Geomorphological and meteorological drivers of ephemeral pond hydrology in the Canadian shield forest

Abstract

Ephemeral ponds in cold and humid forested regions are often vulnerable because of their small size and ephemeral nature. The aim of this study was to identify the geomorphological and meteorological drivers of ephemeral pond hydrology in the forests of cold and humid climates. A multi‐year study of 40 ponds was conducted in the Kenauk forest located in the Canadian Shield of the Outaouais region (Quebec, Canada). Pond bathymetry, mineral and organic sediment thickness, watershed area, slope, canopy cover and maximum depth were measured in‐situ. The spring hydroperiod (the period during which there is water in the ponds between April and October) as well as the surface and groundwater recession rates were measured throughout the study period, from 2016 to 2020. Data from this study show that ponds located at lower altitudes in the landscape are larger, receive water from a larger area, and have longer hydroperiods than ponds located at higher altitudes. The results demonstrated a connection between the ponds and the surrounding aquifer. Spring and early summer precipitation was shown to affect hydroperiods the most, while summer precipitation influenced the presence of water in the ponds from April to October. Winter precipitation appear determinant for pond recession rates. Simple multiple regression models were able to simulate hydroperiods and hydroperiod indices relatively well, but pond recession rates were not well represented by the models. This study brings original multi‐year and multi‐site data identifying parameters and variables that determine ephemeral pond hydrology in cold and humid climates. The results provide new insights into their resilience on the landscape and bring new arguments for their long‐term protection.

Improvement of Soil Water Assessment Tool (SWAT) wetland module for modelling of ephemeral pond hydrology

“…The shape parameter p suggested by Brooks and Hayashi (2002) to represent pond geometry varies between 0.87 (HP17) and 4.7 (HP27) ( p < 1 corresponding to a convex profile, p > 1 corresponding to a concave profile and p = 1 corresponding to straight slopes). Roux et al (2023) also showed that the EPs are located in small bedrock depressions and are underlain by a layer of low permeability material (fine sand, silt, clay or organic material). Their maximum areas vary between 50.2 m 2 (S6) and 1808.8 m 2 (HP26), and their maximum water depths vary between 0.12 m (HP27) and 0.67 m (S6).…”

“…Potholes represent small depressional areas at the HRU scale and are isolated wetlands with no flows exchanged with the main channel unless maximum storage is exceeded. Differences between the two algorithms are in the spatial representation, in the T A B L E 1 Morphology and geology of the 10 studied ephemeral ponds, including maximum volume, maximum area, maximum depth, underlying sediment type, sediment thickness, watershed area, spring hydroperiod (SHP) and hydroperiod index (HPi) (data from Roux et al, 2023). The values in brackets are the maximum and minimum observed values over the monitoring period.…”

“…For unmonitored wetlands (other EPs, marsh, peatlands), the areas identified from map data were assumed to represent maximum values and were used to determine maximum water depths and maximum volumes following the fitted equations given in Figure 3 (Roux et al, 2023). For SWAT-EPb, the empirical parameters of Equations ( 10) and ( 11) (α, β and γ) were determined specifically for each of the 10 studied EPs (Table 3; Roux et al, 2023). The unmonitored wetlands were parametrized the same as for SWAT-EPa.…”

“…The spring hydroperiod (SHP) was calculated by Roux et al (2023) as the number of wet days between the spring freshet and the first day when the water level in the pond fell below 0.02 m.…”

“…Research has shown that their hydroperiods (i.e., the period during which a pond holds water), as well as the subsequent dry period, are key elements influencing the reproduction of amphibians and invertebrate species (Brooks, 2000;Schrank et al, 2015). Pond hydroperiods are regulated by morphologic properties, such as maximum pond volume, area and maximum depth (Brooks & Hayashi, 2002), by their position on the landscape (Roux et al, 2023), as well as by precipitation and evapotranspiration (Brooks, 2004), seepage to the underlying soil and flow exchange with the groundwater (Brooks & Hayashi, 2002;Roux et al, 2023).…”