Impact of macrozoobenthic structures on near-bed sediment fluxes

Sandy sediments in shallow coastal waters of the Baltic Sea are often characterised by large numbers of biogenic structures which are produced by macrozoobenthos species. A series of experiments was devised to quantify how the interaction of such structures with the near-bed flow regime affects the sediment flux. Most experiments were done with simplified replicates of structures generated by typical species commonly found in the Mecklenburg Bight, starting with solitary structures and regularly-spaced arrays in a range of characteristic population densities, followed by a complex benthic macrofauna community, both artificial and alive. A laboratory flume channel, equipped with an acoustic Doppler flow sensor and a topography scanning laser, was used for high-resolution measurements (2 mm horizontal step size and 0.3 mm vertical resolution) of sand erosion (220 µm median grain size, at 20 cm s^− 1) and fine particle deposition (8 µm grain size, at 5 cm s^− 1). Sediment transport threshold values were measured for each layout. As a rule-of-thumb, both the erosion fluxes and the deposition of suspended matter increased considerably at low population densities (below 2%, expressed as percent of the sediment surface covered, i.e. roughness density RD). Above densities of 4%, erosion almost stopped inside the test arrays, and deposition remained well below the level of unpopulated areas. An attempt to extrapolate these findings to field conditions (using field current velocity data from 2001) showed that the net flux switched from erosion to deposition for densities above 5%. These parameters can now be integrated into a numerical sediment transport model coupling waves, currents, sediment dynamics and biological processes, which is currently under construction at the Baltic Sea Research Institute (IOW), Rostock, Germany.     

Quantifying erosion rates and stability of bottom sediments at mussel aquaculture sites in Prince Edward Island,Canada

Downward fluxes of organic biodeposits under suspended mussel culture cause benthic impacts such as microbial mat production. Quantifying sediment erosion in these coastal ecosystems is important for understanding how fluxes of organic matter and particulates contribute to benthic–pelagic coupling. Critical shear velocity (u?), erosion rates and particle size distributions of resuspended sediment were measured at two sites; an impacted muddy site with extensive mussel culture (site 1), and a coarser sandier site with less mussel influence (site 2), using a new method for assessing sediment erosion at Tracadie Bay, Prince Edward Island in August 2003. Shear forces were generated by vertically oscillating a perforated disc at controlled frequencies. These forces correspond to shear velocity, using a re-designed and calibrated Particle Erosion Simulator. Undisturbed sediment cores obtained by divers and grab (sub-cored using a Plexiglas? cores) were exposed to shear stress to compare differences between collection methods. Microbial mats were present at site 1 which initially biostabilized sediment against erosion due to ‘armoring’ of the sediment, but onset of erosion was abrupt once these mats failed. Erosion sequences at site 2 (without mat cover) were smoother resulting in less material being eroded. Mean mass of material eroded was 47 and 23 g m^? 2 min^? 1 at sites 1 and 2 respectively. Mat area cover and shear velocity was strongly related. Critical shear velocities varied between 1.70 and 1.77 cm s^? 1, with no obvious differences between location or collection method, so sediments from these two contrasting sites had identical mean critical shear velocities. Significant differences existed in the concentrations of chlorophyll a, colloidal and bulk carbohydrates, between mats and bare sediment from site 1. Particle sizes measured by videography of resuspended sediment at different shear velocities ranged from 100 μm (the minimum diameter capable of being detected by the system), to large mat fragments of 1700 μm for both sites. These results provide evidence of the relevance of using a portable erosion device to indicate how sediment erodability is affected by mussel–microbial relationships.     

Lagrangian flow in the California Undercurrent, an observation and model comparison

During the period 1992–1998, 38 isobaric RAFOS floats were deployed to sample the subsurface flow of the California Undercurrent. The deployments, released over the California continental slope west of San Francisco, have sampled robust year-round poleward subsurface flow associated with the Undercurrent most seasons and the combined inshore current and Undercurrent in winter. Two other types of flow have been seen: a region of weak flow with little net displacement just west of the California Undercurrent, and an active westward propagating eddy field. This eddy field appears to be the primary mechanism for moving floats from the Undercurrent into the ocean interior. The observations and statistics from the RAFOS floats are compared with Lagrangian estimates of particles tracked in a global high resolution ocean simulation in order to evaluate the fidelity of the model along an eastern boundary. The results show that the model reproduces the general character of the flow reasonably well, but underestimates both the mean and eddy energies by a substantial amount.     

