Summer phytoplankton composition and nitrogen limitation of the deep, naturally-acidic (pH2.2) Lake Caviahue, Patagonia, Argentina

During the warm seasons of 1998–2004, the naturally-acidic (pH2.2) Lake Caviahue was sampled for conductivity, temperature, oxygen, light, nutrients, and phytoplankton (density, biomass and chlorophyll a) with a view to studying the summer phytoplankton population changes with relation to environmental factors, as well as the significance of nitrogen limitation on the phytoplankton yield. Lake Caviahue is characterized by its low transparency, CO₂, and N concentration; significant P values; a distinctive vertical distribution of phytoplankton biomass with high values along the water column; and sometimes maximum meta-hypolimnion values. Biodiversity is very low as a result of extreme environmental conditions, Chlorophyceae being the prevailing algae group. Two types of bioassays were carried out to assess nitrogen limitation. For the first bioassay, a solution of ammonium–nitrogen chloride and/or wastewater (rich in ammonium and phosphorus) was used, while one of the lake's sediments was the source of nutrients for the second bioassay. Contrary to the case of acidic mining lakes, N-ammonium proved to be a significant supportive capacity limiting factor as to phytoplankton yield. The present paper provides for the first time information on phytoplankton nitrogen limitation in a naturally-acidic lake.     

Analysis of patterns of vertical and temporal distribution of phytoplankton using multifactorial analysis: Acidic Lake Caviahue, Patagonia, Argentina

Most existing studies on the algal communities of acid lakes are based on environments that have been caused by anthropogenic disturbances. Such lakes have a different origin compared to the natural acidic lakes and could be expected to differ also in the mechanisms controlling phytoplankton and trophic status. Planktonic community in Lake Caviahue is somewhat diverse in spite of the low pH of the water. Algae have a distinctive vertical distribution: the values of phytoplankton biomass remain constant throughout the water column and at times were highest in the upper end of the hypolimnion, forming a maximum or a layer of chlorophyll a at depth. The goal of this work was to investigate the factors influencing the seasonal and vertical distribution of phytoplankton. The lake was sampled between the years 2004 and 2006. Physical, chemical and biological parameters at different depths throughout the water column were determined. The interrelationships between environmental variables at different sampling dates were analyzed using an integration of multivariate matrices, multiple factor analysis, to analyze any joint partnerships in the samples. We found that phytoplankton biomass is dominated by Keratococcus rhaphidioides. With regard to zooplankton, we found a single species of rotifers (Philodina sp.). The two arms of the lake and the depths have different behaviours showing differences in the arms' conductivity, dissolved oxygen and pH. The more superficial layers were characterized by high values of phytoplankton and zooplankton biomass, organic and inorganic carbon, dissolved oxygen and pH. The deeper layers showed high values of chlorophyll a, ammonium and phosphorus (dissolved and particulate). From the multivariate analysis the relationships of the each algal species with pH, as a possible indicator of the degree of “acidophilia”, could be extracted.     

Volcanic nutrient inputs and trophic state of Lake Caviahue,Patagonia, Argentina

The strategies for eutrophication control, remediation, and policy management are often defined for neutral to alkaline freshwater systems, as they are most suitable for human use. The influence of nutrients on eutrophication in a naturally-acidic lake is poorly known. The main purpose of the present work is to evaluate the significance of volcanic nutrients in the control of the trophic state of the acidic Lake Caviahue, located at North Patagonia, Argentina.     

Optical properties and light penetration in a deep,naturally acidic,iron rich lake: Lago Caviahue (Patagonia,Argentina)

The optical properties and light climate in the deep and extremely acid Lake Caviahue have been studied in order to better understand its characteristics and the possible influence upon the phytoplankton community. The absorption coefficients for the dissolved fraction were maximal in the ultraviolet (UV) region and the water absorption spectra showed a shoulder around 300 nm, which was attributed to the concentration of Fe(III). No radiation was detected in the water column below 360 nm. The depth of the 1% incident radiation was dependent of wavelength, showing its maximum of 13.3 m at 565 nm, compared to 1.7 m and 4.8 m at 400 nm and 700 nm, respectively. Phytoplankton biomass was low and showed an almost constant profile with depth despite the relative darkness of the water column. Optical climate of Lake Caviahue is not typical of high elevation lakes but is more similar to low elevation shallow lakes of the Andean region. The chemical composition of the water, mainly Fe oxidation state and concentration, is the responsible for the high attenuation of the UV radiation (UVR). Living organisms are protected of UVR because Lake Caviahue waters are a shield against UV-B.     

