一座南亚热带小型贫营养水库浮游植物群落结构及季节变化

库容大小是影响水体水动力学过程的一个重要变量,它能在很大程度决定生态系统的结构,特别是浮游植物的群落结构.为了解小型贫营养水库浮游植物的群落特点,于2006年4、8、12月对位珠海市的贫营养小型水库-吉大水库的浮游植物群落结构进行采样和计数分析.3次采样共检出浮游植物32种,浮游植物细胞丰度的变化范围在69～342 cells·mL^-1,生物量的变化范围在1.34～3.69 mg·L^-1,夏季浮游植物的丰度和生物量明显高于冬季.甲藻是最主要的优势种类,且相对优势度较为稳定.夏季,隐藻门的隐藻(Cryptomonas sp.)和绿藻门的鼓藻(Cosmarium spp.)大量出现,甲藻的相对优势度有所降低.冬季,隐藻数量急剧下降,但硅藻门的颗粒直链藻(Aulacoseira granulata)大量出现,与甲藻共同成为水体中的优势种.由降雨引起的营养盐浓度增加是浮游植物变化的主要影响因子,而透明度全年维持较高的水平为浮游植物的生长形成了有利条件,此外,较为稳定的水体和甲藻利用营养盐的能力使得甲藻成为浮游植物中的最主要的优势种.     

Short term spatial and temporal variation of phytoplankton in a shallow tropical oligotrophic reservoir,southeast Brazil

Locally called IAG pond, system is a small, oligotrophic, shallow, urban reservoir located in the Parque Estadual das Fontes do Ipiranga Biological Reserve, south of São Paulo municipality, southeastern Brazil. Study was carried out in two phases to cover the two climatic periods (dry and rainy) that characterize the area. Daily samples were collected on seven consecutive days (dry = 20–26 August 1996; rainy = 22–28 January 1997), three times a day (07:00 h, 13:00 h, and 19:00 h), following the water column vertical profile at reservoir’s deepest site (Z _max = 4.7 m). The phytoplankton’s community structure’s diurnal variation was compared with environmental variables (thermal structure of the water column, pH, CO₂, dissolved oxygen, total phosphorus, and NH₄). Analysis of variance (ANOVA) showed significant variation among sampling hours and days but not among depths for most species, thus revealing a tendency towards a homogeneous vertical distribution of phytoplankton in the reservoir. Canonical Correspondence Analysis (CCA) showed a significant relationship between distribution of phytoplankton species and environmental variables used for ordination. Water temperature was the environmental variable that best explained distribution of sample units. Atelomixis was the only possible explanation for how a non-motile alga as, for example, the chlorococcal Oocystis lacustris Chodat and the diatom Cyclotella stelligera Cleve &; Grunow, can be so widespread and abundant in the IAG pond during the stratified period.     

Benthic algal response to N and P enrichment along a pH gradient

Nutrient enrichment and its effect on benthic algal growth, community composition, and average cell size was assessed across two sites of differing pH within a single habitat. Nutrients were added using in situ substrata, which released either N, P, or no additional nutrients (controls) at each site for 21 days. Upon collection, chlorophyll and biovolume standing stocks of the attached algal microflora were measured. Chlorophyll concentration was different among all treatments, accumulating greatest on P, followed by N, and the least on C substrata (P < 0.001) and was highest at site-2 (P < 0.001), while total algal biovolume was highest on P compared to both N and C substrata (P < 0.05) and did not vary between sites. Increased growth on P substrata was due to the enhanced biovolume of filamentous green algae, although the affected taxa varied between sites. Biovolume to cell density ratios (as a measure of average cell size) were highest on P substrata over both N-enriched and control substrata (P < 0.05) and this pattern was similar between sites. Progression towards a community composed of larger cells following P enrichment observed along this pH gradient, seems to be related to the dominance of larger celled filamentous green algae. Thus, nutrients exhibited greater control on benthic algal growth than did changes in hydrogen ion concentration.Contribution number 581, Great Lakes Environmental Research LaboratoryContribution number 581, Great Lakes Environmental Research Laboratory     

Effects of the Nile tilapia (Oreochromis niloticus L.) on the plankton community of a tropical reservoir during and after an algal bloom

Hydrobiologia - The invasive species Nile tilapia is a filter-feeding omnivorous fish that can have a negative effect on zooplankton and phytoplankton resources. However, the strength of its...     

