Surface water quality and information about the environment surrounding Inle Lake in Myanmar

Inle Lake is the second largest lake in Myanmar and one of the nine key sites for sightseeing there. An analysis of its water quality has not been published before. The objective of this study is to reveal the current situation and find any major problems with the lake. For this purpose, the natural and cultural environments were examined. Some physical and chemical aspects of the surface water were assayed in situ for 2 days in November 2004. The principal ions were analyzed in our laboratory. The main cation and anion species in the lake surface water are Ca²⁺ and HCO₃ ⁻. Its high calcium content can be attributed to the limestone of Shan Plateau around the lake. The alkalinity of the lake water was 3829–4114 acid-neutralizing capacity (ANC) (pH 7.8–8.0); it can be attenuated by Ca²⁺. The concentrations of PO₄-P, NO₂-N, and NO₃-N were relatively high; these could originate from domestic and agriculture uses. The trophic state is eutropic. The concentrations of coliform bacteria indicated that the lake water was unfit to drink, but some people use it for drinking anyway. The bacteria could enter the lake through the direct latrine system used there. The thermal type of the lake is presumed to be warm polymictic. More extensive studies are needed because the lake is thought to be the most changing site in Myanmar as a result of both the tourism boom and increasing agricultural activity.     

不同施肥模式调控沿湖农田无机氮流失的原位研究——以南四湖过水区粮田为例

为探索山东南四湖沿岸麦玉轮作区玉米季内减少土壤无机氮素淋溶和径流损失的施肥策略,降低其对湖区水质产生的潜在威胁,采用田间原位安装淋溶水采集器和地表水径流池收集水样结合室内分析不同形态氮含量的方法,研究了不同施肥模式下无机氮素淋溶和径流损失特征。结果表明：土壤淋溶水量及地表水径流量与降水呈显著正相关关系,其水量受秸秆类物质还田的影响;硝态氮(NO3--N)与铵态氮(NH4 -N)随地表水径流损失的浓度及总量均明显高于淋溶水,由径流方式损失的氮素占2/3以上,是氮素以水溶液形式流失的主要途径;淋溶和径流均以NO3--N损失为主(径流损失中NO3--N占总量的82.9%-90.8%,淋溶损失中NO3--N占63.5%-72.9%),地表径流水NO3--N浓度对水质有较大影响,但土壤淋溶水NO3--N浓度对地下水污染不构成威胁;农民习惯施肥处理在玉米整个生育期淋溶和径流氮损失最高。在保证玉米产量前提下,降低氮素流失造成湖区的污染,平衡施用氮磷钾肥、施用控释氮肥、有机替代无机和秸秆还田等措施均可在沿南四湖区农田使用。     

Nitrification and Denitrification in Lake and Estuarine Sediments Measured by the 15N Dilution Technique and Isotope Pairing

The transformation of nitrogen compounds in lake and estuarine sediments incubated in the dark was analyzed in a continuous-flowthrough system. The inflowing water contained ¹⁵NO₃^-, and by determination of the isotopic composition of the N₂, NO₃^-, and NH₄⁺ pools in the outflowing water, it was possible to quantify the following reactions: total NO₃^- uptake, denitrification based on NO₃^- from the overlying water, nitrification, coupled nitrification-denitrification, and N mineralization. In sediment cores from both lake and estuarine environments, benthic microphytes assimilated NO₃^- and NH₄⁺ for a period of 25 to 60 h after darkening. Under steady-state conditions in the dark, denitrification of NO₃^- originating from the overlying water accounted for 91 to 171 μmol m^-2 h^-1 in the lake sediments and for 131 to 182 μmol m^-2 h^-1 in the estuarine sediments, corresponding to approximately 100% of the total NO₃^- uptake for both sediments. It seems that high NO₃^- uptake by benthic microphytes in the initial dark period may have been misinterpreted in earlier investigations as dissimilatory reduction to ammonium. The rates of coupled nitrification-denitrification within the sediments contributed to 10% of the total denitrification at steady state in the dark, and total nitrification was only twice as high as the coupled process.     

