficult to analyse in a quantifiable manner. Consequently, individual management decisions are often taken without consideration of the wider, regional coastal system with its physical linkages between geomorphological elements.

This study develops a definition of what mangrove-fisheries can encompass, incorporating a broad range of their possible characteristics. A detailed case study was conducted to develop a typology of mangrove-fishing in the Perancak Estuary, Bali, Indonesia, using interview surveys to investigate the fishing activities associated with mangroves. This case study demonstrated the complexity that a mangrove-fishery can entail, where fishing is connected to the mangrove forest by fishers of multiple sectors, functions, locations and temporal scales. Through a comparison with other mangrove-fishing communities in Bali, it also highlighted that mangrove-fisheries are variable even when in close proximity. With particular reference to this case study, a framework was developed as a flexible tool for identifying the multiple dimensions of a mangrove-fishery in a local context. Following this framework should encourage researchers and managers to look outside of the groups of fishers traditio...

Vegetated shorelines have been increasingly recognized for their contribution to natural coastal protection due to their ability to dissipate wave energy. Within the UK, salt marshes are beginning to be included in flood defence schemes. Predicting wave dissipation over vegetation requires accurate representation of salt marsh canopies and the feedback relationship between vegetation and wave conditions. We present a modification to the SWAN vegetation model, which includes a variable drag coefficient and a spatially varying vegetation height. Its application is demonstrated by modelling wave propagation over UK salt marshes. The third generation wave model, SWAN includes a vegetation module for calculation of wave attenuation over vegetation. Wave dissipation is determined based on the vegetation properties and a drag coefficient. This drag coefficient, C_D, is used to calibrate the model, and a fixed value is used per model run. Empirically the drag coefficient has been found to v...

Risks relating to water oversupply (eg: extreme flood events) and undersupply (eg: drought) first appeared in the World Economic Forum’s ‘Top 5 Global Risks’ in 2011 and have persisted in every year since then. Erosion and flooding resulting from events such as Hurricane Sandy or the UK’s 2013/14 winter storms demonstrate how the sum of impact and consequence can be especially severe at the coast. Often, erosion and flooding risks are analysed separately owing to complex relationships between driving processes, morphological response and risk receptors. This complexity makes it difficult to extract general rules for erosion-flooding interaction; rather it demands detailed longitudinal studies with explicit attention to local setting.

1. The Nature of Physical Geography Today 2. The Nature of Global Environmental Change 3. The Challenges for Physical Geography 4. High Latitudes: Ozone Depletion, Climate Change, Permafrost Degradation 5. Mid-Latitudes: Climate, Land Cover and Desertification 6. Low Latitudes: Forest Climates, Deforestation and Environmental Change 7. The Uncertain Environmental Future

Physical processes are thought to be a critical control on shallow water communities in the tropics. Past studies of seagrass community patterns have tended to be qualitative and failed to empirically link observed structures with the processes that govern them. Remote sensing technology, in the form of imagery acquired using a Compact Airborne Spectrographic Imager (CASI), has been used to

An array of three bottom-mounted pressure transducers (placed approximately 200 metres apart along a shore-normal transect centred on the sandflat/saltmarsh transition) was used to measure changes in wave characteristics across sandflat and saltmarsh on the Norfolk coast, UK. Pressure readings were taken at a frequency of 5Hz over periods of 5 and 7 minutes at different times during the tidal cycle over a range of tides between September 1994 and May 1995. The time-series were corrected to offset attenuation with depth of the high frequency fluctuations. A comparison of surface waves computed in this way with observations made using a video camera showed a significant positive correlation. Analysis of all 54 records showed a consistent energy decrease of between 47.4 % and effectively 100% across the saltmarsh section of the transect. This differed significantly from the much lower wave energy reduction (1.9 to 55.3%) across the sandflat section of the transect. Reduction in wave en...

Coastal ecosystems such as mangroves can reduce risk to people and infrastructure from wave damage and flooding. The continued provision of these coastal defence services by mangroves is dependent on their capacity to adapt to projected rates of sea level rise. This report explores the capacity of mangrove soil surfaces to increase in elevation in response to local rises in sea level. Historical evidence suggests that mangrove surface elevations have kept pace with sea level rise over thousands of years in some places, such as Twin Cays, Belize. Rates of surface elevation increase ranged between 1 mm/yr and 10 mm/yr in different locations and settings. Key controls on this include external sediment inputs and the growth of subsurface roots. Recent evidence based on measurements using the Surface-Elevation Table – Marker Horizon methodology (from studies published between 2006 and 2011) suggest that mangrove surfaces are rising at similar rates to sea level in a number of locations. ...

