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101.
Neilson MA Painter DS Warren G Hites RA Basu I Weseloh DV Whittle DM Christie G Barbiero R Tuchman M Johannsson OE Nalepa TF Edsall TA Fleischer G Bronte C Smith SB Baumann PC 《Environmental monitoring and assessment》2003,88(1-3):103-117
The Great Lakes Water Quality Agreement stipulates that the Governments of Canada and the United States are responsible for restoring and maintaining the chemical, physical and biological integrity of the waters of the Great Lakes Basin Ecosystem. Due to varying mandates and areas of expertise, monitoring to assess progress towards this objective is conducted by a multitude of Canadian and U.S. federal and provincial/state agencies, in cooperation with academia and regional authorities. This paper highlights selected long-term monitoring programs and discusses a number of documented ecological changes that indicate the present state of the open and nearshore waters of the Great Lakes. 相似文献
102.
Gavin Hilson 《Natural resources forum》2005,29(2):144-153
Over the past 10–15 years, several governments have implemented an array of technology, support‐related, sustainable livelihoods (SL) and poverty‐reduction projects for artisanal and small‐scale mining (ASM). In the majority of cases, however, these interventions have failed to facilitate improvements in the industry's productivity and raise the living standards of the sector's subsistence operators. This article argues that a poor understanding of the demographics of target populations has precipitated these outcomes. In order to strengthen policy and assistance in the sector, governments must determine, with greater precision, the number of people operating in ASM regions, their origins and ethnic backgrounds, ages, and educational levels. This can be achieved by carrying out basic and localized census work before promoting ambitious sector‐specific projects aimed at improving working conditions in the industry. 相似文献
103.
104.
How Climate and Vegetation Influence the fire Regime of the Alaskan Boreal Biome: The Holocene Perspective 总被引:2,自引:0,他引:2
Feng Sheng Hu Linda B. Brubaker Daniel G. Gavin Philip E. Higuera Jason A. Lynch T. Scott Rupp Willy Tinner 《Mitigation and Adaptation Strategies for Global Change》2006,11(4):829-846
We synthesize recent results from lake-sediment studies of Holocene fire-climate-vegetation interactions in Alaskan boreal
ecosystems. At the millennial time scale, the most robust feature of these records is an increase in fire occurrence with
the establishment of boreal forests dominated by Picea mariana: estimated mean fire-return intervals decreased from ≥300 yrs to as low as ∼80 yrs. This fire-vegetation relationship occurred
at all sites in interior Alaska with charcoal-based fire reconstructions, regardless of the specific time of P. mariana arrival during the Holocene. The establishment of P. mariana forests was associated with a regional climatic trend toward cooler/wetter conditions. Because such climatic change should
not directly enhance fire occurrence, the increase in fire frequency most likely reflects the influence of highly flammable
P. mariana forests, which are more conducive to fire ignition and spread than the preceding vegetation types (tundra, and woodlands/forests
dominated by Populus or Picea glauca). Increased lightning associated with altered atmospheric circulation may have also played a role in certain areas where
fire frequency increased around 4000 calibrated years before present (BP) without an apparent increase in the abundance of
P. mariana. When viewed together, the paleo-fire records reveal that fire histories differed among sites in the same modern fire regime
and that the fire regime and plant community similar to those of today became established at different times. Thus the spatial
array of regional fire regimes was non-static through the Holocene. However, the patterns and causes of the spatial variation
remain largely unknown. Advancing our understanding of climate-fire-vegetation interactions in the Alaskan boreal biome will
require a network of charcoal records across various ecoregions, quantitative paleoclimate reconstructions, and improved knowledge
of how sedimentary charcoal records fire events.
In this paper, charcoal refers to macroscopic (≥180 μm) as opposed to microscopic (< 180 μm) particles unless indicated otherwise.
Radiocarbon ages were converted to calibrated years before AD 1950 using the atmospheric calibration data set (Stuiver et
al. 1998). 相似文献
105.
Edge Effects on Lizards and Frogs in Tropical Forest Fragments 总被引:4,自引:1,他引:3
Abstract: We investigated whether forest-pasture edges affect the distribution of an assemblage of small vertebrate ectotherms in a consistent and predictable manner. We describe the abundance and distribution of two species of anoline lizards ( Norops ) and five species of leaf-litter frogs ( Eleutherodactylus ) along the edges and in the interiors of nine forest fragments near Las Cruces, Costa Rica. Over 4 months, we surveyed 44 pairs of plots by visual encounter. In each pair of plots, one was immediately adjacent to the pasture and the second was within the forest "interior." Both plots of a pair were searched simultaneously. This block design controlled for the effects of weather, topography, and searcher ability. The distribution of all species was highly variable with respect to edges. Only two species of frogs, Eleutherodactylus podiciferus and E. cruentus , were significantly more abundant in interior plots than in edge plots, although not consistently so. Both species of Norops lizards were more abundant along forest edges during the dry season. Both Norops species and several Eleutherodactylus species, however, appeared to become more abundant in the forest interior after the onset of the wet season, suggesting a seasonal edge effect. In Norops polylepis , the most abundant anole, rates of ectoparasitism were lower along edges than in forest interiors. The magnitude of the edge effect on any one species was not influenced by the size of fragments or by the distance of the interior plot from the nearest edge. We believe that edge effects should not be defined by the distance to which they are detected. Rather, they should be viewed as highly dynamic in space and time; taxa appear to respond to different components of edge effects according to their particular biological requirements. 相似文献
106.
