Nursery Function Drives Temporal Patterns in Fish Assemblage Structure in Four Tropical Estuaries

Despite estuary-to-estuary differences in assemblage composition, fish faunas of tropical Indo-Pacific estuaries show parallel patterns of temporal change, suggesting a common set of ecological drivers. One potentially important driver is the interaction of different patterns of occupancy by functional groups that display different life-history patterns. However, most studies that have considered temporal change lack the detail needed to understand life-history utilisation. Most have focussed on changes in catch per unit effort (CPUE) or probability of encounter, with only one study going further and investigating changes in size structure and then only for a single estuary. One of the reasons for this lack of detail is the large volume of work needed to collect comprehensive data on size structures of species rich assemblages across multiple estuary systems over time. To overcome the logistical limitations on data collection, we used joint patterns of change in CPUE and mean biomass per fish (BPF) as proxies for changes in size structure. We investigated how different life-history strategies contributed to overall temporal patterns of assemblage change across four tropical Indo-Pacific estuaries. The three life-history strategies displayed characteristically different patterns in CPUE and BPF and the relationships between CPUE and BPF that reflect differences in the way that the three groups use estuaries. These different patterns interacted to produce complex assemblage patterns that are likely to be sensitive to location-specific differences in the mix of species from each group, providing at least part of the explanation for the site-specific fish assemblage structures that are characteristic of tropical estuarine fish fauna.     

Simulation of the interannual variability of the wind-driven Arctic sea-ice cover during 1958–1998

A thermodynamic-dynamic sea-ice model based on a granular material rheology developed by Tremblay and Mysak is used to study the interannual variability of the Arctic sea-ice cover during the 41-year period 1958–98. Monthly wind stress forcing derived from the National Centers for Environmental Prediction (NCEP) Reanalysis data is used to produce the year-to-year variations in the sea-ice circulation and thickness. We focus on analyzing the variability of the sea-ice volume in the Arctic Basin and the subsequent changes in sea-ice export into the Greenland Sea via Fram Strait. The relative contributions of the Fram Strait sea-ice thickness and velocity anomalies to the sea-ice export anomalies are first investigated, and the former is shown to be particularly important during several large export events. The sea-ice export anomalies for these events are next linked to prior sea-ice volume anomalies in the Arctic Basin. The origin and evolution of the sea-ice volume anomalies are then related to the sea-ice circulation and atmospheric forcing patterns in the Arctic. Large sea-ice export anomalies are generally preceded by large volume anomalies formed along the East Siberian coast due to anomalous winds which occur when the Arctic High is centered closer than usual to this coastal area. When the center of this High relocates over the Beaufort Sea and the Icelandic Low extends far into the Arctic Basin, the ice volume anomalies are transported to the Fram Strait region via the Transpolar Drift Stream. Finally, the link between the sea-ice export and the North Atlantic Oscillation (NAO) index is briefly discussed. The overall results from this study show that the Arctic Basin and its ice volume anomalies must be considered in order to fully understand the export through Fram Strait. Received: 27 January 1999 / Accepted: 8 July 1999     

Fluoride in Nebraska's Ground Water

Fluoride concentrations in ground water are generally low but play an important role in dental health. This study evaluates the vertical and spatial distribution of fluoride in Nebraska's ground water and examines the geological and geochemical processes that control its concentration. Data from 1794 domestic wells sampled by the Nebraska Department of Health and Human Services. Regulation, and Licensure (NDOH) had a range of fluoride concentrations from <0.1 to 2.6 mg/L. and a median concentration of 0.3 mg/L. The median fluoride concentrations for Nebraska's 13 ground water regions varied from 0.2 to 0.7 mg/L. In each of these regions, individual wells may have either insufficient or overabundant F concentrations; we recommend that individual private water systems be tested for fluoride. Based on these data, system-specific recommendations can be made regarding the necessity for fluoridation.
Geochemical data indicated that the majority of fluoride occurs as F. Dissolution of F-bearing minerals controls fluoride occurrence. Apatite plus minor amounts of fluorite along with significant ground water residence times are the primary factors controlling F in the water from the Dakota Formation in Knox County, as well as in other parts of northeastern Nebraska. In western and southwestern Nebraska, dissolution of volcanic glass is the most probable source of F Long residence times plus fluorite also may contribute to the F concentrations in the Chadron Formation.     

