Why are we so “salty” about saltwater intrusion?
Ever since taking Fundamentals of Soil Science at the University of Maryland (UMD), I was intrigued by how the hydrosphere, lithosphere, and biota all influence one another. Saltwater intrusion is a great example of how interconnected these elements are. You might be wondering, what is saltwater intrusion, and what is the concern? I had these same questions when I was first learning about the topic.
Saltwater intrusion (SWI) is “the landward movement of seawater” [1]. This has been occurring in coastal areas due to sea level rise, storms and tides, drought, water management, and connectivity [1]. As saltwater moves more landward, salt is being deposited in the soil where it previously was not, thus increasing salinization. Not only does the concentration of salt in the soil increase, but this excess amount of salt prevents important nutrients from being held tightly by the soil. This causes those nutrients to leach from the soil during precipitation events and drain into local waterways. Consequences of SWI include: creation of inhospitable soil to staple crops in agricultural areas, alteration of the diversity of environments near the coast, reduced water quality due to eutrophication, coastal forest loss, salt-tolerant species invasion, and landward marsh migration [1].
To measure the extent and effects of saltwater intrusion on the soil of coastal agricultural land in Maryland, we quantified one important nutrient, inorganic nitrogen. The total measure of inorganic nitrogen is calculated by combining nitrate (NO3) and ammonium (NH4) concentrations. To do this, I performed potassium chloride (KCl) extractions in the Agroecology Lab. During a KCl extraction, I combine 2M KCl with field fresh soils and then incubate and shake the mixture for 16 hours. The contents are then filtered to separate the nitrate from the rest of the soil, and the filtered sample is analyzed using color spectrometry.
Furthermore, the effects of SWI on the water in the Chesapeake Bay estuary were also observed by the Tully Lab. Dr. Tully and Dr. Weissman found “concentrations of NH4‐N were significantly higher in salt marsh soil porewater than in any other habitat measured” [2]. This continues to show how saltwater intrusion causes the leaching of nitrogen, thus decreasing nitrogen content in soil and increasing nitrogen content in water[1] . SWI affects the movement of nitrogen through its biogeochemical cycle, which may lead to undesired environmental consequences.
References
Kate Tully, Keryn Gedan, Rebecca Epanchin-Niell, Aaron Strong, Emily S Bernhardt, Todd BenDor, Molly Mitchell, John Kominoski, Thomas E Jordan, Scott C Neubauer, Nathaniel B Weston, The Invisible Flood: The Chemistry, Ecology, and Social Implications of Coastal Saltwater Intrusion, BioScience, Volume 69, Issue 5, May 2019, Pages 368–378, https://doi.org/10.1093/biosci/biz027
Katherine L. Tully, Danielle S. Weissman, Saltwater intrusion affects nutrient concentrations in soil porewater and surface waters of coastal habitats, The Ecological Society of America, 21 Feb 2020, https://doi.org/10.1002/ecs2.3041