A mechanistic and trait-based approach to investigating macroinvertebrates distribution and exposure to microplastics in riverine systems
- Authors: Owowenu, Enahoro Kennedy
- Date: 2024-10-11
- Subjects: Microplastics Environmental aspects , Water quality biological assessment , Hydrodynamics , Hydrogeomorphology , Biotope , Flow type
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466666 , vital:76765 , DOI https://doi.org/10.21504/10962/466666
- Description: Microplastics in rivers pose an ecological risk. Hydraulic biotopes form distinct flow patches that vary longitudinally along the river, potentially influencing the transport dynamics of microplastics. Macroinvertebrates exhibit adaptations to different hydraulic biotopes through their unique traits. These traits can mediate their exposure to microplastics, thereby imposing selective pressures on these organisms. Different taxa often demonstrate preferences for specific hydraulic biotopes characterized by distinct flow regimes. Understanding the transport dynamics of microplastics mediated by hydraulic biotopes and the potential exposure of macroinvertebrates at the hydraulic biotope scale is important for determining the fate of riverine microplastics and detecting species at risk. Both empirical and theoretical studies have highlighted the interconnectedness of hydrology, geomorphology, and microplastic transport in rivers, yet, there remains a gap in understanding how a hydro-geomorphological approach could enhance the understanding of the microplastic transport process. Little is known about the role of traits in driving macroinvertebrate exposure to microplastics at a scale relevant to ecological dynamics. This study addressed these gaps by applying a hydro-geomorphological approach to investigate the distribution of microplastics at the hydraulic biotope scale and assessed the potential exposure of macroinvertebrates using a trait-based approach. This study also explored the relationship between microplastic abundance and selected water physicochemical properties, as well as the influence of adjacent land use types. By integrating these aspects the research provided a comprehensive understanding of microplastics dynamics in river systems, shedding light on both environmental factors shaping their distribution and the potential impacts on aquatic organisms. The study was conducted over the wet and dry seasons (October 2021 – July 2022) at 10 sites located in the upper, middle, and lower reaches of the Swartkops and Buffalo River systems in the Eastern Cape Province of South Africa. The hydraulic biotopes (i.e., pools, runs, riffles) were grouped into two conceptualised forms, namely, sink and flush hydraulic zones and were characterized by hydraulic indices such as the Froude number and the Reynolds number. The flush hydraulic zone represents hydraulic biotopes where microplastics can potentially be remobilized quickly into suspension, and the sink represents biotopes where microplastics can potentially accumulate and remobilisation is far slower. Fast-to-moderate flowing hydraulic biotopes were conceptualised as microplastics flush zones while slow-flowing to still biotopes as microplastic sink zones. Samples were collected at different depths in each hydraulic zone to quantify suspended and settled forms of microplastics. Microplastics targeted in this study ranged in size from 0.063 mm to less than 5 mm. Classification was achieved through microscopic observation, and confirmation via Fourier Transform Infrared Spectroscopy (FTIR-ATR) was conducted for samples ranging from 0.5 mm to less than 5 mm. At the site level, settled microplastics showed statistically significant spatial and temporal variations between the sites, and between the seasons (P < 0.05). The suspended microplastic varied only spatially. Fibres and fragments were the dominant microplastic shape, while polyethylene and polypropylene were the dominant microplastic polymers. Suspended microplastics showed statistically significant variation between urban land cover and other land cover categories (industrial, agricultural, rural, and natural land cover). Microplastics abundance was associated with high levels of turbidity, total suspended solids, total inorganic nitrogen, higher temperatures and increasing electrical conductivity. At the hydraulic biotope scale, the mean occurrence of suspended microplastics (1.76 ± 1.44 items/L; mean + SD) in the flush hydraulic zone was higher than that in the sink zone (1.54 ± 1.46 items/L), while