Carbon burial by shallow lakes on the Yangtze floodplain and its relevance to regional carbon sequestration

Abstract Floodplain lakes may play an important role in the cycling of organic matter at the landscape scale. For those lakes on the middle and lower reaches of the Y angtze ( MLY ) floodplain which are subjected to intense anthropogenic disturbance, carbon burial rates should, theoretically, be substantial due to the high nutrient input, increased primary production and high sediment accumulation rates. There are more than 600 lakes >1 km 2 on the Y angtze floodplain including 18 lakes >100 km 2 and most are shallow and eutrophic. 210 Pb ‐dated cores were combined with total organic carbon ( TOC ) analyses to determine annual C accumulation rates ( C AR ; g C m −2 yr −1 ) and the total C stock (since ~1850). The sediment TOC content is relatively low with an average <2% in most lakes. C AR ranged from ~5 to 373 g C m −2 yr −1 , resulting in C standing stocks of 0.60–15.3 kg C m −2 (mean: ~5 kg C m −2 ) since ~1850. A multicore study of C haohu lake (770 km 2 ) indicated that spatial variability of C burial was not a significant problem for regional upscaling. The possible effect of changes in lake size and catchment land use on C burial was examined at T aibai lake and indicated that lake shrinkage and declining arable agriculture had limited effects on C AR . The organic C standing stock in individual lakes is, however, significantly dependent on lake size, allowing a simple linear scaling for all the MLY lakes. Total regional C sequestration was ~80 Tg C since ~1850, equivalent to ~11% of C sequestration by soils, but in ~3% of the land area. Shallow lakes from MLY are a substantial regional C sink, although strong mineralization occurs due to their shallow nature and their role as C sinks is threatened due to lake drainage.