Hygienic and microbiological examinations of watercourses are usually not carried out during heavy rainfall and runoff events. After rainfall or snowmelt, there are often massive increases in turbidity in flooding creeks in mountain ranges, which are frequently interpreted as an indication of microbial contamination. The aim of this study was to quantify the microbial loads of watercourses during such runoff events and to compare these loads with loads occurring during regular conditions. In a 14-month monitoring period we investigated the microbial loads of three tributaries of different drinking water reservoirs. A total of 99 water samples were taken under different runoff conditions and analyzed to determine physical, chemical, bacterial, and parasitic parameters. Thirty-two water samples were considered event samples during nine measuring series. The criteria for events, based on duration and intensity of precipitation, water depth gauge measurements, and dynamics, had been fixed before the investigation for each creek individually. Of the physical and chemical parameters examined, only the turbidity, pH, and nitrate values differed clearly from the values obtained for regular samples. Most of the bacteriological parameters investigated (colony, Escherichia coli, coliform, fecal streptococcal, and Clostridium perfringens counts) increased considerably during extreme runoff events. If relevant sources of parasitic contamination occurred in catchment areas, the concentrations of Giardia and Cryptosporidium rose significantly during events. The results show that substantial shares of the total microbial loads in watercourses and in drinking water reservoirs result from rainfall and extreme runoff events. Consequently, regular samples are considered inadequate for representing the microbial contamination of watercourse systems. The procedures for raw water surveillance in the context of multiple-barrier protection and risk assessment ought to include sampling during extreme runoff situations.In some regions of Germany surface reservoirs are the main source of drinking water. In the state of North Rhine-Westphalia, 60% of the drinking water production in 1999 was based on surface water resources (2). Surface water bodies are presumed to be more vulnerable to fecal contamination than groundwater reservoirs due to the absence of natural soil protection and filtration and the possibly short distances between the occurrence of contamination and water extraction. It is argued that especially in the case of heavy rainfall the microbial loads of running waters may suddenly increase substantially and reach reservoir bodies very quickly (18,19). For this reason monitoring microbiological raw water quality is an essential component of the protection strategy in catchment areas of surface drinking water reservoirs (8). In Germany, catchment areas of surface water supplies are usually protected by buffer zones, and the intensity of protection increases with proximity to the water body. Protection of entire catchment areas i...

The carbon-dioxide response of photosynthesis of leaves of Quercus suber, a sclerophyllous species of the European Mediterranean region, was studied as a function of time of day at the end of the summer dry season in the natural habitat. To examine the response experimentally, a "standard" time course for temperature and humidity, which resembled natural conditions, was imposed on the leaves, and the CO2 pressure external to the leaves on subsequent days was varied. The particular temperature and humidity conditions chosen were those which elicited a strong stomatal closure at midday and the simultaneous depression of net CO2 uptake. Midday depression of CO2 uptake is the result of i) a decrease in CO2-saturated photosynthetic capacity after light saturation is reached in the early morning, ii) a decrease in the initial slope of the CO2 response curve (carboxylation efficiency), and iii) a substantial increase in the CO2 compensation point caused by an increase in leaf temperature and a decrease in humidity. As a consequence of the changes in photosynthesis, the internal leaf CO2 pressure remained essentially constant despite stomatal closure. The effects on capacity, slope, and compensation point were reversed by lowering the temperature and increasing the humidity in the afternoon. Constant internal CO2 may aid in minimizing photoinhibition during stomatal closure at midday. The results are discussed in terms of possible temperature, humidity, and hormonal effects on photosynthesis.

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