A Study Of The Biological Effects Of The Helena Municipal Wastewater Treatment Plant Effluent On The Aquatic Macroinvertebrate Community Of Prickly Pear Creek

Abstract

Prickly Pear Creek originates south of Jefferson City. As it flows north, it is fed by a number of small streams including Spring Creek, Warm Springs Creek, Clancy Creek, and Lump Gulch Creek. Prickly Pear Creek flows through East Helena and its mouth is located on the southwest shore of Lake Helena. The stream has suffered from a variety of stresses imposed by man. Pollutants of Spring Creek have notably affected the water quality of Prickly Pear Creek, many of which have existed as a result of historic mining activities. Examples include increases in turbididty due to placer tailings and dangerous levels of arsenic, lead, iron, and manganese (3). In the construction of Interstate Highway 15 south of Helena to Boulder, Prickly Pear Creek had to be channeled straight; the velocity in this area increased as a result. The ASARCO smelter in East Helena has also had an impact on the stream by increasing levels of arsenic and sediment (3), and may very well have contributed to the loosely consolidated, sandy substrates noted at the test sites. It is evident that many stress factors are at work in Prickly Pear Creek. The design of this experiment incorporates the idea of aquatic macroinvertebrates as pollution indicators into a study of the biological effects of the Helena Wastewater Treatment Plant effluent on Prickly Pear Creek. The treatment plant consists of two grit separators with a comminutor and bar screen, one primary clarifier, an ABF biological tower, an aeration basin, two secondary clarifiers, and a chlorine contact chamber (9). After leaving the chlorine chamber, the treatment plant effluent flows down a ditch and enters Prickly Pear Creek approximately 1.75 miles north of the plant. The use of artificial substrate samplers to collect the organisms provides a reliable sampling technique in order to study the macroinvertebrate community as they can standardize such important sampling variables as substrate type, surface area, and depth. The complete monitoring of the effects of a sewage discharge on a stream such as Prickly Pear Creek should involve not only biological parameters, by physical parameters as well (1,6) Total suspended solids (TSS) concentrations are pertinent as they may relate to the food supply of the filter-feeding members of the macroinvertebrate community (6). Algal nutrient (nitrogen and phosphorus) measurements are important as they relate to the streams potential for growth of aquatic plants, which are important sources of food and habitat for macroinvertebrates (2). Also, it is through these measurements that the quantity of un-ionized ammonia (NHyN), a very toxic compound, can be determined. Streamflow measurements can relate how much of these substances is being propogated. Dissolved oxygen (DO) content is important as it may indicate an oxygen stress due to the presence of incompletely oxidized organic waste material or increased metabolic rates of the bacteria population.