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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    Solute export from forested and partially deforested chatchments in the central Amazon (1997)
    Springer
    Biogeochemistry 38 (1997), S. 67-102 
    Details
    ISSN: 1573-515X
    Keywords: Amazon ; catchments ; deforestation ; slash-and-burn agriculture ; solutes ; water balance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The hydrochemical responses to slash-and-burnagriculture in a small rainforest catchment of thecentral Amazon were investigated for one year. Disturbances in the partially deforested catchmentbegan in 1987, and during the study a 2-ha plot was cut(July 1989) and burned (October 1989) in preparationfor the cultivation of manioc; the partially deforestedcatchment was approximately 80% deforested at the timeof this study. Solute fluxes exported by base flowwere estimated from solute concentrations of stream watermeasured at least once per week. Solute fluxesfor storm flow were estimated by measuring streamwaterconcentrations during two storms. Baseflow runoffrepresented about 94% of the water outflow from thestudy basin and was the dominant pathway of soluteexport. Total rainfall during the study period was2754 mm of which 2080 mm was exported from thepartially deforested catchment as stream runoff. Theratio of surface runoff to annual rainfall for asimilar study conducted in the same catchment whilecompletely forested in 1984 was lower than after thecatchment was 80% deforested in 1990 (0.57 versus0.76), while evapotranspiration (ET) was lower by about afactor of two in 1990 compared to 1984. Particulateremoval from the partially deforested catchment was 151kg ha−1 yr−1. Nutrient losses from thepartially deforested catchment were higher than thosemeasured when the catchment was undisturbed in 1984 byfactors of 1.4, 1.8, and 2.1 for total inorganicnitrogen (TIN), total dissolved nitrogen (TDN), and totalnitrogen (TN); and by factors of 4.0, 6.6, and 7.9 for solublereactive phosphate (PO3− 4), total dissolvedphosphorus (TDP), and total phosphorus (TP),respectively. These data show that deforestation andcolonization in upland catchments of the central Amazonalter the hydrochemical balance of streams bydecreasing ET, thereby increasing discharge and soluteexport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005774431820
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  • 5
    Electronic Resource
    Electronic Resource
    Composition and deposition of throughfall in a flooded forest archipelago (1999)
    Springer
    Biogeochemistry 45 (1999), S. 169-195 
    Details
    ISSN: 1573-515X
    Keywords: Amazon ; flooded forest ; Negro River ; rain ; solutes ; throughfall
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The sources of spatial and temporal variation and rates of nutrient deposition via throughfall were studied for 9 months in the Anavilhanas archipelago of the Negro River, Brazil. A total of 30 events was sampled individually for rain and throughfall chemistry in a 1-ha plot of flooded forest. Throughfall samples were collected in 40 collectors distributed in five parallel transects in the study plot, while rain was collected in 4 collectors in an adjacent channel. Volume-weighted mean (VWM) concentrations of solutes in rain were consistently lower than in throughfall, except for H+, NO3- and NH4+. Ratios of VWM concentrations of rain to throughfall indicated that K+, followed by Mg2+ and PO43-, were the most enhanced solutes as rain passed through the forest canopy. The deposition of solutes varied significantly among transects, except for Na+ and Ca2+, and was significantly correlated with maximum flooding depth, foliar nutrient content soil fertility and canopy closure for most solutes. The concentrations of PO43- and most major ions were higher in throughfall compared to those in rain due to canopy exchange and dry deposition. In contrast, NO3-, NH4+ and H+ were retained due to immobilization by leafy canopy and ion exchange processes. Solute inputs via throughfall (not including stemflow) to a floodplain lake (Lake Prato) of the archipelago accounted for 30 to 64% of the total for most solutes in the lake at high water, which indicates that throughfall is an important source of nutrients to the aquatic ecosystem of the Anavilhanas archipelago.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006108618196
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  • 6
    Electronic Resource
    Electronic Resource
    Methane emissions from an Amazon floodplain lake: Enhanced release during episodic mixing and during falling water (2000)
    Springer
    Biogeochemistry 51 (2000), S. 71-90 
    Details
    ISSN: 1573-515X
    Keywords: Amazon floodplain ; episodic mixing ; lakes ; methane emission
