1. Importance of Dense Aquatic Vegetation in Seasonal Phosphate and Particle Transport in an Agricultural Headwater Stream.
- Author
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Field, Hannah R., Sawyer, Audrey H., Welch, Susan A., Benefiel, Ryan K., Mathie, Devan M., Hood, James M., Pawlowski, Ethan D., Karwan, Diana L., Kreiling, Rebecca M., Johnson, Zackary I., Hanrahan, Brittany R., and King, Kevin W.
- Subjects
AGRICULTURE ,DITCHES ,SPRING ,RIPARIAN plants ,STAGNATION flow ,PARTICULATE matter ,ALGAL blooms - Abstract
Agricultural headwater streams and ditches commonly host dense stands of aquatic vegetation that grow and decay over seasons and exert physical and biological controls on the transport of nutrients from cropland to larger rivers. This study examined changes in the transport of phosphorus (P) in an agricultural drainage ditch in the Maumee River Basin (Ohio, USA) by conducting constant rate injections of a novel tracer mixture (conservative salt [Cl as NaCl], dissolved P [KH2PO4], and a fluorescent fine particle) in spring, summer, and fall. We quantified transport behavior for solutes and particles using a traditional transient storage modeling framework consisting of mobile and immobile storage zones connected by a first‐order exchange rate constant. Transient storage was greatest during the spring, when thicker vegetation caused more pooling and flow stagnation, and decreased through fall, as vegetation thinned. Soluble P uptake lengths were 8.7 times longer in fall than spring, likely due to declines in biological uptake rates with colder temperatures and immobile zone storage with thinning vegetation. Particle capture lengths also decreased by a factor of 4.3 from fall to spring. With the increasing eutrophication of Lake Erie and waterbodies around the world that lie downstream from agricultural landscapes, it is beneficial to understand nutrient transport across watersheds, including small agricultural streams. This study highlights the physical and biological roles that aquatic vegetation plays in small agricultural streams by creating seasonally variable immobile zones that slow the flow of nutrients, providing surface area for biofilms, and capturing particles that bind nutrients. Plain Language Summary: In the Midwestern United States and many parts of the world, headwater streams in agricultural lands are often thickly vegetated with reed grasses or other water‐loving plants. An important question is how this vegetation slows down or holds back nutrients, particularly phosphorus (P), which reduces water quality in downstream water bodies by contributing to algal blooms. To explore this question, we introduced a novel combination of chloride, dissolved P, and brightly colored particles to the same headwater stream over three seasons when vegetation was in various stages of growth or decay. We found that vegetation was most effective at capturing fine particles in spring when stands were thickest. Similarly, rates of plant and microbial uptake of dissolved P were faster in spring, leading to stronger retention of dissolved P. This study shows that aquatic plants in headwater agricultural streams and ditches play an important role in the downstream movement of both dissolved and particulate forms of nutrients. They form a storage zone that expands and contracts over the year in terms of its size, biological demand for dissolved nutrients, and efficiency at capturing suspended particles. Key Points: Aquatic vegetation stands are the dominant storage zone for dissolved phosphorus and fine particles in an open‐canopy agricultural ditchSoluble phosphorus uptake velocity was 27 times greater in spring than fall, likely due to biofilm growth on dense vegetationParticle capture efficiencies were 3 times greater in spring than fall due to denser vegetation [ABSTRACT FROM AUTHOR]
- Published
- 2023
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