A study of the mixing of natural flows using ICP-MS and the elemental composition of waters.

摘要

Determining flow patterns and the distribution of chemical constituents in the environment is critical to understanding and solving problems in freshwater, estuarine, and coastal environments. Computer models describing flows in the environment usually use empirical estimates of key parameters and are difficult to validate. The objective of this research was to develop a method to trace flows in surface waters by directly measuring existing conditions. Inductively coupled plasma-mass spectrometry (ICP-MS) was used to establish elemental "fingerprints" for water sources, and fractions of "fingerprinted" waters in a sample containing these source waters were estimated. Two different, complex systems were studied: the Sacramento-San Joaquin Delta and the near-coastal environment of Oahu, Hawai'i. If the method could be successfully used in these highly complicated environments, it should be applicable in almost any other natural environment. Successful application in three smaller, simpler systems supports this conclusion.; Within the Delta, source "fingerprints" were established, and their variation both temporally and spatially was determined. Elemental behavior was determined by laboratory work and field studies, and a simple mathematical model was used to calculate the fraction of source water in samples collected throughout the system. Mixing was consistently determined for most flow conditions using the tracer elements sodium, magnesium, calcium, and strontium. The method was used to establish the sources of water pumped from the Delta into major aqueducts and the effects of various operational changes.; Because of Hawai'i's uniform geology and difficulties measuring trace elements in saline waters, the method was significantly less successful in Hawai'i. Concentrations of major ions were used to estimate dilution for stream and wastewater flows to 25:1 in receiving waters; rare earth elements (lanthanum, praseodymium, and neodymium) were added to a wastewater flow to qualitatively determine mixing at dilution levels of about 300:1.; The procedures for ICP-MS analysis developed for this study are presented, as are the criteria for selecting and using elemental tracers in freshwater, estuarine, and certain saltwater environments. The method can be used to directly determine mixing levels and the distribution of chemical constituents, to validate computer models, and to address a variety of specific environmental issues.