Multispectral remote sensing approach of predicting the potential distribution and evaluating the current spread of water hyacinth (Eichhornia crassipes)

The term invasive plant is synonymous with exotic and non-indigenous plant taxa, that quickly invade non-native habitats through natural and man-made effects (Colautti et al. 2014; Crystal-Ornelas et al. 2021; Hartley et al. 2006). They are non-native plants, also called alien plants, which invade natural habitats causing environmental destruction, modification, and immense socio-economic losses in the natural habitat (Crystal-Ornelas et al. 2021). Furthermore, invasive plant species have the potential for rapid expansion to new habitats and become a threat to native biodiversity (Early et al. 2016; Rohr et al. 2015). As an invasive alien species, the water hyacinth has a unique ability to produce a large number of offspring and easily spread over a considerable area (Bradley et al. 2022; Rejmánek 2000). The origin of the water hyacinth is traced to the Amazon basin in South America, and north-eastern Brazil (Oliveira Junior et al. 2021; Simpson et al. 2022). The plant species later invaded Columbia, Guyana, Surinam, Venezuela, and other parts of the world (Karouach et al. 2020; Pagad et al. 2016). The worldwide distribution of water hyacinth has been documented in more than fifty countries since the plant was first discovered in the early 1800s (Karouach et al. 2020). Subsequently, water hyacinth has been listed as one of the worst weeds in the world (Sindhu et al. 2017; Weidlich et al. 2020; Zenni et al. 2021). Water hyacinth presently covers large areas of global water bodies and has become a challenge for developmental activities and the environment (Enyew et al. 2020; Hartley et al. 2006). Its rapid expansion depends on anthropogenic activities such as urbanization, agriculture, water transport, and natural factors such as wind direction and wind-induced waves (Adhikari et al. 2019; E. Asmare 2017).

In addition to natural and anthropogenic activities, accidental mechanical removal and animal movement have increased water hyacinth expansion and invasion over the years (Amgoth et al. 2023; E. Asmare 2017; Weidlich et al. 2020). In a favourable reproductive environment, the water hyacinth grows and replicates itself two times every five days (Firehun 2017; Pérez et al. 2008). The plant’s life cycle shows that it is perennial, herbaceous, and free-floating over the water body (Subash 2016; Kgabo H. Thamaga & Dube 2019). However, its rapid infestations resulted in high competition with native species, as it prevents oxygen and sunlight from penetrating water bodies (Oliveira Junior et al. 2021; Subash 2016). The plant can tolerate changes in environmental parameters such as water temperature, nutrient concentration, and pH levels (Hartley et al. 2006; Van Kleunen et al. 2010). At newly covered wetlands the plant can easily adapt to the new habitat but causes oxygen blockages into the water body which diminishes biological diversity in the ecosystems (Eguavoen & Tesfai 2012; Subash 2016).

The invasion of water hyacinth harms water quantity and quality by reducing the irrigation capability of the water; affecting the fishing and fish products industry; threatening human health, and damaging the environment (Mainali et al. 2015). Its expansion over the water bodies has negative impacts on socioeconomic and environmental health, and these impacts are detected through reduced fish breeding and low fishing grounds, closing of the irrigation canals, and restricting swimming and boat traffic (Adhikari et al. 2019; Harun et al. 2021; Mainka & Howard 2010). In Africa, the spread of invasive plants is a well-known phenomenon affecting aquatic habitats in the Sub-Saharan region (Cordeiro et al. 2020; Early et al. 2016; Mukarugwiro et al. 2021; Yan et al. 2017). Ethiopia is a Sub-Saharan country, where the country's aquatic system, including freshwater bodies, marshes, and wetlands, has been severely impacted, and its native species' biodiversity richness and evenness have been dominated critically by the water hyacinth (Merga et al. 2020; Weidlich et al. 2020). This invasive plant has become a major problem in Ethiopia, as it has degraded the quality and quantity of wetlands, as some have dried up, becoming a breeding ground for hazardous vectors such as insects (Hartley et al. 2006; Tewabe et al. 2017).

