The Potential Link Between El Nino and Water Hyacinth Blooms in Winam Gulf of Lake Victoria, East Africa: Evidence from Satellite Imagery

Abstract

This study evaluates the link between the occurrence of El Nino events in East Africa and water hyacinth blooms in Winam Gulf of Lake Victoria using remote sensing technology. A time-series of the Normalized Difference Vegetation Index (NDVI) analyzed from data acquired by the multispectral Aqua/Terra sensors aboard the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite are used to monitor areal extent and density of the aquatic plants. We related the NDVI derived from MODIS imagery to data on El Niño South Oscillation (ENSO) events that were obtained from NOAA and rainfall data from the study site. Our results from the 11-year time-series data show a statistically significant positive correlation (R=0.6, P=0.021) between the occurrence of El Niño events and water hyacinth blooms in Winam Gulf. The proliferation of water hyacinth rafts in Winam Gulf may be a response to dramatic environmental and water quality changes in Lake Victoria. The patterns of impact of ENSO events and rainfall show spatial and temporal variation patterns in the region, depending on the time and space evolution of each individual ENSO event that could explain the differences in general patterns of water hyacinth cover in Lake Victoria during different El Niño events. Although the problems eutrophication and water hyacinth are severe in the Winam Gulf of Lake Victoria some of the solutions to the problem are located several hundreds of kilometers away in the rich agricultural farmlands of the Lake Victoria catchment area. These include better land management practices and strategies aimed at limiting pollution and soil erosion within the lake's drainage basin.

Evaluating MERIS-Based Aquatic Vegetation Mapping in Lake Victoria

“…The challenge, however, is the correct identification of suitable thresholds separating various feature classes in the scene. The authors of [13] applied NDVI = 0.1 as a threshold to detect presence of vegetation, while [15] estimated the aquatic vegetation cover in Lake Victoria using a three-level NDVI scale:…”

“…Many studies on Lake Victoria have used vegetation indices, for example, [12] used NDVI to investigate the dependency of hyacinth biomass production on nutrients levels. In [13], the authors used a time-series of NDVI to evaluate the link between the occurrence of El Nino events in East Africa and water hyacinth blooms in Winam Gulf section of Lake Victoria. The authors of [14] used NDVI and several of its derivatives to monitor Lake Victoria's water level and drought conditions.…”

Sources of variance in a female fertility signal: exaggerated estrous swellings in a natural population of baboons

“…The first of our study’s two time periods occurred during the end of this period of extreme drought (June 2009–October 2009). The second of our study’s two time periods (February through June 2010) occurred during a period of heavy rains, which were probably due to an El Nino effect (Kiage and Obuoyo 2011). …”

Spatial Temporal Mapping of Spread of Water Hyacinth in Winum Gulf, Lake Victoria

“…The study area is the Kenyan part of Lake Victoria around Winum Gulf, with latitude and longitude 0.1 degrees South and 34.2 degrees East respectively. The location is located around the equator with a depth of 10 meters and a width of 25 kilometres with its extension of approximately 64 kilometres to Rusinga Island (Obuoyo et al, et al, 2011). This area is one of the most polluted areas, with its proximity to the city that discharges effluents in to the lake plus the discharges from the agricultural runoff water worsening the situation.…”

“…This area is one of the most polluted areas, with its proximity to the city that discharges effluents in to the lake plus the discharges from the agricultural runoff water worsening the situation. This area is also high on chlorophyll, total phosphorus and Secchi content (Obuoyo et al, et al, 2011). The lake is located within the tropical convergence zone (ITCZ) with bimodal rains that contributes to more than 75 percent of its recharge (Kizza et al, 2009).…”