滇池流域退耕区植物群落构建对地表径流污染物的削减效应

为探索不同群落的构建在滇池流域的实际应用,以确定削减污染物最优植物群落的配置方式,该研究选取地表径流悬浮物(SS)、COD含量、总氮(TN)、总磷(TP)、氨氮(NH_4~+-N)、硝氮(NO_3~--N)六个指标作为主要的分析对象,在滇池流域退耕区开展了不同植物群落配置对地表径流污染物削减效应的试验研究。结果表明:三个植物群落对SS、COD、TN、TP、NO_3~--N在2014年和2015年间均表现出显著性的削减趋势,且三个植物群落对SS、TP和NO_3~--N的削减率均在45%以上,但并未对NH_4~+-N表现出削减效果。不同植物群落对污染物的削减效应存在一定的差异性,但是三个不同群落与年度的交互作用对SS、COD、TN、TP、NO_3~--N五个养分指标的削减并没有表现出显著的差异性。从整体上来看,三种植物群落类型中,以乔-灌-草构建的立体式植物群落对地表径流污染物的削减效果最佳。     

Effect of influent substrate ratio on anammox granular sludge: performance and kinetics

Effect of influent substrate ratio on anammox process was studied in sequencing batch reactor. Operating temperature was fixed at 35 ± 1 °C. Influent pH and hydraulic retention time were 7.5 and 6 h, respectively. When influent NO₂ ^?-N/NH₄ ⁺-N was no more than 2.0, total nitrogen removal rate (TNRR) increased whereas NH₄ ⁺-N removal rate stabilized at 0.32 kg/(m³ d). ΔNO₂ ^?-N/ΔNH₄ ⁺-N increased with enhancing NO₂ ^?-N/NH₄ ⁺-N. When NO₂ ^?-N/NH₄ ⁺-N was 4.5, ΔNO₂ ^?-N/ΔNH₄ ⁺-N was 1.98, which was much higher than theoretical value (1.32). The IC₅₀ of NO₂ ^?-N was 289 mg/L and anammox activity was inhibited at high NO₂ ^?-N/NH₄ ⁺-N ratio. With regard to influent NH₄ ⁺-N/NO₂ ^?-N, the maximum NH₄ ⁺-N removal rate was 0.36 kg/(m³ d), which occurred at the ratio of 4.0. Anammox activity was inhibited when influent NH₄ ⁺-N/NO₂ ^?-N was higher than 5.0. With influent NO₃ ^?-N/NH₄ ⁺-N of 2.5–6.5, NH₄ ⁺-N removal rate and NRR were stabilized at 0.33 and 0.40 kg/(m³ d), respectively. When the ratio was higher than 6.5, nitrogen removal would be worsened. The inhibitory threshold concentration of NO₂ ^?-N was lower than NH₄ ⁺-N and NO₃ ^?-N. Anammox bacteria were more sensitive to NO₂ ^?-N than NH₄ ⁺-N and NO₃ ^?-N. TNRR would be enhanced with increasing nitrogen loading rate, but sludge floatation occurred at high nitrogen loading shock. The Han-Levenspiel could be applied to simulate nitrogen removal resulting from NO₂ ^?-N inhibition.     

山西运城盐湖土壤沉积物细菌多样性及影响因素分析

地处山西省西南部的运城盐湖历史悠久,气候特征与地理环境独特,蕴藏着丰富的微生物资源,研究其土壤沉积物生态系统对了解盐碱地土壤细菌多样性及其功能具有重要意义。【目的】探究运城盐湖土壤与沉积物中细菌的多样性,分析其影响因素,为盐碱地土壤生态系统的可持续管理和纯培养物挖掘提供科学依据与参考。【方法】对运城盐湖6个采样点的18个样品进行土壤理化分析,结合16S rRNA基因的扩增子高通量测序,分析环境因素对细菌多样性的影响。【结果】假单胞菌门(Pseudomonadota)、拟杆菌门(Bacteroidota)和芽孢杆菌门(Bacillota)为运城盐湖土壤微生物的优势类群,多样性和群落组成分析显示不同采样点间的微生物存在明显差异。典型相关分析(canonical correlation analysis, CCA)表明,总溶解固体(total dissolved solids, TDS)、总氮(total nitrogen, TN)、总碳(total carbon, TC)和SO₄^2-对土壤微生物多样性的影响最大,其次为Na⁺、Ca²⁺、Cl^-、土壤有效磷(available phosphorous, A-P)和pH,HCO₃^-、硝态氮(nitrate nitrogen, NO₃^--N)、氨态氮(ammonia nitrogen, NH₄⁺-N)、K⁺和Mg²⁺的影响较小。【结论】运城盐湖土壤微生物拥有较高的多样性,与环境因子关系密切。本研究完善了运城盐湖土壤细菌资源的生物信息,为盐湖细菌资源的挖掘和研究提供了理论依据。     

