Distribution and abundance of the zooplankton of the Ems estuary (North Sea)

From 1974 to 1977 a study was made of the abundance and the distribution of the zooplankton species of the Ems estuary (The Netherlands and the Federal Republic of Germany), an area of about 500 km² with extensive tidal flats.The most important component of the zooplankton consisted of holoplanktonic calanoid copepods with, during the summer, a significant contribution of meroplankton, mainly consisting of polychaete and cirripede larvae. Zooplankton abundance showed a marked seasonality, with a pronounced spring peak and a smaller late summer/autumn peak. In the low salinity area the spring bloom was dominated by Eurytemora affinis, which persisted in the salinities below S=5 upriver during the whole year. In the polyhaline area Acartia bifilosa was the main component of the spring bloom. The late summer maximum from August to October was dominated by Acartia tonsa in the meso- and polyhaline area and by A. discaudata and Centropages hamatus in the euhaline part of the estuary bordering on the Wadden Sea proper. The number of abundant (> 1000 ind·m⁻³) species increased from the inner, fresher part of the estuary towards the Wadden Sea but, except for April, average zooplankton density in salinities <18 was similar (2768 ind·m⁻³) to the density in salinities >18 (2817 ind·m⁻³).The distribution patterns show that there are only a few autochthonous species and that the majority of species is allochthonous and penetrates more or less deeply into the estuary from the Wadden Sea and North Sea, varying with species and season.     

Daily fecundity of Temora longicornis (Copepoda calanoida) in the Oosterschelde estuary (SW Netherlands)

Daily fecundity of Temora longicornis in the Oosterschelde was estimated in 1986 and 1987 after 24 h incubation of female copepods collected in the estuary. Daily egg production fluctuated between 3 and 25 eggs per female.Egg production rates increased with temperature in the range of 3 to 15°C when algal food was present in excess. Limiting food conditions were found at the end of the phytoplankton spring bloom and occasionally in summer at concentrations of ⩽2 μg chlorophyll·dm⁻³. When chlorophyll maxima were found, predominantly consisting of Phaeocystis, daily fecundity of Temora was suppressed. It could increase, however, in Phaeocystis blooms mixed with diatoms (Rhizosolenia delicatula).Standing stocks of eggs in the springs of 1986 and 1987 were calculated on the basis of the established temperature/fecundity relation and compared with observed numbers, both in the years 1986 and 1987 (estuary provided with a storm-surge barrier in the mouth) and in the years 1983 and 1984 (open estuary).Smaller differences between observed and calculated egg numbers in 1986 and 1987 could be ascribed to possible errors in calculated egg development time and to the different age structure of females in the course of time.Much larger differences were found between the years 1986–1987 and 1983–1984. These are discussed in relation to the following phenomena: sinking of eggs, cannibalism, predation, food quantity and availability, density-dependent effects, hydrodynamical changes of the estuary. Arguments are given for density-dependent factors being responsible for the strongly reduced egg numbers in 1984.     

不同经营措施下毛竹林土壤有机碳组分研究

通过在四岭水库流域代表性毛竹林地建立不同经营措施的定位试验,研究竹林土壤总有机碳(TOC)、可溶性有机碳(DOC)、微生物量碳(MBC)以及土壤呼吸等的动态变化。试验设有对照（CK,粗放经营）、农民常规高产营林(FFP)与适地养分科学管理(SSNM)3个处理。结果表明,毛竹林土壤TOC和DOC的季节变化总体趋势为秋冬高于春夏,MBC的季节变化为夏季>春季>秋季>冬季。试验虽只进行了1年,与CK相比,SSNM处理对土壤各形态碳含量没有产生显著影响;而FFP集约经营中土壤活性碳和总有机碳含量明显下降,其中DOC和MBC分别减少13.3%和14%。土壤呼吸CO2的释放通量季节变化曲线为单峰曲线,整个生长季,FFP集约经营毛竹区的土壤呼吸略高于粗放经营(CK)毛竹林,而适地养分管理(SSNM)集约经营措施减少了毛竹林土壤呼吸CO2的释放,但有待于长期的验证。     

