Studies on the algae of the polluted River Kelvin

The macroscopic and microscopic vegetation of the River Kelvin was studied in relation to pollution during the period October 1979 - September 1982. The main sources of pollution in the river were from treated domestic sewage and industrial effluents. Water samples from 10 stations on the river were analysed chemically for the amounts of nutrients based on monthly sample collections. The parameters used for estimating the pollution were phosphate P, nitrate + nitrite N, ammonia, dissolved oxygen and biological oxygen demand. The results showed high but variable nutrient levels at the different stations, being almost always highest at Luggie Water, one of the tributaries of the Kelvin, and the lowest were always nearer the source. No signs of deoxygenation were observed in the river, with average oxygen levels not less than 6 mg l-1. The average BOD5 values were not very high, being always < 5 mg l-1. During summer the nutrient levels were higher than in autumn and winter. Analysis of river samples for heavy metals indicated that levels were not significant, and flow rates were analysed from gauging station data supplied by the Clyde River Purification Board. Dissolved silica was also measured in the river as it is an essential element for diatom growth. Unlike the other nutrients, the dissolved silica was found in high levels near the source. Microscopic examination of the samples was carried out as well as determination of chlorophyll a, phaeopigments and carbon fixation measurements. The phytoplankton (= tychoplankton) in the River Kelvin was composed mainly of diatoms with the largest populations at stations with highest nutrient levels. The phytoplankton was present in maximum numbers during April-June, followed by a decrease during July and another peak during August. Thirty eight different species of diatoms were recorded in the River Kelvin, dominated by Cyclotella meneghiniana, Gomphonema parvulum, Navicula avenacea, Nitzschia thermalis and Synedra ulna. The carbon fixation results coincided more with chlorophyll a peaks than with the numbers of diatoms. The phytoplankton population reflected the epiphytic flora; thus they were mainly attached species on the river macrophytes and other substrata dislodged by water movement. The epiphytic flora of the macrophytic angiosperms also consisted mainly of diatoms with the above species being the most numerous. The numbers of the epiphytic diatoms were determined for three different regions of Potamogeton spp., e.g. top, middle and basal regions, and the carbon fixation of the epiphytic diatoms from the three regions was also measured. Whilst the diatom numbers were often more on the basal and middle regions, carbon fixation by diatoms from the apical region was always of a higher value. An attempt was also made to estimate algal colonisation on sterilised natural substrata. The filamentous algae formed the larger populations during the mid summer periods, being dominated by Cladophora glomerata, Cladophora fracta, Oedogonium sp. and Vaucheria sp. Cladophora spp. were observed forming a green blanket at some stretches of the river. Four species of macrophytic angiosperms were recorded in the River Kelvin, Potamogeton filiformis, Potamogeton natans and Sparganium emersum. Of these, Potamogeton natans was the most abundant macrophyte. These were prominent in spring and summer with rapid defoliation at the onset of autumn. Algal bioassay experiments were carried out to assess the water quality of the river using the coenobial green alga Scenedesmus quadricauda as the test organism. Its growth in the water samples from the river was compared with the growth in a balanced medium and estimated by measuring the cell numbers per unit volume. Chlorophyll a and the phaeopigments were also measured as well as the cell appearance in the cultures and measurements of photosynthesis rates. The bioassay results showed higher growth rates always in the water samples from the station with the highest nutrient levels and the lowest in the sample from near the source of the river. Abnormal cells in the coenobia of Scenedesmus guadricauda were noticed in the river cultures, being of higher percentages during winter than in summer. Chlorophyll a measurements were high during spring and summer, particularly during August when maximum values were recorded, then a dramatic fall during September. The phaeopigments were recorded in high proportions in the cultures during winter months. The photosynthesis rates were also at maximum during August with a fall during September in all the river cultures. In general, the River Kelvin, whilst containing large quantities of treated domestic and industrial effluents, by virtue of its relatively high flow rates at most times of the year, can be described as having a "physiologically rich" lotic system which supports an abundant and diverse algal flora. The diatoms and filamentous green algal species found at the stations are typical of the "recovery zones" of polluted rivers and it would seem that the effluent loading of the river is well contained by its natural recovery processes