Testing of maintenance material from the Estero Salado and some side bays off the Bay of Guayaquil was conducted, including chemical and bacteriological analyses of sediment and suspended particulate phase (SPP) bioassays, using both the Pacific white shrimp, Penaeus vannamei, in Guayaquil, Ecuador and the “opossum shrimp”, Mysidopsis bahia in Houston, Texas. The SPP was prepared from channel or bay sediments and shrimp farm intake water. The work was designed to determine the potential environmental short-term (acute) impact of the proposed openbay disposal of maintenance material to be dredged from the Estero Salado.
The chemical analyses demonstrated no cause for concern relative to usual estuary sediments but demonstrated metals concentrations well above those normally found in sediments from shrimp ponds near Guayaquil. The bioassays with P. vannamei showed almost no acute toxicity but, did show some sublethal effects, including counts of Vibrio bacteria, a bacteria of concern to shrimp farmers worldwide. The mysid bioassays demonstrated both lethal and sublethal effects from the 100% SPP of several channel stations.
An analysis of the material to be dredged suggests that the plume from the proposed discharge can generate a significant and easily detectable increase over background turbidity near the discharge.The area affected by the increase in suspended sediment could encompass many of the shrimp farm intakes, which could provide an environmental stress to shrimp in the farms. All of this leads to the conclusion that the open bay discharge of material from the Estero Salado may cause problems to the shrimp farms that fringe Guayaquil Bay. Measures to reduce the amount of additional turbidity that would be generated during disposal were suggested.