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<p>Accurate contaminant yield estimation in rivers is essential to developing water quality policies and monitoring their effectiveness over time. We assessed the contribution of high-flows (≥90th percentile) to total yields of nitrate-nitrogen, total nitrogen, total phosphorus, and <i>E. coli</i> calculated from monthly data over 15 years (310–325 sites) in New Zealand, and at 24 sites with high-frequency (30-min) nitrate-nitrogen and total phosphorus. High flows contributed 51–74% of annual contaminant yields at long-term sites and 48% of nitrate-nitrogen and 63% of total phosphorus in the high-frequency sites. Mean uncertainties in annual yields estimated from monthly monitoring data (compared to the true yield, calculated from high-frequency records) were 29% for nitrate-nitrogen and 52% for total phosphorus. Daily sampling was needed to reduce uncertainty to &lt;10% especially in catchments with a high proportion of agricultural land use.</p>

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High flows contributed a large part of annual contaminant yields in New Zealand’s rivers

  • 期刊论文

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  • 发表日期：

    2025年4月30日

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  • Richard W. McDowell,
  • Esther Meenken,
  • Alasdair Noble,
  • Mike Kittridge,
  • Olivier Ausseil,
  • Laura Keenan,
  • Ton Snelder,
  • Crile Doscher

摘要

Accurate contaminant yield estimation in rivers is essential to developing water quality policies and monitoring their effectiveness over time. We assessed the contribution of high-flows (≥90th percentile) to total yields of nitrate-nitrogen, total nitrogen, total phosphorus, and E. coli calculated from monthly data over 15 years (310–325 sites) in New Zealand, and at 24 sites with high-frequency (30-min) nitrate-nitrogen and total phosphorus. High flows contributed 51–74% of annual contaminant yields at long-term sites and 48% of nitrate-nitrogen and 63% of total phosphorus in the high-frequency sites. Mean uncertainties in annual yields estimated from monthly monitoring data (compared to the true yield, calculated from high-frequency records) were 29% for nitrate-nitrogen and 52% for total phosphorus. Daily sampling was needed to reduce uncertainty to <10% especially in catchments with a high proportion of agricultural land use.