Modeling Nutrient Export From Coastal California Watersheds

Abstract

Nitrate and phosphate export coefficient models were developed for coastal watersheds along the Santa Barbara Channel in central California. One approach was based on measurements of nutrient fluxes in streams from specific land use classes and included a watershed response function that scaled export up or down depending on antecedent moisture conditions. The second approach for nutrient export coefficient modeling used anthropogenic nutrient loading for land use classes and atmospheric nutrient deposition to model export. In an application of the first approach to one watershed, the nitrate and phosphate models were within 20% of measured values for most storms. When applied to another year, both nitrate and phosphate models generally performed adequately with annual, storm-flow, and base-flow values within 20% of measured nutrient loadings. Less satisfactory results were found when applied to neighboring watersheds with difference percentages of land use and hydrologic conditions. Application of the second approach was less successful than the first approach.(KEY TERMS: nutrient export coefficient modeling; nitrate; phosphate; nutrient flux; watersheds; streams; event-based modeling; coastal; watershed response function; high-frequency sampling.)Robinson, Timothy H., and John M. Melack, 2013. Modeling Nutrient Export from Coastal California Watersheds.

Relationships Among Nutrient and Sediment Fluxes, Hydrological Variability, Fire, and Land Cover in Coastal California Catchments

“…Our regression models identified increased fluxes with increased agricultural land cover for most nutrients (except ammonium), as has been demonstrated for other regions (Beaulac & Reckhow, ; Kaushal et al, ; Seitzinger et al, ). Fertilizer application is a major source of elevated nitrate concentrations in our agricultural watersheds (Robinson et al, ; Robinson & Melack, ). Nitrate is soluble and prone to be transported in runoff generated during rainfall.…”

“…Previous studies of streams in mediterranean ecosystems in southern California focused on export associated with very high atmospheric inputs of nitrogen (Fenn & Poth, ; Riggan et al, ). In central coastal California, Coombs and Melack () dealt with changes in nutrient and sediment transport in the first year after a fire, Goodridge and Melack () and Aguilera and Melack () examined relationships between discharge and concentrations of nutrients, and Robinson and Melack () and Robinson et al () applied export coefficient models. Warrick et al () compared concentrations and fluxes of suspended sediments from four different watersheds.…”

“…Urban and agricultural development have had marked influences on aquatic environments in regions with mediterranean climates . discharge and concentrations of nutrients, and Robinson and Melack (2013) and Robinson et al (2005) applied export coefficient models. Warrick et al (2015) compared concentrations and fluxes of suspended sediments from four different watersheds.…”

Improving and parameterising nitrogen and phosphorus modelling for application of LUCI in New Zealand

“…Maps and data summarising the results of each analysis are generated with each LUCI application to assist with analysis and interpretation. LUCI is readily applicable to a number of countries and a wide range of environments, and has been extensively applied in New Zealand (Ballinger 2011;Scott 2015;Marapara, 2016;Trodahl et al 2016), Wales (Jackson et al 2013a;Robinson et al 2013;Emmett et al 2014;Emmett et al 2015;Emmett et al 2016), and elsewhere (Bhatterei 2009;Jackson et al 2013b;Benavidez et al 2016).…”

“…A criticism of models employing an export coefficient approach is that they often consider only land cover, but climate, soil, topography, and land management are also significant influencing nutrient export variables (Khadam and Kaluarachchi 2006;Shi et al 2006;Ding et al 2010;Abell et al 2011;Robinson and Melack 2013;White et al 2015). This issue has been addressed using a variety of methods.…”