Changes in land use/land cover (LULC) are a global environmental concern that has a significant i... more Changes in land use/land cover (LULC) are a global environmental concern that has a significant impact on sustainable land and water resource management and development as well as hydrological processes. The primary driving forces of LULC changes in developing countries are population pressure, demand for firewood collection and construction material, shortage of cultivated land, land tenure insecurity, and deforestation. Focusing on the Ethiopian Birr river watershed, the study investigates changes in LULC trends, extents, and magnitudes over the last 32 years using geospatial technologies such as Landsat images of 1986, 2001, and 2018. The supervised land use land cover classification technique was applied to classify the LULC classes using the maximum likelihood algorithm technique. Between 1986 and 2018, agricultural land increased significantly from 56.39% to 70.19%, while settlements increased from 0.73%) to 1.42%. On the other hand, bushlands, forest areas, and grasslands LULC classes in the study area decreased from 26.18% to 19.30%, 4.94%-1.92%, and 11.77%-7.16%, respectively. The findings suggest that integrated watershed management and land use planning should be concerned and implemented in the Birr River watershed.
Low-order streams contribute to the abiotic and biotic character of large rivers and are renowned... more Low-order streams contribute to the abiotic and biotic character of large rivers and are renowned for harboring unique forms of aquatic flora and fauna. However, most studies on headwater streams mainly focus on the mainstems and overlook the contribution of the tributary systems. Moreover, low-order streams are generally overlooked in legislation and bioassessment programs, and consequently not protected in many countries. To contribute to the recognition of the ecological importance of low-orders streams, this study focused on determining whether river network characteristics and associated physico-chemical parameters can be used to effectively predict the variabilities in macroinvertebrate assemblage characteristics between first-order and second-order streams in the headwaters of the Nzoia River Basin, Kenya. The study quantified the structural and functional community composition, diversity, similarity, and richness of macroinvertebrate communities between the two river systems. Dissolved oxygen, coarse particulate organic matter, conductivity, stream width, depth, discharge and flow velocity were the main predictors of the diversity and distribution of macroinvertebrates in the first order and second-order streams. The first order streams recorded higher abundance of macroinvertebrates than the second-order streams. Taxa from families Ephydridae, Elmidae, Gomphidae, and genera Euthraulus, Neoperla, Orthothrichia and Prosopistoma were limited to the second-order stream sites while families Ceratopogonidae, Pisuliidae, Dytiscidae and genus Trichosetodes occurred exclusively in the first-order stream sites. Collector-filterers and collector-gatherers were the most abundant functional feeding groups (FFGs) in the two river systems. Scrapers were abundant in the second-order stream while shredders were abundant in the first order streams. The distinctness in the structural and functional composition of macroinvertebrates between the two river systems suggests that linkages among streams in a network as exemplified in the Nzoia River Basin, support and foster biodiversity.
