Ana Carolina Ruiz-Fernández

The environmental impact of shrimp aquaculture and the coastal pollution in Mexico

The moderated, but continual development of the shrimp aquaculture in Mexico, in conjuction with municipal and agriculture effluents, in the last decade has created the first symptoms of negative environmental impacts, due mainly to the discharge of nutrients and organic matter into adjacent coastal waters. Similarly, the increasing impairment of coastal water quality resulting from the discharge of domestic, agricultural and industrial wastes into coastal waters has affected the aquaculture profitability in certain areas. The cumulative impact of the main anthropogenic sources of nutrients in the Mexican coastal states was estimated in 190 088 ton N yr−1 and 51 831 ton P yr−1. The input from shrimp aquaculture is only 1.5% and 0.9% of the main sources of nitrogen and phosphorus. This last input, though small, is related to local and adverse effects on coastal ecosystems. The introduction of management measures to mitigate the adverse environmental impacts of shrimp aquaculture development has now become necessary and urgent.

Discharge of Nutrients from Shrimp Farming to Coastal Waters of the Gulf of California

This work deals with phosphorus (P) and nitrogen (N) loads resulting from shrimp farming in the NW coast of Mexico and a mass balance model for N and P is presented. Using such a model and the feed coefficients obtained in the NW region, nutrient loads for all shrimp farms in each state were estimated. The P and N loads from NW Mexican shrimp farming in 1993 were ca 345 and 1209 tons, and for 1998 were predicted to be 834 and 2903 tons, respectively. These loads correspond to 0.7 and 1.3% for 1993, and 1.7 and 3.1% for 1998, of the total sources of P and N in the region on the adjacent coastal waters. The contribution estimated of nutrients for 1998 via agriculture (2 6714 tons of P and 53476 tons of N) corresponds to 54.9 and 57.7%, and the municipal sources (1730 tons of P and 3806 tons of N) have an intermediate position with 3.6 and 4.1% of the total sources of P and N, respectively. The total nutrient load from aquaculture is small in comparison with other nutrient sources, however, local and adverse effects on coastal ecosystems can be of significance and subject to restrictions.

A long-term record of land use change impacts on sediments in Oualidia lagoon, Morocco

An integrated approach, involving land use patterns and heavy metal contents of the surficial and cored sediment, was proposed to detect the characteristic spatial and temporal scale of point and non-point source human disturbances on the Oualidia lagoon in Morocco. Identification and description of the temporal and spatial distributions of the main contamination sources of heavy metals are analyzed using statistics and GIS methods. The results show that surficial sediments are highly enriched in heavy metals compared to their preindustrial background levels. Land-use types affected lagoon sediment pollution in different ways: 1) agricultural areas had the highest potential for sediment contamination by heavy metals, particularly Pb, Cu and Hg, 2) Ni and Cr are the main pollutants originating from urban sewage and 3) oyster farming and traditional land uses such as salt flats, pastures showed low levels of others metals. The enrichment factors (normalized by Al) obtained from the sediment cores indicated that the lagoon is (strongly/moderately) polluted by all metals which were attributed to agricultural activities and wastewater discharges from urbanized areas.

Long-range atmospheric transport of persistent organic pollutants to remote lacustrine environments

Concentrations, temporal trends and fluxes of persistent organic pollutants (POPs: PAHs, PCBs and PBDEs) were determined in soil and (210)Pb-dated sediment cores from remote lacustrine environments (El Tule and Santa Elena lakes) in rural areas of Central Mexico. In both areas, the concentrations of target analytes in soil and sediment samples were comparable and indicative of slightly contaminated environments. The prevalence of low-molecular-weight PAHs in soils suggested their mainly atmospheric origin, in contrast to the aquatic sediments where runoff contribution was also significant. Increasing contamination trends of PCBs and PBDEs were evident, showing maximum fluxes of 4.8 ± 2.1 and 0.3 ± 0.1 ng cm(-2) a(-1) for PCBs and PBDEs, respectively. The predominance of lower-brominated PBDEs and lower-chlorinated PCBs in soils and sediments indicated that their presence is mostly due to long-range atmospheric transport.

