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  • 1
    Electronic Resource
    Electronic Resource
    Outgassing from Amazonian rivers and wetlands as a large tropical source of atmospheric CO 2 (2002)
    [s.l.] : Nature Publishing Group
    Nature 416 (2002), S. 617-620 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Terrestrial ecosystems in the humid tropics play a potentially important but presently ambiguous role in the global carbon cycle. Whereas global estimates of atmospheric CO2 exchange indicate that the tropics are near equilibrium or are a source with respect to carbon, ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/416617a
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  • 2
    Electronic Resource
    Electronic Resource
    Simulation of the effect of methane bubble plumes on vertical mixing in Mono Lake (1996)
    Springer
    Aquatic sciences 58 (1996), S. 210-223 
    Details
    ISSN: 1420-9055
    Keywords: Methane ebullition ; vertical mixing ; hypolimnetic heating ; saline lake ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A one-dimensional vertical mixing model modified for application to hypersaline Mono Lake reproduced mixed layer dynamics well but hypolimnetic heating was underestimated. One possible source of increased hypolimnetic heating is vertical mixing caused by bubble plumes of methane rising from the sediments. Estimates of vertical mixing from methane seepage in Mono Lake were made with the inclusion of a bubble plume algorithm. A methane ebullition rate three hundred times greater than the maximum estimate for Mono Lake was required to simulate the observed hypolimnetic heating.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00877509
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  • 3
    Electronic Resource
    Electronic Resource
    Responses of phytoplankton to experimental fertilization with ammonium and phosphate in an African soda lake (1982)
    Springer
    Oecologia 52 (1982), S. 321-326 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Phytoplankton abundance in tropical lakes is more often judged to be limited by nitrogen than phosphorus, but seldom does the evidence include controlled enrichments of natural populations. In January 1980 we performed the first experimental fertilization in an equatorial African soda lake, Lake Sonachi, a small, meromictic volcanic crater lake in Kenya. During our study the natural phytoplankton abundance was ca. 80 μg chl a/l, and the euphotic zone PO4 and NH4 concentrations were less than 0.5 μM. In the monimolimnion PO4 reached 180 μM and NH4 reached 4,600 μM. Replicate polyethylene cylinders (5 m long, 1.2 m3) were enriched to attain 10 μM PO4 and 100 μM NH4. Phytoplankton responses were measured as chlorophyll, cell counts and particulate N, P and C. After two days, the chlorophyll increase in the P treatment was significantly higher than the control (P〈0.01) while the N treatment was not. After five days the molar N/P ratio of seston was the same in the N treatment and control (23) but only 6 in the P treatment. The molar N/P ratio of seston in an unenriched Lake Sonachi sample was 21 and in samples from Lakes Bogoria and Elmenteita, two shallow soda lakes in Kenya, the ratios were 12 and 70 respectively. We conclude that limitation of phytoplankton abundance by phosphorus can occur even in some tropical African soda lakes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00367954
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  • 4
    Electronic Resource
    Electronic Resource
    Temporal variability of phytoplankton in tropical lakes (1979)
    Springer
    Oecologia 44 (1979), S. 1-7 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Temporal variability of ecological systems continues to receive theoretical and empirical attention but remains inadequately documented at low latitudes. Results of my comparative investigation of photosynthetic rates of phytoplankton in 6 equatiorial African lakes and similar information from 20 South American, Asian and African lakes studied by others provide the data for an assessment of the range of seasonal variability (expressed as coefficients of variation, CV) among tropical lakes. Sampling intervals varied from 1 week to 3 months and usually spanned at least one year. Within Africa the coefficient of variation ranged from 15% to 61%, and among all the lakes the coefficient of variation ranged from 15% to 86%. The Spearman rank correlation coefficient of the CV's of photosynthesis versus latitude is 0.24 and is not significant at the 0.05 level. Coefficients of variation of photosynthetic rates of phytoplankton in a diverse set of 45 temperate and arctic lakes ranged from 29% to 155% and were significantly different from the set of 26 tropical lakes by the Mann-Whitney U test. When all 71 lakes are compared, the Spearman rank correlation coefficient of CV's of photosynthesis versus latitude is 0.71 and is significant at the 0.0005 level. Three temporal patterns were recognized among tropical lakes. Most tropical lakes exhibit pronounced seasonal fluctuations that usually correspond with variations in rainfall, river discharges or vertical mixing. A second pattern occurs in lakes with muted fluctuations (coefficient of variation less than 20%) in which diel changes often exceed month to month changes. A third pattern is distinguished by an abrupt change from one persistent algal assemblage (i.e., extant for at least 10 generations) and level of photosynthetic activity to another persistent condition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00346388
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  • 5
    Electronic Resource
    Electronic Resource
    Nitrogen yields from undisturbed watersheds in the Americas (1999)
    Springer
