Seasonal Changes in Phytoplankton Biomass and Dominant Species in the Changjiang River Estuary and Adjacent Seas：General Trends Based on Field Survey Data 1959-2009

The characteristics of seasonal variation in phytoplankton biomass and dominant species in the Changjiang River Estuary and adjacent seas were discussed based on field investigation data from 1959 to 2009. The field data from 1981 to 2004 showed that the Chlorophyll-a concentration in surface seawater was between 0.4 and 8.5 ktg dm-3. The seasonal changes generally presented a bimodal trend, with the biomass peaks occurring in May and August, and Chlorophyll-a concentration was the lowest in winter. Seasonal biomass changes were mainly controlled by temperature and nutrient levels. From the end of autumn to the next early spring, phytoplankton biomass was mainly influenced by temperature, and in other seasons, nutrient level （including the nutrient supply from the terrestrial runoffs） was the major influence factor. Field investigation data from 1959 to 2009 demonstrated that dia- toms were the main phytoplankton in this area, and Skeletonerna costatum, Pseudo-nitzschia pungens, Coscinodiscus oculus-iridis, Thalassinoema nitzschioides, Paralia sulcata, Chaetoceros lorenzianus, Chaetoceros curvisetus, and Prorocentrum donghaiense Lu were common dominant species. The seasonal variations in major dominant phytoplankton species presented the following trends： 1） Skeletonema （mainly S. costatum） was dominant throughout the year; and 2） seasonal succession trends were Coscinodiscus （spring） →Chaetoceros （summer and autumn） → Coscinodiscus （winter）. The annual dominance of S. costatum was attributed to its environmental eurytopicity and long standing time in surface waters. The seasonal succession of Coscinodiscus and Chaetoceros was associated with the seasonal variation in water stability and nutrient level in this area. On the other hand, long-term field data also indicated obvious interannual variation of phytoplankton biomass and community structure in the Changjiang River Estuary and adjacent seas： average annual phytoplankton biomass and dinoflagellate proportion both presented inc     

Responses of maximum photosystem II photochemical efficiency of phytoplankton communities to nutrient limitation in the coastal sea of Qingdao,China

Nutrient enrichment experiments with nitrogen (N) and phosphorus (P) were conducted with samples from two stations in the coastal waters of Qingdao, China, during summer to identify limiting nutrients. In late July of 2009, low P concentrations and the maximum photochemical efficiency of photosystem II (F _v /F _m ) in the initial samples together with F _v /F _m and chlorophyll a (Chl a) responses to P addition indicated P limitation at the two stations. In early August, low P levels still limited phytoplankton growth at station A. F _v /F _m and Chl a were the highest in the NP treatments at station B, suggesting an N/P co-limitation. In mid-September, nutrient concentrations and F _v /F _m were elevated and phytoplankton communities were healthy. Greater F _v /F _m and Chl a in the treatments with added P than those without the addition suggested potential P limitation at station A. Lack of F _v /F _m and Chl a responses following nutrient additions indicated N and P repletion at station B. At the end of July 2010, neither N nor P was limited at station B. Additionally, F _v /F _m coupled with 24-h-long nutrient enrichment experiments can be used to detect P limitation and N/P co-limitation to natural populations. This method can be more accurate for assessing co-limitation than the use of criteria of nutrient concentrations and ratios as indicators, and can provide more rapid results than nutrient addition bioassays using chlorophyll response as an indicator, when a population is potentially limited. Compared with the two conventional methods, the results based on F _v /F _m can also provide more detailed information about physiological states of the populations.     

The impact of topography on social factors,a case study of Montenegro

Relationships between environmental and social factors have long been studied by geographers.Nowadays,GIS-aided statistical analysis provides new tools to explore these relationships.In order to detect the impact of topography on social factors,we selected the country of Montenegro as a case example due to its high topographic variability.We compared the spatial pattern of population,settlements and ethnic minorities to physical geographic factors,especially to topography,but lithology and land cover data were also taken into consideration.We found that certain factors are closely correlated,e.g.the settlement density linearly decreases with elevation,while the characteristic settlement area shows an exponential increase upwards.The population density is not related to absolute elevation,but it is in close correlation with height（i.e.elevation relative to the local minimum）.Population change and illiteracy are also topography-related social factors.On the contrary,the variable ethnic pattern of Montenegro is influenced by historical,political and economic effects rather than by environmental factors or topographic features.As a conclusion we state that in the scale of a country or a region,the environment can strongly impact some social factors.     

Long-term nutrient variation trends and their potential impact on phytoplankton in the southern Yellow Sea,China

The concentration and composition of nutrients, such as N, P, and Si, respond to biogeochemical processes and in turn, impact the phytoplanktons’ community structure and primary production. In this study, historical data was systematically analyzed to identify long-term variations in nutrient trends, red tide frequency, phytoplankton community abundance, and dominant species succession in the southern Yellow Sea(SYS). Results showed that N/P concentration ratios dramatically increased as a funct...     

