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61.
Green sea urchins, Strongylocentrotus droebachiensis OF Müller, collected off the coast of New Hampshire, USA, in late February 1995, were brought into the laboratory and fed
an artificial diet ad libitum, and subjected to a photoperiod advanced by 4 months. During this study, temperatures and salinities
for experimental urchins mirrored those recorded at the collection site. We examined the effects of changes in feeding regime
and photoperiod on gametogenesis and compared the experimental urchins with those from the source population. During the 7-month
period, experimental urchins showed no detectable changes in mean test height or diameter. Experimental urchins had a significantly
higher gonad index (GI) in March, April and May (18 ± 6%) compared with field urchins in March (11 ± 3%). Subsequently, experimental
urchins had a mean monthly GI of 25 to 30%, while the mean GI for field urchins was 11 to 13%. Gonial cell mitosis and gametogenesis
occurred earlier in experimental male and female urchins compared with field urchins. Stereological and histological observations
and stage–frequency data showed that the ovaries of experimental urchins were large because of the accelerated development
of nutritive phagocytes, the volume fraction (V
v) of which was 89 to 90% of the gonad, while new vitellogenic primary oocytes occupied <1% V
v. In males, stereological and histological observations and stage–frequency data suggested a mobilization of materials from
the nutritive phagocytes beginning between June and August, i.e. earlier than in females, and, by September, new gametes occupied
a V
v of 49 ± 3% of the testes. Oocyte size–frequency distributions demonstrated that most primary oocytes were <80 μm in diameter
between March and September, suggesting that cold temperatures may be needed for completion of vitellogenesis. We describe
changes in the two principal cell types in the germinal epithelium of urchin gonads and indicate how knowledge of their population
dynamics may be useful in aquaculture applications.
Received: 21 February 1997 / Accepted: 3 June 1998 相似文献
62.
63.
The effects of soil amendments on heavy metal bioavailability in two contaminated Mediterranean soils 总被引:19,自引:0,他引:19
Walker DJ Clemente R Roig A Bernal MP 《Environmental pollution (Barking, Essex : 1987)》2003,122(2):303-312
Two heavy metal contaminated calcareous soils from the Mediterranean region of Spain were studied. One soil, from the province of Murcia, was characterised by very high total levels of Pb (1572 mg kg(-1)) and Zn (2602 mg kg(-1)), whilst the second, from Valencia, had elevated concentrations of Cu (72 mg kg(-1)) and Pb (190 mg kg(-1)). The effects of two contrasting organic amendments (fresh manure and mature compost) and the chelate ethylenediaminetetraacetic acid (EDTA) on soil fractionation of Cu, Fe, Mn, Pb and Zn, their uptake by plants and plant growth were determined. For Murcia soil, Brassica juncea (L.) Czern. was grown first, followed by radish (Raphanus sativus L.). For Valencia soil, Beta maritima L. was followed by radish. Bioavailability of metals was expressed in terms of concentrations extractable with 0.1 M CaCl2 or diethylenetriaminepentaacetic acid (DTPA). In the Murcia soil, heavy metal bioavailability was decreased more greatly by manure than by the highly-humified compost. EDTA (2 mmol kg(-1) soil) had only a limited effect on metal uptake by plants. The metal-solubilising effect of EDTA was shorter-lived in the less contaminated, more highly calcareous Valencia soil. When correlation coefficients were calculated for plant tissue and bioavailable metals, the clearest relationships were for Beta maritima and radish. 相似文献
64.
There is critical need for a practical indicator to assess the potential for phosphorus (P) movement from a given site to surface waters, either via surface runoff or subsurface drainage. The degree of phosphorus saturation (DPS), which relates a measure of P already adsorbed by a soil to its P adsorption capacity, could be a good indicator of that soil's P release capability. Our primary objective was to find a suitable analytical protocol for determining DPS and to examine the possibility of defining a threshold DPS value for Florida's sandy soils. Four farmer-owned dairy sprayfields were selected within the Suwannee River basin and soil profiles were randomly obtained from each site, as well as from adjacent unimpacted sites. The soil samples were divided either by horizon or depth, and DPS was determined for each soil sample using ammonium-oxalate (DPS(Ox)), Mehlich-1 (DPS(M1)), and Mehlich-3 (DPS(M3)) extracts. All methods of DPS calculations were linearly related to one another (r2 > 0.94). Relationships between water-soluble P and DPS indicate that the respective change points are: DPS(Ox) = 20%, DPS(M1) = 20%, and DPS(M3) = 16%. These relationships include samples from Ap, E, and Bt horizons, and various combinations thereof, suggesting that DPS values can be used as predictors of P loss from a soil irrespective of the depth of the soil within a profile. Taking into consideration the change points, confidence intervals, agronomic soil test values, and DPS values from other studies, we suggest replacing Mehlich-1 P values in the Florida P Index with the three DPS categories (DPS(M1) = <30, 30-60, and >60%) to assign different P loss ratings in the P Index. 相似文献
65.
