Paradox of lake nitrogen concentration change response to watershed management: Case study of China

Abstract

Human activities have caused rapid increases in lake nutrient loads over the past few decades, resulting in severe eutrophication. To mitigate eutrophication in lakes, watershed management is conducted worldwide. After decades of watershed environmental management practices, some lakes have significantly improved in water quality, whereas others continue to deteriorate. Differentiations in watershed environmental management practices have been a conundrum for watershed managers for many years. This study analyzed over 20 years of nitrogen concentration data from 13 different types of lakes in China, exploring the driving forces behind water quality changes. The results showed that agricultural nitrogen management has emerged as a predominant driver of lake nitrogen concentration changes, with the impacts of climatic factors diminishing post-transition. Two obstacles hinder the achievement of water quality goals: time lags and climate change. The time lag between agricultural management measures and water quality improvements maybe decades. Meanwhile, climate change, especially extreme weather events, introduces uncertainties that may trigger short-term deterioration. Despite the uncertainty surrounding lake nitrogen concentration changes, lakes with advanced governance structures still exhibited greater resilience to climatic changes compared to those in the early stages of environmental management. To improve water quality, more efforts and patience are required.