Numerical Study On The Population Dynamics Of Typical HAB Species In The East China Sea

In recent years, eutrophication has become an overwhelming phenomenon inthe Changjiang estuary and its adjacent area, and harmful algal blooms (HABs) areoccurring more frequently. To understand the mechanism of HABs in theChangjiang estuary and its adjacent area, two box models were built, using thephysiological features of P. donghaiense and S. costatum. The parameters werecalibrated carefully using experimental counterparts and several numericalsimulations were performed to compare the results with laboratory outcomes. Then,the two models were elaborated in ecosystem model focusing on the Changjiangestuary and its adjacent area to research the effects of irradiance, temperature,salinity, and nutrients on the process of blooms in spring. Many results wereobtained which can definitely provide valuable scientific evidence and theoreticalfoundation for revealing the occurrence mechanism of HABs in this area. The resultsare shown as followed:1. Base on the phytoplanktonic part of Eco3M, two box models for typical HABspecies (P. donghaiense and S. costatum) were built. After the calibration ofseveral sensitive parameters, models could reproduce the general characteristicsof algal growth and the use of nutrients under different irradiances andnutritional conditions.2. By coupling two mono-species models, we investigated the utility of mechanismmodels in the research of bi-algal cultures. The simulated results were consistentwith the laboratory findings, indicating that the models could reproduce theresults of nutrient competition between the two algae.The models were limited insimulating interactions besides nutrient competitiondel.3. By coupling the two box models with physical model, the model was in general capable of reproducing observed temperature, salinity, and current. The observedfield of nutrients in the key area was well reproduced. These comparisonsbetween simulated Chl-a and remote-sensing images suggested the model was ingeneral capable of reproducing the horizontal distribution of high concentrationChl-a area and the succession from diatom to dinoflagellate.4. By analyzing the effects of variables on the horizontal variation of growth rate,we find that: For S. costatum, the most influential area of temperature andsalinity is located at Changjiang Diluted Water, and is mainly governed bysalinity. The nearshore and offshore boundary of growth is governed byirradiance and nutrients, respectively. The influential area of nutrients is mainlygoverned by P-limited. The influence of mortality on net growth rate is weak.The influences of variables on dinoflagellate growth are similar with that on S.costatum. The distribution of P was the critical factor during the process ofsuccession.5. We proved the model’s ability to reproduce the process of P. donghaiense bloom,including the incubation at the subsurface layer and the bloom later at thesurface layer. By analyzing the effects of variables on the vertical distribution ofgrowth rate, we found that: For P. donghaiense, the influential area of irradianceis located at deeper water layer. There is an area with low growth rate, which isP-limited, located at the surface layer. However, the growth rate is relativehigher below this area. The simulated results proved this may lead to theincubation at the subsurface layer.