Spatial-temporal Distribution Characteristics and Influencing Factors of Total Organic Carbon in Erhai Lake

In order to study the spatial distribution characteristics of total organic carbon (TOC) in the Erhai water body, the total organic carbon content at 11 points in the Erhai water body from March 2018 to February 2019 was investigated monthly. The relationship among TOC and environmental factors (water temperature (WT), pH value, transparency (SD), dissolved oxygen (DO), COD_Cr, COD_Mn, total phosphorus (TP), total nitrogen (TN), ammonia nitrogen (NH₃-N), chlorophyll a (Chl a), algae cell density are studied. The results showed that the concentration of TOC in Erhai Lake ranged from 3.04-10.83mg/L, and the annual average was 6.10±1.72mg/L., the TOC concentration showed a trend from large to small in the following seasons summer (June-August), autumn (September-November), winter (December-February) and spring (March-May). Pearson correlation analysis showed (n=132) that TOC showed positive relationship with COD_Cr (r=0.913, p<0.01), WT (r=0.801, p<0.01), TP (r=0.730, p<0.01), COD_Mn (r=0.689, p<0.01), NH₃-N (r=0.615, p<0.01), Chla (r=0.530, p<0.01), TN (r=0..383, p<0.01), D (r=0.301, p<0.01). It significantly negatively correlated with SD (r=-0.654, p<0.01), DO (r=-0.461, p<0.01). There is no significant correlation between pH and TOC (0.183, p<0.05). The TOC content in Erhai Lake is the result of the dynamic balance of multiple processes such as exogenous input, endogenous production, and migration and transformation in the lake. The temporal and spatial distribution of TOC concentration was also affected by rainfall, agricultural activities, sewage discharge, construction, tourism activities, and the biological activities etc.