Physical, chemical, biological and management aspects of coastal ecosystems facing eutrophication : the Guaymas Bay, Sonora, Mexico

Botello-Ruvalcaba, Martin Armando

Abstract

The present study has encompassed a series of field observations and theoretical considerations related to physical, chemical, and biological factors defining the process of eutrophication in the Guaymas system. Additionally, the work has produced the basic ecosystem model of the system through the modelling of the hydrodynamics, sediment dynamics, budget dynamics, net ecosystem metabolism and the potential for eutrophication. These findings produce an overall assessment of the system, which together with the environmental legislation and socio-economic concerns, allows those factors influencing decision making to be highlighted. In general, the knowledge of the hydrodynamic features indicates that the flushing capacity of the system may be insufficient to remove pollution discharged into the Guaymas sub-system and Estero el Rancho. There is a residual mass of water that exchanges from the Empalme sub-system to the Guaymas sub-system. Simulation of the trends for potential net transport of sediment indicates that bedload transport is likely to occur toward the head of the Guaymas sub-system. For the Empalme subsystem, there was a net bedload displacement toward the mouth. Mathematical interrelationships between measured phytoplankton biomass and environmental parameters shows through a MRA model that nearly 100% of its variance is influenced by nutrients, pH, temperature and salinity. The stoichiometric Redfield approach indicates that nitrogen is a limiting factor of the phytoplankton biomass growth in the Guaymas system, when other factors such as light, sinking, grazing, temperature and salinity gradients are not. However, an analysis of the two major subsystems shows that nutrients limiting in the Guaymas sub-system are closely related to phosphorus loads from wastewater sources, whereas for the Empalme sub-system, nutrient limitation was alternately by nitrogen and phosphorus. A primary quantitative outcome of the eutrophic status is given, using a simple biochemical budgetary approach, indicating that the Guaymas system is a net heterotrophic system, with a value of -4811.72 mmol.C.m^.y'1. Using a simple box model to characterise the potential hyper-trophic conditions suggests that phosphorus reduction in the system is accompanied by an improvement in water quality, hence management strategies must encourage P control from wastewater discharges into the sub-system. An analysis of the particular case of the Guaymas system in the context of the Mexican Environmental Legislation indicates that the quality standards set for the system will depend very much upon the designation ultimately used for the system. For instance, if some areas of the Guaymas sub-basin are designated for industrial use, a polluted influence is likely to occur in an area near the development. However, the areas influenced by this development must not pose a threat for the people living the Guaymas basin as stated in the Mexican Environmental Legislation.

Citation

Botello-Ruvalcaba, M. A. Physical, chemical, biological and management aspects of coastal ecosystems facing eutrophication : the Guaymas Bay, Sonora, Mexico. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4221102

• Thesis Type: Thesis
• Deposit Date: Dec 17, 2018
• Publicly Available Date: Feb 23, 2023
• Keywords: Biological sciences
• Public URL: https://hull-repository.worktribe.com/output/4221102
• Additional Information: Department of Biological Sciences, The University of Hull
• Award Date: Jun 1, 1999