Impacts Of Several Herbicides On Aquatic Organisms And Decomposition Function Of Microcosms Aquatic Ecosystem

The use of herbicides in China has increased faster than that of insecticides and fungicides since 1980's.Herbicide application has covered almost all habitats .including crop fields,orchards,forests,parks and natural water body. Therefore, herbicides may be moved into aquatic ecosystem via precipitation, leaking and runoff. Heribicides may be of negative impact on aquatic organisms and aquatic ecosystem.The present dissertation studied the impacts of several herbicides on Spirodela polyrhiza (L.) Schleid, Ceratophyllum demersum and Chlorella vulgaris,and the impacts of butachlor on decomposition function of microcosms aquatic ecosystem was investigated.The results were reported as follows:l.This study was conducted to investigate the effect of 12 common herbicides (i.e.acetochlor,butachlor,metribuzm,fuazifop-P-butyl,isoprotuin,benazolin-ethyl,MCPA, quinclorac,fenoxaprop-P-ethyl,2,4-D,fluroxypyr,and cinmethylin) on the growth and development of two hydrophytes, C. demersum and 5. polyrhiza (L.) Schleid,which were collected from natural water body in the suburbs of Yangzhou City,and to determine changes in chlorophyll content,photosynthetic rate,respiratory rate and glutathione-S-transferase (GSTs) of C.demersum in response to treatment of water body with butachlor at five different concentrations.The results showed that acetochlor,butachlor and cinmethylin significantly suppressed the growth and development of C.demersum and S.polyrhiza(L.)Scbleid.The biomass(dried weight) of C.demersum under the laboratory condition of controlled temperature and illumination decreased with increase of butachlor concentrations at 12 days after treatment(DAT),though at 5 DAT and 10 DAT.the biomass did not change significantly as compared to the control(untreated).At 16 DAT, significant negativecorrelation was shown between the dried weight of C.demersum and butachlor concentration,with the regression equation:Y=0.6638-0.03347 X(r=-0.9167*).The photosynthetic experiment demonstrated that the oxygen emitting rate of C.demersum following butachlor treatment declined significantly while the rate of the untreated control was relatively constant during test periods.At 16 DAT,the oxygen emitting rate of the samples treated with 2,4,6,8mg/L of butachlor reduced by 36.02%,41.64%,42.74 %and 48.43% in comparison to the control,respectively.The oxygen emitting rate of C.demersum was negatively correlated with the butachlor treatment(r=-0.8690*).The oxygen consumption rate of C.demersum subjected to treatment at 4,6 and 8mg/L of butachlor also decreased by 25.87%,66.64% and 67.94% at 10 DAT as compared to the control.Furthermore,the treatment of butachlor influenced other two physiological indexes of the hydrophyte as well.The chlorophyll content of C.demersum tended to decrease with increase of butachlor concentration at 12,14 and 16 DAT. The glutathione-S-transferase(GSTs)activity of C.demersum following the herbicide treated varied with butachlor concentration.At a high concentration(8mg/L),the GSTs activity was minimized at 5 DAT and then gradually recovered to a normal level at 12 DAT;at a low concentration(lmg/L),the activity was significantly higher than that of the control and those of the samples treated with higher concentrations at 5 and 10 DAT.but significantly lower than that of the control at 16 DATA butachlor caused low activity indicates that the herbicide treatment can reduce the function of detoxification in C.demersum due to the GSTs is a detoxification enzyme.2.The relative sensitivity of Chlorella vulgaris to three commonly used herbicides metribuzin,puma and alachlor were determined by toxicity tests of 96-h static exposures.The results showed that the toxicities of metribuzin and alachlor to C.vulgaris increased with exposure time,and the density of C.vulgaris decreased with increase of concentrations of these two herbicides in the test media.The maximum specific growth rate of C.vulgaris exposed to metribuzin(0.24mg/L)and alachlor(12.8mg/L)was 12.38%and 31.58% of the control,respectively.At low concentration,puma stimulated...