Modelling the dynamics of the North Sea's Mesozooplankton

A simple biomass-only zooplankton submodel is presented, describing the dynamics of copepods and carnivorous zooplankton in the North Sea. This submodel together with the other process-oriented submodels (viz. phytoplankton dynamics, the microbial food web, benthic processes, fish dynamics and large-scale advective transport) forms a spatially resolved simulation model of the North Sea ecosystem, the European Regional Seas Ecosystem Model (ERSEM). A large set of field measurements of zooplankton abundance has been assembled against which to compare the ERSEM's performance. These data are not only internally consistent, but have also gathered at the large spatial scales appropriate to the ERSEM. In addition to the spatially resolved, monthly estimates of zooplankton abundance, several instantaneous, in situ estimates of the carbon fluxes between different components of the planktonic web in the northern North Sea are presented. Simulated dynamics are in good agreement with the data only during the mid-summer to mid-winter period. During the latter part of the winter and throughout the spring period zooplankton abundance is underpredicted and the simulated zooplankton growth rate is overpredicted during spring. The excessive decline of mesozooplankton biomass during winter may be caused by failing to capture many of the behavioural/physiological changes which zooplankton manifest during winter. It is suggested that the excessive spring growth is a consequence of a. a failure to properly distinguish between somatic and population growth, b. an inadequate representation of the small scale processes which influence feeding success, and c. an excessive spring phytoplankton bloom. The large phytoplankton bloom is, in part at least, a consequence of the excessively low simulated standing crop of omnivorous zooplankton in spring.     

Nutrient dynamics in the North Sea: Fluxes and budgets in the water column derived from ERSEM

Nutrient dynamics for phosphate, nitrate, ammonium and silicate have been simulated with ERSEM, the European Regional Seas Ecosystem Model. From the model results budgets for the dissolved inorganic nutrients and the corresponding particulate fractions have been calculated. The annual cycles of the nutrients phosphate and silicate compare quite well with the observed ranges of variability. This does not hold for ammonium and nitrate. Biologically mediated transformations such as nutrient uptake and pelagic and benthic mineralization are the dominant processes in changing the nutrient concentrations with the horizontal advective contributions playing a minor role during the productive season.Vertical advection and vertical diffusion have a clear seasonal signal, with a maximum in February. The decay of the advective nutrient transport in summer is caused by the depletion of the upper layer of dissolved inorganic nutrients by algal uptake. The inflow of nutrients in the northwest is almost balanced by the outflow in the northeast, without causing large nutrient transports into the shallower areas from the north. However, from the coastal areas there is a nutrient flow towards the central North Sea, enhancing primary production in the central area.     

The light and temperature dependence of growth rate and elemental composition of Phaeocystis globosa scherffel and P. Pouchetii (HAR.) Lagerh. in batch cultures

The light and temperature dependence of growth, cellular elemental composition (C, N, P) and chlorophyll content during exponential growth and phosphate starvation of batch cultures of the temperate algal species Phaeocystis globosa were investigated. Temperature-dependent minimum generation time and cell phosphorus content were compared with those of the cold water species P. pouchetii. The variation in growth and cell carbon content was due to the different origin of seawater used for the culture media. Coastal, estuarine seawater enabled shorter doubling times than “offshore” and oceanic-influenced seawater. At nutrient-saturated growth, P. globosa was able to compete with diatoms only if high temperature (14°C) and high irradiances (180 μE·m⁻²·s⁻¹) predominated. P. pouchetti showed markedly shorter generation times than P. globosa did at temperatures below 10°C. At 6°C, the cell carbon content exceeded the value at 18°C by a factor of 1.7. High C/N atomic ratios of 6.9±0.7 and high C/Chl a ratios of ≥ 54.0 during exponential growth could not entirely be explained by the carbon content of the colony mucus. There was no significant light and temperature dependence of the : N : P ratio during exponential growth. At phosphate starvation (subsistence P quota of cells) this was so only at temperatures higher than 10°C. With their stored phosphorus quota P. globosa and P. pouchetii were capable of only two cell divisions. Hence, because of their limited ability to store phosphorus, the two Phaeocystis species cannot compete with planktonic diatoms for growth. The frequent change in nutrient concentrations (particularly of silicate and phosphate) in coastal and estuarine waters at summer temperatures and light conditions causes a rapid alternation of smaller blooms of P. globosa and diatoms.     