In many regions of the world, large populations of native wildlife have declined or been replaced... more In many regions of the world, large populations of native wildlife have declined or been replaced by livestock grazing areas and farmlands, with consequences for terrestrial-aquatic ecosystem connectivity and trophic resources supporting food webs in aquatic ecosystems. The river continuum concept (RCC) and the riverine productivity model (RPM) predict a shift of energy supplying aquatic food webs along rivers: from terrestrial inputs in low-order streams to autochthonous production in mid-sized rivers. In Afromontane-savanna landscapes, the shifting numbers of large mammalian wildlife present a physical continuum whose ecological implications for rivers is not clearly understood. Here, we studied the influence of replacing large wildlife (mainly hippos) with livestock on the fractional contribution of C3 vegetation, C4 grasses and periphyton on macroinvertebrates in the Mara River, which is an African montane-savanna river known to receive large subsidy fluxes of terrestrial organic matter and nutrients mediated by large mammalian herbivores (LMH), both wildlife and livestock, in its middle and lower reaches. Using stable carbon (δ13C) and nitrogen (δ15N) isotopes, we identified spatial patterns in the fractional contribution of allochthonous organic matter from C3 and C4 plants (woody vegetation and grasses, respectively) and autochthonous energy from periphyton for macroinvertebrates at various sites of the Mara River and its tributaries. Potential energy sources and invertebrates were sampled at 80 sites spanning stream orders 1 to 7, various catchment land uses (forest, agriculture and grasslands) and different loading rates of organic matter and nutrients by LMH (livestock and wildlife, i.e., hippopotamus). The fractional contribution of different sources of energy for invertebrates along the river did not follow predictions of the RCC and RPM. First, the fractional contribution of C3 and C4 carbon was not related to river order or location along the fluvial continuum but to the loading of organic matter (dung) by both wildlife and livestock. Notably, C4 carbon was important for macroinvertebrates even in large river sections inhabited by hippos. Second, even in small 1st -3rd order forested streams, periphyton was a major source of energy for macroinvertebrates, and this was fostered by livestock inputs fuelling aquatic primary production throughout the river network. Importantly, our results show that replacing wildlife (hippos) with livestock shifts river systems towards greater reliance on autochthonous sources of energy through an algae-grazer pathway as opposed to reliance on allochthonous inputs of C4 carbon through a detrital pathway.
Journal Of Geophysical Research: Biogeosciences, Nov 1, 2019
Anthropogenic activities have led to increases in nitrous oxide (N 2 O) emissions from river syst... more Anthropogenic activities have led to increases in nitrous oxide (N 2 O) emissions from river systems, but there are large uncertainties in estimates due to lack of data in tropical rivers and rapid increase in human activity. We assessed the effects of land use and river size on N 2 O flux and concentration in 46 stream sites in the Mara River, Kenya, during the transition from the wet (short rains) to dry season, November 2017 to January 2018. Flux estimates were similar to other studies in tropical and temperate systems, but in contrast to other studies, land use was more related to N 2 O concentration and flux than stream size. Agricultural stream sites had the highest fluxes (26.38 ± 5.37 N 2 ON μg•m-2 •hr-1) compared to both forest and livestock sites (5.66 ± 1.38 N 2 ON μg•m-2 •hr-1 and 6.95 ± 2.96 N 2 ON μg•m-2 •hr-1 , respectively). N 2 O concentrations in forest and agriculture streams were positively correlated to stream carbon dioxide (CO 2-C (aq)) but showed a negative correlation with dissolved organic carbon, and the dissolved organic carbon:dissolved inorganic nitrogen ratio. N 2 O concentration in the livestock sites had a negative relationship with CO 2-C (aq) and a higher number of negative fluxes. We concluded that in-stream chemoautotrophic nitrification was likely the main biogeochemical process driving N 2 O production in agricultural and forest streams, whereas complete denitrification led to the consumption of N 2 O in the livestock stream sites. These results point to the need to better understand the relative importance of nitrification and denitrification in different habitats in producing N 2 O and for process-based studies. Plain Language Summary Humans affect the emission of nitrous oxide (N 2 O), a potent greenhouse gas, from river systems through land use change and increased nitrogen use in catchments. We know little about this in sub-Saharan Africa, where human activity is increasing rapidly. Previous studies have found that N 2 O may be related to the size of the river, with smaller rivers having higher emissions than large ones, due to their close connection to the catchment. This study addressed whether land use (i.e., native forest, crop production, and livestock watering holes) affect N 2 O emission from the headwaters of the Mara River, Kenya. We found that N 2 O emissions were not related to the stream size but were more strongly affected by land use, with the highest emissions occurring in the agricultural areas. We also examined which processes in the river were responsible for the emissions by relating water quality parameters to N 2 O concentration. We found that different processes were most likely responsible in different land uses, with nitrification dominating in forested and agricultural areas, and denitrification dominating in livestock watering sites. These results illustrate the unique features of tropical rivers in montane ecosystems undergoing land use change. Further research should investigate processes and seasonal dynamics.
