Parameters determining water temperature of a proglacial stream: The Phelan Creek and the Gulkana Glacier, Alaska

Stream surface albedo plays a key role in the energy balance of rivers and streams that are exposed to direct solar radiation. Most physically based analyses and models have incorporated a constant stream albedo between 0.03 and 0.10, based primarily on measurements from low‐gradient streams with low suspended sediment concentrations. However, albedo should vary with solar elevation angle, suspended sediment concentration, aeration, and fraction of direct versus diffuse radiation. The objective of this study was to quantify the dependence of albedo of mountain streams on the controlling factors and to develop a predictive model for use in physically based analysis and modelling of stream temperature, especially for future climate and land‐use scenarios. Stream surface albedo was measured at nine sites with a variety of gradients and suspended sediment characteristics in the southern Coast Mountains of British Columbia, Canada. As expected, albedo of low‐gradient, non‐white water (flatwater) streams increased with solar elevation angle, suspended sediment concentration, and proportion of diffuse to direct solar radiation, ranging between 0.025 during cloudy periods over clear water to 0.25 for turbid water at elevation angles of less than 20°. Albedo was enhanced in steep reaches or at channel steps and cascades where flow was visibly aerated, with a range of 0.09 to 0.33. In clear weather, albedo exhibited notable diurnal variability at flatwater sampling sites. For example, during late summer, surface albedo typically fluctuated between 0.08 and 0.15 on a daily basis at a flatwater site on the highly turbid, glacier‐fed Lillooet River. Multiple regression models explained approximately 60% and 40% of the variance under cross validation for flatwater and white water data subsets, respectively, with corresponding root mean square errors of approximately 0.02 and 0.06.

Section: Discussionsupporting

confidence: 89%

Influence of turbidity and aeration on the albedo of mountain streams

McMahon¹,

Moore

2017

“…Despite the highly turbid water and the dependence of SSC on discharge at Phelan Creek, Chikita et al . () characterised the albedo as a constant value of 0.1, based on albedometer measurements. Richards and Moore () found that SSC at the outlet of Place Lake was consistently between about 60 and 100 mg/L, and did not exhibit a clear relation with discharge, in contrast to the situation at Phelan Creek.…”

Section: Discussionmentioning

confidence: 96%

Discharge dependence of stream albedo in a steep proglacial channel

Richards

Moore

2011

Stream surface albedo was measured at a location downstream of Place Glacier, Canada, in a steep bouldery channel. Portions of the water surface were visibly aerated as a result of the cascading flow even at lower discharges; at high flows, the stream was near-continuous whitewater. Albedo generally increased with discharge, from around 0.1 at the lower flows to 0.4 at the highest flows. This increase is consistent with the known effect of aeration on the reflectance of water. This discharge dependence of albedo needs to be accounted for in physically based models for predicting stream temperature to avoid biased predictions of net radiation. For steep proglacial streams that experience decreasing late-summer flows as a result of ongoing and future glacier recession, the associated decrease in albedo could promote higher stream temperatures, in addition to the effects of reduced flow depth and velocity.

“…Mean water temperature and the relative magnitude of daily thermal variation were broadly similar to Arctic systems at lower latitudes, although the maximum summer temperature was approximately 9 °C lower in Svalbard (79°N) than in Alaskan rivers located between 66°N and 69°N (Irons and Oswood, ; Chikita et al ., ). Water temperature was lower in all of the study rivers when compared with those recorded in alpine environments (Uehlinger et al ., ; Brown et al ., ; Cadbury et al ., ).…”

Section: Discussionmentioning

confidence: 99%

“…Although precipitation inputs were minimal throughout the monitoring season, subperiods with higher precipitation coincided with lower water and air temperatures. Discharge trends were not affected by precipitation events, as documented previously in other glacial basins and elsewhere (Brown et al ., ; Brown & Hannah, ; Chikita et al ., ), most likely because the volume of precipitation during each rainfall event in Svalbard was much lower than typically experienced in alpine regions (Brown and Hannah, ). Such low precipitation inputs are unlikely to have directly induced cooler river temperature by heat advection, as noted by Brown and Hannah ().…”

Section: Discussionmentioning

confidence: 99%

Water temperature dynamics in High Arctic river basins

Blaen

Hannah

Brown

et al. 2012

Despite the high sensitivity of polar regions to climate change, and the strong influence of temperature upon ecosystem processes, contemporary understanding of water temperature dynamics in Arctic river systems is limited. This research gap was addressed by exploring high-resolution water column thermal regimes for glacier-fed and non-glacial rivers at eight sites across Svalbard during the 2010 melt season. Mean water column temperatures in glacier-fed rivers (0.3 -3.2 ºC) were lowest and least variable near the glacier terminus, but increased downstream (0.7 -2.3 ºC km -1 ). Non-glacial rivers, where discharge was sourced primarily from snowmelt runoff, were warmer (mean 2.9 -5.7 ºC) and more variable, indicating increased water residence times in shallow alluvial zones and increased potential for atmospheric influence. Mean summer water temperature and the magnitude of daily thermal variation were similar to those of some Alaskan Arctic rivers but low at all sites when compared to alpine glacierized environments at lower latitudes. Thermal regimes were correlated strongly (p<0.01) with incoming shortwave radiation, air temperature, and river discharge. Principal drivers of thermal variability were inferred to be: (1) water source (i.e. glacier melt, snowmelt, groundwater); (2) exposure time to the atmosphere; (3) prevailing meteorological conditions; (4) river discharge; (5) runoff interaction with permafrost and buried ice and (6) basin-specific geomorphological features (e.g. channel morphology). These results provide insight into the potential changes in high-latitude river systems in the context of projected warming in polar regions. We hypothesise warmer and more variable temperature regimes may prevail in future as the proportion of bulk discharge sourced from glacial meltwater declines and rivers undergo a progressive shift towards snow-and groundwater sources. Importantly, such changes could have implications for aquatic species diversity and abundance and influence rates of ecosystem functioning in high-latitude river systems.