| River as a part of watershed,which has the function of purification of water, water and nutrients transportation and ecological protection.The early research in Duliu River indicates that natural river composed by "riffle-deep pool-benchland" system structure unit presents diverse forms and structures and the "riffle-deep pool-benchland" system is considered as a basic model structure of a natural river, which will continue to repeatedly appears with extended up and down of the river. The study about the "riffle-deep pool-benchland" system can build up theory of basic structure morphology, river water self purification function and pollutant-released theoretical model from the bottom of water. However, if the "riffle-deep pool-benchland system" is the basic structure of the system unit in other river, it needs to be furhtertested, and the relationship between the system and water quality and release of bottom matter also needs to further study for the eventual establishment of the theory of the "riffle-deep pool-benchland" system in the natural rivers. Therefore, based on the field investigation of Chishui r iver, when there is basic structural unit, riffle-deep pool-benchland system, we selected 9 of "riffle-deep pool-benchland system" in the middle and lower reaches and quality indexes in these systems were determined to analyze the relationship between the change of river morphology and r iver water quality, and assessment of heavy metals pollution of sediment nutr ients in different section s of these system. Variability analys is, laboratory static simulation and identif ication of influence factors affecting pollution matter release were conducted. Results indicated that:(1) the water quality of Chishui River presents different in three water period, i.e., the low water period>the normal water period>the high water period. The average concentration of total nitrogen in the deep lake was 0.43mg/L, and 0.41mg/L in the rapid stream; the average concentration of nitrate nitrogen in the deep lake was 0.17mg/L and the average concentration was 0.13mg/L in the riffle. The average concentration of ammonia nitrogen in the deep lake was 0.108mg/L, and the average concentration was 0.089mg/L in the rapid stream. Total phosphorus(TN), chemical oxygen demand(COD), dissolved oxygen(DO), five day biochemical oxygen demand(BOD5) in different sampling periods were shown as: rapids > deep pool. Total phosphorus in the deep pool was 0.018mg/L in average concentration, and 0.027mg/L in the rapids in average concentration; chemical oxygen demand in average concentration was 15.72mg/L in the deep pool, and 30.32mg/L in the rapids; dissolved oxygen in average concentration was 6.59mg/L in the deep pool, and 6.91mg/L in the rapids; five day biochemical oxygen demand in average concentration was 1.54mg/L in the deep ool, and 1.84mg/L in the rapids. By analyzing the water quality of Chishui River, the water quality indexes of all sampling points in Chishui River can reach the II standard of surface water in the middle and lower reaches of the 3 sampling periods.(2) The results showed that the release of nitrogen and phosphorus from sediment is closely related to the different environmental conditions and the low pollutant content of the overlying water was favorable to the release of the nitrogen and phosphorus. When the water was covered by something to be no light in the release device, the average release rate of total nitrogen was 8.86mg/m2/d, and the average release rate of total phosphorus was 0.986mg/m2/d. Total nitrogen average release rate was 45.465mg/m2/d in rapids. The average phosphorus release rate was 0.493mg/m2/d when the overlying water was distilled water, and average release rate of total nitrogen was 31.7mg/m2/d in deep pools and average release of TP rate was 1.214mg/m2/d. The average release rate of total nitrogen was 38.35mg/m2/d in rapids and the average release rate of total phosphorus was 1.01mg/m2/d. Under the condition of avoiding light, it is favorable for the release of nitrogen and phosphorus from sediment. Under the illumination condition, the average release rate of total nitrogen was 23.36mg/m2/d, and the average release rate of total phosphorus was 0.979mg/m2/d in deep pool. Average release rate of total nirogen was 21.41mg/m2/d in rapids and the average phosphorus release rate for 0.815mg/m2/d. In the dark light conditions, in deep pools, total nitrogen presented an average release rate to 31.46mg/m2/d and TP average release rate to 1.16mg/m2/d. The average release rate of total nitrogen was 24.3mg/m2/d in rapids, and the average release rate of total phosphorus was 1.14mg/m2/d.(3) 5 kinds of heavy metal content in the "riffle-deep pool-benchland" systems in the Chishui river are as follows: Zn>Cu>Pb>As>Hg. By comprehensive pollution index(P) evaluation indicated that the pollution degree aranged from micro pollution to slight pollution. Five potential ecological risk of heavy metals in the Chishui River Basin was very low except for the individual located beside the town of sampling points, but heavy metal pollution in the basin was not obvious. Geoaccumulation index(Igeo) method showed that 5 kinds of heavy metals pollution frequency ranged from 67.54% ~ 87.28%, which indicated that in the Chishui River bas in sediment polluted by heavy metals was slight, and the river retained the features of the river matter background.In summary, Chishui River have an obvious "the riffle-deep pool-benchland" system along the river and the "the riffle-deep pool-benchland" is the basic structure of the natural river, which has a great effect on. water quality index, bottom pollutant release. River morphology diversity and complexity to improve the self purification capacity of river water and improve the environment of the river has important ecological signif icance. The relationship between the structure and function of natural riverriffle-deep pool-benchland system provides a theoretical basis for the degradation of river ecological restoration. |
PDF Full Text Request