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排序方式: 共有58条查询结果,搜索用时 15 毫秒
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Annelieke Hijkoop Chiara C.M.M. Lap Moska Aliasi Eduard J.H. Mulder William L.M. Kramer Hens A.A. Brouwers Robertine van Baren Eva Pajkrt Anton H. van Kaam Caterina M. Bilardo Lourens R. Pistorius Gerard H.A. Visser René M.H. Wijnen Dick Tibboel Gwendolyn T.R. Manten Titia E. Cohen-Overbeek 《黑龙江环境通报》2019,39(13):1204-1212
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Jolanda M H Verspagen Jutta Passarge Klaus D J?hnk Petra M Visser Louis Peperzak Paul Boers Hendrikus J Laanbroek Jef Huisman 《Ecological applications》2006,16(1):313-327
To prevent flooding of the Dutch delta, former estuaries have been impounded by the building of dams and sluices. Some of these water bodies, however, experience major ecological problems. One of the problem areas is the former Volkerak estuary that was turned into a freshwater lake in 1987. From the early 1990s onward, toxic Microcystis blooms dominate the phytoplankton of the lake every summer. Two management strategies have been suggested to suppress these harmful algal blooms: flushing the lake with fresh water or reintroducing saline water into the lake. This study aims at an advance assessment of these strategies through the development of a mechanistic model of the population dynamics of Microcystis. To calibrate the model, we monitored the benthic and pelagic Microcystis populations in the lake during two years. Field samples of Microcystis were incubated in the laboratory to estimate growth and mortality rates as functions of light, temperature, and salinity. Recruitment and sedimentation rates were measured in the lake, using traps, to quantify benthic-pelagic coupling of the Microcystis populations. The model predicts that flushing with fresh water will suppress Microcystis blooms when the current flushing rate is sufficiently increased. Furthermore, the inlet of saline water will suppress Microcystis blooms for salinities exceeding 14 g/L. Both management options are technically feasible. Our study illustrates that quantitative ecological knowledge can be a helpful tool guiding large-scale water management. 相似文献
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Byela?TibesigwaEmail author Martine?Visser Jane?Turpie 《Environment, Development and Sustainability》2017,19(2):607-636
South Africa, a main food exporter in SADC, is characterised by a dual agricultural economy consisting of a well-developed commercial sector and smallholder, often subsistence, farming. Using the Ricardian cross-sectional framework, we examine the impact of climate change on a nationwide sample of crop, horticulture, livestock and mixed commercial farming systems. We find that a simultaneous decrease in precipitation and an increase in temperature will reduce productivity; and that an increase in temperature alone negatively affects farm output more than a decrease in precipitation. One of the most robust findings is the difference in the extent to which different commercial production systems will be impacted. That is, the results indicate that the strongest impact will be amongst specialised commercial crop farming system. In contrast, mixed farming systems appear to be the least vulnerable. This finding is consistent with studies on small-holder farms in sub-Saharan Africa. Hence, it appears that despite the likely benefits derived from economies of scale, commercial farms are, somewhat, equally vulnerable to climate change. Further, a province-wise assessment revealed that areas that already face disadvantageous climatic conditions will become even less productive. Overall, the findings suggest that practicing mixed farming methods will strengthen the resilience of commercial farms to climate change and that access to extensions—insurance and irrigation—is likely to reduce the risks. 相似文献
37.
Cretini KF Visser JM Krauss KW Steyer GD 《Environmental monitoring and assessment》2012,184(4):2389-2403
The Floristic Quality Index (FQI) has been used as a tool for assessing the integrity of plant communities and for assessing
restoration projects in many regions of the USA. Here, we develop a modified FQI (FQImod) for coastal Louisiana wetlands and verify it using 12 years of monitoring data from a coastal restoration project. Plant
species that occur in coastal Louisiana were assigned a coefficient of conservatism (CC) score by a local group with expertise
in Louisiana coastal vegetation. Species percent cover and both native and non-native species were included in the FQImod which was scaled from 0–100. The FQImod scores from the long-term monitoring project demonstrated the utility of this index for assessing wetland condition over
time, including its sensitivity to a hurricane. Ultimately, the FQI developed for coastal Louisiana will be used in conjunction
with other wetland indices (e.g., hydrology and soils) to assess wetland condition coastwide and these indices will aid managers
in coastal restoration and management decisions. 相似文献
38.