Immigration and settlement pattern of Paralichthys dentatus and P. lethostigma in an estuarine nursery ground,North Carolina,U.S.A.

Immigration and settlement pattern of 0-group summer flounder (Paralichthys dentatus) and southern flounder (P. lethostigma) in an estuarine nursery are described. Flounders entering the estuary were transforming larvae. Despite their sympatric occurrence during larval immigration, the two species were found concentrated in different habitats. Sampling along transects within the estuary indicated that newly settled southern flounder were concentrated on tidal flats towards the head of the estuary while greatest numbers of summer flounder were captured on tidal flats in the middle reach of the system. Logistic regression analysis of presence/absence data indicated that salinity affected the distribution of southern flounder while substrate type was an important factor affecting the distribution of summer flounder. Numbers of both species on tidal flats declined in the spring, southern flounder appeared to move upstream to oligohaline riverine habitat and summer flounder appeared to move to high salinity salt marsh habitat. The segregated distribution apparent in juveniles is largely established during the immigration period. Differences in settling behaviour and subsequent movement and/or differential mortality occurring during settlement, appear important in determining the observed distribution of juvenile summer and southern flounder.     

Yield variation of spring cereals in relation to selected soil physical properties on three clay soil fields

The crop growth is highly dependent on growth conditions which vary from year to year making precision farming challenging. In the present paper was first investigated whether varying soil physical properties reflect the within-field yield variation of small grain cereals and how do the variations in weather conditions between growing seasons affect the within-field yield variation. Secondly, the potential biomass accumulation of the crop in existing soil and weather conditions was simulated. The simulated and experimentally based site-specific total biomasses were compared in order to find out whether the soil data explains the observed variations in yield.Three experimental fields size of 3–4 ha were established to examine the spatio-temporal yield variation during three years. The clay content of soils was high (> 46%) and soils were classified as Stagni-Vertic Cambisols. Correlations between soil water retention properties and crop yield were studied. Top and subsoil saturated (SWC), field capacity (FC) and permanent wilting point (PWP) water content, and saturated hydraulic conductivity of soil (K_sat), were determined from 19 to 24 places on each field once during the three years experimental period. During growing seasons, soil moisture content and leaf area index (LAI) were determined at same places biweekly, and yield was harvested. Spring barley (Hordeum vulgare) was grown on two fields, and spring wheat (Triticum aestivum, 2 years) and spring oilseed rape (Brassica napus L., one year) were grown on the third field.The measured grain yields correlated with selected soil physical properties only in few cases. The observed spatial variation in the biomass was in most cases found to be higher than the simulated. Therefore, the above mentioned parameters were not enough to predict the yield correctly in case of high variations. There were other factors decreasing the observed yield e.g. lodging, cold summer, extremely high precipitation and slopes in field. According to our results it is evident that it is very difficult to predict site-specific biomass accumulation solely by soil properties in order, for instance, to fertilize in a site-specific manner. Therefore one needs to measure the crop during the growing season in order to simulate the biomass accumulation for precision farming purposes.     

Nutritional status and pigment composition of phytoplankton during spring and summer Phaeocystis blooms in Dutch coastal waters (Marsdiep area)

The general nutritional status and pigment composition of the phytoplankton population during the 1991 spring and summer Phaeocystis blooms in Dutch coastal waters was analysed using the 480/665 nm absorption ratio of 90% acetone extracts as well as reverse-phase HPLC-pigment analysis. A 100% increase in this ratio was indicative of moderate nutrient deficiency at the end of the Phaeocystis spring bloom in the Marsdiep area. During the summer, nitrate was more likely to be the limiting nutrient than phosphate. Both physiological adaptation and species composition were found to influence the absorption ratio. Variations in the absorption ratio did not completely reflect the variations in fucoxanthin and chlorophyll a. Therefore it was concluded that besides nutrient limitation dynamics, the variable abundances of in particular chlorophyll-c3 containing species (such as Prymnesiophyceae) may effect the absorption ratio.     