太湖西北湖区浮游植物和无机、有机氮的时空分布特征

以太湖重度蓝藻水华发生的西北湖区为研究对象,从河口至湖心区设置5个采样点,于2012年10月至2013年10月逐月采集表层水体样品,测定了水温、溶解氧和浮游细菌丰度,并分析了浮游植物群落结构的组成、溶解性无机氮(DIN)和有机氮(DON)浓度以及氮磷比.研究结果表明,太湖西北湖区浮游植物主要由蓝藻、硅藻、绿藻和隐藻组成.可能由于风、浪等混合作用使太湖西北湖区不同采样点之间蓝藻细胞密度没有显著差异.蓝藻生物量在浮游植物中所占比例最高为34%±15%,春季部分点位隐藻生物量高于50%,表明隐藻与蓝藻的相互竞争趋势显著.CCA排序图结果表明,DIN、DON浓度以及总氮∶总磷比(TN∶TP比)是影响西北湖区浮游植物优势属分布的重要环境因子.5个采样点铵态氮(NH_4~+-N)与DIN浓度具有显著差异,与DON浓度没有显著差异.夏季蓝藻水华暴发期间,可能由于蓝藻的吸收利用引起NH_4~+-N和硝态氮(NO_3~--N)浓度迅速降低.此外,由于NH_4~+-N浓度还可能受到沉积物NH_4~+-N释放的影响,因此,蓝藻细胞密度与NO_3~--N的相关系数和显著水平均高于NH_4~+-N.夏季TN∶TP比和DIN∶TP比降至最低,表明该湖区浮游植物,尤其是蓝藻的生长可能受到氮限制.蓝藻细胞密度与DON浓度呈显著负相关,表明在氮限制条件下,DON可能是蓝藻氮素利用的重要补充.     

Effects of nitrogen and phosphorus on phytoplankton composition and biomass in 15 subtropical, urban shallow lakes in Wuhan, China

This study aims at investigating the composition and biomass of the phytoplankton community in 15 urban shallow eutrophic lakes as well as the effects of main environmental factors, including nutrient concentrations and the ratio of nitrogen to phosphorus, temperature, COD, BOD, water depth, etc. on the phytoplankton community structure. Lake water samples were taken and analyzed on a bimonthly basis during the period from March 2004 to March 2006. The redundancy analysis (RDA) and regression analysis (RA) were performed to identify the effects of nutrients on the phytoplankton community and biomass in these typical urban lakes. The results indicate that most of these urban lakes were hypertrophic due to high concentrations of total phosphorus (TP) and total nitrogen (TN), with mean levels of 490 and 5380 mg m⁻³, respectively. The phytoplankton community was dominated by Microcystis aeruginosa and Euglena caudate in summer and Cryptomonas ovata and Cyclotella meneghiniana in winter. The mean biomass of the phytoplankton reached 456.87 mg L⁻¹ in summer months and the annual level was 189.24 mg L⁻¹. Temperature and TP content were found to be the principal limiting factors for phytoplankton growth on an annual basis. On the other hand, the results of RDA and RA demonstrate that the dominant phytoplankton species were not nutrient-limited during summer months. Low TN:TP ratios (<10) were detected accompanied with fewer occurrences of N-fixing cyanobacteria and other filamentous algae in most lakes in summer, which implies that low N:P ratio does not always shifts the dominance of phytoplankton community to the N-fixing cyanobacteria. Moreover, TP always had higher correlation with chlorophyll a (Chl-a) than TN, even when the TN:TP ratios of most samples were lower than 10. Therefore, it is concluded that the TN:TP ratio is not always a suitable index to determine whether nitrogen or phosphorus limits the phytoplankton biomass in urban shallow eutrophic lakes.     