Rain forest logging generally involves substantial changes in soil hydrology which lead to accelerated erosion. Many studies consider surface effects, focusing on increased runoff generation resulting from reduced soil permeability at saturation. Changes in soil profile hydrology are wide ranging and have a wider variety of consequences than simply a reduction in soil permeability. Soil moisture retention, saturated soil moisture content and hydraulic conductivity in the unsaturated zone influence moisture movement through the profile, pore water pressure distributions and moisture availability to plants between rain storms. Soil erosion at the surface is affected, but such factors also control the propensity for mass movement and the likely vegetation regeneration following abandonment of logged areas. This paper explores this range of hydrological properties and considers in detail some of the consequences of changing hydrological behaviour for an area of eastern Malaysia which is currently undergoing extensive logging. The results indicate that as well as a decline in saturated permeability, the soils undergo changes in moisture retention which affects unsaturated zone hydrology. The general model of Campbell is fitted to the data, the results of which indicate substantial changes in the relationship between moisture retention, hydraulic conductivity and soil suction following logging. These results form an essential requirement for the application of physically-based hydrology models which may elucidate in detail processes resulting from rain forest disturbance.

... Coastal problems: geomorphology, ecology and society at the coast. Meld een fout in dit record. Volledige referentie: Auteurs. Viles, H.; Spencer, T. (1995). Coastal problems:geomorphology, ecology and society at the coast. Arnold: London, UK. ...

Salt marshes are important coastal environments and provide multiple benefits to society. They are considered to be declining in extent globally, including on the UK east coast. The dynamics and characteristics of interior parts of salt marsh systems are spatially variable and can fundamentally affect biotic distributions and the way in which the landscape delivers ecosystem services. It is therefore important to understand, and be able to predict, how these landscape configurations may evolve over time and where the greatest dynamism will occur. This study estimates morphodynamic changes in salt marsh areas for a regional domain over a multi-decadal timescale. We demonstrate at a landscape scale that relationships exist between the topology and morphology of a salt marsh and changes in its condition over time. We present an inherently scalable satellite-derived measure of change in marsh platform integrity that allows the monitoring of changes in marsh condition. We then demonstrat...

<p>Intertidal coastal wetlands, including tidal marshes and mangrove forests, are at risk of disappearing under the influence of global sea level rise (SLR). Loss of their ecosystem services could significantly impact global carbon budgets, increase coastal erosion and flooding and lead to loss of fisheries, particularly along densely populated coastal zones such as large estuaries and deltas. Regional to global-scale projections suggest a reduction in present-day coastal wetland area by 20% to 90% in response to projected rates of future SLR. Recent studies have highlighted the importance of coastal squeeze, i.e. the inhibition of inland migration of tidal coastal wetlands due to the existence of anthropogenic infrastructure, in combination with wetland loss due to sea level rise, which is aggravated by a global decline in coastal sediment supply.</p><p>Nature-based adaptation, consisting of the reservation or creation of space for inland wetland expansion, is widely regarded as a promising strategy to counteract coastal squeeze and create/restore natural habitats through inland migration. Based on global and regional modelling outputs, this paper discusses how different scenarios of global population growth, expected declines in global sediment supply, delta subsidence and various coastal management strategies impact on global areas of intertidal coastal wetlands, and coastal squeeze in particular. For example, we estimate that until the year 2100 up to 280,000 km<sup>2</sup> of coastal wetlands may be lost due to coastal squeeze. If strategically implemented on a regional to global scale nature-based solutions to coastal management could increase the global total area of intertidal coastal wetlands by up to 60%.</p><p>However our current understanding of this process is very limited, partly due to the limited field evidence in sedimentary archives (e.g. during the early Holocene where SLR were high). We argue that this is related to the combined effects of wetland inland migration and wetland drowning during periods of high SLR rates, raising the question as to whether or not future coastal wetland will be able to provide ecosystem services comparable to those of natural systems.</p>

The response of coastal wetlands to sea-level rise during the twenty-first century remains uncertain. Global-scale projections suggest that between 20 and 90 per cent (for low and high sea-level rise scenarios, respectively) of the present-day coastal wetland area will be lost, which will in turn result in the loss of biodiversity and highly valued ecosystem services. These projections do not necessarily take into account all essential geomorphological and socio-economic system feedbacks. Here we present an integrated global modelling approach that considers both the ability of coastal wetlands to build up vertically by sediment accretion, and the accommodation space, namely, the vertical and lateral space available for fine sediments to accumulate and be colonized by wetland vegetation. We use this approach to assess global-scale changes in coastal wetland area in response to global sea-level rise and anthropogenic coastal occupation during the twenty-first century. On the basis of...