settled microplastics were more abundant in the sink hydraulic zone (1.82 ± 1.98 items/L) than the flush hydraulic zone (1.32 ± 1.49 items/L). This observation was in line with the prediction in this study. The mean suspended and settled microplastics concentrations were higher during the wet season across the flush and sink hydraulic zones than in the dry season. Global multivariate analysis of variance (MANOVA) and two-way analysis of variance (ANOVA) revealed significant spatial and temporal variations in settled microplastics abundances between the flush and sink hydraulic zones. The results indicated that geomorphologically defined units such as riffles and moderate to fast runs (flush) generally contained lower amounts of settled microplastics compared to pools and backwaters (sink). However, this distinction between the flush and sink microplastic zones was observed only for settled microplastics and not for suspended microplastics. Suspended and settled microplastics showed a statistically significant relationship with the Froude number index. The generalised additive model indicated that settled microplastics abundance distribution decreased significantly with increasing Froude number value in the flush zone. Suspended microplastics decreased at low Froude number values and showed an increasing trend at higher Froude number values of about 0.75. The results indicate the usefulness of the hydraulic biotope scale microplastic monitoring approach in detecting microplastic hotspots and explaining variations in microplastics abundances driven by instream hydraulics. Four traits and ecological preferences of macroinvertebrates including body size, gill type, feeding habit, and velocity preferences were selected and resolved into 17 trait attributes. The sink hydraulic zones such as pools were indicated to favour exposure to and ingestion of microplastics compared to the flush zones such as riffles and fast runs. Large body size macroinvertebrates were associated with the sink zone. Taxa with a very small body size had a higher likelihood for microplastics ingestion than taxa with other body sizes. Collectorgathering macroinvertebrates taxa that have operculate gills with small body sizes were more prone to exposure to microplastics in hydraulic biotopes with slow to very slow velocities. Fibres were the most abundant plastic ingested by macroinvertebrates preferring the flush zone while fibres and fragments were mostly ingested by those preferring the sink zones. The binomial logistic model revealed a highly significant result for the likelihood of operculate gill shape to clog in the sink hydraulic zone. The result of the binomial logistic regression indicates the usefulness of the trait-based approach for predicting exposure to microplastics. Overall, the study reveals the influences of hydro-geomorphological features on the transport dynamics of microplastics and the usefulness of the trait-based approach in the ecological study of microplastics in riverine systems. , Thesis (PhD) -- Faculty of Science, Institute for Water Research, 2024
- Full Text:
- Date Issued: 2024-10-11
- Authors: Owowenu, Enahoro Kennedy
- Date: 2024-10-11
- Subjects: Microplastics Environmental aspects , Water quality biological assessment , Hydrodynamics , Hydrogeomorphology , Biotope , Flow type
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466666 , vital:76765 , DOI https://doi.org/10.21504/10962/466666
- Description: Microplastics in rivers pose an ecological risk. Hydraulic biotopes form distinct flow patches that vary longitudinally along the river, potentially influencing the transport dynamics of microplastics. Macroinvertebrates exhibit adaptations to different hydraulic biotopes through their unique traits. These traits can mediate their exposure to microplastics, thereby imposing selective pressures on these organisms. Different taxa often demonstrate preferences for specific hydraulic biotopes characterized by distinct flow regimes. Understanding the transport dynamics of microplastics mediated by hydraulic biotopes and the potential exposure of macroinvertebrates at the hydraulic biotope scale is important for determining the fate of riverine microplastics and detecting species at risk. Both empirical and theoretical studies have highlighted the interconnectedness of hydrology, geomorphology, and microplastic transport in rivers, yet, there remains a gap in understanding how a hydro-geomorphological approach could enhance the understanding of the microplastic transport