A comprehensive evaluation method for plateau freshwater lakes: a case in the Erhai Lake

Figures & data

Figure 1. Location of Erhai Lake basin (adapted from Lin et al. 2020)

Figure 2. Indicators of “Ecosystem vitality” component

Figure 3. Indicators of “Ecosystem services” component

Figure 4. Indicators of “Governance and stakeholders” component

Table 1. Calculation methods for the sub-indicators

Indicator	Calculation methodology	Reference condition/data sources
C11	The ratio of surface water consumption to total surface water resources in the basin.	China technical guidelines for river and lake health assessment (SL/T793 – 2020)/Dali Water Resources Bulletin (2015–2019)
C12	Comparing the annual, multi-day, and daily average water levels with the minimum ecological water level (ML) at which the lake can operate normally.	China technical guidelines for river and lake health assessment (SL/T793 – 2020)/Dali Water Resources Bulletin (2015–2019)
C13	Documents survey from local government website	Environmental Quality Standards for Surface Water of China (GB 3838–2002)/Dali Bai Autonomous Prefecture Environmental Status Bulletin (2015–2019)
C14	Calculation of the comprehensive trophic level index (TLI).	Literature(Wang, Liu, and Zhang 2002)/Dali Bai Autonomous Prefecture Environmental Status Bulletin (2015–2019)
C15	Changes of lake area in the assessment year and benchmark year.	China technical guidelines for river and lake health assessment (SL/T793 – 2020)/Dali Water Resources Bulletin (2015–2019)
C16	Proportion of vegetation vertical projection area to the area of the lakeshore zone.	China technical guidelines for river and lake health assessment (SL/T793 – 2020)/Remote sensing analysis combined with field investigation.
C17	The extent to which the lakeshore zone is disturbed by human activities. If there are no human activities considered in the assessment, the score of the sub-indicator is 100, and it is subjected to deduction until zero depending on the presence of the related human activities.	China technical guidelines for river and lake health assessment (SL/T793 – 2020)/expert judgment; field investigation
C18	The indicator of biodiversity (BIO) consists of Fish biomass loss index (FBLI), as well as invasive and nuisance species (INS), and, $BIO=\sqrt{FBLI\times INS}$ FBLI = (1-FO/FE)×100 $\mathrm{I}\mathrm{N}\mathrm{S}=\mathrm{m}\mathrm{i}\mathrm{n}\left\{\mathrm{I}\mathrm{N}{\mathrm{S}}_O\sqrt{I_{TE}\times \mathrm{\Delta }SC\times PT},100\right\}$ where, FO represents number of existing fish species in the assessment year, FE indicates number of fish species in the benchmark year, ITE denotes the number of concerned species in the assessment year, ΔSC indicates the change in the number of species which are concerned, PT represents the average population tendency across all species concerned.	Literature (Loh et al. 2005; Wen, Li, and Li 2020) China technical guidelines for river and lake health assessment (SL/T793 – 2020)/Dali Bai Autonomous Prefecture Environmental Status Bulletin (2015–2019); IUCN Red List
C21-C27	Dividing the studied area into spatial units, and three dimensions are considered for the assessment of “Ecosystem Services” indicators (ESI), i.e., the number of spatial units in studied area which are unable to meet the specific objective (F1), the frequency with which the specific objectives are not met (F2), and the gap with which the specific objectives are not met (F3). If only F1 can be measured, ESI = 100 − F1; If F1 and F2 can be measured, $ESI=\sqrt{\left({F_1}^2+{F_2}^2\right)/2}$ ; If all three dimensions can be measured, $\mathrm{E}\mathrm{S}\mathrm{I}=100-\sqrt{\left({F_1}^2+{F_2}^2+{F_3}^2\right)/3}$	Literature(Modarres 2006; Wen, Li, and Li 2020)/Dali Water Resources Bulletin (2015–2019); Dali Bai Autonomous Prefecture Environmental Status Bulletin (2015–2019); Statistical bulletin of national economic and social development of Dali City (2015–2019)
C31-C310	Expert symposium, document surveys, field investigation, questionnaire analysis	Literature(Modarres 2006; Vollmer et al. 2018; Wen, Li, and Li 2020)/Statistical bulletin of national economic and social development of Dali City (2015–2019); questionnaire analysis; stakeholders consultation; field investigation

Table 2. Reclassification of indicator scores in Erhai Lake basin assessment

Levels	Excellent	Good	Fair	Poor	Bad
Original score	≥95	≥90	≥80	≥70	<70
Normalized value (I)	5	4	3	2	1
Cask short board effect considered(log5)	1	0.86	0.68	0.43	0

Figure 5. Summary results for ecosystem health evaluation of the Erhai Lake basin

Table 3. Classifications of three components’ coupling degree

Coupling degrees (C)	Levels	Characteristics
C ∈ [0, 0.3]	Low coupling stage	Three components are in the game state within the low coupling period. When C = 0, the three components have nearly no association with each other and the Erhai Lake basin is developed out of order.
C∈ (0.3, 0.5]	Antagonism stage	The interactions among the three components strengthen. The superiority components become much more potent than others, which weakens other components during the Erhai Lake basin development.
C∈(0.5, 0.8]	Break-in stage	The three components start to present a benign coupling feature, as their balancing and cooperating with each other.
C∈ (0.8, 1]	High coupling stage	The benign coupling among the components improves, toward development with order. When C = 1, the three components achieve the benign resonance coupling and the Erhai Lake basin is managed and developed with a new ordered structure.

Table 4. Classifications of three components’ coupling coordination degree

Coupling coordination degrees (D)	Levels	Characteristics
D∈ [0,0.2]	Serious imbalance	Ecosystem vitality of the Erhai Lake basin deteriorates significantly because of human activities, including disorderly discharge of pollutions, excessive exploitation of the ecosystem products, without effective governance and conservation by stakeholders.
D∈(0.2, 0.4]	Moderate imbalance	Ecosystem vitality of the Erhai Lake basin is still deteriorated significantly because of human activities; stakeholders have realized the importance of the Erhai Lake basin governance.
D∈ (0.4, 0.5]	Basiccoordination	The three components have coordinately developed. Stakeholders begin to put emphasis on the governance and restoration of deteriorated ecosystem vitality led by human activities. The Erhai Lake basin is gradually developed in an intensive and efficient way.
D∈(0.5, 0.8]	Moderate coordination	The ecological restoration starts to get achievements. The ecological vitality has been greatly enhanced, and the ecological services has been strengthened continuously.
D∈(0.8, 1.0]	Good coordination	The three components show the positive relationship, and the Erhai Lake basin is managed and developed orderly.

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