Abstract
AbstractLacustrine groundwater discharge (LGD) can substantially impact ecosystem characteristics and functions. Fibre optic distributed temperature sensing (FO‐DTS) has been successfully used to locate groundwater discharge into lakes and rivers at the sediment–water interface, but locating groundwater discharge would be easier if it could be detected from the more accessible water surface. So far, it is not clear if how and under which conditions the LGD signal propagates through the water column to the water surface–atmosphere interface, and what perturbations and signal losses occur along this pathway. In the present study, LGD was simulated in a mesocosm experiment. Under winter conditions, water with temperatures of 14 to 16 °C was discharged at the bottom of a 10 × 2.8‐m mesocosm. Water within this mesocosm ranged from 4.0 to 7.4 °C. Four layers (20, 40, 60, and 80 cm above the sediment) of the 82 cm deep mesocosm were equipped with FO‐DTS for tracing thermal patterns in the mesocosm. Aims are (a) to test whether the positive buoyancy of relatively warm groundwater imported by LGD into shallow water bodies allows detection of LGD at the lake's water surface–atmosphere interface by FO‐DTS, (b) to analyse the propagation of the temperature signal from the sediment‐water interface through the water column, and (c) to learn more about detectability of the signal under different discharge rates and weather conditions. The experiments supported the benchmarking of scale dependencies and robustness of FO‐DTS applications for measuring upwelling into aquatic environments and revealed that weather conditions can have important impacts on the detection of upwelling at water surface–atmosphere interfaces at larger scales.
Highlights
Lacustrine groundwater discharge (LGD), that is, the discharge of groundwater (GW) into lakes, can substantially impact ecosystem characteristics and functions (Baker et al, 2014; Ridgway & Blanchfield, 1998; Warren, Sebestyen, Josephson, Lepak, & Kraft, 2005)
Quantitative interpretations of warm water upwelling patterns are hampered by the lack of understanding of how the signal propagates from the sediment–water interface through the water column to the water surface–atmosphere interface and which perturbations and signal losses occur along this pathway
The present study demonstrates that during winter conditions, the positive buoyancy of relatively warm water imported by simulated LGD into shallow water bodies allows detection of LGD at the lake's water surface–atmosphere interface by Fibre optic distributed temperature sensing (FO‐DTS)
Summary
Lacustrine groundwater discharge (LGD), that is, the discharge of groundwater (GW) into lakes, can substantially impact ecosystem characteristics and functions (Baker et al, 2014; Ridgway & Blanchfield, 1998; Warren, Sebestyen, Josephson, Lepak, & Kraft, 2005). The aim of this study is to show that during winter, the positive buoyancy of relatively warm LGD to cold SW will allow or enhance detection of GW at the water surface–atmosphere interface (the lake surface). To address this aim, a mesocosm was used as a model system. The conclusions of the paper will summarize briefly the findings on the different data analyses carried out, answering the three research questions
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