Streams in hot, arid environments often exist as a series of isolated pools along main channels. During these periods, shallow alluvial through flow may strongly influence key ecological processes within pools. We measured diel changes in δ13C values of dissolved inorganic carbon (DIC) and dissolved oxygen (DO) in two pools of ephemeral, dryland streams. We quantified alluvial water connectivity through stable isotope analysis (δ18O and δ2H) of pool and alluvial water. We also estimated gross primary productivity (GPP) and ecosystem respiration (ER) rates across a wider set of pools in both streams. δ13CDIC values displayed regular diel cycles, where both pools displayed small but similar daily amplitude (0.7–0.9‰) despite contrasting amplitudes of change in DO (0.8 mg L−1 vs. 2.8 mg L−1) and contrasting alluvial water connectivity (connected vs. disconnected). Water temperature was the strongest predictor of both δ13CDIC values and rates of change in δ13CDIC across both pools. Across both streams, all pools were net heterotrophic. GPP (0.35–1.73 g O2 m−2 d−1) and ER (0.49–2.64 g O2 m−2 d−1) rates were linked to aquatic vegetation cover. The disconnect between diurnal amplitudes of δ13C values and DO concentrations thus suggests that ecological drivers of gas exchange became increasingly localised as pools contracted.

中文翻译：

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δ13​​CDIC 的 Diel 循环和短暂旱地河流中的生态系统代谢

炎热、干旱环境中的溪流通常以一系列沿主要渠道孤立的水池形式存在。在这些时期，浅层冲积流可能会强烈影响池内的关键生态过程。我们测量了两个短暂的旱地溪流中溶解无机碳 (DIC) 和溶解氧 (DO) δ13C 值的日变化。我们通过池和冲积水的稳定同位素分析（δ18O 和 δ2H）量化冲积水的连通性。我们还估计了两条河流中更广泛的水池的总初级生产力 (GPP) 和生态系统呼吸 (ER) 率。δ13​​CDIC 值显示出规律的昼夜循环，尽管 DO 的变化幅度（0.8 mg L-1 对 2.8 mg L-1）和冲积水连通性（连接对比 断开）。水温是两个池中 δ13CDIC 值和 δ13CDIC 变化率的最强预测因子。在两条溪流中，所有池都是净异养的。GPP (0.35–1.73 g O2 m−2 d−1) 和 ER (0.49–2.64 g O2 m−2 d−1) 率与水生植被覆盖有关。因此，δ13C 值的昼夜振幅与溶解氧浓度之间的脱节表明，随着池收缩，气体交换的生态驱动因素变得越来越局部化。