Diel patterns of phytoplankton productivity in Lake Vechten

Summary A review of the literature on phytoplankton primary production studies in lakes indicates that in most cases the daily primary production rates have been derived by multiplying the short-term (usually 3 or 4 hours) production measurement with a light factor. This factor is a ratio between the total irradiance during the day and during the period of incubation. The aim of the present study was to verify this method of calculation. Since the primary production rate is of great importance for the carbon cycle of lakes, this study can be regarded as a fundamental contribution to the integrated research of the ecosystem of lake Vechten (the Netherlands) (BESTet al., 1978).Photosynthetic carbon fixation was determined using the radiocarbon method of STEEMANN NIELSEN (1952). Thein situ measurements were carried out for 2 hours incubation periods starting at 15–30 minutes before sunrise and ending 15–30 minutes after sunset. Also measured were: water temperature, light penetration, oxygen and chlorophyll. Total incident solar radiation data were obtained from the Royal Netherlands Meteorological Institute (K.N.M.I.) at de Bilt (situated at 5 km from lake Vechten). The production during two consecutive 2-hourly periods,e.g. period 1 and period 2, were summed up and using the irradiance data during the 4 hours, daily production was calculated. These calculations were repeated for period 2 and 3, and so on. The sum of all the short-term measurements during a day,i.e. the total daily primary production, was taken for comparison with the production calculated by using the sum of the production during two successive periods and the light factor.Daily production rates obtained by extrapolating from short-term incubation periods both in the morning and in the late afternoon appeared to overestimate the real daily production (Fig. 1) up to 100%. It is likely, that in the morning the lack of nutrient limitation and relatively better physiological state of algae, and in the afternoon increase of phytoplankton biomass during the day can be considered as the factors causing the discrepancy between the calculated and real production. On the other hand, the underestimation of daily production rate based on midday time intervals on sunny days, was about 25%. It is attributed to photoinhibition, especially in the present study where the measurements were limited to the upper water strata (0–4m).Is is concluded that short-termin situ exposures between 10.00 and 14.00 hr appeared to be a good indicator of total primary production, although underestimates up to 25% on sunny days are to be taken into account.     

Biodiversity, productivity and the temporal stability of productivity: patterns and processes

Theory predicts that the temporal stability of productivity, measured as the ratio of the mean to the standard deviation of community biomass, increases with species richness and evenness. We used experimental species mixtures of grassland plants to test this hypothesis and identified the mechanisms involved. Additionally, we tested whether biodiversity, productivity and temporal stability were similarly influenced by particular types of species interactions. We found that productivity was less variable among years in plots planted with more species. Temporal stability did not depend on whether the species were planted equally abundant (high evenness) or not (realistically low evenness). Greater richness increased temporal stability by increasing overyielding, asynchrony of species fluctuations and statistical averaging. Species interactions that favoured unproductive species increased both biodiversity and temporal stability. Species interactions that resulted in niche partitioning or facilitation increased both productivity and temporal stability. Thus, species interactions can promote biodiversity and ecosystem services.     

Effects of wetting and drying on methane emissions from ephemeral floodplain wetlands in south-eastern Australia

Four approaches were used to assess the effect ofinundation on methane emissions from floodplainwetlands in Victoria, Australia: (i) fieldobservations following natural rainfall events; (ii)experimental manipulation of water levels in smallfloodplain depressions; (iii) experimentalmanipulation of water levels in replicated mesocosms;and (iv) in vitro incubation of floodplainsediment under laboratory conditions. Raftery'sSwamp, a large (150 ha) wetland on the floodplain ofthe Goulburn River, became inundated in June 1993following autumn-winter rainfall. Methane emissionspeaked (1.7 ± 0.05 mmol m^-2 h^-1) somesix months later, and the methane content of sedimentgas bubbles reached 59% v/v, even though the positivesediment redox potentials (176 to 243 mV) indicatedthat sediments were only moderately reducing. Threesmall (< 1 ha) depressions on the floodplains of theRiver Murray and Kiewa River were inundated eithernaturally (by rain and/or overflow from nearby rivers)or artificially by flooding at specific times of year;emissions from these sites were usually negligibleafter flooding in autumn or winter. In contrast, theonset of methane emission was very rapid (within 3 to6 days) after the depressions had been flooded insummer, and the methane content of sediment gasbubbles could then reach 36% v/v. At their peak,emissions from the ephemeral wetlands were similar topeak emissions from permanent wetlands insouth-eastern Australia. Emissions from replicatedwetland mesocosms (4.5 m diameter, 0.9 m deep) werealways very small (<0.2 mmol m^-2 h^-1),regardless of time of flooding, water depths, orseason. In vitro incubation of wetland sedimentunder anaerobic conditions indicated a progressivedecrease in benthic methanogenesis with sedimentdesiccation and exposure to air. Ephemerallyinundated floodplain wetlands may be sites ofsignificant methane emission, especially over thesummer months. Moreover, the survival and rapidreactivation of methanogenic archaea after prolongeddrying of wetland sediments suggests thatmethanogenesis is possible even from re-wettedfloodplain environments that had earlier experiencedan extended dry phase.     