process. Little is known about the role of traits in driving macroinvertebrate exposure to microplastics at a scale relevant to ecological dynamics. This study addressed these gaps by applying a hydro-geomorphological approach to investigate the distribution of microplastics at the hydraulic biotope scale and assessed the potential exposure of macroinvertebrates using a trait-based approach. This study also explored the relationship between microplastic abundance and selected water physicochemical properties, as well as the influence of adjacent land use types. By integrating these aspects the research provided a comprehensive understanding of microplastics dynamics in river systems, shedding light on both environmental factors shaping their distribution and the potential impacts on aquatic organisms. The study was conducted over the wet and dry seasons (October 2021 – July 2022) at 10 sites located in the upper, middle, and lower reaches of the Swartkops and Buffalo River systems in the Eastern Cape Province of South Africa. The hydraulic biotopes (i.e., pools, runs, riffles) were grouped into two conceptualised forms, namely, sink and flush hydraulic zones and were characterized by hydraulic indices such as the Froude number and the Reynolds number. The flush hydraulic zone represents hydraulic biotopes where microplastics can potentially be remobilized quickly into suspension, and the sink represents biotopes where microplastics can potentially accumulate and remobilisation is far slower. Fast-to-moderate flowing hydraulic biotopes were conceptualised as microplastics flush zones while slow-flowing to still biotopes as microplastic sink zones. Samples were collected at different depths in each hydraulic zone to quantify suspended and settled forms of microplastics. Microplastics targeted in this study ranged in size from 0.063 mm to less than 5 mm. Classification was achieved through microscopic observation, and confirmation via Fourier Transform Infrared Spectroscopy (FTIR-ATR) was conducted for samples ranging from 0.5 mm to less than 5 mm. At the site level, settled microplastics showed statistically significant spatial and temporal variations between the sites, and between the seasons (P < 0.05). The suspended microplastic varied only spatially. Fibres and fragments were the dominant microplastic shape, while polyethylene and polypropylene were the dominant microplastic polymers. Suspended microplastics showed statistically significant variation between urban land cover and other land cover categories (industrial, agricultural, rural, and natural land cover). Microplastics abundance was associated with high levels of turbidity, total suspended solids, total inorganic nitrogen, higher temperatures and increasing electrical conductivity. At the hydraulic biotope scale, the mean occurrence of suspended microplastics (1.76 ± 1.44 items/L; mean + SD) in the flush hydraulic zone was higher than that in the sink zone (1.54 ± 1.46 items/L), while settled microplastics were more abundant in the sink hydraulic zone (1.82 ± 1.98 items/L) than the flush hydraulic zone (1.32 ± 1.49 items/L). This observation was in line with the prediction in this study. The mean suspended and settled microplastics concentrations were higher during the wet season across the flush and sink hydraulic zones than in the dry season. Global multivariate analysis of variance (MANOVA) and two-way analysis of variance (ANOVA) revealed significant spatial and temporal variations in settled microplastics abundances between the flush and sink hydraulic zones. The results indicated that geomorphologically defined units such as riffles and moderate to fast runs (flush) generally contained lower amounts of settled microplastics compared to pools and backwaters (sink). However, this distinction between the flush and sink microplastic zones was observed only for settled microplastics and not for suspended microplastics. Suspended and settled microplastics showed a statistically significant relationship with the Froude number index. The generalised additive model indicated that settled microplastics abundance distribution decreased significantly with increasing Froude number value in the flush zone. Suspended microplastics decreased at low Froude number values and showed an increasing trend at higher Froude number values of about 0.75. The results indicate the usefulness of the hydraulic biotope scale microplastic monitoring approach in detecting microplastic hotspots and explaining variations in microplastics