We report organic carbon (OC) accumulation rates in three freshwater ecosystems in southern Brazil, along the largest shallow coastal lagoon ecosystem in the world, the Patos-Mirim-Mangueira. After European colonisation in the seventeenth century, regional wetlands started being replaced by agricultural fields (mostly rice). We used excess ²¹⁰Pb to develop chronologies for lagoon sediment cores and quantify bulk sediment and OC accumulation rates. In the past 120 years, OC accumulation rates in Mirim and Mangueira Lagoons, which are influenced by rice paddies, averaged 14.9 ± 8.5 and 6.4 ± 3.7 g C m⁻² year⁻¹, respectively. Greater accumulation rates were estimated for macrophyte-dominated Nicola Lake (69.9 ± 38.5 g C m⁻² year⁻¹) located within the protected Taim Wetland with no direct influence of rice plantations. Starting in the early twentieth century, the construction of dams and drainage canals altered regional hydrology. Despite these anthropogenic changes, only a mild increase in OC accumulation was observed in Mirim Lagoon (15% only in site MIR2) after 1970. Mangueira Lagoon experienced the lowest OC burial rates despite increasing sedimentation rate and OC burial after the mid-1970s. This is probably because these large lakes (> 500 km²) have great nutrient-dilution potential, and their well-mixed water columns prevent nutrients from accumulating in the sediments over time.

我们报告了巴西南部三个淡水生态系统中的有机碳（OC）累积率，以及世界上最大的浅海泻湖生态系统Patos-Mirim-Mangueira。在17世纪欧洲殖民之后，区域性湿地开始被农业领域（主要是稻米）取代。我们使用了过量的²¹⁰ Pb来开发泻湖沉积物芯的年代，并量化了大量沉积物和OC的积累速率。在过去的120年中，受稻田影响的Mirim和Mangueira泻湖中的OC累积率分别平均为14.9±8.5和6.4±3.7 g C m - ² 年^-1。据估计，以大型植物为主的尼古拉湖的蓄积率更高（69.9±38.5 g C m - ² 年^-1）位于受保护的塔伊姆湿地内，没有水稻种植园的直接影响。从20世纪初开始，水坝和排水渠的建设改变了区域水文学。尽管发生了这些人为变化，但1970年以后，在Mirim泻湖中仅观察到了OC累积量的轻度增长（仅在MIR2站点中增加了15％）。尽管在1970年代中期之后沉积率和OC埋藏有所增加，Mangueira泻湖的OC掩埋率却最低。这可能是因为这些大型湖泊（> 500 km ²）具有很大的养分稀释潜力，而且它们充分混合的水柱会阻止养分随时间推移而积聚在沉积物中。