[Impact of drought on snails breeding in the Poyang Lake area].

OBJECTIVE

To examine the impact of arid climates on distribution of snails in the Poyang Lake area, so as to provide insights into precision control of snails in the Poyang Lake area.

METHODS

snails-infested grass islands in Hukou County, Lianxi District and Lushan City in the northern Poyang Lake area, and Jinxian County, Nanchang County and Poyang County in the southern Poyang Lake area were selected as the study areas, and the occurrence of frames with living snails and the mean density of living snails were captured from snail surveys in the study areas in spring and autumn each year from 2006 to 2023. Five years 2007, 2011, 2013, 2019 and 2022 were selected as drought years, and the mean daily water levels were collected at the Xingzi hydrological station in the drought years, normal flow year (2012) and flood year (2020). The numbers of days with water levels ranging from the lower elevation (11 m) to the upper elevation (16 m) for snail survival and the numbers of days with water levels of 11 m and below were collected in the Poyang Lake area, and the changes of snail indicators were compared in different grass islands in the Poyang Lake area before and after drought.

RESULTS

The numbers of days with water levels ranging from 11 to 16 m were 110, 88, 136 d and 125 d at the Xingzi hydrological station in four drought years 2007, 2011, 2013 and 2019, which were less than in the flow year and flood year, and the days with water levels of 11 m and below were 242, 277, 220 d and 198 d in four drought years 2007, 2011, 2013 and 2019, which were longer than in the flow year and flood year. A total of 416 snails-infested marshlands were surveyed in the Poyang Lake area from 2006 to 2021, and the survey marshlands accounted for 43.12% (307/712) and 46.98% (109/232) of total marshlands in the southern and northern Poyang Lake areas, respectively. The median occurrence of frames with living snails and mean density of living snails were 0.60% (interquartile range, 4.04%) and 0.010 1 snail/0.1 m (interquartile range, 0.076 1 snail/0.1 m) in drought years, which were both lower than those [1.33% (5.19%) and 0.022 8 (0.098 9) snail/0.1 m] in non-drought years (χ= 42.170 and 44.911, both values < 0.01). The proportion of grass islands with a continuous decline in snail indicators was higher in the southern Poyang Lake area than in the northern Poyang Lake area after the next year of drought (24.24% vs. 2.33%; χ = 10.633, < 0.01), and the proportion of grass islands with rebounding snail indicators was higher in the northern Poyang Lake area than in the southern Poyang Lake area (53.49% vs. 15.76%; χ = 26.966, < 0.01). A longitudinal analysis of snail indicators in marshlands with rebounding snail indicators after drought showed 1 to 5 years for return to pre-drought snail status, with a median of 2 (interquartile range, 1) years, and snail status was more likely to rebound if the occurrence of frames with living snails and the mean density of living snails were 2.11% and 0.025 5 snail/0.1 m and greater in snails-infested grass islands.

CONCLUSIONS

Drought causes a remarkable decline in snail indicators in the Poyang Lake area, with a more remarkable impact in the southern Poyang Lake area, and 1 to 5 years are required for return to pre-drought snail status.