Study On The Effect Of Plant-benthic Fauna-Fish Functional Group On Self-purification In Micropolluted Water

The water pollution prevention and control in China has achieved remarkable results,but the quality of water environment is unstable,the micro-pollution problems are prominent.Nowadays,China has entered the"14th Five-Year Plan"——A new era of water ecological protection.The current bio-ecological restoration techniques such as bio-manipulation technology and the food web construction technology don't effectively combine the purification of organisms with the improvement effect of organisms on food chain structure.and the self-purification capacity of micro-polluted water has encountered bottlenecks,which is an urgent problem to be solved in water ecology.In this study,a plant-benthic-fish purification system with relatively complete ecosystem structure was constructed by combining feeding characteristics in order to promote self-purification capacity of micro-polluted water,the effects of biological feeding characteristics and biological complexity on self-purification ability were studied to provide technical means and theoretical basis for the construction of stable and efficient self-purification system.The main research results are as follows:(1)Based on functional group analysis and problem identification in Qingyi River,it is found that there is a risk of intermittent water quality exceeding standard in the basin,and the biological self-purification ability needs to be improved.It is proposed to improve the self-purification capacity from three aspects:plants,benthos and fish.Plants should increase the combination of Hydrilla Verticillataand Typhaorientalis Presl,and introduce Vallisneria natans?Rumex japonicus for efficient purification in winter.The benthos should enrich the function groups of filter feeders and scraping feeders such as clam and snail.The fish should introduce scraper-eating Xenocypris davidi Bleeker and filter-eating Hypophthalmichthys molitrix which have self-purification ability,so that the advanced tropic level can also play the purification function.(2)A comparative experimental study on the self-purification capacity of plant,benthos and fish,the results showed that:the purification of plants and animals was better than that of the blank group(K_COD=0.03,K_TN=0.06,K_{ammonia nitrogen}=0.09).In the plant system,the combination of Hydrilla verticillata and Typhaorientalis Presl had better self-purification ability on COD and TP.In the benthic system,the Chironomidae(K_COD=0.237)had the strongest COD degradation ability.The mussels(K_TN=0.134)had the best degradation ability on N,and the degradation effects on COD and P were also good.Snails(R_TP=38%)had the strongest ability to degrade TP.The self-purification ability of fish was affected by its activities,and the disturbed sediment further releases nutrients,the turbidity and chlorophyll content increase to different degrees.However,Hypophthalmichthys molitrix has a stronger degradation effect on COD and P because of its feeding effect on the purification of some pollutants.The N degradation ability of Xenocypris davidi Bleeker was slightly higher than blank group.(3)By constructing the three-level nutrient structure water ecological purification system with four feeding types,The self-purification capacity and approaches of the feeding system were analyzed:the self-purification capacity of filter feeding system(number as M1)is the strongest(K_COD=0.290,R_TP=19.8%),the nitrification rate was the best(K_{ammonia nitrogen}=0.101),system M1 had the best comprehensive self-purification capacity.the removal of N was mainly based on the sedimentation(removal contribution 52%)and microbial activities,the removal of P is mainly by animal assimilation(contribution proportion 65%).The utilization of sediment nutrient needs to be strengthened because there are only filter-feeding animals in M1.The self-purification capacity of M2——scraping feeding system with detritus feeding is average,but the utilization rate of sediment debris is the highest(sediment settlement contribution is only 2%).Debris system(M3)and cold-resistant debris system(M4)had better self-purification ability on N and poorer self-purification ability on P,and M3 is more conducive to promote microbial action.(4)Through gradually enriching the species of functional groups at different trophic levels,carrying out study on the effect of functional group complexity on self-purification capacity,the results show that:There is correlation between the complexity and self-purification ability of functional group system under certain conditions.Increase the complexity of plant functional groups or increase the complexity of functional group of animals under the condition that the ecological structure of the system is more complete and has certain self-purification ability can improve the efficiency and stability of the self-purification capacity.In the slightly polluted water,the system(number as M8),which enriches the biological complexity of three trophic levels,the degradation coefficients of COD,TN,and ammonia nitrogen were 0.25,0.09,and 0.14,and the TP removal rate was 21%,which were higher than those of other systems.It had the conditions for operation throughout the year and the efficient and stable self-purification capacity,which is expected to solve the bottleneck in self-purification capacity of Qingyi River.