abundances driven by instream hydraulics. Four traits and ecological preferences of macroinvertebrates including body size, gill type, feeding habit, and velocity preferences were selected and resolved into 17 trait attributes. The sink hydraulic zones such as pools were indicated to favour exposure to and ingestion of microplastics compared to the flush zones such as riffles and fast runs. Large body size macroinvertebrates were associated with the sink zone. Taxa with a very small body size had a higher likelihood for microplastics ingestion than taxa with other body sizes. Collectorgathering macroinvertebrates taxa that have operculate gills with small body sizes were more prone to exposure to microplastics in hydraulic biotopes with slow to very slow velocities. Fibres were the most abundant plastic ingested by macroinvertebrates preferring the flush zone while fibres and fragments were mostly ingested by those preferring the sink zones. The binomial logistic model revealed a highly significant result for the likelihood of operculate gill shape to clog in the sink hydraulic zone. The result of the binomial logistic regression indicates the usefulness of the trait-based approach for predicting exposure to microplastics. Overall, the study reveals the influences of hydro-geomorphological features on the transport dynamics of microplastics and the usefulness of the trait-based approach in the ecological study of microplastics in riverine systems. , Thesis (PhD) -- Faculty of Science, Institute for Water Research, 2024
- Full Text:
- Date Issued: 2024-10-11
Microplastics as potential vectors for selected organic chemical pollutants in river ecosystems
- Authors: Tumwesigye, Edgar
- Date: 2024-10-11
- Subjects: Microplastics Environmental aspects , Vector , Adsorption (Biology) , Watersheds , Kinetics
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466677 , vital:76766 , DOI https://doi.org/10.21504/10962/466677
- Description: Microplastics (MPs) as pollutants in river ecosystems have received considerable research attention in recent years. However, in Africa, research on MPs is sparse, and more needs to be done. Empirical evidence suggests that MP can act as vectors of organic chemical pollutants due to their diverse functional groups and other physical-chemical properties, such as their small sizes, crystal structure and porosity. MPs acting as vectors of chemical pollutants, adds to the complexity of understanding the risk posed to both the ecosystem and human health. Regarding the so-called vector effect, the role of seasonality, land use type, adsorption kinetics, and MP properties has yet to receive the necessary research in the literature, especially concerning pharmaceutical active compounds and other organic pollutants in river systems. This is particularly true for Africa, including South Africa. This study, therefore, aimed to fill these existing research gaps. Overall, the study aimed to investigate the potential of selected microplastic polymers of a particular size range as vectors of organic pollutants in urban rivers within the Eastern Cape of South Africa. To achieve this aim, the study explored the influence of spatial-temporal variability, MPs particle sizes, and various physicochemical variables on the adsorption of antibiotics: Sulfamethoxazole, ciprofloxacin, and endocrine disruptors: 17β-Estradiol, 4-(2, 6-dimethyl-2-heptyl) phenol. The adsorption kinetics mechanism was also investigated and established. Polyethylene Terephthalate (PET) and polypropylene (PP) MPs were seasonally deployed once in the summer and autumn seasons, i.e. 20th January 2022 in Bloukrans River and 21st January 2022 in Swartkops River for the summer season and 7th April 2022 in Bloukrans River and 8th April 2022 in Swartkops River for the autumn season. Deployed MPs were of two size ranges, type 1 (2 mm<-≤5 mm) and type 2 (0.5mm<-≤2 mm). The sites where the MPs were deployed had different land use practices: informal settlements, discharge points of wastewater treatment works (WWTWs), agricultural farms, and control sites, considered as the least impacted sites. This was done to analyse land use types' role in the adsorption of chemical pollutants onto MPs. MPs were retrieved in periodic intervals of 7 days, 14 days and 35days calculated based on the day of deployment for both summer and autumn seasons and analysed for Sulfamethoxazole, Ciprofloxacin, 17β-Estradiol, 4-(2, 6-dimethyl-2-heptyl) phenol using high-resolution liquid chromatography–mass spectrometry