Sediments in the Port Jackson estuary are polluted by a wide range of toxicants and concentrations are among the highest reported
for any major harbor in the world. Sediment quality guidelines (SQGs), developed by the National Oceanographic and Atmospheric
Administration (NOAA) in the United States are used to estimate possible adverse biological effects of sedimentary contaminants
in Port Jackson to benthic animals. The NOAA guidelines indicate that Pb, Zn, DDD, and DDE are the most likely contaminants
to cause adverse biological effects in Port Jackson. On an individual chemical basis, the detrimental effects due to these
toxicants may occur over extensive areas of the harbor, i.e., about 40%, 30%, 15% and 50%, respectively. The NOAA SQGs can
also be used to estimate the probability of sediment toxicity for contaminant mixtures by determining the number of contaminants
exceeding an upper guideline value (effects range medium, or ERM), which predicts probable adverse biological effects. The
exceedence approach is used in the current study to estimate the probability of sediment toxicity and to prioritize the harbour
in terms of possible adverse effects on sediment-dwelling animals. Approximately 1% of the harbor is mantled with sediment
containing more than ten contaminants exceeding their respective ERM concentrations and, based on NOAA data, these sediments
have an 80% probability of being toxic. Sediment with six to ten contaminants exceeding their respective ERM guidelines extend
over approximately 4% of the harbor and have a 57% probability of toxicity. These areas are located in the landward reaches
of embayments in the upper and central harbor in proximity to the most industrialised and urbanized part of the catchment.
Sediment in a further 17% of the harbor has between one and five exceedences and has a 32% probability of being toxic. The
application of SQGs developed by NOAA has not been tested outside North America, and the validity of using them in Port Jackson
has yet to be demonstrated. The screening approach adopted here is to use SQGs to identify contaminants of concern and to
determine areas of environmental risk. The practical application and management implications of the results of this investigation
are discussed. 相似文献
107.
Green TJ Reeves CE Brough N Edwards GD Monks PS Penkett SA 《Journal of environmental monitoring : JEM》2003,5(1):75-83
The Peroxy Radical Chemical Amplifier (PERCA) technique is a proven method for measurement of ambient levels of peroxy radicals at ground level, but there are no published instances of the technique being used on an aerial platform. Here we describe deployment of a PERCA on the former UK Meteorological Office C-130 Hercules research aircraft. The instrument uses the established method of chemical amplification and conversion of peroxy radicals to nitrogen dioxide (NO2) by doping the sample air-flow matrix with CO and NO, subsequently measuring the NO2 yield with an improved 'Luminox' LMA-3 NO2 detector. NO2 from the amplification chemistry is distinguished from other sources of NO2 reaching the detector by periodically injecting CO approximately 1 s downstream of the NO injection point (termination mode). Chain lengths (CL's) for the amplification chemistry were typically approximately 260 (ground level) to approximately 200 (7,000 m). This variation with altitude is less than the variation associated with the 'age' of the PFA inlet material where the amplification chemistry occurs; CL's of approximately 200 with old tubing to approximately 300 with new clean tubing were typical (ground level values). The CL determinations were made in-flight using an onboard calibration unit based on the 254 nm photolysis of 7.5 to 10 parts per billion (by volume, ppbv) of CH3I in air, producing CH3O2 in a quantitative manner. The noise-equivalent detection limit for peroxy radicals (HO2 + RO2) is 2 parts per trillion (by volume, pptv) at 3,650 m when the background ambient ozone levels are stable, based on a 5 min average of five 30 s amplification cycles and five 30 s termination cycles. This detection limit is a function of several factors but is most seriously degraded when there is large variability in the ambient ozone concentration. This paper describes the instrument design, considers its performance and proposes design improvements. It concludes that the performance of an airborne PERCA in the free troposphere can be superior to that of ground-based instruments when similar sampling frequencies are compared. 相似文献
108.
Gavin M. Jones Berry Brosi Jason M. Evans Isabel G. W. Gottlieb Xingwen Loy Mauricio M. Núñez-Regueiro Holly K. Ober Elizabeth Pienaar Rajeev Pillay Kathryn Pisarello Lora L. Smith Robert J. Fletcher Jr. 《Conservation biology》2022,36(3):e13872
International demand for wood and other forest products continues to grow rapidly, and uncertainties remain about how animal communities will respond to intensifying resource extraction associated with woody bioenergy production. We examined changes in alpha and beta diversity of bats, bees, birds, and reptiles across wood production landscapes in the southeastern United States, a biodiversity hotspot that is one of the principal sources of woody biomass globally. We sampled across a spatial gradient of paired forest land-uses (representing pre and postharvest) that allowed us to evaluate biological community changes resulting from several types of biomass harvest. Short-rotation practices and residue removal following clearcuts were associated with reduced alpha diversity (−14.1 and −13.9 species, respectively) and lower beta diversity (i.e., Jaccard dissimilarity) between land-use pairs (0.46 and 0.50, respectively), whereas midrotation thinning increased alpha (+3.5 species) and beta diversity (0.59). Over the course of a stand rotation in a single location, biomass harvesting generally led to less biodiversity. Cross-taxa responses to resource extraction were poorly predicted by alpha diversity: correlations in responses between taxonomic groups were highly variable (−0.2 to 0.4) with large uncertainties. In contrast, beta diversity patterns were highly consistent and predictable across taxa, where correlations in responses between taxonomic groups were all positive (0.05–0.4) with more narrow uncertainties. Beta diversity may, therefore, be a more reliable and information-rich indicator than alpha diversity in understanding animal community response to landscape change. Patterns in beta diversity were primarily driven by turnover instead of species loss or gain, indicating that wood extraction generates habitats that support different biological communities. 相似文献