Primary production of phytoplankton in a turbid coastal plain estuary,the Westerschelde (The Netherlands)

An extensive survey was carried out in the Westerschelde estuary in 1989 to estimate phytoplankton primary productivity. High nutrient concentrations year round and very high turbidity resulted in light-limited growth of phytoplankton. This was reflected in a conservative behaviour of silicate and phosphate. The same was true for total inorganic nitrogen. However, in the inner part of the estuary nitrification took place. The calculated annual primary production was 200 – 300 gC·m⁻² at the range 29-20 salinity, 100–150 gC·m⁻² at 18-10 salinity and increased sharply to 900 gC·m⁻² at 2.5 salinity due to freshwater populations. In the inner part of the estuary the vertical mixing zone was frequently larger than 5 times the euphotic zone. The high rates of primary production we measured contrast with generally expected values. This corroborates Grobbelaar's hypothesis that the critical depth can be seriously underestimated. Phytoplankton copes with the turbid conditions by adjusting light-utilization efficiencies.     

Oxygen regime,respiratory activity and biomass of microorganisms,and the carbon budget in the Fladen Ground area (Northern North Sea) during spring

A watermass, on the Fladen Grounds, marked with a drifting buoy, was studied daily during one month in spring. Hydrographic parameters, nutrient regime, oxygen regime, biomass of microorganisms and respiratory activity were determined; the high variability of the observations is discussed. From these observations, and earlier publications on the same cruise, a carbon budget is calculated. From oxygen flux calculations it appeared that the net ecosystem production must be more than 2.5 g C m⁻².d⁻¹ which could not be verified by C-14 primary production measurements. Presumably high variability in the system in time and space makes it impossible to get a fitting budget.     

Functional contribution of two perennial grasses to enhance pasture production and drought resistance under a leaf regrowth stage defoliation criterion

Lolium perenne L. (Lp) is the main pasture species in New Zealand, but climate change increases the likelihood of drought during summer and consequently lowers its growth rates. Bromus valdivianus Phil. (Bv) tolerates better the summer soil water restriction, but its competitiveness in a diverse pasture relates to the defoliation management and soil moisture levels. The performance of both species in terms of production, persistence and feed quality across seasons under different defoliation regimens was evaluated when the species were mixed and in monoculture. The treatments were applied in a randomised complete block design with three blocks. Bromus valdivianus and Lp monocultures and the 50/50 mixture (Mx) were grazed at low and high defoliation frequencies (i.e. based on Bv and Lp optimal leaf regrowth stage [LS], respectively). Herbage mass production was 15% higher in the Mx, mainly due to an increase in production in spring and summer. In spring, there was complementarity growth between the species, while during summer/early autumn, the Mx production relayed in the higher participation of Bv. Root biomass at depth (31–70 cm) was 38% greater for Bv monoculture and the Mx compared with Lp monoculture, which demonstrated the contribution of Bv to a better production of the mixture during and following the dry periods. In addition, the maintenance of the Bv tiller population and the higher growth rate during dry periods demonstrated its better fitness to low soil water availabilities than Lp. Although herbage mass was not modified by the defoliation frequency, forage quality of Bv showed values at low defoliation frequency that could compromise animal production during spring. However, there was an increase in root biomass under low defoliation frequencies, which suggested that a flexible grazing management across seasons would increase the niche utilisation between species in the mixture. The defoliation frequency of the mixture could be based on Lp LS during spring and winter, and slowed down, following Bv criteria, during summer and autumn.     

