Monitoring accelerated clogging of a model horizontal sub-surface flow constructed wetland using magnetic resonance transverse relaxation times

Horizontal sub-surface flow wetlands are essentially a bed of porous material in which suitable plants are grown to facilitate the removal of organic matter and particulates from wastewater. The aim of this study is to assess the reliability and accuracy of magnetic resonance transverse relaxation time for monitoring clogging development in a constructed wetland. In this study, three different horizontal sub-surface flow constructed wetland models have been produced using tubes packed with different sizes of glass beads with diameter 3, 8 and 14 mm. Accelerated clogging has been achieved by pumping sludge extracted from a real clogged wetland through the bead pack. A desktop MRI tomography system has been used to monitor the transverse relaxation rate as a function of position along the tube and hydraulic conductivity. To corroborate the clogging with magnetic resonance measurements, the head loss was monitored to determine the hydraulic conductivity. Using a bi-exponential fit to the spin echo train data, the slow relaxation rate contribution shows good correlation with the changing hydraulic conductivity. Both fast and slow contributions map well to the expected clog patterns for a constructed wetland. We have demonstrated that there is a linear correlation between the hydraulic conductivity and both parameters of a bi-exponential fit to R ₂ ^eff , but particularly for the case of the short T ₂ component.     

Responsible fisheries: An overview of FAO policy developments (1945–1994)

The paper outlines the evolution of fisheries development policies (aquaculture excluded), from an international perspective as seen within the various UN and FAO fishery committees. It begins with the first FAO Technical Committee on Fisheries in 1945 and extends through the various periods corresponding to post-war reconstruction (1945–1958), geographical expansion (1959–1972), establishment of a new economic order of the oceans (1973–1982), and transition towards global concerns (1983–1992). It underlines the gaps between government resolutions at the international level and effective implementation at national policy level. This identifies the elements to be considered in responsible fishing policies. Finally, the FAO International Code of Conduct for Responsible fisheries is presented as the conceptual framework for achieving sustainable fisheries development and UNCED's objectives within the framework of the 1992 Convention.     

Controls on surface water chemistry in two lake‐watersheds in the Adirondack region of New York: differences in nitrogen solute sources and sinks

The southwestern Adirondack region of New York receives among the highest rates of atmospheric nitrogen (N) deposition in the USA. Atmospheric N deposition to sensitive ecosystems, like the Adirondacks, may increase the acidification of soils through losses of exchangeable nutrient cations, and the acidification of surface waters associated with enhanced mobility of nitrate (NO₃^?). However, watershed attributes, including surficial terrestrial characteristics, in‐lake processing, and geological settings, have been found to complicate the relationships between atmospheric N deposition and N drainage losses. We studied two lake‐watersheds in the southwestern Adirondacks, Grass Pond and Constable Pond, which are located in close proximity (～26 km) and receive similarly high N deposition, but have contrasting watershed attributes (e.g. wetland area, geological settings). Since the difference in the influence of N deposition was minimal, we were able to examine both within‐ and between‐watershed influences of land cover, the contribution of glacial till groundwater inputs, and in‐lake processes on surface water chemistry with particular emphasis on N solutes and dissolved organic carbon (DOC). Monthly samples at seven inlets and one outlet of each lake were collected from May to October in 1999 and 2000. The concentrations of NO₃^? were high at the Grass Pond inlets, especially at two inlets, and NO₃^? was the major N solute at the Grass Pond inlets. The concentrations of likely weathering products (i.e. dissolved Si, Ca²⁺, Mg²⁺, Na⁺) as well as acid neutralizing capacity and pH values, were also particularly high at those two Grass Pond inlets, suggesting a large contribution of groundwater inputs. Dissolved organic N (DON) was the major N solute at the Constable Pond inlets. The higher concentrations of DON and DOC at the Constable Pond inlets were attributed to a large wetland area in the watershed. The DOC/DON ratios were also higher at the Constable Pond inlets, possibly due to a larger proportion of coniferous forest area. Although DON and DOC were strongly related, the stronger relationship of the proportion of wetland area with DOC suggests that additional factors regulate DON. The aggregated representation of watershed physical features (i.e. elevation, watershed area, mean topographic index, hypsometric‐analysis index) was not clearly related to the lake N and DOC chemistry. Despite distinctive differences in inlet N chemistry, NO₃^? and DON concentrations at the outlets of the two lakes were similar. The lower DOC/DON ratios at the lake outlets and at the inlets having upstream ponds suggest the importance of N processing and organic N sources within the lakes. Although an inverse relationship between NO₃^? and DOC/DON has been suggested to be indicative of a N deposition gradient, the existence of this relationship for sites that receive similar atmospheric N deposition suggest that the relationship between NO₃^? and the DOC/DON ratio is derived from environmental and physical factors. Our results suggest that, despite similar wet N deposition at the two watershed sites, N solutes entering lakes were strongly affected by hydrology associated with groundwater contribution and the presence of wetlands, whereas N solutes leaving lakes were strongly influenced by in‐lake processing. Copyright © 2006 John Wiley & Sons, Ltd.     

