Meltwater temperature in streams draining Alpine glaciers

Abstract

Thermal conditions in river water are of importance as they influence water quality, chemical processes, ecology, and biological conditions in rivers. In meltwater streams draining from Alpine glaciers, temperatures measured close to glacier termini show strong diurnal variation and paradoxical seasonal variation, being cool when energy availability is greatest. This thesis aims to describe temporal variations of water temperatures in five glacier-fed streams, which drain catchments of varying percentage glacierisation, in the Swiss Alps. Contrasting patterns of ablation season meltwater temperatures, and influences of basin characteristics and river channel morphology on water temperature are assessed. Relationships between solar radiation, air temperature, and water temperature were also investigated. A model was developed in order to estimate the impact of glacier recession on meltwater temperature. Observed temperatures in the Findelenbach during one ablation season were used to calibrate the model, which was subsequently validated on other years. Paucity of data in mountainous regions necessitated a model that required few measured variables to be developed. Distinctive seasonal water temperature regime was identified for larger rivers which drain relatively steep catchments, with substantial basin ice coverage. Such a regime is not replicated in streams draining smaller glaciers with lower gradients. Patterns in diurnal ranges of temperature in rivers draining large glaciers have been identified, temperature ranges reducing during days with high radiation and rising riverflows. Stream surface area was found to be the main catchment characteristic influencing temperature in glacier-fed rivers. Measured stream albedo values suggest that surface reflectivity is unlikely to be a major control on water temperature. Stream temperatures simulated by the model demonstrate high fidelity to those measured in the field. The temperature of glacier-fed streams will increase as climate warms as the distance over which heating can occur will lengthen as glaciers retreat, despite volume of flow being augmented by the deglaciation discharge dividend.

Real‐time warming of Alpine streams: (re)defining invertebrates' temperature preferences

“…This analysis revealed that summer water temperature has risen in all study streams and considerably at an average rate of 0.25°C per year (95% CI 0.15–0.35°C), but also that the warming rate does not differ between glacial and nonglacial streams (streams with and without glacial meltwater contribution). Although glacier‐fed rivers have a unique seasonal temperature regime (Niedrist & Füreder, n.d.; Milner et al, 2001), the studied glacial streams warmed at similar rates as nonglacial streams, which finding confirms the recent report about the missing – but long suspected – summer cooling effect in glacial streams (Williamson, Entwistle, & Collins, 2019).…”

“…In contrast to the often‐used proxy for environmental harshness or indicator of glacial influence, that is, the ratio of glacier cover to total catchment area (Brown, Hannah, & Milner, 2007; Brown & Milner, 2012; Fell, Carrivick, Kelly, Füreder, & Brown, 2018; Füreder & Niedrist, 2020; Rott et al, 2006), this study disentangled that the properties of biotic communities were more related to summer water temperatures than to catchment glaciation. We conclude that the temperature of stream water influences the stream biota more directly and depends on many local and small‐scale conditions, such as slope, length, width, current velocity, and exposition of stream reaches (Williamson et al, 2019), which can be derived from a land‐use proxy only to a limited extend. Thus, and although water temperature and glaciated catchment area correlated within the studied stream reaches, this work demonstrated that differences in immediate habitat characteristics, such as the temperature of the water itself, are more crucial for the invertebrate communities.…”

Direct and Indirect Climate Change Impacts on Brown Trout in Central Europe: How Thermal Regimes Reinforce Physiological Stress and Support the Emergence of Diseases

“…We also considered the effects of glaciers located further upstream in the river network that was found as an important descriptor in the thermal regime of medium-sized to large rivers. Larger glaciated areas within the catchment of a river reach led to lower water temperatures in line with several studies that observed summer cooling effects in rivers by glaciers (Collins, 2009;Fellman et al, 2014;Williamson et al, 2019). However, this cooling effect is related to a certain glaciated coverage within the catchment as Fellman et al (2014) showed very low effects in river catchments with <2% glaciated area and very high effects with more than 30% of glaciated area.…”

“…Glaciated areas within the catchment were derived from the Austrian Glacier inventory 3 (Fischer et al, 2015). Summer cooling effects by glaciers were observed for rivers in several studies (Collins, 2009;Fellman et al, 2014;Williamson et al, 2019). Future scenarios for the development of central European glaciers were derived from Marzeion et al (2012).…”

Warming Vistula River – the effects of climate and local conditions on water temperature in one of the largest rivers in Europe

“…Research conducted in many regions around the globe revealed an increase in the temperature of river waters over the last century (O'Reilly et al, 2015;Webb and Nobilis, 2007;Williamson et al, 2019). According to the literature, considerable warming and a substantial increase in mean annual water temperatures at the end of the 1980's were a response to rapid climate change (Woolway et al, 2017;Zhang et al, 2014).…”