Periphyton nutrient content,biomass and algal community on artificial substrate: response to experimental nutrient enrichment and the effect of its interruption in a tropical reservoir

Periphyton plays an important functional role in the retention of nutrients in aquatic ecosystems, especially phosphorus. We evaluated the effects of enrichment with N and P and the effect after 20 days of no additional N and P on periphyton on artificial substratum in open-bottom mesocosms. The aim was to jointly evaluate periphyton, phytoplankton and zooplankton in the presence of macrophytes. Experimental conditions simulated natural conditions and nutrient addition was based on the maximum concentration recorded in mesotrophic reservoir. Our hypothesis is that the periphyton is sensitive to the effects of N and P enrichment and its interruption, despite the positive response of phytoplankton and zooplankton. Two treatments were designed using open-bottom mesocosms (n = 3): control (no nutrient addition); NP+ (combined phosphorus and nitrogen addition). Sampling for the measurement of biotic and abiotic variables was performed, with 10 days of continuous enrichment, on the 3rd, 6th and 11th, and 20 days after enrichment had ended (31st day). Periphyton chlorophyll a, dry mass and algal density increased significantly with the addition of N and P and decreased 20 days after the interruption of the enrichment. The highest periphyton P content was found in the NP+ treatment. The enrichment had a positive effect on Chrysophyceae (Chromulina spp.) and rotifer (Polyarthra spp.) density and the interruption of enrichment favored Bacillariophyceae (Gomphonema sp.) and rotifers (Gastropus stylifer). Phytoplankton responded positively to enrichment. Along with the high macrophyte coverage over the experimental period, we evidenced the positive effect enrichment had on phytoplankton biomass and zooplankton abundance. Therefore, periphyton on artificial substrate was sensitive to effects of N and P enrichment and its interruption, responding promptly to changes in nutrient availability in a scenario of high competition and grazing.     

Colimitation and the coupling of N and P uptake kinetics in oligotrophic mountain streams

Ecosystem element cycles can be tightly linked by both abiotic and biotic processes. Evidence for multi-element limitation (i.e., colimitation) of a variety of ecosystem processes is growing rapidly, yet our ability to quantify patterns of coupled nutrient dynamics at the ecosystem level has been hindered by logistical and methodological constraints. Here we quantify coupled nitrogen and phosphorus uptake kinetics in three oligotrophic mountain streams by using novel experimental techniques that quantify colimitation dynamics across a range of nutrient concentrations and stoichiometries. We show that relative demand for NO₃-N and PO₄-P varied across streams, but that short term availability of one nutrient consistently resulted in elevated, but variable, uptake of the other nutrient at all sites. We used temporally offset, pulsed nutrient additions to parameterize dual-nutrient Michaelis–Menten uptake surface models that represent NO₃-N and PO₄-P uptake at any given concentration or dissolved NO₃-N:PO₄-P stoichiometry. Our results indicated that the uptake of N and P were strongly enhanced in the presence of the other nutrient. Surface models quantitatively reflect patterns of colimitation and multi-element demand in streams, and should allow for parameterization of more realistic stream network models that explicitly account for interactions among element cycles.     