Geochemistry,dispersal, volumes and chronology of Holocene silicic tephra layers from the Katla volcanic system,Iceland

At least 12 silicic tephra layers (SILK tephras) erupted between ca. 6600 and ca. 1675 yr BP from the Katla volcanic system, have been identified in southern Iceland. In addition to providing significant new knowledge on the Holocene volcanism of the Katla system which typically produces basaltic tephra, the SILK tephras form distinct and precise isochronous marker horizons in a climatically sensitive location close to both the atmospheric and marine polar fronts. With one exception the SILK tephras have a narrow compositional range, with SiO₂ between 63 and 67%. Geochemically they are indistinguishable from ocean transported pumice found on beaches in the North Atlantic region, although they differ significantly from the silicic component of the North Atlantic Ash Zone One (NAAZO). Volumes of airborne SILK tephra range from 0.05 to 0.3 km³. We present new isopach maps of the six largest layers and demonstrate that they originate within the Katla caldera. The apparently stable magma system conditions that produced the SILK tephras may have been established as a consequence of the eruption of the silicic component of NAAZO (ca. 10.3 ka) and disrupted by another large‐scale event, the tenth century ad Eldgjá eruption (ca. 1 ka). Despite the current long repose, silicic activity of this type may occur again in the future, presenting hitherto unknown hazards. Copyright © 2001 John Wiley & Sons, Ltd.     

Geochemical stability of fine-grained silicic Holocene tephra in Iceland and Scotland

This paper tests two assumptions fundamental to the use of fine-grained silicic tephras from Iceland for creating chronological frameworks in northwest Europe. It is shown firstly, that glass shards can retain their overall chemical integrity on at least a four millennial time-scale in contrasting depositional environments in Iceland and Scotland, and secondly, that an acid digestion process, the most practical method for extracting tephra from peat, does not significantly bias the results of major element analysis by electron microprobe. The implication is that there is great potential and an appropriate method for developing both the resolution and the spatial coverage of chronologies based on silicic Icelandic tephras in northwest Europe.     

Grossular activity-composition relationships in ternary garnets determined by reversed displaced-equilibrium experiments

Activity-composition relationships of Ca₃Al₂Si₃O₁₂ (grs) in ternary Ca-Mg-Fe garnets of various compositions have been determined by reversed displaced equilibrium experiments at 1000° C and 900° C and pressures of 8 to 17 kbar. The mixing of grs in garnet is nearly ideal at 30 mol% grs, with positive deviations from ideality at lower grs contents. Models of garnet mixing currently in the literature do not predict this trend. Analysis of the present reversals, in conjunction with a garnet mixing model based solely on calorimetry measurements on the binary joins, indicates that a ternary interaction constant for a ternary asymmetric Margules model (Wohl 1953) cannot be constrained. Apparently, some aspects of the garnet binary joins are still not well-known. An alternative asymmetric empirical model, based on analysis of pseudobinary joins of constant Mg/Mg + Fe(Mg #), reproduces the data well and is able to predict grs activity coefficients for garnets with grs contents between 3 and 40 mol% and Mg numbers between 0 and 0.60. The grossular activity coefficient, _grs, is given by:

Catastrophic subsidence: An environmental hazard,shelby county,Alabama

Induced sinkholes (catastrophic subsidence) are those caused or accelerated by human activities These sinkholes commonly result from a water level decline due to pumpage Construction activities in a cone of depression greatly increases the likelihood of sinkhole occurrence Almost all occur where cavities develop in unconsolidated deposits overlying solution openings in carbonate rocks. Triggering mechanisms resulting from water level declines are (1) loss of buoyant support of the water, (2) increased gradient and water velocity, (3) water-level fluctuations, and (4) induced recharge Construction activities triggering sinkhole development include ditching, removing overburden, drilling, movement of heavy equipment, blasting and the diversion and impoundment of drainage Triggering mechanisms include piping, saturation, and loading Induced sinkholes resulting from human water development/management activities are most predictable in a youthful karst area impacted by groundwater withdrawals Shape, depth, and timing of catastrophic subsidence can be predicted in general terms Remote sensing techniques are used in prediction of locations of catastrophic subsidence. This provides a basis for design and relocation of structures such as a gas pipeline, dam, or building Utilization of techniques and a case history of the relocation of a pipeline are described