Metal enrichment and contamination in a karst cave associated with anthropogenic activities in the Witwatersrand Basin,South Africa     

Gerhard du Preez  Victor Wepener  Ingrid Dennis 《Environmental Earth Sciences》2016,75(8):653

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Balance of Catchment and Offshore Nutrient Loading and Biogeochemical Response in Four New Zealand Coastal Systems: Implications for Resource Management     

John R. Zeldis  Dennis P. Swaney 《Estuaries and Coasts》2018,41(8):2240-2259

Nutrient mass balance analyses are a way of obtaining ‘whole system’ viewpoints on coastal biogeochemical functions and their forcing. Seasonal mass balances are presented for four large bay systems in New Zealand (NZ), with the aim of showing how they can inform coastal management. Freshwater volumes, and surface and groundwater, wastewater and atmospheric inorganic and organic nitrogen (N) and phosphorus (P) were balanced with levels of salinity, N and P from ocean surveys, used to determine non-conservative N and P fluxes and, via stoichiometry, carbon (C) fluxes. For Golden and Tasman Bays and Hauraki Gulf, exchange with adjacent shelf waters usually dominated total N supply (80–85%). In contrast, for the Firth of Thames, 51% of total N and 85% of dissolved inorganic N supply originated from its agricultural catchment. Net ecosystem metabolism (NEM; balance of autotrophy and heterotrophy) of Golden and Tasman Bays and Hauraki Gulf was usually nearly balanced. In contrast, Firth NEM was highly seasonally variable, often exhibiting strong heterotrophy coincident with expression of respiration-related stressors (low O₂ and high DIC/low pH). Denitrification accounted for about 51% of total N export across the four systems, signifying its importance as a eutrophication-regulating ecosystem service. Budgets made 12 years apart in the Firth showed decreased denitrification efficiency, coincident with large increases in system N and phytoplankton. The findings for land-ocean nutrient balance, NEM and denitrification showed how mass balance budgeting can inform coastal management, including inventories of nutrient inputs, balances of oceanic and terrestrial nutrient loading, and potential for risk associated with biogeochemical responses.  相似文献   

A comparison of frameworks for separating the impacts of human activities and climate change on river flow in existing records and different near-future scenarios     

Soghra Andaryani  Vahid Nourani  James Ball  Saeed Jahanbakhsh Asl  Hamidreza Keshtkar  Dennis Trolle 《水文研究》2021,35(7):e14301

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Rational noncompliance and the liquidation of Northeast groundfish resources     

Dennis M. King  Jon G. Sutinen 《Marine Policy》2010

The results of a 2007 survey of fishers, managers, scientists, and enforcement officials indicate that noncompliance is a significant problem in the Northeast multispecies groundfish (NEGF) fishery, as it has been for at least 20 years. The percent of total harvest taken illegally is estimated to be 12–24%, which is significantly higher than estimates of 6–14% in the 1980s. Thirty-seven percent of fishers, 61% of fishery managers and 80% of fishery enforcement staff believe that “the combined adverse impact of all violations on the health and manageability of fish resources” is significant, highly significant, or extremely significant. Many fishers believe that illegal fishing will prevent them from ever benefiting from stock rebuilding programs.  相似文献   

Risk identification and perception in the fisheries sector: Comparisons between the Faroes,Greece, Iceland and UK     

Diana Tingley  Jóhann Ásmundsson  Edward Borodzicz  Alexis Conides  Ben Drakeford  Ingi Rúnar Eðvarðsson  Dennis Holm  Kostas Kapiris  Sakari Kuikka  Bogi Mortensen 《Marine Policy》2010

This paper presents the findings of risk identification and risk perception research conducted in relation to the fisheries systems of four distinct and diverse European countries: Faroes, Iceland, Greece and the UK. Risk research traditionally attempts to quantify the potential threat or consequences from a range of risk events or hazards. This research, however, adopted a social sciences perspective and so assumed that a risk event or hazard can mean different things to different people and that these perceptions are also context and culturally dependent. Risk perceptions were examined and risk registers developed in each country for a range of stakeholder groups. A ‘mental modelling’ approach was adopted in a series of qualitative interviews. Findings were examined in terms of a wide range of psychological, social and cultural risk theories. Differences in risk perceptions were noted between stakeholder groups and countries and contextual influences were examined such as the widely differing fisheries management systems used in each country. This research provides one of the first attempts to systematically evaluate risks and perceptions across a range of fisheries-systems. The findings support social science theories which argue that risk is a subjective, as opposed to objective, concept and that this subjectivity will therefore affect our attempts to assess and manage those hazards we think we can potentially influence or control.  相似文献   

Megacryst-bulk rock isotopic disequilibrium as an indicator of contamination processes: The Edgecumbe Volcanic Field,SE Alaska     

Dennis J. Geist  James D. Myers  Carol D. Frost 《Contributions to Mineralogy and Petrology》1988,99(1):105-112

