Defining Reference Nutrient Concentrations in Southeast Eco‐Region Lakes, China

Abstract

Establishing nutrient reference conditions of lakes in eco‐region is beneficial to set realistic restoration targets and guide regulation of water bodies, and aid in the analysis of economic losses derived from eutrophication. In this paper, total phosphorus (TP), total nitrogen (TN), Secchi depth (SD), and planktonic chlorophyll a (Chl‐a) reference conditions in Southeast eco‐region lakes were calculated using lake population distribution method and trisection method. The results indicated that the two methods provided consistently similar values to our predicted baselines of TP, TN, SD, and Chl‐a. Furthermore, multiple linear regression model prediction and a novel extrapolation approach by combining optimal map recognition with pattern recognition inverse mapping were developed for estimating reference nutrient concentrations. Although there is no clear recommendation about the best method for determining nutrient reference values, reference values determined by these methods were nearly consistent for all parameters. The values and ranges considered as nutrients reference conditions for Southeast eco‐region lakes were given as follows: 0.020–0.025 mg/L TP, 0.55–0.65 mg/L TN, 1.6–2.50 mg/m3 Chl‐a, 2.00–2.50 m SD. Overall, the results suggest that multiple linear regression and extrapolation approach can be used to define reference conditions, and the reference condition corresponds to mesotrophic status in Southeast eco‐region lakes.