The invasion of the water hyacinth has gravely threatened the livelihoods of rural communities that rely on ecosystem services, as well as the reduction in the diversity and richness of native vegetation (Navarro and George 2000; Peter 2009). Its invasion was observed in several Ethiopian rivers, including the Abbay River, Baro-Akobo River, and other freshwater bodies (Firehun 2017; Nega et al. 2021). Currently, the plant is being disseminated in Ethiopia in several water bodies (Churko et al. 2023; Type et al. 2023). It has shown a rapid spread in Awash River lakes (Churko et al. 2023; Shiferaw et al. 2018). Water hyacinth was initially purposely imported as an ornamental plant to Ethiopia's water bodies in the mid-nineteenth century (Merga et al. 2020; Shift et al. 2021). The species quickly spread to numerous adjacent bodies of water, including Lake Ziway and Koka. Some findings suggested that the plant started to spread more than 60 years ago, in 1960 (Abhachire 2014; Shift et al. 2021). Its spread in Lake Koka and Lake Ziway is alarming and detrimental to the environment and livelihood of nearby communities (Asmare et al. 2020; Enyew et al. 2020). The vast majority of these communities are small-scale farmers, particularly, those who reside near wetlands (Dersseh Melesse et al. 2019; Van Oijstaeijen et al. 2020). The wetland zone residents are mostly fishermen and smallholder farmers whose livelihoods are highly dependent on these natural systems (Shiferaw et al. 2018). Its invasion has destroyed croplands, and loss of pasture and indigenous grasses including some tree species (Ant et al. 2022; Peter 2009). Remote sensing has been frequently employed in assessing the spread of the water hyacinth. In the categories of supervised classifications, the maximum likelihood algorithm was used to predict the expansion of water hyacinth (Alam 2020; Buchari et al. 2017). Analysis of changes in land use and cover (LULC) is a methodical approach that supports environmental sustainability by helping to understand both the physical and non-physical interactions with the natural environment. An overview of current and potential future development paths is provided by research on the spatiotemporal shifting patterns of LULC and by simulating future scenarios. Using an integrated CA-ANN approach within the MOLUSCE plugin of QGIS, independent variables like distance from roads and DEM were employed. This approach can forecast, assess, and appreciate the plant’s invasive patterns. The assessment of water hyacinth and other invasive plant species expansion using remote sensing is important for integrated water resource management (Ficetola et al. 2007). Hence, quantifying the past, present, and future distribution of water hyacinth over Lake Koka and Ziway and identifying the relative impact on the livelihoods and the environment is critical. This study aimed at formulating policies and plans for long-term land and water resource management practices by assessing past, present, and future potential expansion of water hyacinths on Lake Koka and Ziway, using a multispectral remote sensing approach. The study provides important information on the invasive species and their effects on water resources for designing management plans and strategies.

The study found that water hyacinth invasions were recognizable in the study area after 1960, although the plant species were already present. Table 3 shows the observable effects of water hyacinth expansion in the study area. The findings show that in 2001, only 9.6% (17) of households were aware of water hyacinth expansion, which was true in the Lake Koka riparian zone but not yet in the Lake Ziway areas. However, in the year 2001, the time was not challenging for water hyacinth in both lake areas (Lake Koga and Ziway). Between 2001 and 2010, a gradual expansion of water hyacinth was noticed, and its spread extended to the Lake Ziway riparian zone (Table 3).

The water hyacinth increase in Lake Ziway districts was comparatively lower in the years 2001 to 2010 than in the years 2011–2022 (Table 3). However, since 2011, water hyacinth invasion has been observed completely occupying 100% (212) of residences, neighbouring farm areas, and other residential land use available in Lake Ziway districts. As a result, the plant invasion was 100% (212) at Lake Ziway riparian ecological systems, as reported by those who participated in the study. In addition, the period 2011–2021 witnessed the highest invasions of water hyacinth in both lake regions. Even if its expansion was not fully observed, the impact of water hyacinth was becoming a sensitive issue, for 262 (63.4%) respondents addressed and these individuals are farmland owners residing in the riparian zone of the lake. Above 95% of the households participating in the present survey proved that water hyacinth invasions were recognized in the study area for more than five decades. The level of invasion has been noticeable from the year 1999 and 2022 (Fig. 3).

As can be seen from the results, in the last five decades, water hyacinth expansion, in the years 2011–2022 shows the greatest spread of the plant species, and it has been causing damage and dominating natural ecosystems, potentially endangering other native plant species in the two-study area (Fig. 2).

Ground truth data, interviews with communities, and questionnaires were used to examine and evaluate the distribution patterns of water hyacinth species in the study area. As a result, the findings are useful for guiding effective management actions and for focusing study regionally throughout Africa, notably in Ethiopia's awash upper river basins. Furthermore, responses from government authorities, experts, and community leaders backed up the data acquired via the Google Earth Engine platform application. The average expansion rate every five years was double the previous expansion data from the year 2013 to 2021. The peak wet season, where the water hyacinth cover increases at the lake area was recorded in September to November and the growth becomes at a high level during the early dry season, which is at the end of October or early December. The future expansion predictions showed similar trends for both lakes. To combat the spread of water hyacinth, all stakeholders, including the government, researchers, non-governmental organizations, and the community, must take consistent action. The invasion and expansion of water hyacinth were observed at Lake Koka and Lake Ziway during all study years. The findings suggest that rather than focusing on manual removal, designing to convert the plant to other useful products was suggested as a preferable strategy. The better approach for water hyacinth removal and expansion prevention was to consider factors such as the plant's growing and expansion season, as well as the weather conditions in which the water body provides optimal nutrition to increase biomass. Water hyacinth control would be successful in the study area if a weekly, monthly, or yearly monitoring and prevention strategy were used. Developing a mechanism for other vegetation affected by water hyacinth expansion can aid in the conservation and rehabilitation of dominated and invaded native species. The study provided some guidance or information regarding the creation of plans, policies, and land management strategies and development. Future research can be applied as hinted by the study's findings, which include determining the location and size of water hyacinth and other LULC. Therefore, the findings from this study can be utilized to guide as a precondition for future research studying the effect of water hyacinth on water variability in Lake Koka and Ziway, Upper Awash Basin of Ethiopia.