4.7 Article

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

期刊

JOURNAL OF ENVIRONMENTAL MANAGEMENT
卷 299, 期 -, 页码 -

出版社

ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jenvman.2021.113647

关键词

Nutrients; Nitrate; Phosphorus ponds; Best management practices

资金

  1. Iowa Nutrient Research Center
  2. Grinnell College Innovation Fund award
  3. Grinnell College Mentored Advanced Project program

向作者/读者索取更多资源

Constructed farm ponds are common landscape features in the midwestern United States, but their efficacy in nutrient removal remains uncertain. This study used high-frequency measurements to analyze the nutrient budgets of a typical farm pond in central Iowa, revealing the impact of in-stream nitrogen processing and transport-vs.-supply-limited nitrogen delivery. The study also showed the importance of wet antecedent conditions on supply limited nitrogen delivery within the watershed.
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.

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