The Effect Of Hydrilla Verticillata Decomposition On The Recruitment Of Dormant Microcystis And Growth

The effect of Hydrilla verticillata decomposition on the recruitment of dormantMicrocystis was studied by simulating spring temperature and four levels of residualHydrilla verticillata mass,0g,10g,25g and50g (fresh weight), respectively. The changesof physical and chemical indexes in the sediments and water were monitored to reflect thedecomposition impact on environmental factors, and the effect of environmental factorschange on Microcystis recruitment was discussed. At the same time, the different levels ofresidual Hydrilla verticillata mass decomposition liquid was added into the liquid culturemedium of the Microcystis, the change of ecological and chemical indexs in the mediumwas monitored, and the effect of mass decomposition liquid on Microcystis growth wasdiscussed.1） The84days decomposition experimental results showed that, during the Hydrillaverticillata decomposition process, the concentrations of total nitrogen (TN), totalphosphorus (TP) and total organic carbon (TOC) in the sediment and water, lightintensities of surface sediment and pH values in water were changed along with thedecomposition time and the residual Hydrilla verticillat mass. The Hydrilla verticillatadecomposition increased the TN concentration in sediment. The TN concentration in thewater of the experimental groups with residual Hydrilla verticillata was higher than thegroup without it and the more residual mass, the higher TN concentration. However, theTN concentration in the water of all the groups showed downward trend, most probablyowing to the absorption of sediment and emission from water as gas because of bacterialactivity. The TOC concentration in the sediment and water increased first, and thendecreased. The TOC in water recovered to the initial level at the end of decompositionprocess. The Hydrilla verticillata decomposition raised significantly the TP concentrationin sediment and this trend was maintained till the end of the experimental period. TPconcentration in overlaying water was increased rapidly at the beginning time andrecovered to the initial level after64days. During the decomposition processing, the pH ofthe water was changed during7.2to8.7.2） The situation of resuscitation of Microcystis was refected by chla of the sediment andwater. In the beginning, all the chla of sediment were changed during0.07-0.09μg/g, thenthe chla of sediment were descendent along with the decomposition process, and thelargest rate of descendent was emerged at the19thdays. After that time the change of the chla of sediment were little. At the end of the decomposition process the chla of sedimentwere changed during0.003-0.014μg/g. The initial decomposition,the more the Hydrillaverticillata residue,the higher chla concentration;The chla concentration decreased with theHydrilla verticillata residue group after9thdays,and the lower rate is proportional to theHydrilla verticillata residue between9thto19th.After19thdays,the chla concentionchanges mainly from the recruitment of dormant Microcystis in the overlying water,Themore the mass was, the little the chla of the water was,and there not appeared secondproliferation period comparision to the group without Hydrilla verticillata.The chl-aconcentrations wsa significantly lower than the group without Hydrilla verticillata on64th、84thday.The results suggest that Hydrilla verticillata decomposition does inhibited ontrecruitment of dormant Microcystis,and the more residue,the greater inhibition.The inhibitiong factors of Hydrilla verticillata decomposition on the recruitment ofdormant Microcystis may include total phosphorus concentration,light intensity decreasedand the pH value decreased.In this study,all groups with Hydrilla verticillata residueproduced the highest phosphorus concentration were higher than0.445mg/L in thedecomposition process.that’s can inhibited the recruitment of dormant Microcystisconcentration;In the decomposition early,due to a large number of Hydrilla verticillata wasdecomposition to suspended particles,changing the color of water,increasing the turbidityof water,so the dramatic decline in light intensity,and the more residue of Hydrillaverticillata,the more significantly decreased,the light of groups with Hydrilla verticillatawas lower than150lux before19thday,the light intensity as low as0lux of groups with50gand25g Hydrilla verticillata residue,very conducive to the early the recruitment ofdormant Microcystis,and many dormant of Microcystis loss of activity;The study showsthat the process of decompossion the lowest pH (7.2) values appear in the3th day,50gresidues in experimental group,and the highest pH (8.7) valuese appear in the43th day,10gHydrilla verticillata residues group,and in most time of the decompositiom course,the10gresidue group pH values is higher than the25、50g groups,that show Hydrilla verticillatadecomposing change pH values affected the recruitment of dormant Microcystis,and thehigh pH values is more conducive to the recruitment of dormant Microcystis.3) With Hydrilla verticillata decomposition liquid cultured Microcystis,only6days,theresults show that the number of Microcystis significantly increased,the color of themedium gradully deepened,the experimental groups Microcystis protein,superoxidedismutase (SOD),malondialdehyde (MDA) with the same without Hydrilla verticillatacontrol group,no significant change.That Hydrilla verticillata’s decomposition liquid was not allelopathy to Microcystis growth,but has a facilitating role.