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1.
Response of mesquite to nitrate and salinity in a simulated phreatic environment: Water use,dry matter and mineral nutrient accumulation 总被引:1,自引:0,他引:1
Mesquite plants (Prosopis glandulosa var. Torreyana) were grown in 2-m long columns 20 cm in diameter, and provided with a constant, stable ground water source
10 cm above the sealed base of the column. Ground water contained 0, 1 or 5 mM nitrate, or a mixed salt solution (1.4, 2.8, or 5.6 dS m-1) with the ionic ratios of ground water found in a field stand of Prosopis at Harper's Well (2.8 dS m-1). Water uptake in the highly salinized columns began to decrease relative to low salt columns when soil salinity probes 30
cm above the column base read approximately 28 dS m-1, a potential threshold for mesquite salt tolerance. Prosopis growth increased with increasing nitrate, and decreased with
increasing salinity. Water use efficiency was little affected by treatment, averaging approximately 2 g dry matter L-1 water used. Most fine roots were recovered from a zone about 25 cm above the ground water surface where water content and
aeration appeared to be optimal for root growth. Root-shoot ratio was little affected by nitrate, but increased slightly with
increasing salinity. Plant tissue P concentrations tended to increase with increasing salinity and decrease with increasing
N, approaching potentially deficient foliage concentrations at 5 mM nitrate. The whole-plant leaf samples increased in sodium concentration both with added salt and with added nitrate. Foliar
manganese concentrations increased with increasing salt in the absence of nitrate. Concentrations of sodium in leaves were
low (<10 g kg-1), considering the high salt concentrations in the ground water. Prosopis appears to exclude sodium very effectively, especially
from its younger leaves. Although Prosopis is highly salt tolerant, the degree to which it utilizes soil nitrate in place
of biologically fixed N may lower its salinity tolerance and affect its nutrient relations in phreatic environments. 相似文献
2.
Naidu GS Lee IY Cho OK Park YH 《Journal of industrial microbiology & biotechnology》2001,26(5):309-315
L -Carnitine is an ubiquitous substance that plays a major role in the transportation of long-chain fatty acids. We investigated
crucial factors that influence microbial conversion of γ-butyrobetaine to L-carnitine using an Achromobacter cycloclast strain. Two-stage culture results showed that γ-butyrobetaine induced enzymes essential for the conversion, which suggests
that the precursor should be present in the initial cell growth stage. The addition of yeast extract enhanced L-carnitine production whereas inorganic nitrogen sources inhibited it. Under nitrogen-limiting conditions, the cells accumulated
poly-β-hydroxybutyrate instead of L-carnitine. Among the trace elements tested, nickel addition enhanced L-carnitine production by almost twice that of the control and copper strongly inhibited the conversion. L-Carnitine production was reduced when the medium contained inorganic salts of sodium, potassium, and calcium at a concentration
greater than 2 g l−1. A higher L-carnitine yield was achieved when cells were incubated in a lower culture volume. The optimal pH for L-carnitine production was 5 to 5.5, whereas that of growth was 7.0, indicating that a pH shift was required. Under optimal
conditions, L-carnitine concentrations as high as 15 g l−1 were obtained in 62 h with a 45% molar conversion yield. Journal of Industrial Microbiology & Biotechnology (2001) 26, 309–315.
Received 26 November 2000/ Accepted in revised form 27 February 2001 相似文献
3.
The growth response of a nitrogen fixing cyanobacterium, Anabaena flos-aquae (Lyng) Bréb., to sodium and nitrate was examined in batch culture under controlled laboratory conditions. Sodium (range 0-12 mg Na+· L-1) enhanced growth of the cyanobacterium under nitrate-sufficient (5.7 mg NO3-N · L-1) but not nitrate-limited (0.49 mg NO3- N · L-1) conditions. The magnitude of the growth response was related to the nutritional history of the culture. No significant effect of sodium on nitrate utilization was observed. The increase in ambient sodium levels in many lakes may provide a competitive advantage to cyanobacteria. 相似文献
4.
