A Modeling Framework to Predict Changes in Soil Chemistry and Agricultural Return Flow in Seawater Farming of Halophytes

  • Qingqian Ning

Student thesis: Master's Thesis

Abstract

Growing halophyte plants using seawater offers a sustainable solution for the generation of biomass feedstocks for carbon-neutral biofuels. Seawater irrigation in a planned pilot test in Abu Dhabi is likely to encounter a few problems which were not encountered in past pilots in Mexico and Eritrea. The purpose of this project was to study the water balance and transient salt deposition in soil and irrigation water at more realistic local conditions of high soil and seawater salinity, and high evaporation rates. An evaporation model was used to study the seawater and shallow coastal groundwater evaporation, both of which are highly saline electrolyte solutions. The results showed that evaporation using the PHRQPITZ activity coefficient model (a virial model) started to precipitate minerals earlier than using the B-dot activity coefficient model (an adjusted Debye-Hückel model). In addition, at higher initial salinity of applied water, larger amounts of mineral mass were precipitated. A 1-D finite-difference saturated-flow reactive transport model was constructed to study the water balance and salt deposition in coastal soils of the 5 possible sites for the pilot test in Abu Dhabi. The model soil column was populated using data interpreted from the Abu Dhabi Soil Survey. In order to avoid the salt penalty of seawater irrigation, an additional 25%, 50%, and 100% by volume of water was used to irrigate the soil column. The modeling results showed: 1) The soil type did not have a significant influence on the salinity of agricultural return water, however, hydraulic loading was found to be inversely related to the salinity of the agricultural return water; 2) mineral precipitation was highly influenced by the original soil type; however, irrigation loading rate and activity coefficient model did not appear to make a significant difference on the precipitation; and, 3) owing to mineral deposition, the porosity of all cells decreased over time. The salinity of return water was less saline than the groundwater present at the potential sites, though it was higher than the salinity of the seawater applied. Special attention should be paid to mineral deposition and soil porosity in future seawater farming implementations.
Date of AwardJun 2013
Original languageAmerican English
SupervisorFarrukh Ahmad (Supervisor)

Keywords

  • Halophyte Plants
  • Seawater Irrigation
  • Water Balance
  • Transient Salt Deposition
  • Salt Penalty
  • Hydraulic Loading
  • Return Water.

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