Effects of an annular solar eclipse on montane streamwater quality in New Mexico, USA

We studied the atmospheric and streamwater-quality responses to the 14 October 2023 annular solar eclipse in 7 streams in the Jemez River basin of northern New Mexico, USA. Study sites ranged from 1st-order streams to the 4th-order Jemez River. During the eclipse, across 7 weather stations, we recorded a mean decrease of 92% insolation, a 6.7°C decline in air temperature, a 16.2% increase in relative humidity, and a 1.2 m/s drop in mean wind speed. During the eclipse, we observed distinct, small-magnitude, short-duration changes in the diel cycles of stream temperatures (mean decline of 0.67°C across 7 streams), dissolved O2 (decline of 0.22 mg/L in 5 streams showing responses), and pH (decline of 0.06 in 6 streams showing responses). Streamwater turbidity and conductivity did not show consistent responses during the eclipse. We suggest that decreased insolation directly reduced water temperature and concomitantly curtailed stream periphyton photosynthesis, leading to reduced dissolved O2 production and increased dissolved CO2 concentrations (lowering pH). Declines in dissolved O2 and pH were greatest in 1st- and 2nd-order streams with high sun exposure, low gradients, and the widest arrays of aquatic vegetation (periphyton, filamentous algae, aquatic macrophytes, and emergent vegetation). Streams with morning shade from topography or tree-lined banks had responses that were smaller in magnitude. Stream basin area, discharge volume, and current velocity were not related to the magnitude of stream responses. Although the abiotic and biotic streamwater-quality responses to the eclipse were clear and measurable, the small magnitudes of the changes were well within the realm of diel variation and likely had minimal effect on the ecology of the stream ecosystem.