Abstract
Nitrogen and phosphorus excessive enrichment are major causes of water eutrophication, and variations in nutrients enrichment are strongly influenced by human activities. In this study, annual average water quality from 2001 to 2018 was used to explore the spatiotemporal variations in total nitrogen (TN) and total phosphorus (TP) and their relationships with human activities. Spatially, TN and TP concentrations exhibited significant variations across the five sub-lake zones, and their values were relatively higher in the NW lake zone than the other sub-lake zones. Temporally, TN concentration exhibited weak correlations with years in the NW (R2 = 0.37, p < 0.05) and NE (R2 = 0.43, p < 0.05) lake zones and significant and positive correlations with years in the SW (R2 = 0.62, p < 0.05), SE (R2 = 0.79, p < 0.05), and C (R2 = 0.84, p < 0.05) lake zones. TP concentration exhibited decreasing trends in all lake zones except the NW lake zone (R2 = 0.37, p < 0.05), its value shows a relatively low level and is the restrictive factor to algal growth. The trophic state of the Lake Qiandaohu was determined as mesotrophic. Gross domestic product (GDP) and construction land exhibited strong correlations with TN and TP. Moreover, agriculture nonpoint source pollution was the largest contributor to the excessive enrichment of TN and TP, resulting in water eutrophication. In addition, aquaculture was another major source of nutrients starting in 1999. Although the managers of Lake Qiandaohu implemented a protection-oriented fishery policy, good results cannot be easily achieved with a unilateral policy concerning environmental protection. Thus, comprehensive policies may be more effective than unilateral policies.
Highlights
Freshwater is an indispensable resource and essential for most life [1]
total nitrogen (TN) ranged from 0.55 ± 0.06 mg/L to 1.39 ± 0.15 mg/L, with an average of 0.88 ± 0.05 mg/L
The SW lake zone had the lowest average TN value (0.71 ± 0.03 mg/L), and the C lake zone and SE lake zone were in the middle position values of 0.85 ± 0.07 mg/L and 0.80 ± 0.04 mg/L, respectively
Summary
Freshwater is an indispensable resource and essential for most life [1]. It accounts for 2.5% of all freely available water resources on the Earth’s land surface, of which only 0.3% is available in lakes, reservoirs, and rivers [2]. Throughout the last few centuries, human activities and the excess use of freshwater resources for a variety of purposes have resulted in large-scale contamination or pollution of water [3]. These negative impacts have resulted in water bodies with poor water quality, limited potential use, water eutrophication, and even the degradation of aquatic ecosystems [4,5,6]. A high eutrophication status and algal blooms in Lake Dianchi in China were observed as early as 1977 [7]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call