Hillslope Nutrient Dynamics Following Upland Riparian Vegetation Disturbance

We investigated the effects of removing near-stream Rhododendron and of the natural blowdown of canopy trees on nutrient export to streams in the southern Appalachians. Transects were instrumented on adjacent hillslopes in a first-order watershed at the Coweeta Hydrologic Laboratory (35°03′N, 83°25′W). Dissolved organic carbon (DOC), K⁺, Na⁺, Ca²⁺, Mg²⁺, NO₃ ⁻-N, NH₄ ⁺-N, PO₄ ³⁻-P, and SO₄ ²⁻ were measured for 2 years prior to disturbance. In August 1995, riparian Rhododendron on one hillslope was cut, removing 30% of total woody biomass. In October 1995, Hurricane Opal uprooted nine canopy trees on the other hillslope, downing 81% of the total woody biomass. Over the 3 years following the disturbance, soilwater concentrations of NO₃ ⁻-N tripled on the cut hillslope. There were also small changes in soilwater DOC, SO₄ ²⁻, Ca²⁺, and Mg²⁺. However, no significant changes occurred in groundwater nutrient concentrations following Rhododendron removal. In contrast, soilwater NO₃ ⁻-N on the storm-affected hillslope showed persistent 500-fold increases, groundwater NO₃ ⁻-N increased four fold, and streamwater NO₃ ⁻-N doubled. Significant changes also occurred in soilwater pH, DOC, SO₄ ²⁻, Ca²⁺, and Mg²⁺. There were no significant changes in microbial immobilization of soil nutrients or water outflow on the storm-affected hillslope. Our results suggest that Rhododendron thickets play a relatively minor role in controlling nutrient export to headwater streams. They further suggest that nutrient uptake by canopy trees is a key control on NO₃ ⁻-N export in upland riparian zones, and that disruption of the root–soil connection in canopy trees via uprooting promotes significant nutrient loss to streams. Received 30 January 2001; accepted 25 July 2002.     

The effect of low water levels on the water quality of Lake Biwa

Because of a lack of precipitation, water levels in Lake Biwa, Japan, were extremely low between the beginning of September 1984 and the end of February 1985. Approximately 13 million people depend upon the lake as a source of drinking water and for industrial use, and the severe water shortage became a serious concern for downstream communities. Also, there was concern that deterioration of water quality caused by rotting macrophytes and the release of nutrients from vegetation and nearshore sediments might create additional problems.In this paper, the release of nutrients from vegetation and sediments is examined under conditions which simulate both calm and turbulent water motions in the nearshore, and the magnitude of nutrient loadings are estimated in relation to the specific effects of low lake level.Sample stations were established around the south shore of Lake Biwa. Sampling was undertaken at the time of low water and during the rising water levels. Sediment samples were particle sized into 7 groups (<2000 µm). Other measured values ranged as follows: BOD (0.5–1.3), COD (1.2–3.5), TP (0.019–0.037), SRP (0.013–0.030), SOP (0.005–0.007), TN (0.45–0.90), NO₂-N (0.004–0.007), NO₃-N (0.04–0.08) and NH₄-N (0.026–0.053), all as mgL^-1. The sample data suggest that, overall, there was little impact on lake water quality as a result of low water levels. However, remedial actions may have had an important and beneficial impact on nearshore water quality in the southern basin of Lake Biwa.     

马尾松组培苗对氮素形态的生长响应

马尾松属高氮需求树种,然而在苗木培育中马尾松对氮素,尤其是不同形态氮素的需求尚不明确.该文以马尾松组培苗为试验材料,采用基质培养方法,针对硝态氮、铵态氮两种氮素形态均分别设置了2、4、8、16 mmol·L-14个处理,以不添加氮素为对照,对苗木的高径生长、根构型参数(总根长、总表面积、总体积、平均直径和根尖数)以及生...     

