No abstract

Aquatic ecological health is a global challenge due to its significant impacts, and a real-time method to accurately assess the ecological health is therefore particularly useful. Based on the hydrological, water quality, meteorological, and topographic data collected from field observations and organizations, this study developed a process-based hydrodynamic and water quality model using an environmental fluid dynamics code (EFDC) model of Lake Poyang to simulate the spatiotemporal variations in water levels and the total nitrogen (TN), total phosphorus (TP), and chlorophyll a (Chl a) contents. Compared with the measured values, the models were confirmed to be reliable and acceptable. Then, to achieve a real-time assessment, the simulated results were calculated and transformed into five ordinal rating categories by using a lake ecosystem health assessment framework. Our research revealed the following results: (1) the highest and lowest 10-day water level statuses indicated that the hydrological conditions of this lake were at “good” or “excellent” levels. (2) The health levels of TN were mostly at the “fair” level or below, and most of the real-time assessment health curves of lake zones were close to the single peak type. (3) The TP contents were often at “good” levels, and the health assessment curves of the lake zones exhibited downward trends during the periods of rapid rise or retreat. (4) A fluctuating characteristic was found in the health assessment of Chl a with at least two declining peaks in all lake zones. This study demonstrated the high value of physics-based models for assessing the ecological health of aquatic ecosystems in a robust and accurate manner.

Exploring the value of cultivated land resources around big cities is an important prerequisite for when realizing the “trinity” of cultivated land protection in terms of quantity, quality, and ecology. At present, the value of cultivated land resources faces the problem of having a low comparative efficiency of economic output, inadequate visualisation of asset value, and serious undervaluation. The manifestation of social, ecological, and cultural values in cultivated land plays an important role in accurately calculating the value of cultivated land. Therefore, this study attempted to clarify the composition and account for the logic of the comprehensive value of cultivated land around big cities. Taking the Hefei metropolitan area as an example, we used mathematical modeling and geostatistical analysis to measure the integrated value of cultivated land around big cities from 2010 to 2020 and analyse the spatial and temporal evolution characteristics and influencing factors. The results revealed a 2:7:1 ratio of economic, social, ecological, and cultural values for cultivated land in the metropolitan area. The comprehensive value of cultivated land was higher in 2020 than in 2010, was approximately 7.7 times the current compensation standard, and was significantly affected by the natural geography, economic development, cultivated land conditions, and protection policies. Furthermore, the comprehensive value showed spatial differentiation characteristics of ‘high in the east and south and low in the west and north’, and a spatial agglomeration effect was evident in some areas. A significant increase was observed in the social value of cultivated land, followed by an increase in the ecological and cultural values, whereas a slow downward trend was observed for the economic value. The economic value of cultivated land around big cities showed a downward trend, whereas the social, ecological, and cultural values showed upward trends. In the future, differentiated policy tools should be adopted based on the spatial heterogeneity of the comprehensive value of cultivated land in the Hefei metropolitan area to enhance their comprehensive value. In addition, scientific and reasonable compensation standards should be established, and high-quality agricultural development with the high-level protection of cultivated land should be promoted in metropolitan areas.