No abstract

Regions of Restricted Exchange (RREs) are an important feature of the European coastline. They are historically preferred sites for human settlement and aquaculture and their ecosystems, and consequent human use, may be at risk from eutrophication. The OAERRE project (EVK3-CT1999-0002) concerns 'Oceanographic Applications to Eutrophication in Regions of Restricted Exchange'. It began in July 2000, and studies six sites. Four of these sites are fjords: Kongsfjorden (west coast of Spitzbergen); Gullmaren (Skagerrak coast of Sweden); Himmerfjärden (Baltic coast of Sweden); and the Firth of Clyde (west coast of Scotland). Two are bays sheltered by sand bars: Golfe de Fos (French Mediterranean); and Ria Formosa (Portuguese Algarve). Together they exemplify a range of hydrographic and enrichment conditions. The project aims to understand the physical, biogeochemical and biological processes, and their interactions, that determine the trophic status of these coastal marine RRE through the development of simple screening models to define, predict and assess eutrophication. This paper introduces the sites and describes the component parts of a basic screening model and its application to each site using historical data. The model forms the starting point for the OAERRE project and views an RRE as a well-mixed box, exchanging with the sea at a daily rate E determined by physical processes, and converting nutrient to phytoplankton chlorophyll at a fixed yield q. It thus uses nutrient levels to estimate maximum biomass; these preliminary results are discussed in relation to objective criteria used to assess trophic status. The influence of factors such as grazing and vertical mixing on key parameters in the screening model are further studied using simulations of a complex 'research' model for the Firth of Clyde. The future development of screening models in general and within OAERRE in particular is discussed. In addition, the paper looks ahead with a broad discussion of progress in the scientific understanding of eutrophication and the legal and socio-economic issues that need to be taken into account in managing the trophic status of RREs

Particulate matter concentration (PM, often referred to as total suspended solids [TSS]) is an important parameter in the evaluation of water quality. Several optical measurements used to provide an estimate of water turbidity have also been used to estimate PM, among them light transmission, backscattering, and side-scattering. Here we analyze such measurements performed by the Alliance for Coastal Technologies (ACT) at various coastal locations to establish whether a given optical method performs better than others for the estimation of PM. All the technologies were found to perform well, predicting PM within less than 55% relative difference for 95% of samples (n = 85, four locations). Backscattering performed best as a predictor of PM, predicting PM with less than 37% relative difference for 95% of samples. The correlation coefficient (R) was between 0.96 and 0.98 for all methods with PM data ranging between 1.2 to 82.4 g m -3. In addition, co-located measurements of backscattering and attenuation improves PM prediction and provides compositional information about the suspended particles; when their ratio is high, the bulk particulate matter is dominated by inorganic material while when low, dominated by organic material.

[1] Wind-current relationships at the mouth of a large coastal plain estuary are examined using seasonal current, wind, and sea level records. Observations indicate a small portion of subtidal current is forced by along-shelf (AL) wind-induced coastal sea level fluctuations (remote forcing). However, subtidal fluctuations on the order of 10 cm/s appear to be largely forced by along-estuary wind stress (local forcing). Local forcing dominates the wind-driven subtidal current during principal AL and along-estuary wind conditions, but along-estuary wind stress accentuates the local effect while diminishing the remote effect. A simple two-dimensional analytical model helps clarify the competition between remote and local wind forcing of current near the estuary mouth, supporting the existence of a strong bi-directional current that is locally wind-driven, regardless of principal wind forcing. Both observed and model results indicate that the relative orientation of the wind stress with respect to the estuary and the adjacent shelf are important in determining the roles of remote and local forcing. Findings from this study challenge the application of traditional coastal pumping models for estuary-shelf exchange and have implications for larval recruitment and exchange of material between estuaries and inner shelves.

We report herein a study of the role of hydrodynamics in controlling the food supply to benthic filter feeders in the Menai Strait, a narrow channel between the island of Anglesey and north Wales, UK, which is tidally energetic with pronounced residual flow (~350 to 800 m 3 s -1