Salt your food, not your farm

Maddie in full PPE works on samples.

Saltwater intrusion can be devastating, not just to farmers but to the environment, native species, and ultimately the economy. There are both natural and unnatural factors that drive saltwater intrusion. The five main factors include sea-level, storms and tides, drought, water usage, and hydrologic connectivity [1]. The devastating effects of salinization of farmland due to these factors may include coastal forest loss, salt-tolerant species invasion, decline in crop yields, eutrophication, and marsh migration [1]. While one may think that heavy rainfall and sea-level rise would cause the most rapid salinization of agricultural systems, it is actually drought. Although Maryland’s recorded rainfall this year, 2020, is relatively normal, December 2016 – January 2018 experienced significantly decreased rainfall and even emergency drought conditions in central parts of the state [2]. During a drought, rivers, streams, and other bodies of water become more concentrated with salt, thus allowing nutrient leaching [of fields] to occur at a greater rate. Additionally, the highly concentrated salt affects the ion exchange rate, for example, dehydrated sodium is a powerful positively charged ion, or cation, affected by this change [3]. Legacy nutrients are nutrients that have built up in the soil over time. Soil, particularly clay soil, can hold onto these nutrients via ionic bonds. While these nutrients are not immediately bio-available to crops currently growing, if leached and subsequently washed away these nutrients contribute largely to algae blooms and eutrophication in bodies of water. Yet, with a more attractive, stronger ion (salt), now in the soil, the soil particles may bind to the salt, effectively unbinding from the legacy nutrients (usually nitrogen [N] and phosphorous, [P]). While unbound, the legacy nutrients can be more easily washed away and removed entirely from the field.
There are many methods for evaluation of the level of saltwater intrusion into a farm system. The Tully Laboratory often measures concentrations of different nutrients using extractions. One nutrient often measured is phosphorous. I have been assisting in making the solutions necessary for sequential P extraction in soils, including sodium bicarbonate, sodium hydroxide, and hydrochloric acid. Each sequential extraction (using a different solution) extracts a different form of phosphate found in the soils. Lastly, the P samples are analyzed using the LACHAT (a type of spectrometer) for colorimetric analysis. However, some samples are too acidic, creating bubbles in the tubing of the LACHAT, resulting in a poor curve. This can also be true for a very basic solution. Early in the semester, I assisted in adjusting a very basic (pH 13) extraction to a lower basicity (pH 8) to fix this dilemma.

References
[1] Tully, K., Gedan, K., Epanchin-Niell, R., Strong, A., & Bernhardt, E. S. (May, 2019). The Invisible Flood: The Chemistry, Ecology, and Social Implications of Coastal Saltwater Intrusion. Bioscience, 69(5), 368-378. doi:10.1093/biosci/biz027
[2] Maryland Department of the Environment. (2020, September). Maryland's Drought Status: Current Conditions. Retrieved from https://mde.maryland.gov/programs/water/droughtinformation/currentconditions/Pages/index.aspx
[3] Tully, K. L., & Weissman, D. S. (February, 2020). Saltwater intrusion affects nutrient concentrations in soil porewater and surface waters of coastal habitats. The Ecological Society of America, 11(2). doi:10.1002/ecs2.3041