We studied the sequence of climatic and hydrological events associated with the formation of peat during the Holocene, using pollen, diatoms and environmental magnetism from peat cores at three locations in the Sacramento-San Joaquin Delta of California: Browns Island, Franks Wetland and Webb Track Levee. Our data show that peat first formed under relatively dry conditions in a freshwater environment before 6.5 ka BP. Subsequently, pollen accumulation rates were highest prior to intervals with high peat accretion rates but are inversely correlated with organic accumulation rate. Intervals of high peat accretion were preceded by pulses of terrigenous material. During intensive drainage episodes, high flows delivered abundant, coarser-grained sediment to the marshes, which inundated the existing vegetation and decreased the rate of biochemical decay. The build-up of undecomposed organic material led to the acceleration of peat accretion. Our data support the rarely discussed hypothesis that most of the peat in the Sacramento-San Joaquin Delta formed in freshwater marshes that were fed by rivers draining from the Sierra Nevada, rather than in saltwater wetlands resulting from sea level rise and estuarine submergence. This result has important implications for current attempts to remediate and restore the Delta ecosystem.

我们利用加利福尼亚萨克拉门托-圣华金三角洲三个地点的泥炭芯的花粉、硅藻和环境磁力研究了与全新世泥炭形成相关的气候和水文事件序列：布朗斯岛、弗兰克斯湿地和韦伯轨道堤坝。我们的数据表明，泥炭首先在 6.5 ka BP 之前在淡水环境中相对干燥的条件下形成。随后，花粉积累率在泥炭积累率高的区间之前最高，但与有机积累率呈负相关。高泥炭堆积的间隔之前是陆源物质的脉冲。在密集的排水事件中，高流量向沼泽输送了大量粗粒沉积物，淹没了现有植被并降低了生化腐烂率。未分解的有机物质的堆积加速了泥炭的生长。我们的数据支持很少讨论的假设，即萨克拉门托-圣华金三角洲的大部分泥炭形成于由内华达山脉流出的河流供给的淡水沼泽，而不是海平面上升和河口淹没导致的咸水湿地。这一结果对当前修复和恢复三角洲生态系统的尝试具有重要意义。