Spatiotemporal distribution of the bacterial contamination of agricultural and domestic wastewater discharged to a drainage ditch (Sinaloa, Mexico)

The agricultural drainage water from the Sinaloa valley (Mexico) is often reused in agriculture and aquaculture before reaching coastal water bodies. Discharged water must be of good quality to maintain the health of ecosystems and prevent damage to the organisms that compose them. This research determined the occurrence of coliforms in a drainage ditch known as La Michoacana (Sinaloa) that receives contaminated water from agricultural and urban sources. A section of 3.6 km was studied during 2013 and samples were obtained monthly from five equidistant sampling sites. Each water sample was analyzed for total coliform (TC) and fecal coliform (FC) content, pH, salinity, temperature, and dissolved oxygen percentage (%DO). The sampling sites with the highest bacterial contamination were associated with direct discharges of domestic wastewater and those with the lowest to the output drain. The performance of this agricultural ditch decreased the concentration of coliforms, with median and average values of 96% and 87% for TC, and 98% and 85% for FC, respectively. The most common bacteria were Escherichia coli (67.7%), Kluyvera cryocrescens (10.2%), and Enterobacter agglomerans (6.3%). Coliform concentration was positively correlated with temperature and negatively with %DO. The ditch improved the microbiological quality of the water, demonstrating remediation activities in the system. Proper management and maintenance of agricultural drainage ditches would favorably impact the health and biodiversity, as well as the intensive aquaculture and agricultural activities of the Sinaloa valley. El agua que conducen los canales de drenaje del valle agricola sinaloense (Mexico) es reutilizada con frecuencia en la agricultura y acuacultura antes de ser depositada en las aguas costeras. La calidad del agua descargada debe ser adecuada para mantener la salud de los ecosistemas y evitar dano a los organismos que los componen. Esta investigacion determino la presencia de coliformes en el canal de drenaje agricola conocido como La Michoacana (Sinaloa), que recibe agua contaminada de fuentes agricolas y urbanas. Se estudio una seccion de 3.6 km del canal durante el ano 2013 y se recolectaron mensualmente muestras de agua de cinco puntos de muestreo equidistantes. A cada muestra se le analizo el contenido de coliformes totales (CT) y coliformes fecales (CF), pH, salinidad, temperatura y porcentaje de saturacion de oxigeno disuelto (%OD). Los puntos de muestreo con mayor contaminacion bacteriana estuvieron asociados a las descargas directas de agua residual domestica, y aquellos con menor contaminacion estuvieron asociados a la salida del canal de drenaje. El funcionamiento del canal disminuyo la carga de coliformes, con medianas y valores promedio del 96% y 87% para CT, y 98% y 85% para CF, respectivamente. Las principales bacterias identificadas fueron Escherichia coli (67.7%), Kluyvera cryocrescens (10.2%) y Enterobacter agglomerans (6.3%). La concentracion de coliformes presento una correlacion positiva con la temperatura y negativa con el %OD. El canal de drenaje La Michoacana mejora la calidad microbiologica del agua que conduce, lo cual demuestra funciones de remediacion en el sistema. El mantenimiento y manejo adecuado de los canales de drenaje agricola puede impactar favorablemente la salud y biodiversidad, asi como las actividades acuicolas y agricolas intensivas del valle sinaloense.