Role of Focused, Deep Groundwater Input from Springs in Maintaining Winter Refugia in North-shore Trout Streams

Abstract

North-shore streams provide marginal habitat for trout. Stream discharge and temperature reach extremes in mid-to-late summer, during dry periods, and again in winter, when runoff is essentially non-existent. Deeper groundwater is one of the main sources of flow during winter, and can significantly contribute to maintaining habitable temperatures and flow during the winter. A deep (200+ feet) groundwater spring and associated tributary were identified flowing into Amity Creek and had a significant impact on raising the temperature of the main stem throughout winter. This spring maintained an almost constant temperature between 6 and 7 𝇈C throughout the winter, along with steady conductivity and isotope signatures. The spring was very similar in all aspects to a discharge from a deep bedrock well within the same watershed. The steady properties of the deep spring stood in sharp contrast to the main stem of the Amity, which was consistently below 1𝇈Celsius and fluctuated in conductivity and isotope signature throughout the season. The only time when the groundwater tributary was not affecting the main stem was during two periods of extreme cold, when the tributary may have frozen to the bed of the channel. The tributary itself can also serve as a trout refugium year-round, in addition to maintaining flow in the main stem, as brook trout have been found within the tributary in the past. Trout conservation efforts should focus on identifying and protecting similar deep groundwater inputs to ensure continued streamflow, above zero temperatures, and trout survival throughout winter.