Philosophical Transactions of the Royal Society B: Biological Sciences
Africa is experiencing extensive biodiversity loss due to rapid changes in the environment, where... more Africa is experiencing extensive biodiversity loss due to rapid changes in the environment, where natural resources constitute the main instrument for socioeconomic development and a mainstay source of livelihoods for an increasing population. Lack of data and information deficiency on biodiversity, but also budget constraints and insufficient financial and technical capacity, impede sound policy design and effective implementation of conservation and management measures. The problem is further exacerbated by the lack of harmonized indicators and databases to assess conservation needs and monitor biodiversity losses. We review challenges with biodiversity data (availability, quality, usability and database access) as a key limiting factor that impacts funding and governance. We also evaluate the drivers of both ecosystems change and biodiversity loss as a central piece of knowledge to develop and implement effective policies. While the continent focuses more on the latter, we argue ...
Although several studies have investigated the relationships between water quality in rivers and ... more Although several studies have investigated the relationships between water quality in rivers and the types of land use within their catchments, many aspects of these relationships remain unclear in Afromontane-savanna rivers, especially the interactions between catchment land use, seasonality and stream size. Afromontane-savanna catchments present a unique situation where headwater regions and lowlands have experienced more dramatic land cover change, but mid-elevation regions remained rather natural. We examined the influence of seasonality, catchment land use and stream size, including their interactions, on water physico-chemistry, nutrients and major ions in the Afromontane-savanna Mara River in Kenya, using data collected from 2010 to 2018 at >150 sampling sites in the Kenyan part of the river. We developed generalized linear mixed models (GLMMs) to explore the influence of seasonality (dry and wet seasons), land use (forest, mixed, agriculture and grasslands), stream size (stream orders 1-7), and their interactions on river water quality. Water quality variables included physico-chemical measures (pH, dissolved oxygen [DO] concentration, temperature, electrical conductivity, total dissolved solids [TDS], turbidity, total suspended solids [TSS] and particulate organic matter [POM]), nutrients (NH + 4 , NO − 3 , total dissolved nitrogen [TDN], total nitrogen [TN], soluble reactive phosphorus [SRP], total phosphorus [TP] and dissolved organic carbon), and major ions (
Lake Victoria is the second largest freshwater lake in the world that was once a biodiversity hot... more Lake Victoria is the second largest freshwater lake in the world that was once a biodiversity hotspot hosting over 500 endemic haplochromine cichlids that were later decimated by exotic introductions and anthropogenically driven environmental and ecological changes. The environmental and ecological changes in the lake over the years have been attributed to overfishing, eutrophication, introduction of exotic species, pollution and possibly climate change. The lake's capture fishery, which is the main economic activity directly and indirectly supporting over 40 million people, has continued to decline after experiencing a boom between the 1970s and 1990s following the introduction of Nile Perch (Lates niloticus) and Nile Tilapia (Oreochromis niloticus). In order to augment capture fisheries from the lake, cage culture was introduced in 2005, but its sustainability and influence on the ecology of the lake are not well understood. In this review, we examine the genesis of degradatio...
Many streams and rivers outside conservation areas across the Afrotropics face multiple stressors... more Many streams and rivers outside conservation areas across the Afrotropics face multiple stressors from land use change, urbanization, and excessive water withdrawals. Thus, there is a need to develop cost-effective tools for assessing and monitoring ecological changes to inform management decisions. Studies utilizing macroinvertebrate communities as indicators of the ecological condition of streams and rivers in the Afrotropics use diverse methods, including diversity, richness, biotic and multimetric indices. However, some of these indices are region- or country-specific, which limits their general use across multiple regions or countries. In this study, we address this challenge by testing and comparing the performance of diversity and richness indices (e.g., Shannon-Wiener and Simpson), regional biotic indices (the African Scoring System Version 5 [SASS5], Tanzanian River Scoring System [TARISS] and a biotic index developed for the Ethiopian highlands [ETHbios]), and a macroinver...
