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 1,237 ton N yr−1 and 811 ton 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

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

Submarine 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 3–4 months. The surveys revealed two sites (Balandra and Merito) with a stronger radon signal. Intensive time series (12–24 h) measurements at those sites were used to estimate SGD fluxes using a radon mass balance approach. In Balandra, SGD was estimated to be 0.18 m3 m−2 day−1 and significant correlations between radon and nutrients (NO3 and SiO4) were observed. In Merito, SGD rates were estimated to be 0.10 m3 m−2 day−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, 7–164 mmol m2 day−1 for dissolved inorganic nitrogen, phosphate, and silicate, respectively. These fluxes could explain between 5 and 20 % of the regional marine primary productivity values

Tracing submarine hydrothermal inputs into a coastal bay in Baja California using radon

Hydrothermal fluid fluxes into deep ocean environments can be obtained from heat balance approaches. However, in shallow systems, hydrothermal heat fluxes can be masked by solar heating. In this paper, we use radon (222Rn) as a naturally occurring geochemical tracer to map the location of hydrothermal fluid inputs, as well as low-temperature groundwater discharges, and quantify fluxes into Concepcion Bay, Baja California, Mexico. This fault-bound bay contains intertidal seeps with salinities ranging from 5.3 to 25.6, temperatures reaching 64 °C, and nitrate reaching 900 μM. The bay is subject to natural eutrophication and frequent red tide events. A detailed 222Rn survey around the 100-km perimeter of Concepcion Bay allowed us to map the location of enhanced submarine groundwater inputs. Moorings at three contrasting coastal sites indicated that radon concentrations were higher at low tide and during the winter. Modeled hydrothermal fluid inputs ranged between 0.4 cm/day in the middle of the bay and 43.9 cm/day at the largest hydrothermal coastal seep site. Apparently, faults allow meteoric water to be heated and serve as conduits for its subsequent discharge through permeable marine sediments. When conservatively extrapolated to the entire bay using weighted distributions, these fluxes are estimated at 17.5 m3/s, a flow much higher than local ephemeral rivers. About 42% of the fluxes described consisted of fresh groundwater with the remaining made up of recirculated seawater. New nitrogen inputs associated with groundwater pathways are estimated to directly account for at least 15% of the local primary productivity. Our combined spatial survey/time series strategy can be very useful to quantify hydrothermal fluid inputs in particular at vent sites where a temperature signal in shallow surface waters is difficult to be observed

Paralytic shellfish toxin profile in strains of the dinoflagellate Gymnodium cataenatum and the scallop Argopecten ventricosus G.B. Sowerby II from Bahia Concepción, Gulf of California, Mexico

Gymnodinium catenatum Graham is a paralytic shellfish poison (PSP) producer that was described for the first time from the Gulf of California in 1943. During the last decade, its distribution along the Mexican Pacific coastline has increased. In Bahía Concepción, a coastal lagoon on the western side of the Gulf of California, G. catenatum has been linked to significant PSP concentrations found in mollusks. In this study, we describe the saxitoxin profile of 16 strains of G. catenatum, and catarina scallops (Argopecten ventricosus) from Bahía Concepción. Toxins were analyzed by HPLC with post-column oxidation and fluorescence detection. The average toxicity of the G. catenatum strains was 26.0±6.0 pg and 28.0±18.0 pg STX eq/cell after 17 and 22 days of growth, respectively. Ten toxins were recorded, but only dcSTX, dcGTX2, dcGTX3, C1, and C2 were always present in all strains at both growth stages. Since toxin profiles in scallops were similar to the cultures, biotransformations are not significant in catarina scallop. NeoSTX, GTX2, GTX3, and B2 were present in some G. catenatum strains and their presence varied with the age of the culture. In scallop samples, dcSTX, dcGTX2, and dcGTX3 were the most abundant toxins, and from the C-toxin group, only C2 was found. This unique toxin profile can be used as a biomarker for this population, when compared with strains of G. catenatum from other geographic regions