1. Primary production is a fundamental ecosystem process that influences nutrient and carbon cycling, and trophic structure in streams. The magnitude and timing of gross primary production (GPP) are typically controlled by hydrology, light, nutrient availability and grazers. Estimates of GPP and its drivers in high-mountain streams remain elusive at present.
2. We estimated GPP in streams typical for high-mountain catchments, namely a glacier-fed, groundwater-fed (krenal) and a snowmelt-fed (nival) stream. Using high-resolution sensor data over 2 years in combination with numerical simulations of stream hydraulics, we studied the periods of GPP characteristic for these streams, as well as their major drivers.
3. Favourable windows for GPP were constrained to periods at the onset of the snowmelt and its recession, when photosynthetic active radiation at the streambed and streambed stability facilitated GPP.
4. During these windows of opportunity, GPP was higher in the nival stream (3.7 ± 3.4 g O₂ m⁻² day⁻¹), followed by the glacier-fed (1.5 ± 1.6 g O₂ m⁻² day⁻¹) and the krenal streams (0.6 ± 0.6 g O₂ m⁻² day⁻¹). GPP was largely controlled by photosynthetic active radiation at the stream bottom, however, we were not able to establish an unequivocal relationship between flow-induced bed movement and GPP.
5. Our results highlight the capacity of primary producers to exploit the discrete and relatively predictable windows of opportunities in high-mountain streams. We propose that climate-driven change in snow and glacier melt reduction may ameliorate stream environmental conditions, thereby enhancing the potential autochthonous organic matter supply within the catchment.

中文翻译：

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阿尔卑斯河流中初级生产的制度及其驱动因素

1. 初级生产是影响养分和碳循环以及河流营养结构的基本生态系统过程。初级生产总值 (GPP) 的数量和时间通常受水文、光照、养分供应和食草动物的控制。目前，对高山溪流中 GPP 及其驱动因素的估计仍然难以捉摸。
2. 我们估计了高山集水区典型溪流的 GPP，即冰川补给、地下水补给 (krenal) 和融雪补给 (nival) 的溪流。我们使用超过 2 年的高分辨率传感器数据结合河流水力学的数值模拟，研究了这些河流的 GPP 特征周期及其主要驱动因素。
3. GPP 的有利窗口被限制在融雪开始及其衰退的时期，此时河床的光合有效辐射和河床稳定性促进了 GPP。
4. 在这些机会窗口期间，雨季流中的 GPP 较高（3.7 ± 3.4 g O ₂ m ^-2 day ^-1），其次是冰川喂养（1.5 ± 1.6 g O ₂ m ^-2 day ^-1）和肾流（0.6 ± 0.6 g O ₂ m ^-2天^-1）。GPP 在很大程度上受河流底部的光合有效辐射控制，然而，我们无法在流动引起的床运动和 GPP 之间建立明确的关系。
5. 我们的结果突出了初级生产者利用高山溪流中离散且相对可预测的机会窗口的能力。我们提出，雪和冰川融化减少的气候驱动变化可能会改善河流环境条件，从而增强流域内潜在的本土有机物质供应。