Timing of eclosion in marine insects on Mediterranean shores – studies on Clunio mediterraneus, C. ponticus and Thalassomyia frauenfeldi (Diptera: Chironomidae)

In three Clunio stocks, two from the Mediterranean Sea (Banyuls, Rovinj) and one from the Black Sea (Sosopol), an identical circasemilunar eclosion pattern in combination with a circadian eclosion time of day was evoked in breeding experiments under an artificial moonlight cycle (four nights of 0.3 lux every 30 d, 12 h light:12 h dark). The eclosion peaks occurred on days with artificial moonlight and approximately 2 weeks later, and with regard to the time of day between mid-night and lights-on. In spite of the weak tidal amplitudes on Mediterranean shores, extreme low water levels occur when a nocturnal low-water time coincides on days around full and new moon (spring-tide situation) with winds from land to sea. Field observations at Banyuls and Rovinj agree with the experimental results. In contrast to Clunio spp. adults (life span only a few hours), Thalassomyia frauenfeldi adults (life span up to several days in the laboratory) demonstrated an unsynchronized eclosion pattern in the experiments (no lunar concentration, wide diurnal eclosion gate). Although inhabiting the same intertidal area, T. frauenfeldi walking on exposed intertidal substrates can delay egg-deposition for days and can probably wait for favorable low water levels. The taxonomical status of European Clunio populations is reviewed; minute morphological distinctions are presented for C. mediterraneus in the otherwise morphologically uniform, but ecophysiologically differentiated genus. Received: 15 May 1997 / Accepted: 16 June 1997     

Land Use-related Chemical Composition of Street Sediments in Beijing

BACKGROUND: More than 10 million people are currently living in Beijing. This city faces severe anthropogenic air pollution caused by an intense vehicle increase (11% per year in China), coal combusting power plants, heavy industry, huge numbers of household and restaurant cookers, and domestic heating stoves. Additionally, each year dust storms are carrying particulate matter from the deserts of Gobi and Takla Makan towards Beijing, especially in spring. Other geogenic sources of particulate matter which contribute to the air pollution are bare soils, coal heaps and construction sites occurring in and around Beijing. Streets function as receptor surfaces for atmospheric dusts. Thus, street sediments consist of particles of different chemical compositions from many different sources, such as traffic, road side soils and industry. METHODS: Distributions and concentrations of various chemical elements in street sediments were investigated along a rural-urban transect in Beijing, China. Chemical elements were determined with X-ray fluorescence analysis. Factor analysis was used to extract most important element sources contributing to particulate pollution along a main arterial route of the Chinese capital. RESULTS AND DISCUSSION: The statistical evaluation of the data by factor analysis identifies three main anthropogenic sources responsible for the contamination of Beijing street sediments. The first source is a steel factory in the western part of Beijing. From this source, Mn, Fe, and Ti were emitted into the atmosphere through chimneys and by wind from coal heaps used as the primary energy source for the factory. The second source is a combination of traffic, domestic heating and some small factories in the center of Beijing discharging Cu, Pb, Zn and Sn. Calcium and Cr characterize a third anthropogenic element source of construction materials such as concrete and mortar. Beside the anthropogenic contamination, some elements like Y, Zr, Nb, Ce, and Rb are mainly derived from natural soils and from the deserts. This is supported by mineral phase analysis, which showed a clear imprint of material in road dusts coming from the West-China deserts. CONCLUSIONS: Our results clearly show that the chemical composition of urban road dusts can be used to identify distinct sources responsible for their contamination. The study demonstrates that the chemistry of road dusts is an important monitor to assess the contamination in the urban environment. Chemical composition of street sediments in Beijing comprises the information of different sources of atmospheric particles. RECOMMENDATIONS AND OUTLOOK: This study is only a small contribution to the understanding of substance fluxes related to Beijing's dust. More effort is required to assess Beijing's dust fluxes, since the dust harms the living quality of the inhabitants. Especially the measurable superimposing of long scale transported dust from dry regions with the anthropogenic polluted urban dust makes investigations of Beijing's dust scientifically valuable.     

Input of trichloroacetic acid into the vegetation of various climate zones--measurements on several continents

Trichloroacetic acid (TCA, CCl(3)COOH) is a phytotoxic chemical. Although TCA salts and derivates were once used as herbicides to combat perennial grasses and weeds, they have since been banned because of their indiscriminate herbicidal effects on woody plant species. However, TCA can also be formed in the atmosphere. For instance, the high-volatile C(2)-chlorohydrocarbons tetrachloroethene (TECE, C(2)Cl(4)) and 1,1,1-trichloroethane (TCE, CCl(3)CH(3)) can react under oxidative conditions in the atmosphere to form TCA and other substances. The ongoing industrialisation of Southeast Asia, South Africa and South America means that use of TECE as solvents in the metal and textile industries of these regions in the southern hemisphere can be expected to rise. The increasing emissions of this substance--together with the rise in the atmospheric oxidation potential caused by urban activities, slash and burn agriculture and forest fires in the southern hemisphere--could lead to a greater input/formation of TCA in the vegetation located in the lee of these emission sources. By means of biomonitoring studies, the input/formation of TCA in vegetation was detected at various locations in South America, North America, Africa, and Europe.     

Effects of zooplankton diel vertical migration on a phytoplankton community: A scenario analysis of the underlying mechanisms

A mechanistic model was applied to study the influence of diurnal vertical migration (DVM) of planktonic crustaceans on the succession and composition of the phytoplankton community. While zooplankton was restricted to only one functional group, the phytoplankton community was divided into two functional groups which are distinguished by their maximum growth rates and vulnerability to zooplankton grazing. DVM causes a pulsed grazing regime and may also entail a corresponding reduction of the cumulative daily rates of ingestion and losses of zooplankton. To study the relative importance of these two mechanisms of DVM to phytoplankton we performed a scenario analysis consisting of 5 different scenarios. The results show that DVM has a strong influence on the phytoplankton community. Well edible algae benefit during the first 3–4 weeks of summer stratification by reduced daily grazing. The typical shift from small, well edible algae to larger, poorly or non-edible phytoplankton is distinctly delayed. Under the assumption of unchanged daily grazing, however, a pulsed grazing regime has nearly no influence on the resulting phytoplankton composition. As similar effects are also found for completely non-edible phytoplankton, indirect effects via phosphorus availability must be assumed. Thus, the scenario analysis reveals that the observed effects of DVM on phytoplankton can be explained by a combination of two mechanisms: (1) reduction of the daily zooplankton grazing, and (2) changed assimilation and remineralisation of phosphorus. Surprisingly and in contradiction to earlier reports there is almost no DVM effect on phytoplankton due to the sole action of a pulsed grazing regime.