Concentracion De Nutrientes Y Su Proporcion C:N:P En Sedimentos Superficiales De Un Complejo Lagunar Costero Tropical Afectado Por Los Escurrimientos Agricolas

Nutrients in sediments C:N:P

NUTRIENT CONCENTRATIONS AND THEIR C:N:P RATIOS IN SURFICIAL SEDIMENTS OF A TROPICAL COASTAL LAGOON COMPLEX AFFECTED BY AGRICULTURAL RUNOFF

CONCENTRACION DE NUTRIENTES Y SU PROPORCION C:N:P EN SEDIMENTOS SUPERFICIALES DE UN COMPLEJO LAGUNAR COSTERO TROPICAL AFECTADO POR LOS ESCURRIMIENTOS AGRICOLAS

G de la Lanza-Espino,
FJ Flores-Verdugo,
SHernandez-Pulido,
I Penié-Rodríguez

ABSTRACT
Nutrient contents and C:N:P ratios in sediment were studied in a tropical coastal lagoon complex on the north-west coast of Mexico, between 15 most contaminated to the country, because of has received heavy agricultural runoff since the 1950’s. In this paper is evaluated the relationship between the C:N:P ratios with the sediment type in the AltataBay-Ensenada del Pabellón coastal lagoon complex to discriminate the possible origins of organic matter from phytoplankton, mangroves, river inflow and agricultural wastewaters. In general, the nutrient content results analyses fall into two groups based on the sediment grain size: sandy sediments with carbon concentrations between 662 to 974 µmol/g, nitrogen from 11 to 75 µmol/g, phosphorus from 11 to 27µmol/g and C:N:P molar ratios between 34-66:1-5:1, and silt-clay sediments with higher contents of carbon (2 324 to 4 080 µmol/g), nitrogen (121 to 635 µmol/g), phosphorus (18 to 40 µmol/g), and larger C:N:P molar ratios (102-202:6-16:1) which are associated with agricultural runoff and discharges from a sugar cane processing factory.
Keyword: nutrient sediments, C:N:P, tropical coastal-lagoon,agriculture runoff.
RESUMEN
Se analizaron los contenidos de nutrientes y sus proporciones C:N:P en sedimentos de un complejo lagunar costero tropical al noroeste de México que recibe fuertes escurrimientos agrícolas desde 1950. Se evaluó la relación entre las proporciones C.N:P y el tipo de sedimento en el complrjo lagunar costero de la Bahía de Altata-Ensenada del Pabellón. En general, de losresultados de los análisis del contenido de nutrientes estuvieron dentro de dos grupos basados en el tamaño del grano de sedimentos: 1) sedimentos arenosos de la Bahía de Altata donde la concentración de carbono varío entre 662 a 974 µmol/g, nitrógeno 11 a 75 µmol/g y fósforo de 11 a 27 µmol/g con una proporción molar entre 34-66:1-5:1 y 2) sedimentos limo arcillosos de la Laguna Ensenada del Pabellón,con altos contenidos de carbono 2 324 a 4 080 µmol/g, nitrógeno 121 a 635 µmol/g, fósforo 18 a 40 µmol/g y una proporción C:N:P:, alta (102-202:6-16:1), dicha distribución asociada con el escurrimiento agrícola y con descargas de una industria azucarera.
Palabras clave: nutrientes en sedimentos, laguna costera tropical, escurrimiento agrícola.
INTRODUCTION
Organic matter (OM) origins incoastal waters are highly diverse. They can come from autochthonous sources such as phytoplankton, micro algae and aquatic macrophytes and also from allochthonous sources such as terrestrial vegetation, freshwater marshes and organic pollution from the upper parts of the hydrological basin. Beside, OM can exist as dissolved organic matter or as particulate organic matter (POM) from organic detritus.Because of its nature, the OM has a great affinity to be adsorbed or absorbed by suspended clays and finally to be deposited in sediment where is partially mineralized, becoming part of the sediment or to make new compounds such as humic substances. Knowledge of the sources, chemical activity, and the final destiny of the OM and the mixture of the dynamics of estuaries are critical to theunderstanding of global biochemical cycles and OM diversity (Bianchi & Canuel, 2001). Bianchi (2007) considers that the concentration and molar ratios of C with other elements can provide relatively good information related to the OM cycle, considering that the Total Organic Carbon (TOC) corresponds to approximately the 50 % of the OM. Even so the TOC/TN ratio, like the Carbon isotopic ratio, can be...