Analysis of water quality problems in the VPI & SU Duck Ponds and suggested management alternatives

Abstract

Allochthonous nutrients were monitored during three storm events on one of the major tributaries entering the shallow VPI&SU Duck Ponds. Autochthonous nutrients were monitored for a period of ten months. During these storms, the stormwater runoff contributed large amounts of organic matter and fertilizer nutrients that settled in the ponds and during anoxic conditions, recycled to stimulate algal blooms. Alum was applied to one pond to reduce internal cycling of nutrients. A 25 mg/L dose of alum produced an aluminum hydroxide floc that settled to the bottom and afterwards, lowered othophosphate-phosphorus concentrations below 10 µg/L in the water column. The longevity of the one-time treatment in reducing the sediment-phosphate release rate is unknown because the monitoring program was not continued beyond July of 1988. A pond-treatment program involving copper sulfate was initiated to control algal blooms consisting mainly of the green alga, Chlamydomonas. Based on the complexing properties of the water, such as alkalinity and humics, a copper sulfate dose of 13.6 kg was determined to be a safe and effective dose that reduced algal densities but did not result in any visible adverse effects upon other aquatic life. Both of the pond management schemes were designed to aid managers of small urban ponds who have low operating budgets and a lack of technical equipment.