Benthic Macroinvertebratre Community Structure And Health Assessement Of Li River, Guilin, Guangxi

Li River is an important river in Guilin, Guangxi autonomous region. With the rapid development of economy in Li River watershed, the ecological condition of Li River seems getting worse. The aim of our study is to establish a benthic index of biotic integrity by using the data from the survey on benthic macroinvertebrate assemblages, and assessing the health condition of Li River.70 macroinvertebrate samples and water quality samples from Li River were collected in March and October,2008. In March, the concentration of TP, TN, NH3-N and CODMn of test sites were two times higher than reference sites, moreover the conductivity of test sites was seven times higher than reference sites. However the Dissolved oxygen, pH and the temperature were similar. In October, the concentration of TP and conductivity in test sites was 3 times higher, TN was 5 times higher, NH3-N was 8 times higher and CODMn was no more than 2 times higher than reference sites. The temperature in test sites was 3.2℃higher than in reference sites. However the Dissolved oxygen and pH and the temperature were similar. Collectively, the TP, TN, NH3-N and CODMn in October were lower than in March.In the March collection, a total of 169 taxa belonging to 136 genera,82 families,7 classess and 4 phylus were indentified based on the present literatures. The insecta of 143 taxa belonging to 9 orders, composed of 84.61% of the total taxa richness, and 46959 individuals composed of 94.86% of total abundance. Crustacea, mollusca and oligochaeta were only composed of 5.14% of total abundance. In October,125 taxa belonging to 114 genera,75 families,7 classess and 4 phylus were indentified. The insecta had 104 taxa belonging to 9 orders, composed 83.2% of total taxa richness, and 80225 individuals composed 91.26% of total abundance, others composed 8.74%.The abundance of main streams is less than the branches, especially sites in Guilin city. In March, the most taxa of main stream is 24, and the least is 6, which site sites in Guilin city. The highest density is 255ind/m2 and the lowest is 20 ind/m2. In October, the main stream's condition is the same to that of March:the most taxa is 31,and the least is 5. The highest density is 810 ind/m2, and the lowest is 37 ind/m2. The condition of the macroinverterbrate for branches:the most taxa is 56, and the least is 11 in March, the highest density is 2059 ind/m2, the lowest is 75 ind/m2. In October, the most and the least taxa is 57 and 14, the highest and the lowest density is 2473 ind/m2 and 56 ind/m2.The B-IBI of March was composed of four metrics:total taxa, EPT taxa, Heptageniidae(Ephemeroptera)% and dominant taxa. The suggested criteria of B-IBI used in Li River catchment was as follows:B-IBI≥21, healthy and<21, unhealthy. The assessment using B-IBI of March found that the mainstream of Li River was unhealthy and most of the branches in the middle and upstream of Li River were healthy. And the B-IBI of October was also composed of four metrics:total taxa, EPT Taxa, BI, and EPT%. The suggested criteria was as follows:B-IBI≥18, healthy and<18, unhealthy. The assessment using B-IBI of October found that the 21 sites were in healthy condition and 18 sites in unhealthy condition.A new B-IBI using the composited data of March and October was established. It was composed of the total taxa richness, BI, the two dominant taxa% and EPT abundance%. The suggested criteria of B-IBI used in Li River catchment was as follows:B-IBI≥21, healthy and<21, unhealthy. The results of assessment using the above B-IBI showed that two sites are unhealthy of 17 reference sites,11 sites were unhealthy of 14 test sites for March, while 5 sites were unhealthy of 21 reference sites and 16 sites were unhealthy of 18 test sites. It suggested that the accurancy of new B-IBI was normal. We recommoned that in the limitation of enough reference sites in a ecoregion or watershed, it could be alternative to using the data of selected seasons of reference sites to establish a good B-IBI.From the Apearman analyses, there are highly significant correlation between B-IBI and total nitrogen, ammonia nitrogen, permanganate index, conductivity, and river width. So the nitrogen compound maybe is the main pollution factors of Li River.