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首页> 外文期刊>Journal of Marine Research >Carbon cycling in mesohaline Chesapeake Bay sediments 2: Kinetics of particulate and dissolved organic carbon turnover
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Carbon cycling in mesohaline Chesapeake Bay sediments 2: Kinetics of particulate and dissolved organic carbon turnover

机译：中盐在切萨皮克湾沉积物中的碳循环2：颗粒动力学和溶解的有机碳周转

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Temporal and depth variations in benthic carbon metabolism rates were examined in relation to particulate organic carbon (POC) deposition rates and particulate and dissolved organic carbon degradation kinetics in two sediments from the mesohaline region of Chesapeake Bay. The depth distribution of a single pool of metabolizable POC (MPOC) in mid-Bay sediments was estimated by curve-fitting of dry weight POC profiles (″1-G″ approach). Estimated MPOC pools accounted for 3-4% of total POC content in the upper 10 cm of sediment. First-order MPOC decay constants of ≈ 10 yr~(-1) during the warm season were estimated from the ratio of MPOC pool size to weighted-average MPOC deposition rate derived from mid-water column sediment trap deployments. These results indicated that the MPOC pool defined by the 1-G approach corresponded to the most readily degradable component of coastal marine phytoplankton detritus. Transient-state kinetic models of MPOC turnover, based on observed MPOC deposition rates and temperature-dependent mineralization, predicted MPOC accumulation in sediments during the spring followed by depletion during the summer. The models also predicted an early summer maximum in MPOC mineralization rate associated with the degradation of MPOC accumulated during the spring, in agreement with the seasonal pattern of sulfate reduction rates in mid-Bay sediments. Model results suggested that MPOC deposition during the summer is important in maintaining high rates of benthic carbon metabolism throughout the warm season. Steady-state and transient-state models of depth-dependent POC degradation suggested that particle mixing influences the depth distribution of MPOC concentration and turnover rate within the upper 4-6 cm of mid-Bay sediments. However, because of the rapid rate of MPOC decay, random particle mixing is unlikely to transport significant quantities of MPOC below 4-6 cm. A steady-state diagenetic model was used to test the hypothesis that downward diffusion of acetate produced by anaerobic decomposition of MPOC in the upper 4-6 cm fuels sulfate reduction deeper in the sediment. The results suggest that because of the very rapid turnover of acetate pools ( ≥ 2 hr~(-1)), acetate diffusion does not influence the depth distribution of carbon metabolism in the sediment. Therefore, sulfate reduction occurring at depths below 4-6 cm must be fueled by decomposition of some portion of the large pool of relatively refractory sediment POC. Degradation of this material is likely responsible for ≈ 1/3 of total warm season benthic carbon metabolism.
机译：与切萨皮克湾中盐区的两种沉积物中的底质碳代谢速率的时间和深度变化有关，与颗粒有机碳（POC）的沉积速率以及颗粒和溶解的有机碳降解动力学有关。通过干重POC曲线的曲线拟合（“ 1-G”方法）估算了海湾中部沉积物中单个可代谢POC（MPOC）池的深度分布。估计的MPOC池占沉积物上部10 cm的POC总量的3-4％。根据MPOC池大小与中水柱沉积物捕集阱部署的加权平均MPOC沉积率之比估算出暖季期间一阶MPOC衰减常数≈10 yr〜（-1）。这些结果表明，由1-G方法定义的MPOC库对应于沿海海洋浮游植物碎屑中最容易降解的成分。基于观察到的MPOC沉积速率和与温度有关的矿化作用，MPOC转换的瞬态动力学模型预测了春季MPOC在沉积物中的积累，然后在夏季逐渐枯竭。这些模型还预测了夏季初MPOC矿化速率的最大值与春季积累的MPOC的降解有关，这与海湾中部沉积物的硫酸盐还原速率的季节性模式一致。模型结果表明，夏季的MPOC沉积对于在整个暖季期间维持较高的底栖碳代谢率非常重要。深度依赖的POC降解的稳态和瞬态模型表明，颗粒混合影响中海湾沉积物上部4-6 cm内MPOC浓度的深度分布和周转速率。但是，由于MPOC的快速衰减，随机颗粒混合不太可能在4-6 cm以下传输大量的MPOC。使用稳态成岩模型来检验以下假说：由MPOC厌氧分解产生的乙酸盐向下扩散到上部4-6 cm处使沉积物中的硫酸盐还原更深。结果表明，由于乙酸盐池的快速周转（≥2 hr〜（-1）），乙酸盐的扩散不会影响沉积物中碳代谢的深度分布。因此，在4-6厘米以下的深度发生的硫酸盐还原反应必须通过分解大量相对难熔的沉积物POC的某些部分来促进。这种材料的降解可能是整个温暖季节底栖碳代谢的约1/3的原因。

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