We used genotypic data from three highly polymorphic microsatellite loci (two autosomal and one sex-linked) to examine micro-spatial
and temporal arrangements of genetic paternity for more than 1,500 embryos housed along 12 egg-case strings of the knobbed
whelk, Busycon carica. Multiple paternity proved to be the norm in these single-dam families, with genetic contributions of several sires (at least
3.5 on average) being represented among embryos within individual egg capsules as well as along the string. Two strings were
studied in much greater detail; five and seven fathers were identified, none of which was among the several males found in
consort with the female at her time of egg-laying. Each deduced sire had fathered roughly constant proportions of embryos
along most of the string, but those proportions differed consistently among fathers. A few significant paternity shifts at
specifiable positions along an egg-case string were also observed. Although the precise physical mechanisms inside a female
whelk’s reproductive tract remain unknown, our genetic findings indicate that successive fertilization events (and/or depositions
of zygotes into egg capsules) normally occur as near-random draws from a well-but-not-perfectly blended pool of gametes (or
zygotes) stemming from stored ejaculates, perhaps in different titers, of a dam’s several mates. 相似文献
66.
William R. Walker Carol J. Haley Phyllis Bridgeman Stephen H. Goldstein 《Environmental management》1991,15(3):441-449
A literature search and survey of Virginia, USA, campgrounds with RV pump-out stations were used to determine whether boat
holding-tank deodorant chemicals would have deleterious effects on marina septic systems or package treatment plants. Laboratory
studies reported in the literature indicate that these chemical additives could affect septic system function in three ways:
(1) active ingredients in the additives can impair sewage degradation in septic tanks, causing sludge buildup and overflow
of solids into the drainfield, (2) additive chemicals might enter the drainfield and, in high enough concentrations, reduce
the drainfield's ability to degrade waste, or (3) toxic additive chemicals might migrate from the drainfield to ground or
surface water. Laboratory studies also show that some ingredients added to holding tanks interfere with functioning of activated
sludge treatment process. Experience in the field and in other laboratory studies suggests that factors such as dilution of
treated waste with untreated waste and the characteristics of the sewage to be treated can reduce the possibility of damage
to septic and activated sludge systems. The campground owners surveyed indicated that they have few problems with their septic
systems in spite of the presence of chemical additives in the RV waste. However, most of them practice good septic system
maintenance and have devised other means of ensuring that their systems function efficiently. In addition, the survey indicates
that most Virginia campgrounds get only seasonal use (as would marinas in Virginia), allowing their systems to recover between
peak seasons. 相似文献
67.
恢复力与可持续发展:在瞬息万变的世界中增强适应能力 总被引:27,自引:0,他引:27
Carl Folke Steve Carpenter Thomas Elmqvist Lance Gunderson C.S. Holling Brian Walker 《Ambio-人类环境杂志》2002,31(5):437-440
由于在以往的自然资源政策上逐渐暴露出了两个带根本性的错误,人们开始意识到在环境管理理论和实践方面需要进行一场全球性的重大改革.第一个错误是毫无保留地假定生态系统对人类利用所作出的反应是呈线性关系、是可以预测和控制的.第二个错误是认定人类社会与天然系统可以分别对待,不必联系在一起进行考虑.然而,从世界各地收集到的证据表明,天然系统和人类社会系统是以非线性方式运行的、在其动态运行过程中均有其显著的极限,而且,人类社会与生态系统表现为一种紧密相联的、复杂的且不断演变的综合系统.本文是代表瑞典政府环境咨询委员会编写的一份报告的摘要,这份报告是作为向2002年8月26日~9月4日在南非约翰内斯堡召开的可持续发展世界首脑会议献礼的论文而撰写的.从概念上说,恢复力是一种能缓冲变化所带来的影响、学习知识和求得发展的能力,我们将它作为在一个纷纭复杂、快速变化的世界中,是否真正懂得如何维护和提高适应能力的一种参照标准来使用.在社会、生态综合系统中,有两种有用的工具可用来提高恢复力,一种是结构严谨的工作方案,另一种是积极的适应力管理.这两种工具都需要而且有助于形成这样一种社会环境:具有灵活开放的组织机构和多层次的监管体制,允许学习适应力方面的知识和提高适应力但又不妨碍对未来的发展作出选择. 相似文献
68.