African Journal of Education,Science and Technology, May 8, 2021
Detritivorous invertebrates play major roles in organic matter processing and nutrient cycling in... more Detritivorous invertebrates play major roles in organic matter processing and nutrient cycling in headwater streams. In this study, three common leaf species in upland Kenyan streams (Vernonia myriantha, Syzygium cordatum and the exotic Eucalyptus globulus) were used to determine the influence of deployment period (14 vs 28 days) on relative decomposition rates and colonization by detritivorous invertebrates in headwater streams of the Nzoia River Basin. Leaf decomposition rates were measured by placing 216 litterbags made of coarse-and fine-mesh in six streams draining forested (n =3) and agricultural (n = 3) land-use during the dry months of February-March 2020. For each stream, physico-chemical water characteristics and habitat quality were determined. Measurements of electrical conductivity, pH, temperature, dissolved oxygen concentration and salinity were performed in situ using portable probes. There were no major differences in physical and chemical characteristics between forested and agricultural streams, except for significantly higher canopy cover (p < 0.05) in forested streams, and electrical conductivity and mean water temperature in agricultural streams. Decomposition rates were faster during the first 2 weeks (day 14), and differences between fine-and coarse-mesh litterbags were significant for Vernonia and Syzygium, but not for Eucalyptus. After 14 days, differences between microbial and shredder + microbial breakdown of leaves were clearer than after 28 days, suggesting that short deployment periods (14 days) are enough to establish relative roles of shredders and microbes in leaf litter decomposition experiments in tropical streams. There were inter-specific differences in colonization rates of the leaves by detritivores (shredders) with Vernonia having the highest number of shredder taxa and abundance followed by Syzygium and Eucalyptus. However, there were minimal differences in taxon richness and abundance of shredders and non-shredders between day 14 and day 28. Therefore, this study recommends shorter deployment periods of 14 days rather than long periods of one month or more when studying leaf litter decomposition and colonization by detritivores in tropical streams.
Changes in land use/land cover (LULC) are a global environmental concern that has a significant i... more Changes in land use/land cover (LULC) are a global environmental concern that has a significant impact on sustainable land and water resource management and development as well as hydrological processes. The primary driving forces of LULC changes in developing countries are population pressure, demand for firewood collection and construction material, shortage of cultivated land, land tenure insecurity, and deforestation. Focusing on the Ethiopian Birr river watershed, the study investigates changes in LULC trends, extents, and magnitudes over the last 32 years using geospatial technologies such as Landsat images of 1986, 2001, and 2018. The supervised land use land cover classification technique was applied to classify the LULC classes using the maximum likelihood algorithm technique. Between 1986 and 2018, agricultural land increased significantly from 56.39% to 70.19%, while settlements increased from 0.73%) to 1.42%. On the other hand, bushlands, forest areas, and grasslands LULC classes in the study area decreased from 26.18% to 19.30%, 4.94%-1.92%, and 11.77%-7.16%, respectively. The findings suggest that integrated watershed management and land use planning should be concerned and implemented in the Birr River watershed.
Low-order streams contribute to the abiotic and biotic character of large rivers and are renowned... more Low-order streams contribute to the abiotic and biotic character of large rivers and are renowned for harboring unique forms of aquatic flora and fauna. However, most studies on headwater streams mainly focus on the mainstems and overlook the contribution of the tributary systems. Moreover, low-order streams are generally overlooked in legislation and bioassessment programs, and consequently not protected in many countries. To contribute to the recognition of the ecological importance of low-orders streams, this study focused on determining whether river network characteristics and associated physico-chemical parameters can be used to effectively predict the variabilities in macroinvertebrate assemblage characteristics between first-order and second-order streams in the headwaters of the Nzoia River Basin, Kenya. The study quantified the structural and functional community composition, diversity, similarity, and richness of macroinvertebrate communities between the two river systems. Dissolved oxygen, coarse particulate organic matter, conductivity, stream width, depth, discharge and flow velocity were the main predictors of the diversity and distribution of macroinvertebrates in the first order and second-order streams. The first order streams recorded higher abundance of macroinvertebrates than the second-order streams. Taxa from families Ephydridae, Elmidae, Gomphidae, and genera Euthraulus, Neoperla, Orthothrichia and Prosopistoma were limited to the second-order stream sites while families Ceratopogonidae, Pisuliidae, Dytiscidae and genus Trichosetodes occurred exclusively in the first-order stream sites. Collector-filterers and collector-gatherers were the most abundant functional feeding groups (FFGs) in the two river systems. Scrapers were abundant in the second-order stream while shredders were abundant in the first order streams. The distinctness in the structural and functional composition of macroinvertebrates between the two river systems suggests that linkages among streams in a network as exemplified in the Nzoia River Basin, support and foster biodiversity.