Nitrogen dynamics in Lake Okeechobee: forms,functions, and changes

Total nitrogen (TN) in Lake Okeechobee, a large, shallow, turbid lake in south Florida, has averaged between 90 and 150 μM on an annual basis since 1983. No TN trends are evident, despite major storm events, droughts, and nutrient management changes in the watershed. To understand the relative stability of TN, this study evaluates nitrogen (N) dynamics at three temporal/spatial levels: (1) annual whole lake N budgets, (2) monthly in-lake water quality measurements in offshore and nearshore areas, and (3) isotope addition experiments lasting 3 days and using ¹⁵N-ammonium (¹⁵NH₄ ⁺) and ¹⁵N-nitrate (¹⁵NO₃ ⁻) at two offshore locations. Budgets indicate that the lake is a net sink for N. TN concentrations were less variable than net N loads, suggesting that in-lake processes moderate these net loads. Monthly NO₃ ⁻ concentrations were higher in the offshore area and higher in winter for both offshore and nearshore areas. Negative relationships between the percentage of samples classified as algal blooms (defined as chlorophyll a > 40 μg l⁻¹) and inorganic N concentrations suggest N-limitation. Continuous-flow experiments over intact sediment cores measured net fluxes (μmol N m⁻² h⁻¹) between 0 and 25 released from sediments for NH₄ ⁺, 0–60 removed by sediments for NO₃ ⁻, and 63–68 transformed by denitrification. Uptake rates in the water column (μmol N m⁻² h⁻¹) determined by isotope dilution experiments and normalized for water depth were 1,090–1,970 for NH₄ ⁺ and 59–119 for NO₃ ⁻. These fluxes are similar to previously reported results. Our work suggests that external N inputs are balanced in Lake Okeechobee by denitrification.     

中国西北典型冰川区大气氮素沉降量的估算——以天山乌鲁木齐河源1号冰川为例

高寒冰川区氮素沉降量的变化会对区域生态系统产生显著影响,定量评估冰川区的氮沉降状况可以为修正相关模型提供重要的原始数据。通过2004年1月至2006年12月在天山乌鲁木齐河源1号冰川连续采样,分析了中国西北典型冰川区大气氮素的沉降特征,并估算了该区域的年均氮素沉降量。研究结果表明,1号冰川湿沉降中的硝态氮 (NO₃^--N)、铵态氮 (NH₄⁺-N) 与总无机氮 (TIN) 存在着明显的季节变化特征:夏季沉降量最大,冬季最少,且与降水量表现出较好的对应关系。1号冰川氮素湿沉降的硝铵比 (NO₃^--N / NH₄⁺-N) 月平均值在0.3-1间波动。1号冰川TIN湿沉降量年平均值为1.51 kg/hm² (其中NH₄⁺-N沉降量占总量的69%,而NO₃^--N沉降量仅占31%),干湿沉降总量年均值为1.56 kg/hm²,总氮 (TN) 的干湿沉降总量年均值为3.85 kg/hm²。得到的冰川区氮素沉降量符合中国西部高寒区的一般水平,代表了该区域的本底值。     

Occurrence and intensity of wild boar disturbances, effects on the physical and chemical soil properties of alpine grasslands

Background and aims

Physical and chemical soil properties determine local plant conditions and resources, affecting plants’ ability to respond to disturbances. In alpine grasslands, wild boar disturbances occur at different intensities, what may affect differently their soil properties. Alpine soils from five contrasted plant communities were explored within and outside disturbances, accounting for an overall and community scale effect. Additionally, we analysed the effect of disturbance intensity on soil NO₃ ^--N and NH₄ ⁺-N.

Methods

Soils were analyzed for physical (bulk density, moisture content and electrical conductivity), and chemical properties (pH, total N and C, oxidizable C, C:N ratio, available K, P, Ca²⁺, Na⁺ and Mg²⁺). Resin bags were used to compare the effect of the disturbance occurrence and intensity on soil NO₃ ^--N and NH₄ ⁺-N.

Results

Bulk density, total N and NO₃ ^--N concentration were significantly higher in disturbed areas, while soil moisture, C:N, NH₄ ⁺-N, Na⁺, Mg²⁺ and Ca²⁺ concentrations were significantly lower. However, low disturbance intensity reduced NO₃ ^--N and increased NH₄ ⁺-N concentrations.

Conclusions

Wild boar occurrence and intensity strongly alter physical and chemical conditions of alpine soils, increasing soil compaction, and altering the availability of N forms. These changes may affect most plant species, thus affecting the structure and dynamics of alpine plant communities.     

