Aquaculture Production is a Large, Spatially Concentrated Source of Nutrients in Chinese Freshwater and Coastal Seas

Abstract

As Chinese aquaculture production accounts for over half of the global aquaculture production and has increased by 50% since 2006, there is growing concern about eutrophication caused by aquaculture in China. This paper presents a model-based estimate of nutrient flows in China’s aquaculture system during 2006–2017 using provincial scale data, to spatially distribute nutrient loads with a 0.5° resolution. The results indicate that with the increase in fish and shellfish production from 30 to 47 million tonnes (Mt) during 2006–2017, the nitrogen (N) release increased from 1.0 to 1.6 Mt/year and that of phosphorus (P) from 0.1 to 0.2 Mt/year. Nutrient release from freshwater aquaculture was concentrated in Guangdong, Jiangsu, and Hubei, and that from mariculture in Shandong, Fujian, and Guangdong. Aquaculture is an important strongly concentrated nutrient source in both freshwater and marine environments. Its nutrient release is >20% of total nutrient inputs to freshwater environments in some provinces, and nutrients from mariculture are comparable to river nutrient export to Chinese coastal seas. Aquaculture production and nutrient excretions are now comparable to those of livestock production systems in China and need to be accounted for when analyzing causes of eutrophication and harmful algal blooms and possible mitigation strategies.

Spatially Explicit Inventory of Sources of Nitrogen Inputs to the Yellow Sea, East China Sea, and South China Sea for the Period 1970–2010

“…Riverine export and atmospheric deposition are responsible for most of the nitrogen inputs in most coastal areas (Figures 6 and S8). However, with the rapid increase in fish and shellfish production in marine waters particularly in China (Wang et al, 2020), mariculture is now locally as important as riverine export and atmospheric deposition (Figure S8).…”

“…However, our results indicate that much of the nitrogen load is from population centers close to the coast, and an initial policy focus on these regions may be more effective than on regions more upstream. Only 24% of the nitrogen in feed are retained by the cultured species and 66% are released from China's mariculture system to coastal waters (Wang et al, 2020), which means that the feed efficiency needs to be improved by adopting formulated feed (Cao et al, 2007; Wu, 1995). The policy of zero increase in fertilizer use is a first step toward reducing nitrogen losses from agriculture (Yu et al, 2019; Y. Zhang , 2015), but more stringent reductions may be needed in view of the legacy of the nitrogen that is temporarily stored in aquifers and that may add to future river export (Bouwman, Bierkens, Griffioen, et al, 2013).…”

“…Aquaculture production data per country, species group, sea area, and type of environment are available in units of live weight for the period 1970–2010 from the FISHSTAT database (FAO, 2012). Aquaculture is spatially distributed within provinces or countries on the basis of water body type, population density, and temperature for inland and brackish aquaculture and coastal type, coastline length, and temperature as described by Wang et al (2020). The model scheme is in Figure S4.…”

“…The nitrogen dynamics due to water exchange (e.g., ocean currents) and water‐sediment exchange in the seas were not considered. We used the Integrated Model to Assess the Global Environment–Global Nutrient Model (IMAGE‐GNM) (Beusen et al, 2015, 2016; Bouwman, Beusen, Glibert, et al, 2013; Wang et al, 2020) to estimate the spatial distribution of annual nitrogen inputs from river discharge, submarine fresh groundwater discharge and mariculture to the three Large Marine Ecosystems (LMEs, i.e., Yellow Sea/Bohai Sea, YS/BS; East China Sea, ECS; South China Sea, SCS, Figure 1) that border the coasts of China and several other countries for the period 1970–2010. Estimates of atmospheric nitrogen deposition to the seas were based on TM5‐FAst Scenario Screening Tool (TM5‐FASST) (Figure 2).…”

Green Agriculture and Blue Water in China: Reintegrating Crop and Livestock Production for Clean Water

“…The contribution of the synthetic fertilizers was generally higher to the southern rivers (Yangtze, Pearl) than to the northern rivers (Yellow, Huai, Hai) [12] . Wastewaters [11] and aquaculture [36,37] are also important pollution sources but their contribution varies with scale (e.g., national, basin, sub-basin) [11,37] . At the national scale, livestock and crop production are dominant sources of nutrient pollution in water systems in 2012 [3,12] .…”