Phosphorus and nitrogen limitation of algal biomass across trophic gradients

Regression results based on data from 46 northern temperate lakes show that total phosphorus (TP) is the best predictor for phytoplankton (as chl-a) at lower trophic levels, TP < 200 mg · m^–3. A regression including both TP and TN as regressors is the best predictor for lakes with TP > 200 mg · m^–3. However, the good correlation is probably due to a high correlation between lake average chl-a (all years observed) and lake average TP and TN. Within single hypereutrophic lakes, TN alone is the best predictor. It was not possible to identify a medium trophic domain where TN and TP in combination was the best predictor for chl-a. The ratio TN:TP in the water decreases from about 40 to about 5 with increasing trophic level. Optimum TN:TP ratio for algal species with high abundance during late summer and autumn reflects this decreasing ratio, but within a lesser range, i.e., 20 to 5. In contrast, TN:TP ratios for species abundant during the early vernal period showed no, or an inverse, relation to the TN:TP ratio of the water.     

Seasonal dynamics of a large, shallow lake, laguna Chascomús: The role of light limitation and other physical variables

The most conspicuous waterbodies in the Pampa region of Argentina are the so-called “lagunas”. A typical Pampean laguna may be described as a relatively large (100+ha), permanent, shallow lake. Here, we report the dynamics of laguna Chascomús, sampled weekly, from April 2001 to June 2003. During the period, the lakes experienced three consecutive floods waves that affected the concentration of major ions and the optical signature of the dissolved organic matter. Despite these hydrological alterations, laguna Chascomús was permanently limited by light. Transparency was to a great extent controlled by the incident photosynthetic available radiation irradiance. We hypothesize that wind contributes to the permanent mixing of the lake, as well as to lessen the sedimentation losses of photoautotrophs.     

Chemical composition and the nitrogen-regulated trophic state of Patagonian lakes

Chemical composition and nutrient concentrations of 39 relatively poorly known Patagonian lakes (38–50°S and from 70° to 68°W) are described and analysed using principal component analysis (PCA). The general relationships between nutrients (total phosphorus, bioavailable phosphorus and dissolved inorganic nitrogen) and plankton biomass are examined.We seek to demonstrate that the extreme oligotrophy characterising many lakes and reservoirs of the Argentine Patagonian region of South America owes more to nitrogen deficiency than to a shortage of available phosphorus. The data show a range of trophic conditions with variable water chemistry characteristics.The first two axes of the PCA ordination explain most of the variance (63%). The first component of the variance in the environmental data is a trophic gradient, with positive correlations with the concentrations of nutrients (TP, SRP, DIN) and electrical conductivity and a negative correlation with transparency. For all the reservoirs considered, the calculated annual, summer and winter chlorophyll-a carrying capacities of the available phosphorus were consistently and significantly (P<0.05) in excess of observations but maximum chlorophyll-a values correlate with DIN availability. Indeed the chlorophyll-a carrying capacities, as an index of the resource-sustainable maximum biomass, of the available nitrogen gives a better predictive yield relationship than does P. Our findings are remarkable in so far as the general expectation that dinitrogen-fixing phytoplankton should thrive in the absence of dissolved inorganic nitrogen, at least to the supportive limits of the available phosphorus, is unfulfilled.     

江苏滆湖北部区整治后浮游植物时空分布及环境因子变化规律

滆湖是我国长江中下游典型的浅水型湖泊,为了解其治理后浮游植物群落时空分布规律,2013年1 12月对其北部区浮游植物及环境因子进行调查.调查期间共检出浮游植物7门43属61种,春、冬季以栅藻(Scenedesmus)和小环藻(Cyclotella)为主要优势种属,夏、秋季以微囊藻(Microcystis)和颗粒直链藻(Melosira granulata)为主要优势种属,采样期间浮游植物生物量最高值为90.6 mg/L,出现在8月份,铜绿微囊藻(Microcystis aeruginosa)占绝对优势.浮游植物平均密度呈现由西向东递减的趋势,植被覆盖区低于敞水区.环境因子分析表明:总氮浓度、总磷浓度、水温是影响滆湖北部区浮游植物密度和生物量的主要因子.比较相同月份湖区内部菱角芦苇区和未治理的敞水区的平均生物量,菱角区生物量较敞水区低约72.7%~91.1%,芦苇区生物量较敞水区低约63.9%~83.7%.在8、9月湖区内敞水区暴发水华时菱角区浮游植物生物量仅为敞水区的14.6%,芦苇区为敞水区的30.3%.     

