Thermal effect of climate change on groundwater‐fed ecosystems

Abstract

Groundwater temperature changes will lag surface temperature changes from a changing climate. Steady state solutions of the heat‐transport equations are used to identify key processes that control the long‐term thermal response of springs and other groundwater discharge to climate change, in particular changes in (1) groundwater recharge rate and temperature and (2) land‐surface temperature transmitted through the vadose zone. Transient solutions are developed to estimate the time required for new thermal signals to arrive at ecosystems. The solution is applied to the volcanic Medicine Lake highlands, California, USA, and associated springs complexes that host groundwater‐dependent ecosystems. In this system, upper basin groundwater temperatures are strongly affected only by recharge conditions. However, as the vadose zone thins away from the highlands, changes in the average annual land‐surface temperature also influence groundwater temperatures. Transient response to temperature change depends on both the conductive time scale and the rate at which recharge delivers heat. Most of the thermal response of groundwater at high elevations will occur within 20 years of a shift in recharge temperatures, but the large lower elevation springs will respond more slowly, with about half of the conductive response occurring within the first 20 years and about half of the advective response to higher recharge temperatures occurring in approximately 60 years.

The Influence of Episodic Shallow Magma Degassing on Heat and Chemical Transport in Volcanic Hydrothermal Systems

“…The basal conductive heat flux beneath the volcano is estimated to be about 0.34 W/m 2 based on the measured geothermal gradient, which is in the range of reasonable values (e.g., Blackwell et al, 1990;Burns et al, 2017;Hochstein, 1995;Ingebritsen et al, 1989;Morgan et al, 1977;Williams & DeAngelo, 2008). The regional heat flux on the crest of the Lesser Antilles arc, 0.1 W/m 2 (Manga et al, 2012), is much lower than that nearer the volcano, where it is elevated by conduction from the underlying magma reservoir.…”

“…Burns et al (2016Burns et al ( , 2017 provides an expanded discussion and limitations associated with this approach. Temperature alternates between hot pulse temperature and cool background temperature, and P is the number of periods used to define heat pulses.…”

“…For heat transport, we consider both heat advection and dispersion within the aquifer along the flow path and conductive heat exchange between the aquifer and the vadose zone and basal layers (Burns et al, 2017). The governing equation for heat transport in the aquifer with multiple heat pulses is…”

Springs as hydrologic refugia in a changing climate? A remote‐sensing approach

“…Thermal responses of springs to increasing temperatures of groundwater recharge and of the land surface may also have important ecological implications, but are challenging to predict in the context of changes in precipitation timing and type (Burns et al. ). In this study, the possibility that NDVI in high‐elevation SMZs was constrained in part by energy limitation creates additional uncertainty about how high‐elevation spring systems might respond to combined changes in precipitation inputs and growing‐season length.…”

Working backwards from streambed thermal anomalies: hydrogeologic controls on preferential brook trout spawning habitat in a coastal stream

“…Shallow groundwater flowpaths, particularly those within 120 approximately 5 m of the land surface, will be more sensitive to annual air temperature patterns 121 and longer term warming trends due to strong vertical conductive heat exchanges (Kurylyk et al, 122 2015). The distance of seeps from upgradient groundwater recharge zones will also affect 123 seepage temperature dynamics and associated aquatic ecosystems due to future changes in 124 temperature or precipitation (Burns et al, 2017). Therefore, working backwards from thermal 125 anomalies into the landscape is critical to understanding the thermal stability of current and 126 future point-scale preferential brook trout habitat (Briggs et al, 2017a Coarse-grained mineral-dominated aquifers with little fine particulate organic matter and 131 low dissolved organic carbon supply tend to result in generally oxic groundwater conditions 132 (Back et al, 1993).…”