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Aquatic ecology and management assessment in Valle de Bravo
reservoir and its watershed
V. Olvera-Viascána,b,
L Bravo Inclána, J Sánchez-Cháveza
aInstituto Mexicano
de Technología del Agua (IMTA), Paseo Cuauhnáhuac
8532, Jiutepec, C. P. 62550 Mor., Mexico
bIDECA, .S.A. de CV (Investigación
y Desarrollo de Estudios de Calidad del Agua),Sur 71 No. 413,
Col. Banjidal, C.P. 09450. D.F Mexico
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Abstract
The Valle
de Bravo reservoir provides 30% of Mexico City's drinking water.
Unfortunately, human activities in the watershed have affected the
water quality in this reservoir. Its trophic state changed from
oligotrophic in 1980 to mesotrophic in 1987. Research conducted
from March1992 to February 1993 defined the main limnological characteristics
of the water body and identified the most highly polluted subbasins
in the Amanalaco River Watershed. For this purpose, water, sediments
and vascular plants were sampled in the waterbody. In the Amanalaco
River Watershed land use and nutrient loadings in each subbasin
were quantified.
The study dam is warm and monomictic, with a nine-month
period of stratification and an overturn in December. Bottom anoxia
occurred during the stratified phase. The reservoir was eutrophic
during summer and mesotrophic the rest of the year. In the Amanalaco
basin, the highest phosphorus and nitrogen loadings (P, N in t y-1)
entered by way of the Becerra (4.9, 47.2), Pipioltepec (8.6, 61.9)
and Candelaria (8.5, 69.5) subbasins. A good agreement was found
in a comparison between the export coefficients estimates in the
Amanalaco River Watershed and the measured amounts of phosphorus
and nitrogen transported to 38 US waterbodies. Nevertheless, the
phosphorus export coefficients for the forested subbasins within
the Amanalaco River Watershed were rather high in relation to the
typical values found in the literature, and the values for agricultural
land were low ii' relation to the same source.
For the first time in Mexico, export coefficients for
phosphorus and nitrogen were estimated, both of which will be useful
in assigning priorities in land management. The export coefficients
estimates presented in this study can be applied to other scenarios
in Mexico which have the same temperate semihumid climate. ©
1999 Published by Elsevier Science Ltd and AEHMS. All rights reserved.
Keywords: Basin
management; Applied limnology; Aquatic weeds; Nonpoint sources;
Export coefficients;
Nutrient loading
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