Archive for January, 2010

Water quality indicators

Sunday, January 10th, 2010
Waterhole on a drying creek in Central Victoria

A waterhole on a drying creek in Central Victoria The water is very discoloured and has an earthy smell with abundant protozoans and a few algae The ORP value (oxygenation) has dropped to the low side of the desirable range.

At Apps Laboratories we measure a range of factors in water samples.  Some like dissolved metals can be compared directly to the Australian Water Quality  Guidelines. Others like salinity indicate what the water can be used for for example depending on the salt tolerance of irrigated crops. More often we want to give the landowner an idea of what is wrong with the water; an indicator of  ‘health’ or quality.

This gives a better understanding of management of the water or possible treatments. Here is what we found in a recent dam water sample. The water has a smell like compost and was discoloured green by algae. A quick check of ORP level showed very low oxygenation. High ammonia (unionized form) confirmed that there was probably high organic contamination of the water and that under low oxygen conditions some was being converted to ammonia. We also didn’t find any nitrates but this was expected because of the low oxygen. UVA absorbance was very high further suggesting high levels of organics in the water. The water also had elevated salts and a calculated significant sodium hazard.

Very high densities of algae usually indicate high nutrient inputs. The fact that we found some phosphate was a bit worrying as algae usually use up all the phosphate as they grow. Perhaps a check on the water coming into the dam would be recommended. The water was also very alkaline (pH 9.2). Algal blooms remove carbon dioxide especially during the day and send the pH upwards. At night the pH should return to more normal levels. There were two unusual characteristics of this water; the pH stayed high overnight and there was higher than expected alkalinity.  Some of this water is waste water from a food processing plant.

Overall the ‘quality’ was low and several problems were indicated both in the source water and in the stored water.