Nitrogen loadings to two small estuaries, Prince Edward Island, Canada: a 2-year investigation of precipitation, surface water and groundwater contributions

摘要

In this research the dissolved inorganic nitrogen (DIN) loadings from direct precipitation, stream flow and groundwaterndischarge to two small estuaries located in Prince Edward Island (PEI), Canada, were quantified over a 2-year period. The twonestuaries, like many around the world, exhibit deteriorating conditions that are believed to be related to excessive nitrogenntransport from adjacent catchments. The significance of the groundwater transport pathway and the temporal variability of thenloadings have not been previously investigated. The wet fraction of the atmospheric loading was quantified using availablenprecipitation and DIN concentration records. Stream water entering the estuaries and the discharge from numerous shorelinensprings, the predominate form of groundwater discharge, were monitored periodically during the study. The annual DIN loadsndelivered to both estuaries were dominated by streams, although groundwater discharge provided significant contributions ofnapproximately 15–18%. Temporal variability of DIN loading was large, with monthly loads varying by a factor of 5; thisnvariability was found to be primarily related to the variability of freshwater discharge. Concentrations of nitrate in streamnwater discharging to the estuaries and shoreline groundwater springs were similar in each catchment, suggesting that therenwas minimal differential attenuation during transport via these two pathways. The McIntyre Creek estuary had one of thenhighest normalized loads reported in the literature (1700 kg NO3-N/ha estuary/year), more than four-fold that of the TroutnRiver estuary, and this result appears to be related to the larger percentage of land area used for potato production in thencatchment. This study demonstrates that direct groundwater discharge to estuaries in PEI should not be ignored and thatnseasonal variations in loading may be important for managing DIN delivery to such estuaries.