Agricultural nitrate load attenuation in a small groundwater-influenced wetland system

Abstract

Nitrate contamination of fresh water in agricultural watersheds, such as those in Prince Edward Island (PEI), is a significant human and environmental health concern. This field study (August 2023 – July 2024) investigated the nitrate loads delivered to and exported from a small (1.2 ha), groundwater-influenced, stream-wetland system in PEI. High frequency monitoring revealed that the annual nitrate load delivered to the wetland was 30,000 kg NO3 N/year. Groundwater discharge contributed about 67% of the nitrate load, while a small stream contributed the remainder. Variations in discharge rates were determined to be the dominant factor affecting the variation in nitrate loads. The wetland acted as a nitrate sink for 49 of 52 weeks, attenuating 39% of the imported nitrate load. The results of this study suggest that small, constructed wetlands can effectively reduce nitrate levels in agriculturally dominated watersheds; however, high-frequency data are required to obtain accurate estimates of nitrate load reductions.