Surface soil distribution of phosphorus fractions in the Yellow River Delta

Phosphorus (P) is an important nutrient for organisms and plays an essential role in regulating primary production in estuarine and marine environments．To investigate spatial distribution of phosphorus fractions and influencing factors in surface soils in the Yellow River Delta wetlands, surface soil samples in typical wetlands were collected in October 2016．TP, IP, OP, Fe/Al-P and Ca-P were extracted by Standard Measurements Testing Program of European Union (SMT)．Average content of surface soil TP in the Yellow River Delta was found to be 581.02 mg·kg⁻¹, higher than that found in the second national soil survey．The contents of various fractions of phosphorus in surface soils followed the sequence of IP , Ca-P , OP, Fe/Al-P．The content of IP was the highest and accounted for 86.98% of TP．Ca-P was the main fraction of IP, accounting for about 85.30% of IP．The distribution of phosphorus in different fractions showed high spatial heterogeneity. Soils near the Yellow River generally had lower TP and IP content, soils with vegetation showed higher OP．Correlation analysis revealed significant negative TP and IP correlations with WC, significant positive OP correlations with soil carbon (w (C)/ w (P), w (TOC) and w (TIC)), and significant positive Fe/Al-P correlations with terrain factor SOS (P < 0.05)．Principal component analysis (PCA) indicated that IP was more related to physicochemical properties of wetlands, while OP was largely related to nutrient level of wetland soil．