Late‐summer thermal regime of a small proglacial lake

Abstract

ABSTRACT:This study was motivated by an interest in understanding the potential effects of climate change and glacier retreat on late summer water temperatures in alpine areas. Fieldwork was carried out between July and September 2007 at Place Lake, located below Place Glacier in the southern Coast Mountains of British Columbia. Place Lake has an area of 72 000 m 2 , a single inlet and outlet channel, and an approximate residence time of 4 days. Warming between the inlet and outlet of the lake ranged up to 3 C and averaged 1.8 C, which exceeds the amount of warming that occurred over the 1 km reach of Place Creek between the lake outlet and tree line. Over a 23-day period, net radiation totalled about 210 MJÁm , with sensible heat flux adding another 56 MJ m -2 . The latent heat flux consumed about 8% of the surface heat input. The dominant heat sink was the net horizontal advection associated with lake inflow and outflow. Early in the study period, temperatures between the surface and 6-m depth were dominantly at or above 4 C and were generally neutral to thermally stable, whereas temperatures decreased with depth below 6 m and exhibited irregular sub-diurnal variations. The maximum outflow temperature of almost 7 C occurred in this period. We hypothesize that turbidity currents associated with cold, sediment-laden glacier discharge formed an underflow and influenced temperatures in the deeper portion of the lake but did not mix with the upper layers. Later in the study period, the lake was dominantly well mixed with some near-surface stability associated with nocturnal cooling. Further research is required to examine the combined effects of sediment concentrations and thermal processes on mixing in small proglacial lakes to make projections of the consequences of glacier retreat on alpine lake and stream temperatures.

Stream temperature response to variable glacier coverage in coastal watersheds of Southeast Alaska

“…Lakes had a warming effect in late spring and summer (May through August) for all streams as a result of a sensitivity to atmospheric heating during the day. Similar heating of water downstream of exposed lentic environments has also been found in watersheds with large lakes, swamps and reservoirs (Webb and Walling, ; Mellina et al ., ; Moore, ) and in proglacial lakes between the lake inlet and outlet (Uehlinger et al ., ; Richards et al ., ). On the other hand, proglacial lakes in the Eagle and especially Mendenhall River watersheds had a cooling effect on stream temperature in August through October.…”

“…However, temperature in Herbert River, which is a heavily glaciated watershed but does not contain a proglacial lake, reached its summer minimum of 1.7 °C in early August but gradually increased thereafter to nearly 4.0 °C by the end of October. This contrasting pattern is due to the accumulation of glacial meltwater in Mendenhall Lake during the summer glacial run‐off season that slowly drains and cools stream temperature during the late summer and early fall (Richards et al ., ).…”

Discharge dependence of stream albedo in a steep proglacial channel

“…The model is expressed as where Q r is net radiation (W m −2 ), K ↓ is incident solar radiation (W m −2 ), α is modelled albedo, L ↓ is incident longwave radiation (W m −2 ), ε w is the emissivity of the water surface (assumed to be 0.95), σ is the Stefan‐Boltzmann constant (5.67 × 10 −8 W m −2 K −4 ), and T w is measured water temperature (K). Incident solar and longwave radiation were computed from the measured values at the Place Glacier and ridge sites, with adjustments to account for topographic shading and view factors at the stream site (Richards, ; Richards et al ., in review). Equation was applied with three representations of stream surface albedo: (i) discharge dependent, using an empirical model fitted to the 2008 data; (ii) a constant value of 0.05; and (iii) a constant value of 0.1.…”

“…Further details of the site can be found in Moore and Demuth (), Richards and Moore (), and Richards et al . (in review).…”

Identifying spatial and temporal dynamics of proglacial groundwater–surface-water exchange using combined temperature-tracing methods

“…Groundwater-fed proglacial rivers and lakes can affect the wider catchment hydrology (Mellina et al 2002, Richards et al 2012, biogeochemistry (Goodman et al 2010(Goodman et al , 2011, and ecology (Roy and Hayashi 2009), often causing enhanced biodiversity in streams directly affected by ground water (e.g., Milner and Petts 1994, Brown et al 2007b, Crossman et al 2011, Roy et al 2011, Jacobsen et al 2012. Climate change, including glacial retreat and changes in precipitation patterns and melt timing, is projected to significantly affect proglacial groundwater systems with, for instance, expected increases in groundwater contributions and changes to hydrochemical conditions and nutrient cycling (Milner et al 2009, Rutter et al 2011, Blaen et al 2013.…”