T/CSES 05-2019 Lakes algal control process water quality target management technical guidelines for evaluating lake nutrient status using the Nutrient Footprint Index (TFI) method

Scope

Main technical content: 1. Collect historical data of lakes: The main water quality indicators are CHLa (or transparency), TP, and TN. Auxiliary indicators include annual outflow from the lake and the lake volume at the average annual water level, as well as the average annual water temperature at the lake hydrological station or the average annual temperature at the meteorological station. 2. Conduct time-filtering of CHLa, TP, and TN by individual indicators, then establish a two-dimensional filtering trajectory diagram of CHLa versus TP and TN. Adjust the filtering cycle and optimize the relationship between filtering bandwidth W and filtering period T, with W approximately equal to 2T. The recommended filtering method is LOESS (Local Weighted Smoothing), which retains the trend signal of low-frequency components while removing high-frequency random and cyclical signals. The minimum value of W is 5, and the upper limit of W is generally limited by the length of the data. For longer data, the upper limit can be set to 22, corresponding to the main solar cycle period (since lakes primarily obtain energy from solar radiation, and the fluctuations of various background environmental factors are influenced by this cycle). Alternatively, spectral analysis of the annual CHLa data series can be conducted to identify quasi-periodic patterns, with the first main cycle T1 as the focus. If both T1 and T2 are relatively short, the product of the two periods can also be used as the focus. For shorter data, the upper limit of W is generally not more than half of the total data. 3. Select the trajectory diagram. By comparing trajectories with different W values, a trajectory with relatively smooth curves and clear inflection points (period T) can be selected as the modeling object. 4. Based on the trajectory diagram, follow the chronological order from the starting point to the inflection point to the ending point. 5. Conduct segmented and standardized analysis of nutr

Development Information

Related Standards