Historical PCB fluxes in the Mexico City Metropolitan Zone as evidenced by a sedimentary record from the Espejo de los Lirios lake

The accumulation of PCBs over time was studied in a sediment core collected from Espejo de los Lirios, an ecological reserve located within the heart of Cuatitlan Izcalli, in the Northern part of Mexico City Metropolitan Zone. A (210)Pb-derived chronology, was used to reconstruct the historical PCB fluxes to the site during approximately 84 yr (1911-95). The highest input fluxes occurred in the 1977, after a significant increase after the late 1940s. This trend is clearly the consequence of the increasing emissions that are related to the onset of industrial activities starting from early 1970s. A phase of decrease, after the ban of the use in open systems, ended in 1989 and in 1995, at the time of sampling, the trend was toward a new increase to the highest levels. A reconstruction of PCB atmospheric concentration from sedimentary fluxes is attempted; and the estimate suggests that PCBs concentrations in the air of the Cuautitlán Izcalli seem not of concern. Nonetheless, the contamination levels found in the sediments are relatively high, reaching values above the threshold effect level (TEL) guidelines and, in two cases, close to the probable effect level (PEL) which mean that some adverse effects on the fauna may have occurred all over the time interval represented by the core.

Dominance patterns in macroalgal and phytoplankton biomass under different nutrient loads in subtropical coastal lagoons of the SE Gulf of California

Nine macroalgal blooms were studied in five coastal lagoons of the SE Gulf of California. The nutrient loads from point and diffuse sources were estimated in the proximity of the macroalgal blooms. Chlorophyll a and macroalgal biomass were measured during the dry, rainy and cold seasons. Shrimp farms were the main point source of nitrogen and phosphorus loads for the lagoons. High biomasses were found during the dry season for phytoplankton at site 6 (791.7±34.6 mg m(-2)) and during the rainy season for macroalgae at site 4 (296.0±82.4 g m(-2)). Depending on the season, the phytoplankton biomass ranged between 40.0 and 791.7 mg m(-2) and the macroalgal biomass between 1 and 296.0 g m(-2). The bulk biomass (phytoplankton+macroalgal) displayed the same tendency as the nutrient loads entering the coastal lagoons. Phytoplankton and macroalgal biomass presented a significant correlation with the atomic N:P ratio.

Accretion rates in coastal wetlands of the southeastern Gulf of California and their relationship with sea-level rise

Sea-level rise (SLR) is one of the most conspicuous examples of the environmental impact of recent climate change. Since SLR rates are not uniform around the planet, local and regional data are needed for proper adaptation plans. 210Pb-dated sediment cores were analyzed to determine the trends of sediment accretion rates (SARs) at three tropical saltmarshes in the Estero de Urias lagoon (Gulf of California, Mexico), in order to estimate the SLR trends during the past ~100 years, under the assumption that these ecosystems accrete at a similar rate to SLR. A chemometric approach, including multivariate statistical analysis (factor analysis) of geochemical data (including δ13C; δ15N; C/N ratios; and Br, Na, and Cl as proxies for marine transgression) was used to identify the marine transgression in the sediment records. Based on core geochemistry, only one of the three cores provided a long-term record attributable to marine transgression. SLR trends, estimated from SARs, showed increasing values, from a minimum of 0.73 ± 0.03 mm yr−1 at the beginning of the 20th century and up to 3.87 ± 0.12 mm yr−1 during the period 1990–2012. The estimated SLR trend between 1950 and 1970 was comparable to the tide gauge records in Mazatlan City for the same period. Results showed the caveats and strengths of this methodology to reconstruct decadal SLR trends from the sedimentary record, which can be used to estimate long-term SLR trends worldwide in regions where monitoring data are scarce or absent.

