长江口泥螺的种群特征及其生态学意义

20 0 0年 5月中、下旬对长江口南汇边滩泥螺种群进行了调查和统计分析 ,结果表明 :泥螺种群呈聚集型分布 ;泥螺种群密度分别为 2 1.2 /m2 和 32 .8/m2 ;生物量分别为 2 5.60g/m2 WW和4 4 .89g/m2 WW或 2 .0 5g/m2 DW和 3.4 9g/m2 DW ;平均壳高分别为 1.19cm和 1.34cm ,壳高日生长量为 98.7μm ,月生长率达 2 4 .9% ;种群分别以壳高 1.0 0～ 1.2 0cm ( 4 7.0 6% )和 1.2 0～ 1.4 0cm( 4 1.90 % )的种群占绝对优势 ;性成熟个体比例分别占 32 .4 %和 78.3% ,整个泥螺种群处于生长期向繁殖期过渡阶段。壳高 (H)与壳宽 (B)、湿重 (WW )、存水量 (F1)、相对存水量 (F2 )与WW之间回归方程分别为 :H =0 .180 4 3+1.2 750 B、WW =0 .4 4 75 H2 .512 8、F1=0 .760 2 WW -0 .4 661、F2 =34 .0 2 1 WW - 8.666,相关显著。平均肥满度 ( 0 )和鲜出肉率 (PF)分别为 2 99.2 7%和 62 .15% ,它们与 WW呈负相关 ,回归方程分别为 :0 =34 7.0 8- 38.11 WW和PF =10 5.74 -34 .72 WW ,前者相关性较差 ,后者显著。 2 0 0 0年 5月初泥螺旺发与水动力条件、营养盐累积及饵料密切相关 ;目前的人工捕捞水平不会导致泥螺资源种群的数量下降 ,反而有助于发挥泥螺种群的环境净化功能。     

佛山大沥镇发展再生金属行业的必要性及有利条件分析

再生资源行业是21世纪世界性的朝阳产业,其“低开采,高利用,低投入,高回报”的特点及我国明朗的政策,该行业市场前景广阔。大沥是我国唯一的“再生金属物流加工基地”,大沥宽松的经营环境、优越的区位条件、闻名海内外的区域品牌、稳定的进货渠道、快捷的信息来源,为大沥再生金属行业健康、可持续发展创造了有利条件。     

儒家思想中的“诚“、“信“及其现实意义

古老的儒家思想中,"诚"和"信"是一对包含不同内涵及思维过程的互生词,代表了不同的思维和认识层面.搞清楚这一点,对于我们在全社会领域倡导诚信,推动精神文明建设,会在方法和措施上有一定的启示和帮助.     

重质燃料油中主要芳烃在自然条件下的风化规律

文章在自然环境条件下对重质燃料油进行了风化模拟实验,采用气质(GC/MS)联用仪分析了重质燃料油中主要芳烃组分及其变化。结果表明:该重质燃料油中主要芳烃为苯类(C_nB)、萘(C_nN)类、菲(C_nP)类、二苯并噻吩(C_nD)类;在自然条件下,经过1周的风化,C_nB和C_0N完全损失;经过6周风化,C_1N完全损失;经过12周的风化,C_2N完全损失,3环的PAHs无明显变化。同时指出C_2D/C_2P和C_3D/C_3P的比值以及烷基化二苯并噻吩的同分异构体分布可用于区别其它油品,并且风化后变化不大,仍可较好地用于油品的鉴定。     

A cost analysis technique for research management and design

A classic research approach is to optimize experimental design and available resources. However, that approach does not guarantee that results will be useful. This article takes the view that research should not be undertaken unless there is assurance that final results will be significant to a level specified before any work is begun. Given that assurance, the relationship between cost and statistical significance is explored, a new approach to optimization s developed, and the use of models in research design is considered.     

A Critical Appraisal of Field Evidence From A Regional Survey for Acid Deposition Effects On Scottish Moorland Podzols

Samples have been collected from major horizons of 34 podzol profiles distributed throughout Scotland, all developed from granite or granitic tills and under Calluna moorland. the pH in water and calcium chloride pastes, exchangeable cations and cation exchange capacity, and extractable aluminium of the soils collected have been measured, and the results studied in relation to reported atmospheric deposition of H⁺, non-marine sulphur and nitrate. for all horizons, significant positive correlations were found between soil pH and rainfall mean pH, as might be expected when the critical load of H⁺ deposition is exceeded. Acidifying pollutant deposition also apparently increased soil extractable aluminium concentrations in the B and C horizons. However, exchangeable base cation concentrations tended to increase, rather than decrease, with increasing precipitation acidity. This effect was attributed to increases in biogeochemical cycling of base cations, increases in leaching inputs of base cations from overlying A/E horizon soils, and increases in the inputs of base cations leached from upslope. the results suggest that the simple steady state mass approach to the quantification of critical loads, as often applied, may be an oversimplification.     

