Biogechemistry Of Sedimentary Organic Matter And Phosphorus In Rivers And Salt Marsh

In this work,two cores from the Andong salt marsh off Hangzhou Bay were used to study the impact of climate change and human activities on the sedimentary phosphorus(P)fractions;and surface sediments from some Zhejiang rivers such as Qiantang River,Shuang Creek,Jiao River,Ximen Island,Feiyun River and Ao River,were determined for TOC,C/N ratio and lignin phenols in order to study the sources and distribution of sedimentary organic matter in these rivers.The core samples were then compared with previous lignin results,and the river samples were compared with their corresponding P fractions,in order to improve our understanding on the biogeochemistry of sedimentary organic matter and P in these systems.Our results showed that total phosphorus(TP)contents in the Andong salt marsh were quite low(ranged from 14.97 mg/kg to 137.45 mg/kg),indicating almost no P pollution.However,significant positive correlations between TP with OP and NAIP indicate potential for P pollution,as OP and NAIP are easily releasable to the water via decomposition and physical perturbations.C2 has higher concentrations of most P fractions than C1,mainly due to the smaller sediment particle size at C2(ranged from 7.76μm to 33.03 μm;mean = 20.30 μm)compared to C1(25.92 μm to 34.92 μm;mean = 30.4 μm).The super typhoon "Winnie" in 1997 has caused increase in most sedimentary P forms,and the rapid increase of aquaculture in Hangzhou Bay may have lead to the high contents of most P forms after 2000.The Three Gorges Dam and the 2006 drought have reduced sediment input from the Yangtze River Basin,resulting in decrease of sediment accumulation,and thus most P forms,in Andong salt marsh.Study of lignin in Zhejiang rivers showed predominance of non-woody angiosperms.Higher(Ad/Al)v and(Ad/Al)s in Qiantang River and Ximen Island were due to erosion and human activities.The values of(Ad/Al)v of Feyun River and Jiaojiang River varied due to many distributaries discharging into both rivers.Most of the lignins in Ao River and Shuang Creek were moderately degraded.Correlation analyses showed that trends of terrestrial organic matter were similar with OP in Andong salt marsh and most areas of Zhejiang rivers.There were opposite trends between degree of lignin decomposition stage and NAIP,indicating that release of NAIP was more affected by the degradation of lignin in areas which have more human activities.Besides,use of OC/OP molar ratio in conjunction with total lignin,δ13C and C/N ratios showed that the Andong salt marsh has higher abundance of more degraded terrestrial organic matter further down the cores,and there were trends of decrease in abundance of terrestrial organic matter but slight increase in fresher materials towards the present.