In many regions of the world, large populations of native wildlife have declined or been replaced... more In many regions of the world, large populations of native wildlife have declined or been replaced by livestock grazing areas and farmlands, with consequences for terrestrial-aquatic ecosystem connectivity and trophic resources supporting food webs in aquatic ecosystems. The river continuum concept (RCC) and the riverine productivity model (RPM) predict a shift of energy supplying aquatic food webs along rivers: from terrestrial inputs in low-order streams to autochthonous production in mid-sized rivers. In Afromontane-savanna landscapes, the shifting numbers of large mammalian wildlife present a physical continuum whose ecological implications for rivers is not clearly understood. Here, we studied the influence of replacing large wildlife (mainly hippos) with livestock on the fractional contribution of C3 vegetation, C4 grasses and periphyton on macroinvertebrates in the Mara River, which is an African montane-savanna river known to receive large subsidy fluxes of terrestrial organic matter and nutrients mediated by large mammalian herbivores (LMH), both wildlife and livestock, in its middle and lower reaches. Using stable carbon (δ13C) and nitrogen (δ15N) isotopes, we identified spatial patterns in the fractional contribution of allochthonous organic matter from C3 and C4 plants (woody vegetation and grasses, respectively) and autochthonous energy from periphyton for macroinvertebrates at various sites of the Mara River and its tributaries. Potential energy sources and invertebrates were sampled at 80 sites spanning stream orders 1 to 7, various catchment land uses (forest, agriculture and grasslands) and different loading rates of organic matter and nutrients by LMH (livestock and wildlife, i.e., hippopotamus). The fractional contribution of different sources of energy for invertebrates along the river did not follow predictions of the RCC and RPM. First, the fractional contribution of C3 and C4 carbon was not related to river order or location along the fluvial continuum but to the loading of organic matter (dung) by both wildlife and livestock. Notably, C4 carbon was important for macroinvertebrates even in large river sections inhabited by hippos. Second, even in small 1st -3rd order forested streams, periphyton was a major source of energy for macroinvertebrates, and this was fostered by livestock inputs fuelling aquatic primary production throughout the river network. Importantly, our results show that replacing wildlife (hippos) with livestock shifts river systems towards greater reliance on autochthonous sources of energy through an algae-grazer pathway as opposed to reliance on allochthonous inputs of C4 carbon through a detrital pathway.
