Diatoms In The Des Moines River

Diatoms were observed to be the dominant algal group in all seasons in the 860 km long Des Moines River, from April 1961 through September 1964. The 9 most abundant diatom taxa were: Diatoma vulgare, Gomphonema olivaceum, Melosira granulata, Nitzschia dissipata, N. palea, Stephanodiscus hantzschii, Synedra acus and S.ulna. Of the 60 most abundant diatom taxa in the Des Moines River, 36 are important components of diatom floras in other major United States Rivers. From over 600 samples collected year around and throughout the length of the river, 274 diatom taxa representing 38 genera were identified. No new diatom taxa were recognized. Diatoms and a water sample were collected weekly. Water samples were analysed for: temperature, pH, turbidity, sulfate, iron, phosphate, silica, nitrite, nitrate, methyl orange alkalinity, chloride, calcium hardness, total hardness, oxygen, and manganese. The river basin climate produced 5 distinct positive growth periods for diatoms each year; these were characterized by heavy benthic, attached, and planktonic (except in winter) diatom growth; and delimited or terminated by one of 5 distinct respective \u27\u27antigrowth periods\u27\u27 of highwater. The latter periods were typified by heavy silt loads, and removal of most diatoms from the river by flushing and scouring. Sources of diatoms for repopulating the river were the two headwater lakes, numerous tributaries, migratory animals, and impoundments in the upper and middle zones of the river itself. Motility is an important survival factor for diatoms settling out with silt in river impoundments, and 80% of the Des Moines River diatoms are motile forms. Flow (water volume) and available light were probably the most important limiting factors for diatom growth in all seasons in the Des Moines River, both in turn limited by precipitation in the drainage basin. Light penetration most probably was limited by ice and snow cover and turbidity; in addition to precipitation, high turbidity was also caused by effluents from commercial washing of sand and gravel. Seasonal temperature variation also regulated the kinds of dominant and abundant diatoms. Ample nutrients, especially nitrates and phosphates, for diatom growth were provided by inorganic fertilizers washed from farmlands and sewage and related effluents from over 500,000 people. The intrinsic fertility of the Des Moines River is insignificant under these conditions. It is estimated that during positive growth periods over l000 tons per month of diatoms and other algae were produced in and carried out of the river; the vast amount of diatom primary production in the Des Moines River is probably utilized negligibly by other organisms. Two large dams, at Saylorville and Red Rock, will alter the diatom growth patterns in the Middle and Lower portions of the river as well as providing the opportunity for a stratified sedimentary deposition of diatoms. The impoundments from these dams will probably result in a change in the kinds of dominant diatoms and increase the number of taxa collectable