    Biogeochemistry 46 (1999), S. 149-162 
    Details
    ISSN: 1573-515X
    Keywords: dissolved organic nitrogen ; nitrogen concentrations ; nitrogen cycle ; nitrogen yields ; nitrate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Yields of total fixed nitrogen and nitrogen fractions are summarized for thirty-one watersheds in which anthropogenic disturbance of the nitrogen cycle, either through land use or atmospheric deposition, is negligible or slight. These yields are taken as representative of background conditions over a broad range of watershed areas, elevations, and vegetation types. The data set focuses on watersheds of the American tropics, but also includes information on the Gambia River (Africa) and some small watersheds in the Sierra Nevada of California. For the tropical watersheds, total nitrogen yield averages 5.1 kg ha−1 y−1. On average, 30% of the total is particulate and 70% is dissolved. Of the dissolved fraction, an average of 50% is organic and 50% is inorganic, of which 20% is ammonium and 80% is nitrate. Yields are substantially lower than previously estimated for background conditions. Yields of all nitrogen fractions are strongly related to runoff, which also explains a large percentage of variance in yield of total nitrogen (r2=0.85). For total nitrogen and nitrogen fractions, yield increases at about two-thirds the rate of runoff; concentration decreases as runoff increases. There is a secondary but significant positive relationship between elevation and yield of DIN. Ratios DON/TDN and PN/TN both are related to watershed area rather than runoff; DON/TDN decreases and PN/TN increases toward higher stream orders. The analysis suggests for tropical watersheds the existence of mechanisms promoting strong homeostasis in the yield of N and its fractions for a given moisture regime, as well as predictable downstream change in proportionate representation N fractions. Yields and concentrations for small tropical watersheds are much larger than for the few temperate ones with which comparisons are possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01007577
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  • 6
    Electronic Resource
    Electronic Resource
    Nitrogen yields from undisturbed watersheds in the Americas (1999)
    Springer
    Biogeochemistry 46 (1999), S. 149-162 
    Details
    ISSN: 1573-515X
    Keywords: dissolved organic nitrogen ; nitrogen concentrations ; nitrogen cycle ; nitrogen yields ; nitrate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Yields of total fixed nitrogen and nitrogen fractions are summarized for thirty-one watersheds in which anthropogenic disturbance of the nitrogen cycle, either through land use or atmospheric deposition, is negligible or slight. These yields are taken as representative of background conditions over a broad range of watershed areas, elevations, and vegetation types. The data set focuses on watersheds of the American tropics, but also includes information on the Gambia River (Africa) and some small watersheds in the Sierra Nevada of California. For the tropical watersheds, total nitrogen yield averages 5.1 kg ha −1 y−1. On average, 30% of the total is particulate and 70% is dissolved. Of the dissolved fraction, an average of 50% is organic and 50% is inorganic, of which 20% is ammonium and 80% is nitrate. Yields are substantially lower than previously estimated for background conditions. Yields of all nitrogen fractions are strongly related to runoff, which also explains a large percentage of variance in yield of total nitrogen (r2 = 0.85). For total nitrogen and nitrogen fractions, yield increases at about two-thirds the rate of runoff; concentration decreases as runoff increases. There is a secondary but significant positive relationship between elevation and yield of DIN. Ratios DON/TDN and PN/TN both are related to watershed area rather than runoff; DON/TDN decreases and PN/TN increases toward higher stream orders. The analysis suggests for tropical watersheds the existence of mechanisms promoting strong homeostasis in the yield of N and its fractions for a given moisture regime, as well as predictable downstream change in proportionate representation N fractions. Yields and concentrations for small tropical watersheds are much larger than for the few temperate ones with which comparisons are possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006108315578
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  • 7
    Electronic Resource
    Electronic Resource
    Primary producer dynamics associated with evaporative concentration in a shallow, equatorial soda lake (Lake Elmenteita, Kenya) (1988)
    Springer
    Hydrobiologia 158 (1988), S. 1-14 
    Details
    ISSN: 1573-5117
    Keywords: Saline lakes ; phytoplankton ; benthic and planktonic photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Lake Elmenteita (0°27′S, 36°15′E) lies on the floor of the rift valley at 1776 m above sea level in Kenya. As a consequence of lower than average rainfall, the mean depth decreased from 1.1 to 0.65 m during the study period (February 1973 to August 1974). The initiation of major biological changes coincided with a period of rapid evaporative concentration in 1973 (February to April) when the conductivity increased from 19.1 to 27.0 mmhmos cm-1. Spirulina platensis, Spirulina laxissima and Anabaenopsis arnoldii decreased in abundance precipitously in parallel with large declines in chlorophyll a concentration and phytoplankton photosynthetic rates. Once the overall abundance of phytoplankton had declined and the transparency had increased, primary productivity by benthic algae increased significantly. Paradiaptomus africanus, the only copepod living in the lake, was abundant in February and March 1973, but was gone by May. Eight hypotheses to explain these changes are evaluated and converge on the suggestion that a rate of change of salinity greater than 5 mmhmos cm-1 per month and a salinity exceeding 25 mmhmos cm-1 cannot be tolerated by P. africanus and adversely effects the nitrogen fixer, A. arnoldii. Furthermore, the loss of P. africanus and oxygenation of the sediments by benthic algae reduce the rate of recyling of nutrients which alters phytoplankton abundance and species composition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00026264
