The export of anthropogenic nitrate to coastal waters, which depends on the interplay between many factors such as land use and meteorological forcing, is a rising concern in many regions of the world. The present study investigates the effect of precipitation event magnitude on baseflow and associated groundwater‐driven nitrate export in Prince Edward Island, Canada. Twenty‐year time‐series of precipitation, stream flow, and groundwater levels across the island were analysed to establish a three‐way relationship between precipitation, groundwater level rise, and baseflow increase along a hydrological response pathway in this island setting. The analysis was performed by extracting hydrological responses for groundwater level and baseflow for a selected subset of relatively isolated precipitation events. The results reveal a non‐linear relationship between precipitation event magnitude and baseflow change that is also observed for precipitation events associated with hurricanes and post tropical storms. A time‐series of streamflow nitrate concentrations during Hurricane Dorian's passage (September 2019) was used to evaluate the relevance of these findings for nitrate export. The data show that baseflow increases after a heavy precipitation event have limited impact on streamflow concentrations, but result in substantial and sustained increase of nitrate export (calculated by multiplying concentration by flow). These observations are consistent with a recharge‐induced water table rise leading to increased hydraulic gradients that drive discharge of shallow nitrate‐containing groundwater. Due to the similarity of the processes governing groundwater flow to the sea and to streams, the results can be used to gain insights into the impacts of precipitation event magnitude on direct groundwater discharge to coastal waters. On Prince Edward Island, this applies to at least the 13% of the island's surface area that is closer to the ocean than to any stream and likely feeds submarine groundwater discharge pathways.

Linkages between the micro‐scale of soil water and landscape scale of hydrological data could be improved with the analysis of soil factors in preferential flow rates. This rearrangement of the terminology on soil pore size from published literature focused on the relationship between aggregate and pore size. In the range of pore size relevant to water flow (>0.005 mm), a 2:1 ratio of aggregate to pore diameter approximated the mean of proposed pore size categories. Major functional change points in soil pore size were identified where water becomes mobile in soil (0.005 mm), where preferential flow among aggregate surfaces begins (0.3 mm), and where water flows without soil interaction (bypass flow ∼1.0 mm). A number of published equations supported the application of soil pore size in permeability estimation for modeling hydraulic conductivity. Common understanding of soil pore terminology would support water flow estimation from soil to landscape scales.

Core Ideas: Fall plowing created more post–fall‐plowing nitrate leaching than spring plowing. Fall or spring plowing did not influence post–potato‐harvest nitrate leaching and potato yield. Increasing fertilizer N input to potato crops increased post–potato‐harvest nitrate leaching. Increasing fertilizer N input to potato crops suppressed potato yield. Excessive nitrate leaching from potato (Solanum tuberosum L.) production has been linked to groundwater nitrate contamination and eutrophication in receiving surface water. This study was conducted to assess the effects on nitrate leaching and potato yield of delaying red clover (Trifolium pratense L.) plowing from late fall to spring in a barley (Hordeum vulgare L.)–red clover–potato rotation and varying additions of fertilizer N to potato crops in Prince Edward Island, Canada, between 2014 and 2017. The experiment used a split‐plot arrangement in a completely randomized design with three replications. A stainless steel lysimeter was installed in each plot to collect soil water to test nitrate concentrations in leachate. Nitrate leaching occurred primarily between late fall, after the potato harvest, and in spring. Delaying forage plowing from late fall to spring reduced post–fall‐plowing nitrate leaching but had no influence on either post–potato‐harvest nitrate leaching or potato yield. Increasing fertilizer N input to the potato crops was shown to not only increase the risk of excessive nitrate leaching but also to suppress potato yield. Higher levels of soil N supplies from the mineralization of the plowed‐down red clover and soil organic matter to the potato crops in combination with a shorter than ideal growth period for the long‐season Russet Burbank potato appear to create overfertilizing situations, resulting in excessive post–potato‐harvest nitrate leaching and suppressed yields. Adequately accounting for soil N supplies is critical for enhancing potato productivity while minimizing nitrate leaching.