Ecological impacts of dams,water diversions and river management on floodplain wetlands in Australia

Australian floodplain wetlands are sites of high biodiversity that depend on flows from rivers. Dams, diversions and river management have reduced flooding to these wetlands, altering their ecology, and causing the death or poor health of aquatic biota. Four floodplain wetlands (Barmah‐Millewa Forest and Moira Marshes, Chowilla floodplain, Macquarie Marshes, Gwydir wetlands) illustrate these effects with successional changes in aquatic vegetation, reduced vegetation health, declining numbers of water‐birds and nesting, and declining native fish and invertebrate populations. These effects are likely to be widespread as Australia has at least 446 large dams (>10 m crest height) storing 8.8 × 10⁷ ML (10⁶ L) of water, much of which is diverted upstream of floodplain wetlands. More than 50% of floodplain wetlands on developed rivers may no longer flood. Of all of the river basins in Australia, the Murray‐Darling Basin is most affected with dams which can store 103% of annual runoff and 87% of divertible water extracted (1983–84 data). Some floodplain wetlands are now permanent storages. This has changed their biota from one tolerant of a variable flooding regime, to one that withstands permanent flooding. Plans exist to build dams to divert water from many rivers, mainly for irrigation. These plans seldom adequately model subsequent ecological and hydrological impacts to floodplain wetlands. To avoid further loss of wetlands, an improved understanding of the interaction between river flows and floodplain ecology, and investigations into ecological impacts of management practices, is essential.     

Spatial distribution patterns of phytoplankton biomass and primary productivity in six coral atolls in the central South China Sea

Coral Reefs - Nutrients’ concentration, phytoplankton biomass, and primary productivity were investigated in six coral atolls in the central South China Sea during the southwest monsoon in...     

盐碱池塘浮游植物初级生产力日变化的研究

用黑白瓶测氧法对盐碱池塘浮游植物初级生产力的日变化进行了研究．结果表明,盐碱池塘浮游植物初级生产力存在着明显的日变化,其分布规律与光照、温度、浮游植物现存量等环境因子的变化是相关的．用黑白瓶法连续曝光24h测定初级生产力结果大大偏低于每次曝光2h的全天累积结果．对养鱼池而言,在10：00—14：00时曝光4h再推算全天的初级生产力较为适当．     

Effects of bottle size in determinations of primary productivity by phytoplankton

Determinations of primary productivity were made by the radiocarbon method at regular intervals over a year in samples, taken from the eutrophic waters of the Menai Strait, North Wales, and contained in bottles of capacities from 135 ml up to 2290 ml. Fixation per unit volume in particulate matter retained by 0 · 45 m pore size membrane filters was independent of bottle size over most of the year. There was a consistent divergence, however, during the period of rapid phytoplankton growth in the spring, when small bottles gave up to three times higher values than large ones. Possible effects of bottle size on primary productivity determinations are discussed but the cause of this particular result is not apparent.     