Metal Retention Experiments for the Design of Soil‐Mix Technology Permeable Reactive Barriers

Soil‐mix technology is effective for the construction of permeable reactive barriers (PRBs) for in situ groundwater treatment. The objective of this study was to perform initial experiments for the design of soil‐mix technology PRBs according to (i) sorption isotherm, (ii) reaction kinetics and (iii) mass balance of the contaminants. The four tested reactive systems were: (i) a granular zeolite (clinoptilolite–GZ), (ii) a granular organoclay (GO), (iii) a 1:1‐mixture GZ and model sandy clayey soil and (iv) a 1:1:1‐mixture of GZ, GO and model soil. The laboratory experiments consisted of batch tests (volume 900 mL and sorbent mass 18 g) with a multimetal solution of Pb, Cu, Zn, Cd and Ni. For the adsorption experiment, the initial concentrations ranged from 0.01 to 0.5 mM (2.5 to 30 mg/L). The maximum metal retention was measured in a batch test (300 mg/L for each metal, volume 900 mL, sorbent mass 90–4.5 g). The reactive material efficiency order was found to be GZ > GZ‐soil mix > GZ‐soil‐GO mix > GO. Langmuir isotherms modelled the adsorption, even in presence of a mixed cations solution. Adsorption was energetically favourable and spontaneous in all cases. Metals were removed according to the second order reaction kinetics; GZ and the 1:1‐mix were very similar. The maximum retention capacity was 0.1–0.2 mmol/g for Pb in the presence of clinoptilolite; for Cu, Zn, Cd and Ni, it was below 0.05 mmol/g for the four reactive systems. Mixing granular zeolite, organoclay and model soil increased the chemisorption. Providing that GZ is reactive enough for the specific conditions, GZ can be mixed to obtain the required sorption. Granular clinoptilolite addition to soil is recommended for PRBs for metal contaminated groundwater.     

Trophic structure and pathways of biogenic carbon flow in the eastern North Water Polynya

In the eastern North Water, most of the estimated annual new and net production of carbon (C) occurred during the main diatom bloom in 1998. During the bloom, at least 30% of total and new phytoplankton production occurred as dissolved organic carbon (DOC) and was unavailable for short-term assimilation into the herbivorous food web or sinking export. Based on particle interceptor traps and ²³⁴Th deficits, 27% of the particulate primary production (PP) sank out of the upper 50 m, with only 7% and 1% of PP reaching the benthos at shallow (≈200 m) and deep (≈500 m) sites, respectively. Mass balance calculations and grazing estimates agree that ≈79% of PP was ingested by pelagic consumers between April and July. During this period, the vertical flux of biogenic silica (BioSi) at 50 m was equivalent to the total BioSi produced, indicating that all of the diatom production was removed from the euphotic zone as intact cells (direct sinking) or empty frustules (grazing or lysis). The estimated flux of empty frustules was consistent with rates of herbivory by the large, dominant copepods and appendicularians during incubations. Since the carbon demand of the dominant planktivorous bird, Alle alle, amounted to ≈2% of the biomass synthesized by its main prey, the large copepod Calanus hyperboreus, most of the secondary carbon production was available to pelagic carnivores. Stable isotopes indicated that the biomass of predatory amphipods, polar cod and marine mammals was derived from these herbivores, but corresponding carbon fluxes were not quantified. Our analysis shows that a large fraction of PP in the eastern North Water was ingested by consumers in the upper 50 m, leading to substantial carbon respiration and DOC accumulation in surface waters. An increasingly early and prolonged opening of the Artic Ocean is likely to promote the productivity of the herbivorous food web, but not the short-term efficiency of the particulate, biological CO₂ pump.     

