Publications

  • ALAN L. BAKER, KATHLEEN KROMER BAKER
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    ABSTRACT: Temperature and current discharge regulated phytoplanktonic concentration, chlorophyll-a concentration, the light-saturated rate of photosynthesis (Pmax), and photosynthetic capacity (Pcap) in the Mississippi River at Prairie Island, Minnesota. The chlorophyll-a maximum was 48 mg m−3 in 1975, a wet year with a high current discharge, and 190 mg m−3 in 1976, a relatively dry year. The highest values of Pmax were 0.37 (mgO2 I−1h−1) in 1975 and 1.60 in 1976. Pcap varied from 3 to 21 (gO2 per g chlorophyll-a h−1) both years, and its value was highly correlated with temperature. The temperature optimum shifted from 16°C for Pcap in the spring, to greater than 28°C in the summer. Multiple regression analysis indicated a second-order relationship of Pcap in the spring to temperature. Other independent variables explained only negligible variation of Pcap.
    Freshwater Biology 05/2006; 9(3):191 - 198. · 3.93 Impact Factor
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    ABSTRACT: 1Use of a multi-column thin-layer pneumatic sampler and modified analytic procedures has enabled resolutions of chemical and biological strata at 2.5 or 5.0 cm depth intervals. Examination of meromictic Lake Fidler, Tasmania, indicates the presence of a thin, intense stratum of bacteriochlorohyll d in the upper monimolimnion, associated with a discrete stratum of Chlorobium cf. limicola at the microaerobic interface between the oxygenated and sulphide-rich zones.2Algae included small populations of Chlorophyceae, Chrysophyceae, Bacillariophyceae and Cryptophyceae. Bacteria included microaerophils and obligate anaerobes, pigmented and colourless, in well-defined strata in the upper monimolimnion. A population of the microcrustacean Calamoecia tasmanica tasmanica was present in the mixolimnion. Chaoborus larvae were concentrated within the Chlorobium layer.3The chemical profile of Lake Fidler was stable, with a chemocline constant in position relative to the lake bottom. The surface water levels rose and fell through a distance of 1m in conjunction with heavy rainfall in the rainforest, and with river level variation, but had no measurable effect on the absolute position of the chemocline. Marked heterogeneity of dissolved substances at depths in the vicinity of bacteria suggested endogenous influence on pH and gelbstoff (‘gilvin’ in Australia).4Downwelling light attenuation was influenced primarily by gelbstoff (‘gilvin’) in the mixolimnion, with only red light (peak at 700 nm) measurable below 2 m. Light was absorbed mainly by Chlorobium in the monimolimnion, and was unmeasurable deeper than 3 m.5The absorption spectrum of the bacteriochlorophyll d in vivo, with a maximum absorbance at 721 nm, corresponds with the available downwelling light penetrating the mixolimnion to the Chlorobium layer.
    Freshwater Biology 05/2006; 15(6):735 - 747. · 3.93 Impact Factor
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    ABSTRACT: Depth profiles of horizontal light-beam attenuation and in situ fluorescence recorded at 1 to 2 cm depth intervals in Lake Vechten contained pronounced maxima related to phytoplankton and bacterioplankton layers. This was confirmed by microscopy and HPLC analysis of pigments in discrete samples. Algae were sparse throughout the oxic water column compared with green and purple sulphur bacteria in the anoxic zone of the lake, but plankton layers comprising diatoms, green algae, euglenophytes and cryptomonads were observed. Maximum concentrations of phototrophic bacteria, with dominant representatives Synechococcus, Thiopedia, Chloronema and Chlorobium, occurred very close to one another and within the anoxic zone at depths of pigment maxima and major fluorescence peaks. Plankton layers affected downwelling irradiance in two ways: first, by markedly increasing overall light extinction in the vicinity of the layers, e.g. between 4 m and 8 m the minimum wavelength-specific extinction coefficient, which was at 580 nm (k580) increased from 0.5 m−1 to 1.5 m−1; secondly, changes in the shape of extinction (k) spectra corresponded to in vivo absorbance characteristics of photosynthetic pigments of plankton in the layers. It is inferred that field microbial ecological studies may greatly benefit from simultaneous use of in situ optical techniques.
    FEMS Microbiology Letters 06/1989; 62(4):209-219. · 2.72 Impact Factor
  • Carl J. Watras, Alan L. Baker
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    ABSTRACT: For freshwater cyanobacteria, the autofluorescence of phycocyanin is quite high while the in vivo fluorescence (IVF) yield of chlorophyll-a is relatively low, apparently because of low chlorophyll concentrations associated with photosystem II. In eucaryotic phytoplankton, even those with phycobili-protein accessory pigments (e.g. some cryptophytes), the opposite is true. Thus, an IVF ratio which relates phycocyanin to chlorophyll-a signals could be a good index of relative cyanobacterial abundance in the field. Spectrofluorometric scans of whole cells from laboratory cultures indicated that the ratio Em660 @ Ex630/Em680 @ Ex430 could be a very sensitive cyanobacterial indicator. Tandem flowthrough fluorometers were then fitted with the appropriate interference filters and their discriminatory power was evaluated with mixtures of cyanobacterial and eucaryotic phytoplankton. Although subject to many of the constraints of other IVF assays, tandem fluorometry should be particularly appropriate for real-time mapping of the relative spatial and temporal distributions of broad phytoplankton taxa in continuous vertical of horizontal profiles in lakes.
