Diel Variation in Species Composition and Diversity, Density, and Chlorophyll Content of Phytoplankton in an Intermittent Stream in Oklahoma

Abstract

-Physicochemical measurements and phytoplankton were collected every 3 h during four, 24-h sampling periods in summer, 1976 and 1977, from Otter Creek, Oklahoma. Chlorophyll concentration and phytoplankton density were correlated with highest values occurring in late morning or afternoon. Ninety-four taxa of phytoplankton were collected; most were planktonic diatoms, green algae, or euglenophytes. Diel variations in species diversity and equitability was small and generally reflected changes in one or two dominant species. The algal pollution index exhibited considerable diel variation, indicating the importance of considering time of day when using the index. Most of the early literature on stream phytoplankton was qualitative. Numerous lists of the species of phytoplankton present in a stream have been published (Fritsch, 1903; Butcher, 1932; Lackey, 1942; Brinley and Katzin, 1942). In recent years the use of quantitative measures such as species diversity and density of phytoplankton has increased. Staub et al. (1970) studied the species diversity of phytoplankton in the Wolf River and its tributaries in Memphis, Tennessee. Diversity of phytoplankton was measured in the Cape Fear River, North Carolina (Carpenter, 1971) and in the Arkansas River near Ponca City, Oklahoma (Wilhm et al., 1977). Numerous authors have reported density values for stream phytoplankton (Williams, 1964; Weber and Moore, 1967; Carpenter, 1971; Wilhm et al., 1977). Diel periodicities of phytoplankton have been shown in many studies. The phytoplankton of the Saline River, Michigan, exhibited a diel pulse in downstream drift of certain benthic algae, apparently due to daytime oxygen production, which makes them more buoyant and easily carried away by the current (Blum, 1954). Rhythms also have been reported in uptake of nitrogen (Goering et al., 1964), photosynthetic activity (Lorenzen, 1963), and chlorophyll content (Yentsch and Ryther, 1957; Shimada, 1958). Diel rhythm in species diversity of stream phytoplankton has not been studied. The objectives of this study are to: (1) observe the diel rhythm of density, chlorophyll a and pheophytin a content, species diversity, and equitability of stream phytoplankton and (2) measure the diel rhythm of water temperature, dissolved oxygen, pH, and conductivity. STUDY AREA.-Otter Creek is an intermittent stream which flows through Garfield and Logan counties in north-central Oklahoma. The stream originates near Covington, flows 42 km southward, and empties into Skeleton Creek, a tributary of the Cimarron River. The elevation is 363 m at the source and 287 m at the mouth, with an average gradient of 1.8 m/km. The stream has narrow, eroding valleys which reach a depth of 23 m. Stream depth was 1 m at the sampling station. Otter Creek's drainage basin is 302 km2 and is in the mixed-grass prairie association. Broad-leaf trees line the stream banks. Most land in the basin is cultivated or used for pasture. T E SOUTHWESTERN NATURALIST 27(1):79-86 February 19, 1982 This content downloaded from 207.46.13.136 on Sat, 01 Oct 2016 05:52:34 UTC All use subject to http://about.jstor.org/terms The Southwestern Naturalist Further information about the stream is given by Harrel and Dorris (1968) and Seyfer and Wilhm (1977). MATERIALS AND METHODS.-Phytoplankton samples were collected on 28 June 1976 and 11 June, 11 July, and 21 August 1977. Surface samples were taken every 3 h beginning at 0500 h. Eight surface l-liter water samples were taken at each sampling time; four for analysis of phytoplankton were preserved in Lugol's solution and four for chlorophyll determination were placed in an ice chest. Water temperature and conductivity were measured with a Yellow Springs Instrument Co. YSI Model 33 54 oxygen meter. A portable Beckham pH meter was used for determining hydrogen-ion concentration. Three surface measurements of each physiocochemical parameter were made at each sampling time. In the laboratory, l-liter samples for chlorophyll a and pheophytin a determinations were extracted in 20 ml of 90% aqueous acetone. Following storage in a refrigerator at 4? C for 24 h, the optical density of the liquid extract was read before and after acidification with concentrated HC1 on a Beckman DBG spectrophotometer. The optical density readings were used to calculate chlorophyll a using the equations of Lorenzen (1967). Samples for species identification of diatoms were cleaned on a hot plate according to the method described by Weber (1971). Total counts of all species were made on cleared 0.45 jum membrane filters using a magnification of OOO1X. Species diversity and equitability were calculated for each sample by the equations of Shannon and Weaver (1963) and Pielou (1966), respectively. Density was computed for each phytoplankton sample by the equation,