LC-MS/MS equipped with a triple quadrupole (QqQ) analyser. Concurrent with MP retrieval water physicochemical variables: pH, dissolved oxygen (DO), temperature, turbidity, electrical conductivity (EC), total suspended solids (TSS), total dissolved solids, total alkalinity and total hardness. The adsorption kinetics mechanism was studied in the laboratory between PET and PP of two size ranges and Sulfamethoxazole, Ciprofloxacin, and 17β-Estradiol model chemical. The results indicate that land use practices significantly impacted the concentration of the adsorbed chemicals on MPs. Sites downstream of the WWTW had higher concentrations of Sulfamethoxazole: 11119.6001±12552.4120ngL-1 and ciprofloxacin: 30285.19± 28783.7821ngL-1 adsorbed onto MPs in the Bloukrans River compared to the concentration of same compounds from other land use types along the same River catchment. Agriculturally impacted sites had higher concentrations of 17β-Estradiol on MPs; 11624.5611 ± 15382.2923ngL-1 and 100.3635± 29.6321ngL-1 in Swartkops and Bloukrans Rivers respectively compared to other sites. These results suggest that land use is an essential factor influencing chemical inputs into rivers and their adsorption onto MPs. Adsorption was higher for the MP of smaller sizes compared to MPs with bigger sizes, indicating that size is an essential factor that influences the vector effects of MPs. Adsorption was significantly higher after 35 days than all other days during the two seasons (P< 0.05). The adoption kinetics data fitted well with the pseudo-second-order model (R2> 0.99), indicating that chemisorption mechanisms may be the rate-limiting step. Data did not fit the intraparticle diffusion model. Both film diffusion and intraparticle diffusion possibly influenced the rate-limiting adsorption step simultaneously. Regarding the relationship between adsorption and water physico-chemical variables, of special interest a positive correlation between total alkalinity, electrical conductivity, total hardness, and total suspended salts (TDS) and the concentration of the adsorbed chemicals was observed. While the relationship between adsorption and dissolved oxygen was negative. The physicochemical variables with a positive relationship with adsorption are indicative of pollution. Therefore, the result suggests that increasing pollution tends to favour higher adsorption. The results in this study highlight the insights on i) the influence of land use on adsorption, ii) the role of exposure duration on adsorption, iii) the influence of seasonality and MP sizes on adsorption iv) relationship between water physicochemical parameters and adsorption as well as v) establishing adsorption kinetic mechanism. These findings are critical to better understanding the so-called vector effects of MPs and the management associated with MPs in river systems and form essential data sets needed in developing effective pollution mitigation strategies that are region-specific. , Thesis (PhD) -- Faculty of Science, Institute for Water Research, 2024
- Full Text:
- Date Issued: 2024-10-11
- Authors: Tumwesigye, Edgar
- Date: 2024-10-11
- Subjects: Microplastics Environmental aspects , Vector , Adsorption (Biology) , Watersheds , Kinetics
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/466677 , vital:76766 , DOI https://doi.org/10.21504/10962/466677
- Description: Microplastics (MPs) as pollutants in river ecosystems have received considerable research attention in recent years. However, in Africa, research on MPs is sparse, and more needs to be done. Empirical evidence suggests that MP can act as vectors of organic chemical pollutants due to their diverse functional groups and other physical-chemical properties, such as their small sizes, crystal structure and porosity. MPs acting as vectors of chemical pollutants, adds to the complexity of understanding the risk posed to both the ecosystem and human health. Regarding the so-called vector effect, the role of seasonality, land use type, adsorption kinetics, and MP properties has yet to receive the necessary research in the literature, especially concerning pharmaceutical active compounds and other organic pollutants in river systems. This is particularly true for Africa, including South Africa. This study, therefore, aimed to fill these existing research gaps. Overall, the study aimed to investigate the potential of selected microplastic polymers of a particular size range as vectors of organic pollutants in urban rivers within the Eastern Cape of South Africa. To