Haifeng Yu 《Journal of applied phycology》2012,24(4):669-673
The effects of organic carbon sources on cell growth and exopolysaccharide (EPS) production of dissociated Nostoc flagelliforme cells under mixotrophic batch culture were investigated. After 7?days of cultivation, glycerol, acetate, sucrose, and glucose increased the final cell density and final EPS concentrations, and mixotrophic growth achieved higher biomass concentrations. The increase in cell growth was particularly high when glucose was added as the sole carbon source. On the other hand, EPS production per dry cell weight was significantly enhanced by adding acetate. For more effective EPS production, the effects of the mixture of glucose and acetate were investigated. Increasing the ratio of glucose to acetate resulted in higher growth rate with BG-11 medium and higher EPS productivity with BG-110 medium (without NaNO3). When the medium was supplemented with a mixture of glucose (4.0?g?L?1) and acetate (2.0?g?L?1), 1.79?g?L?1 biomass with BG-11 medium and 879.6?mg?L?1 of EPS production with BG-110 medium were achieved. Adopting this optimal ratio of glucose to acetate established in flask culture, the culture was also conducted in a 20-L photobioreactor with BG-11 medium for 7?days. A maximum biomass of 2.32?g?L?1 was achieved, and the EPS production was 634.6?mg?L?1. 相似文献
5.
A family of 10 competing, unstructured models has been developed to model cell growth, substrate consumption, and product formation of the pyruvate producing strain Escherichia coli YYC202 ldhA::Kan strain used in fed-batch processes. The strain is completely blocked in its ability to convert pyruvate into acetyl-CoA or acetate (using glucose as the carbon source) resulting in an acetate auxotrophy during growth in glucose minimal medium. Parameter estimation was carried out using data from fed-batch fermentation performed at constant glucose feed rates of
qVG=10 mL h–1. Acetate was fed according to the previously developed feeding strategy. While the model identification was realized by least-square fit, the model discrimination was based on the model selection criterion (MSC). The validation of model parameters was performed applying data from two different fed-batch experiments with glucose feed rate
qVG=20 and 30 mL h–1, respectively. Consequently, the most suitable model was identified that reflected the pyruvate and biomass curves adequately by considering a pyruvate inhibited growth (Jerusalimsky approach) and pyruvate inhibited product formation (described by modified Luedeking–Piret/Levenspiel term).List of symbols cA
acetate concentration (g L–1)
- cA,0
acetate concentration in the feed (g L–1)
- cG
glucose concentration (g L–1)
- cG,0
glucose concentration in the feed (g L–1)
- cP
pyruvate concentration (g L–1)
- cP,max
critical pyruvate concentration above which reaction cannot proceed (g L–1)
- cX
biomass concentration (g L–1)
- KI
inhibition constant for pyruvate production (g L–1)
- KIA
inhibition constant for biomass growth on acetate (g L–1)
- KP
saturation constant for pyruvate production (g L–1)
- KP
inhibition constant of Jerusalimsky (g L–1)
- KSA
Monod growth constant for acetate (g L–1)
- KSG
Monod growth constant for glucose (g L–1)
- mA
maintenance coefficient for growth on acetate (g g–1 h–1)
- mG
maintenance coefficient for growth on glucose (g g–1 h–1)
- n
constant of extended Monod kinetics (Levenspiel) (–)
- qV
volumetric flow rate (L h–1)
- qVA
volumetric flow rate of acetate (L h–1)
- qVG
volumetric flow rate of glucose (L h–1)
- rA
specific rate of acetate consumption (g g–1 h–1)
- rG
specific rate of glucose consumption (g g–1 h–1)
- rP
specific rate of pyruvate production (g g–1 h–1)
- rP,max
maximum specific rate of pyruvate production (g g–1 h–1)
- t
time (h)
- V
reaction (broth) volume (L)
- YP/G
yield coefficient pyruvate from glucose (g g–1)
- YX/A
yield coefficient biomass from acetate (g g–1)
- YX/A,max
maximum yield coefficient biomass from acetate (g g–1)
- YX/G
yield coefficient biomass from glucose (g g–1)
- YX/G,max
maximum yield coefficient biomass from glucose (g g–1)
-
growth associated product formation coefficient (g g–1)
-
non-growth associated product formation coefficient (g g–1 h–1)
-
specific growth rate (h–1)
- max
maximum specific growth rate (h–1) 相似文献
6.
