Assessing Impacts of Changes in External Nutrient Loadings on a Temperate Chinese Drinking Water Reservoir

Qingchuan Chou,Erik Jeppesen,Fenjuan Hu,Tobias K Andersen,Xiaolin Zhang,Te Cao,Leyi Ni,Weiyu Chen,Dennis Trolle,Anders Nielsen

doi:10.3389/fenvs.2021.632778

Abstract

The safety of drinking water is constantly being evaluated. In the last few decades, however, many drinking waters sources in the world, including in China, have undergone serious eutrophication and consequently water quality deterioration due to anthropogenic induced stressors such as elevated external nutrient inputs. In this study, we used the state-of-the-art complex, dynamic, mechanistic model GOTM-FABM-PCLake (a coupled one-dimensional hydrodynamic-lake ecosystem model) to quantitatively assess the impacts of external nutrient loading on the temperate Jihongtan reservoir in Shandong Province, China. Simulated values of all variables targeted in calibration (water temperature, dissolved oxygen, total nitrogen, total phosphorus, and chlorophyll a) agreed well with observations throughout the entire calibration and validation period and generally mimicked seasonal dynamics and inter-annual variations as found in the monitoring data. A series of scenarios, representing changed external nutrient loadings (both increasing and decreasing compared to the current nutrient load), were set up to quantify the effects on the reservoir water quality. Changes relative to the current external nutrient load had a significant effect on the simulated TN and TP concentrations in the reservoir. Our impact assessment indicate that TN will meet the Chinese water quality requirements of the water source (Class III) when the external nitrogen load is reduced by 70%, whereas TP will meet the requirements even if the external phosphorus load is increased by 100% relative to current loads. The model predicts progressively higher summer and autumn phytoplankton biomasses in the scenarios with increasing external phosphorus loading and potential toxic cyanobacteria will become more dominant at the expense of diatoms and other algae. Strict control of the external nutrient loading is therefore needed to maintain good drinking water quality in the reservoir.

Highlights

In the past 200 years, many lakes have experienced increasing eutrophication due to anthropogenic increases in the external input of nutrients (Wetzel, 1990; Wetzel, 1992)
Our study applied the coupled hydrodynamic-ecosystem model GOTM-FABM-PCLake (Hu et al, 2016) and the ACPy automatic calibration tool to a temperate reservoir ecosystem combined with a likelihood function as the objective function
We conclude that the performance of the GOTM-FABM-PCLake model complex for Jihongtan reservoir was satisfactory and can be applied in predicting and evaluating the effects of changes in the external nutrient loading on the water quality of the reservoir

Summary

Introduction

In the past 200 years, many lakes have experienced increasing eutrophication due to anthropogenic increases in the external input of nutrients (point and non-point sources) (Wetzel, 1990; Wetzel, 1992). During the past few decades, great efforts and vast amounts of financial resources have been used globally to improve the ecological state of lakes by reducing the external nutrient loadings (Sas, 1989; Jeppesen et al, 2007). Phosphorus was recognized as the critical nutrient for primary production in aquatic ecosystems (Schindler, 1977), but recently focus has been directed at the role of nitrogen in algae blooms (Trolle et al, 2008; Ma et al, 2018). Discussions of the roles of N and P continues, the urgent need to reduce external nutrient loadings to surface waters to protect drinking water resources and to reduce eutrophication, is widely recognized (Conley et al, 2009)

Methods

Results

Conclusion