Characteristics of phosphorus species identified by 31P NMR in different trophic lake sediments from the Eastern Plain, China

Abstract

Because phosphorus (P) is a vital biogenic element for aquatic ecosystems, a deeper understanding for the turnover of P in lake sediments is much needed. In this study, seven lakes representing major lake types in the Eastern Plain region of China were selected so to identify and quantify the characteristics and lability of sediment P. A relatively new approach called Phosphorus-31 nuclear magnetic resonance spectroscopy (31P NMR) was adopted to detect the different P species in the lake sediments. The experimental results indicate that NaOH–EDTA extraction by 31P NMR analysis is a useful technique for determining and measuring each P compound in the studied shallow lake sediments. Orthophosphate, orthophosphate monoesters and orthophosphate diester are identified as the major chemical forms of phosphorus in the sediments. There is a greater content of these compounds in the sediments of the highly polluted lakes than the less-polluted lakes. Moreover, the content of orthophosphate, orthophosphate monoesters and orthophosphate diester (sediment) is in proportion to the total P and Chla (chlorophyll a) (overlying water) in the lakes of the Eastern Plain, indicating their potential bioavailability. This positive correlation also implies that the role organic P plays in lake eutrophication should be given more attention, particularly for the heavily polluted sediments. Finally, a significant correlation exists between APA and TP and IP in the Eastern Plain lake region. A possible hydrolytic pathway for the various organic phosphorus compounds by APA is also discussed.