Study On Spectral Discrimination Method For Different Stages Of The Growth And Decay Process Of Huangtai Algae

At present,the eutrophication of inland lakes has become one of the hot issues.Lake Wuliangsuhai has accepted the irrigation water,urban sewage and industrial wastewater discharged from Hetao-irrigated region,which leads to serious degradation of ecological function,eutrophication and frequent occurrence of Huangtai algae blooms.How to monitor and control Huangtai algae blooms has become a major environmental problem to be solved urgently.In this paper,According to the wet weight data of all boxes and the chlorophyll concentration and the apparent morphological characteristics of Huangtai algae,the whole growth period of Huangtai algae was divided into three stages:the development stage,stable stage and decay stage.Based on the apparent optical parameters of Huangtai algae,the optical characteristic parameters reflecting the growth and decay process of Huangtai algae were analyzed,and the different stages of the growth and decay process of Huangtai algae were distinguished.The main factors affecting the growth and decay process of Huangtai algae were discussed by using the environmental parameters.The main conclusions of this paper are as follows:?1?By analyzing the changes of chlorophyll a?Chl-a?concentration and wet weight of Huangtai algae,it was found that the trend of Chl-a concentration was consistent with that of weight,the Chl-a concentration gradually increased in the development stage and the relative growth rate of Huangtai algae was 5.89%.The Chl-a concentration was bigger,the relative growth rate was 2.07%in the stable stage.The Chl-a concentration gradually decreased in the decay stage,and the relative growth rate was-6.63%.?2?Based on the time series remote sensing reflectance(R_rs),the spectral characteristics of Huangtai algae were analyzed.The R_rss of Huangtai algae on different dates showed typical algae spectral characteristics.The average R_rs value at the development stage was biggest,the stable stage was bigger than the decay stage.?3?The correlation analysis between R_rs and Chl-a concentration showed that the correlation between R_rs?800?/R_rs?685?and Chl-a content of Huangtai algae was the highest,between-0.24⁰.74.?4?The Red edge position moved to short wave direction with 9nm and the Blue edge position moved to the long wave direction with 12nm.?5?The ratio vegetation index?RVI?'s fluctuation range was uniform in the development and the stable stages and there was no significant difference between the two.The RVI was low and decreased continuously in the decay stage.The RVI<5 can be used to distinguish the decay stages of Huangtai algae.Also,the reflectance valley depth at 810nm in the development stage is lower than that in the stable and decay stages,and H₈₁₀<1.95×10^-3 can be used to distinguish the development stage,those didn't conform to the above two conditions were classified as stable stage.The accuracy of verification was 80.09%by using 221 samples of Huangtai algae.?6?The major factors affecting the growth of Huangtai algae were analyzed.Pearson correlation coefficients of total phosphorus?TP?concentration and Huangtai algae?box 26-30?wet weight were negative in the development stage,ranging from-0.65 to-0.06;positive in the decay stage,ranging from 0.03 to 0.59;and mean in the satble stage was-0.03.The correlation between Huangtai algae wet weight and total nitrogen?TN?concentration in each box and cistern was less than 0.3.In addition,temperature indirectly affected the growth of Huangtai algae through water temperature.Pearson correlation coefficients of water temperature and Huangtai algae wet weight in the development stage and in the decay stage were 0.70 and 0.61respectively,while the Pearson correlation coefficients in the satble stage were-0.16.