Assemblage structure and dynamics of large branchiopods in Mediterranean temporary wetlands: patterns and processes

1. To monitor the diversity and distribution patterns of large branchiopods and the effects of local and regional processes, 30 temporary wetlands in a nature reserve in the Camargue (southern France) were sampled and characterised during three consecutive inundations (2005–08). Additional species were added to the list for each wetland by hatching animals from the resting egg bank, after determining the optimal hatching conditions.
2. A total of five species were found, representing 28% of the species known in France and 56% of the known Camargue species. Tanymastix stagnalis , Branchipus schaefferi , Chirocephalus diaphanus (Anostraca), Triops cancriformis (Notostraca) and Imnadia yeyetta (Spinicaudata) were distributed over a total of 19 wetlands.
3. More than one species was present in 79% of the wetlands containing large branchiopods. Individual wetlands harboured on average 2.8 species, with a maximum of five coexisting species. Large branchiopod assemblages were temporally variable, differing among the three inundations with different climatological conditions.
4. The most important habitat factor influencing the distribution of large branchiopods was salinity, adversely affecting the density and survival of hatchlings. The persistence of large branchiopods in these temporary waters may be threatened by increasing salinisation driven by intensive water management and climate change.     

Size and species-specific primary productivity and community structure of phytoplankton in Tokyo Bay

Combined methods of size fractionation and single-cell isolationwere used to investigate the seasonal variation of phytoplanktondynamics in Tokyo Bay with an emphasis on primary productivity.Red tides occurred in Tokyo Bay from spring to autumn; a diatom,Skeletonema costatum, and a raphidophycean, Heterosigma akashiwo,were the most important primary producers. Small diatoms andflagellates, including these species, were dominant and showedrapid changes of phytoplankton community structure within severaldays in summer. The nanoplankton (3–20 µm) fractioncontributed most to chlorophyll a concentration and primaryproductivity during spring to autumn, whereas the microplankton(>20 µm) contribution was remarkable in winter. Picoplankton(<3 µm phytoplankton) remained relatively constantthroughout the year. A significant reverse relationship wasobtained between assimilation rate and chlorophyll a contentfor the total and nanoplankton population; the assimilationrate was high at the initial phase of the bloom, then decreasedto a minimum level at the peak of the bloom. Factors controllingthe reduction of assimilation rates at the peak, and changesin phytoplankton community structure, are discussed.     

Antibiotic resistance patterns of coliforms isolated from six protected wetlands in the southeast of Spain

Coliforms and thermotolerant coliforms were isolated from six protected lakes in the Antequera area of Spain in order to assess the sanitary quality of these wetlands. The thermotolerant coliform group consisted of several bacterial genera with a wide spectrum of antibiotic resistance. Resistance amongEscherichia coli strains was correlated with the origin of the sample and three homogeneous groups of wetlands were distinguished. One of them, which corresponded to wetlands where fæcal indicators were indigenous, exhibited no correlation between these bacteria and fæcal pollution. Non-coli strains showed a similar range of antibiotic susceptibility for this group. In the other two groups a fæcal pollution was detected and antibiotic resistance forE. coli strains established the origin of pollution.     

Retention of phytoplankton and planktonic microbes on coral reefs within the Great Barrier Reef,Australia

Concentrations of phytoplankton (coccoid cychobacteria and total chlorophyll) and planktonic microrial communities (heterotropic bacteria, nanoflagellates and ciliates) were lower over leeward reef flats than over open water or reef faces, around Davies Reef and Myrmidon Reef in the central Great Barrier Reef, Australia. Concentrations of cyanobacteria, which accounted for approximately 15–50% of the carbon biomass of phytoplankton in open water, decreased from the reef face towards the leeward reef flat. Concentrations of ciliates were consistently lower at the leeward reef flat than at the reef face. For Davies Reef, the retention rates of phytoplankton and planktonic microbial communities were estimated to reach 253 gC d^-1 per 1 m strip of the reef or about 0.09 gC m^-2 d^-1. This value is virtually equal to estimates of net community production (0.1 gC m^-2 d^-1). This allocthonous organic subsidy may help maintain spositive carbon balance on both Davies and Myrmidon Reefs on the Great Barrier Reef.     