Temporal changes in the phytoplankton community structure in a tropical and eutrophic reservoir (Barra Bonita, S.P.--Brazil)

A study of the temporal changes in the phytoplankton communitystructure in the eutrophic Barra Bonita Reservoir (SãoPaulo State, Brazil) was carried out during 30 days (sampleswere taken daily for 10 days and, thereafter, on every otherday) in two distinct seasonal periods (dry and rainy seasons).Monthly sampling occurred in the period July 1993 to June 1994.One hundred and thirty-one taxa were registered. A greater diversity(112 taxa) was observed in winter than in summer (79 taxa).In the monthly analysis, 90 taxa were identified. The highestvalues for species diversity and richness were observed in July1993 and the lowest in April 1994. The phytoplankton dynamicsin this system are apparently dominated by competitive exclusionand disturbance. Within theseasonal cycle, the phytoplanktoncommunity structure was determined by underwater light availability,mixing by wind, precipitation and the consequent loss of Cyanophyceaebiomass in the upper waters by spillage, and nutrient (principallyphosphorus) inputs from anthropogenic sources. The environmentalvariability in this polymictic system may be favouring a phytoplanktoncommunity in equilibrium, with dominance alterations of Bacillariophyceaebiomass (Aulacoseira granulata), R-strategists, and Cyanophyceaebiomass (Microcystis aeruginosa), S-strategists. Short periods(i.e. 10 days) in non-equilibrium conditions with increasedspecies diversity and coexistence can perhaps be explained bythe intermediate disturbance hypothesis.     

Litterfall seasonality and adaptive strategies of tropical and subtropical evergreen forests in China

中国热带和亚热带常绿林凋落物季节特征及适应策略 本研究收集了来自中国热带/亚热带常绿林共85个站点的凋落物量季节性变化数据,并采用线性回归、结构方程模型构建以及相位差分析等方法,综合探究中国热带/亚热带地区常绿阔叶林和针叶林叶片脱落对土壤水分、饱和水气压差和辐射强度等气候因子的响应机制。研究结果显示,在雨热同期和雨热异期两种热带/亚热带气候类型中,呈现出两种典型凋落物的物候类型(单峰季节型/双峰季节型)。在雨热同期气候条件下,光照强度和降水呈现季节性正相关,单峰的凋落物峰值和双峰的第一个峰值约出现在3–4月,不断增加的光照能促进新叶的萌发,老叶被代谢更强的新叶所替代,该类型属于一种最大程度利用光照来实现树木生长的自适应策略。双峰的第二个峰值出现在雨季末期,约在8–10月,是由不断增强的水分亏缺所导致的(常绿阔叶林：大气水分亏缺;常绿针叶林：土壤水分亏缺),这种类型是一种凋落老叶减少水分丢失来应对水分胁迫的自适应策略。在雨热异期气候条件下,光照强度和降水呈现季节性负相关,饱和水气压差与光照强度表现出一致的季节性动态变化,诱导了常绿阔叶林单峰和双峰物候的第一个凋落峰(约在3–4月),是一种权衡大气干旱胁迫和最大程度利用光照进行生长的综合自适应策略。在雨季初期,显著的土壤水分亏缺加速叶片凋落,诱导了常绿阔叶林双峰物候的第二个凋落峰(约在11月),属于凋落老叶应对土壤水分胁迫的自适应策略。这些研究结果可以为地球系统模式中热带物候的精确模拟提供重要参考。     

Utilization of immobilized benthic algal species for N and P removal

Laboratory experiments were performed to study the growth rate and phosphorus (P) and nitrogen (N) uptakes of eight benthic microalgae species isolated from different sources of pig manure. Cells immobilized in calcium alginate beads were cultured with three replicates for each species. P removal rates obtained for the unicellular self-aggregating benthic species (Palmellopsis gelatinosa, Chlorosarcinopsis sp., and Macrochloris sp.) were markedly higher than those obtained in previous published experiments. N removal rates were highest for Macrochloris sp., Chlorosarcinopsis sp., and Euglena sp. 2 and comparable to the maximum rates obtained by other authors. Our results show an excellent efficiency of autochthonous benthic species for nutrient removal, especially for P, and call attention to their use for wastewater treatment.     

