Sediment Budgets for Small Salinized Agricultural Catchments in Southwest Australia and Implications for Phosphorus Transport

Robert J Wasson,David M Weaver

doi:10.3390/w13243564

Abstract

Examples of sediment budgets are needed to document the range of budget types and their controls. Sediment budgets for three small agricultural catchments (7.6 to 15.6 km2) in southwestern Australia are dominated by channel and gully erosion, with sheet and rill erosion playing a subordinate role. Erosion was increased by clearing naturally swampy valley floors and hillslopes for agriculture and grazing, and episodic intense rainstorms. The proportion of sediment from channel and gully erosion in the sediment budget appears to be determined by the depth of alluvial fills. Dryland salinization caused by clearing native vegetation has connected hillslopes to channels across narrow floodplains, increasing the Sediment Delivery Ratio (SDR). Yield and SDR are found to be insensitive to major in-catchment changes of vegetation cover after initial clearing, the ratio of sheet and rill erosion/channel and gully erosion, and sediment storage masses. This supports the idea that yield alone is often a poor indicator of the impact of land use and land management change. Riparian vegetation would reduce sediment yield but not phosphorus yield. This study demonstrates the value of mixed methods where field observations and chemical analysis are combined with information from local people.

Highlights

Sedimentation and estuarine eutrophication have been identified as serious problems globally
The Kalgan River catchment [6,7,8], along with other rivers in southwestern Western Australia, suffers from issues associated with sediment and P transport
Sediment yield decreases as the channel network walls and beds stabilize, and some gullies infill, in some cases particulate P may stay high as soluble P is absorbed on particles, and as sediment yield falls soluble P may rise because there is less sediment to absorb P

Summary

Introduction

Sedimentation and estuarine eutrophication have been identified as serious problems globally. Recent studies in sandy catchments identify soluble P as the dominant P form being transported [2,3,4,5], bringing into question the use of practices that reduce P transport through sediment control. Soluble P is often the dominant form of P in sandy catchments because phosphate is not removed from the solution by adsorption processes [2]. The Kalgan River catchment [6,7,8], along with other rivers in southwestern Western Australia, suffers from issues associated with sediment and P transport. Water quality measurements at different scales in the Kalgan River catchment suggest unconnected sources of sediment and P [2]. The Kalgan River catchment is a place where the conjunction of land-use/land cover change, salinization, erosion, and loss of P can be investigated together to contribute to our understanding of material budget changes

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Discussion

Conclusion