New metrics for managing and sustaining the ocean's bounty

Policies are arising around the world, most recently in the United States, that mandate the implementation of marine spatial planning as a practical pathway towards ecosystem-based management. In the new United States ocean policy, and several other cases around the globe, ecosystem services are at the core of marine spatial planning, but there is little guidance on how ecosystem services should be measured, making it hard to implement this new approach. A new framework is shown here for practical, rigorous ecosystem service measurement that highlights contributions from both natural and social systems. The novel three-step framework addresses traditional shortcomings of an ecosystem services approach by giving managers and scientists the tools to assess and track: (1) the condition of the ecosystem (supply metrics), (2) the amount of ocean resources actually used or enjoyed by people (service metrics), and (3) people's preference for that level of service (value metrics). This framework will allow real world progress on marine spatial planning to happen quickly, and with a greater chance for success.     

Behaviour and modelling of partial‐strength beam‐to‐column composite joints for seismic applications

A refined component model is proposed to predict the inelastic monotonic response of exterior and interior beam‐to‐column joints for partial‐strength composite steel–concrete moment‐resisting frames. The joint typology is designed to exhibit ductile seismic response through plastic deformation developing simultaneously in the column web panel in shear, the bolted end‐plate connection, the column flanges in bending and the steel reinforcing bars in tension. The model can handle the large inelastic deformations consistent with high ductility moment‐resisting frames. Slip response between the concrete slab and the beams was taken into account. A fibre representation was adopted for the concrete slab to accurately capture the non‐uniform stress distribution and progressive crushing of the concrete at the interface between the concrete slab and the column flange. The model is validated against results from full‐scale subassemblages monotonic physical tests performed at the University of Pisa, Italy. A parametric study is presented to illustrate the capabilities of the model and the behaviour of the joints examined. Copyright © 2006 John Wiley & Sons, Ltd.     

Quantitative evaluation of the performance of a permit auction system in reducing bycatch of sea turtles in the Hawaii Swordfish longline fishery

Many authors have suggested the use of a cap and trade auction system to help reduce bycatch—the incidental take of species by fishing gear targeting other species—of sea turtles in the Hawaii-based swordfish longline fishery. However, we know of no quantitative evaluations of the method. We present a simple mathematical model to serve as a framework to evaluate bycatch auction systems quantitatively. We conclude that cap and trade auction systems have the potential to reduce sea turtle bycatch by creating a financial incentive, while keeping permit costs down to 2–3% of total revenues. While stringent regulations aimed at conserving endangered sea turtles would still be essential, implementation of an auction for issuing transferable bycatch permits would likely enhance the economic efficiency of the fleet. Sea turtle mortality could be reduced further if a shrinking cap on total turtle mortality was introduced, taking advantage of the incentives for reducing turtle mortality that are introduced by the cap and trade auction system.     

Regional controls on geomorphology, hydrology, and ecosystem integrity in the Orinoco Delta, Venezuela

Interacting river discharge, tidal oscillation, and tropical rainfall across the 22,000 km² Orinoco delta plain support diverse fresh and brackish water ecosystems. To develop environmental baseline information for this largely unpopulated region, we evaluate major coastal plain, shallow marine, and river systems of northeastern South America, which serves to identify principal sources and controls of water and sediment flow into, through, and out of the Orinoco Delta.The regional analysis includes a summary of the geology, hydrodynamics, sediment dynamics, and geomorphic characteristics of the Orinoco drainage basin, river, and delta system. Because the Amazon River is a major source of sediment deposited along the Orinoco coast, we summarize Amazon water and sediment input to the northeastern South American littoral zone. We investigate sediment dynamics and geomorphology of the Guiana coast, where marine processes and Holocene history are similar to the Orinoco coast.Major factors controlling Orinoco Delta water and sediment dynamics include the pronounced annual flood discharge; the uneven distribution of water and sediment discharge across the delta plain; discharge of large volumes of water with low sediment concentrations through the Río Grande and Araguao distributaries; water and sediment dynamics associated with the Guayana littoral current along the northeastern South American coast; inflow of large volumes of Amazon sediment to the Orinoco coast; development of a fresh water plume seaward of Boca Grande; disruption of the Guayana Current by Trinidad, Boca de Serpientes, and Gulf of Paria; and the constriction at Boca de Serpientes.