Trends of carbon and nutrient accumulation through time in the Andong salt marsh,Hangzhou Bay,China

Salt marshes are important carbon and nutrient sinks that are threatened by climate changes and human activities.In this study,the accumulation rates of sedimentary total organic carbon(TOC),total nitrogen(TN),and total phosphorus(TP)from two cores in the Andong salt marsh,Hangzhou Bay,were investigated to determine whether TOC,TN,and TP show increasing or decreasing trends toward the present.The TOC accumulation rates at the relatively lower marsh were lower during 1990-1996(1.63-2.37 g/(cm^(2)·a))than 1997-2014(1.15-4.30 g/(cm^(2)·a)).The TN accumulation rates increased from 1990(0.14 g/(cm^(2)·a))toward 2012(0.40 g/(cm^(2)·a)),then decreased toward 2014(0.16 g/(cm^(2)·a)).The TP accumulation rates were lower during 1990-1999(0.10-0.21 mg/(cm^(2)·a)),and decreased from 2000(0.32 mg/(cm^(2)·a))toward 2014(0.15 mg/(cm^(2)·a)).The TOC accumulation rates along the relatively upper marsh during 1982-1992(1.18-3.25 g/(cm^(2)·a))were lower than during 1998-2010(2.30-4.20 g/(cm^(2)·a)),and then decreased toward 2015(2.15 g/(cm^(2)·a)).TN increased from 1982(0.18 g/(cm^(2)·a))to 2005(0.41 g/(cm^(2)·a)),then decreased toward 2015(0.22 g/(cm^(2)·a)).TP accumulation rates fluctuated within a narrow range during 1982-1997(0.21-0.41 mg/(cm^(2)·a)),increased from 1998(0.50 mg/(cm^(2)·a))to 2004(0.87 mg/(cm^(2)·a)),then decreased to 2015(0.38 mg/(cm^(2)·a)).Thus,increases in accumulation rates of TOC,TN,and TP from the 1980s to 1990s indicates that the marsh likely served as carbon and nutrient sinks,then the rates decreased during 2000-2015 due probably to the reduced sediment inputs from rivers and intensified sea level rise.