The metabolism of estuarine environments is often estimated by measuring changes in dissolved oxygen concentrations. A central assumption of common oxygen-based approaches is that oxygen consumption rates (primarily respiration) are similar under light and dark conditions. Evaluating this assumption is critical, especially in benthic-dominated systems, because differences between daytime and nighttime respiration could result in underestimation or overestimation of ecosystem productivity. We evaluated rates of gross oxygen production over hourly to seasonal time scales in a shallow, temperate salt marsh pond. To assess whether a dissolved oxygen diel mass balance underestimated gross oxygen productivity, we compared rates using this traditional approach and using the triple oxygen isotope tracer of photosynthesis. This is a powerful combination because the triple oxygen isotope approach is theoretically insensitive to respiration. The methods agreed well over daily to seasonal time scales. However, during midday periods of peak light and productivity, the triple oxygen isotope approach resulted in higher hourly scale gross oxygen production rates. The timing and magnitude of this short-term difference is consistent with light-dependent oxygen uptake fluxes including photoreduction and/or light-stimulated community respiration. Finally, aquatic vegetation was associated with variability in productivity across the pond. Such small-scale environmental heterogeneity is evidence that this shallow pond was not laterally well mixed, and likely contributes to the dynamism of these common estuarine environments.

通常通过测量溶解氧浓度的变化来估算河口环境的新陈代谢。常见的基于氧气的方法的主要假设是，在明暗条件下的耗氧率（主要是呼吸）相似。评估此假设至关重要，尤其是在以底栖生物为主的系统中，因为白天和夜间呼吸之间的差异可能会导致生态系统生产力的低估或高估。我们评估了浅温带盐沼池塘在每小时到季节性时间内的总氧气生产速率。为了评估溶解氧diel的质量平衡是否低估了总氧气生产率，我们比较了使用这种传统方法和使用光合作用的三重氧同位素示踪剂的速率。这是一个有力的组合，因为理论上三重氧同位素方法对呼吸不敏感。这些方法在每天到季节性的时间尺度上都非常吻合。但是，在高峰采光和生产力的正午时段，三重氧同位素方法导致每小时规模的总氧生产率更高。这种短期差异的时间和大小与光依赖的氧气吸收通量一致，包括光还原和/或光刺激的社区呼吸。最后，水生植被与整个池塘生产力的变化有关。如此小规模的环境异质性证明了该浅塘在横向上没有很好地混合，并且可能有助于这些常见河口环境的动力。