Journal Of Geophysical Research: Biogeosciences, Nov 1, 2019
Anthropogenic activities have led to increases in nitrous oxide (N 2 O) emissions from river syst... more Anthropogenic activities have led to increases in nitrous oxide (N 2 O) emissions from river systems, but there are large uncertainties in estimates due to lack of data in tropical rivers and rapid increase in human activity. We assessed the effects of land use and river size on N 2 O flux and concentration in 46 stream sites in the Mara River, Kenya, during the transition from the wet (short rains) to dry season, November 2017 to January 2018. Flux estimates were similar to other studies in tropical and temperate systems, but in contrast to other studies, land use was more related to N 2 O concentration and flux than stream size. Agricultural stream sites had the highest fluxes (26.38 ± 5.37 N 2 ON μg•m-2 •hr-1) compared to both forest and livestock sites (5.66 ± 1.38 N 2 ON μg•m-2 •hr-1 and 6.95 ± 2.96 N 2 ON μg•m-2 •hr-1 , respectively). N 2 O concentrations in forest and agriculture streams were positively correlated to stream carbon dioxide (CO 2-C (aq)) but showed a negative correlation with dissolved organic carbon, and the dissolved organic carbon:dissolved inorganic nitrogen ratio. N 2 O concentration in the livestock sites had a negative relationship with CO 2-C (aq) and a higher number of negative fluxes. We concluded that in-stream chemoautotrophic nitrification was likely the main biogeochemical process driving N 2 O production in agricultural and forest streams, whereas complete denitrification led to the consumption of N 2 O in the livestock stream sites. These results point to the need to better understand the relative importance of nitrification and denitrification in different habitats in producing N 2 O and for process-based studies. Plain Language Summary Humans affect the emission of nitrous oxide (N 2 O), a potent greenhouse gas, from river systems through land use change and increased nitrogen use in catchments. We know little about this in sub-Saharan Africa, where human activity is increasing rapidly. Previous studies have found that N 2 O may be related to the size of the river, with smaller rivers having higher emissions than large ones, due to their close connection to the catchment. This study addressed whether land use (i.e., native forest, crop production, and livestock watering holes) affect N 2 O emission from the headwaters of the Mara River, Kenya. We found that N 2 O emissions were not related to the stream size but were more strongly affected by land use, with the highest emissions occurring in the agricultural areas. We also examined which processes in the river were responsible for the emissions by relating water quality parameters to N 2 O concentration. We found that different processes were most likely responsible in different land uses, with nitrification dominating in forested and agricultural areas, and denitrification dominating in livestock watering sites. These results illustrate the unique features of tropical rivers in montane ecosystems undergoing land use change. Further research should investigate processes and seasonal dynamics.
Philosophical Transactions of the Royal Society B: Biological Sciences
Africa is experiencing extensive biodiversity loss due to rapid changes in the environment, where... more Africa is experiencing extensive biodiversity loss due to rapid changes in the environment, where natural resources constitute the main instrument for socioeconomic development and a mainstay source of livelihoods for an increasing population. Lack of data and information deficiency on biodiversity, but also budget constraints and insufficient financial and technical capacity, impede sound policy design and effective implementation of conservation and management measures. The problem is further exacerbated by the lack of harmonized indicators and databases to assess conservation needs and monitor biodiversity losses. We review challenges with biodiversity data (availability, quality, usability and database access) as a key limiting factor that impacts funding and governance. We also evaluate the drivers of both ecosystems change and biodiversity loss as a central piece of knowledge to develop and implement effective policies. While the continent focuses more on the latter, we argue ...
Although several studies have investigated the relationships between water quality in rivers and ... more Although several studies have investigated the relationships between water quality in rivers and the types of land use within their catchments, many aspects of these relationships remain unclear in Afromontane-savanna rivers, especially the interactions between catchment land use, seasonality and stream size. Afromontane-savanna catchments present a unique situation where headwater regions and lowlands have experienced more dramatic land cover change, but mid-elevation regions remained rather natural. We examined the influence of seasonality, catchment land use and stream size, including their interactions, on water physico-chemistry, nutrients and major ions in the Afromontane-savanna Mara River in Kenya, using data collected from 2010 to 2018 at >150 sampling sites in the Kenyan part of the river. We developed generalized linear mixed models (GLMMs) to explore the influence of seasonality (dry and wet seasons), land use (forest, mixed, agriculture and grasslands), stream size (stream orders 1-7), and their interactions on river water quality. Water quality variables included physico-chemical measures (pH, dissolved oxygen [DO] concentration, temperature, electrical conductivity, total dissolved solids [TDS], turbidity, total suspended solids [TSS] and particulate organic matter [POM]), nutrients (NH + 4 , NO − 3 , total dissolved nitrogen [TDN], total nitrogen [TN], soluble reactive phosphorus [SRP], total phosphorus [TP] and dissolved organic carbon), and major ions (
Lake Victoria is the second largest freshwater lake in the world that was once a biodiversity hot... more Lake Victoria is the second largest freshwater lake in the world that was once a biodiversity hotspot hosting over 500 endemic haplochromine cichlids that were later decimated by exotic introductions and anthropogenically driven environmental and ecological changes. The environmental and ecological changes in the lake over the years have been attributed to overfishing, eutrophication, introduction of exotic species, pollution and possibly climate change. The lake's capture fishery, which is the main economic activity directly and indirectly supporting over 40 million people, has continued to decline after experiencing a boom between the 1970s and 1990s following the introduction of Nile Perch (Lates niloticus) and Nile Tilapia (Oreochromis niloticus). In order to augment capture fisheries from the lake, cage culture was introduced in 2005, but its sustainability and influence on the ecology of the lake are not well understood. In this review, we examine the genesis of degradatio...