Natural and anthropogenic hydrocarbons in sediments from the Chubut River (Patagonia, Argentina)

In March of 2001 a study was carried out to evaluate hydrocarbon levels in the lower course of the Chubut River. The study included 12 sample stations along the river from San Cristóbal Bridge to the confluence with the sea, in a 25 km straight-line extension in a urbanized area. In the first 11 stations, resolved aliphatic (RAli) hydrocarbons presented low values, between 0.07 and 0.96 microg/g dry weight (dw); the unresolved complex mixture (UCM) between 0.42 and 2.72 microg/g dw, and the total aliphatic (TAli) hydrocarbons between 0.55 and 3.07 microg/g dw. In the last station, at the mouth of Chubut river, these values increased to 460, 284, and 741 microg/g dw for RAli, UCM and TAli, respectively. The n-alkanes distribution indices and the compositional parameters suggested a predominantly biogenic origin in eleven stations, and a predominantly anthropogenic origin in the last station, with the highest hydrocarbon values. It is possible to conclude that the stations with low hydrocarbon values and biogenic origin predominance would constitute the baseline of aliphatic hydrocarbons for river sediments at this zone. The station with the highest hydrocarbon concentration and predominantly anthropic origin was related to the presence of Rawson city's port, where its activities (harbor and fishing vessels) generate hydrocarbon wastes unrelated to the river base profile in the study zone. Offshore, but within the river influence, there is an important fishing area of Argentine Red and Patagonian shrimps (Pleoticus muelleri and Artemesia longinaris, respectively).     

南京玄武湖隆腺溞(Daphnia carinata)牧食对浮游植物的影响

隆腺溞(Daphnia carinata)是许多湖泊的常见大型浮游动物,习居于富营养的水域中,以浮游植物为食,且滤食效率较高.通过浮游动物添加实验,研究了隆腺潘对南京玄武湖叶绿素和浮游植物群落结构的影响.结果表明,在隆腺涵组,浮游植物密度较对照组降低了83%,叶绿素较对照组下降了81%,氮、磷营养盐与叶绿素的相关性不显著.浮游植物的群落结构较对照组也发生了很大变化,蓝藻、绿藻和硅藻的比例有显著上升,隐藻呈显著下降趋势,金藻、甲藻和裸藻在实验结束时已没有检出.说明隆腺潘的摄食能有效控制浮游植物的生物量,可对浮游植物的群落结构产生显著影响.     

白洋淀浮游植物群落结构与水质评价

为掌握白洋淀浮游植物的群落结构及水质状况,对白洋淀8个典型采样点进行了采样调查,共发现浮游植物133种(属),群落组成以绿藻、硅藻和蓝藻为主;春季以绿藻和硅藻为优势门类,小球藻、尖尾蓝隐藻、不定微囊藻为优势种(属),浮游植物的密度在496×104 - 6256×104cells/L之间,平均密度为2384×104 ce...     

流速对浮游藻类生长和种群变化影响的模拟试验

采集夏季崇明岛中心湖原水,在环形有机玻璃水槽开展了不同流速对浮游藻类生长和种群变化影响的研究.相对于静止水槽,实验前期不同的流速条件均对浮游藻类的生长产生了一定的抑制作用,实验后期浮游藻类叶绿素a含量均稳定在一定水平,且流动水槽中叶绿素a含量略大于静止水槽,这可能与静止围隔中出现大量枝角类浮游动物有关,而流动条件则抑制了浮游动物的生长,减轻了对浮游藻类的捕食压力.水体流动导致了浮游藻类种群的变化,蓝藻的迅速消失、绿藻和硅藻形成生长优势是主要特征,表明持续的流动条件是导致浮游植物种属减少和群落结构变化的直接原因.该研究可为调水引流在河道、湖泊和水库中的富营养化控制和水华防治提供基础依据.     

