Lawrence Berkeley National Laboratory Recent Work Title NITROGEN FIXATION IN CLEAR LAKE, CALIFORNIA. 4. DIEL STUDIES ON APHANIZOMENON AND ANABAENA BLOOMS. Permalink https://escholarship.org/uc/item/7k44g4xs Author Home, A.J. Publication Date 1976-12-01 eScholarship.org Powered by the California Digital Library University of California Submitted to Limnology and Oceanography LBL-9159U Prepri nt NITROGEN FIXATION IN CLEAR LAKE, CALIFORNIA. 4. DIEL STUDIES ON APHANIZOMENON AND ANABAENA BLOOMS RECE1VD A. J. Home LAWRE E BERKLY LA...AT0RV LV 2o YI9 December 1976 L1RARY AND OCUMgNTS sECTION Prepared for the U. S. Department of Energy under Contract W-7405-ENG-48 TWO-WEEK LOAN COPY This is a Library Circulating Copy which may be borrowed for two weeks. For a personal retention copy, call Tech. Info. DivIsIon, Ext. 6782 çYOF c. 1- & 0 DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. 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Oceanogr., 24(2), 1979, 329-341 © 1979, by the Amencan Society of Limnology and Oceanography, Inc. Nitrogen fixation in Clear Lake, California. 4. Diel studies on Aphanizomenon and Anabaena blooms 1 A.J.Horne Department of Sanitary Engineering, and Sanitary Engineering Research Laboratory, University of California, Berkeley 94720 Abstract Day and night measurements of N. fixation (as acetylene reduction) were made during spring blooms of Aphanizomenonflos-aquae and two autumn blooms of Anabaena spp. From 9 to 23% of the 24-h fixation occurred between 1100 and 1300 hours. Nitrogen fixation in spring showed complex, physically shallow but optically deep and mobile subsurface peaks of nitrogenase activity, which were totally unrelated to Aphanizomenon biomass but may have been due to diel changes in light penetrating the relatively clear water. Nocturnal fixation was uniformly distributed with depth and accounted for 1/ to Y3 of daylight fixation. In more turbid autumn waters, the pattern of N, fixation for Anabaena blooms was simpler, with a surface (or near-surface) peak decreasing with depth. Nocturnal cixation was more uniformly distributed with depth. The difference in fixation patterns between the two species is attributable to the interactions of oxygen with the nItrogenase enzyme system. The diel changes in nitrogenase activity suggest a need to establish whether the precursors of nitro- genase accumulate in an oxygen-stable form. Nitrogen fixation requires more energy photorespiration may not be inevitable than any other biological process. Thus since the algae can regulate their position it should be highly light-dependent in in the waterco1umn (Waisby 1972; Reyn- 'lakes, since only photosynthetic organ- olds 1972, 1973). Thus there may be less isms are quantitatively significant in lake need for nocturnal N 2 fixation as after- N2 fixation (Home 1975a; Fogg et al. noon activity should be less depressed- 1973). However, phytoplanktonic N 2 fix- at least in lakes with several meters of ation may occur at low light levels and photic zone. The work reported here was even in total darkness (Home and Fogg designed to test this hypothesis and to 1970; Duong 1972; Vanderhoef et al. provide a quantitative method of calcu- 1975; Burns and Peterson 1978). lating daily and hence annual N 2 fixation Quantities fixed are generally but not al- amounts using incubation normally for ways low; there are disadvantages to high only a couple of hours at midday. photosynthesis, particularly the onset of A further reason for carrying out five photorespiration which successfully diel studies in both blooms spread over competes with N 2 fixation for available 3 years was to improve the meaningful- energy (Home 1975b). Photorespiration ness of the data. Generalizations based is enhanced by the afternoon low CO 2 on any one of the diel studies reported and high 02 levels, which are possible in here would not be significant without planktonic algal colonies and inevitable guidance from the other four. inside gelatinous Nostoc communities in I thank C. J. W. Carmiggelt and P. streams, despite the constant 0 2 and CO2 Kellar for technical assistance. environment provided by the well aer- ated stream water (Home and Carmiggelt 1975). Methods In the more open "flake" association of Samples were usually collected at .1 Aphanizomenon or coils of Anabaena, depths of 0, 0.5, 2.0, 3.0, and 4.0 m with an opaque