RESUMO
Abstract Lima, the capital of Peru, and Callao form one of the largest urban centers in South America, with a total population of 10.9 million as of 2017. Three rivers supply water to Lima; however, water for municipal use is mainly taken from the Rimac and Chillon Rivers. Correlating the historic of Rimac flow with the static level of a well in Miraflores, 1 km from Pacific Ocean, was estimated that the residence time, this is the time passing after water infiltrates the ground during a rainfall event until it reaches the Miraflores well, is three years, which agrees with the permeability of the valley, which is in the order of 10-4 ms-1. The average age of water from Lima wells is 6 years, which is consistent with the hypothesis that wells have water from several soil shells. In other hand, the relative abundance of 2H and 18O in wells in the Lima aquifer are in agreement with the hypothesis that the aquifer is recharged with water from rainfall events that occur in the highlands between 3000 and 5000 m above sea level (a.s.l). The contents of 2H,18O, Ca and SO4 of the Graton tunnel sample suggest that it corresponds to water coming from altitudes of 4500 m a.s.l.
Resumen Lima, la capital de Perú, y Callao forman uno de los centros urbanos más grandes de América del Sur, con una población total de 10.9 millones en 2017. Tres ríos abastecen de agua a Lima; sin embargo, el agua para los municipios se toma principalmente de los ríos Rímac y Chillón. Correlacionando el flujo histórico del Rímac con el nivel estático de un pozo en Miraflores, a 1 km del océano Pacífico, se calculó que el tiempo de residencia, esto es el tiempo que transcurre después de que el agua se infiltra en el suelo durante un evento de lluvia, hasta que llega a dicho pozo, es de tres años, lo que está de acuerdo con la permeabilidad del valle, que es del orden de 10-4ms-1. La edad promedio del agua de los pozos de Lima es de 6 años, lo que es consistente con la hipótesis de que los pozos tienen agua de varias capas de suelo. Por otro lado, la abundancia relativa de 2H y 18O en los pozos del acuífero de Lima está de acuerdo con la hipótesis de que el acuífero se recarga con agua de los eventos de lluvia que ocurren en las tierras altas entre 3000 y 5000 m. sobre el nivel del mar (s.n.m). El contenido de 2H, 18O, Ca y SO4 de la muestra del túnel Graton (3100 m.s.n.m.) sugiere que corresponde al agua proveniente de altitudes de 4500 m.s.n.m.
RESUMO
The canonical Redfield C:N:P ratio for algal biomass is often not achieved in inland waters due to higher C and N content and more variability when compared to the oceans. This has been attributed to much lower residence times and higher contributions of the watershed to the total organic matter pool of continental ecosystems. In this study we examined the effect of water residence times in low latitude lakes (in a gradient from humid to a semi-arid region) on seston elemental ratios in different size fractions. We used lake water specific conductivity as a proxy for residence time in a region of Eastern Brazil where there is a strong precipitation gradient. The C:P ratios decreased in the seston and bacterial size-fractions and increased in the dissolved fraction with increasing water retention time, suggesting uptake of N and P from the dissolved pool. Bacterial abundance, production and respiration increased in response to increased residence time and intracellular nutrient availability in agreement with the growth rate hypothesis. Our results reinforce the role of microorganisms in shaping the chemical environment in aquatic systems particularly at long water residence times and highlights the importance of this factor in influencing ecological stoichiometry in all aquatic ecosystems.