Dibueng Prudence Mokoena Sihle V. Mngadi Masixole Sihlahla Mogolodi K. Dimpe 《Soil & Sediment Contamination》2019,28(3):323-333
In this study, a simple and rapid methodology based on the hot-plate digestion method using dilute nitric acid solution was used to extract trace metals (such as As, Cd, Cr, Cu, Pb, Fe, and Zn) from freshwater sediments. The concentrations of the elements were determined using inductively coupled plasma-optical emission spectrometry (ICP-OES). The factors (temperature, nitric acid concentration, and volume) affecting the digestion method were optimized using one-factor-at-a-time (OFAT) or univariate methodology, and the optimization process was carried out using freshwater sediment certified reference material (CRM015). The optimal conditions for temperature, nitric acid concentration, and time in the method were 180°C, 10 mL of 5 mol L?1 HNO3, and 45 min, respectively. Under optimum conditions, the limit of detection (LOD) ranged between 0.02 and 0.08 µg L?1 and the limit of quantification (LOQ) ranged from 0.07 and 0.27 µg L?1. In addition, the method detection limits (MDLs) and method quantification limits (MQLs) were 0.10–0.17 and 0.30?0.57 µg g?1, respectively. The overall accuracy of the method determined by recovery of the trace elements in the CRMs ranged from 98 to 111% with the precision ranging from 1.4 to 5.8%. The method was successfully applied for the determination of target metals from real freshwater sediment samples. 相似文献
7.
Tetraspores of Sarcothalia crispata from San Juan Bay, Strait of Magellan, Chile, were cultivated under different combinations of photon flux densities and agricultural
fertilizers in the laboratory. In the experiment, the S. crispata specimens were cultured in combinations of different photon flux densities (50, 100, 150 μmol photons m-2 s-1) and enriched seawater solutions (sodium nitrate + monocalcium phosphate, urea + monocalcium phosphate, ammonium nitrate
+ monocalcium phosphate), always adjusting the N and P concentrations to 10 and 3 mg L-1, and in sea water as control. After 45 days, the tetrasporeling plants were found to be larger at photon flux densities of
50 and 100 μmol photons m-2 s-1 in the nutrient enrichment experiments; growth was greatest in the sea water enriched with ammonium nitrate and urea. An
analysis of the combined effect of the photon flux density and nutrients revealed that the best combination for sporeling
growth was the ammonium nitrate and urea solution at 50–100 μmol photons m-2 s-1. 相似文献
8.
Effects of nitrogen source and concentration on growth rate and fatty acid composition of Ellipsoidion sp. (Eustigmatophyta) 总被引:6,自引:0,他引:6
Nianjun Xu Xuecheng Zhang Xiao Fan Lijun Han Chengkui Zeng 《Journal of applied phycology》2001,13(6):463-469
In order to study the effects of different nitrogen source and concentrationon the growth rate and fatty acid composition, a marine microalga Ellipsoidion sp. with a high content of eicosapentaenoic acid (EPA) wascultured in media with different nitrogen sources and concentrations.During the pre-logarithmic phase, the alga grew faster with ammoniumas N source than with nitrate, but the reverse applied during thepost-logarithmic phase. The alga grew poorly in N-free mediumor medium with urea as the sole N source. In the same growth phase,ammonium medium resulted in higher yield of total lipid, but the EPA yielddid not differ significantly different from that using nitrate medium. Themaximum growth rate occurred in medium containing 1.28 mmolL-1 sodium nitrate, while maximum EPA and total lipid contents werereached at 1.92 mmol L-1, when EPA accounted for 27.9% totalfatty acids. The growth rate kept stable when NH4Cl ranged from0.64 to 2.56 mmol L-1, and the maximum content of total lipidand EPA occurred in the medium with 2.56 mmol L-1NH4Cl. The EPA content was higher in the pre- thanpost-logarithmic phase, though the total lipid content was lower. Thehighest EPA content expressed as percent total fatty acid was 27.9% innitrate medium and and 39.0% in ammonium medium. 相似文献
9.
Jan Peter van der Hoek Paul J. M. Latour Abraham Klapwijk 《Applied microbiology and biotechnology》1988,28(4-5):493-499
Summary In the combined ion exchange/biological denitrification process for nitrate removal from ground water anion exchange resins are regenerated in a closed circuit by way of an upflow sludge blanket denitrification reactor. The regenerant (a concentrated sodium bicarbonate solution) is recirculated through the ion exchanger in the r generation mode and the denitrification reactor. In the closed system sulfate accumulates to very high concentrations. For that reason it was examined under what process conditions sulfate reduction occurs in an upflow sludge blanket denitrification reactor, when the influent contains high sulfate concentrations (5.45 g SO
4
2-
/l) and high sodium bicarbonate concentrations (19.8 g NaHCO3/l) in addition to nitrate and methanol. It appeared that at a hydraulic residence time of 5 h sulfide production started, when the nitrate loading rate was 20% of the denitrification reactor capacity and methanol was added in excess. The excess of methanol was converted into acetate after nitrate was depleted. Conversion of methanol into acetate was a function of the hydraulic residence time. At hydraulic residence times above 8 h this conversion was complete. Also in batch experiments it was observed that excess of methanol was converted into acetate, and that sulfate reduction started when nitrate was depleted. From all experiments it is clear that, provided that methanol is added in good relation to the quantity of nitrate that has to be denitrified, acetate will not be produced and sulfate reduction will not occur in the denitrification reactor, even in the presence of very high sulfate concentrations. 相似文献
10.