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Methane fluxes to the troposphere were measured inLake Calado, a dendritic floodplain lake located inthe central Amazon Basin. Methane concentrations inthe surface water of the lake were less than 0.5 µM during a period of high and rising water inApril and May, except when episodic, deep mixingoccurred and surficial concentrations reached as highas 4.8 µM. Diffusive fluxes ranged from ca.2–20 mg CH4 m−2d−1 (mean: 6.6 mg CH4 m−2d−1) normally, but increased up to 220 mg CH4 m−2d−1 during the passageof a rare cold front. During six weeks of risingwater, the volume-weighted methane content of the lakeincreased during periods of stable thermalstratification (accumulation rates ranging from16–1411 mg CH4 m−2d−1) and decreasedduring episodes of partial mixing (rates of decreaseranging from 63–1792 mg CH4 m−2d−1). Surface water methane concentrations during low andfalling water in September varied by more than anorder of magnitude (range, 0.3–9 µM), anddiffusive fluxes ranged from 3–158 mg CH4m−2d−1 (mean, 54 mg CH4 m−2d−1). During falling water in September, total methane flux from the lake to the troposphere measured with a floating chamber rangedfrom 53–328 mg CH4 m−2d−1 (mean, 163 mgCH4 m−2d−1). Ebullitive flux averaged 69% of total flux. Total methane flux was highest when thermal stratification was lost due to decreasing lake depth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006389124823
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  • 7
    Electronic Resource
    Electronic Resource
    Mass balance of major solutes in a rainforest catchment in the Central Amazon: Implications for nutrient budgets in tropical rainforests (1996)
    Springer
    Biogeochemistry 32 (1996), S. 115-142 
    Details
    ISSN: 1573-515X
    Keywords: Central Amazon ; nutrient budgets ; tropical rainforests
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract A solute mass balance for a 23.4 ha catchment of undisturbed rainforest in the central Amazon Basin was computed from detailed measurements of water and solute fluxes via rainfall, streamflow, and subsurface outflow over an annual cycle. Annual atmospheric deposition fluxes are lower than previously reported among mass balance studies conducted in the Amazon. Nutrient export fluxes are lower than previously reported for the Amazon, despite the fact that export fluxes via flow paths not previously measured were included. Given that climatic conditions were representative of a one in 10 wet year, the ecosystem was expected to show a net loss of nutrients rather than net gain. Instead, an excess of nutrient inputs via rainfall over ecosystem outflows was detected, ranging in annual quantities from 0.30 to 0.50 of the measured input. Among several mechanisms that could reconcile this budget, two are supported by the information presently available while two others cannot be evaluated without further research. Interannual variability in the amount of water available for runoff at the spatial scale of small catchments varies by a factor of two, in contrast to rainfall variability of ±20%, and may be a critical control on the apparent changes in ecosystem storage detected by annual-scale nutrient budgets in rainforests. Entrainment of materials from the terrestrial ecosystem to the atmosphere, including particulates containing elements which do not exist as gases, may be a particularly important loss pathway in rainforests existing on deeply weathered or nutrient poor soils.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00000355
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  • 8
    Electronic Resource
    Electronic Resource
    Solute dynamics in soil water and groundwater in a central Amazon catchment undergoing deforestation (1997)
    Springer
    Biogeochemistry 38 (1997), S. 303-335 
    Details
    ISSN: 1573-515X
    Keywords: Amazon ; deforestation ; hydrologic pathway ; groundwater ; nitrogen ; rain forest ; slash-and-burn agriculture ; solutes ; tropical
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Hydrochemical changes caused by slash-and-burnagricultural practices in a small upland catchment inthe central Amazon were measured. Soluteconcentrations were analyzed in wet deposition,overland flow, shallow throughflow, groundwater andbank seepage in a forested plot (about 5 ha) and anadjacent plot (about 2 ha) which had been deforestedin July 1989 and planted to manioc, and in streamwater in partially deforested and forested catchments. Measurements were made from November 1988 to June1990. The effects of slash-and-burn agriculturalpractices observed in the experimental plot includedincreased overland flow, erosion, and large losses ofsolutes from the rooted zone. Concentrations ofNO3 -, Na+, K+, SO4 2-,Cl- and Mn in throughflow of the experimentalplot were higher than those of the control plot bymore than a factor of 10. Extensive leaching occurredafter cutting and burning, but solute transfers werediminished along pathway stages of throughflow togroundwater, and particularly within the riparian zoneof the catchment. High concentrations of N and P inoverland flow indicate the importance of usingforested riparian buffers to mitigate solute inputs toreceiving waters in tropical catchments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005801303639
