Water quality assessment in mosquito breeding habitats based on dissolved organic matter and chlorophyll measurements by laser-induced fluorescence spectroscopy

Abstract

Rapid urbanization and its associated pollution can affect water quality in mosquito breeding habitats and, as a result, the ecology and control of mosquito vectors. To understand the effects of pollution on mosquito vectors, an accurate assessment of water quality in breeding habitats is needed. Presently, water quality assessment of mosquito breeding habitats is usually based on the measurement of individual physicochemical parameters. However, several parameters are sometimes difficult to interpret or may not give a clear picture of the overall water quality of the breeding habitats, especially when the pollutants are in complex mixtures. This study employed the use of Laser-Induced Fluorescence (LIF) spectroscopy to assess water quality in breeding habitats of Anopheles, Aedes, and Culex mosquitoes in urban areas in Cape Coast, Ghana. The LIF spectra, using a 445-nm diode laser, were measured from field-collected water samples in the laboratory. The LIF spectra showed the presence of dissolved organic matter (DOM) and chlorophyll in the breeding habitats. The DOM and chlorophyll fluorescence signals were normalised by the Raman vibrational signals to determine water quality in each habitat. The overall water quality was better in Aedes breeding habitats than in Anopheles and Culex breeding habitats. The poor water quality in Anopheles and Culex breeding habitats was due to the presence of high fulvic acid and chlorophyll content, which often reflect pollutants from anthropogenic sources. Anopheles and Aedes habitats were made up of mainly An. coluzzii and Ae. aegypti respectively while Culex species were identified to genus level. The results add up to the growing concern about the breeding of Anopheles in polluted habitats. The study demonstrated for the first time the ability of LIF spectroscopy to assess water quality in mosquito breeding habitats.

Fig 1

Breeding habitats of A. Anopheles (An. coluzzii), B. Aedes (Ae. aegypti), and C. Culex mosquitoes where water was collected and measured for Laser-Induced Fluorescence spectra.

Fig 2. Experimental setup used to measure the LIF spectra of water samples from the mosquito breeding sites.

Fig 3. LIF spectra of water samples collected from three different breeding sites of mosquito species (Anopheles, Aedes, and Culex) in Cape Coast, Ghana.

Fig 4

A-Fitted LIF spectra showing the DOM, water Raman band and chlorophyll fluorescence after spline interpolation separately. B- the water Raman and chlorophyll band for the various mosquito breeding sites after subtracting the DOM.

Fig 5. The relationship between the Chlorophyll to water Raman band ratio (C/R) and DOM to water Raman band ratio (D/R) for water samples from the mosquitoes’ various breeding habitats.

It enables the determination of the water quality of the samples from multiple breeding sites.

Fig 6

PCA of LIF spectra of water samples from the various breeding sites with (A) Score plot showing distribution pattern among samples and (B) loading plot for PCs 1 and 2 showing specific regions (wavelengths) causing the distribution pattern in the score plot; (i) 460 nm– 515 nm, and (iii) 535 nm– 660 nm representing the DOM region, (ii) 515 nm– 535 nm representing the water Raman band and (iv) 660 nm– 780 nm representing the Chlorophyll region.

Fig 7. Deconvolved LIF spectra showing the constituents of water samples from mosquito breeding sites.