Carlos H. Lechuga-Devéze

Submarine groundwater discharge as a source of dissolved nutrients to an arid coastal embayment (La Paz, Mexico)

AbstractSubmarine groundwater discharge (SGD) was investigated in the southeastern portion of La Paz Bay (Baja California, Mexico) using radon (222Rn) as a natural tracer. In the absence of permanent surface flows in this arid region, we hypothesize SGD is a major regional source of dissolved nutrients. Four spatial surveys showed higher radon and nutrient (NH4, NO3, NO2, PO4 and SiO4) values in the winter than summer lagging rainfall by 3–4xa0months. nThe surveys revealed two sites (Balandra and Merito) with a stronger radon signal. Intensive time series (12–24xa0h) measurements at those sites were used to estimate SGD fluxes using a radon mass balance approach. In Balandra, SGD was estimated to be 0.18xa0m3xa0m−2xa0day−1 and significant correlations between radon and nutrients (NO3 and SiO4) were observed. In Merito, SGD rates were estimated to be 0.10xa0m3xa0m−2xa0day−1 and no correlations between nutrients and 222Rn were observed. The difference between the two sites was interpreted to be related to different components dominating SGD (i.e., fresh SGD in Balandra and saline SGD in Merito). The estimated SGD-derived nutrients fluxes were 2–52, 0.04–0.94, 7–164xa0mmolxa0m2xa0day−1 for dissolved inorganic nitrogen, phosphate, and silicate, respectively. These fluxes could explain between 5 and 20xa0% of the regional marine primary productivity values.

Ecology of Callinectes arcuatus and C. bellicosus (Decapoda, Portunidae) in a coastal lagoon of northwest Mexico

Some ecological aspects of the swimming crabs, Callinectes arcuatus and C. bellicosus are presented. Specimens were collected with a trawl net, both day and night, on a monthly basis from March 1998 to February 2000 in a coastal lagoon in northwest Mexico. A total of 1235 specimens were captured, C. bellicosus (n = 878) (abundance 0.5 to 60 ind. ha-1) was more abundant than C. arcuatus (n = 357) with an abundance from 0 to 38 ind. ha-1 during the study period. Both species were more abundant at night and usually were found in conjunction with macroalgae. Salinity (32 to 40‰) tended to favour the dominance of C. bellicosus over C. arcuatus (2.4 : 1) and the water temperature appeared to govern the breeding season (21 to 32°C). For both species, the breeding season runs from March until September (spring-summer), the recruitment of juveniles occurs during January and February (winter), and the lowest abundance of both species is found during October and November (fall). For both species, ovigerous females were observed in the mouth of the lagoon, and juveniles were found in the lagoons interior parts. The authors think that the observed ecological patterns of the species could be extrapolated to other coastal lagoons with a similar climate, oceanography, and geomorphology.

Effects of Sewage Discharge on Trophic State and Water Quality in a Coastal Ecosystem of the Gulf of California

This paper provides evidence of the effects of urban wastewater discharges on the trophic state and environmental quality of a coastal water body in a semiarid subtropical region in the Gulf of California. The concentrations of dissolved inorganic nutrients and organic matter from urban wastewater primary treatment were estimated. La Salada Cove was the receiving water body and parameters measured during an annual cycle were temperature, salinity, dissolved oxygen, nitrite, nitrate, ammonia, orthophosphate, and chlorophyll a. The effects of sewage inputs were determined by using Trophic State Index (TRIX) and the Arid Zone Coastal Water Quality Index (AZCI). It was observed that urban wastewater of the city of Guaymas provided 1,237u2009ton N yr−1 and 811u2009ton P yr−1 and TRIX indicated that the receiving water body showed symptoms of eutrophication from an oligotrophic state to a mesotrophic state; AZCI also indicated that the environmental quality of the water body was poor. The effects of urban wastewater supply with insufficient treatment resulted in symptoms of eutrophication and loss of ecological functions and services of the coastal ecosystem in La Salada Cove.