Wondim, Y. K. | bioRxiv Science

bioRxiv2024

Mapping of Shore Area Wetlands in Lake Tana Biosphere Reserve, Ethiopia Using Sentinel-1A SAR and Multi-Source Data

Shore area wetlands (lacustrine fringe) play a critical role as ecotones that support biodiversity, provide habitats for spawning and refuge, and exhibit high levels of primary productivity. They facilitate significant exchanges of materials between aquatic and terrestrial ecosystems. To effectively manage and preserve these important resources, it is essential to understand their distribution, size, and dynamic changes. This study aimed to create an accurate map of shoreline wetlands using multi-temporal and multi-source data, wetland indicators (hydrology, vegetation, hydric soils), and radar imagery from Sentinel-1A, employing Geomatica software. Additionally, ArcGIS software was used to map the topographic position, Lake Bathymetry, and hydric soil indicators for wetlands. The analytical hierarchy process and weighted overlay methods were also applied in the mapping process for integrating all the indicators to obtain the final extent of shoreline wetlands. The topography position wetland indicator map covered about 55,364ha, while hydric soils covered around 55,151 ha within a 3 km buffer from Lake Tana. The map of hydrology indicator for wetlands revealed that permanently inundated areas accounted for roughly 591,312 ha, and when temporarily inundated areas were included, the total coverage increased to 607,053 ha. Hydrophytic vegetation, including invasive water hyacinth, covered over 74,772 ha. Overall, shoreline wetlands were predominantly located within three kilometers of the terrestrial area from Lake Tana, totaling 26,664 ha. The overall accuracy of land use and cover classification was recorded at 79%, with a Kappa statistic of 0.70, indicating that the resulting map is of acceptable quality. The integration of multi-temporal and multi-source data, along with wetland indicators and radar imagery from Sentinel-1A using Geomatica software, has provided valuable insights into the spatial distribution of shoreline wetlands in Lake Tana. The findings from this study will serve as an important reference for future research aimed at effectively managing and conserving these vital resources.

ecology↗

bioRxiv2024

Development and use of integrated wetland condition index for lacustrine fringe wetlands of Lake Tana, Ethiopia

The primary objective of this research was to develop an integrated wetland condition index (IWCI) for lacustrine fringe wetlands (LFWs) in Lake Tana, Ethiopia, which has been highly impacted by recessionary agriculture, water hyacinth infestation, and both short- and long-term water level fluctuations (WLFs), as well as a heavy sediment load. The index of lacustrine wetland condition was developed based on four wetland characteristics that define wetlands: hydrology, water quality, sediment quality, and wetland biota. The value obtained from field and laboratory measurements of each wetland hydrology, water chemistry, and sediment characteristics indicator was normalized by allocating scores based on literature information and the results of this research project from three different disturbance-level lacustrine wetlands in Lake Tana. Macrophyte, diatom, and zooplankton indicator species tests (IndVal% and p (raw)) were calculated using PAST (PAleontological STatistics). Scores were allocated on a scale from 1 to 10, in such a way that the highest scores reflected the best conditions and the lowest scores the most disturbed and unhealthy conditions. Within four sub-indexes, there is more than one measure, with each measure given equal weighting, whereas the four wetland components (hydrology, water chemistry, sediment, and biota) are weighted as per their contribution to the overall wetland condition. Weights were assigned using the Decision Support System Software of DEFINITE. Finally, the total IWCI was classified into five wetland condition categories, namely: very poor or very far from the reference (0-3), poor (3-5), moderate (5-7), good (7-9), and excellent wetland condition or reference condition (9-10). According to the IWCI of the low water level period, eight wetland sampling sites were found within a moderately impacted condition (44.44%); similarly, eight wetland sampling sites were found within a good or mildly impacted condition; and only two wetland sampling sites (11.11%) were found in an excellent or reference condition. Thus, this IWCI developed and tested in this study could be a powerful tool to inform decision-makers on lacustrine wetland conservation and restoration priorities throughout the Lake Tana Ecosystem.

ecology↗