Effect On Macrobenthos Disturbance For Nutrients In Intertidal Sediments

In recent years,with the discharge of tidal flat aquaculture wastewater and the development of tourism,the contents of nutrients,such as nitrogen and phosphorus in coastal intertidal zone of Tianjin gradually increase,showing eutrophication tendency,and the large macrobenthic community structure diversity also showing a downward trend.The eutrophication in intertidal sediments has gradually been attracting the attention of academics.Scholars both inland and abroad have begun to conduct a series of explorations on the eutrophication in sediments.Based on the investigation of the environmental background of the Gaoshaling intertidal zone in the spring,summer and autumn,and a micro-universe experiment system was established in the laboratory.Taking Perinereis aibuhitensis,Bullacta exarata,Scapharca subcrenata and Helice tientsinensis as the research object of study which about the growth characteristics of macrobenthos in muddy intertidal zone,the growth characteristics of different benthic organisms under different natural conditions were analyzed and the optimum growth conditions were obtained.Based on the experimental results of growth characteristics,the effects of bioturbation on nutrients in sediments were studied by taking Perinereis aibuhitensis as an example.The main conclusions are as follows:(1)The conversion range of dissolved oxygen in pore water of the intertidal zone at spring,summer and autumn was 6.81?8.58 mg/L,and the mean was 7.98 mg/L,which was consistent with the first level water quality standards of the nation.The content of inorganic nitrogen in the three seasons varied from 0.197 to 0.518 mg/L with an average of 0.390 mg/L.Autumn and summer contents met the fourth level national standards,while spring met the third level.The content of active phosphate varied from 0.008 to 0.034 mg/L,with an average of 0.019 mg/L,of which the national third level water quality standards was fulfilled in autumn and summer,while the first level water quality standards was met in spring.The contents of organic matter in spring,summer and autumn were 3.71?4.27 g/kg,3.02?4.04 g/kg and 3.38?4.17 g/kg respectively,and the average of three seasons was spring>autumn>summer.The average values of total nitrogen in the sediments in spring,summer and autumn were 535.33 mg/kg,431.19 mg/kg and 518.78 mg/kg,respectively,and the total phosphorus in the sediments was 475.01 mg/kg,461.67 mg/kg and 623.23 mg/kg in spring,summer and autumn.Except the contents of total phosphorus in autumn was highest,the total nitrogen content is the same as the organic matter in spring,which is significantly higher than that of the other two seasons.The analysis of each station granularity in three seasons indicates,Except the high tide is silty sand,all the other seasons are normal sand.The biomass of macrobenthos in spring,summer and autumn in this area were 67.96 g/m2,326.57 g/m2 and 310 g/m2 respectively;the habitat density was 179.17 ind/m2,549.67 ind/m2 and 750 ind/m2 respectively.In three seasons,the mean of biomass is summer>autumn>spring,and the mean of habitat density is the same with the mean of biomass.The distribution of macrobenthos biomass in the intertidal zone in this area is as follows:low-tide>mid-tide>high-tide;the habitat density also range as low-tide>mid-tide>high-tide.(2)By analyzing the growth characteristics of different macrobenthos in different natural conditions(density,pH and salinity),the main conclusions are as follows:the optimum density of Perinereis aibuhitensis was 325 ind/m2;the optimum density of Bullacta exarata was 130 ind/m2;the optimum density of Scapharca subcrenata was 65 ind/m2;the optimum density of Helice tientsinensis was 130 ind/m2.The optimum salinity range of Perinereis aibuhitensis was 20?30,the optimum salinity of Bullacta exarata was about 30,the optimum salinity of Scapharca subcrenata was about 30,and the optimal salinity range of Helice tientsinensis was 10?40,of which Helice tientsinensis has the widest range of adaptation to salinity.The optimum range of pH value is 8?9 for Perinereis aibuhitensis;the optimal pH range of Bullacta exarata is 7?8;the optimal pH of the Scapharca subcrenata is about 8;The optimal pH range of Helice tientsinensis is 7-8.(3)On the basis of analyzing the influence of different environmental factors on the survival of benthic animals,the effect of the perturbation on the nutrient salt in sediments was studied.The total nitrogen content in the sediments of the experimental groups tended to decrease as a whole.Compared with the blank group S1,the total nitrogen in the other groups increased at first and then decreased gradually.On the seventh day of experiment,the total nitrogen content in S5 with the highest density increased by 17.6%compared with that in the blank group.At the end of the experiment,the S5 group decreased by 4.7%compared with the blank S1 group.At the end of the experiment,the total nitrogen content in sediments are:S4<S5<S3<S1<S2.The total phosphorus content in sediments showed an increasing tendency firstly and then decreased.During the experiment,the content of total phosphorus in S4 group was the lowest.At the end of the experiment,the total phosphorus content in S4 group decreased by 7.1%.The change of organic matter in sediment showed a trend of increasing firstly and then decreasing.On the seventh day,the content of organic matter in the experimental group increased with a increase of density.After 21 days,the content of organic matter in sediments decreased with the increase of density.At the end of the experiment,the content of organic matter in S5 was the lowest,8.9%less than that in the blank group.After the experiment,the organic matter content in the sediments was S5<S1<S4<S3<S2.