This work presents updated reconstructions of watershed runoff to San Francisco Estuary from tree-ring data to AD 903, coupled with models relating runoff to freshwater flow to the estuary and salinity intrusion. We characterize pre-development freshwater flow and salinity conditions in the estuary over the past millennium and compare this characterization with contemporary conditions to better understand the magnitude and seasonality of changes over this time. This work shows that the instrumented flow record spans the range of runoff patterns over the past millennium (averaged over 5, 10, 20 and 100 years), and thus serves as a reasonable basis for planning-level evaluations of historical hydrologic conditions in the estuary. Over annual timescales we show that, although median freshwater flow to the estuary has not changed significantly, it has been more variable over the past century compared to pre-development flow conditions. We further show that the contemporary period is generally associated with greater spring salinity intrusion and lesser summer–fall salinity intrusion relative to the pre-development period. Thus, salinity intrusion in summer and fall months was a common occurrence under pre-development conditions and has been moderated in the contemporary period due to the operations of upstream reservoirs, which were designed to hold winter and spring runoff for release in summer and fall. This work also confirms a dramatic decadal-scale hydrologic shift in the watershed from very wet to very dry conditions during the late 19th and early 20th centuries; while not unprecedented, these shifts have been seen only a few times in the past millennium. This shift resulted in an increase in salinity intrusion in the first three decades of the 20th century, as documented through early records. Population growth and extensive watershed modification during this period exacerbated this underlying hydrologic shift. Putting this shift in the context of other anthropogenic drivers is important in understanding the historical response of the estuary and in setting salinity targets for estuarine restoration. By characterizing the long-term behavior of San Francisco Estuary, this work supports decision-making in the State of California related to flow and salinity management for restoration of the estuarine ecosystem.

中文翻译：

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通过整合年轮和建模数据支持恢复决策：重建过去千年旧金山河口的水流和盐度

这项工作展示了从树木年轮数据到公元 903 年对旧金山河口流域径流的更新重建，以及将径流与淡水流到河口和盐度侵入相关的模型。我们描述了过去千年河口开发前淡水流量和盐度条件的特征，并将这种特征与当代条件进行比较，以更好地了解这段时间变化的幅度和季节性。这项工作表明，仪器化流量记录跨越了过去千年（平均超过 5、10、20 和 100 年）的径流模式范围，从而为河口历史水文条件的规划级评估提供了合理的基础. 在每年的时间尺度上，我们表明，尽管流入河口的淡水流量中值没有显着变化，与开发前的流动条件相比，它在过去的一个世纪里变化更大。我们进一步表明，相对于开发前时期，当代时期通常与更大的春季盐度入侵和较小的夏秋季盐度入侵有关。因此，夏季和秋季月份的盐渍入侵在开发前条件下很常见，并且由于上游水库的运行而在当代得到缓和，这些水库旨在保持冬季和春季径流以在夏季和秋季释放。这项工作还证实了 19 世纪末和 20 世纪初流域从非常潮湿到非常干燥的十年尺度水文变化。虽然并非史无前例，但这些转变在过去千年中只出现过几次。正如早期记录所记载的那样，这种转变导致了 20 世纪前三个十年的盐度入侵增加。这一时期的人口增长和广泛的流域改造加剧了这种潜在的水文变化。将这种转变放在其他人为驱动因素的背景下，对于理解河口的历史反应和为河口恢复设定盐度目标很重要。通过表征旧金山河口的长期行为，这项工作支持加利福尼亚州有关恢复河口生态系统的流量和盐度管理的决策。这一时期的人口增长和广泛的流域改造加剧了这种潜在的水文变化。将这种转变放在其他人为驱动因素的背景下，对于理解河口的历史反应和为河口恢复设定盐度目标很重要。通过表征旧金山河口的长期行为，这项工作支持加利福尼亚州有关恢复河口生态系统的流量和盐度管理的决策。这一时期的人口增长和广泛的流域改造加剧了这种潜在的水文变化。将这种转变放在其他人为驱动因素的背景下，对于理解河口的历史反应和为河口恢复设定盐度目标很重要。通过表征旧金山河口的长期行为，这项工作支持加利福尼亚州有关恢复河口生态系统的流量和盐度管理的决策。