    Hydrobiologia 10/1988; 169(1):77-84. · 2.21 Impact Factor
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    ABSTRACT: A series of inexpensive, pneumatic thin layer water samplers is described. They can be operated from small boats, and permit sampling at 2.5 cm intervals with little or no disturbance of stratified systems such as oxyclines or redoxclines of meromictic lakes, or microstratification of flagellates in sheltered epilimnia. Some models permit replicate sampling at closely-spaced intervals in a two-dimensional array. Their performance abilities are illustrated with examples of microstratification.
    Hydrobiologia 02/1985; 122(3):207-211. · 2.21 Impact Factor
  • Kenneth D. Kimball, Alan L. Baker
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    ABSTRACT: The emergent floral stem, apex, sub-apex, mid-stem, lower stem, and roots of Myriophyllum heterophyllum Michx were analyzed for ash, P, Na, K, Ca, Mg, Fe, Mn, Zn, Cu and Pb. Samples were collected 14 times from June 1979 through July 1980 from Lake Winnipesaukee, New Hampshire, U.S.A.The plant segments sampled differed significantly in mineral content, but seasonal pulses for each mineral were usually in synchrony between the different segments sampled. Sodium (range, 0.8–2.7% dry wt.) and potassium (range, 1.4–3.3% dry wt.) were the dominant elements in the submersed stem. The dominant element in the floral spike was Ca (range, 2.4–4.1% dry wt.) and in the roots was Fe (range, 2.8–8.0% dry wt.). Sodium concentrations were greater in the submersed stem (range, 0.8–2.7% dry wt.), relative to the roots (range, 0.5–0.9% dry wt.) and flora stem (range, 0.3–1.1% dry wt.). Lead concentrated in the roots significantly more (range, 0.0040–0.0115% dry wt.), than in other plant parts (range, 0–0.0037% dry wt.).The submersed stem had spring or summer peaks in ash, P, Na, K, Ca, Mg, and Zn content, whereas Fe and Mn exhibited late winter to early spring peaks. No evidence of nutrient storage during the non-growing season was evident in the segments sampled. Explanations for the seasonal and morphological differences observed are presented.
    Aquatic Botany 06/1983; 16(2):189-205. · 1.47 Impact Factor
  • Kenneth D. Kimball, Alan L. Baker
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    ABSTRACT: The mineral composition of submersed apical shoots of Myriophyllum heterophyllum Michx from Lees Pond and Lake Winnipesaukee, New Hampshire, U.S.A., was analyzed from 1976 to 1978. Minerals analyzed were P, Na, K, Ca, Mg, Fe, Mn, Zn and Cu, as well as ash. Apical mineral content was influenced by both the seasons and sample site location. Seasonal variations in mineral content were largest for Fe and Mn. A generalized seasonal pattern for Na, K, Ca and Mg was a summer maximum. Fe and Mn had late winter maxima, while ash, P and Zn had no significant seasonal variation. Recurrent seasonal patterns were most pronounced for Fe, Mn and Na. Seasonal maxima in Fe content were greater at tributary sampling sites than at non-tributary sites. The recurrent seasonal variations in mineral content observed in this study suggest that the time of sampling can greatly influence the results and therefore the interpretation of tissue chemistry studies of submersed hydrophytes.
    Aquatic Botany 01/1982; 14:139-149. · 1.47 Impact Factor
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    K. Kromer Baker, Alan L. Baker
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    ABSTRACT: Species composition and seasonal succession of the phytoplankton were investigated on the upper Mississippi River at Prairie Island, Minnesota, U.S.A. Both the numbers and volume of individual species were enumerated based on cell counts with an inverted microscope. A succession similar to algal succession in the local lakes occurred. The diatoms were dominant during the spring and fall and blue-green algae were dominant during the summer. The algal concentrations have increased up to 40 fold the concentrations of the 1920's, since the installation of locks and dams. The maximum freshweight standing crop was 4 mg l–1 in 1928 (Reinhard 1931), 13 mg l–1 in 1975 a wet year, and 47 mg l–1 in 1976, a relatively dry year with minimal current discharge. The diatoms varied from 36–99%, the blue-green algae from 0–44% and the cryptmonads from 0–50% of the total standing crop. The green algae were always present but never above 21% of the biomass. The dominant diatoms in recent years were centric -Stephanodiscus andCyclotella spp. (maximum 50,000 ml–1). The dominant blue-green algae wereAphanizomenon flos-aquae (L.) Ralfsex Born.et Flahault andOscillatoria agardhii Gomont (maximum 800 ml–1). These algal species are also present in local lakes. Shannon diversity values indicated greatest diversity of algae during the summer months.
    Hydrobiologia 08/1981; 83(2):295-301. · 2.21 Impact Factor
  • ALAN L. BAKER, KATHLEEN KROMER BAKER
    Limnology and Oceanography 01/1976; 21(3):447-452. · 3.62 Impact Factor

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