太湖地区河蟹“养殖-净化”复合系统氮磷循环模拟模型研究

以"养殖-净化"复合系统为对象,探讨河蟹养殖尾水达标排放(地表Ⅲ类水)的工程与技术措施。通过构建系统动力学模型,模拟河蟹养殖尾水达标排放的最佳养殖塘与净化塘的面积比,及不同饵料替代比例、水质调控技术与净化效率对养殖塘和净化塘水体TN和TP浓度的影响。模拟结果显示,在常规养殖条件下,要使净化尾水达到地表Ⅲ类水标准,养殖塘与净化塘的最佳面积比为20.5∶1。商品饲料代替5%、10%和15%时,养殖塘TN浓度分别降低3.1%、6.3%和10.0%,TP浓度分别降低4.2%、8.3%和8.3%;净化塘TN浓度分别降低4.5%、10.1%和14.6%。养殖塘水质调控技术对养殖塘和净化塘水体的TN和TP浓度无显著影响。与水葫芦收获1次相比,收获2次和3次的养殖塘TN浓度分别显著降低10.0%和10.0%,TP浓度降低11.1%和11.1%;净化塘TN浓度分别降低16.1%和17.2%。水葫芦收获2次与3次对养殖塘和净化塘水体TN、TP浓度变化无显著影响。以上结果表明,河蟹养殖工程可以按照养殖塘与净化塘的面积比为20.5∶1进行构建,二塘水体的TN、TP浓度随商品饲料替代比例增加而降低;净化塘水葫芦只需收获2次,净化水质即可达标地表Ⅲ类水。

A Modeling Simulation for Nitrogen and Phosphorus Cycling in the Crab Cultivation-Purification System in the Taihu Lake District,China

This study aims to integrate the'Crab-Grass-Snail'system and the'Cultivating-Purifying'system into a more comprehensive re-cycling ecosystem, and theoretically investigate the engineering practice to meet the Ⅲtype surface water standard. Through constructing a system dynamic model, this study simulated the optimal area ratio between crab cultivation pond and purification pond, as well as testing the effects of feed substitution ratio, water quality regulation technology and purifying efficiency on TN and TP concentration. The simulation re-sults showed that the optimal area ratio for cultivation pond and purification pond was 20.5 to meet the Ⅲ type surface water standard. It was reduced by 3.1%, 6.3%and 10.0%for TN concentration and by 4.2%, 8.3%and 8.3%for TP concentration in the cultivation pond with a substitution of commercial feeds for 5%, 10%and 15%, respectively. TN concentration was decreased by 4.5%, 10.1%and 14.6%in the pu-rification pond with a substitution of commercial feeds for 5%, 10%and 15%, respectively. Water quality regulation technology did not affect TN and TP concentration in the cultivation and purification ponds. Compared with one time's harvest for water hyacinth, it was reduced 10.0%and 10.0%for TN concentration and 11.1%and 11.1%for TP concentration in the cultivation pond by harvest two times and threetimes, respectively. TN concentration was decreased by 16.1%and 17.2%in the purification pond. In summary, N and P input from commer-cial feeds were an important cause for the over-range of N and P concentration in the residue water. TN and TP concentration will decrease with increasing substitution rate for commercial feeds in the cultivation and purification ponds. It needs only to harvest two times for water hyacinth when the purifying water will meet the Ⅲ type surface water standard. These results will provide theoretical evidence for engineering design and the mating management practice for the crab ecological cultivation.