Analysis of Stable Isotopic Composition of Precipitation in Katsina State In Nigeria As An Indication of Water Cycle

Abstract

The seasonal nature of precipitation in recent years had seriously affected the industrial and agricultural activities in Katsina state. Thus, stable isotopes composition of precipitation was used to check water cycle which delineated the nature of precipitation. The phase changing characteristic of water during successive cycle of evaporation and condensation (hydrological cycle) reveals the magnitude of isotope fractionation which reflect a wide range of ?²H and ?¹⁸O values in precipitation. The isotopic concentration changes, whenever condensation occurs to form precipitation. 19 precipitation samples were collected from different areas across Katsina state in Nigeria. The delta values for both deuterium and oxygen-18 of the samples were determined using Geo 20-20 Mass-Gas Spectrometer. Katsina State precipitation  shows a wide range of stable isotopes variation; the ?²H values range from -74‰ to -4.4‰ standard mean ocean water (SMOW) with weighted mean of -39.3‰ and the ?¹⁸O values range from -10.20‰ to –1.88‰ (SMOW) with a weighted mean value of -6.1‰. Thus the delta values distribution for the State define a straight line on a cross-plot of ?²H against ?¹⁸O represented by approximate equation known as Local Meteoric Water Line (LMWL); ?²H = 8.2 ?¹⁸O + 11.5‰. The slope in LMWL of the Katsina state indicates very minute or no evaporation effect during precipitation and thus confirms the continental nature of its precipitation (water form in the atmosphere which was raised from the land).

Keywords: Fractionation, Stable isotope, Meteoric water, Deuterium, Oxygen-18