Bacteria–algae association in batch cultures of phytoplankton from a tropical reservoir: the significance of algal carbohydrates

Summary 1. The dissolved organic matter, especially carbohydrates, released by phytoplanktonic organisms may be ecologically important, through its influence on carbon cycling and microbial diversity. Here axenic cultures of three phytoplanktonic species, Cryptomonas tetrapyrenoidosa (Cryptophyceae), Staurastrum orbiculare (Zygnematophyceae) and Thalassiosira duostra (Bacillariophyceae), were inoculated with a microbial community from the same habitat in which the algae had been isolated (a tropical reservoir). Replicate cultures were not inoculated.
2. In both axenic and co-inoculated cultures, phytoplanktonic density and extracellular carbohydrate production were monitored microscopically and by high performance liquid chromatography with a pulse amperometric detector, respectively. Bacterial population density was also monitored by epifluorescence microscope in the microbial co-inoculated cultures.
3. Both bacterial and phytoplanktonic densities increased for 11 days in all cases. The use of extracellular carbohydrates by bacteria was also showed for all phytoplanktonic species. Of the three species of phytoplankton, only T. duostra had a faster population growth in the presence of bacteria, and reached a higher biomass than in axenic culture.     

Effects of nutrient (N,P, C) enrichment upon the littoral diatom community of an oligotrophic high-mountain lake

The effects of nutrient additions upon the epilithic diatom communities and the algal standing crop were investigated in the oligotrophic, softwater Lake Piccolo Naret, situated in the Swiss alps. Nutrient-diffusing flower pot substrates were filled with either N (0.15 mol NaNO₃), P (0.015 mol Na₂HPO₄) or C (0.15 mol NaHCO₃) or combinations of them. Twenty-five pots representing eight treatments were placed into the lake in July 1991 and sampled after 42 days of exposure.On the surfaces of all pots containing P we measured higher algal biomasses as on the control pots. The chlorophyll-a maximum of 12.9 µg cm^{– 2} was obtained on NPC pots (0.47 µg cm^{– 2} on control pots). On pots with P, NP or NPC supply high amounts of green algae were detected, also reflected in an increased chl-b/chl-c ratio related to the controls which showed algal communities dominated by diatoms.The diatom communities on the control pots as well as on the pots with N, P and NP had a structure similar to the epilithic community in Lake Piccolo Naret (dominance identity > 58 %). However, the community structures of the diatoms from pots with C addition (C, NC, PC and NPC) differed considerably. This is discussed in view of the cell densities of dominant diatom species. For further comparisons the results of two additional high-mountain lakes are used. By means of a cluster analysis it could be shown that epilithic diatom communities were considerably influenced by C addition, while N and P supply were of minor importance.     

Diatom fluxes in a tropical,oligotrophic lake dominated by large-sized phytoplankton

Alchichica is a warm-monomictic, oligotrophic lake whose phytoplanktonic biomass is dominated by large size (average ca. 55 μm) diatoms. The fast sinking phytoplankton leads to silica, and other nutrient exportation out of the productive zone of the lake. The aim of the present study was to identify and measure the sedimentation fluxes of the diatom species and their temporal dynamics to better understand the magnitude of silica and carbon fluxes. Sediment-traps were exposed at three different depths and collected monthly. A total of 13 diatom species were observed in the traps. The maximum diatom flux was in February (304 × 10⁶ cells m⁻² day⁻¹) related to the winter diatom bloom. The diatom silica (DSi) fluxes varied from 2.2 to 2,997 mg m⁻² day⁻¹ and the diatom carbon (DC) fluxes from 1.2 to 2,918 mg m⁻² d⁻¹. Cyclotella alchichicana was the main contributor (>98%) to the total DSi and DC fluxes. The annual diatom (15 × 10⁹ cells m⁻² year⁻¹), DSi (147 g m⁻² year⁻¹) and DC (92 g m⁻² year⁻¹) fluxes are higher than in other aquatic ecosystems of similar or even higher trophic conditions. Our findings in Alchichica are indicative of the relevance of the phytoplankton type and size in understanding the role tropical and oligotrophic lakes play regarding silica and carbon fluxes. In addition, our results support previous findings suggesting that inland aquatic ecosystems are more important than formerly thought in processing carbon, and can, therefore, affect regional carbon balances.     