Sr and Nd isotopic ratios are reported from mineral separates and bulk rock samples from the Edgecumbe Volcanic Field in southeast Alaska, a suite of lavas that has developed by assimilation. Megacrysts in the basaltic unit and the rhyodacites are in isotopic equilibrium with their matrices. Because the rhyodacites developed as the result of assimilation, the assimilate must have been completely dissolved. In contrast, megacrysts in the two andesitic units are in isotopic disequilibrium with their matrix. These megacrysts must be a mixture of those inherited from the contaminant, crystals in equilibrium with the groundmass, and possibly crystals inherited from a mafic liquid.  相似文献   

Turbulence in an almond orchard: Spatial variations in spectra and coherence     

Dennis D. Baldocchi  Boyd A. Hutchison 《Boundary-Layer Meteorology》1988,42(4):293-311

The spatial variability of turbulence in a fully-leafed almond orchard was studied. Two three-dimensional sonic anemometers were used to measure turbulence spectra and coherence at different vertical and lateral separations inside the canopy. Peak frequencies of the horizontal velocity components, normalized by local horizontal wind speed, are greater in the canopy crown than in the trunkspace. Peak-normalized frequencies for the vertical velocity power spectra are similar in the canopy crown and in the subcanopy trunkspace. Spectral slopes in the inertial subrange are more negative than those predicted with Kolmogorov's -2/3 theory. It is thought that the foliage elements act to short-circuit the eddy cascade. Lateral separation of the instruments in the subcanopy trunkspace has little effect on the shape of the velocity spectra. On the other hand, lateral and vertical velocity coherences between spatially separated sensors are low inside the canopy. These low coherences are due to the Eulerian length scales being of the same order of magnitude as the separation distances of the anemometers. Phase angles between velocity components are about zero for small separation distances. When the two instruments are separated by 9 m and one instrument is positioned in a row while the other is between two rows, vertical velocities are about 180 deg out of phase and the streamwise velocities are about 40 to 60 deg out of phase. These data support the contention that preferred differences occur between within- and between-row wind flow regimes.  相似文献   

Comparison Between Pump and Treat, Biorestoration, and Biorestoration/ Pump and Treat Combined: Lessons from Computer Modeling     

Samuel A. Marquis Jr.  Dennis Dineen 《Ground Water Monitoring & Remediation》1994,14(2):105-119

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Geochronology and sedimentology of the lower Passaic River,New Jersey     

Steven L. Huntley  Richard J. Wenning  Steave H. Su  Nancy L. Bonnevie  Dennis J. Paustenbach 《Estuaries and Coasts》1995,18(2):351-361

In an attempt to characterize localized rates of sediment accretion, 10 sediment cores were collected from the lower reach of the Passaic River, a major tributary of Newark Bay, New Jersey. Sediments were assayed for ²¹⁰Pb activity at predetermined depths and the rate of sediment accretion (cm yr^?1) was estimated from the least squares regression of the log of unsupported activity versus depth. Sediment accretion rates, derived from ²¹⁰Pb measurements (R_Pb) were used to predict the depth interval within the core containing sediments deposited around 1954; subsequent ¹³⁷Cs analyses were focused on this depth interval. Sediment accretion rates derived from ¹³⁷Cs measurements (R_Cs) were extrapolated from the depth of the 1954 horizon. Lead-210 derived sediment accretion rates in cores collected from a sediment bench extending along the inside bend on the southern shore of a meander in the river, ranged from 4.1 cm yr^?1 to 10.2 cm yr^?1 and averaged 6.8 cm yr^?1. The R_Cs estimates for cores from this area ranged from 3.8 cm yr^?1 to 8.9 cm yr^?1 and averaged 6.6 cm yr^?1. The R_Cs for cores collected in a more hydrologically dynamic reach of the river upstream of the sediment bench, were only 0.41 cm yr^?1 and 0.66 cm yr^?1. The results of this investigation indicate that this reach of the lower Passaic River is an area of high sediment accumulation, retaining much of the sediment load deposited from upstream and downstream sources. The rates of sediment accretion in the lower Passaic River are among the highest reported anywhere in the Newark Bay estuary.  相似文献   

Ultra-wideband radar studies of steep crested waves with scanning laser measurements of wave slope profiles     

Dennis B. Trizna  James P. Hansen  Paul Hwang  Jin Wu 《Dynamics of Atmospheres and Oceans》1993,20(1-2)

We report results of ultra wide-band radar sea spike experiments using steep and weakly breaking non-linear water surface features in a wave tank. To generate these features we used a 1 s paddle wave and wind waves for a sequence of wind speeds. A scanning laser was used to measure synchronously the surface slope profile across 12 cm along the wave propagation direction once per radar pulse. A time domain reflectometer (TDR) radar transmitted short horizontally polarized pulses at X-band, several hundred picoseconds long, to give a range resolution of 10 cm. A radar range of 36 cm was digitally sampled so that surface feature echoes could be tracked through the area continuously with 5 ms temporal resolution with each instrument. We report results considering the wave slope component in the propagation direction and the corresponding curvature component. For the conditions studied, two types of features which produce sea spike radar echoes were generated–a non-linear feature near the crest front of the wind wave, caused by extreme steepening as a result of the passage of the paddle wave, and a steepened blocked wind wave in the trough of the paddle wave, caused by the local orbital current of the 1 s wave being nearly equal to and opposite the phase velocity of the wind wave.  相似文献