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The quality of results of an environmental monitoring plan is limited to the weakest component, which could be the analytical approach or sampling method. Considering both the possibilities and the fragility that sampling methods offer, this environmental monitoring study focused on the uncertainties caused by the time component. Four time series of nutrient concentration at two sampling points (PB1 and PB2) in the Ribeirão Garcia basin in Blumenau, Brazil, which were significantly correlated to the spatial component, were considered with a 2-hour resolution to develop efficient sampling models. These models were based on the time at which there was the highest tendency toward adverse environmental effects. Fourier spectral analysis was used to evaluated the time series and resulted in two sampling models: (1) the SMCP (sampling model for critical period) that operated with 100% efficiency for registering the highest concentration of nutrients and was valid for 83% of the studied parameters; and (2) the SMGCP (sampling model for global critical period) that operated with 83 and 50% efficiency for PB1 and PB2, respectively.

The modified tracer gas technique is used to determine the reaeration coefficient in six different water bodies of the Itajai River basin, three with rural land use and three in urban areas. Propane was used as the tracer gas and Rhodamine WT as the conservative tracer, providing information on dilution, mixing and dispersion. Liquefied petroleum gas was used instead of high purity propane, aimed at reducing the costs associated with the field trials. Reaeration-rate coefficients observed in the field ranged from 25.8 to 367.7 d−1. Two data sets could be observed where smaller streams had substantially larger coefficients of between 133.1 and 367.7 d−1, while the larger streams had values ​​ranging from 25.8 to 54.5 d−1. Five empirical equations were evaluated by comparing the values ​​obtained in the field. The equations proposed by Tsivolgou and Wallace and Tsivoglou and Neal showed greater adherence to the values ​​determined in the tests. Reaeration-rate coefficients obtained in the field were correlated with the hydrodynamic characteristics of the watercourses, thus establishing a mathematical function through which to obtain estimates for future evaluations. The R2 value obtained using this equation was 0.959, indicating a high correlation between the calculated values ​​and those estimated in the field. Copyright © 2012 John Wiley & Sons, Ltd.

This study evaluated the performance of two carbon analyzer catalyzers, one with high sensitivity and another with regular sensitivity, used in the determination of carbon concentration in a total organic carbon analyzer – TOC. Its applicability was then evaluated in an environmental monitoring study. They have been constructed two calibration curves with 5 points each, first in the interval of 2 mgL-1 at 10 mgL-1 and the second in the interval of 10 mgL-1 at 100 mgL-1. Both calibration curves showed a high level of linearity that can be observed by R2 values that were 0.9996 for the concentration range of 2 mgL-1 to 10 mgL-1, 0.9999 for the concentration range of 10 mgL-1 to 100 mgL-1, and 0.9999 for the concentration range of 100 mgL-1 to 1.000 mgL-1. The limits of detection and quantification for inorganic carbon were, respectively, 0.003 mgL-1 and 0.009 mgL-1. The limits of detection and quantification for the different catalyzers were also evaluated and showed the following values: regular sensitivity: 0.015 mgL-1 and 0.050 mgL-1, respectively, and high sensitivity; 0.004 mgL-1 and 0.013 mgL-1, respectively. The environmental monitoring was performed in two points (PB1 and PB2) in the Garcia stream. Carbon concentrations were monitored during 24 hours with 2-hour intervals between sampling. It was observed that the concentrations of carbon remained constant throughout the experiment, with the exception of the period between 10:00 am and 04:00 pm, probably due to the input of carbonates and bicarbonates derived from textile companies in the region or still had to the launching of urban sewers. Comparing the average carbon concentration, values of point PB2 were always higher than those observed at point PB1. In high concentration analysis, only irrelevant variations were observed with the use of both catalyzers.