Temporal Changes of Water Quality

To determine the influence of sampling frequency on the reliability of water quality estimates in small streams, a cultivated (0.12 km ) and a forested basins (0.07 km ) were studied in spring and autumn [28]. During the 2-month spring season and 3-month autumn season 97%-99% of the annual loads of total nitrogen, total phosphorus, and suspended solids was acquired from the cultivated basin and 89%-91% from the forested basin. During the same seasons 99% and 87% of the total armual runoffs were recorded in the cultivated and forested basins. This means that in only 5 months of the year more than 95% of the nutrient and water rimoff occurred in the cultivated catchment, and about 90% in the forested catchment. Thus the values of nonpoint loads, normally presented as 

It is also worth noting that the procedure known as catchment quality control, though intended for a different purpose, includes the identification of most important effluents entering a river system from a viewpoint of water quality [31]. 

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