V. Saranya V. Rajeswari P. Abirami K. Poornimakkani P. Suguna 《Preparative biochemistry & biotechnology》2016,46(5):446-453
Polyhydroxyalkanoate (PHA) is a promising polymer for various biomedical applications. There is a high need to improve the production rate to achieve end use. When a cost-effective production was carried out with cheaper agricultural residues like molasses, traces of toxins were incorporated into the polymer, which makes it unfit for biomedical applications. On the other hand, there is an increase in the popularity of using chemically defined media for the production of compounds with biomedical applications. However, these media do not exhibit favorable characteristics such as efficient utilization at large scale compared to complex media. This article aims to determine the specific nutritional requirement of Pseudomonas sp. MNNG-S for efficient production of polyhydroxyalkanoate. Response surface methodology (RSM) was used in this study to statistically design for PHA production based on the interactive effect of five significant variables (sucrose; potassium dihydrogen phosphate; ammonium sulfate; magnesium sulfate; trace elements). The interactive effects of sucrose with ammonium sulfate, ammonium sulfate with combined potassium phosphate, and trace element with magnesium sulfate were found to be significant (p?.001). The optimization approach adapted in this study increased the PHA production more than fourfold (from 0.85?g?L?1 to 4.56?g?L?1). 相似文献
11.
James L. Botsford 《Archives of microbiology》1984,137(2):124-127
A defined medium of low osmolarity was developed permitting growth of Rhizobium meliloti with generation times of approximately 2.8 h doubling-1. The effects of sodium, potassium, magnesium, ammonium, chloride, sulfate, phosphate, bicarbonate and acetate ions on the growth rate of R. meliloti were determined. Sodium, potassium and ammonium ions had little effect on growth at concentrations of 100 mEq or less; magnesium ion inhibited growth severely at concentrations of 50 mEq (25 mM). Of the anions, chloride and sulfate appeared to have little effect while phosphate, bicarbonate, and acetate inhibited growth at concentrations of as little as 25 mEq. The addition of proline, glutamate, or betaine to cells growing in inhibitory concentrations of NaCl did not relieve the inhibition. When grown in the presence of inhibitory levels of NaCl, the intracellular concentration of glutamate but not of proline or gamma amino butyric acid increased 5-fold. 相似文献
12.
Mostafa El-Sheekh Abd El-Fatah Abomohra Dieter Hanelt 《World journal of microbiology & biotechnology》2013,29(5):915-922
Nowadays, microalgae are discussed as a promising feedstock for biodiesel production. The present study examines the possibility of enhancement of fatty acid productivity of Scenedesmus obliquus by modifications of the culture medium composition. The effect of different concentrations of sodium bicarbonate, salinity, potassium nitrate, glycerol and sugarcane molasses on the enhancement of biomass and esterified fatty acids production was studied. NaHCO3 caused an increase in the biomass productivity at low concentrations (0.5 g L?1), while negatively affected fatty acid productivity at all tested concentrations. Increase of salinity enhanced both biomass and fatty acid productivity. The optimum NaCl concentration and sea water ratio were 0.94 g L?1 and 25 % which resulted in 56 and 39 % increase in fatty acid productivity, respectively. Nitrogen deficiency showed increase in fatty acid content by 54 % over control but fatty acid productivity was decreased as a result of growth inhibition. Nitrogen-free cultures and cultures treated with ?50 % concentrations of KNO3 showed 96 and 42 % decrease in EFA productivity, respectively, as compared with the control. Addition of 0.05 and 0.1 M of glycerol increased the biomass productivity by 6 and 5 %, respectively but showed no significant effect on fatty acid productivity as a result of decrease in fatty acid content. Finally, usage of sugarcane molasses stimulated both biomass and fatty acid content. The increase in fatty acid productivity was 32, 65 and 73 % above the control level at 1, 3 and 5 g L?1 of sugarcane molasses, respectively. 相似文献
13.