Damming river shapes distinct patterns and processes of planktonic bacterial and microeukaryotic communities

Planktonic bacterial and microeukaryotic communities play important roles in biogeochemical cycles, but their biogeographic patterns and community assembly processes in large damming rivers still remain unclear. In this study, 16S rRNA and 18S rRNA coding genes were used for sample sequencing analysis of planktonic bacterial and microeukaryotic communities in the upper Yangtze River. The upper Yangtze River was divided into dam-affected zones and river zones based on the influence of dams. The results showed that there were significant differences in the bacterial and microeukaryotic communities between the two zones and that dams significantly reduced the α-diversity of the bacterial communities. Co-occurrence network analysis indicated that networks in the river zone were denser than those in the dam-affected zone. The relationships among species in bacterial networks were more complex than those in microeukaryotic networks. Dispersal limitation and ecological drift were the main processes influencing planktonic bacterial and microeukaryotic communities in the dam-affected zone respectively, whereas the role of deterministic processes increased in the river zone. Anthropogenic activities and hydraulic conditions affected suspended sediment and controlled microbial diversity in the river zone. These results suggest that dams impact planktonic bacteria more strongly than planktonic microeukaryotes, indicating that the distribution patterns and processes of the bacterial and microeukaryotic communities in large rivers are significantly different.     

A comparison of methods for measuring primary productivity and community respiration in streams

Carbon dioxide and oxygen exchange procedures for measuring community metabolism (two open stream methods and three chamber methods) were compared on the same reach of a third-order stream. Open stream methods were complicated by high diffusion rates and yielded net community primary productivity estimates lower than those obtained with chamber methods. Chamber methods yielded variable productivity and respiration data. However, when normalized for chlorophyll a, productivity estimates from the chamber methods were within an expected range for the system. Balances of photosynthesis and respiration from the chamber methods were similar between methods and indicated that autotrophic or heterotrophic processes could dominate the system. Considerations in applying the various procedures are discussed.     

太湖梅梁湾浮游植物叶绿素a和初级生产力

1998年5月～1999年8月对太湖梅梁湾4站点进行了每季1次、为期1年的初级生产力及相关因子研究,分析了梅梁湾叶绿素a含量和初级生产力的时空分布特征．结果表明,梅梁湾的叶绿素a含量、初级生产力均存在明显的季节变化和空间差异,春、夏季浮游植物叶绿索a含量和初级生产力要比秋、冬季高,空间上位于污染严重的直湖港口6#点叶绿索a含量和初级生产力要高,并大致呈现从湾内向湾口递减的趋势;在春、夏、秋季光照较强时,初级生产力最大指值出现在水下20～50cm处。到冬季垂直差异不明显;10～30℃之间初级生产力基本上随温度的上升而呈指数增加趋势．浮游植物生物现存量与初级生产力存在显著的正相关．营养盐与初级生产力相关性变化很大．光照显著地影响初级生产力的日变化。春、夏季强光作用下表面光抑制现象比较明显．     

Spatial patterns of China's carbon sinks estimated from the fusion of remote sensing and field-observed net primary productivity and heterotrophic respiration

Accurately assessing the carbon sink and spatial distribution pattern of China's terrestrial ecosystems is of great significance to the implementation of climate change and carbon neutrality strategy. However, the views of various studies are still very controversial due to the differences in carbon sink estimation methods and data sources. In this study, vegetation net primary productivity (NPP) and ecosystem heterotrophic respiration (Rh) estimation models were constructed based on machine learning methods by fusing multisource data, such as remote sensing and ground observation data. The magnitude and spatial pattern of carbon sink in China from 2000 to 2018 were then revealed, and the carbon sink capacity of various ecosystems was quantitatively assessed. The main conclusions include the following: (1) The use of scale-matched carbon input and output data can help reduce the system error in carbon sink estimation. (2) China's terrestrial ecosystem carbon sink since the twenty-first century is approximately 0.458 Pg C/yr, which is equivalent to 22.72% of China's anthropogenic carbon emissions. (3) Deciduous forest has a higher carbon sink capacity than evergreen forest, while coniferous forest has a more stable carbon sink capacity than broad-leaved forest. The magnitude and spatial distribution of carbon sink in China reported in this study provides a scientific reference for achieving carbon neutrality and sustainable development.     

