Drained, farmed, and forgotten – Relic depressional wetlands endure as conduits for nutrient loss

Authors: Williams, Mark; Penn, Chad; Yen, Haw

Submitted to: Popular Publication
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2026
Publication Date: 3/16/2026
Citation: Williams, M.R., Penn, C.J., Yen, H. 2026. Drained, farmed, and forgotten – Relic depressional wetlands endure as conduits for nutrient loss. Resources, Environment and Sustainability. https://doi.org/10.1016/j.resenv.2026.100326.
DOI: https://doi.org/10.1016/j.resenv.2026.100326

Interpretive Summary: Wetlands used to be common in many areas, but most have been drained for farming. This study looked at the low-lying areas left behind after wetlands were drained, called depressions. Researchers studied these areas to understand their soil, water quality, and the potential impact of conservation. The results showed that depressions often collect more nutrients than higher parts of the field. Because they have more nutrients, there is a greater risk that these nutrients could be washed away into nearby water. Even though depressions can lose a lot of nutrients, they are often overlooked when determining how much nutrients are in a field or watershed. Soil tests usually cover large areas and can miss these small spots. When that happens, depressions keep getting extra fertilizer, which makes the nutrient buildup and risk of loss even worse. The study shows that depressions are a great place to focus on conservation efforts, like using blind inlets to filter nutrients. By identifying depressions as spots where nutrients build up, and by sharing this information with stakeholders, we can create better and more targeted ways to improve farm productivity and water quality.

Technical Abstract: Wetlands were once common landscape features; most of them have been drained for agricultural purposes. The objective of this study was to examine depressional areas left behind after wetland drainage from the perspective of soils, water quality, and conservation. Results show that depressions can accumulate nutrients at levels significantly greater than upland field positions. Greater soil nutrient supply in depressions poses a greater potential risk of nutrient loss, especially since the high organic matter subsoils in depressions are limited in nutrient sorption capacity compared to mineral soils. Despite the risk of nutrient loss, depressions are underrepresented in field and watershed nutrient accounting. Soil sampling of agricultural fields often has a spatial grain greater than the depression; thus, failure to identify nutrient accumulation in depressions leads to a positive feedback loop – nutrient-rich depressions continue to receive additional inputs which leads to further accumulation and amplified risk of loss. Findings highlight that depressions are low-hanging fruit for targeted conservation implementation of practices such as blind inlets. Recognizing depressions as nutrient hotspots through improved soil testing and stakeholder communication opens the door to many opportunities for effective and targeted conservation implementation.