SOME POSSIBLE EFFECTS OF TRACE ELEMENTS ON FRESH‐WATER MICROCRUSTACEAN POPULATIONS1

Among 10 tract elements considered, aluminum was shown to bc positively correlated and phosphorus negatively correlated with the density of Daphnia schgklleri in Kepple Lake, Washington; chromium and vanadium were positively corrclatcd and iron and strontium were negatively correlated with the density of Diuptomus Zeptopus. Hutchinson (1957) has reviewed the world-wide distribution of trace elements in fresh water and, where known, the effects of these elements on planktonic organisms, The study reported here was designed to evaluate possible relationships between the densities of two zooplankters, Daphnia schedleri and Diaptomus leptopus, and the concentrations of commonly occurring trace elements. Samples were collected from Kepple Lake, Washington, at intervals of approximately two weeks beginning on 2 July, 1959, and terminating on 21 June, 1960. Kepplc Lake is located in northeastern Washington and was formed artificially in 1941 in an area underlain by basalt. Its arca is 32 hectares; the maximum depth is 2.5 m and the mean depth is 1.5 m. Water temperatures averaged about 21°C in midsummer of 1959, and the lake was icccovered in the winter (5 November-18 March). The pH was always above 7.5 an d usually above 8.3. Aphanixomenon formed an intense bloom from the start of this study until 10 September, 1959 (except for a short period about 13 August) and again during the last two weeks of the study. Botryococcus bloomed from 29 April until 27 May, 1960. Dissolved oxygen exceeded 2 ppm except on 13 August ( week 7) when none was detected. Zooplankton samples were collected with a Clarke-Bumpus sampler and enumerated by conventional methods. Water was taken _---1 Supported in part by National Science Foundation Research Grant G-89 11. 2 Present address: Department of Zoology, University of Missouri, Columbia, Missouri. from a depth of 0.5 m with a Kemmerer water bottle and immediately filtered through number 25 silk bolting cloth into 1-L polyethyelcne bottles. Upon returning to the laboratory the water was filtered through HA MilliporeO filters” (pore diameter 0.45 -+1 0.02 p) and stored at 6°C until the following day when it was turned over to the Washington State University Division of Industrial Research for analysis. The concentrations of all elements except phosphorus were determined by an emission spectrograph (carbon arc) whereas the concentration of phosphorus (inorganic only) was determined chemically. Elements appearing at some time during the study were aluminum, barium, boron, chromium, copper, iron, manganese, phosphorus, strontium, vanadium, lead, molybdenum, nickel, silver, tin, titanium, and zinc. All have been found in marine crustaceans according to a recent review by Fukai and Meinke ( 1959). Nicholls, Curl, and Bowcn ( 1959 ) spectrographically detected boron, copper, lead, molybdenum, nickel, tin, titanium, and vanadium in the marine copepods Calanus finmarchicus, Centropages typicus, and Centropages hamatus. In addition, chromium was present in Centropages. Only the first 10 elements in the foregoing list of those found in Kepple Lake occurred consistently enough to warrant inclusion in the study of relationships with zooplankton density; however, all are included in Table 1 which shows the mean concentration of each, together with its standard deviation, range, frequency of de_--3 Registered trademark, Millipore Filter Corp.,