Andrew J. Plater

Ecohydrology as a new tool for sustainable management of estuaries and coastal waters

Throughout the world, estuaries and coastal waters have experienced degradation. Present proposed remedial measures based on engineering and technological fix are not likely to restore the ecological processes of a healthy, robust estuary and, as such, will not reinstate the full beneficial functions of the estuary ecosystem. The successful management of estuaries and coastal waters requires an ecohydrologybased, basin-wide approach. This necessitates changing present practices by official institutions based on municipalities or counties as an administrative unit, or the narrowly focused approaches of managers of specific activities (e.g., farming and fisheries, water resources, urban and economic developments, wetlands management and nature conservationists). Without this change in thinking and management concept, estuaries and coastal waters will continue to degrade, whatever integrated coastal management plans are implemented. To help in this process of change there is a need to (1) develop a profound understanding of the effects of biota and biotic processes on mediating estuary response to changing hydrology, sediment and nutrient flux and of the biota on hydrology at the river basin scale, and (2) to develop science-based remediation measures at the river basin scale, with elements of ecohydrology and phytotechnology at their core, to strengthen the ability of the biota to sustain and adapt to human-induced stresses.

Uranium series disequilibrium in river sediments and waters: the significance of anomalous activity ratios

Abstract Samples of river water, suspended and bottom sediments from the Fenland catchment system draining into the Wash, U.K., have been analysed for the longer-lived U/Th series radionuclides (238U, 234U, 230Th and 232Th). The aim of this work was to assess the effects of open-system phase-transfer on the U series disequilibria observed in the river waters and sediments and to investigate the controls exerted on this phase-transfer by the hydrological regime. Two important aspects of the U series radionuclide mobilisation in this modern river system have been observed: (1) U series radionuclides are in a continuous state of flux between river sediments and river water; and (2) U sorption on sediment particles is seasonably variable. Sequential extraction of whole sediments revealed that the U-series isotopic characteristics of the ion-exchangeable, organic-bound, carbonate, amorphous Fe Mn oxyhydroxides and crystalline Fe Mn oxides are controlled to a significant degree by the acquisition of U isotopes from the aqueous phase. During summer when surface run off and river discharges are generally low, the U isotope acquisition by sediment particles results in “anomalously” high234U/238U activity ratios (>1). This is of importance for studies which rely upon the isotopic and elemental separation of U series radionuclides in the weathering system i.e. mass balance, weathering rate and sediment yield assessments.

Rapid coastal change during the mid- to late Holocene: the record of barrier estuary sedimentation in the Romney Marsh region, southeast England

A common problem facing sea-level researchers lies in determining the cause of rapid changes observed in coastal stratigraphic sequences. Such changes are commonly ascribed to the interaction of processes that operate over differing temporal and spatial scales, i.e. rapid local and regional sea-level trends and storm magnitude/frequency. At least some of the difficulty in distinguishing between these processes lies in the often limited stratigraphic database upon which palaeoenvironmental reconstruction is based. Here, we present the results of detailed morphostratigraphic and micropalaeontological investigations from a series of sites located at the interface between the protective gravel barrier complex of Dungeness and the barrier estuary sediments of Romney Marsh, England. A period of rapid coastal regression is identified between c. 4500 and 3000 cal. yrs BP, during which time the sea level continued to rise but was outpaced by sediment accretion and peat accumulation. A subsequent acceleration in the rate of rise led to a reversal of this excess of sediment supply over sea-level rise, and to rapid inundation of the entire barrier estuary between c. 2800 and 1900 cal. yrs BP. At the local level, coastal development reflects an interdependence between storms and long-term relative sea-level (RSL) rise; processes which lie at opposite ends of the magnitude/frequency spectrum. However, when viewed from a holistic perspective encompassing the Holocene development of Romney Marsh as a whole, storms are of secondary importance in controlling coastal evolution. Rather, our study suggests that at this macro-scale coastal evolution responds primarily to the combined effects of RSL rise and sediment supply

Reconstruction of Holocene foreland progradation using optically stimulated luminescence (OSL) dating: an example from Dungeness, UK:

Dungeness Foreland, southeast UK, is comprised of a series of distinctive gravel ridges overlying sub- and intertidal sands. The successful application of optically stimulated luminescence (OSL) to the Holocene sub- and intertidal sands at Dungeness provides a well-resolved chronology (precision ~5%) for exploring the sedimentary response of a gravel foreland to changes in sea level, storms, sediment supply and coastal dynamics. The nature of foreland progradation at Dungeness is revealed through a three-dimensional network of 35 new quartz OSL ages, and these data also constrain the timing of gravel emplacement. The OSL chronology places the early formation of the underlying shoreface in the west at ~5000 years ago, with ages decreasing progressively eastwards to ~2000 years ago beneath the main body of the present foreland, and 1000—600 years ago under the present-day ness in the east. The uppermost OSL ages for the subgravel sand unit provide maximum limiting ages for emplacement of the gravel, which together with 14C ages from organic deposits on the gravel surface provide bracketing ages for the deposition of the gravel. The short lag time between shoreface sand deposition and gravel ridge formation is indicative of a high degree of dependency of gravel foreland progradation on the pre-existence of an emergent sand substrate. Sigmoidal isochrons constructed using the subgravel sand OSL ages, and consideration of down-core OSL ages, demonstrates nonlinearity in coastal response; this is expressed in the form of changes in the direction of foreland progradation rather than temporal changes in sedimentation rate.

