The Effect of Hydrological and Anthropogenic Factors on the Chemical Properties of Water in the Canal Network of Southeastern Srem - page 06

Similar to pH, SAR values decreased, but much more, in the extremely wet period from October 2009 to November 2010 (Fig. 13). The dramatic decline in SAR values during the wet period is attributable to the measured concentrations of Na, Ca and Mg ions at monitoring point 6 (Galovica), which are shown in Table 2 2. SAR is expressed as:

For01

and represents the ratio of the concentrations of sodium ions to the sum of calcium and magnesium ions. Heavy precipitation from October 2009 to November 2010 (71.2 mm/month) had different impacts on Na, Ca and Mg ion concentrations in the drainage canal network, compared to the previous period in which the monthly average was 43.9 mm. Heavy precipitation reduced Na ion concentrations in the canal network by about 20%, relative to the previous period (Table 2), as the water in the drainage canal network was diluted. However, the Mg and Ca ion concentrations were significantly elevated (Mg about double and Ca as much as 7.5 times higher), probably as a result of leaching. It is therefore reasonable to expect that SAR values will drop considerably during periods of heavy precipitation.

The results shown in Table 2 can also be used to explain the variation in RSC (Residual Sodium Carbonate) parameter during the study period (Fig. 14).

 

Tab02

 

Fig14
Figure 14: RSC during the study period.

 

If RSC is less than 1.25 meq/l, the water is suitable for irrigation. If RSC is between 1.25 and 2.5 meq/l, there is a moderate risk. If RSC is greater than 2.5 meq/l, using such water for irrigation poses a high risk. In the present case study, through to the end of the summer of 2009, RSCindicated moderate and high risk. The RSC expression is:

RSC = [HCO3-]+[CO32-] – ([Ca2+]+[Mg2+])

The carbonate ion concentrations were lower than the bicarbonate ion concentrations by a factor of about five (Table 2). Heavy precipitation from October 2009 to November 2010 did not reduce HCO3 and CO3 ion concentrations by much (Table 3). However, it did increase Mg and Ca ion concentrations considerably (Table 2), such that RSC was negative (Fig. 14), indicating that the use of water from the canal network for irrigation would not pose a risk.

Finally, something should be said about pollution in the Galovica drainage area. Namely, there are several point sources in that drainage area, largely farms and industry, which impact the physical and chemical characteristics of the canal network water. One example is the wastewater outlet of a dairy (point 13 on Fig. 4).

Measurements were conducted on 15 July 2009, in the middle of summer, when the environmental impact is the greatest. The most important results (ECw, HCO3- and Cl-) are shown in Table 3. The values were compared with the averages for the Galovica Canal at monitoring point 6, up to the time of measurement.

The table shows the high risk cut-off values of the parameters. The conductivity at the dairy was about double the average at point 6 on the Galovica Canal, but still below the high risk limit for irrigation. The concentration of chlorine at the dairy was nearly four times the average for the Galovica Canal and slightly below the high risk cut-off value. The bicarbonate ion concentrations at the dairy were nearly double the average for the Galovica Canal and the high risk cut-off value.

Direct wastewater discharges into the canal network are inadmissible. If the practice persists, the water quality will continue to deteriorate.

 

Tab03

 

Conclusion

The outcomes of the three-year study of water quality in southeastern Srem, Serbia, from 2008 to 2010, showed that hydrological and anthropogenic factors can have a major impact on the quality of drainage canal water if used for irrigation. Namely, the water quality of the Sava River, which acts as recipient of the water drained from southeastern Srem, is much better than that of the drainage canal network in southeastern Srem. The analyzed water samples exhibited elevated salinity, posing a low to moderate risk if used for crop irrigation. The canal water generally measured such bicarbonate concentrations that the water cannot be recommended for drip or sprinkler irrigation.

If substantial amounts of water from the existing canal network are to be used for irrigation, the pumping stations will have to be converted to support a dual-function (i.e. to also be able to pump water from the Sava River into the system of drainage canals in southeastern Srem).

Given that the water quality of the Sava is better, injection of river water into the canal network would reduce the concentrations of dissolved salts and thus mitigate elevated salinity problems.

 

Acknowledgment

This paper is part of research project 31005 (A Modern Biotechnological Approach to Resolving Drought Issues of Serbia's Agriculture) and project 37005 (Assessment of Climate Change Impact on Serbia's Water Resources), both financed by the Ministry of Education and Science of the Republic of Serbia.