achieve this aim, the study explored the influence of spatial-temporal variability, MPs particle sizes, and various physicochemical variables on the adsorption of antibiotics: Sulfamethoxazole, ciprofloxacin, and endocrine disruptors: 17β-Estradiol, 4-(2, 6-dimethyl-2-heptyl) phenol. The adsorption kinetics mechanism was also investigated and established. Polyethylene Terephthalate (PET) and polypropylene (PP) MPs were seasonally deployed once in the summer and autumn seasons, i.e. 20th January 2022 in Bloukrans River and 21st January 2022 in Swartkops River for the summer season and 7th April 2022 in Bloukrans River and 8th April 2022 in Swartkops River for the autumn season. Deployed MPs were of two size ranges, type 1 (2 mm<-≤5 mm) and type 2 (0.5mm<-≤2 mm). The sites where the MPs were deployed had different land use practices: informal settlements, discharge points of wastewater treatment works (WWTWs), agricultural farms, and control sites, considered as the least impacted sites. This was done to analyse land use types' role in the adsorption of chemical pollutants onto MPs. MPs were retrieved in periodic intervals of 7 days, 14 days and 35days calculated based on the day of deployment for both summer and autumn seasons and analysed for Sulfamethoxazole, Ciprofloxacin, 17β-Estradiol, 4-(2, 6-dimethyl-2-heptyl) phenol using high-resolution liquid chromatography–mass spectrometry LC-MS/MS equipped with a triple quadrupole (QqQ) analyser. Concurrent with MP retrieval water physicochemical variables: pH, dissolved oxygen (DO), temperature, turbidity, electrical conductivity (EC), total suspended solids (TSS), total dissolved solids, total alkalinity and total hardness. The adsorption kinetics mechanism was studied in the laboratory between PET and PP of two size ranges and Sulfamethoxazole, Ciprofloxacin, and 17β-Estradiol model chemical. The results indicate that land use practices significantly impacted the concentration of the adsorbed chemicals on MPs. Sites downstream of the WWTW had higher concentrations of Sulfamethoxazole: 11119.6001±12552.4120ngL-1 and ciprofloxacin: 30285.19± 28783.7821ngL-1 adsorbed onto MPs in the Bloukrans River compared to the concentration of same compounds from other land use types along the same River catchment. Agriculturally impacted sites had higher concentrations of 17β-Estradiol on MPs; 11624.5611 ± 15382.2923ngL-1 and 100.3635± 29.6321ngL-1 in Swartkops and Bloukrans Rivers respectively compared to other sites. These results suggest that land use is an essential factor influencing chemical inputs into rivers and their adsorption onto MPs. Adsorption was higher for the MP of smaller sizes compared to MPs with bigger sizes, indicating that size is an essential factor that influences the vector effects of MPs. Adsorption was significantly higher after 35 days than all other days during the two seasons (P< 0.05). The adoption kinetics data fitted well with the pseudo-second-order model (R2> 0.99), indicating that chemisorption mechanisms may be the rate-limiting step. Data did not fit the intraparticle diffusion model. Both film diffusion and intraparticle diffusion possibly influenced the rate-limiting adsorption step simultaneously. Regarding the relationship between adsorption and water physico-chemical variables, of special interest a positive correlation between total alkalinity, electrical conductivity, total hardness, and total suspended salts (TDS) and the concentration of the adsorbed chemicals was observed. While the relationship between adsorption and dissolved oxygen was negative. The physicochemical variables with a positive relationship with adsorption are indicative of pollution. Therefore, the result suggests that increasing pollution tends to favour higher adsorption. The results in this study highlight the insights on i) the influence of land use on adsorption, ii) the role of exposure duration on adsorption, iii) the influence of seasonality and MP sizes on adsorption iv) relationship between water physicochemical parameters and adsorption as well as v) establishing adsorption kinetic mechanism. These findings are critical to better understanding the so-called vector effects of MPs and the management associated with MPs in river systems and form essential data sets needed in developing effective pollution mitigation strategies that are region-specific. , Thesis (PhD) -- Faculty of Science, Institute for Water Research, 2024
- Full Text:
- Date Issued: 2024-10-11
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