Study On Water Footprint Of Freshwater Cultured Fish And Spatial Optimization Of Cultured Policy In China

China’s soaring consumption of animal products aggregates its water scarcity under urbanization.As the dominant player of global aquaculture,China takes up 60%of the world’s production.The current study usually assume the zero water footprints of fish consumption that sources from marine captures.Replacing protein of territory-animal by wild fish-protein is regard as an effective way to conserve water.However,China’s freshwater cultured fish requires massive water-intensive feed from crop,thus generating water footprints,except for discharging pollutants and degrading water quality.Thus,the water footprints of freshwater fed fish can’t be ignored in China.Quantifying this water footprints and optimizing fish-cultured composition is significant to lower water footprint and increase protein and economic outputs.This study quantified the feed,evaporation,discharge grey water footprints and fish meal input of China’s freshwater cultured fish in 28 provinces.Von Bertalanffy model and Monte Carlo simulations were used.Then we predicted the yields of each fish species at national and provincial scales in 2020,and investigated the optimal freshwater cultured fish pattern to minimize water footprints and fish meal consumption,and maximize economic and protein outputs at national and provincial scales.The results are as follows:（1）Grey water footprint of pollutant discharge from freshwater pond-cultured system in China is 2.26-3.49×10¹⁰ m³,national pollutant loadingas of total nitrogen,total phosphours and COD is 61 388 t,11 273 t,592 288 t,respectively.Futhermore,the dominant pollutant varies across provinces:Gray water of 19 provinces are dominiated by COD,and 9 provinces by total phosphours.On projection of provincial fish production at provincial scale by multi-linear regressions,the total discharge of grey water will reach up to 2.85-4.79×10¹⁰ m³;and total nitrogen,total phosphorus and COD will reach up to 8.42-9.59×10⁶ t,1.61-1.83×10⁶ t and 8.70-9.91×10⁷ t.（2）In 2014,China’s total water footprint of freshwater cultured fish is 213.47?10⁹ m³,along with 4.54?10⁹ kg of protein,265.16×10⁹ RMB of economic output and 11.15?10⁵ t of fish meal consumption.The total water footprint of freshwater cultured fish is 0.0038-37.49?10⁵ m³ at provincial scale,along with 0.016-6.13?10⁸ kg of protein,0.14-48.37?10⁹RMB of economic output and 0.00047-1.28?10⁵ t of fish meal consumption.（3）Optimization results show that siginificant difference of fish-cultured pattern exists at both national and provincial scales.Compared to optimal results at provincial scale,the total water footprint,protein and economic outputs,and fish meal consumption are decreasing12.14?10⁹ m³（6%）,0.16?10⁹ kg（3%）,8.62?10⁹ RMB（3%）and 1.10?10⁵ t（14%）,respectively.Furthermore,compared to the simulation rerults in 2020,the total water footprint and fish meal consumption optimal results of provincial scale have declined 11%and 29%,protein and economic outputs have increased 1%and 5%,respectively.China’s freshwater cultured fish generates water footprint due to pollutant discharge,feed input,and evaporation.Thus,replacing territory-animal protein by fish-protein sourced from fish culturing is not necessary benefit water conservation compared with foreign countries where fish is dominated by oceanic captures.Besides,different fish species varies across geopgraphically,optimal cultured policy bottom-to-top has advantage over that of top-to-bottom.