北亚热带3种典型森林群落对降水中氮、磷、硫的截留及分配特征

森林群落在净化空气、截留沉降污染物、改善地表水质等方面具有重要作用。本研究以北亚热带地区3种典型森林群落（毛竹林、杉木林、青冈阔叶林）为研究对象,通过分析沉降污染物（NH₄⁺-N、NO₃^--N、NO₂^--N、TP和SO₄^2-）在大气降水、林内穿透雨、树干茎流、枯透水和地表径流中的浓度和通量变化特征,探讨不同森林群落对氮、磷、硫的截留净化作用和分配特征。结果表明,该区域大气降水中NH₄⁺-N、NO₃^--N、NO₂^--N、TP和SO₄^2-年均浓度分别为1.06、0.61、0.04、0.07、1.84 mg/L,其年均pH为5.88;各森林群落林冠层能够调升降雨的pH且全年稳定,对TP和NH₄⁺-N均有吸附作用,截留率分别为79.09%-84.68%和30.88%-69.36%;而枯落物层则是林下氮、磷、硫的主要释放源,对NH₄⁺-N、NO₃^--N、TP和SO₄^2-均具有淋溶作用;此外,由地表径流（输出）与大气降水（输入）的对比分析可知,各林地对沉降污染物中氮、磷、硫的截留率均超过98%;3种森林群落对沉降污染物中氮、磷、硫的截留能力依次为：青冈阔叶林 > 毛竹林 > 杉木林,阔叶林对沉降污染物的净化能力要高于毛竹林及针叶的杉木林。     

Glomus mosseae,endomycorrhizal with Liquidambar styraciflua L. seedlings retards NO3, NO2 and NH4 nitrogen loss from a temperate forest soil

Summary The influence of a mycorrhizal fungus on downward movement of NH₄, NO₂, and NO₃ nitrogen in forest soil was determined by establishing combinations of soil, fungus and seedlings in plastic pipes and monitoring the nitrogen content of water percolating to two depths. Compared with controls of soil alone and of soil + seedling alone, treatments containing the mycorrhizae showed a significant reduction of NH₄-N loss from 5 and 25 cm depths and significant reduction of NO₃-N loss from the 5 cm depth. No significant effect was observed on nitrite loss. re]19750603     

Transformation and Transport of Nitrogen Forms in a Sandy Entisol Following a Heavy Loading of Ammonium Nitrate Solution: Field Measurements and Model Simulations

Understanding the factors influencing water and nutrient transport through soil profile is important for the efficient management of nutrient and irrigation to minimize nutrient leaching below the rootzone. Transport of NO₃-N and NH₄-N was studied in a Candler fine sand following a heavy loading of a liquid fertilizer containing ammonium nitrate. Both NO₃-N and NH₄-N transported quite rapidly (within 3?d) and accumulated above the clay layer at about depth of 2.7?m. The concentrations of NH₄-N and NO₃-N approached background levels throughout the soil profile by 184?d. More than 50% of ammonium and nitrate contained in the spilled solution leached from the entire depth of soil profile sampled during the first 95?d. The cumulative amount of rainfall during this period was 329?mm, which accounted for 65% of the total rainfall for the entire study period. The concentrations of NH₄-N and NO₃-N at various depths within the entire soil profile reasonably predicted by the Leaching Estimation and Chemistry Model (LEACHM) and compared favorably with the measured concentrations, however, there are few places with high concentrations. The cumulative amount of leachate at the bottom of the soil profile predicted by LEACHM represented 90% of total rainfall that occurred during the study period. This demonstrated a substantial potential for leaching of soluble nutrients through the sandy soil profile.     

Long-term and seasonal changes in the chemical composition of precipitation and surface waters of lakes and tarns in the English Lake District

