Eco-environmental changes due to human activities in the Erhai Lake Basin from 1990 to 2020

Human activities have increased with urbanisation in the Erhai Lake Basin, considerably impacting its eco-environmental quality (EEQ). This study aims to reveal the evolution and driving forces of the EEQ using water benefit-based ecological index (WBEI) in response to human activities and policy variations in the Erhai Lake Basin from 1990 to 2020. Results show that (1) the EEQ exhibited a pattern of initial degradation, subsequent improvement, further degradation and a rebound from 1990 to 2020, and the areas with poor and fair EEQ levels mainly concentrated around the Erhai Lake Basin with a high level of urbanisation and relatively flat terrain; (2) the EEQ levels were not optimistic in 1990, 1995 and 2015, and areas with poor and fair EEQ levels accounted for 43.41%, 47.01% and 40.05% of the total area, respectively; and (3) an overall improvement in the EEQ was observed in 1995-2000, 2000-2005, 2005-2009 and 2015-2020, and the improvement was most significant in 1995-2000, covering an area of 823.95 km2 and accounting for 31.79% of the total area. Results also confirmed that the EEQ changes in the Erhai Lake Basin were primarily influenced by human activities and policy variations. Moreover, these results can provide a scientific basis for the formulation and planning of sustainable development policy in the Erhai Lake Basin.

Scale-dependent responses of ecosystem service trade-offs to urbanization in Erhai Lake Basin, China

Urbanization is an important factor affecting ecosystem services (ESs) and their trade-offs. However, little is known about the responses of ES trade-offs to urbanization at different scales. Here, the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) model was used to evaluate water yield (WY), water purification (WP), carbon storage (CS), and habitat quality (HQ) in Erhai Lake Basin using earth observation data, and the percentage of urban land (PUL), population density (POP), gross domestic product (GDP), and night light index (NLI) were used as urbanization indicators. We quantified the ES trade-offs using the root mean square error and analyzed spatiotemporal changes in urbanization indicators, ESs, and their trade-offs. Finally, we characterized the relationship between urbanization and ES trade-offs using correlation analysis and curve regression at the grid and town scales. From 2000 to 2020, values of PUL/GDP/NLI/POP were high in the south and low in the north; specifically, they were 15, 8, 2, and 0.42 times higher in the south than in the north, respectively. The urban expansion area in the Erhai Basin from 2000 to 2020 resulted in a 123.24% and 77.03% increase in WY and WP, respectively, and a 32.38% and 100% decrease in CS and HQ, respectively. The trade-offs between WY and CS and between WY and HQ increased, and other ES trade-offs decreased. Urbanization was significantly correlated with most ES trade-offs at the grid scale, but not at the town scale. There was a significant positive correlation between all urbanization indicators and the trade-off between CS and WP (p < 0.05), and the magnitude of the correlation increased with scale. The relationship between ES trade-offs and urbanization was mostly U-shaped and inverted U-shaped at the grid scale, but N-shaped and inverted N-shaped at the town scale. This study provides information that could be used for multi-scale urban planning.

Spatial and temporal variation of multiple eco-environmental indicators in Erhai Lake Basin of China under land use transitions

Environmental degradation is a global ecological concern, and land use transitions play a critical role in a region's ecological well-being and long-term sustainability. In this paper, indicators related to land use transitions, including the regional eco-environmental quality index (EV), the remote sensing ecological index (RSEI), and soil erosion, are selected to analyze the eco-environmental quality of Erhai Lake Basin from 2000 to 2020. The results showed that (1) from 2000 to 2020, forestland, grassland, and cultivated land were the major land use types in the study region, and also the land use types where land use transition was notable; (2) over the 20 years of study, the EV value of Erhai Lake Basin increased by 0.003, its average RSEI increased by 0.14, and the average soil erosion modulus there decreased by 15.48 t/(km²·a), indicating that the eco-environment of the Erhai Lake Basin was improving. Evaluation based on multiple ecological indicators was superior to assessment relying on single indicators; (3) all three ecological indicators showed that the ecological environment of the basin was improving, but with significant regional differences. Forestland had the best ecological quality, while unused land and built-up land had the worst. RSEI was more regionally adaptable than the other two indices. (4) The transition of cultivated land into other land use types was the main reason for the improved ecological quality in the basin, while tourism had accelerated land use transformation. Compared with assessment based on single ecological indicators, evaluation based on a combination of multiple ecological indicators can more accurately reflect the ecological condition of the study area and provide a basis for eco-environmental protection in Erhai Lake Basin.

Impact of human activities on phosphorus flows on an early eutrophic plateau: A case study in Southwest China

The net anthropogenic phosphorus inputs (NAPI) model has been used extensively to assess changes in phosphorus (P) inputs and cycling in the environment. However, temporary populations have generally been unconsidered in these assessments. In this study, the NAPI model was used to estimate P loads from the 16 towns and villages in the Erhai Lake Basin (ELB), Southwest China and to evaluate the potential impact from temporary residents (tourism). The results showed that the average value P inputs in the basin (estimated at 2384 kg P km^-2 year^-1) were 5 times the national average level, and that temporary residents contributed 1%. Agriculture accounted for most of the net P, with chemical fertilizers (55% of the inputs) as the main source, followed by food and animal feed. Only 9.54% of the P inputs to the basin were exported. River water quality and NAPI were significantly correlated (P < 0.01). Tourism industry contributes significantly to regional economic growth and prosperity, but its beneficial effects on the economy does not equate with the adverse impact on environment. This study illustrates what is happening in Southwest China and provides scientific evidence that shows we need to find novel ways to reduce nutrients.