Alkaline phosphatase activity (APA) and the availability of dissolved organic phosphorus (DOP) to marine algae were determined in Xiamen Bay and in algal batch culture systems. Results showed that APA changed with seasons, increasing to the highest value in summer and decreasing to the lowest in autumn and spring in Xiamen Bay. Tests on natural populations of planktonic algae and bacteria community showed that algae were mostly responsible for DOP utilization, while bacteria could not take up DOP compounds. Results from algal batch cultures also supported the above conclusion. Relationships between APA and environmental factors indicated that APA was negatively correlated with phosphorus level such as phosphate and small molecular DOP, and APA played an important role in utilization of DOP by algae. All the results emphasized the ecological significance of DOP in subtropical coastal waters. 相似文献
Bioassesment by the use of the macroalga, Ulva lactuca L., was carried out in the Limfjord, Denmark, to assess the significance of nitrogen and phosphorus as limiting factors for primary production during 1985, 1993, 1994 and 1995 and for the detection of changes in eutrophication levels.
Minimum and critical tissue concentrations for nitrogen and phosphorus in macroalgae were identified. The concentrations of nitrogen were generally below the critical concentration level in June–October in 1985, 1993, and 1995 but in 1994 nitrogen was only limiting for primary production in short periods. Only in early spring in 1985 and 1993 were the tissue concentrations of phosphorus below the critical concentration level, whereas in 1994 up to 3–4 months showed phosphorus limited growth, indicating that significant changes in limitation patterns can occur between different years.
It was concluded that the use of biomonitoring techniques is well suited as a bioassessment method for direct detection and for providing a time-integrated measure of nutrient availability in coastal waters, and thus for assessing ecosystem health with regard to eutrophication. It is recommended that biomonitors and the concept of critical tissue concentrations should be used in environmental management and incorporated in future monitoring programmes. 相似文献
The development of a new observational system called LISDAD (Lightning Imaging Sensor Demonstration and Display) has enabled a study of severe weather in central Florida. The total flash rates for storms verified to be severe are found to exceed 60 fpm, with some values reaching 500 fpm. Similar to earlier results for thunderstorm microbursts, the peak flash rate precedes the severe weather at the ground by 5–20 min. A distinguishing feature of severe storms is the presence of lightning ‘jumps' — abrupt increases in flash rate in advance of the maximum rate for the storm. The systematic total lightning precursor to severe weather of all kinds — wind, hail, tornadoes — is interpreted in terms of the updraft that sows the seeds aloft for severe weather at the surface and simultaneously stimulates the ice microphysics that drives the intracloud lightning activity. 相似文献
Palar River Basin, a crystalline rock region in North Arcot District (Tamil Nadu), India, possesses vast groundwater potential
along and near the river course and its lands are fertile. Serious contamination of both surface water and groundwater has
been reported in this basin as a result of uncontrolled discharge of untreated effluents by the tanning industries for the
last three decades. The health of the rural farming community and people working in the tanning industries has been seriously
affected and they are suffering from occupational diseases such as asthma, chromium ulcers and skin diseases. About an 11000
hectares area of fertile land has lost its fertility. Total dissolved solids (TDS) concentration in groundwater at some pockets
varies from 3000 to 10000 mg/l. As the discharge of effluents is continuing, a prognosis of further pollutant migration is
carried out using a mathematical model. A numerical model of the Upper Palar River Basin was developed using the finite difference
technique coupled with method of characteristics and used to predict TDS migration for the next 20 years. Sensitivity analysis
was carried out to identify the parameters which are influencing the contaminant migration. Sensitivity analysis shows that
advection and not dispersion is the predominant mode of solute migration in Palar Basin. Prognosis using the model confirms
that the polluted area zone as well as the concentration of pollutants in the groundwater will continue to increase in future.
The study also indicated that even if the pollutant sources are reduced to 25% of the present level, the TDS concentration
level in the groundwater, even after 20 years, will not be reduced below 50% of its 1992 level.
Received: 20 June 1998 · Accepted: 26 October 1998 相似文献