SUMMARY. The composition of bulk (wet and dry) precipitation in 1975 and 1976 was similar to that found 22 years previously. In 1975, mean values for nine precipitation samplers at one site (Wraymires) ranged from pH 4.3 to 4.5; similar values were obtained in 1976. Samplers covered with fine-mesh plastic gauze caught substantially more Ca²⁺ and K⁺ than open samplers, but pH and SO^2-₄+ NO₃^- concentrations were similar in open and covered samplers. In precipitation, c. 50% of H⁺ was balanced by NO₃^- and c. 50% by SOi; 80% of the SO^2-₄ was balanced by Ca²⁺ and Mg²⁺. Conccntrations of major cations (H⁺, Na⁺, K⁺,Ca²⁺, Mg²⁺) and anions (CI^-, NO₃^- SO^2-₄ and alkalinity [Alk—largely HCO₃^-]) in upland water- bodies were similar to those found in precipitation, but pH levels were generally higher and above 6.0 m some tarns. At lower altitudes, on base-rich roeks and soils, Ca²⁺ and Alk become dominant. Results of a survey of lakes and tarns in 1974–78 are compared with a survey in 1953–56 and published data (chiefly for pH and Alk) for 1947–50, 1932 and 1928. Comparisons are also made with other measurements of Alk in three productive lakes (Blelham Tarn, Esthwaite Water and Windermere) for 1936–39 and 1945–80. Winter levels of NO₃-N, PO₄-P and Si are given for these lakes; although the first two have increased during the late 1960s and the 1970s there has been no significant change in the last. NO₃^- and probably some SO^2-₄. In productive lakes a substantial (c. 50%) rise in mean Alk occurred during the late 1960s and the 1970s, possibly related to increased winter levels of NO₃-N and PO₄-P derived from sewage and fertilizers. In this period the maximum pH levels reached in summer were notably high, sometimes exceeding pH 10. The rise in Alk, conductivity and pH of surface waters is influenced by climatic factors (a decade of drier years), sewage input and biological productivity within the lakes. Considerable seasonal fluctuations in the concentrations of major ions, a characteristic feature of surface waters in the English Lake District, are illustrated and some implications for cation-anion balance briefly discussed. Mid-winter concentrations are usually high forNa⁺, K⁺, Cl^-. NO₃^-and low for Ca²⁺, Mg²⁺, Alk. SO^2-₄. Alkalinity. pH and conductivity of Lake District tarns and lakes show no signs of acidification during the period 1928–80. On the contrary, productive lakes have become more alkaline and some unproductive low-alkalinity (< 100 μ-equiv. 1^-1) lakes also show signs of alkalization, with increased mean concentrations of Na⁺. Ca²⁺ and Mg²⁺, balanced by Alk.     

Effects of different nitrogen forms on photosynthetic rate and the chlorophyll fluorescence induction kinetics of flue-cured tobacco

Net photosynthetic rate (P _N) of tobacco plants grown with NH₄-N as the only N source was the lowest all the times, while P _N grown only with NO₃-N was the greatest until 22^nd day, and P _N grown with both NO₃-N and NH₄-N (1 : 1) was the greatest. Maximal photochemical efficiency of photosystem 2 (PS2), F_v/F_m, and actual quantum yield of PS2 under actinic irradiation (Φ_PS2) in plants grown with only NH₄-N were greatest at early stage and then decreased and were smaller than those of other treatments. Photochemical quenching coefficient (q_P) and non-photochemical quenching coefficient (q_NP) in the NH₄-N plants were the greatest at all times. Hence excessive NH₄-N can decrease not only photochemical efficiency but also the efficiency of utilization of photon energy absorbed by pigments for photosynthesis. Therefore, excessive NH₄-N is a hindrance to photosynthesis of flue-cured tobacco. On the other hand, tobacco cultured with an appropriate mixture of NO₃-N with NH₄-N can sufficiently utilize photon energy and increase the efficiency of energy transformation.     

Growth of Salvinia molesta as affected by water temperature and nutrition I. Effects of nitrogen level and nitrogen compounds

The growth of Salvinia molesta D.S. Mitchell was studied in a greenhouse using controlled-temperature water-baths at 16, 19 and 22°C and 4 different nitrogen compounds (NO₃^?, NH₄⁺, NH₄NO₃ and urea) at levels up to 60 mg N l^?1. Little growth occurred at 16°C even if 20 mg N l^?1 was supplied together with other nutrients including phosphorus (2 mg H₂PO₄-P l^?1). The highest relative growth rate and total dry matter production occurred at 22°C when plants were supplied with 20 mg NH₄-N l^?1. At this temperature, the NH₄⁺ ion was superior to the NO₃^? ion or urea as a nitrogen source (almost doubling the biomass), but was not significantly better than NH₄NO₃. Over a period of 19 days for plants receiving 0.02 mg NH₄-N l^?, biomass increased 4-fold at 16°C, 9-fold at 19°C and 10-fold at 22°C. In contrast, for plants receiving 20 mg NH₄-N l^?1, biomass increased 4-fold at 16°C, 18-fold at 19°C and 38-fold at 22°C.     

