Nutrient removal in a closed silvofishery system using three mangrove species (Avicennia germinans, Laguncularia racemosa, and Rhizophora mangle).

The removal of ammonium (NH4(+)), nitrite (NO2(-)), nitrate (NO3(-)), and phosphate (PO4(-3)) in a closed silvofishery system was examined using three mangrove species (i.e., Avicennia germinans, Laguncularia racemosa, and Rhizophora mangle). Specifically, six closed tanks were installed for this experiment with a population of 60 Dormitator latifrons fishes per tank. We planted 40 seedlings in each of three experimental tanks separated by species, while the remaining tanks were used as control. During 15 weeks, nutrient concentrations among the three mangrove systems presented no significant differences (P>0.05). However, nutrient removal variability was minimum during the last 2-5 weeks. Mangroves presented an average efficiency of 63% for the removal of NH4(+) and NO2(-). Contrary, the average removal potential of NO3(-) and PO4(-3) was 50%. Results from this study suggest that the three mangrove species could be used in a closed silvofishery systems for the biological removal of NH4(+), NO2(-), NO3(-), and PO4(-3).

Pesticides distribution in sediments of a tropical coastal lagoon adjacent to an irrigation district in northwest Mexico.

This work presents the content of organochlorine (OCs) pesticides in sediments of both, agricultural drains from the Irrigation District 076, El Carrizo, Sinaloa, and of the adjacent coastal lagoon ecosystem of Agiabampo-Bacorehuis-Jitzamuri, located in northwest Mexico. A questionnaire was applied to the farmers of this irrigation district, to evaluate the usage of pesticides and to determine if banned OCs are still used. Around 31 tons of active ingredients were applied in the autumn-winter cycle (1997-1998). There were eighteen different pesticides; of them 61% are insecticides, 28% herbicides, 6% fungicides and 6% other compounds. Around 73% of the pesticides applied are organophosphorus, carbamates and sulfur, OCs are still applied and represent 4% of the total. All the pesticides applied in the irrigation district are authorized in the Official Pesticide Catalog, nevertheless forbidden and restricted compounds were detected in the sediment samples. The presence of heptachlor, heptachlor epoxide, alpha-endosulfan, beta-endosulfan, endosulfan sulfate, alpha-HCH, beta-HCH, lindane, delta-HCH, aldrin, dieldrin p,p'-DDT, p,p'-DDE and p,p'-DDD was recorded in the sediment sample. The analysis of the sediments suggest that the principal pesticides input to the coastal ecosystem is mainly through three of the seven agricultural drains, that collect the excess irrigation water and runoff from the district surface. A gradient of pesticide residues in sediments exists from the agricultural drains (52 ng OCs g(-1) dry weight) to the Jitzamuri bay (32 ng OCs g(-1) dry weight).

Distribution, fate and effects of pesticide residues in tropical coastal lagoons of northwestern Mexico.

Analyses of pesticide residues in sediments, water and biota of the Altata-Ensenada del Pabellon coastal lagoon system in Sinaloa, Mexico, showed the presence of organochlorine and organophosphorus compounds. For all the compounds analysed, concentrations in sediments were higher near the points of water discharge from ponds and drainage from the agricultural area. Among the organochlorines, total DDTs displayed the largest sedimentary reservoir, followed by total endosulfans and chlorpyrifos. In sediments, as well as in biota, pp'-DDT concentrations were lower than those of DDT metabolites, which confirms the reduction in the previous massive use of this compound in agriculture. Endosulfan is currently used in the region and endosulfan residues in lagoon sediments attained levels considered to be toxic to meiofauna, therefore constituting an ecological risk to lagoon ecosystems. There was a large sedimentary reservoir of chlorpyrifos but its ecotoxicological risk is difficult to assess due to lack of adequate comparative data. Nevertheless, concentrations of chlorpyrifos which approach acute toxic levels for shrimp were recorded in lagoon water. This suggests that drainage from agricultural fields during high runoff may, on occasion, cause mass mortality of shrimp and fish Organophosphorus pesticides are widely regarded to degrade very rapidly in aquatic systems. Experimental research performed with 14C-labelled chlorpyrifos and parathion has shown that they may be stabilised for relatively long periods of time through sediment-water partitioning. This extension of their environmental half-lives increases their potential for impacting on coastal ecosystems. Since organophosphorus pesticides are highly toxic for aquatic organisms at concentrations generally lower than organochlorines, their presence in the lagoon water and sediment is a matter for much concern. The increased use of tropical coastal lagoons for shrimp and fish farming requires the implementation of environmental management practices to protect these ecosystems from the impact of agricultural activities. Environmental management aims to preserve the ecosystem integrity of these coastal lagoons and, through improving the water quality, to allow the development of aquaculture and reduce human exposure to pesticide residues in food.