Tuesday, 8 November 2005
8

This presentation is part of: Phosphorus Chemistry in Soils: II. P Fluxes in Soil and Water Systems

Phosphorus Retention in Irrigation Canals.

Nathan Nelson and Dale Westermann.

Irrigation canals transport irrigation return flow, including water, sediment, and nutrients, back to surface water bodies. Phosphorus transformations during canal transport can affect both P bioavailability and the best management practices selected to minimize P inputs to waters of the US. The objective of this study was to determine P retention in an irrigation canal. Dissolved reactive P (DRP) concentrations in canal waters were increased from 0.08 mg L-1 to 0.25 mg L-1 by constantly injecting a P solution for 2.5 hrs. Br was used as a conservative tracer to determine dilution effects. Water was sampled at 10 min intervals 90, 180, 360, 760, and 1540 m downstream from the injection site. When at steady state, P concentration only decreased by 5% over 1540 m, equating to a P uptake length of 16.1 km, which is 2 to 3 orders of magnitude greater than P uptake lengths typical of natural streams. The linear P uptake rate was 1.1 μg P m-1 s-1. Longer P uptake length and lower uptake rate compared to natural streams may be a result of lower algal growth and higher water velocities.

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