Regulators often require mining companies to monitor the water quality of pit lakes during closure. Aerial drones, or unmanned aerial vehicles (UAVs), are poised to revolutionise pit lake monitoring and management by: (i) reducing risks associated with water sampling, (ii) lowering costs associated with sampling, and (iii) increasing the frequency of data acquisition. This paper demonstrates how in situ profiles of temperature and specific conductance collected by aerial drones in advance of water sampling can be used to select optimal sampling depths and to inform samplers of the physical state of the pit lake. We provide case studies of drone water sampling at two pit lakes located 295 km apart in the northwest United States. These pit lakes have similar maximum depths, latitudes, and surface elevations, and both require drone water sampling. The Montana Tunnels Pit Lake near Jefferson City, Montana is inaccessible to both foot and vehicle traffic due to previous pit wall failures. The Thompson Creek Pit Lake near Clayton, Idaho has unstable pit walls that as recently as 2016 generated a large landslide that entered the pit lake and produced a tsunami. The health and safety risks associated with future tsunamis have suspended boat-based water sampling. Both pit lakes were sampled during a three-week period in autumn 2018 when most temperate-zone lakes in North America undergo complete top-to-bottom circulation, called 'turnover'. The aerial drone first suspended a conductivity-temperature-depth (CTD) probe capable of measuring in situ parameters to a depth of 100 m, and then suspended a water sampling device capable of collecting 2 L water samples up to 120 m deep. On 23 October 2018, in situ profiles collected in the Montana Tunnels Pit Lake showed that complete turnover had occurred and informed samplers that a minimum number of water samples would be sufficient to characterise the geochemistry of the water column. The sampling team collected three water samples from 0, 28 and 56 m depths, and subsequent lab results confirmed homogeneous conditions. State and federal regulators observed the sampling event and accepted the water samples for compliance purposes. In contrast, on 13 November at the Thompson Creek Pit Lake, in situ profiles indicated variable water chemistry with depth and the persistence of summer stratification. As a result of this complexity, samplers collected eight water samples from 3, 8, 15, 17, 36, 40, 55, and 83 m depths. In both studies, the aerial drone methods presented herein provided pit lake managers with important information about pit lake behaviour and water quality which could not have been obtained with boat-based methods owing to access and health and safety risks. These studies highlight the potential for future aerial drone water sampling applications during closure.

Pit lakes present significant safety risks for boat-based water sampling crews. The Matrice-HydraSleeve method improves the safety of water sampling in pit lakes by eliminating the need for a boat-based sampling crew. The method connects an off-the-shelf unmanned aircraft system, or drone (DJI, Matrice 600) to an off-the-shelf water sampling device (GeoInsight, HydraSleeve). It is capable of collecting 1.75 L water samples from up to 122 m deep and is simpler than previous drone water sampling methods. To validate the method, water samples were collected from similar depths in Dillon Reservoir, Colorado, USA using the Matrice-HydraSleeve method and traditional boat sampling methods using a Van Dorn water sample bottle. Concentrations of Ca, Na, K, HCO 3 , SO 4 , Cl, and Zn showed less than 20% relative percent difference, and concentrations of Cd were within ± the detection limit, meaning variability between samples met the data quality objective for duplicate samples. The method was also used on two occasions to collect eight water samples from the 101 m deep pit lake at the Thompson Creek mine in Idaho, USA including a sample from 92 m deep. Calcium and sodium concentration profiles were nearly identical, indicating little change in water chemistry and providing confidence in the method. In situ profiles of temperature and electrical conductivity collected with a conductivity-temperature-depth probe (YSI, CastAway) suspended below the drone indicated the lake was meromictic during both sampling events. To date, the Matrice-HydraSleeve method has been used at 10 pit lakes in the USA to collect 81 samples. Use of this method at other pit lakes has the potential to improve safety while lowering sampling costs and increasing data acquisition, leading to better pit lake management.

Ice climbing is important to the culture and economies of mountain communities worldwide. However, warming winters call into question the future of livelihoods associated with ice climbing. In response, this case study presents observed and simulated ice climbing conditions in the Mount Washington Valley, New Hampshire, USA, as well as local climbing guide's experiences of and responses to these changes. First, variability in ice conditions were evaluated by classifying and summarizing ice characteristics depicted in a 20-year collection of conditions reports (n = 372) including photos and written observations for a benchmark ice climb (Standard Route). Next, climate model ensembles were used to simulate probable changes in future ice season lengths according to intermediate and high climate forcing scenarios (i.e., RCP 4.5 & RCP 8.5). Finally, a survey and focus group were conducted with Mount Washington Valley ice climbing guides to examine observations and lived experiences of warming winters. This study, which is the first formal assessment of the implications of warming winters for ice climbing, reveals significant effects of climate change for current and projected ice climbing conditions as well as marked, and often differentiated, vulnerability and adaptability to these changes amongst climbing guides. The unique mixed-methods approach used is applicable in other locales where climate change is impacting ice climbing activities and associated livelihoods.