Scenario Analysis of Heavy Metal Ecological Risk in Cropland Soils from Livestock and Poultry Manure Application: A Case Study of Hunan Province, China

Abstract

Heavy metals in livestock and poultry manure cause significant contamination; however, there is currently a lack of scenario analysis research on soil pollution risks under the influence of manure application. This study integrated multiple methods, including multi-source data fusion, heavy metal emission accounting, and ecological risk assessment, to investigate regional soil heavy metal pollution risks under baseline and improved scenarios of manure application, using Hunan Province, China, as a case study. The results indicate that pig manure (49.5%) and cattle manure (47.6%) are the primary sources of heavy metal emissions from livestock and poultry manure. The heavy metal loads on cropland (g/ha) were as follows: Cd (0.51), Hg (0.027), As (0.87), Pb (4.69), Cr (5.38), Cu (93.10), Zn (131.05), and Ni (5.07). Among the eight heavy metals, Cd poses the most prominent soil pollution risk. Under the baseline scenario (100% manure application), the study area exhibited an overall moderate ecological hazard level after 37 years of continuous application, with 71.93% of the cropland classified as Risk Level II and 7.04% as Risk Level III. After 184 years, a strong ecological hazard level was reached, with 54.93% of the cropland classified as Risk Level III and 19.64% as Risk Level IV. Under improved scenarios (75%, 50%, and 25% manure application), the overall moderate ecological hazard level was reached after 49, 74, and 147 years of continuous application, respectively. This study provides a theoretical and methodological basis for regional soil heavy metal pollution control and source analysis.