Studies on enhanced degradable plastics. II. Weathering of enhanced photodegradable polyethylenes under marine and freshwater floating exposure

The weatherability of three types of enhanced photodegradable polyethylene films and corresponding control films were studied under outdoor and marine floating conditions at two exposure sites. Progress of weathering was monitored using tensile elongation at break. In general, both the enhanced-degradable plastics and the corresponding controls degraded slower in marine exposure than in outdoor exposure. This is attributed to the lower sample temperatures (compared to samples exposed outdoors) and to shielding from light afforded by surface fouling in samples exposed floating in sea water. Enhanced-photodegradable polyethylenes disintegrated faster than the control samples in the case of both outdoor and marine exposures. The improvement obtained in marine exposures was greater than that for outdoor exposure of corresponding sample types. This is due to the extremely slow rates of disintegration of control films under marine floating conditions.     

Studies on enhanced degradable plastics. III. The effect of weathering of polyethylene and (ethylene-carbon monoxide) copolymers on moisture and carbon dioxide permeability

Two enhanced-photodegradable polyethylenes were studied to determine the effect of photooxidative degradation upon transport properties. Water vapor permeability of LDPE films containing metal compound prooxidants, weathered to different extents under outdoor exposure was studied. A film made of LDPE blended with 20 wt% of polycaprolactone was also examined to determine if biodegradation over a 40-day period resulted in a measurable change in its water vapor transport characteristics. A gravimetric technique was used to study the effects of outdoor and weather-ometer exposures on the permeability of carbon dioxide of both the LDPE film and (ethylene-carbon monoxide) copolymer films. Generally, photooxidative degradation was seen to be accompanied by a change in transport characteristics of the polymer films.     

The significance of environmental impacts: an exploration of the concept

Since environmental impact assessment (EIA) is concerned primarily withsignificant environmental impacts, the concept of impact significance deserves to be defined and applied rigorously. In this article use of the term over the past 15 years in EIA documentation is reviewed. Some recent attempts at elucidating the concept are summarized. Four perspectives on impact significance that emerged from a series of workshops on the ecological basis for EIA are presented. These perspectives include (a) statistical (related to problems of isolating project-induced changes from natural variation), (b) ecological (related to the importance of project-induced changes from a purely ecological perspective), (c) social (related to the acceptability of project-induced changes in important environmental attributes), and (d) project (related to whether project-induced changes will indeed influence project decision making). The following synthesis is proposed: Any exercise in judging the significance of an environmental impact should thoroughly consider (a) the importance of the environmental attribute in question to project decision makers, (2) the distribution of change in time and space, (c) the magnitude of change, and (d) the reliability with which change has been predicted or measured. The implications of considering these factors are discussed.     

CHEMICAL COMPOSITION OF SOFTWATER FLORIDA LAKES AND THEIR SENSITIVITY TO ACID PRECIPITATION1

ABSTRACT: Based on alkalinity data for 596 lakes, 31 percent of Florida's 7300 lakes have < 100 μeq/l alkalinity and are sensitive to acid depostion. More than two-thirds of the lakes in 12 northern Florida counties fit this criterion. Increasing aluminum and decreasing nutrient and chlorophyll a concentrations were observed with decressing pH in a survery of 20 softwater lakes. Maximum measured aluminum values (100-150 μg/L) are below levels asociated with fish toxicity. Factor analysis showed that lake chemistry was related to three principal factors, representing three major processes: watershed weathering, acidification, and nutrient inputs. An acidification index defined as the difference between excess SO₄^2- and excess (Ca²⁺+Mg²⁺) accounted for 74 percent of the variance in lake pH. Comparison of historical (late 1950a) and present data for pH, alkalinity, and excess SO₄^2- indicated loss of alkalinity (>25 μeq/L) and increase in excess SO₄^2- (16-34 μeq/L) in several softwater lakes.