A geochemical baseline study of giant kelp (macrocystis pyrifera) at the kelp blue farm to assess carbon sequestration potential
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Date
2024
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Publisher
University of Namibia
Abstract
The raised levels of carbon dioxide (CO2) in the earth’s atmosphere have contributed to global
climate change, which has adversely affected a wide range of individuals, communities, and
organizations. One of the ways to mitigate climate change is to grow a huge amount of kelp
forests that can absorb carbon dioxide from the atmosphere and sequester it in the deep ocean.
To grow these forests, the right biogeochemical conditions (temperature, nutrients, oxygen,
salinity, pH, trace metals and ions) within the ocean is vital to assess the sequestration potential
and the impacts on the ocean health. This study aimed at monitoring the biogeochemical
changes at the proposed Kelp Blue farm and surrounding areas further away from the farm.
This study also aims to create a baseline of the chemical composition of the farm and Lüderitz
areas, which has not been done before. Using the results obtained from the study, the potential
of the cultivated giant kelp to sequester CO2 will be evaluated. This study measured the
geochemical parameters using both in-situ probes and laboratory analyses at 10 different
locations in Lüderitz (both offshore and coastal): offshore (within the Kelp Blue Pilot project
farm, upstream of the farm in the Dumfudgeon rocks, downstream of the farm at Boot Bay and
further south of Lüderitz at the Halifax island) and the coastal areas which are adjacent to the
offshore study areas including at coastal site of Guano Bay which is about 17 km and the coastal
area of Grossebucht which is about 20 km south the town of Lüderitz as another control site.
This study also collected sediment samples at these offshore sites including further north of
Walvis Bay at the different latitudinal transects. The sediments were analysed for trace metals
by using a portable XRF and for carbon content by LOI (Loss on Ignition) method. Another
geochemical analysis done was the titrimetric method to CO2 determination of seawater by
using NaOH as a titrant the end points were determined. The concentrations of nutrients
(phosphates and nitrites) in seawater samples were determined by adding them to a 10 mL
cuvette, which had been zeroed first. A specific nutrient reagent was then introduced, and using
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prescribed sample preparation techniques, a spectrophotometer was employed to measure the
concentrations of the nutrients in µg/L and mg/L. The geochemical parameters changed in
relation to the seasonality and geographical positioning. In a season when the upwelling system
was strong, the concentration of nutrients, acidity and the value of the pH, salinity, other
geochemical parameters increased more, compared to other seasons and the further southern
sampling sites resembled to that of the Southern Benguela Upwelling System (SBUS). Higher
concentrations of phosphates (614 µg/L) were found in areas close to the islands. This is due
to the presence of guanos. These remarkable long duration geochemical measuring results
shows that the cultivated kelp can co-exist with other natural existing kelp beds in this
ecosystem, and they can thrive more predominantly in season of great influx of nutrients during
the season of strong winds. With a dynamic Benguela upwelling eastern boundary, these kelp
forests have an enormous potential to grow more and will function as carbon absorber and
eventually sequester more carbon when cultivated at larger scale. To quantify the carbon
sequestration potential of these giant kelps, there are other areas to be investigated such as
developing a sediment carbon baseline using isotopic analyses, lipid biomarkers, identifying
sediment hotspots where the kelp will be deposited, developing a carbon dioxide removal
model and geochemical dispersion models. All these other areas will be developed from the
baseline being developed by this study. This study recommends that a continuous and rigorous
monitoring of the water and sediment geochemical changes be done as the kelp forest grows
and as the scale of operation expands
Description
A thesis submitted in fulfilment of the requirements for the Degree of Master of Science (Chemistry)
Keywords
Kelp blue farm, Carbon sequestration, Giant kelp, Namibia, Global climate change, Biochemical conditions