An inexpensive medium for production of arachidonic acid by <Emphasis Type="Italic">Mortierella alpina</Emphasis> 总被引:4,自引:0,他引:4
The production of arachidonic acid was studied in the fungus Mortierella alpina using an inexpensive medium. Glucose derived from maize starch hydrolysate was the sole carbon source and defatted soybean
meal and sodium nitrate were the nitrogen sources. Optimal arachidonic acid yield (1.47 g l-1) was observed at a glucose concentration of 100 g l-1. Various treatments of defatted soybean meal to extract soluble nitrogen nutrients were evaluated. Alkali extract was the
most effective for arachidonic acid production. A mixture of soybean alkali-extract protein and sodium nitrate was an excellent
nitrogen source for fungal growth, lipid accumulation, and arachidonic acid production. A maximum yield of 1.87 g arachidonic
acid l-1 was obtained with a soybean protein concentration of 4.6 g l-1 and a sodium nitrate concentration of 2.3 g l-1.
Electronic Publication 相似文献
14.
Dark fermentative hydrogen gas production from cheese whey powder solution was realized at 55°C. Experiments were performed at different initial biomass concentrations varying between 0.48 and 2.86 g L?1 with a constant initial substrate concentration of 26 ± 2 g total sugar (TS) per liter. The highest cumulative hydrogen evolution (633 mL, 30°C), hydrogen yield (1.56 mol H2 mol?1 glucose), and H2 formation rate (3.45 mL h?1) were obtained with 1.92 g L?1 biomass concentration. The specific H2 production rate decreased with increasing biomasss concentration from the highest value (47.7 mL g?1 h?1) at 0.48 g L?1 biomass concentration. Total volatile fatty acid concentration varied beetween 10 and 14 g L?1 with the highest level of 14.2 g L?1 at biomass concentration of 0.48 g L?1 and initial TS content of 28.4 g L?1. The experimental data were correlated with the Gompertz equation and the constants were determined. The most suitable initial biomass to substrate ratio yielding the highest H2 yield and formation rate was 0.082 g biomass per gram of TS. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 28: 931–936, 2012 相似文献
15.
Effects of nitrogen sources on cell growth and lipid accumulation of green alga <Emphasis Type="Italic">Neochloris oleoabundans</Emphasis> 总被引:8,自引:0,他引:8
Microalgal lipids are the oils of future for sustainable biodiesel production. However, relatively high production costs due
to low lipid productivity have been one of the major obstacles impeding their commercial production. We studied the effects
of nitrogen sources and their concentrations on cell growth and lipid accumulation of Neochloris oleoabundans, one of the most promising oil-rich microalgal species. While the highest lipid cell content of 0.40 g/g was obtained at
the lowest sodium nitrate concentration (3 mM), a remarkable lipid productivity of 0.133 g l−1 day−1 was achieved at 5 mM with a lipid cell content of 0.34 g/g and a biomass productivity of 0.40 g l−1 day−1. The highest biomass productivity was obtained at 10 mM sodium nitrate, with a biomass concentration of 3.2 g/l and a biomass
productivity of 0.63 g l−1 day−1. It was observed that cell growth continued after the exhaustion of external nitrogen pool, hypothetically supported by the
consumption of intracellular nitrogen pools such as chlorophyll molecules. The relationship among nitrate depletion, cell
growth, lipid cell content, and cell chlorophyll content are discussed. 相似文献
16.
Vieira Costa Jorge Alberto Cozza Karla Leal Oliveira Lucielen Magagnin Glênio 《World journal of microbiology & biotechnology》2001,17(5):439-442
Spirulina platensis was cultivated, in comparative studies, using several sources of nitrogen. The standard source used (sodium nitrate) was the same as that used in the synthetic medium Zarrouk, whereas the alternative nitrogen sources consisted of ammonium nitrate, urea, ammonium chloride, ammonium sulphate or acid ammonium phosphate. The initial nitrogen concentrations tested were 0.01, 0.03 and 0.05 M in an aerated photobioreactor at 30 °C, with an illuminance of 1900 lux, and 12 h-light/12 h-dark photoperiod over a period of 672 h. Maximum biomass was produced in medium containing sodium nitrate (0.01–0.03–0.05 M), followed by ammonium nitrate (0.01 M) and urea (0.01 M). The final biomass concentrations were 1.992 g l–1 (0.03 M sodium nitrate), 1.628 g l–1 (0.05 M sodium nitrate), 1.559 g l–1 (0.01 M sodium nitrate), 0.993 g l–1 (0.01 M ammonium nitrate) and 0.910 g l–1 (0.01 M urea). This suggested that it is possible to utilize nitrogen sources other than sodium nitrate for growing S. platensis, in order to decrease the production costs of scaled up projects. 相似文献
17.
