Impacts Of Ulva (Enteromorpha) Prolifera In The Green Tide On The Yellow Sea Ecological Environment-implications From Migration And Transformation Of Biogenic Elements

Field surveys were conducted to study the chemical composition and pigmentsin U. prolifera from different coastal area in the Yellow Sea, analyse the relationshipbetween this change and the environmental nutrients. Laboratory simulationexperiments in the natural seawater were conducted to research consumption,transformation and release of carbon, nitrogen, phosphorus and sulfur by U.and investigate the influence by these processes in the green tide on the Yellow Seaecosystem.The chemical composition and pigments in U. prolifera from different coastalarea in the Yellow Sea were determined and the impact on the color and pigment bynutrients were studied. The results showed that the content of the major chemicalcompositions, such as C, N, P, crude protein and crude fat etc., in thalli sampledfrom Jiangsu coastal area was obviously higher than that in thalli from Shandongpeninsula costal area. The same trend was noted with respect to the content of sixpigments (chlorophyll a, chlorophyll b, lutein, β-Carotene, neoxanthin andviolaxathin). Significant positive correlations (P<0.05) were noted betweenchlorophyll and C、N、Fe、Al、K and crude protein. Experimental results indicatedincreased pigment content (of chlorophyll a, chlorophyll b and lutein) in thalli towhich nitrate and phosphate had been added. It was also noted that, under low nitrateconditions, the addition of phosphate had no impact on the pigment content of thalli.Results also indicated major changes in green color of thalli (from dark to light) andthe content of chemical composition and pigments during the green tide driftingfrom Jiangsu coastal area to Shandong peninsula costal area. A change in nutritionalstatus, from rich to poor, was also noted. The physiological state transition of U.prolifera in the yellow sea was closely related to the distribution of the nutrients inone of environment factors.The consumption of biological elements by U. prolifera at different growthstages was researched to show that in the high biomass group (2.5g/L) of adult thalli,the DIN and DIP consumption from seawater in one day was approximately70% and25%, respectively. In the same group, the DIC and DIS consumption fromseawater in one day was approximately42%and1%, respectively. No significantdifference between floating and attached thalli for average DIN and DIPconsumption from seawater was observed (p>0.05). However, a significantdifference between floating and attached adult thalli was noted for daily growth rate(p<0.05). The NH4+and PO43-consumption in the fixation stage was significantlyhigher than that in the germination stage (p<0.05). In the green tide the high DINand DIP consumption by thalli could reduce the concentration of nitrogen andphosphorus nutrients in the seawater. The DIC and DIS consumption by thallicouldn t obviously impact on the seawater environment.Experiments were conducted to compare the absorption of nitrogen andphosphorus nutrient by U. prolifera in flowing-water and non-flowing water systemand study the transformation of biological elements by U. prolifera. The resultsshowed that DIN, DIP and DOP in seawater was absorbed by U. prolifera, but DONwas released in2days in the experimental system with the no-flowing water. Thallicould convert DIN to DON. DIN, DIP, DON and DOP in seawater was all absorbedby the thalli in the flowing water experiment. The average absorption rates were10.87μmol·g-1·d-1,2.41μmol·g-1·d-1,0.183μmol·g-1·d-1and0.023μmol·g-1·d-1,respectively. The transformation efficiency of inorganic form into organic form of N,P, C and S were97.33%,99.99%,96.84%and95.31%, respectively. U.prolifera inthe green tide could transform inorganic nutrients into organic nutrients, andtransport them to the Shangdong coastal area.In simulation experiments of the U. prolifera decomposition, the results showedthat the decomposed thalli mainly released organic nutrients. The highestconcentrations of organic carbon, organic nitrogen and organic phosphorus nutrientsincreased to1.65mmol/L,80.71μmol/L and1.605μmol/L, which were about3-9times higher than the initial concentrations. The TN concentration was over watereutrophication standards. However, the concentration of ammonia nitrogen (NH4+-N)was higher than the initial, about2.46μmol/L. The concentration of sulphur nutrientsincreased slightly, which couldn t impact on the environment. The dissolved oxygen was lower than4mg/L in the seawater with2.5g/L thalli after17th day, and theseawater with5g/L thalli was in the hypoxia state for a longer period. The pH valuewas less than7.5after12days. The dissolved oxygen and pH was in grade IV after17days. The green tide decomposition had obvious harmful effect on theenvironment.From what has been discussed above, the large green tide outbreaks ofU.prolifera had important influence on the migration and transformation ofbiological elements in the Yellow Sea. The total absorbed dose of nitrogen,phosphorus, carbon and sulfur by U. prolifera of huge biomass in the flourishingperiods was estimated to be360thousand tons,23.2thousand tons,400tons and16thousand tons respectively. The amount of biological elements absorbed by U.prolifera in the Jiangsu coastal area was transported to the seawaters of theShandong coastal area following current drift. The nutrients consumption by thegreen tide accounted for fewer than15%of the annual emissions of ammonianitrogen in Jiangsu province, which didn t significantly reduce the nutrients level inthe Jiangsu coastal area with seawater eutrophication. However, the high nutrientsconsumption (79%/d and36%/d) reduced the nutrients level to lower in theShandong peninsula southern seas with low nutrients, which may go against otherprimary producers, such as the growth of phytoplankton and reduce the chance ofred tides. The demise and decomposition time of green tide was about80daysduring the sinking of thalli in the shandong peninsula coastal waters, and releasedalmost all its nutrients into the sea, which may change the original nutrientsproportion in the seawater, for example, the percentage of organic nutrients ratiorised from about25%to more than90%, and cause the nutrients levels higher inShandong peninsula coastal area (TN concentration was higher than80μmol/L) andcause seawater hypoxia (DO less than4mg/L). It may play an important role on thenutrients re-distribution in that sea for nutrients absorption, migration and re-releaseby the large green tide in the Yellow sea, which could also cause the correspondingecological effects.