Search Results - (Author, Cooperation:M. Scheffer)

2011-07-19

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Animals ; Biodiversity ; *Ecosystem ; *Extinction, Biological ; Feeding Behavior ; *Food Chain ; Humans ; Introduced Species ; Population Dynamics ; Predatory Behavior

2011-10-15

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Africa ; Australia ; *Ecosystem ; Rain ; South America ; *Trees ; *Tropical Climate

2011-12-27

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Biomass ; Cyanobacteria/growth & development/*radiation effects ; Feedback/*radiation effects ; Kinetics ; *Light ; *Models, Biological ; Photosynthesis/radiation effects ; Stochastic Processes

2012-11-20

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

China ; Diatoms/isolation & purification ; *Eutrophication ; Forecasting/*methods ; Geologic Sediments/analysis/chemistry ; History, 19th Century ; History, 20th Century ; History, 21st Century ; *Lakes/chemistry ; Phosphorus/analysis ; Time Factors

2015-03-21

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Animals ; *Conservation of Natural Resources ; *Coral Reefs ; *Forests ; *Greenhouse Effect ; *Wetlands

2016-02-26

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2016-04-16

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2013-06-28

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

*Eutrophication ; Forecasting/*methods ; *Lakes

2012-10-23

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Animals ; *Forecasting ; Humans ; Risk Assessment/*statistics & numerical data

2018-05-03

American Association for the Advancement of Science (AAAS)

2375-2548

Natural Sciences in General

2018-12-21

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Geosciences

Computer Science

Medicine

Natural Sciences in General

Physics

1365-2427

Blackwell Publishing Journal Backfiles 1879-2005

Biology

SUMMARY 1. We analysed the vegetation structure of 215 lakes in the flood plain of the river Lower Rhine in relation to environmental variables related to hydrological connectivity, lake morphometry, lake age and land use on adjacent land.2. The frequency distribution of the cover of submerged macrophytes was not normal, implying that submerged macrophytes in any one lake were either scarce or abundant.3. We observed clear water lakes with submerged macrophyte dominance over a wide range of total P concentration (0.020–0.40 mg total P L−1).4. Multiple logistic regression indicated that the probability of dominance by submerged macrophytes decreased markedly with the surface area, depth and age of the lakes. The surface area effect occurred independently of the depth. Further, there was a negative relationship between submerged macrophyte dominance and the long-term annual duration of inundation by the river.5. Nymphaeid cover showed a distinct optimum with respect to mean lake depth, being almost absent in lakes shallower than 0.5 m. In contrast to what was found for submerged plants, the probability of occurrence of nymphaeids increased with lake age.6. The probability of helophyte occurrence increased with lake age, and decreased with the presence of trees, cattle grazing, surface area, use of manure and mean lake depth.7. In all cases the critical level of one factor (e.g. mean lake depth) depended on other factors (e.g. surface area or age of lake). Thus, in the present study, small lakes tended to remain dominated by submerged macrophytes up to a greater depth than large lakes, and helophytes colonised smaller lakes in an earlier phase.8. The effect of inundation by the river was modest. This could be because most of our lakes are rarely inundated during the growing season and experience only moderate current velocities while flooded.9. The results have practical implications for future management of flood plains for conservation purposes. In new water bodies, macrophyte domination will be promoted if many small shallow lakes, rather than few large deep ones, are excavated.

Electronic Resource

1365-2427

Blackwell Publishing Journal Backfiles 1879-2005

Biology

SUMMARY 1. We sampled a set of 93 lakes situated in the floodplains of the lower River Rhine in search for morphometric and other factors that explain their variation in clarity.2. Lakes with a drop in summer water level were less turbid at the time of sampling, mainly because of a lower concentration of inorganic suspended solids (ISS).3. We also found that older lakes were more turbid than younger lakes and that this was largely because of an increase in phytoplankton.4. Water clarity was positively related to lake depth and the presence of vegetation.5. Model calculations indicated that the underwater light climate was strongly affected by chlorophyll and ISS, the latter being the dominant factor affecting Secchi depth. Dissolved organic carbon (DOC) was less important.6. The high concentration of ISS suggests that intensive resuspension occurs in most of the lakes. Using a simple wave model, and assuming that vegetation protects sediments against resuspension, we could eliminate wind resuspension as an important process in 90% of the lakes, leaving resuspension by benthivorous fish as probably the most important factor determining transparency.7. Chlorophyll a concentration showed a strong positive correlation to ISS concentration, suggesting that resuspension may also have a positive effect on phytoplankton biomass in these lakes.8. In conclusion, in-lake processes, rather than river dynamics, seem to be driving the turbidity of floodplain lakes along the lower River Rhine.

