A coupled ice-ocean ecosystem model for 1-D and 3-D applications in the Bering and Chukchi Seas

Primary production in the Bering and Chukchi Seas is strongly influenced by the annual cycle of sea ice. Here pelagic and sea ice algal ecosystems coexist and interact with each other. Ecosystem modeling of sea ice associated phytoplankton blooms has been understudied compared to open water ecosystem model applications. This study introduces a general coupled ice-ocean ecosystem model with equations and parameters for 1-D and 3-D applications that is based on 1-D coupled ice-ocean ecosystem model development in the landfast ice in the Chukchi Sea and marginal ice zone of Bering Sea. The biological model includes both pelagic and sea ice algal habitats with 10 compartments： three phytoplankton （pelagic diatom, flagellates and ice algae： D, F, and Ai） , three zooplankton （copepods, large zooplankton, and microzooplankton ： ZS, ZL, ZP） , three nutrients （ nitrate ＋ nitrite, ammonium, silicon ： NO3 , NH4, Si） and detritus （Det）. The coupling of the biological models with physical ocean models is straightforward with just the addition of the advection and diffusion terms to the ecosystem model. The coupling with a multi-category sea ice model requires the same calculation of the sea ice ecosystem model in each ice thickness category and the redistribution between categories caused by both dynamic and thermodynamic forcing as in the physical model. Phytoplankton and ice algal self-shading effect is the sole feedback from the ecosystem model to the physical model.     

COUPLED PHYSICAL-ECOLOGICAL MODELLING IN THE CENTRAL PART OF JIAOZHOU BAY Ⅱ.COUPLED WITH AN ECOLOGICAL MODEL

Sharpies‘ 1-D physical rrozlel maploying tide-wind driven turbulence closure and surface heating-cooling physics, was coupled with an eculogical rnodet with 9-biochemical components: phytoplankton, zooplankton, shellfish, autotmphic and heterotrophic bacterioplankton, dissolved organic carbon (DOC), suspended detritus and sinking particles to simulate the armual evolution of ecosystem in thecentral part of Jiaozhou Bay. The coupled modeling results showed that the phytoplankton shading effectcould reduce seawater temperamre by 2℃, so that photosynthesis efficiency should be less than 8% ; that the loss of phytoplankton by zooplankton grazing in winter tended to be compensated by phytoplankton advection and diffusion from the otrtside of the Bay; that the incidem irradiance intensity could be the mostimportant factor for phytoplankton grcr, wth rate; and that it was the bacterial secondary prnduction that maintained the maximum zooplankton biomass in winter usually observed in the 1990s, indicating that themicrobial food loop was extremely important for ecosystem study of Jiaozhou Bay.     

Pelagic Nitrogen Cycling in Jiaozhou Bay, a Model Study I： the Conceptual Model

A zero-dimensional box model (PNCMjzb) with six state variables (ammonium, nitrate, dissolved organic nitrogen, phytoplankton, zooplankton and detritus) was developed to study nitrogen cycling in the Jiaozhou Bay pelagic ecosystem. The dominant processes within these compartments are considered with nitrogen as flow currency. Phytoplankton and zooplankton are treated as separate state variables, assuming that the species composition was dominated by two or three species the dynamic constants of which are similar and that they represent the entire plankton community. The microbial loop has not been integrated explicitly in the model. The turnover of bacteria is included implicitly in processes such as detritus decomposition, DON remineralization, pelagic nitrification and denitrification. The model is driven by two forcing variables, viz. water temperature and light intensity. Historical data from the1980s and 1990s were compiled and used for model calibration. In this paper (part Ⅰ), the consideration of every main compartment in the model is interpreted in detail. And the applied equations and parameters are presented. The main results from the simulations together with discussion about phytoplankton dynamics and primary production in Jiaozhou Bay are presented in the next paper (part Ⅱ).     

