SPECIES COMPOSITION AND DISTRIBUTION OF FLOATING MAT IN LAKE ERHAI

The growth and propagation of aquatic plants will be greatly suppressed if the water level rises promptly. Some aquatic plants, especially for some emergent plants, can form floating mats to avoid the effects of deep flooding. We studied the species composition and distribution pattern of floating mat to find which species could form floating mats more easily and survive in the process of increasing water level in Lake Erhai in 2017. A total of 26 aquatic species (attached to 15 families and 19 genera) were recorded. The concentrations of total nitrogen (TN), total phosphorus (TP) and total dissolved phosphorus (TDP) in the water under the floating mat were greater than those in the open water, while the concentration of dissolved oxygen (DO) was vice versa. The results showed that both species richness and biomass of the floating mat were positively correlated with the area of floating mat (P<0.01), and the mean biomass of the floating mat was not significantly correlated with the area of floating mat (P>0.05). The longest root of the floating mat was significantly correlated with the area of floating mat in summer (P<0.01) but not in winter (P>0.05). Most of the floating mats distributed in the region within an offshore distance of 60 m and the water depth less than 2 m. The area of the most floating mats was less than 600 m² (87% for summer and 95% for winter), and the number of species in the floating mats is less than 10, the longest root in the floating mats ranged from 40 to 120 cm. The frequency and relative biomass of Zizania latifolia were the greatest among all recorded species on the floating mats in two seasons (frequency: 73.33% in summer and 66.67% in winter; relative biomass: 43.38% in summer and 41.91% in winter). These results indicated that Z. latifolia was easier to form floating mats in escape of the stress of deep water than the other emergent species to explain its sino-dominance in the emergent community. The mechanism that Z. latifolia is easier to form floating mats than the other emergent plants deserves further investigations.