应对不确定性:呼吁建立新的科学政策论坛 总被引:4,自引:1,他引:4
Ann Kinzig David starrett Kenneth Arrow Sara Aniyar Bert Bolin Partha Dasgupta Paul Ehrlich Carl Folke Michael Hanemann Geoff Heal Michael Hoel AnnMari Jansson Bengt-Owe Jansson Nils Kautsky Simon Levin Jane Lubchenco Karl-Gran Miler Stephen W.Pacala Stephen H.Schneider Domenico Siniscalco Brian Walker 《Ambio-人类环境杂志》2003,32(5):330-335
科学界和政策界具有不同的目标,这就自然导致了对构成某种变化或现象的"检验"标准的差异,以及用不同的方法去描述不确定性和风险的持性及传达不确定性和风险.这些差异可能损害科学家、决策者和公众之间的有效沟通,同时也限制了科学家所愿意研究的社会紧迫问题的类型.本文主要回顾了一系列处理不确定性问题的方法,阐述了当科学和政策不能很好协调时所可能引起的一些错误.并在此基础上,特别针对解决不确定性问题提出了一些具体建议,包括重构科学规范,建立由科学、政策两方面领导广泛参加的科学政策论坛. 相似文献
69.
Walker TR Crittenden PD Young SD 《Environmental pollution (Barking, Essex : 1987)》2003,125(3):401-412
The chemical composition of snow and terricolous lichens was determined along transects through the Subarctic towns of Vorkuta (130 km west-east), Inta (240 km south-north) and Usinsk (140 km, southwest-northeast) in the Usa river basin, northeast European Russia. Evidence of pollution gradients was found on two spatial scales. First, on the Inta transect, northward decreases in concentrations of N in the lichen Cladonia stellaris (from 0.57 mmol N g(-1) at 90 km south to 0.43 mmol N g(-1) at 130 km north of Inta) and winter deposition of non-sea salt sulphate (from 29.3 to 12.8 mol ha(-1) at 90 km south and 110 km north of Inta, respectively) were attributed to long range transport of N and S from lower latitudes. Second, increased ionic content (SO42-, Ca2+, K+) and pH of snow, and modified N concentration and the concentration ratios K+:Mg2+ and K+: (Mg2++Ca2+) in lichens (Cladonia arbuscula and Flavocetraria cucullata) within ca. 25-40 km of Vorkuta and Inta were largely attributed to local deposition of alkaline coal ash. Total sulphate concentrations in snow varied from ca. 5 micromol l(-1) at remote sites to ca. 19 micromol l(-1) near Vorkuta. Nitrate concentration in snow (typically ca. 9 micromol l(-1)) did not vary with proximity to perceived pollution sources. 相似文献
70.
Kinzig A Starrett D Arrow K Aniyar S Bolin B Dasgupta P Ehrlich P Folke C Hanemann M Heal G Hoel M Jansson A Jansson BO Kautsky N Levin S Lubchenco J Mäler KG Pacala SW Schneider SH Siniscalco D Walker B 《Ambio》2003,32(5):330-335
The scientific and policy worlds have different goals, which can lead to different standards for what constitutes "proof" of a change or phenomena, and different approaches for characterizing and conveying uncertainty and risk. These differences can compromise effective communication among scientists, policymakers, and the public, and constrain the types of socially compelling questions scientists are willing to address. In this paper, we review a set of approaches for dealing with uncertainty, and illustrate some of the errors that arise when science and policy fail to coordinate correctly. We offer a set of recommendations, including restructuring of science curricula and establishment of science-policy forums populated by leaders in both arenas, and specifically constituted to address problems of uncertainty. 相似文献