Luis Walter Daesslé

Relationship between metal enrichments and a biological adverse effects index in sediments from Todos Santos Bay, northwest coast of Baja California, México.

In 1992 and 2004, heavy metals concentrations were measured in surficial sediments from Todos Santos Bay, located in Ensenada, Baja California, Mexico. The aim was to search for relationships between metal enrichment factors and a biological adverse effects index. Unlike Ni, the elements Cd, Cu and Zn showed significant correlations (p<0.05) between enrichment factors and the biological adverse effects index. Cu showed a 0.74:1 relationship, which means that any enrichment above 0.74 could represent biological adverse effects. On the other hand, Cd and Zn enrichments must be >5.5 and >1.5, respectively, in order for the sediments to be considered toxic. In general, data showed that most of the metal concentrations in Todos Santos Bay sediments could not cause adverse effects to biota. Only Ensenadas harbor and the zone next to a dredging dumping site showed metal enrichments that could be toxic.

Clay dispersal and the geochemistry of manganese in the Northern Gulf of California

The regional distribution of Fe and Mn in bulk sediments, and in different geochemical fractions, has been determined in surficial sediments from the Northern Gulf of California. The regional distribution of Fe (0.35–2.83%) and Mn (97–922m gg � 1 ) in the sediments is mainly controlled by the distribution of fine-grained particles.Unlike silt (4– 62.5mm), clay (o4mm) in the NGC is mainly derived from the eroding Colorado River Delta and transported southward adjacent to the Baja California coast, making up to 50% of the sediments.Normalisation of Fe and Mn against the relative abundance of clay indicates that the main source of these metals toward the Central Gulf of California is the re-suspension and re-deposition of the estuarine sediments derived from the Colorado River Delta. Iron and Mn correlate statistically; their concentrations are similar to other coastal sediments in Baja California and in seston from the Colorado River Delta.While the partition geochemistry of Fe suggests a dominant association of this element with the lithogenic phases throughout the NGC, Mn is significantly partitioned in the exchangeable (average 15%) and carbonate (average 32%) sediment phases, especially in clayey sediments derived from the estuarine region. The influence of Colorado River Delta-derived exchangeable Mn extends at least as far as the central Tibur ! on Basin, being probably responsible for the anomalously high Mn concentrations found in near-bottom waters in the Central Gulf of California. r 2002 Elsevier Science Ltd.All rights reserved.

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.

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.