Increasing dissolved nitrogen and phosphorus export by the Pearl River (Zhujiang): a modeling approach at the sub-basin scale to assess effective nutrient management

Abstract

The Pearl River (Zhujiang in Chinese) has been exporting excess of nitrogen (N) and phosphorus (P), causing eutrophication in the coastal waters of southern China for decades. However, sources of these nutrients and their locations are not well studied for the Pearl River basin. As a consequence, it is difficult to formulate effective management options to reduce these nutrients in the river and to prevent further eutrophication. We developed a sub-basin model based onto the Global NEWS-2 (Nutrient Export from WaterSheds) model for the period of 1970-2050 to analyze trends in dissolved inorganic N and P (DIN and DIP) and to identify the main sources of these nutrients and their locations. We validated our model by comparing modeled nutrient fluxes with observed. Future analyses are based on Millennium Ecosystem Assessment scenario that assumes a globalized world with a reactive environmental management. DIN and DIP inputs to the coastal waters are calculated to increase by a factor of 2-2.5 between 1970 and 2050. Over two-thirds of the DIN and DIP inputs to the coastal waters stem from two down-stream basins (Zhujiang delta and Dongjiang), where agriculture and sewage are important drivers of this increase. Agriculture accounts for over 40 % of DIN inputs to coastal waters. Sewage and agriculture account for over 90 % of DIP inputs. Thus nutrient management in agriculture and sewage in down-stream areas is more effective in reducing coastal eutrophication than nutrient management in up-and middle-stream areas of the Pearl River basin.

Alarming nutrient pollution of Chinese rivers as a result of agricultural transitions

“…Our study is based on two models: Global NEWS-2 (Nutrient Export from WaterSheds) [16,17] and NUtrient flows in Food chains, Environment and Resources use (NUFER) [18]. Global NEWS-2 is a spatially explicit model that has been applied to analyze nutrient-related problems worldwide [19][20][21][22][23][24][25][26][27][28][29][30] including China [17,[31][32][33]. This model quantifies river export of different nutrients (nitrogen, phosphorus, carbon, silica) in different forms (dissolved inorganic, dissolved organic, particulate) as a function of human activities on land (e.g., agriculture, sewage) and basin characteristics (e.g., hydrology, land use).…”

Temporal and spatial variations of net anthropogenic nitrogen inputs (NANI) in the Pearl River Basin of China from 1986 to 2015

“…However, there are few studies on the evaluation of N sources from human activities in the Pearl River Basin. A recent study estimated DIN and dissolved inorganic phosphorus (DIP) between 1970~2050 using the Global NEWS-2 model, and pointed out that it was difficult to identify the key areas of N source input by estimating NANI from provincial scale data [36]. In order to improve the management of N in the watershed, it is necessary to estimate NANI at the level of the Pearl River Basin, as well as investigate the N source emission patterns of sub-basins.…”

Modeling increased riverine nitrogen export: Source tracking and integrated watershed-coast management

“…Global NEWS-2 is an ideal tool for management purposes in data-poor regions such as China's coastal watersheds because it requires mainly social-economic input data and simple model parameters. The model has been applied to large Chinese rivers including the Pearl River (Strokal et al, 2015) and the Yangtze River (Yan et al, 2010). However, how the model assists in controlling nutrient pollution is still under studied.…”