Nutrient capture in an Iowa farm pond: Insights from high-frequency observations

Christopher E Brunet; Eva R C Gemrich; Savanna Biedermann; Peter J Jacobson; Keith E Schilling; Christopher S Jones; Andrew M Graham

doi:10.1016/j.jenvman.2021.113647

Nutrient capture in an Iowa farm pond: Insights from high-frequency observations

J Environ Manage. 2021 Dec 1:299:113647. doi: 10.1016/j.jenvman.2021.113647. Epub 2021 Sep 6.

Authors

Christopher E Brunet¹, Eva R C Gemrich², Savanna Biedermann², Peter J Jacobson³, Keith E Schilling⁴, Christopher S Jones⁵, Andrew M Graham⁶

Affiliations

¹ Grinnell College Department of Chemistry, USA; University of Iowa Department of Civil and Environmental Engineering, USA.
² Grinnell College Department of Chemistry, USA.
³ Grinnell College Department of Biology, USA.
⁴ Iowa Geological Survey, USA; University of Iowa IIHR, USA.
⁵ University of Iowa IIHR, USA.
⁶ Grinnell College Department of Chemistry, USA. Electronic address: grahaman@grinnell.edu.

PMID: 34523537
DOI: 10.1016/j.jenvman.2021.113647

Abstract

Shallow constructed ponds are abundant landscape features in the midwestern United States, suggested as an edge of field best management practice (BMP) in voluntary nutrient reduction strategies. The efficacy of such features is highly uncertain, however, and previous studies have lacked sufficient temporal resolution to determine N and P removals during critical periods of transport. We utilized high-frequency in-situ measurements and flow-weighted grab sampling to determine water and nutrient budgets for a typical constructed "farm pond" in central Iowa situated within the Iowa Southern Drift Plain. Our monitoring approach yielded insight into in-stream nitrogen processing and the relative importance of transport-vs. supply-limited N delivery. Diel patterns in NO₃-N observed during early Spring, prior to canopy closure, revealed that in-stream primary production and NO₃-N assimilation can influence downstream N delivery in a stream with nitrate pollution (mean annual NO₃-N of nearly 5 mg/L). Analysis of discharge-concentration hysteresis for NO₃-N showed a shift from transport to supply limitation for NO₃-N delivery over the growing season, influenced by antecedent moisture, with wet antecedent conditions leading to supply limitation. Significant NO₃-N removal (64% of 19.8 kg/ha inputs) occurred within the 4.2 ha pond (230 ha watershed), but total N removal was much lower (36% removal of 22.3 kg/ha inputs). The lower total N removal highlights the importance of both particulate N and dissolved organic N and ammonia export to the N budgets of hypereutrophic small ponds. Total P removal in the pond was only 8% of 2.3 kg/ha inputs, likely due to internal loading of recent and legacy sedimentary P within the pond. High-flow events dominated N and P inputs, during which removal efficacy of the pond was significantly diminished. Poor process performance during critical moments may partially explain lower than expected water quality improvements post-BMP implementation. Accordingly, shifting hydroclimatic regimes (e.g., frequency of intense rainfall events) will impact the efficacy of small ponds and other edge of field BMPs for nutrient reduction.

Keywords: Best management practices; Nitrate; Nutrients; Phosphorus ponds.

MeSH terms

Environmental Monitoring
Farms
Iowa
Nitrogen / analysis
Nutrients
Phosphorus / analysis
Ponds*
Water Pollutants, Chemical* / analysis

Substances

Water Pollutants, Chemical
Phosphorus
Nitrogen