Vertical mixing in a shallow tropical reservoir

Limnology - This paper presents observations of diurnal cycles of stratification and vertical mixing in Kranji Reservoir, a shallow tropical reservoir with an average depth of 6.7&nbsp;m...     

一座热带浅水水库敞水区浮游甲壳动物群落结构

为了解热带中小型浅水型水库枯水期浮游动物群落组成与结构稳定性,于2006至2007的三个枯水期,对位于我国雷州半岛甘村水库敞水区进行了每周一次的高频采样,主要以个体大小作为变量分析了浮游甲壳类动物的群落结构的组成.三次枯水期采样中,敞水区中只检测到枝角类4种和桡足类4种.浮游甲壳类的体长范围多集中在400～700μm之间.枝角类的优势种为模糊秀体溞平均体长为533μm,桡足类成体优势种台湾温剑水蚤的平均体长为787μm,无节幼体和剑水蚤桡足幼体丰度与生物量也相对较高.水库浮游甲壳类种类数和丰度的峰值均出现在体长为300～400μm和400-500μm两个等级内.浮游甲壳类的种类和数量均是以小个体为主,除了营养水平还与水体中的捕食压力紧密相关,鱼类的捕食对于浮游甲壳类群落结构的形成作用显著.     

Bacterial utilization of algal extracellular products in a southwestern reservoir

Rates of carbon flow from phytoplankton to bacteria were estimated for Lake Arlington, Texas. The lake is a warm (annual temperature range 7 to 35 °C), shallow, monomictic reservoir with limited macrophyte development in the littoral zone. Samples were collected from 6 depths within the photic zone from a site located over the deepest portion of the lake. Primary production and exudate production were calculated from NaH¹⁴CO₃ incorporation. Bacterial production was calculated from [methyl-³H]-thymidine incorporation. Depth averaged primary production ranged from a seasonal low of 9.0 μg C l⁻¹ h⁻¹ in January to a seasonal maximum of 153 μg C l⁻¹ h⁻¹ during holomixis in September. Annual depth-averaged production was 67.8 ± 7.3 μg C l⁻¹ h⁻¹. Exudate production ranged between 21.9 and 54.2% of primary production and annually averaged 30.8%. Bacterial production ranged between 1.7 and 46.0 μg C l⁻¹ h⁻¹ and annually averaged 16.0 ± 1.9 μg C l⁻¹ h⁻¹. Bacteria processed approximately 70% of exudate and incorporated 35% into biomass. Bacterial production was positively correlated with total primary production (r = 0.38, p < 0.003, n = 6), particulate primary production (r = 0.34, p < 0.004, n = 70) and bacterial uptake of exudate (r = 0.43, p < 0.001, n = 68). While exudate was readily utilized by bacteria it dit not appear to be produced in sufficient quantity or at a sufficient rate to serve as the sole or a major source of carbon supporting bacterial growth.     

The nutritional status of zooplankton in a tropical reservoir: effects of food quality and community structure.

The temporal variability of energetic reserves of zooplankton in the eutrophic Pampulha reservoir was investigated during two successive annual cycles. The effects of dominance of large filter-feeding cladocerans (Daphnia) and the occurrence of massive blooms of the cyanobacteria Microcystis on the energetic reserves of zooplankton were tested. This study showed that phytoplankton composition has a greater effect on energetic reserves of zooplankton. Some associations between lipid levels and the specific composition of zooplankton were also found. This study also demonstrated that the elementary composition of phosphorus in zooplankton can be used as an estimator of the nutritional status of zooplankton.