A minimal growth medium containing glucose, acetate, vitamins, and eight amino acids allowed for growth of Lactococcus lactis subsp. lactis, with a specific growth rate in batch culture of μ = 0.3 h-1. With 19 amino acids added, the growth rate increased to μ = 0.7 h-1 and the exponential growth phase proceeded until high cell concentrations were reached. We show that morpholinepropanesulfonic acid (MOPS) is a suitable buffer for L. lactis and may be applied in high concentrations. 相似文献
18.
Jan R. Andreesen Ebtisam El Ghazzawi Gerhard Gottschalk 《Archives of microbiology》1974,96(1):103-118
In a medium containing a trace element solution and 10-4 M ferrous ions the growth yield ofClostridium formicoaceticum on fructose was 5.5 g of weight per l; in the absence of metal ion solution it was 1 g per l. The specific activity of methyl viologen dependent formate dehydrogenase under both conditions was 0.28 and 0.03 units per mg of protein, respectively. It could be increased to 9.75 units when the growth medium contained 10-4 M tungstate and 10-5 M selenite in addition. Molybdate was only about 40% as effective as tungstate. Tungstate or molybdate could not be replaced by vanadate, selenite not by sulfide. The formate dehydrogenase catalyzed also the reduction of CO2 to formate. The highest rate of formate synthesis was observed when pyruvate served as the reductant. No pyruvate: formate exchange but rapid pyruvate: CO2 exchange could be observed with cell-free extracts ofC. formicoaceticum. Pyruvate is fermented byC. formicoaceticum to yield up to 1.16 mole acetate per mole of pyruvate. Resting cells accumulated some formate in addition to acetate. 相似文献
19.
The unicellular chlorophyte Ankistrodesmus convolutus Corda was grown in the light using inorganic medium (Bold's Basal Medium, BBM) and BBM enriched with 0.1% w/v of glucose,
sodium acetate, sodium citrate or sodium bicarbonate. Glucose supported the highest specific growth rate (μ = 0.93 d-1) and gave the highest biomass (453 mg dry weight L-1) at the time of harvest. Of four glucose concentrations (0.05, 0.1, 0.25, 0.5% w/v), best growth was attained at 0.1% w/v.
At 0.5% w/v glucose, the cells had high carbohydrates but low lipids and proteins. The relative amounts of 16:0, 18:0, 18:1
and 18:2 increased at the expense of 18:3(n-3) in the carbon-supplemented cultures and at glucose concentrations higher than 0.1% w/v. Cultures grown on glucose had
less chlorophyll and carotenoid contents than cultures grown on other carbon sources. Chlorophyll and carotenoid contents
decreased with increasing glucose concentrations in the medium. 相似文献
20.
A survey of the spatial distribution of benthic macroalgae in a fluvial lake of the St. Lawrence River (Lake Saint‐Pierre, Quebec, Canada) revealed a shift in composition from chlorophytes to cyanobacteria along the flow path of nutrient‐rich waters originating from tributaries draining farmlands. The link between this shift and changes in water quality characteristics was investigated by sampling at 10 sites along a 15 km transect. Conductivity, current, light extinction, total phosphorus (TP; >25 μg P · L?1), and ammonium (8–21 μg N · L?1) remained fairly constant along the transect in contrast to nitrate concentrations, which fell sharply. Filamentous and colonial chlorophytes [Cladophora sp. and Hydrodictyon reticulatum (L.) Bory] dominated in the first 5 km where nitrate concentrations were >240 μg N · L?1. A mixed assemblage of chlorophytes and cyanobacteria characterized a 1 km transition zone where nitrate decreased to 40–80 μg N · L?1. In the last section of the transect, nitrate concentrations dropped below 10 μg N · L?1, and cyanobacteria (benthic filamentous mats of Lyngbya wollei Farl. ex Gomont and epiphytic colonies of Gloeotrichia) dominated the benthic community. The predominance of nitrogen‐fixing, potentially toxic cyanobacteria likely resulted from excessive nutrient loads and may affect nutrient and trophic dynamics in the river. 相似文献