Many streams and rivers outside conservation areas across the Afrotropics face multiple stressors... more Many streams and rivers outside conservation areas across the Afrotropics face multiple stressors from land use change, urbanization, and excessive water withdrawals. Thus, there is a need to develop cost-effective tools for assessing and monitoring ecological changes to inform management decisions. Studies utilizing macroinvertebrate communities as indicators of the ecological condition of streams and rivers in the Afrotropics use diverse methods, including diversity, richness, biotic and multimetric indices. However, some of these indices are region- or country-specific, which limits their general use across multiple regions or countries. In this study, we address this challenge by testing and comparing the performance of diversity and richness indices (e.g., Shannon-Wiener and Simpson), regional biotic indices (the African Scoring System Version 5 [SASS5], Tanzanian River Scoring System [TARISS] and a biotic index developed for the Ethiopian highlands [ETHbios]), and a macroinver...
African Journal of Education,Science and Technology, May 8, 2021
Detritivorous invertebrates play major roles in organic matter processing and nutrient cycling in... more Detritivorous invertebrates play major roles in organic matter processing and nutrient cycling in headwater streams. In this study, three common leaf species in upland Kenyan streams (Vernonia myriantha, Syzygium cordatum and the exotic Eucalyptus globulus) were used to determine the influence of deployment period (14 vs 28 days) on relative decomposition rates and colonization by detritivorous invertebrates in headwater streams of the Nzoia River Basin. Leaf decomposition rates were measured by placing 216 litterbags made of coarse-and fine-mesh in six streams draining forested (n =3) and agricultural (n = 3) land-use during the dry months of February-March 2020. For each stream, physico-chemical water characteristics and habitat quality were determined. Measurements of electrical conductivity, pH, temperature, dissolved oxygen concentration and salinity were performed in situ using portable probes. There were no major differences in physical and chemical characteristics between forested and agricultural streams, except for significantly higher canopy cover (p < 0.05) in forested streams, and electrical conductivity and mean water temperature in agricultural streams. Decomposition rates were faster during the first 2 weeks (day 14), and differences between fine-and coarse-mesh litterbags were significant for Vernonia and Syzygium, but not for Eucalyptus. After 14 days, differences between microbial and shredder + microbial breakdown of leaves were clearer than after 28 days, suggesting that short deployment periods (14 days) are enough to establish relative roles of shredders and microbes in leaf litter decomposition experiments in tropical streams. There were inter-specific differences in colonization rates of the leaves by detritivores (shredders) with Vernonia having the highest number of shredder taxa and abundance followed by Syzygium and Eucalyptus. However, there were minimal differences in taxon richness and abundance of shredders and non-shredders between day 14 and day 28. Therefore, this study recommends shorter deployment periods of 14 days rather than long periods of one month or more when studying leaf litter decomposition and colonization by detritivores in tropical streams.
Uploads
Papers by Frank O Masese