**8.2. Basic organic pollution parameters**

**Figure 12.** Changes in the average monthly sodium concentration in the waters of the Turawa reservoir in the hydro-

**Figure 13.** Changes in the average monthly potassium concentration in the waters of the Turawa reservoir in the hy-

Surface waters can contain a wide spectrum of organic compounds belonging to different classes. The most important are carbohydrates, proteins, amino acids, esters, fats, organic acids, surfactants, soaps, ketones, alcohols, hydrocarbons, phenols, and also humic and fulvic substances. Most organic substances are of natural origin. Many are produced by animals and

**8. Concentration changes of organic substances**

logical years 2004–2006.

390 Water Quality

drological years 2004–2006.

**8.1. Classes of organic compounds**

Organic compounds differ greatly in physico-chemical properties and in threat to living organisms so they should be determined as groups or individual compounds. This could be and is costly and also labour- and time-consuming activity, and therefore as the first step of the determination of organic pollution, the total organic pollution parameters are used. The most typical and delivering important information on water quality are biochemical oxygen demand (BOD5) and chemical oxygen demand (COD). The former is a measure of content in water of organic matter that can be decomposed biologically, while the latter shows the amount of organic matter which can be oxidized by strong oxidizer as potassium permanganate (CODMn) or potassium chromate (CODCr), respectively.

The basic water quality indicators mentioned above were monitored for the Turawa reservoir. In hydrological years 2004–2006, the monthly average BOD5 for the whole studied period was 5.2 mg O2 dm−3; it was changing in a wide range from 0.6 to 16.7 mg O2 dm−3 (**Figure 14**). The annual average BOD5 increased from 3.6 mg O2 dm−3 in 2004 to 8.6 mg O2 dm−3 in 2006. Occasionally, very high concentrations were found. In the period from June to September 2006, the maximum BOD5 values exceeded 40 mg O2 dm−3.

**Figure 14.** Changes in the average monthly BOD5 concentration in the waters of the Turawa reservoir in the hydrological years 2004–2006.

In the above-measuring period, the monthly average CODMn parameter was 9.2 mg O2 dm−3 and changed from 5.2 to 9.2 mg O2 dm−3 (**Figure 15**). Occasionally, very high values of CODMn were measured, for example, from September to October 2006 the maximum CODMn values exceeded 25 mg O2 dm−3.

Both BOD5 and CODMn values were season dependent; in winter were the lowest while in summer the highest (**Figures 14** and **15**) due to intensive eutrophication and resulting growth of algae and green algae during hot season. These organisms emit considerable amounts of organic compounds in metabolic processes and during decaying.

If water contains neither toxic substances nor organic matter resistant to biodegradation, the good correlation between BOD5 and CODMn can be expected. For the water of the Turawa reservoir, correlation coefficient was 0.79.

In October 2006, a series of other pollution parameters were determined. They included total organic carbon (TOC), and indicators of industrial pollution such as free cyanides, phenolic index, anionic surfactants, mineral oils and polycyclic aromatic hydrocarbons. Fortunately, the indicators of industrial pollution were found quite low. This shows that the water in the Turawa reservoir was polluted mainly with organic matter of natural origin, which is caused by increasing eutrophication.

**Figure 15.** Changes in the average monthly CODMn concentration in the waters of the Turawa reservoir in the hydrological years 2004–2006.
