Dissolved phosphorus (DP) lost from agricultural sources is subject to various transformations during transport. Phosphorus (P) uptake length is a measure of the average distance a phosphate molecule travels prior to undergoing transformation. Accurate estimates of P uptake length are helpful in determining the fate and transport of P in waterways.
In irrigated agroecosystems, elaborate canal networks transport water great distances prior to returning the water to natural waterways. For example, the Twin Falls Canal Co. diverts up to 108 m3 s-1 through a 180 km main canal network and 1600 km lateral network. Irrigation return flow from this irrigation tract contributes up to 150 kg DP d-1 to the P-limited Snake River. Phosphorus transformation in the network, such as biotic uptake and sorption to sediment, affect both P bioavailability and transportability as well as potential remediation strategies.

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