Myers, D.T., D. Oviedo-Vargas, S. Ensign, M. Daniels, J.P. Schmit, M. Peipoch, and J. Kan. 2025. Freshwater Science, early online access.
Permalink/DOI (Open access)
Abstract
Protected areas constitute considerable portions of watersheds throughout the United States and play a critical role in freshwater conservation. Yet streams and rivers in protected areas can be vulnerable to degradation by human activities. One major emerging threat to water quality is the freshwater salinization syndrome. However, there is much to be known about where and how salinization affects protected areas, such as national parks. Here, we examined specific conductance (SC; an indicator of salinization) data for the National Capital Region of the United States National Park Service to understand how salinization is affecting water quality and, potentially, aquatic life in park streams and to guide stream management. We asked if SC has exceeded thresholds for aquatic life, and we hypothesized that SC would be related to proportions of watershed developed land area and that trends in SC would be related to expansion and intensification of watershed developed area. We identified spatial relationships between SC and watershed conditions as well as trends in SC for 37 streams in 10 parks over 18 y (2005–2023). Increasing SC affected ~60 to 65% of monitored park streams in the region and was related to watershed urban land cover and estimated deicing salt application (median increase 5–15 µS cm−1 y−1). Streams with watersheds extending beyond national park boundaries had higher SC than those entirely contained within national parks because of salt pollution from developed areas. Contrary to our expectations, urban growth rates (expansion + infill) were not linearly related to SC trends. Instead, SC in already urbanized watersheds with little growth also increased by 10 to 15 µS cm−1 y−1. Stream SC measurements often exceeded regional and national SC thresholds to protect aquatic life. Collaboration with communities in watersheds upstream is key to managing drivers of current and future stream salinization.