Modeling study of seasonal variation of the pelagic-benthic ecosystem characteristics of the Bohai Sea

Based on experiment data of the Sino-German comprehensive investigations in the Bohai Sea in 1998 and 1999, a simple coupled pelagic-benthic ecosystem multi-box model is used to simulate the ecosystem seasonal variation. The pelagic sub-model consists of seven state variables： phytoplankton, zooplankton, TIN, TIP, DOC, POC and dissolved oxygen （DO）. The benthic sub-model includes macro-benthos, meiobenthos, bacteria, detritus, TIN and TIP in the sediment. Besides the effects of solar radiation, water temperature and the nutrient from sea bottom exudation, land-based inputs are considered. The impact of the advection terms between the boxes is also considered. Meanwhile, the effects of the micro- bial-loop are introduced with a simple parameterization. The seasonal variations and the horizontal distributions of the ecosystem state variables of the Bohai Sea are simulated. Compared with the observations, the results of the multi-box model are reasonable. The modeled results show that about 13% of the photosynthesis primary production goes to the main food loop, 20% transfers to the benthic domain, 44% is consumed by the respiration of phytoplankton, and the rest goes to DOC. Model results also show the importance of the microbial food loop in the ecosystem of the Bohai Sea, and its contribution to the annual zooplankton production can be 60%-64%.     

Simple ecosystem model of the central part of the East China Sea in spring

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Modelling nitrogen and phosphorus dynamics in a mesocosm pelagic ecosystem in Laizhou Bay in China

A model of nitrogen and phosphorus dynamics in mesocosm experiments was established on the basis of a summary and synthesis of the existing models. The established model comprised seven state variables(DIN,PO4-P,DON,DOP,phytoplankton,zooplankton and detritus) and five modules - phytoplankton,zooplankton,dissolved inorganic nutrients,dissolved organic nutrients and detritus. Comparison with the in situ experimental data in Laizhou Bay at the end of August 2002 showed that this model could properly simulate t...     

Diagnosis of physical and biological control over phytoplankton in the Gulf of Maine-Georges Bank region using an adjoint data assimilation approach

The linkage between physical and biological processes, particularly the effect of the circulation field on the distribution of phytoplankton, is studied by applying a two-dimensional model and an adjoint data assimilation approach to the Gulf of Maine-Georges Bank region. The model results, comparing well with observation data, reveal seasonal and geographic variations of phytoplankton concentration and verify that the seasonal cycles of phytoplankton are controlled by both biological sources and ad-vection processes which are functions of space and time and counterbalance each other. Although advective flux divergences have greater magnitudes on Georges Bank than in the coastal region of the western Gulf of Maine, advection control over phytoplankton concentration is more significant in the coastal region of the western Gulf of Maine. The model results also suggest that the two separated populations in the coastal regions of the western Gulf of Maine and on Georges Bank are self-sustaining.     

A model study on dynamical processes of phytoplankton in Laizhou Bay

A three-dimensional ecosystem model, using a PIC (Particle-In-Cell) method, is developed to reproduce the annual cycle and seasonal variation of nutrients and phytoplankton biomass in Laizhou Bay. Eight state variables, i.e., DIN (dissolved inorganic nitrogen), phosphate, DON (dissolved organic nitrogen), DOP (dissolved organic phosphorus), COD (chemical oxygen demand), chlorophyll-a (Chl-a), detritus and the zooplankton biomass, are included in the model. The model successfully reproduces the observed temporal and spatial variations of nutrients and Chl-a biomass distributions in the bay. The nutrient concentrations are at high level in winter and at low level in summer. Double-peak structure of the phytoplankton (PPT) biomass exists in Laizhou Bay, corresponding to a spring and an autumn bloom respectively. Several numerical experiments are carried out to examine the nutrient limitation, and the importance of the discharges of the Yellow River and Xiaoqinghe River. Both DIN limitation and phosphate limitation exist in some areas of the bay, with the former being more significant than the latter. The Yellow River and Xiaoqinghe River are the main pollution sources of nutrients in Laizhou Bay. During the flood season, the algal growth is inhibited in the bay with the Yellow River discharges being excluded in the experiment, while in spring, the algal growth is enhanced with the Xiaoqinghe River excluded.     