Collaborative Management of Natural Resources in San Diego Bay

This article presents the results of a three-year effort at applying information technology to the problem of collaborative natural resource management in San Diego Bay. As such, it represents an approach to integrated coastal zone management (ICZM). This effort resulted from a collaboration between the San Diego Supercomputer Center at the University of California, San Diego and the San Diego Bay Interagency Water Quality Panel for the purpose of (1) developing an environmental data repository to facilitate the acquisition and sharing of data and (2) the development of a visual model of the bay in support of the development of a comprehensive, coordinated management plan for San Diego Bay. It was determined from this study that information technology is an important and key component to ICZM but that sociopolitical factors may override the benefits of decision-support systems and should be considered at the outset of any project of this kind.     

Attitudes toward Participation in Cooperative Coastal Management: Four European Case Studies

Findings are reported of the VALCOAST project that had as one of its research objectives to ascertain: (a) stakeholder willingness to participate and cooperate in coastal management (CM), given local and national CM practices; and (b) stakeholder assessment of the "accessibility" and "friendliness" of current CM processes. The project involved case studies and stakeholder interviews in Belgium, Greece, Spain, and the UK. Major findings include: (1) most stakeholders are willing to cooperate in three out of the four case areas, but not to the same extent; (2) the participating "officials" in the case studies are expecting the stakeholders to be less willing to cooperate than the latter indicate; (3) stakeholders in all case studies do not expect to be heard by those responsible for CM, find it difficult to learn about the relevant institutional arrangements, and consider the communication of the objectives and anticipated impacts of CM policies to be inadequate. It is concluded that the strong evidence of stakeholders' potential willingness to cooperate in local initiatives is very encouraging for a devolved, regional approach to European Union coastal management policies, provided that this potential is capitalized upon in such policy processes.     

Can Coastal Management Programs Protect and Promote Water-Dependent Uses?

Anecdotal evidence indicates that commercial and recreational water-dependent uses have been under development pressure in recent years, and in some cases have been converted to other uses. The conversion of water-dependent uses, which range from commercial shipyards to recreational marinas, may have many public costs, including the loss of access to public trust waters, the loss of jobs and associated economic activity, and the loss of traditional working waterfronts. This two-part study investigated the role of five coastal management programs in the northeastern United States in managing, monitoring, and protecting water-dependent uses. First, coastal managers in Massachusetts, Rhode Island, Connecticut, New York and New Jersey were interviewed to assess the conversion problem. Second, in collaboration with New York City-based Regional Plan Association, follow-up interviews were conducted with coastal managers and local planners in Connecticut, New York, and New Jersey to gain greater insight into the role of coastal management programs and local governments in managing and promoting water-dependent uses. This article presents select findings from this study and discusses recommendations for improving the capacity of coastal management programs and local governments to manage water-dependent uses for the benefit of the public.     

Some economic aspects of conflicts over land use in the coastal zone

Abstract

Recent land use legislation pays particular attention to the coastal zone where age‐old conflicts have recently accelerated. Flexibility is required in policy because visible conflicts are tied into complex physical and social systems which may require changing patterns of land use over time. Public policy is altering property rights and a thorough understanding of the economic and social roles played by those rights is required. Economic models can be used to understand some major changes such as types of alteration of the environment, but may be ignored or misused unless a better understanding of coastal decision processes is developed.     

A user‐resource planning framework for offshore recreational artificial reefs

Abstract

Artificial reefs have been used extensively in coastal waters to attract and enhance recreational fishery resources. In the United States, they have been traditionally built from “materials of opportunity”; using limited budgets. This paper explores some past planning philosophies and presents a recent artificial reef deployment case that demonstrates a lack of sensitivity to local and regional recreational demand. A systems framework is developed to guide future planning efforts in artificial reef development. The framework is intended to integrate previously fragmented knowledge and to demonstrate the interdisciplinary nature of artificial reef planning. Emphasis is given to advance planning, user dimensions, and the integral issue of reef access.