The Chillán River in Central Chile plays a fundamental role in local society, as a source of irrigation and drinking water, and as a sink for urban wastewater. In order to characterize the spatial and temporal variability of surface water quality in the watershed, a Water Quality Index (WQI) was calculated from nine physicochemical parameters, periodically measured at 18 sampling sites (January-November 2000). The results indicated a good water quality in the upper and middle parts of the watershed. Downstream of the City of Chillán, water quality conditions were critical during the dry season, mainly due to the effects of the urban wastewater discharge. On the basis of the results from a Principal Component Analysis (PCA), modifications were introduced into the original WQI to reduce the costs associated with its implementation. WQI DIR2 and WQI DIR , which are both based on a laboratory analysis (Chemical Oxygen Demand) and three (pH, temperature and conductivity), respectively, four field measurements (pH, temperature, conductivity and Dissolved Oxygen), adequately reproduce the most important spatial and temporal variations observed with the original index. They are proposed as useful tools for monitoring global water quality trends in this and other, similar agricultural watersheds in the Chilean Central Valley. Possibilities and limitations for the application of the used methodology to watersheds in other parts of the world are discussed.

No abstract

Abstract. Gracilaria tenuistipitata Zhang et Xia was cultured for 15 d at low, normal and high inorganic carbon concentrations under constant light, temperature and nutrient conditons. Carbonic anhydrase (CA; EC 4.2.1.1.) activity, ribulose-l,5-bisphosphate carboxylase/ oxygenase (Rubisco; EC 4.1.1.39) content, pigment content and C/N ratio were measured, and also the photosynthesis and growth rates. Both Rubisco content and CA activity increased under conditions of low inorganic carbon (CO but decreased at high C~ with respect to the control. The amount of pigments declined considerably at high Ci and was slightly higher at low C~. The maximum rate of photosynthesis and the photosynthetic efficiency increased in low Ci and the opposite was found at high C~ concentration. The effects of Ci concentration on maximum rate of photosynthesis and photosynthetic efficiency are discussed in relation to the variation in pigment and Rubisco contents and CA activity. The data indicate that Ci may be an important factor controlling the photosynthetic physiology of G. tenuistipitata with regard, not only to the enzymes of C~ metabolism, but also to the pigment content.

No abstract

The regulation by light (especially blue light) and NO3- of the nitrate reductase (NR) activity was studied in the marine green macroalga Ulva rigida C. Agardh. NR activity was measured in situ as no available in vitro method exists for Ulva rigida. The effectiveness spectrum of NR-enhancement by light was determined. Blue light was clearly the most effective wavelength, being more effective than white or red light. Blue light enhancement of NR was strictly dependent on photosynthesis since it was inhibited by 95% in presence of 5 × 10-5 M DCMU. The time course of NR enhancement by blue light was hyperbolic in shape, the semimaximal level of increase was reached in 24 min in N-sufficient algae. Blue light activation of NR is dependent upon photo flux density in a sigmoidal manner; 95% of the maximum increase was reached at 137 μmol m-2 s-1. Blue light enhancement of NR is linearly dependent on the amount of KNO3 available in the medium at the beginning of the experiment. Increase in NO3- by itself, in dark or without a concomitant increase in photon flux density, only increases NR activity by 12% (darkness) or 25% (white light, 4 μmol m-2 s-1) with respect to a blue light control. The blue light enhancement of NR was inhibited by actinomycin D (33%), rifampicin (32%) and cycloheximide (88%). Therefore, in Ulva rigida the blue light enhancement of NR occurs mainly by induction of de novo synthesis.