Annual cycle and budgets of nutrients in the Bohai sea

The environmental problems in the Bohai Sea have become more serious in the last decade. High nutrient concentration contributes much to it. A Sino-German cooperation program has been carried out to improve the understanding of the ecosystem by observations and modelling. A three-dimensional ecosystem model, coupled with a physical transport model, is adopted in this study. The simulation for the year 1982 is validated by the data collected in 1982/1983. The simulated annual mean nutrient concentrations are in good agreement with observations. The nutrient concentrations in the bohai Sea, which are crucial to the algal growth, are high in winter and low in summer. There are depletion from spring to summer and elevation from autumn to winter for nutrients. The nutrients’ depletion is a response to the consumption of the phytoplankton bloom in spring. Internal recycle and external compensation affect the nutrient cycle. Their contributions to the nutrient budgets are discussed based on the simulated results. Production and respiration are the most important sink and source of nutrients. The process of photosynthesis consumes 152 kilotons-P and 831.1 kilotons-N while respiration releases 94.5 kilotons-P and 516.6 kilotons-N in the same period. The remineralization of the detritus pool is an important source of nutrient regeneration, It can compensate 23 percent of the nutrient consumed by the production process. The inputs of phosphates and nitrogen from rivers are 0.55 and 52.7 kilotons respectively. The net nutrient budget is −3.05 kilotons-P and 31.6 kilotons-N.     

Numerical simulation of nutrient and phytoplankton dynamics in Guangxi coastal bays,China

The increasing riverine pollutants have resulted in nutrient enrichment and deterioration of water quality in the coastal water of Guangxi Province, China. However, the quantitative relationship between nutrient loads and water quality responses, which is crucial for developing eutrophication control strategies, is not well studied. In this study, the riverine fluxes of nutrients were quantified and integrated with nutrient cycling and phytoplankton dynamics by using box models for Guangxi coastal bays. The model concepts and biogeochemical equations were the same; while most model parameters were specific for each bay. The parameters were calibrated with seasonal observations during 2006–2007, and validated with yearly averaged measurements in 2009. The general features of nutrient and phytoplankton dynamics were reproduced, and the models were proved feasible under a wide range of bay conditions. Dissolved inorganic nitrogen was depleted during the spring algal bloom in Zhenzhu Bay and Fangcheng Bay with relatively less nutrient inputs. Phosphorus concentration was high in spring, which decreased then due to continuous phytoplankton consumption. Chlorophyll-a concentration reached its annual maximum in summer, but was the minimum in winter. Eutrophication was characterized by both an increase in nutrient concentrations and phytoplankton biomass in Lianzhou Bay. Either about 80% reduction of nitrogen or 70% reduction of phosphorus was required to control the algal bloom in Lianzhou Bay. Defects of the models were discussed and suggestions to the environmental protection of Guangxi coastal bays were proposed.     

Estimating the budgets of nutrients for phytoplankton bloom in the central Yellow Sea using a modified lower tropic ecosystem model

A modified lower trophic ecosystem model (NEMURO) is coupled with a three-dimensional hydrodynamic model for an application in the central Yellow Sea. The model is used to simulate the horizontal distributions and annual cycles of chlorophyll-a and nutrients with results consistent with historical observations. Generally, during the winter background and spring bloom periods, the exchange with neighboring waters constitutes the primary sources of nutrients. Howerver, during the winter background period, the input of silicate from the layer deeper than 50 m is the most important source that contributes up to 60% to the total sources. During the spring bloom period, the transport across the thermocline makes significant contribution to the input of phosphate and silicate. During the post spring bloom period, the relative contribution of relevant processes varies for different nutrients. For ammonium, atmospheric deposition, excretion of zooplankton and decomposition of particulate and dissolved nitrogen make similar contributions. For phosphate and silicate, the dominant input is the transport across the thermocline, accounting for 62% and 68% of the total sources, respectively. The N/P ratio averaged annually and over the whole southern Yellow Sea is up to 51.8, indicating the potential of P limitation in this region. The important influence of large scale sea water circulation is revealed by both the estimated fluxes and the corresponding N/P ratio of nutrients across a section linking the northeastern bank of the Changjiang River and Cheju Island. During the winter background period, the input of nitrate, ammonium, phosphate and silicate by the Yellow Sea Warm Current is estimated to be 4.6×10¹⁰, 2.3×10¹⁰, 2.0×10⁹ and 1.2×10¹⁰ mol, respectively.     

Spatial-Temporal Change of Phytoplankton Biomass in the East China Sea with MODIS Data

A ten-year chlorophyll-a concentration dataset from Moderate Resolution Imaging Spectro-radiometer(MODIS) were used to analyze the variation of phytoplankton biomass and its potential relation with climate in the East China Sea. The result indicated that the phytoplankton biomass generally had a regular pattern every year, and phytoplankton bloom mainly occurred between May and July. The highest phytoplankton biomass appeared near the Yangtze River Estuary. The lowest phytoplankton biomass located near the Taiwan Strait. In general, the starting bloom time was earlier in the south than in the north, and the span time of the former was also longer. During the recent ten years, the phytoplankton biomass around the Yangtze River Estuary decreased obviously. The change of phytoplankton biomass was found to be related with the Ni?o3.4 Index. The correlation between the intensity of phytoplankton bloom with the number and square of red tide were 0.63 and 0.74, respectively.     