太湖湖岸带浮游植物初级生产力特征及影响因素

利用高频溶解氧监测,估算了太湖梅梁湾湖岸带浮游植物初级生产力的高频变化特征。结合同步气象监测及浮游植物、浮游动物和营养盐的周年逐周观测数据,分析了气象和环境条件对富营养化湖泊浮游植物初级生产力的影响。结果发现,高频溶解氧监测估算的初级生产力变化与浮游藻类生物量的变化一致,能够反映出浮游植物生产力的昼夜变化、季节变化等规律。统计分析表明,气温对太湖这一富营养化湖泊初级生产力影响很大;氮的供给与浮游动物的选择性牧食也是影响浮游植物初级生产力的重要因素。湖岸带的水华堆积过程对初级生产力影响巨大,气象、水文过程又加剧了蓝藻水华初级生产力的变化幅度,反映出富营养化湖泊初级生产力可能存在极大的时空不均一性。研究表明,溶解氧高频监测法估算初级生产力能够捕捉到湖泊初级生产力的快速变化过程,可以用于富营养化湖泊初级生产力监测、蓝藻水华灾害预警中。     

2010年中国农作物净初级生产力及其空间分布格局

采用2011-2012年全国实测水稻、小麦、玉米、大豆、油菜、棉花6种作物的生物量获得的干燥系数（DC）、收获指数（HI）和根冠比（R/S）,结合2010年以县为单位的农业统计数据估算了2010年中国农作物产生的净初级生产力（NPP）。2010年中国农作物产生的NPP为596 Tg C,其中地上NPP为517 Tg C,地下NPP为80 Tg C。NPP空间分布不平衡,主要集中在东北的松嫩三江平原、黄淮海平原、长江中下游平原、西南的四川盆地和华南的珠江流域。单位面积农作物产生的NPP介于9-2094 g C m^-2 a^-1之间,平均密度为519 g C m^-2 a^-1。NPP密度（NPPD）较高的地区主要分布在中国的东部的湿润、半湿润地区以及内陆灌溉条件较好的地区。9个农业区中,黄淮海区农作物产生的NPP最多,东北区NPPD最高,青藏区农作物NPPD最低,产生的NPP也最少。作物种植面积能解释98%农业区之间NPP差异。通过对每个区域内县域NPPD与气候因子和化肥因子做相关分析,发现化肥施用量、日照时数、气温和降水均对NPPD的空间分异有影响,但是9个区域的主导因素不同。     

Ecological monitoring to support Water Sharing Plan evaluation and protect wetlands of inland New South Wales,Australia

Government‐funded flow response monitoring and modelling programmes (flow science) provided by the New South Wales Office of Water (NOW) have supported water resource management since 1997. Flow science has a core technical component defined by hypothesis‐driven long‐term monitoring and analysis, but it also represents many activities that support committees involved in environmental flow management. This is done through collaborations and contracting and has fostered considerable research and analysis into flow ecology, including modelling for the recent Murray–Darling Basin Plan. We describe the performance of environmental flows against legislated wetland objectives to improve wetland function and diversity using flow science. On‐ground monitoring at wetland sites has largely ceased but the flow science done so far indicates that the environmental flow rules written into Water Sharing Plans improve wetland diversity and function. Determination of the long‐term flow needs of NSW wetlands, including how well current Water Sharing Plans aid the delivery of environmental flows, requires finding the means to build on current flow science knowledge from across Australia.     

Dependence of phytoplankton assimilation quotients on light and nitrogen source: implications for oceanic primary productivity

Photosynthetic production of oxygen by phytoplankton assemblagedominated by Peridinium in Lake Kinneret, Israel, generallyexceeds the molar equivalent rate of carbon assimilation. Carbonassimilation occurs only if oxygenic photosynthesis exceedsa light-dependent threshold. Assimilation quotients (mol C molO₂^–1) are a variable function of irradiance, and typicallyonly about one-half of the photoreductant produced during oxygenicphotosynthesis is used for reduction of carbon dioxide. Mostof the residual oxygenic photoreductant probably is used forlight-dependent reduction of nitrate, which competes with carbondioxide for oxygenic photoreductant. Nitrate is an importantsource of nitrogen for this algal assemblage, and light-dependentnitrate reduction probably is much larger than carbon dioxidereduction at lowest irradiances in the euphotic zone. Oxygenproduction also may be much larger than carbon assimilationat low light levels in other environments where oxidized formsof nitrogen are important nitrogenous nutrients for phytoplankton,as in the lower euphotic zone of the sea, where low rates ofcarbon assimilation by phytoplankton have been thought to beinconsistent with the amount of oxygen that accumulates duringsummer.     

Use of coastal waters as condenser coolant in electric power plants: Impact on phytoplankton and primary productivity

(1) Studies on phytoplankton entrained in cooling system of a power plant revealed a reduction in biomass and gross primary productivity (GPP) at outfall, compared to intake.