Michael Janzen Kaitlyn Visser Darcy Visscher Ian MacLeod Dragomir Vujnovic Ksenija Vujnovic 《Environmental monitoring and assessment》2017,189(10):527
Remote cameras are an increasingly important tool for ecological research. While remote camera traps collect field data with minimal human attention, the images they collect require post-processing and characterization before it can be ecologically and statistically analyzed, requiring the input of substantial time and money from researchers. The need for post-processing is due, in part, to a high incidence of non-target images. We developed a stand-alone semi-automated computer program to aid in image processing, categorization, and data reduction by employing background subtraction and histogram rules. Unlike previous work that uses video as input, our program uses still camera trap images. The program was developed for an ungulate fence crossing project and tested against an image dataset which had been previously processed by a human operator. Our program placed images into categories representing the confidence of a particular sequence of images containing a fence crossing event. This resulted in a reduction of 54.8% of images that required further human operator characterization while retaining 72.6% of the known fence crossing events. This program can provide researchers using remote camera data the ability to reduce the time and cost required for image post-processing and characterization. Further, we discuss how this procedure might be generalized to situations not specifically related to animal use of linear features. 相似文献
39.
Demonstrating trend reversal of groundwater quality in relation to time of recharge determined by 3H/3He 总被引:3,自引:0,他引:3
Visser A Broers HP van der Grift B Bierkens MF 《Environmental pollution (Barking, Essex : 1987)》2007,148(3):797-807
Recent EU legislation is directed to reverse the upward trends in the concentrations of agricultural pollutants in groundwater. However, uncertainty of the groundwater travel time towards the screens of the groundwater quality monitoring networks complicates the demonstration of trend reversal. We investigated whether trend reversal can be demonstrated by relating concentrations of pollutants in groundwater to the time of recharge, instead of the time of sampling. To do so, we used the travel time to monitoring screens in sandy agricultural areas in the Netherlands, determined by (3)H/(3)He groundwater dating. We observed that concentrations of conservative pollutants increased in groundwater recharged before 1985 and decreased after 1990. Thereby, we demonstrated trend reversal of groundwater quality. From this research we concluded that (3)H/(3)He dating can be used to facilitate (re)interpretation of existing groundwater quality data. The presented approach is widely applicable in areas with unconsolidated granular aquifers and large agricultural pressures on groundwater resources. 相似文献
40.
Mieke W. J. C. Jansen Karin Korver-Hakkennes Dik van Leenen Willy Visser Peter A. in 't Veld Christianne J. M. de Groot Juriy W. Wladimiroff 《黑龙江环境通报》2001,21(12):1022-1026
Although the pathophysiology of pre-eclampsia is unknown, several studies have indicated that abnormal placentation early in pregnancy might play a key role. It has recently been suggested that this abnormal placentation may result in transfusion of fetal cells (feto-maternal transfusion) in women with pre-eclampsia. In the present study, fetal nucleated red blood cells were isolated from 20 women with pre-eclampsia and 20 controls using a very efficient magnetic activated cell sorting (MACS) protocol. The number of male cells was determined using two-color fluorescence in situ hybridization (FISH) for X and Y chromosomes. Significantly more XY cells could be detected in women with pre-eclampsia (0.61±1.2 XY cells/ml blood) compared to women with uncomplicated pregnancies (0.02±0.04 XY cells/ml blood) (Mann–Whitney U-test, p<0.001). These results suggest that fetal cell trafficking is enhanced in women with pre-eclampsia, and this finding may contribute to the understanding of the pathophysiology of the disease. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献