Coupling of an individual-based model of anchovy with lower trophic level and hydrodynamic models

Anchovy (Engraulis japonicus), a small pelagic fish and food of other economic fishes, is a key species in the Yellow Sea ecosystem. Understanding the mechanisms of its recruitment and biomass variation is important for the prediction and management of fishery resources. Coupled with a hydrodynamic model (POM) and a lower trophic level ecosystem model (NEMURO), an individual-based model of anchovy is developed to study the influence of physical environment on anchovy’s biomass variation. Seasonal variations of circulation, water temperature and mix-layer depth from POM are used as external forcing for NEMURO and the anchovy model. Biomasses of large zooplankton and predatory zooplankton which anchovy feeds on are output from NEMURO and are controlled by the consumption of anchovy on them. Survival fitness theory related to temperature and food is used to determine the swimming action of anchovy in the model. The simulation results agree well with observations and elucidate the influence of temperature in over-wintering migration and food in feeding migration.     

Simulation of coupled pelagic-benthic ecosystem of the Yellow Sea Cold Water Mass

A one-dimensional coupled pelagic-benthic box model for the Yellow Sea Cold Water Mass （YSCWM） is developed. The model is divided into three boxes vertically according to the depths of thermocline and euphotic layer. It simulates well the oligotrophic shelf ecosystem of the YSCWM considering effects of nutrients deposition and microbial loop. Main features of vertical structure of various variables in ecosystem of the YSCWM were captured and seasonal variability of the ecosystem was well reconstructed. Calculation shows that the contribution of microbial loop to the zooplankton can reach up to 60%. Besides, input of inorganic nutrients from atmospheric deposition is an important mechanism of production in upper layer of the YSCWM when stratified.     

Zooplankton spatial and diurnal variations in the Changjiang River estuary before operation of the Three Gorges Dam

Estuarine plankton communities can serve as indicators of ecosystem modification in response to anthropogenic influences. The main objectives of this study were to describe the spatial distribution and diurnal variability in zooplankton abundance and biomass over almost entire salinity gradient of the Changjiang (Yangtze) River estuary and to provide a background reference for future studies. To accomplish this, data were collected from 29 stations in the estuary from May 19 to 26, 2003, including two anchor stations. The spatial and diurnal variations in zooplankton characteristics, i.e. abundance, biomass, and gross taxonomic composition, were examined. Generally, both the abundance and biomass gradually increased seaward and presented distinct spatial variations. In addition, the spatial data revealed a significant correlation between abundance and biomass; however, there was no significant correlation between abundance and biomass for the diurnal data. Although the zooplankton composition indicated distinct spatial differences in terms of dominant groups, copepods accounted for >50% of the total zooplankton abundance in most regions and times. Three zooplankton assemblages were recognized through hierarchical cluster analysis. These assemblages existed along the salinity gradient from fresh water to seawater, and their positions coincided with those of the three principal water masses in the estuary. The assemblages were classified as: (1) true estuarine, (2) estuarine and marine, and (3) euryhaline marine, which were characterized by the copepods Sinocalanus dorrii, Labidocera euchaeta, and Calanus sinicus, respectively. Both spatial and diurnal data indicated that there was no significant correlation between zooplankton abundance/biomass and depth-integrated phytoplankton abundance.     

Contrasting patterns of free-living bacterioplankton diversity in macrophyte-dominated versus phytoplankton blooming regimes in Dianchi Lake,a shallow lake in China

