Elsevier

Science of The Total Environment

Volume 664, 10 May 2019, Pages 865-873
Science of The Total Environment

Excess nutrient loads to Lake Taihu: Opportunities for nutrient reduction

https://doi.org/10.1016/j.scitotenv.2019.02.051Get rights and content
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open access

Highlights

  • Rivers discharged around 61 kton of TDN and 2 kton of TDP to Lake Taihu in 2012.

  • Over half of TDN and TDP loads were from Sub-basins I (north) and IV (south).

  • Diffuse sources contributed 90% to TDN and point sources 52% to TDP to Lake Taihu.

  • To meet critical loads, river export of TDN and TDP needs to be reduced by 46–92%.

  • Opportunities are reducing synthetic fertilizer and improving wastewater treatment.

Abstract

Intensive agriculture and rapid urbanization have increased nutrient inputs to Lake Taihu in recent decades. This resulted in eutrophication. We aim to better understand the sources of river export of total dissolved nitrogen (TDN) and phosphorus (TDP) to Lake Taihu in relation to critical nutrient loads. We implemented the MARINA-Lake (Model to Assess River Inputs of Nutrients to seAs) model for Lake Taihu. The MARINA-Lake model quantifies river export of dissolved inorganic and organic N and P to the lake by source from sub-basins. Results from the PCLake model are used to identify to what extent river export of nutrients exceeds critical loads. We calculate that rivers exported 61 kton of TDN and 2 kton of TDP to Lake Taihu in 2012. More than half of these nutrients were from human activities (e.g., agriculture, urbanization) in Sub-basins I (north) and IV (south). Most of the nutrients were in dissolved inorganic forms. Diffuse sources contributed 90% to river export of TDN with a relatively large share of synthetic fertilizers. Point sources contributed 52% to river export of TDP with a relatively large share of sewage systems. The relative shares of diffuse and point sources varied greatly among nutrient forms and sub-basins. To meet critical loads, river export of TDN and TDP needs to be reduced by 46–92%, depending on the desired level of chlorophyll-a. There are different opportunities to meet the critical loads. Reducing N inputs from synthetic fertilizers and P from sewage systems may be sufficient to meet the least strict critical loads. A combination of reductions in diffuse and point sources is needed to meet the most strict critical loads. Combining improved nutrient use efficiencies and best available technologies in wastewater treatment may be an effective opportunity. Our study can support the formulation of effective solutions for lake restoration.

Keywords

Critical nutrient loads
River export of nutrients
Nutrient sources
Sub-basins
MARINA-Lake
PCLake model

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