Effects of suspended particles on the growth of two dominant phytoplankton species of Bohai Bay,China

Suspended particles (SP) are increasing dramatically in Bohai Bay, China and may affect the growth and composition of phytoplankton assembly. To determine the effects of SP on the growth of two dominant phytoplankton species, Phaeodactylum tricornutum Bohlin and Gymnodinium sp., we cultured and tested their growth characteristics under SP concentrations ranging from 0 g L⁻¹ to 0.8 g L⁻¹. Our results show that the increase in the SP concentrations results in significant decrease in the maximum cell densities and the maximum specific growth rates of these two species. The half maximal inhibitory concentration (IC₅₀) of SP to P. tricornutum and Gymnodinium sp. were 1.07 g L⁻¹ and 0.68 g L⁻¹ respectively, indicating the inhibitory effect of SP on Gymnodinium sp. was greater than on P. tricornutum. These results suggest that SP inhibits the growth of the two algal species and P. tricornutum is more tolerant to SP than Gymnodinium sp.     

白洋淀围隔中不同生物组合调控水质实验

在白洋淀建成10个原位围隔,研究穗花狐尾藻(Myriophyllum spicatum)、金鱼藻(Ceratophyllum demersum)、圆顶珠蚌(Unio douglasiae)和圆顶珠蚌+金鱼藻等不同生物组合在调控水体富营养化方面的效能与稳定性.在围隔中,分别种(投)入密度为10株/m2穗花狐尾藻、20株/m2金鱼藻、195 g/m2圆顶珠蚌和20株/m2金鱼藻+195 g/m2圆顶珠蚌.结果表明,穗花狐尾藻和金鱼藻能有效控制浮游植物的生物量,并改善水体透明度,使水体中总氮含量和总磷含量明显下降,透明度增加,浮游植物多样性明显增加,水体富营养化指数明显下降;圆顶珠蚌对水体中的总氮、总磷和叶绿素a有一定的去除作用,但对水体透明度、氨氮含量和营养状态影响不大;金鱼藻和圆顶珠蚌组合的水体净化效果要优于单一种植金鱼藻和穗花狐尾藻.     

Analysis of creep settlement of pile groups in linear viscoelastic soil

This paper presents the analysis of creep settlement of pile groups for line pile groups, square pile groups, and rectangular pile groups undergoing creep settlements over a period of time. The soil is treated as a viscoelastic material and is modeled using a three-parameter viscoelastic model. The damping component (dashpot) takes care of the permanent time-dependent deformations in three-parameter viscoelastic model. An approach suggested by Mindlin has been employed to calculate the stress distribution along the pile length in a group. The viscoelastic problem is converted into an elastic problem by the application of Laplace transform. Results in the form of variation of interaction factors for parameters such as pile length to diameter ratio, pile spacing, Poisson's ratio, and modulus ratio have been presented. Comparison has been made between interaction factors for piles groups undergoing immediate settlements and creep settlements. Finally, a typical predictive example has been presented for a 3 × 3 pile group showing creep settlement. The load rearrangement due to creep settlements causes about 5% to 35% increase in base resistance over time. Interaction factors for pile groups (2 × 1, 3 × 1, 2 × 2, and 3 × 2) undergoing creep settlement is about 15% to 55% higher than the interaction factors considering only the immediate settlements for pile group spacing less than or equal to 5d.     

Analysis of lateral loading of pile groups using embedded beam elements with interaction surface

The numerical simulation of soil-pile interaction problems, by means of full 3D finite element models, involves a large number of degrees of freedom (DOF) and difficulties during the mesh generation process. In order to reduce the unknowns and simplify and properly analyze such class of geotechnical problems, the so-called embedded beam elements (EBE) have recently been developed. In a preceding contribution of the authors, an improved EBE formulation, which brings into play the soil-pile interaction surface, was proposed with the aim to localize material plasticity in the soil surrounding the pile. This embedded beam model couples two different finite elements, each described by distinct kinematics (ie, solid and beam). The coupling is incorporated in the formulation by means of kinematical constrains established over the solid and beam displacement fields on the interaction surface. One of the main advantages of the embedded elements is that the addition of beams structural members immersed within the 3D soil model does not represent a constraint for the solid mesh, which can be adopted independently from the beam mesh. In this paper, the lateral loading of pile groups is studied by means of the proposed EBE approach with elasto-plastic interfaces. In order to represent a rigid cap, a master node and a special set of kinematical restrictions are incorporated into the formulation. The paper presents results obtained by means of the present formulation compared against other well-established analysis methods and test results published in the literature, for both elastic and elasto-plastic cases.     

Different levels of macroalgal sampling resolution for pollution assessment

The effects of using reduced sampling resolutions to study macroalgal vegetation patterns have not been studied sufficiently. Here, we test the influence of taxonomic resolution level, removal of occasional species, aggregation of species abundances into functional groups and data transformation in the detection of a long-term recovery process by phytobenthic intertidal assemblages. Results indicate that the aggregation of species data into the genus level has very little influence. Likewise, almost any significant information is lost when occasional algae are removed. Analyses at the level of families and orders still clearly detect differences between highly degraded and reference vegetation. By contrast, analyses based on class and functional group abundances capture quite different information. The effect of transformation is similar at the different taxonomic levels. Most surrogate measures properly reflect changes in diversity. It is concluded that genus level is the most appropriate surrogate approach for detecting the recovery process.