A nested catchment approach for defining the hydrological controls on non-point phosphorus transport

• Published in: Journal of hydrology (Amsterdam) Vol. 291; no. 3; pp. 218 - 231
• Main Authors: Scanlon, Todd M., Kiely, Ger, Xie, Qiushi
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.06.2004; Elsevier Science
• Subjects: Catchment; Discharge; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Freshwater; Geochemistry; Hydrology; Hydrology. Hydrogeology; Mineralogy; Phosphorus; Pollution, environment geology; Sediment; Silicates; Topography; Water geochemistry; Ireland; Western Europe; Eire; Phosphorus; Sediment; Catchment; Topography; Discharge; particulate matters; stream transport; models; Europe; streams; topography; concentration; covariance; slopes; pollution; nonpoint sources; drainage basins; suspended materials; hydrochemistry; discharge; erosion; soils; phosphorus
• ISSN: 0022-1694; 1879-2707
• DOI: 10.1016/j.jhydrol.2003.12.036

Stream water phosphorus (P) concentrations for three nested pastureland catchments located in southern Ireland, having areas of 0.14, 2.11, and 15.24 km 2, were monitored for the purpose of defining the hydrological controls on the P transport. Concentration–discharge ( C– Q) relationships were developed for total phosphorus (TP) and its two components, dissolved phosphorus (DP) and particulate phosphorus (PP), where Q is the area-normalized discharge. An analysis of covariance statistical test was applied to determine if any differences in C– Q relationships existed between sub-catchments. Significant differences ( p<0.01) between sites were found for the TP and PP C– Q relationships, but not for the DP C– Q relationships, indicating that phosphorus transport in its sediment-bound particulate form was alone responsible for the differences in overall P fluxes between sites. The intermediate-scale catchment possessed the highest discharge-specific PP and suspended solid concentrations. An analysis of catchment topography was undertaken in an attempt to explain the observed differences in the C– Q relationships for the individual sub-catchments. The distributions of the ln(A s / tan β) topographic index, where A s is the upslope contributing area per unit contour width and β is the local slope, were first considered in order to test the conceptual model of variable saturated area control on the overland PP transport. Next, the distributions of the length–slope ( LS) factor from the universal soil loss equation were evaluated as an index of erosion to describe PP transport. Neither topographic descriptor was found to satisfactorily conform to the C– Q observations, indicating that local catchment sediment delivery factors or in-stream channel processes are likely to be responsible for the observed differences.