Particle size characterisation of Holocene back-barrier sequences from North Atlantic coasts (SW Spain and SE England)

Abstract In this paper, we present the results of bivariate plots of grain size parameters (mean against sorting) in the reconstruction of Holocene environmental change in coastal environments where barrier formation has had an important control on sedimentation. Sites on the North Atlantic coast with differing histories of climate, sediment flux, sea-level change and barrier integrity are investigated to determine the general efficacy of this bivariate parameter model in distinguishing between open- and closed-basin conditions, and in reviewing the significance of aperiodic high-energy geomorphic events in controlling late stage back-barrier sedimentation.

Holocene coastal sedimentation in the Eastern English Channel: New data from the Romney Marsh region, United Kingdom

Abstract Multiproxy analysis (grain size, mineral magnetics, pollen, diatoms and radiocarbon dates) of deep (20 m+) cores collected from the Rye area of the Romney Marsh region are used to reconstruct coastal evolution between ca. 7000 and 2000 yr “conventional radiocarbon” B.P. A rapid phase of sea-level rise and tidal flat sedimentation occurred between ca. 7000 and 6000 “conventional radiocarbon” yr B.P., after which peat accumulation took place as a coastal barrier of sand and gravel extended eastward across Rye Bay and the rate of sea-level rise fell. Marine conditions returned to these areas at ca. 3000-2000 yr B.P. Erosion and landward migration of the barrier accompanied this return, heralding a change in the stability of the barrier and its ability to afford protection to back-barrier areas of the Romney Marsh region. Comparison with other sites in the central and eastern English Channel and the Thames estuary suggests that the prolonged removal of marine conditions from the study site accompanying barrier establishment reflects an ample sediment supply and the large volume of material within the barrier, which would have provided considerable scope for internal re-organisation when faced with changing coastal processes.

Historical contaminant fluxes in the Tees estuary, UK : Geochemical, magnetic and radionuclide evidence

Abstract Geochemical, magnetic and radionuclide analyses were undertaken on deep and shallow cores from the Tees estuary in an investigation of sediment flux during the historical past, using the record of contamination from mining and industrial activity to link Holocene coastal change with present-day sedimentary processes. The extent of contamination can be identified from XRF and environmental magnetism data, and is variable in magnitude and thickness. Concentrations of Pb and Zn are particularly effective in the identification of far-field mining contamination, whilst As concentration and the concentration of magnetic minerals ( χ , magnetic susceptibility) are used to characterise near-field industrial contamination. Radionuclide chronologies ( 210 Pb and 137 Cs) confirm limited post-depositional disturbance of the shallow sedimentary record and place the onset of industrial contamination at c . 1925, with a peak level in the mid-1950s. Although contamination has decreased since the early-1980s, the marked spatial and vertical variation in the extent of this contamination adds a significant level of complexity to any future assessment programme where sediment erosion and redistribution are important concerns.

An investigation into the efficiency of particle size separation using Stokes’ Law

The accuracy of gravimetric fractionation as a means of obtaining size fractions from marine sediments has been explored. Analysis of the particle size distribution and sediment properties of fractions obtained using this method was undertaken. This has highlighted the extent to which experimental artefacts rather than variations in sediment characteristics may adversely affect the efficiency of the fractionation process.

Modelling approaches for coastal simulation based on cellular automata: the need and potential

The paper summarizes the theoretical and practical needs for cellular automata (CA)-type models in coastal simulation, and describes early steps in the development of a CA-based model for estuarine sedimentation. It describes the key approaches and formulae used for tidal, wave and sediment processes in a prototype integrated cellular model for coastal simulation designed to simulate estuary sedimentary responses during the tidal cycle in the short-term and climate driven changes in sea-level in the long-term. Results of simple model testing for both one-dimensional and two-dimensional models, and a preliminary parameterization for the Blackwater Estuary, UK, are shown. These reveal a good degree of success in using a CA-type model for water and sediment transport as a function of water level and wave height, but tidal current vectors are not effectively simulated in the approach used. The research confirms that a CA-type model for the estuarine sediment system is feasible, with a real prospect for coupling to existing catchment and nearshore beach/cliff models to produce integrated coastal simulators of sediment response to climate, sea-level change and human actions.

Sediment yield determination using uranium-series radionuclides: the case of the Wash and Fenland drainage basin, eastern England

Abstract Water and sediment samples were collected from the Fenland drainage basin to assess the fluvial contribution to the sediment budget of The Wash, on the east coast of England. Using the uranium-series disequilibrium found in the products of the weathering system (river sediment and water), the ratio of material carried in solid form to that dissolved ( U s / U w ) was assessed and the total flux of weathered material (sediment yield) was quantified. The results show that the U s / U w ratio is controlled to a degree by catchment geology and hydrology, and that there is a marginal seasonal increase from between 3.28 ± 3.95 and 4.60 ± 0.44 (summer mean and weighted mean) to between 5.35 ± 3.05 and 6.07 ± 0.63 (winter mean and weighted mean). The best estimate of annual sediment flux from the Fenland to The Wash is between 2800 and 17,700 tonnes yr −1 , equivalent to a rate of 0.22–1.42 tonnes km −2 yr −1 . This is lower than previous estimates for the region, but reinforces the argument that sediment reworking within The Wash and erosion of the adjacent coasts and sea beds are important sources of sediment for the intertidal flats and salt marshes.