Electronic Resource

0005-2760

(Human) ; Endothelial cell ; LDL modification ; Lipoprotein

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Chemistry and Pharmacology

Medicine

Physics

Electronic Resource

0304-3770

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Electronic Resource

0040-5809

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Electronic Resource

0169-2046

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Architecture, Civil Engineering, Surveying

Geography

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Electronic Resource

1432-1246

Hand-arm vibration ; Cold ; Combined stress ; Peripheral circulation ; Skin temperature

Springer Online Journal Archives 1860-2000

Medicine

Summary Under laboratory conditions 14 healthy male subjects were exposed to hand-arm vibration (ahzw = 6.3 m/s2) at different air temperatures (5°, 12°, 18° and 25°C). Static load (grip force 15 N, push force 40 N) was kept constant. Finger tip temperature as an indirect criterion of the peripheral blood circulation was measured. As expected, low air temperatures (5°, 12° and 18°C) cause a strong decrease of skin temperature. Under additional stress of vibration connected with static load, a further decrease of the mean skin temperature was noted. At this, static load proved to have a predominant influence on the acute diminution of skin temperature. The individual reaction to the stressors varied considerably. Field tests during practical work with a chain saw at low air temperatures showed results similar to those of the laboratory tests. The protective effect of a grip heating system could be demonstrated.

Electronic Resource

1432-1912

Vasodilation ; Coronary blood flow ; Myocardial O2-consumption ; Regional myocardial wall function ; Dihydropyridine derivative ; Pig

Springer Online Journal Archives 1860-2000

Medicine

Summary The cardiovascular effects of intravenous (1.5–10 nmol · kg−1) and intracoronary (50 nmol) administration of felodipine, 4-(2,3-dichlorophenyl)-1,4-dihydro-2,6-dimethyl-3-ethoxycarbonyl-5-methoxycarbonylpyridine, were studied in anaesthetized pigs. Following intravenous administration dose-dependent decreases were observed in left ventricular systolic blood pressure (up to 30%) and in the resistances of the systemic (up to 40%) and coronary vascular beds (up to 45%), whereas heart rate, cardiac output, myocardial contractility (regional and global), and left ventricular end-diastolic pressure were minimally affected. Myocardial blood flow increased independently of the dose (20%), while the coronary venous O2-content more than doubled. The concomitant decrease in myocardial O2-consumption (up to 30%) was dose-dependent in the range from 1.5–6.75 nmol·kg−1. Intracoronary administration of 50 nmol had only minor effects on global and regional myocardial performance but produced a doubling of the coronary blood flow which was accompanied by a 70% decrease in myocardial O2-extraction. O2-consumption decreased considerably more (35%) than after intravenous administration in spite of the minimal decrease in O2-demand (7%). We conclude that felodipine dilates both systemic and coronary blood vessels. Although the reduction in myocardial O2-consumption is primarily caused by the reduction in afterload, a direct effect on myocardial metabolism can also be involved.

Electronic Resource

1573-5125

model ; fish ; vegetation ; eutrophication ; stability

Springer Online Journal Archives 1860-2000

Biology

Abstract A simple mathematical model was constructed, describing the relationships between pike, bream, aquatic macrophytes and the nutrient loading of shallow lakes. The model is analyzed with the use of zero-isoclines. It is concluded that, over a certain range of nutrient concentrations, the ecological relations incorporated in the model can give rise to the existence of two alternative stable equilibria;viz. a turbid bream-dominated one, and a clear state in which pike and aquatic vegetation are abundant. Under oligotrophic conditions, the clear-water state represents the only stable equilibrium; however, at high nutrient levels, the clear state is absent, or only locally stable. The response of the model to both increase and decrease of the nutrient level is characterised by hysteresis. The results indicate that manipulation of fish densities as a measure to improve water quality is only likely to produce long-term results when the nutrient level is below a certain threshold.

Electronic Resource