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  • 9
    Electronic Resource
    Electronic Resource
    Effects of prescribed burning and drought on the solute chemistry of mixed-conifer forest streams of the Sierra Nevada, California (1997)
    Springer
    Biogeochemistry 39 (1997), S. 225-253 
    Details
    ISSN: 1573-515X
    Keywords: California ; catchments ; drought ; mass balances ; prescribed burning ; solutes ; Sierra Nevada ; stream water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Solute concentrations in atmospheric depositionand stream water were measured in two mixed-conifercatchments (Tharp‘s and Log creeks) in the SierraNevada of California from 1984 through 1995, a periodincluding a 6-year drought and a prescribed burn inone catchment. The effects of prescribed burning inthe Tharp‘s Creek catchment significantly increasedthe concentrations of most solutes in stream water. In the first year after prescribed burning, the VWM(volume-weighted mean) concentrations of acid anionsin stream water increased proportionally more thanthose of the base cations, and ANC (acid neutralizingcapacity) more than doubled. Sulfate and NO 3 - increased proportionally more in streamwater than any other ions after the fire, but pre- andpost-burn VWM pH were not significantlydifferent. VWM SO 4 2- and NO 3 - concentrations the first year after burning occurredwere about 16- and 2,000-fold above pre-burnbaselines, respectively, while that of Cl-increased 4-fold. Net retention (precipitationinputs minus streamwater outputs) of H+,NO 3 - , NH 3 + , SO 4 2- and Cl- occurred in both catchments, except afterprescribed burning of the Tharp’s Creek catchment inthe fall of 1990, which caused a net export ofSO 4 2- , Cl- and K+ thefirst year after the burn. Most solutes remained abovepre-disturbance concentrations by the end of the thirdyear after burning, whereas H+ and SiO2remained below. Periodic increases in theconcentrations of Na+, Ca2+ and SO 4 2- , and decreases in ANC and SiO2occurred during a 6-year drought monitored in theadjacent undisturbed catchment of Log Creek.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005858219050
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  • 10
    Electronic Resource
    Electronic Resource
    Composition and deposition of throughfall in a flooded forest archipelago (Negro River, Brazil) (1999)
    Springer
    Biogeochemistry 45 (1999), S. 169-195 
    Details
    ISSN: 1573-515X
    Keywords: Amazon ; flooded forest ; Negro River ; rain ; solutes ; throughfall
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The sources of spatial and temporal variation and rates of nutrient deposition via throughfall were studied for 9 months in the Anavilhanas archipelago of the Negro River, Brazil. A total of 30 events was sampled individually for rain and throughfall chemistry in a 1-ha plot of flooded forest. Throughfall samples were collected in 40 collectors distributed in five parallel transects in the study plot, while rain was collected in 4 collectors in an adjacent channel. Volume-weighted mean (VWM) concentrations of solutes in rain were consistently lower than in throughfall, except for H+, NO 3 − and NH 4 + . Ratios of VWM concentrations of rain to throughfall indicated that K+, followed by Mg2+ and PO 4 3− , were the most enhanced solutes as rain passed through the forest canopy. The deposition of solutes varied significantly among transects, except for Na+ and Ca2+, and was significantly correlated with maximum flooding depth, foliar nutrient content, soil fertility and canopy closure for most solutes. The concentrations of PO 4 3− and most major ions were higher in throughfall compared to those in rain due to canopy exchange and dry deposition. In contrast, NO 3 − , NH 4 + and H+ were retained due to immobilization by leafy canopy and ion exchange processes. Solute inputs via throughfall (not including stemflow) to a floodplain lake (Lake Prato) of the archipelago accounted for 30 to 64% of the total for most solutes in the lake at high water, which indicates that throughfall is an important source of nutrients to the aquatic ecosystem of the Anavilhanas archipelago.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01106780
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