| Due to salinity stress,most constructed wetland plants have poor treatment effect on pollutants in mariculture tail water,which restricts the application of constructed wetland technology in mariculture tail water purification.In this study,Kandelia candel,Aegiceras corniculatum,Rhizophora stylosa and Avicennia marina were selected.Ammonia nitrogen,nitrate nitrogen and phosphate in artificial seawater with different concentrations of nitrogen and phosphorus pollution load were treated by mangrove hydroponic experiment,mangrove constructed wetland and mangrove wetland system with introduction of Sipunculus nudus.The removal effect of mangrove plants on mariculture tail water was investigated,and the feasibility of using S.nudus in constructed wetland system was preliminarily explored.(1)Absorption and removal of nitrogen and phosphorus by mangrove plantsThe experiment group of K.candel,A.marina and the control group without plants were set up.The artificial seawater with different concentrations of ammonia nitrogen,nitrate nitrogen and phosphate load was used for hydroponic absorption test,and the water samples were collected for the determination of nitrogen and phosphorus nutrient content within a certain period(0,4,8,11,15,22 and 29d).The results showed that when the concentration of ammonia nitrogen in water was 5.83 mg/L,A.marina and K.candel had better removal effect on ammonia nitrogen in water,and the removal effect on ammonia nitrogen in water was significantly higher than that in control group(P < 0.05).With the increase of ammonia nitrogen concentration in water,the total amount of ammonia nitrogen removal increased,but the removal rate decreased.There was no significant difference in the removal efficiency of ammonia nitrogen between A.marina and K.candel(P > 0.05).The removal rate of nitrate nitrogen in water by A.marina and K.candel was less than 40%.When the concentration of nitrate in water was 29.15 mg/L,the removal rate of nitrate by mangrove plants was significantly higher than that of the blank control group(P < 0.05).When the phosphate concentration in water was 0.33 mg/L and 1.65 mg/L,there were significant differences between the two groups(P < 0.05),and there were interspecific differences between the two groups(P < 0.05).The results showed that mangrove plants had better removal effect on different forms of nitrogen and phosphorus nutrients under the condition of low concentration pollution load,mangrove plants could enhance the nitrification of the system,and K.candel had better removal effect on phosphate than A.marina.(2)Effect of mangrove wetland system on nitrogen and phosphorus removal from mariculture tail waterConstructed wetland systems with K.candel,R.stylosa,A.corniculatum and without plant blank control were constructed outdoors.Artificial seawater with different nitrogen and phosphorus pollution loads(set as 5 times,10 times,15 times and 25 times concentration group),and the water samples were collected for the determination of nitrogen and phosphorus nutrient content within a certain period(0,3,6,9,14,19,24,29d).The results showed that the removal rate of ammonia nitrogen decreased with the increase of nutrient concentration,and the removal effect of K.candel was significantly higher than that of R.stylosa and A.corniculatum(P < 0.05).At the end of the experiment,the concentration of nitrate nitrogen in the blank control group continued to increase,and the concentration of nitrate nitrogen in mangrove plant treatment system was relatively stable.Mangrove treatment system had a good effect on the removal of nitrite nitrogen in the water during the whole test period,and nitrite nitrogen accumulated in the water of the blank control group.Three days before the experiment,the phosphate concentration in the system decreased rapidly,showing a good removal effect on phosphate.The removal rate of mangrove treatment group was higher than that of the blank control group,but there was no significant difference(P > 0.05).The results showed that mangrove system had a good effect on the removal of nitrogen and phosphorus in mariculture tail water,the nitrification of mangrove wetland system was better than the blank control group without plants,and the removal of phosphate was dominated by substrate adsorption.(3)Nitrogen and phosphorus removal efficiency of mariculture tail water by S.nudus and mangrove wetland systemS.nudus was added into the constructed wetland system of K.candel,A.marina,A.corniculatum and no plant blank control.Artificial seawater with different nitrogen and phosphorus pollution loads(set as original,2 times,5 times and 10 times concentration group),and the water samples were collected for the determination of nitrogen and phosphorus nutrient content within a certain period(0,3,6,9,14,19,24 and 29d).The results showed that the introduction of S.nudus promoted the removal of nitrogen and phosphorus nutrients in the constructed wetland system.The removal efficiency of ammonia nitrogen,nitrite nitrogen and phosphate reached the maximum in the 0-6 days and the 0-3 days respectively.The addition of S.nudus effectively promoted the nitrification reaction and improved the removal efficiency of ammonia nitrogen in the constructed wetland system.The death of S.nudus may aggravate the risk of system pollution,and the existence of mangrove plants can improve the living environment of S.nudus in high pollution environment.Due to the low tolerance of S.nudus to environmental pollutants,more research is needed to apply it to constructed wetland water treatment technology. |
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