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  • 8
    Electronic Resource
    Electronic Resource
    Photosynthetic activity of phytoplankton and its relation to environmental factors in hypersaline Mono Lake, California (1988)
    Springer
    Hydrobiologia 158 (1988), S. 69-88 
    Details
    ISSN: 1573-5117
    Keywords: Mono Lake ; photosynthesis ; salt lake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The photosynthetic activity of phytoplankton in hypersaline Mono Lake, California was measured over the three year period, 1983–1985. The maximum chlorophyll-specific rate of carbon uptake (Pm B) and the light-limited slope (alpha) were derived from laboratory measurements of photosynthesis vs. irradiance (P-I) relationships. Annual estimates of primary production were 340–540 g C m-2 yr-1. Production was two to three times higher during the spring of 1983 than in the springs of 1984 and 1985; higher standing biomass of algae occurred in 1983. While Pm B rates followed water temperatures and varied over 40-fold over the year, integral primary production varied less since periods of high Pm B occurred when algal biomass was low. Sixty-eight percent of the seasonal variation in the Pm B was explained by a regression on temperature (53%), chlorophyll a (12%), and the carbon:chlorophyll a ratio (3%). Light-saturated and light-limited rates of photosynthesis generally covaried, evidenced by the strong seasonal correlation between Pm B and alpha. Sixty-one percent of variation in alpha was explained by a regression on Pm B, temperature, grazing, water column stability, and self-shading. There was no correlation of carbon uptake with ambient levels of inorganic nitrogen. The regression coefficient of the dependence of Pm B on the seasonal temperature trend was much larger than that determined from individual samples incubated at several different temperatures; this indicates that uptake is limited by more than low temperatures in the spring. Regression equations including only temperature, chlorophyll and depth were sufficient to estimate patterns of seasonal and year to year variation in integral primary productivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00026267
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  • 9
    Electronic Resource
    Electronic Resource
    In situ hatching of Artemia monica cysts in hypersaline Mono Lake, California (1988)
    Springer
    Hydrobiologia 158 (1988), S. 183-190 
    Details
    ISSN: 1573-5117
    Keywords: Artemia monica ; cyst hatching ; emergence traps
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Two emergence trap designs were tested in Mono Lake, California, to measure in situ hatching of Artemia monica cysts on the lake bottom. One design incorporated a removable sample bottle; the other had a catch tube which was pumped from the surface. Both traps rested on the bottom and had a narrow gap between the collecting funnel and bottom flange to allow the chemical conditions within the trap to be similar to those outside. This gap was open during April and May but, because some animals entered from outside the area enclosed by the trap, the gap was covered with 400 µm or 800 µm screen during June and July. The two trap types without screens sampled a station in oxic water 7 m deep similarly in April and May 1985. Mean daily hatching rates from April to May 1985 ranged from 720 to 25 340 shrimp m-2 day-1. In contrast, mean daily hatching rates during the same period at a station in anoxic water 21 m deep were from 3 to 138 shrimp m-2 day-1. June and July hatching rates in the shallow station were lower than in the spring, usually less than 1000 shrimp m-2 day-1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00026276
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  • 10
    Electronic Resource
    Electronic Resource
    Artemia monica cyst production and recruitment in Mono Lake, California, USA (1990)
    Springer
    Hydrobiologia 197 (1990), S. 233-243 
    Details
    ISSN: 1573-5117
    Keywords: Artemia monica ; cyst production ; recruitment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Annual egg production was determined for Artemia monica in Mono Lake, California, from 1983 to 1987. Annual oviparous (overwintering cyst) production was 3 and 7 million cysts m−2 yr−1 in 1986 and 1987, respectively, as measured by in situ sediment traps. Cyst production for the entire five year period was calculated using Artemia census data and inter-brood duration derived from mixolimnetic temperature. These estimates ranged from 2 to 5 million cysts m−2 yr−1. This method underestimated annual production by 30%, when compared to estimates using sediment traps. Cyst production was similar during 1983–1986 and showed a significant increase in 1987, which was due primarily to a larger reproductive population later in the year. Recruitment into the adult populations of the following spring ranged between 1.4 to 3.2%. Overall abundance of this generation reflected the patterns in annual cyst production. Compensatory effects must operate on the second generation of each year, since summer populations were similar in all years despite differences in cyst production.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00026953
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