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Nitrogen and phosphorus annual cycle in the Paso Bonito reservoir (Cienfuegos, Cuba)The Paso Bonito reservoir is a source of supply for the city of Cienfuegos and part of the city of Santa Clara. Concentrations of nitrogen and phosphorous in the reservoir and their relationships with the watershed and reservoir management were analyzed on seven dates between September 2006 and November 2007. The reservoir's management was evaluated with respect to water inƀuxes and discharges and the water residence time. In the water column near the reservoir discharge intake the ratio of dissolved inorganic nitrogen to phosphorus indicated that phytoplankton growth was most commonly co-limited by nitrogen and phosphorus or by phosphorus alone. Fifty-two percent of the phosphorous measurements classiſed the reservoir as eutrophic. Only N-NH 4 and P T concentrations changed signiſcantly with depth. Eighty seven percent of the N-NO 3 values, as well as N-NH 4 during the month of October, indicated water contamination according to the Cuban Regulation used. These results were expected due to watershed and reservoir management. Finally, some issues related to reservoir management are discussed.

Temporal distribution patterns of some physical and chemical variables in the Paso Bonito reservoir, Cienfuegos, CubaA study is presented on the pH, redox potential (Eh), dissolved oxygen (DO), and temperature (T) in the Paso Bonito reservoir, used as a source of drinking water supply for the Cienfuegos City. This reservoir has its basin located mainly in a mountain area, affected by the organic, physical, and residue pollution from an old pyrite mine. From September 2006 through November 2007 samples were collected at meter intervals from the surface to bottom near water withdrawal site. The reservoir was polymictic during wet summers, and monomictic during dry summers. During thermal stratiſcation it had a clinograde oxygen distribution pattern, a pH between 7.0 and 8.1 and a negative hypolimnetic Eh during thermal stratiſcation. We derived an empiric model relating Eh, DO and T. The correlations between the studied indicators were also determined. These results will facilitate the interpretation of highly complex phenomena such as the release of nutrients, metals, and organic matter from the sediments.

Ionic variability and trophic characteristics of the Abreus reservoir, CubaThe Abreus reservoir is located in the Cienfuegos province, in mid-southern Cuba. It was built in 1986 for irrigation purposes but at present it is also used for industrial purposes. It is affected by agricultural, human and industrial wastes. In order to investigate the ionic variation, a temporal series of main compounds taken from a database generated from 1987 to 2005 was used. The descriptive statistics, seasonal behavior, and the relationship among variables were evaluated, and a principal component analysis was performed for data reduction. Water was slightly saline and very hard, with a high correlation among variables, which allowed them to be grouped in a new variable called "mineralization". This new variable had a marked seasonal behavior with signiſcant differences between two periods, from November to May, in which the water has a higher saline content and is inƀuenced by evaporation, and from June to October, when the composition of the water is inƀuenced by the rain. The values obtained for the seasonal indexes of the variables studied corroborate the signiſcant differences in the mineralization between both periods. This information is considered relevant for better water management. To evaluate the trophic status, ſve sampling campaigns were carried out between 2008 and 2009, in which water transparency was measured using Secchi's Disc, as well as total phosphorous (P T ) concentration, total inorganic nitrogen (Ni T ), and chlorophyll a. In spite of the high values of hardness, P T registered high values, classifying the reservoir as eutrophic. The nitrogen was the limiting nutrient for the phytoplanktonic growing. For this reason it must be regulated in order to control the reservoirs eutrophication.