Land‐use comparison of depression‐focussed groundwater recharge in the Canadian prairies

Abstract

In the cold semiarid Canadian prairies, groundwater recharge is focussed under numerous topographic depressions, in which snowmelt runoff converges. Agricultural land uses on the uplands surrounding the depressions affect snow accumulation, snowmelt infiltration, evapotranspiration (ET) and soil moisture dynamics, thereby influencing snowmelt runoff and depression-focussed recharge. The objective of this study is to compare the differences in hydrological processes under two common land uses in the Canadian prairies, namely grazed grass and annual crop, and examine how they affect groundwater recharge. A short-term (3 years) paired catchment study was used for detailed observation of hydrological processes in two depressions, supplemented by a longer-term (17 years) data set covering a larger scale to quantify the differences in snowmelt runoff between the two land uses. Compared to the grazed grassland, the cropland had a shorter and more intense period of ET, and root water uptake restricted to the shallower (top 0-80 cm) soil zone. The amount of snowmelt runoff was greater in the grazed grassland primarily due to a higher amount of snow accumulation, which was dictated by differences in topography. This finding was contrary to previous studies in the Canadian prairies that indicated substantially smaller snowmelt runoff in ungrazed grassland, but was consistent with the larger-scale remote sensing results, which showed only a marginal difference between grazed grasslands and croplands. Groundwater recharge rates were estimated using the chloride mass balance method for the present condition using "modern" pore water containing tritium. The rates were similar between the grazed grassland and croplands, implying similarity in snowmelt runoff characteristics.These results suggest that groundwater recharge will continue to be focussed under depressions in the future, though the amount and seasonality of recharge may be influenced by warmer winters.

Impact of land cover changes on Long‐Term Regional‐Scale groundwater recharge simulation in cold and humid climates

“…In the similar cold climate environments, the roles of agriculture and forest in GWR changes seems to be mainly linked to the cold period. For example, Morgan et al (2021) did not find a clear difference in depression‐focussed GWR between grassland and cropland environments in the Canadian Prairies due to very similar snowmelt runoff dynamics. Destouni et al (2013) and Jaramillo et al (2013) linked historical agricultural development at the expense of grassland to increases in runoff and actual evapotranspiration in several watersheds in Sweden, thus reducing the available water for recharge.…”

“…Studies in cold climates with seasonal snowpack have emphasized the role of snow accumulation and melting in GWR (Aygün et al, 2020; Dubois et al, 2022, 2021a; Greenwood & Buttle, 2018; Morgan et al, 2021; Wright & Novakowski, 2020; Young et al, 2019). Winter‐related model parameters (snowmelt coefficient, melting temperature, freezing soil) are also known to be very sensitive when simulating cold region hydrology (Dubois et al, 2021a; Mai et al, 2022; Nemri & Kinnard, 2020).…”

“…However, this study showed that the intense afforestation simulated for RCP4.5 scenarios produced significant changes in HB LC for smaller changes in climate conditions than were observed for RCP8.5 scenarios (Figure 7). Studies in cold climates with seasonal snowpack have emphasized the role of snow accumulation and melting in GWR (Aygün et al, 2020;Dubois et al, , 2021aGreenwood & Buttle, 2018;Morgan et al, 2021;Wright & Novakowski, 2020;Young et al, 2019).…”

“…Some studies have demonstrated that changes in GWR were linked to land use and LC changes at the field scale (Greenwood & Buttle, 2018;Zhang et al, 2018Zhang et al, , 2021, at the local scale (tens of km 2 ; Cochand et al, 2021), or at the regional scale (thousands of km 2 ; Anurag et al, 2021). Others have found that land use and LC had little impact on GWR simulation, or that land use and LC impacts were smaller than those of climate change (Guerrero-Morales et al, 2020;Mohan et al, 2018;Morgan et al, 2021;Shuler et al, 2021). These differences are most likely due to the fact that it can be challenging to distinguish the impacts of climate change from the impacts of land use and LC changes on GWR, and on all components of the water budget more generally (Assani et al, 2021;Goodbrand et al, 2022;Young et al, 2019).…”

Disconnectivity matters: the outsized role of small ephemeral wetlands in landscape-scale nutrient retention

“…They are also generally smaller than most riparian wetlands and contain water for only a part of the year [12]. GIWs typically receive seasonal water inputs through snowmelt or intense storms and lose water in subsequent months through evapotranspiration or groundwater recharge [19,22]. From a biogeochemical perspective, GIWs often receive the first flush of solutes from the landscape [23] and the lack of direct connection to the river network increases processing times and nutrient retention, making them landscape biogeochemical hotspots [5,24].…”