Comparison of phosphorus fraction distribution and influencing factors of suspended and surface sediments in the Tiaoxi watershed, China

Abstract

Suspended and surface sediments from the Tiaoxi watershed, fed by the Xitiaoxi and Dongtiaoxi rivers, were analyzed for total phosphorus (TP) and the inorganic P fractions of loosely adsorbed P that were extractable with NHCl (NHCl-P), reductant P (BD-P), metal oxide-bound P extractable with NaOH (NaOH-P), and calcium-bound, HCl-extractable P (HCl-P), while other physicochemical compositions were also determined. The spatial variations of P fractions in these sediments were investigated, and the major factors influencing the various fractions were explored by multivariate statistics. Compared to surface sediments, suspended sediments contained considerably higher concentrations of total nitrogen, TP, organic matter, Al, Fe, Mn and biologically available P (BAP, given as NHCl-P, BD-P and NaOH-P combined) and lower concentrations of Si, Ca and HCl-P in the studied catchments. Dongtiaoxi sediments had higher TP, inorganic phosphorus and HCl-P concentrations and a lower BAP content compared with Xitiaoxi sediments, trends that were associated with local geological backgrounds, landscapes and anthropogenic characteristics. The results of principal component analysis showed different effects of sediment properties on P fraction distributions for Xitiaoxi and Dongtiaoxi sediments. The sediment components and structure exert a strong influence on BAP in Xitiaoxi sediments, in contrast to Dongtiaoxi sediments, where P fractions are mainly affected by urbanization and other anthropogenic activities such as shipping.

Risk Assessment Based on Nitrogen and Phosphorus Forms in Watershed Sediments: A Case Study of the Upper Reaches of the Minjiang Watershed

“…TP was measured by the alkali melting molybdenum antimony resistance spectrophotometry [17]. The particle size distributions of the sediments including clay (< 4 μm), silt (4~64 μm), and sand fractions (> 64 μm) were determined by the Mastersizer 2000 (Malvern, UK) [13,15]. The major elements (Ca, Al, Fe, Mn and Si) were determined using X-ray fluorescence spectrometer (PW2440, Philips, Almelo, The Netherlands).…”

“…Indeed, HCl-P is the most stable form and can be regarded as a permanent sink of phosphorus. In other words, IP is difficult to be utilized by organisms [13,19,20]. The extraction processes of phosphorus are shown in Figure 2b.…”

“…The extraction processes of phosphorus are shown in Figure 2b. Each phosphorus fraction was quantitatively assessed by the molybdenum blue/ascorbic acid method [13,15]. The experiments were repeated three times and the relative deviations of the results were controlled below 5%.…”

“…TP in sediments can be divided into inorganic phosphorus (IP) and organic phosphorus (OP). IP can be divided into weakly adsorbed phosphorus (NH 4 Cl-P), reduced phosphorus (BD-P), metal oxide bound phosphorus (NaOH-P) and calcium bound phosphorus (HCl-P) [13,19]. Among them, NH 4 Cl-P, BD-P and NaOH-P are the bioavailable forms of phosphorus (where BAP = NH 4 Cl-P + BD-P + NaOH-P = IP-HCl), while HCl-P primarily comes from clastic rocks and autogenous sources [13,15].…”

“…Thus, these indices cannot accurately reflect the nutrient release, migration and biological activity in sediments. Since bio-availability and environmental geochemical behaviors are related to the forms of nitrogen and phosphorus in sediments [12,13], there is an urgent need for a comprehensive assessment method based on the biological effective index, considering both the total amount of nitrogen and phosphorus and their ecologically bioavailable fractions. Accurate and effective evaluation of the comprehensive eco-environmental effects of nutrient elements in sediments is of great significance.…”