模拟氮沉降对藏北高寒草甸温室气体排放的影响

目前,高寒草甸对全球温室效应的贡献仍具有不确定性,而随着N沉降的增加,该系统温室体气排放也必将发生变化。为揭示高寒草甸对N沉降的响应机制,探讨其对全球变化的反馈作用,利用人工添加氮素的方法,于2014年生长季(6-9月)在那曲地区那曲县设置不同水平N添加梯度(0、7、20kg hm~(-2)a~(-1)和40 kg hm~(-2)a~(-1)),模拟氮沉降增加对藏北高寒草甸温室气体排放的影响。经过1a的研究结果表明:1)施氮显著促进了CO_2排放但对CH_4的吸收和N_2O的排放无显著影响。总体而言,添加氮素明显增加了温室气体排放总量,其中N2O处理下高寒草甸温室气体排放总量最高。2)回归分析结果表明,CO_2与NPP(总生物量)和TOC(土壤有机碳)线性相关(P0.05),而与TN(总氮)、NH_4~+-N和NO_3~--N均无显著相关关系(P0.05),CH_4与TN/NPP/TOC/NH_4~+-N/NO_3~--N均不相关(P0.05),N_2O与NPP/TOC/NO_3~--N均显著线性相关(P0.05),而与TN/NH_4~+-N不相关。综合初步研究结果,未来氮沉降增加条件下,藏北高寒草甸温室气体排放通量将有可能明显增加,从而对气候变化产生重要的反馈作用。     

Interannual variability of algal populations and their influence on lake metabolism

• 1 An input-output phosphorus budget is given for Windermere and its two basins based on data available for the late 1980s. The annual areal total phosphorus loading for the whole lake was 1.04 g P m^-2 yr^-1 and for the North and South Basins were 1.08 and 1.70 g P m^-2 yr^-1, respectively. For the whole lake and its South Basin the values were similar to the upper range of critical loads calculated according to the equation of Vollenweider (1976) for the transition between oligotrophy and eutrophy while that for the North Basin (1.08 g P m^-2 yr^-1) was within this range of critical loadings but towards its lower end.
• 2 Changes in the quality of summer phytoplankton are described for Windermere, particularly its South Basin, between 1978 and 1989 in relation to the utilization of nitrate-nitrogen (NO³-N) in the epilimnion, deoxygenarion of the hypolimnion and the ratio of epilimnetic volume to hypolimnetic volume, E_v/H_v The two basins of Windermere with values of E_v/H_v of 0.79 (South Basin) and 0.50 (North Basin) have contrasting conditions of summer deoxygenarion. The shallower South Basin shows marked interannual variability in the development of hypolimnetic anoxia. Years with large hypolimnetic anoxia during autumn are correlated with the production during summer of large populations of the poorly grazed blue-green alga Oscillatoria bourrellyi and exhaustion of NO₃-N in the upper layers. During years when anoxia does not develop the summer phytoplankton consists of small easily grazed algae or larger ones subject to parasitic epidemics. The deeper North Basin never becomes anoxic even though it can contain similar sized populations of O. bourrellyi to the South Basin.
• 3 A possible explanation of the between basin and, for the South Basin, between year variation of utilization of NO₃-N and level of hypolimnetic deoxygenarion is that algal quality can determine lake metabolism dependent upon lake or basin morphology. Poorly grazed large forms such as O. bourrellyi act as sinks for NO₃-N. On sedimentation such populations act as a ‘short circuit’ mechanism descending into deeper layers in sufficient quantities to cause anoxia. Other species subject to crustacean or microbial grazing are mineralized in the epilimnion with little sedimentation to the deeper waters. Subsequent recycling of nitrogen as NH₄-N takes place in the upper layers or thermocline which is more readily taken up by subsequent production. The influence of such ‘short circuit’ mechanisms is reduced in deep lakes and exacerbated in shallow ones.
• 4 The success of species such as O. bourrellyi is dependent upon a sufficient inoculum, an adequate supply of nutrients and the depth of intermittent mixing. The importance of these factors in regulating presence and timing of summer populations is illustrated and discussed.