排序方式: 共有7条查询结果,搜索用时 15 毫秒
1
1.
The coastline of South Africa is characterized by extensive dune fields which are threatened by development, and thus the
demand of stabilization of drift sand will increase. The non-invasive alien grass speciesAmmophila arenaria is at present the dominant sand stabilizer. Due to its foreign origin and invasiveness in North America its use was criticized
and indigenous sand-binding species would be preferred. The germination requirements of the nativeArctotheca populifolia, Ipomoea pes-caprae. Myrica cordifolia andScaevola plumieri were investigated. The results showed that for all four species the total germination time and germination phase could be
shortened and germination success (number of germinated seeds) improved. The different scarification and stratification treatments
broke the dormancy ofI. pes-caprae, M. cordifolia andS. plumieri, whereas the seeds ofA. populifolia were not dormant. Seeds ofI. pes-caprae andM. cordifolia had induced an innate dormancy, respectively, whereas the type of dormancy in seeds ofS. plumieri dormancy processes remained unknown. 相似文献
2.
Venema Henry D. Schiller Eric J. Bass Brad 《Mitigation and Adaptation Strategies for Global Change》1996,1(2):139-165
The ongoing drought in the Sahel region of West Africa highlights the vulnerability of food-producing systems to climate change
and variability. Adaptation to climate should therefore increase the sustainability of agriculture under a long-term drought.
Progress towards sustainability and adaptation in the the Senegal River Basin is hampered by an existing set of social and
ecological relationships that define the control over the means of production and how people interact with their environment.
These relationships are sensitive to the technological inputs and the administration of food production, or the factor bias
in the different policy alternatives for rural development. One option is based on state-controlled, irrigated plantations
to provide rice (Oryza) for the capital, Dakar. This policy emphasizes a top-down management approach, mechanized agriculture and a reliance on
external inputs which strengthens the relationships introduced during the colonial period.
A time series decomposition of the annual flow in the Senegal River at Bakel in Senegal suggests that water resources availability
has been substantially curtailed since 1960, and a review of the water resources budget or availability in the basin suggests
that this policy's food production system is not sustainable under the current climate of the basin. Under these conditions,
this program is exacerbating existing problems of landscape degradation and desertification, which increases rural poverty.
A natural resource management policy offers two adaptation strategies that favour decentralized management and a reduction
of external inputs. The first alternative, “Les Perimetres Irrigués”, emphasizes village-scale irrigation, low water consumption
cereal crops and traditional socio-political structures. The second alternative emphasizes farm-level irrigation and agro-forestry
projects to redress the primary effects of desertification. 相似文献
3.
Williams Paula Alessa Lilian Abatzoglou John T. Kliskey Andrew Witmer Frank Lee Olivia Trammell Jamie Beaujean Grace Venema Rieken 《Regional Environmental Change》2018,18(2):547-559
Regional Environmental Change - Many papers have addressed the differing approaches to observation by scientists collecting instrumented data and by community or local knowledge-based observations.... 相似文献
4.
5.
The water quality management of The Netherlands' part of the North Sea (57 000 km2 continental shelf of which 7600 km2 is territorial sea to 12 miles) and the Wadden Sea (a wetland area behind the northern coastal islands), is described on the basis of recent scientific studies and governmental policy documents. The links with international conventions and treaties are mentioned. The overall water quality in these areas has significantly deteriorated over the last century, notably since the post-war industrial revival, due to a great number of emissions of heavy metals and organochlorine substances. A dramatic decline of seals and porpoises has occurred. However, over the last few years some emissions have been reduced. A national ecological research programme for the North Sea is developing. Monitoring is concentrated on levels of pollutants as well as on effects upon biota. Baseline standards are now being developed as references for further action against pollution. If the recent trend towards improvement is to continue, it requires that the increased economic activities (notably the mining of oil and gas, petrochemical production, and incineration and dumping of chemical wastes) be kept sufficiently under control. A need is felt for a continued rational harmonization and planning of all activities on the North Sea. An even more stringent planning is required for the Wadden Sea which is now an international nature reserve under the Wetland Convention and is eligible for designation as a Biosphere Reserve under the UNESCO-MAB-programme. The river Rhine as greatest polluter of the North Sea and Wadden Sea urgently needs a clean-up. 相似文献
6.
Monitoring large (underwater) surfaces, with rapidly varying composition, requires a sampling density which exceeds the capabilities of standard techniques. These techniques involve sample collection and a number of treatments and measurements in the laboratory; both steps are laborious, tedious and costly. This paper presents an in situ method in which a detector system is trailed over the surface and measures continuously the gamma rays emitted by the natural radionuclides in the sediment. Since each sediment component has its own characteristic set of activity-concentration values (radiometric fingerprint), the composition of the sediment can be deduced quantitatively. This paper shows the application of this technique for monitoring the dispersal of dredge spoil from Rotterdam harbour, dumped in the North Sea. In addition to a qualitative picture of dredge spoil dispersal, a mass balance equation has been used to quantitatively assess the dredge spoil transport with time. 相似文献
7.
1