| Huguangyan Maar Lake(21°09’N,110°17’E) was Located in southwest ofZhanjiang city, guangdong province of China. it was formed by Maar volcanoexplosion160000years ago, after cooling down and then waterlogging. it is also theworld’s largest maar lake and kept very well. It is a typical subtropical lake which Canbe used as an ideal place for modern ecology research for maar lake. In lakeecosystem, the nitrogen and phosphorus nutrient concentration in water is related toenvironment physical and chemical factors, Phytoplankton community structure andrichness of phytoplankton. Therefore, through the modern ecology method to carryout quantitative and qualitative analysis is the current hot issue. The biogeochemicalcycle of nitrogen in the lake ecosystem is an important part of the biosphere thematerial energy cycle, and Phytoplankton absorption and transformation of dissolvednitrogen is a key link in the process of nitrogen in the lake biological cycle. In thispaper, Huguangyan Maar lake’s dissolved nitrogen and other physical and chemicalfactors on the anniversary of the investigation and study were carried out, andsurveyed the phytoplankton population structure in season. the15N stable isotopelabeling techniques was used to reveal the kinetics of dissoved nitrogen uptake byphytoplankton. It is show from the study results as followed:1. Dissolved nitrogen content showed the characteristics of seasonal change inHuguangyan Maar Lake. Among them, variation range of Dissolved total nitrogen,dissolved inorganic nitrogen and dissolved organic nitrogen concentration range was0.224~0.942mg/L、0.150~0.860mg/L、0.045~0.123mg/L, respectively. Annualaverage was0.445mg/L、0.365mg/L、0.080mg/L, respectively. In the differentforms of dissolved nitrogen, Scope of the change of nitrate nitrogen concentrationswas0.114~0.726mg/L, the mean value was0.315mg/L. the nitrate nitrogenconcentration range was0.0010~0.0060mg/L，the mean value was0.0027mg/L.Ammonia nitrogen concentration range was0.022~0.128mg/L, the mean value was0.048mg/L. urea concentration range was0.026~0.075mg/L, the mean value was0.041mg/L.2. Other major physical and chemical factors in water presents seasonal variation characteristics in Huguangyan Maar Lake. Water temperature range for the whole yearwas18.7~31.1℃, the mean value was24.5℃. pH value variation range was7.50~8.24, the mean value was7.94, which presents Weakly alkaline. Range for thedissolved oxygen content was6.61~8.10mg/L, the mean value was7.30mg/L. Rangefor transparency was3.4~4.0m, the mean value was3.7m. Range for CODMnwas2.59~4.85mg/L, the mean value was3.57mg/L.3. Chlorophyll a content is a key indicators of water phytoplankton biomass.content of chlorophyll a range for all the year round was1.08~4.22μg/L, the meanvalue was2.33μg/L. On the anniversary of chlorophyll a and other physical andchemical factor change of correlation analysis, Chlorophyll a concentration anddissolved total nitrogen was significantly positively related to relationship, Thecorrelation coefficient is0.529. Among them, Chlorophyll a concentration with ahighly positive correlation between ammonia nitrogen concentration, the correlationcoefficient was0.907, which was Significantly higher than correlation coefficient ofchlorophyll a concentration and the nitrate nitrogen, nitrate nitrogen and ureaconcentration.4. The nitrogen and phosphorus ratio for the whole year in Huguangyan MaarLake was in average of20.9, Show the phosphorus is a nutrient limiting factors. Butfrom the point of view that the relative content of nitrogen and phosphorus, bothNitrogen and phosphorus are the lake nutrient limiting factors. According to thenutrition state of Huguangyan Maar Lake, it has not yet constitute a nutritionalcondition of blooms. Therefore, the content of nitrogen and phosphorus in the lake isthe key to the lake water self-purification capacity.5. The average Carlson trophic state index(TSI) were42.1, according to theevaluation criteria, the water in huguangyan maar lake was of Mesotrophic type;However, the annual average chlorophyll a sub-index TSIM(Chl a) suggest that thewater quality of this area belongs to oligotrophic type.6. In total,135species8phylum of phytoplankton were identified(includingvariants and form), Within the samples, great majority belonged to chlorophyta,cyanophyta, bacillariophyta, the proportion of the species were33.3%、30.4%、22.2%,respectively. the density of Phytoplankton significantly changed with seasons, rangedfrom35.1×104~95.2×104ind/L for cell desity. It was exist that phytoplanktoncommunities have seasonal succession, in addition to green algae and Cryptophyta,the seasonal succession regular pattern of diatoms and cyanobacteria were more in line with PEG model.30dominant species were identified, the most common wereMicrocystis flos-aquae、Microcystis aeruginosa、Melosira granulata、Chlorellavulgaris as dominant species throughout the year. In all seasons, the Shannondiversity index and evenness ranged from3.68to5.22and0.62to0.83, respectively,indicating a fairly stable community composition in this area.7. The result of phytoplankton nitrogen uptake study show that the the absoluteabsorption rate of NH4+、NO3-、Urea were0.211μmol/(L·h)、0.034μmol/(L·h)、0.043μmol/(L·h), respectively. Phytoplankton nitrogen uptake relative priority indexperfomed NH4+> Urea> NO3-, were2.907、0.190、1.192, respectively. Normally,borth NO3-and Urea were avaliable nitrogen speciation for Phytoplankton, but NH4+absorption rate were much higher, indicating that Phytoplankton was prefer to absorbNH4+.8. The three kinds of dissoved nitrogen (NH4+, NO3-, Urea) absorption kineticscan be described by the Michaelis-Menten equation. Kinetic parameters: themaximum absorption rate (Vmax) of NH4+、NO3-, Urea were2.943h-1,0.109h-1,1.465h-1, respectively. the Michaelis constant (Ks) were1.927μmol/L,0.837μmol/L,3.911μmol/L, respectively. |
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