Climatic Changes and Impacts on Water Quality of Erhai Lake in Dali Area, Yunnan Province over the Period from 1989 to 2019

doi:10.19657/j.geoscience.1000-8527

Abstract

Abstract:

In this study, we characterized the climatic changes and their impacts on lake eutrophication in Erhai Lake and assessed the relationships between air temperature, precipitation amount, and trophic status index of the lake using the climate data collected from 12 monitoring stations in Dali of Yunnan Province, and water quality monitoring data of Erhai Lake from 1989 to 2019. During this time, the annual mean air temperatures showed a fluctuating upward pattern which clearly indicated a warming trend with the largest temperature increases in the wintertime; meanwhile, the annual precipitation amount showed a fluctuating downward tendency with the most substantial declines in autumns. Comprehensive trophic status index, total nitrogen, total phosphorus, and permanganate index levels increased, while levels of water transparency declined. The changes in overall water quality were characterized by two distinct stages: before 2003, the comprehensive trophic status index, total nitrogen, total phosphorus, and permanganate index levels increased rapidly, while water transparency measured by Secchi Depth declined; after 2003, these same indices were relatively stable with minor fluctuations. We found that the comprehensive trophic status index of Erhai Lake was positively correlated with the annual mean air temperatures, but negatively correlated with the annual precipitation amount. Total nitrogen and water transparency levels showed a distinct correlation with both the annual mean air temperatures and precipitation. Total phosphorus was correlated clearly with the average winter air temperature, and the permanganate index levels correlated with the mean summer/winter air temperatures, respectively. In terms of monthly changes, both the water pollution index and comprehensive trophic status index increased substantially between June and October from 2015 to 2019, indicating water quality during the dry season was significantly better than during flood season. In summary, the comprehensive trophic status index of Erhai Lake increased continuously due to rising air temperatures, and reduced precipitation and lake inflow from 1989 to 2019, and the intensification of lake eutrophication has not improved and the water environmental condition of Erhai Lake remains relatively fragile.

Key words: climate change, water environment, lake eutrophication, Erhai Lake, Dali area

CLC Number:

P641.6
X143

AN Guoying, GUO Zhaocheng, YE Pei. Climatic Changes and Impacts on Water Quality of Erhai Lake in Dali Area, Yunnan Province over the Period from 1989 to 2019[J]. Geoscience, 2022, 36(02): 406-417.

Figures/Tables 15

Fig.1 Map showing the location of weather stations and Erhai Lake in Dali area

Table 1 Correlation coefficients (rij and γ2ij) between chla and some parameters of lakes in China

参数	chla	TP	TN	SD	COD_Mn
$r 1 j$	1	0.84	0.82	-0.83	0.83
$r 12 j$	1	0.705 6	0.672 4	0.688 9	0.688 9

Table 1 Correlation coefficients (rij and γ2ij) between chla and some parameters of lakes in China

参数	chla	TP	TN	SD	COD_Mn
$r 1 j$	1	0.84	0.82	-0.83	0.83
$r 12 j$	1	0.705 6	0.672 4	0.688 9	0.688 9

Fig.2 Mean, maximum, and minimum annual air temperature and precipitation amount and their linear trends in Dali area from 1989 to 2019

Fig.3 Annual mean temperature anomalies and variation trend in Dali area from 1989 to 2019

Fig.4 Seasonal temperatures and their linear trends in Dali area from 1989 to 2019

Table 2 Decadal means and anomalies of annual and seasonal temperatures in Dali area from 1989 to 2019

年代际	年均/℃		春季/℃		夏季/℃		秋季/℃		冬季/℃
年代际	平均值	距平	平均值	距平	平均值	距平	平均值	距平	平均值	距平
1991—2000	15.7	-0.1	16.7	0.0	21.0	-0.1	15.9	-0.1	9.0	-0.3
2001—2010	16.0	0.2	17.0	0.3	21.2	0.1	16.1	0.1	9.7	0.4
2011—2019	16.4	0.6	17.6	0.9	21.6	0.5	16.5	0.5	10.1	0.8
1989—2019	16.0	0.2	17.0	0.3	21.2	0.1	16.2	0.2	9.6	0.3

Table 3 Decadal minimum and maximum temperatures for individual stations and averages of Dali area from 1989 to 2019

年代际		1991—2000	2001—2010	2011—2019	1989—2019
最低气温/℃	不同站点 (剑川)	11.8 (1992)	12.3 (2004)	12.9 (2011)	11.8 (1992)
最低气温/℃	全区平均	15.0	15.6	16.0	15.0
最高气温/℃	不同站点 (南涧)	19.9 (1998)	19.7 (2006)	20.4 (2019)	20.4 (2019)
最高气温/℃	全区平均	16.4	16.6	16.8	16.8

Fig.5 Annual precipitation anomalies in percentage and its trend in Dali area from 1989 to 2019

Fig.6 Seasonal precipitation amount and their linear trends in Dali area from 1989 to 2019

Table 4 Decadal means and precipitation anomalies in percentage in Dali area from 1989 to 2019

年代际	年均		春季		夏季		秋季		冬季
年代际	平均值 /mm	距平 /%	平均值 /mm	距平 /%	平均值 /mm	距平 /%	平均值 /mm	距平 /%	平均值 /mm	距平 /%
1991—2000	880.0	5.26	94.5	-9.16	500.8	7.93	247.0	5.55	39.6	16.61
2001—2010	847.0	1.32	132.5	27.40	463.1	-0.19	222.1	-5.08	28.6	-15.93
2011—2019	725.4	-13.22	80.1	-22.95	440.0	-5.17	169.7	-27.50	35.1	3.14
1989—2019	822.2	-1.65	104.8	0.74	465.5	0.31	218.0	-6.85	34.3	0.97

Table 5 Decadal minimum and maximum precipitation amount for individual stations and their mean in Dali area from 1989 to 2019

年代际		1991—2000	2001—2010	2011—2019	1989—2019
最小降水量/mm	不同站点	474.7	416.0	357.0	357.0
最小降水量/mm	全区平均	758.6	662.5	621.0	621.0
最大降水量/mm	不同站点	1 300.0	1 417.0	1 216.8	1 417.0
最大降水量/mm	全区平均	1 009.3	1 039.4	884.0	1 039.4

Fig.7 Comprehensive trophic status index and its linear trend in Erhai Lake from 1989 to 2019

Fig.8 Total nitrogen, total phosphorus, permanganate index levels and water transparency and their linear trends in Erhai Lake from 1989 to 2019

Fig.9 Correlations between annual mean air temperature, annual precipitation amount in Dali area and water quality parameters of Erhai Lake from 1989 to 2019

Fig.10 Monthly variation of water quality parameters of Erhai Lake in the different periods

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