Coexisting sea-based and land-based sources of contamination by PAHs in the continental shelf sediments of Coatzacoalcos River discharge area (Gulf of Mexico)

The oldest refinery and the major petrochemical complexes of Mexico are located in the lower reach of the Coatzacoalcos River, considered the most polluted coastal area of Mexico. A (210)Pb-dated sediment core, from the continental shelf of the Coatzacoalcos River, was studied to assess the contamination impact by the oil industry in the southern Gulf of Mexico. The sedimentary record showed the prevalence of petrogenic PAHs between 1950s and 1970s, a period during which waste discharges from the oil industry were not regulated. Later on, sediments exhibited higher contents of pyrogenic PAHs, attributed to the incineration of petrochemical industry wastes and recurrent wildfires in open dumpsites at the nearby swamps. The total concentration of the 16 EPA-priority PAHs indicated low levels of contamination (<100 ng g(-1)), except a peak value (>1000 ng g(-1)) during the late 1970s, most likely due to the major oil spill produced by the blowout of the Ixtoc-I offshore oil rig in deep waters of the southwestern Gulf of Mexico. Most of the PAH congeners did not show defined temporal trends but, according to a Factor Analysis, apparently have a common origin, probably waste released from the nearby oil industry. The only exceptions were the pyrogenic benzo(b)fluoranthene and benzo(a)pyrene, and the biogenic perylene, that showed increasing concentration trends with time, which we attributed to erosional input of contaminated soil from the catchment area. Our study confirmed chronic oil contamination in the Coatzacoalcos River coastal area from land based sources for more than 60 years (since 1950s).

Magnetic record of extreme marine inundation events at Las Salinas site, Jalisco, Mexican Pacific coast

Abstract Extreme marine inundation events (i.e. severe storms and tsunamis) denote a major hazard to coastal communities around the globe. In order to assess this hazard, long-term (beyond the instrumental and historic records) information on the magnitude and frequency of these events is critical. The coastal sedimentary record, together with other proxies, is now being tested to distinguish and reconstruct evidence of ancient inundation events. Recent studies commonly use anisotropy of magnetic susceptibility (AMS) parameters without statistical evaluation of the lateral variability of sedimentary layers. Here, we provide results from tested sedimentary layers. Moreover, we discuss the most recent strategies to identify deposits produced by major inundation events using the full battery of rock magnetic properties of sediments in Careyes Bay on the Jalisco coast, Eastern Pacific, a tectonically active coast subject to hurricanes. Oriented samples of lagoonal sediments were taken from a dug pit at Las Salinas site. The sampled stratigraphic sequence was basically composed of an upper sand and lower clay units. The upper part of the Las Salinas profile shows a drop in magnetic susceptibility by 50%. Two distinct magnetic fabrics are clearly identified. Fabric from the upper part of the profile most probably reflects a sedimentary structure which was originated in a more dynamic environment than the magnetic fabric recognized in the lower part of the profile. Hysteresis parameters also show variation in behaviour between the upper and lower parts of the profile. We propose here that the origin of the upper sand unit at the study site is most probably related to an extreme marine inundation event.

Reconstruction of Pyrodinium blooms in the tropical East Pacific (Mexico): are they related to ENSO?

Some microplanktonic species, mostly dinoflagellates, causing Harmful Algal Blooms (HABs), produce toxins which may affect the environment and human health, thus causing important economic losses. The dinoflagellate Pyrodinium bahamense var. compressum is one of the main species causing harmful algal blooms along the tropical Pacific. Although it was first reported along the Mexican coast in the 1970s, here we report that a sedimentary record of Pyrodinium cysts from the Gulf of Tehuantepec in the tropical East Pacific (Mexico), which spans from the 1860s, showed the continuous occurrence of Pyrodinium cysts and that their presence has been declining in the last few decades. Although Pyrodinium HABs have been attributed to El Niño events in the tropical Indo-West Pacific, the record shows that most blooms in the tropical East Pacific appear in periods of low sea surface temperature and higher rainfall, as can be observed during rapid shifts from cold (La Niña) to warm (El Niño) conditions in that region. This mechanism offers new ways to better predict and facilitate early detection of Pyrodinium HABs worldwide.