This study explores the uncertainty introduced in global assessments of coastal flood exposure and risk by not accounting for water level attenuation due to land–surface characteristics. We implement a range of plausible water level attenuation values in the flood module of the Dynamic Interactive Vulnerability Assessment (DIVA) modelling framework and assess the sensitivity of flood exposure and flood risk indicators to differences in attenuation rates. Results show a reduction of up to 47 % in area exposure and even larger reductions in population exposure and expected flood damages. Despite the use of a spatially constant rate for water attenuation the reductions vary by country, reflecting the differences in the physical characteristics of the floodplain as well as in the spatial distribution of people and assets in coastal regions. We find that uncertainties related to the omission of this factor in global assessments of flood risk are of similar magnitude to the u...

Saltmarshes can play a vital role in mitigating the effects of global environmental change by dissipating incident storm wave energy and, through accretion, tracking increasing water depths consequent upon sea level rise. Atmospheric CO2 concentrations and nutrient availability are two key variables that can affect the biological processes that contribute to marsh surface elevation gain. We measured the effects of CO2 concentrations and nutrient availability on surface elevation change in intact mixed-species blocks of UK saltmarsh using six open-top chambers receiving CO2 enriched (800 ppm) or ambient (400 ppm) air. We found more rapid surface elevation gain in elevated CO2 conditions: an average increase of 3.4 mm over the growing season relative to ambient CO2 . Boosted regression analysis to determine the relative influence of different parameters on elevation change identified that a 10% reduction in microbial activity in elevated CO2 grown blocks had a positive influence on elevation. The biomass of Puccinellia maritima also had a positive influence on elevation, while other saltmarsh species (e.g. Suaeda maritima) had no influence or a negative impact on elevation. Reduced rates of water use by the vegetation in the high CO2 treatment could be contributing to elevation gain, either directly through reduced soil shrinkage or indirectly by decreasing microbial respiration rates due to lower redox levels in the soil. Eutrophication did not influence elevation change in either CO2 treatment despite doubling above ground biomass. The role of below ground processes (transpiration, root growth and decomposition) in the vertical adjustment of European saltmarshes, which are primarily minerogenic in composition, could increase as atmospheric CO2 concentrations rise and should be considered in future wetland models for the region. Elevated CO2 conditions could enhance resilience in vulnerable systems such as those with low mineral sediment supply or where migration upwards within the tidal frame is constrained. This article is protected by copyright. All rights reserved.

Coral reefs are a critical global resource, both biologically, and in socio-economic terms. They are the most diverse marine habitat, with an estimated one million different species. They are also widely used by coastal communities as a source of food and as the basis for ...

The idea of landscapes as shifting patch mosaics, structured by a range of biological and physical stochastic forces, is well suited to shallow tropical environments, where seagrass patches lie within a matrix of soft sediments or rocky substrates. The interaction of wave fields and tidal currents with carbonate sediment transport can result in linear morphologies of reef flat material with alternating sand tongues and seagrass beds. Patch-level metrics capture phenomena such as linearity in one variable, which can be evaluated over a gradient of predictable environmental change. Interrogating the statistical properties of patch ensembles enables the links between observed structures and the processes that govern them to be empirically investigated. This study demonstrates how habitat maps derived from remotely sensed Compact Airborne Spectrographic Imager (CASI) data can be used to investigate critical controls of landscape mosaics through the application of geostatistical techniqu...

There is evidence of Holocene emergence on several of the Cook Islands. On Suwarrow Atoll there are extensive outcrops of emergent, but truncated, reef on the northern atoll rim, radiocarbon-dated 4680–4310 years B. P., overlain by younger cemented boulder conglomerates. On the northeast of the atoll there are fossil algal ridges indicating up to 1 m of emergence; the landwardmost

On an annual basis 80.7% of the 3627 mm precipitation at a site of the East Ridge at Danum Valley, September 1989 to September 1990, reached the forest floor as throughfall and 1.9% as stemflow, giving an interception loss of 17.4%. The proportion of total rainfall intercepted decreases with storm magnitude. Stemflow amounts vary greatly from tree to tree. Under forest, removal of the ground cover and understorey vegetation led to changes in runoff and soil loss; soil faunal activity under natural forest produced higher soil loss from undisturbed natural plots, than from adjacent, partly cleared plots. Between 2.0 and 2.5% of the rain reaching the ground forms overland flow, the remainder infiltrates and much may be evacuated by pipeflow. Storms of 35 mm or more, which accounted for less than 35% of all rain events, produced 70% of the runoff and soil loss.