Ecological Modelling 187 (2005) 60–70 Modelling the effects of land-use modifications to control nutrient loads from an agricultural catchment in Western Australia C. Zammit a,b , M. Sivapalan a,∗ , P. Kelsey b , N.R. Viney c a Centre for Water Research, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia b Western Australian Department of Environment, Hyatt Building, 3 Plain Street, East Perth, WA 6004, Australia c CSIRO Land and Water, Private Bag No. 5, Wembley, WA 6913, Australia Available online 19 February 2005 Abstract The estuary of the Swan and Canning Rivers in Western Australia is becoming increasingly prone to algal blooms, fish deaths and other biochemical problems that are thought to be associated with increasing eutrophication. Phosphorus and nitrogen en- richment are seen as the two most common causes of such eutrophication, with both elements being transported in streamflow and with concentrations strongly dependent upon land-use in the catchment. Many of the efforts to prevent and control eutroph- ication in the estuary are focused on managing land-use within the catchment. In this paper, the large-scale catchment model (LASCAM) is applied to Ellen Brook, a rural catchment located within the Swan River catchment, to simulate catchment exports of phosphorus and nitrogen, under a range of land cover scenarios that are designed to control the eutrophication. The scenarios, which are related to different management options for the catchment, are: (i) reforestation of agricultural land; (ii) reduction in fertiliser application; and (iii) urbanisation following a highway development. The model results show that: (i) full reforestation of agricultural land is expected to reduce phosphorus and nitrogen export by 50 and 85%, respectively; (ii) a proportionally greater reduction of phosphorus and nitrogen export occurs for smaller areas of reforestation than for larger areas; (iii) reduction in phosphorus fertiliser application produces a linear response with respect to phosphorus export; (iv) urbanisation increases runoff due to the larger impermeable areas causing an increase of overland flow during storms; and (v) phosphorus and nitrogen loads are expected to increase about 4 and 12%, respectively, during the 10 years following urbanisation. © 2005 Elsevier B.V. All rights reserved. Keywords: Land-use management; Nutrient loads; Agricultural catchments; Water quality modelling; Eutrophication ∗ Corresponding author. Tel.: +61 8 6488 2320; fax: +61 8 6488 1015. E-mail address: sivapala@cwr.uwa.edu.au (M. Sivapalan). 1. Introduction Ecological processes and biodiversity of estuarine and coastal waters in many parts of the world are under threat from increasing anthropogenic inputs of nutri- ents (Cloern, 2001). Many of these increases are at- tributed to expansion of human populations along the 0304-3800/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.ecolmodel.2005.01.024