title: Turnover and release of P-, N-, Si-nutrients in the Mexicali Valley (Mexico): interactions between the lower Colorado River and adjacent ground- and surface water systems.
abstract: A study on dissolved nitrate, ammonium, phosphate and silicate concentrations was carried out in various water compartments (rivers, drains, channels, springs, wetland, groundwater, tidal floodplains and ocean water) in the Mexicali Valley and the Colorado River delta between 2012 and 2013, to assess modern potential nutrient sources into the marine system after river damming. While nitrate and silicate appear to have a significant input into the coastal ocean, phosphate is rapidly transformed into a particulate phase. Nitrate is, in general, rapidly bio-consumed in the surface waters rich in micro algae, but its excess (up to 2.02 mg L(-1) of N from NO3 in winter) in the Santa Clara Wetland represents a potential average annual source to the coast of 59.4×10(3)kg N-NO3. Despite such localized inputs, continuous regional groundwater flow does not appear to be a source of nitrate to the estuary and coastal ocean. Silicate is associated with groundwaters that are also geothermally influenced. A silicate receiving agricultural drain adjacent to the tidal floodplain had maximum silicate concentrations of 16.1 mg L(-1) Si-SiO2. Seepage of drain water and/or mixing with seawater during high spring tides represents a potential source of dissolved silicate and nitrate into the Gulf of California.
authors.affiliation: Instituto de Investigaciones Oceanológicas, Universidad Autónoma de Baja California, Carretera Transpeninsular Tijuana-Ensenada No. 3917, Fraccionamiento Playitas, CP 22860 Ensenada, Baja California, Mexico.
authors.forename: A
authors.initials: A
authors.lastname: Orozco-Durán
authors.affiliation: Instituto de Investigaciones Oceanológicas, Universidad Autónoma de Baja California, Carretera Transpeninsular Tijuana-Ensenada No. 3917, Fraccionamiento Playitas, CP 22860 Ensenada, Baja California, Mexico; University of Erlangen-Nuremberg (FAU), Department of Geography and Geosciences, GeoZentrumNordbayern, Schlossgarten 5, 91054 Erlangen, Germany. Electronic address: walter@uabc.edu.mx.
authors.forename: L W
authors.initials: LW
authors.lastname: Daesslé
authors.affiliation: Instituto de Investigaciones Oceanológicas, Universidad Autónoma de Baja California, Carretera Transpeninsular Tijuana-Ensenada No. 3917, Fraccionamiento Playitas, CP 22860 Ensenada, Baja California, Mexico.
authors.forename: V F
authors.initials: VF
authors.lastname: Camacho-Ibar
authors.affiliation: Instituto de Investigaciones Oceanológicas, Universidad Autónoma de Baja California, Carretera Transpeninsular Tijuana-Ensenada No. 3917, Fraccionamiento Playitas, CP 22860 Ensenada, Baja California, Mexico.
authors.forename: E
authors.initials: E
authors.lastname: Ortiz-Campos
authors.affiliation: University of Erlangen-Nuremberg (FAU), Department of Geography and Geosciences, GeoZentrumNordbayern, Schlossgarten 5, 91054 Erlangen, Germany.
authors.forename: J A C
authors.initials: JAC
authors.lastname: Barth
mesh_terms: D003120:Colorado; D004784:Environmental Monitoring; D060587:Groundwater / Q000737:chemistry; D008800:Mexico; D009584:Nitrogen / Q000032:analysis*; D010758:Phosphorus / Q000032:analysis*; D045483:Rivers / Q000737:chemistry; D012822:Silicon Dioxide / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D014874:Water Pollutants, Chemical; D010758:Phosphorus; D012822:Silicon Dioxide; D009584:Nitrogen
keywords: Colorado River delta; Fluxes; Groundwater; Nitrate; Silicate; Wetland