Spatial and Temporal Dynamics of Water Hyacinth and Its Linkage with Lake-Level Fluctuation: Lake Tana, a Sub-Humid Region of the Ethiopian Highlands

Increasing anthropogenic stressors influenced the water quality and shifted trophic status of northern Lake Tana Gulf, Ethiopia

Nutrients in an aquatic system determine productivity, integrity and ecological status of the aquatic system. However, the excessive enrichment of these nutrients emanating from severe anthropogenic activity has substantially impacted water quality and biodiversity. There is diminutive information available on the water quality and trophic status of the northern Gulf of Lake Tana, Ethiopia due to accessibility difficulties. Therefore, this study aimed to assess the spatio-temporal changes in water quality and trophic status of Lake Tana, specifically the Gulf of Gorgora. Samples were collected from five sampling points between May 2023 to April 2024, and sampling sites were selected based on their proximity to human interference. The physico-chemical parameters were measured in situ or determined in water samples using standard methods. There were significant (p < 0.05) variations in temperature, dissolved oxygen (DO), electrical conductivity (EC) and turbidity between the dry and rainy seasons. The mean concentrations of nutrients such as NO3-N (0.48 mg/l), soluble reactive phosphorus (SRP) (1.2 mg/l) total nitrogen (TN) (1.27 mg/l), and total phosphorus (TP) (2.1 mg/l), showed significant spatio-temporal variations, with higher concentrations recorded at the Megech and Dablo sites during the rainy seasons. The depth-wise distributions of the parameters exhibited a consistent pattern, with a slight increase in the levels of EC, turbidity, TP, and TN, and a decrease in temperature, DO and NO3-N. The concentrations of SRP, TP, and TN, were slightly higher than the USEPA's threshold concentrations for causing eutrophication. The shift in the trophic status of Lake Tana from oligo-mesotrophic to eutrophic is likely due to nutrient enrichment associated with anthropogenic stressors. Therefore, continuous monitoring is essential to avert future ecological imbalances in the lake.

Global impact of water hyacinth (Eichhornia Crassipes) on rural communities and mitigation strategies: a systematic review

The proliferation of water hyacinths (Eichhornia crassipes), recognized as one of the most invasive aquatic plants worldwide, presents profound ecological and socioeconomic challenges across diverse ecosystems, particularly in rural communities. This systematic review examines the extensive global impacts and explores various mitigation strategies to manage and utilize this pervasive species. Ecologically, water hyacinth disrupts aquatic ecosystems by depleting oxygen levels, obstructing sunlight, and displacing native species, which in turn compromises water quality and biodiversity. Economically, its rapid spread affects agriculture, fishing, and navigation, imposing significant costs on local economies and livelihoods. In response, this review assesses integrated management approaches combining mechanical, chemical, and biological controls that have been implemented to curb its growth. Moreover, innovative strategies that repurpose the biomass for bioenergy, handicrafts, and bio-remediation are discussed, highlighting their potential to transform an ecological menace into an economic resource. These strategies not only mitigate the plant's negative impacts but also contribute to sustainable development by providing economic opportunities and enhancing ecosystem services. This review stresses the necessity for a holistic approach to water hyacinth management that is adaptive, sustainable, and beneficial to affected communities.

Spatiotemporal variability of lake surface water temperature and water quality parameters and its interrelationship with water hyacinth biomass in Lake Tana, Ethiopia

Urbanization, agriculture, and climate change affect water quality and water hyacinth growth in lakes. This study examines the spatiotemporal variability of lake surface water temperature, turbidity, and chlorophyll-a (Chl-a) and their association with water hyacinth biomass in Lake Tana. MODIS Land/ Lake surface water temperature (LSWT), Sentinel 2 MSI Imagery, and in-situ water quality data were used. Validation results revealed strong positive correlations between MODIS LSWT and on-site measured water temperature (R = 0.90), in-situ turbidity and normalized difference turbidity index (NDTI) (R = 0.92), and in-situ Chl-a and normalized difference chlorophyll index (NDCI) (R = 0.84). LSWT trends varied across the lake, with increasing trends in the northeastern, northwestern, and southwestern regions and decreasing trends in the western, southern, and central areas (2001-2022). The spatial average LSWT trend decreased significantly in pre-rainy (0.01 ℃/year), rainy (0.02 ℃/year), and post-rainy seasons (0.01℃/year) but increased non-significantly in the dry season (0.00 ℃/year) (2001-2022, P < 0.05). Spatial average turbidity decreased significantly in all seasons, except in the pre-rainy season (2016-2022). Likewise, spatial average Chl-a decreased significantly in pre-rainy and rainy seasons, whereas it showed a non-significant increasing trend in the dry and post-rainy seasons (2016-2022). Water hyacinth biomass was positively correlated with LSWT (R = 0.18) but negatively with turbidity (R = -0.33) and Chl-a (R = -0.35). High spatiotemporal variability was observed in LSWT, turbidity, and Chl-a, along with overall decreasing trends. The findings suggest integrated management strategies to balance water hyacinth eradication and its role in water purification. The results will be vital in decision support systems and preparing strategic plans for sustainable water resource management, environmental protection, and pollution prevention.

Genus-Level Mapping of Invasive Floating Aquatic Vegetation Using Sentinel-2 Satellite Remote Sensing

Invasive floating aquatic vegetation negatively impacts wetland ecosystems and mapping this vegetation through space and time can aid in designing and assessing effective control strategies. Current remote sensing methods for mapping floating aquatic vegetation at the genus level relies on airborne imaging spectroscopy, resulting in temporal gaps because routine hyperspectral satellite coverage is not yet available. Here we achieved genus level and species level discrimination between two invasive aquatic vegetation species using Sentinel 2 multispectral satellite data and machine-learning classifiers in summer and fall. The species of concern were water hyacinth (Eichornia crassipes) and water primrose (Ludwigia spp.). Our classifiers also identified submerged and emergent aquatic vegetation at the community level. Random forest models using Sentinel-2 data achieved an average overall accuracy of 90%, and class accuracies of 79–91% and 85–95% for water hyacinth and water primrose, respectively. To our knowledge, this is the first study that has mapped water primrose to the genus level using satellite remote sensing. Sentinel-2 derived maps compared well to those derived from airborne imaging spectroscopy and we also identified misclassifications that can be attributed to the coarser Sentinel-2 spectral and spatial resolutions. Our results demonstrate that the intra-annual temporal gaps between airborne imaging spectroscopy observations can be supplemented with Sentinel-2 satellite data and thus, rapidly growing/expanding vegetation can be tracked in real time. Such improvements have potential management benefits by improving the understanding of the phenology, spread, competitive advantages, and vulnerabilities of these aquatic plants.