不同冬季覆盖作物轮作对农田土壤碳氮影响

风蚀是干旱区农田生态系统中土壤质量降低的关键因素,冬季作物覆盖可有效减少农田的土壤风蚀。通过探究河西灌区不同冬季覆盖作物轮作复种绿肥对农田土壤碳氮影响,以期为构建合理的周年覆盖轮作模式提供理论依据。本研究在热量一熟有余两熟不足的河西灌区春小麦种植区把冬小麦、冬油菜两种冬季覆盖作物和绿肥还田处理嵌套种植形成：（1）春小麦—冬油菜—箭筈豌豆(WCP)、（2）春小麦—冬小麦—箭筈豌豆(WWP)、（3）春小麦—箭筈豌豆(WP)、(4)春小麦—春小麦(W,CK)不同种植模式,在360 kg/hm² (N2)、270 kg/hm² (N1)、0 kg/hm² (N0) 3个施氮水平下,研究不同轮作模式对农田土壤碳、氮含量的提升效应。结果表明：在同一种植模式下土壤有机碳、土壤可溶性有机碳、热提取态有机碳、硝态氮、氨态氮、微生物量碳氮含量随施氮量的增加而增加,但在氮肥减量(N1)的条件下,与常规施氮(N2)相比较WCP轮作模式土壤有机碳、土壤可溶性有机碳、热提取态有机碳含量及微生物量氮无显著降低。相同施氮条件下,轮作模式间差异不显著,但与CK间差异显著;其中,0~10 cm土层,WCP轮作模式土壤有机碳、土壤可溶性有机碳、土壤热提取态有机碳、硝态氮、氨态氮、微生物量碳氮含量平均较CK提高5.42%、9.78%、10.96%、20.51%、15.76%、18.94%;10~30 cm土层,提高9.54%、7.06%、12.99%、20.12%、16.51%、18.16%。因此,春小麦轮作冬油菜复种绿肥模式在氮肥减量条件下仍对农田土壤碳氮有明显的提升效应,为河西灌区良好的周年覆盖作物轮作模式。     

影响山西夏季降水的水汽输送研究

利用山西省58个代表站近50年的夏季降水资料和NCAR/NCEP逐月再分析资料,分析影响山西夏季降水的水汽输送特征,应用SVD方法等探讨影响山西夏季降水异常的水汽源地和水汽输送关键区。结果表明：山西夏季降水与热带西太平洋—南海的东风气流,热带印度洋越赤道气流以及南海—华南的水汽输送带有关,同时也受到中纬度西风带中水汽输送影响。夏季水汽输送与山西夏季降水具有显著的遥相关关系,山西夏季降水异常的水汽异常来源包括副高南侧的热带西太平洋—南海的偏东风水汽输送异常,和印度洋—阿拉伯海地区越赤道气流的偏西风水汽输送异常,山西夏季降水的水汽输送“关键区”位于云贵高原中部到四川盆地东部的矩形区域。由整层水汽输送通量标准化处理建立的水汽输送源指数和水汽输送指数,可以表征水汽输送异常对于山西夏季降水的影响。研究结果可以为山西汛期降水异常分析和汛期预测提供参考依据。     

闽江口湿地的气候变化及其对生态环境的影响

利用闽江口湿地分布区4个常规气象观测站1971-2004年的气象资料,分析了闽江口湿地日照、气温、极端最低气温、降水量的年际变化特征及其对闽江口湿地生态环境的影响情况。结果表明：年平均气温和季平均气温显著上升,冬季增温幅度最大,夏季最小;日照时数总体下降,极端最低气温、年降水量和季降水量（春季除外）呈上升趋势,但趋势都不显著;日照时数和降水量年际波动大。气象因子的年际变化给区域生态环境带来不同程度的利弊影响。研究结果对于闽江口湿地的保护、合理开发和利用具有重要的指导意义。     

山茱萸茎的解剖结构特征研究

通过石蜡切片方法制片,光学显微镜观察,研究了山茱萸（Cornus officinalis）一年生和二年生茎的横切面形态解剖特征。结果表明,山茱萸茎的初生结构：从外到内由表皮、皮层和中柱组成。表皮由一层排列紧密的表皮细胞构成,细胞外壁乳头状剧烈增厚约1-1.5 ?m,且外方被发达的角质层;皮层发达,且具有大量的厚角组织;髓发达,环髓带明显。次生结构：从外到内由周皮和次生维管组织组成,主要特征体现在年轮线不明显,次生木质部为散孔材。初生结构和次生结构均表现出山茱萸对旱生环境的高度适应。     