Freshwater shallow lakes typically exhibit two alternative stable states under certain nutrient loadings:macrophyte-dominated and phytoplankton-dominated water regimes.An ecosystem regime shift from macrophytes to phytoplankton blooming typically reduces the number of species of invertebrates and fishes and results in the homogenization of communities in freshwater lakes.We investigated how microbial biodiversity has responded to a shift of the ecosystem regime in Dianchi Lake,which was previously fully covered with submerged macrophytes but currently harbors both ecological states.We observed marked divergence in the diversity and community composition of bacterioplankton between the two regimes.Although species richness,estimated as the number of operational taxonomic units and phylogenetic diversity(PD),was higher in the phytoplankton dominated ecosystem after this shift,the dissimilarity of bacterioplankton community across space decreased.This decrease in beta diversity was accompanied by loss of planktonic bacteria unique to the macrophyte-dominated ecosystem.Mantel tests between bacterioplankton community distances and Euclidian distance of environmental parameters indicated that this reduced bacterial community differentiation primarily reflected the loss of environmental niches,particularly in the macrophyte regime.The loss of this small-scale heterogeneity in bacterial communities should be considered when assessing long-term biodiversity changes in response to ecosystem regime conversions in freshwater lakes.     

RESEARCH ON RED TIDE OCCURRENCES USING ENCLOSED EXPERIMENTAL ECOSYSTEM IN WEST XIAMEN HARBOR, CHINA RELATIONSHIP BETWEEN NUTRIENTS AND RED TIDE OCCURRENCE

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Effect of enclosure and nutrient enrichment on Microcystis blooms in Donghu Lake

1 INTRODUCTION Surface blooms of nuisance cyanobacteria are often a signal of eutrophication (Jacoby et al., 2000). They are generally favored by conditions of low nitrogen to phosphorus ratios, high total phosphorus content, high water temperature, high …     

Abundance, biomass and composition of spring ice algal and phytoplankton communities of the Laptev Sea （Arctic）

Abundance,biomass and composition of the ice algal and phytoplank-ton communities were investigated in the southeastern Laptev Sea in spring 1999.Diatoms dominated the algal communities and pennate diatoms dominated the dia-tom population.12 dominant algal species occurred within sea ice and underlyingwater column,including Fragilariopsis oceanica,F.cylindrus,Nitzschiafrigida,N.promare,Achnanthes taeniata,Nitzschia neofrigida,Naviculapelagica,N.vanhoef fenii,N.septentrionalis,Melosira arctica,Clindrothecaclosterium and Pyrarnimonas sp.The algal abundance of bottom 10 cm sea icevaried between 14.6 and 1562.2×10~4 ceils l~(-1)with an average of 639.0×10~4cells l~(-1),and the algal biomass ranged from 7.89 to 2093.5μg C l~(-1)with an av-erage of 886.9μg C l~(-1),which were generally one order of magnitude higherthan those of sub-bottom ice and two orders of magnitude higher than those ofunderlying surface water.The integrated algal abundance and biomass of lower-most 20 cm ice column were averagely 7.7 and 12.2 times as those of upper 20 mwater column,respectively,suggesting that the ice algae might play an importantrole in maintaining the coastal marine ecosystem before the thawing of sea ice.Icealgae influenced the phytoplankton community of the underlying water column.However,the“seeding”of ice algae for phytoplankton bloom was negligible be-cause of the iow phytoplankton biomass within the underlying water column.     

Trophic interactions, ecosystem structure and function in the southern Yellow Sea

The southern Yellow Sea is an important fishing ground, providing abundant fishery resources. However, overfishing and climate change have caused a decline in the resource and damaged the ecosystem. We developed an ecosystem model to analyze the trophic interactions and ecosystem structure and function to guide sustainable development of the ecosystem. A trophic mass-balance model of the southern Yellow Sea during 2000–2001 was constructed using Ecopath with Ecosim software. We defined 22 important functional groups and studied their diet composition. The trophic levels of fish, shrimp, crabs, and cephalopods were between 2.78 and 4.39, and the mean trophic level of the fisheries was 3.24. The trophic flows within the food web occurred primarily in the lower trophic levels. The mean trophic transfer efficiency was 8.1%, of which 7.1% was from primary producers and 9.3% was from detritus within the ecosystem. The transfer efficiency between trophic levels II to III to IV to V to >V was 5.0%, 5.7%, 18.5%, and 19.7%–20.4%, respectively. Of the total flow, phytoplankton contributed 61% and detritus contributed 39%. Fishing is defined as a top predator within the ecosystem, and has a negative impact on most commercial species. Moreover, the ecosystem had a high gross efficiency of the fishery and a high value of primary production required to sustain the fishery. Together, our data suggest there is high fishing pressure in the southern Yellow Sea. Based on analysis of Odum’s ecological parameters, this ecosystem was at an immature stage. Our results provide some insights into the structure and development of this ecosystem.