Abstract Salt marshes are highly productive ecosystems and yet we have only a preliminary understanding of how net ecosystem exchange varies on daily and seasonal time scales. We used the eddy-covariance method to examine the behaviour of the net ecosystem exchange as influenced by tidal flooding in daytime conditions in a coastal salt marsh dominated by Spartina alterniflora in Georgia, USA. Two different analyses both found that the net ecosystem exchange was ~ 60% greater during neap high tides than during spring high tides; the largest differences occurred early in the growing season. The effect of tidal flooding varied continuously with the degree to which plants were inundated versus emergent. The total monthly reduction (less negative) in daytime net ecosystem exchange due to flooding was 7-38% and 1-64% in 2014 and 2015 respectively. The highest CO2 flux reductions were observed early and during the peak growing season (February, March, April and May) and the lowest during the summer season in both years. Our findings suggest that daytime CO2 flux was reduced (less negative) 20-60% during the peak growing season due to tidal flooding. A better understanding of the impact of seasonal tidal flooding on net ecosystem exchange may allow more sophisticated predictions of how sea level rise will affect marsh function and survival over the coming century.

中文翻译：

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盐沼白天条件下潮汐淹没对净生态系统交换的影响

摘要 盐沼是高产的生态系统，但我们对净生态系统交换如何在每日和季节性时间尺度上变化只有初步了解。我们使用涡流协方差方法来检查在美国乔治亚州互花米草占主导地位的沿海盐沼中受潮汐洪水影响的净生态系统交换行为。两种不同的分析都发现，小涨潮期间的净生态系统交换比春季高潮期间高约 60%；最大的差异发生在生长季节的早期。潮汐洪水的影响随着植物被淹没与出水的程度而不断变化。2014 年和 2015 年，洪水造成的白天净生态系统交换的每月总减少量（负值较小）分别为 7-38% 和 1-64%。在这两年的早期和高峰生长季节（2 月、3 月、4 月和 5 月）观察到的 CO2 通量减少最高，而在夏季则最低。我们的研究结果表明，由于潮汐洪水，白天的 CO2 通量在生长高峰期减少了（负值较小）20-60%。更好地了解季节性潮汐洪水对净生态系统交换的影响可能有助于更复杂地预测海平面上升将如何影响未来一个世纪的沼泽功能和生存。