营养液中添加不同浓度矮壮素对夏季

无基质营养液育苗是一种新的育苗技术。幼苗整个苗期都生长在营养液中,如何控制徒长,特别是夏季如何培育出壮苗是一个急待解决的技术问题。试验研究了在营养液中添加5、10、15mg/kg矮壮素对夏季黄瓜幼苗生长发育、徒长抑制和培育壮苗的效果。结果表明：在营养液中添加矮壮素能降低幼苗下胚轴长度和植株高度、缩短最大节间距,植株叶片颜色加深,根冠比和壮苗指数增大。5、10、15mg/kg矮壮素处理植株的壮苗指数为0.042、0.048、0.038,比对照分别增加27.3%、45.5%、15.2%。说明添加矮壮素处理能较好的抑制黄瓜幼苗徒长和地上部物质积累,同时促进地下部的生长,从而有利于壮苗的形成。夏季采用无基质营养液育苗,在整个育苗期间于营养液中添加10mg/kg矮壮素效果最好。     

基于NOAA/AVHRR数据的天津地区净初级生产力时空格局分析

本文基于CASA模型,充分考虑植被覆盖类型对光能利用率的影响及植被反照率对净辐射的影响,利用NOAA/AVHRR 1B卫星资料和气象资料估算了天津地区的植被净初级生产力（NPP）。估算结果表明：2007年天津地区植被NPP为3.86×109 gC/a,年平均NPP为335 gC/m2/a;蓟县、宁河与宝坻年NPP估算值居前三位;各季度对NPP总量贡献率依次为：夏季（62％）,秋季（21％）、春季（16％）,冬季（1％）;受物候和气候因素的综合影响,天津地区NPP具有明显的年际变化,利用年均NDVI可以较好地模拟天津地区NPP年总量,其模拟表达式为：     

The phytoplankton component of seston in San Francisco Bay

Phytoplankton biomass (as carbon) was estimated from chlorophyll a concentrations (Chla) and a mean value for the ratio of phytoplankton carbon to chlorophyll a in San Francisco Bay. The ratio was determined as the slope of a Model II regression of POC' against (Chla), where POC' is total particulate organic carbon minus sediment-associated non-phytoplankton carbon. Samples from 30 fixed sites in the channel and lateral shoals of San Francisco Bay were collected once or twice a month from April to November 1980, and at irregular intervals in South Bay during 1984 and 1985. For all data the calculated mean value of phytoplankton C:Chla was 51 (95% confidence interval = 47–54). No significant differences were found in the C:Chla ratio between shallow and deep sites (where light availability differs) or between northern and southern San Francisco Bay (where phytoplankton community composition differs). Using the mean C:Chla ratio of 51, we calculated that phytoplankton biomass constitutes about one third of seston carbon under most circumstances, but this fraction ranges from about 95% during phytoplankton blooms to less than 20% during spring periods of low phytoplankton biomass and high suspended sediment concentration.     

春大白菜生长和营养品质的动态变化

从卷心1周后开始每隔7天取样调查春大白菜‘菊锦’生长和营养品质的动态变化,结果表明:卷心2周后叶球高度就不再增加,4周后叶球周长达到最大值;外叶叶片面积和外叶总面积在4周时达到最大值,而外叶叶柄面积在卷心1周后基本保持恒定。从外到内,叶片停止伸长生长的时间逐渐延迟。外叶、内叶、根的鲜重和干重逐渐增加,卷心4周后达到最大值,但是外叶增加幅度较小。从卷心开始,外叶、内叶、根的干物质含量均呈下降趋势,外叶在2周后、内叶和根在3周后不再降低;净菜率则呈增加趋势,卷心开始3周后达到最大值。蛋白质、总糖含量以叶片高于叶柄,而氨基酸、可溶性糖含量相反,以叶柄高于叶片。内叶的营养物质含量随着发育进程降低或保持不变,而心叶营养物质含量均呈升高趋势。