The effect of aquatic vegetation on water quality (particularly phosphorus) in farm dams

This research investigates the value of aquatic vegetation (particularly lypha sp. ) in managing the phosphorus levels in the water column and thereby reducing the likelihood of eutrophication. Nine farm dams were chosen with varying degrees of aquatic vegetation (three not vegetated, three vegetated and three vegetated including Typha sp.) and the total phosphorus in the water column measured at each dam. The dams had the same hydrology and amount of riparian vegetation, however, they differed in respect to size, age, dam use, surrounding paddock use and soil type. Although it is generally believed by researchers that aquatic vegetation in natural wetlands will reduce the phosphorus levels in the water column of that wetland, the actual ability of the vegetation to do this is yet to be demonstrated. In this research no significant difference between the phosphorus levels in each of the vegetation categories was detected because all the dams were significantly different to each other, irrespective of vegetation status. The significant difference between all nine dams could have been due to variability in the amount of phosphorus reaching the dams (with diffuse source phosphorus it is difficult to ascertain loadings and sources of phosphorus), in addition the nature of phosphorus in solution (continually changing speciation) makes it difficult to get a true measure of the phosphorus in the system. Other factors that influenced the findings were that the power of the experiment was too low, the age of the dam was confounded with the vegetation status of the dam and temporal variability was not accounted for