Van Dorn bottle. The photic 'This study was supported by the Clear Lake zone is generally between 1 and 4 m in Algal Research Unit, Lake County, California, and Clear Lake, shallowest in autumn and the California Department of Water Resources. winter. Since the main purpose of the ex- 329 330 Home Table 1. Diel variation in nutrients (in g !iter 1 ) spring and early summer clouds are rare during an Aphanizomenon bloom, 21-22 June and some near-surface thermal stratifica- 1972. tion re-forms each day. Afternoon winds Period Time P0P NH-N NO,-N usually destroyed thermal stratification for at least part of each day on which 3 0930 42 11 14 studies were carried out and the regular 5 1500 45 45 1 7 2200 43 1 1 stirring mixed such nutrients as were 9 0600 10 15 1 available from the sediments into the photic zone. Nevertheless, biologically important nutrients were scarce, having periments was to document the diel been depleted by the first nitrate-fueled changes in N2 fixation, relatively few oth- stages of the massive Aphanizomenon er measurements were made. Collections bloom. For example, in June 1972 nitrate were taken at intervals of a few hours ranged from 1-14 gliter', ammonium either from dawn to dusk (3 days) or over from 1-45 jLgliter 1 , and phosphate from a 36-h period (2 days) during spring 1970, 10-45 gliter 1 (Table 1). The imbal- 1971, 1972 (Aphanizomenon bloom), and ance between P and N produced a severe autumn 1970, 1971 (Anabaena bloom). nitrogen stress and was the reason for the Details of methods were given by Home N2 fixation at this time (Home and Gold- and Goldman (1972). Measurements man 1972). were made of N 2 fixation as acetylene re- An overall view of the diurnal, changes duction, carbon fixation, chlorophyll a, in N2 fixation and chlorophyll a in the general chemistry, algal species, biomass water column for the three seasons and heterocyst counts, water transparen- (1970-1972) is given in Fig. 1. In general cy as Secchi depths, solar energy with chlorophyll a, which was contained time using a Belfort pyrheliometer, and mainly in Aphanizomenon, showed no estimated wind speed and direction. Al- regular pattern but fluctuated consider- gae were counted in spring 1972 at each ably due to patchiness (Wrigley and depth sampled for all nine periods over Home 1975) and vertical migration 36 h, to distinguish the effects of Apha- (Reynolds and Walsby 1975). Nitrogen nizomenon from those of other less abun- fixation showed a broadly constant pat- dant algae that may have contributed tern in all 3 years but considerable vari- disproportionately to photosynthesis and ation within that general trend. Early nutrient uptake (Watt 1971; Dozier 1976; sunlight around 0700-0800 hours pro- Stull et al. 1973). Such influence is un- duced only a small increase in N2 fixation likely in eutrophic lakes where the most over nocturnal rates, but by midmorning common algae physically can dominate rates were almost as high as at any other the struggle to gain the most favorable time of day. Early morning activity was light climate. definitely dependent on sunlight, since a cloudy start to the day depressed fixa- Results tion below normal nocturnal levels. Pre- All studies were carried out at the sumably nocturnal fixation after an ab- height of N 2 fixation activities in Upper normal (totally cloudy) day would be Arm, which comprises 70% of the area of negligible (Home 1975b). During the the lake. There were many similarities major part of the day activity was high and differences between the three spring, and quite constant (200-600 ttmol Aphanizomenon-dominated blooms and C2 H4 liter 1 h 1). It decreased at dusk, the two autumn, Anabaena-dominated but not proportionately with illumina- blooms. The most convenient way of con- tion. Most unexpected at the time of the sidering the results is to separate them experiments was the nocturnal fixation into those of spring and autumn. activity which persisted all night, gener- Spring Aphanizomenon blooms—In ally at moderately high levels. Relatively Nitrogen fixation. 4. 331 400 600 r 1 1.0 200 200 0.5 z —I 0 0 400 1.0 b >< 0.5 c.1 Z 600 200 200 2400 0600 1200 1800 2400 . 0600 Fig. 1. Diel variations in N2 fixation (as ethylene produced in gmolliter'h), chlorophyll a, and sunlight at height of three spring Aphanizomenon blooms. a-26 June 1970; b-16 June 1971; 0-21-22 June 1972.