2013年洱海水华期间微囊藻毒素和浮游植物动态变化

2013年秋季,洱海再次出现大规模水华,周边几十万居民的饮用水安全引起当地政府的极大关注.为了解水华发生期间洱海水体微囊藻毒素的含量和浮游植物的种类及丰度,分别在2013年9月和10月两次在洱海采集水样,测定其中两种主要微囊藻毒素MC-LR和MC-RR含量,探讨微囊藻毒素含量对洱海周边水源地的安全影响.同时也对水华期间的浮游植物特别是蓝藻进行研究,从而分析微囊藻毒素与浮游植物种类和丰度的关系.结果表明,洱海水体中微囊藻毒素含量偏低,暂不会对人类健康产生威胁,但在洱海的水鸟体内仍然检测到微囊藻毒素的富集,显示洱海蓝藻水华对水生生物的潜在危害不容忽视.浮游植物的研究发现,洱海水华的优势种属为微囊藻(Microcystis)和暗丝藻(Psephonema aenigmaticus).9月份暗丝藻更占优势,10月份则是微囊藻更占优势.研究结果显示处于富营养化初期的洱海水体中湖湾微囊藻毒素的含量与浮游植物中产毒蓝藻的种类和丰度密切相关.     

Sources of dissolved silica to the fjords of northern Patagonia (44–48°S): the importance of volcanic ash soil distribution and weathering

Dissolved silica (DSi) plays an important biogeochemical role in the fjords of northern Chilean Patagonia (44–48°S), where it drives high biogenic productivity and promotes carbon burial. It is generally believed that the DSi riverine input to lakes and coastal environments is controlled by a combination of factors including lithology, climate, topography, vegetation, and meltwater input. In northern Chilean Patagonia several authors have proposed that the postglacial volcanic ash soils (andosols) may play a significant role in the high supply of DSi to the regional fjords. To assess the influence of andosols on DSi concentrations in north Patagonian rivers, we mapped andosol thickness and compared our results with river chemistry. The mineralogical and geochemical composition of three representative andosol profiles was also examined to evaluate the efficiency of weathering processes. The andosol thickness map clearly demonstrates that volcanic ash was predominantly deposited on the eastern side of the regional volcanoes, reflecting the influence of the prevailing westerly winds on the distribution of pyroclastic material. Mineralogical and geochemical results show that the andosol parent material has the typical andesitic basaltic signature of the regional volcanoes, i.e. high amounts of amorphous material, plagioclase, K‐feldspar, and pyroxene. Down‐profile variations in soil mineralogy and geochemistry indicate increased leaching of silica with depth, resulting from weathering of the volcanic parent material. For the five studied watersheds, a highly positive correlation (R²=0.98) was found between average andosol thickness and DSi concentrations, suggesting that andosol thickness is the main parameter affecting DSi concentrations in north Patagonian river systems. On seasonal timescales, increased precipitation (winter) and glacial meltwater (summer) input can significantly reduce DSi concentrations. We argue that the weathering of andosols constitutes the most important source of DSi to the lakes and fjords of northern Chilean Patagonia, explaining the particularly high regional rates of biogenic silica production. Copyright © 2015 John Wiley & Sons, Ltd.     

Trophic scaling of Percichthys trucha (Percichthyidae) in monospecific and multispecific lakes in western Patagonia

Percichthys trucha is a freshwater fish, endemic to southern South America and widely distributed in both, eastern and western sides of the Andes. P. trucha has been described as top native predator in lacustrine ecosystems, experimenting diet shifting during their life history development. Salmonid invasions have impacted their natural ecology through trophic niche interference and predation over alternative high quality prey. This study focuses on populations of P. trucha in western Patagonia, where its trophic ecology have been less understood. We hypothesised a diet shift between juveniles and adults from lower-trophic position prey towards higher-trophic position prey. Fish were collected from 7 lakes belonging to Puelo and Baker river basins, covering a high diversity of environmental conditions. Stomach content and δ¹⁵N stable isotope ratio of muscle tissues of 313 individuals were analysed. Results indicate significant differences in diet between juveniles and adults, shifting from planktonic/benthic preys towards benthic/piscivory, and concomitantly enrichment in heavier nitrogen isotope suggest trophic scaling. No trophic scaling was observed in populations inhabiting lakes with any other fish species present, essentially due to lack of Galaxias sp. as available prey and absence of cannibalism. Despite the fact that P. trucha and Galaxias sp. co-occur in studied river basins, no salmonid-free lakes harbouring this two native species were found, making it difficult to elucidate exact effects of salmonids on trophic scaling of P. trucha. Consumption of aquatic Odonata nymphs, however, arises as one of potential key mechanism for resilience of native food webs to salmonid invasion.