Response of phosphorus in estuaries to soil erosion – A new insight into sediment phosphorus fractions and sources

Phosphorus (P) is a chemical element that can cause lake eutrophication, tracing the source of P in lake sediments is crucial in the management and control of nutrient discharges in a watershed. To combine watersheds with lakes and provide watershed surface feature support for the traceability of sediment P fractions, the estuary was used as the key location collecting sediments. The Revised Universal Soil Loss Equation was used to simulate the spatiotemporal distribution characteristics of soil erosion, the relationship between sediment P fractions to soil erosion was analyzed for different watersheds and buffer zones, thus revealing the mechanism of this relationship. The proportion of P fractions first respond to the manner of P loss in a watershed, then the factors affecting the sediment P fractions are determined. When calcium-bound P (Ca-P) accounted for more than 40% total P (TP), forest land soil erosion plays an important role in increasing the proportion of Ca-P in sediment, the correlation coefficient can reach 0.66 when the soil erosion in mountainous area is large. When P bound by iron oxides or hydroxides (Fe-P) and aluminum-bound P (Al-P) were the main components of TP in sediment, the P fractions in the sediment is affected complexly. The phosphate fertilizer application and arable land soil erosion increased the Fe-P and Al-P contents in sediments. As the buffer distance increased, the correlation coefficient between soil erosion modulus and Fe-P showed a decreasing trend. The adsorption capacity of the sediments for P was influenced by water quality, which led to changes in Fe-P and Al-P contents of sediments over time.Soil erosion has an influence on the P fractions of sediments. Ca-P comes from forest land, while Fe/Al-P are active P, which are affected by phosphate fertilizer, land use, buffer distance and human activities.