Browsing by Author "Kiwango, Halima"

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Application of estuarine ecohydrology approach for Studying the key hydrological and ecological Processes of the Wami estuary, Tanzania
(NM-AIST, 2017-12) Kiwango, Halima
This study was conducted in the Wami Estuary in Saadani National Park (SANAPA) to understand the key hydrological and ecological processes that influence the ecosystem functioning. It focused at the dynamics of water quantity, quality and their impact to the organisms, the fate of riverine nutrients and the role of the mangrove ecosystem. Data obtained from the fieldwork, laboratory analyses and secondary sources were used to assess the estuarine condition. The land-ocean Interaction in the Coastal Zone (LOICZ) and UNESCO- Estuarine Ecohydrology (UEE) models were used to study the nutrients processing within the estuarine food web, estimating the nutrients budget, the residence time and the net ecosystem metabolism (NEM). The results indicate the declining trend of freshwater flow to the estuary particularly during the dry season and increasing sediment loading that result to seasonal and tidal variations in the plankton community structure. Seasonal variations in salinity gradient indicate a highly stratified system and a well- mixed system during the wet and dry seasons respectively. The model results indicate the estuary shifts from an autotrophic, denitrifying, flushed in ~ 0.5 day and freshwater-dominated to a heterotrophic, nitrifying, flushed in ~ 7 days, marine-water dominated system from the wet to dry season. The presence of mangroves doubles the shrimp and phytoplankton communities. The mangroves trapped about 12% of the riverine sediments during the wet season while during the dry season the riverine sediment sediment inflow accounted for only 10% of the sediment trapped. The mangrove litter contributes to nutrient recycling whereby crabs recycled 57% of the mangrove litter, 32% was exported to the estuary and 11% remained to decomposed in the mangrove floor. The findings indicate that water quality parameters are within the acceptable levels recommended to sustain a healthy aquatic ecosystem. The study provides a scientific understanding of the Wami Estuary ecosystem functioning for proper management and decision-making process. It recommends an effective governance mechanism in the Wami River basin, emphasizing on sustainable use of water, and reducing sediment loading. Under the worst-case scenario, SANAPA should construct a water reservoir to serve for the estuarine ecosystem, wildlife, and people during the dry season.
The application of nutrient budget models to determine the ecosystem health of the Wami Estuary, Tanzania
(Elsevier, 2018-04) Kiwango, Halima; Njau, Karoli; Wolanskic, Eric
Using the LOICZ and the UEE models we estimated the nutrient budget in the Wami River estuary, Tanzania, to better understand the functioning of the ecosystem and assess its health. We found that during the wet season, when river flows are high, the residence time of the estuary is typically one day or less, and thus little of the riverine nutrients are processed in the estuary. During the dry season the residence time is much longer and as a result the nutrients are processed in the system. The nutrient budget reveals the importance of other sources of nutrients than just dissolved riverine nutrients; these include riverine detritus inflow, mangrove litter fall, and nutrients from hippo excretion. We found no sign of eutrophication. The estuarine food web thus appears healthy in the saline region of the estuary. However, excessive water abstraction in the catchment has resulted in severely decreased flows in the Wami River in the dry season, to the point that the freshwater part of the estuary has essentially disappeared, i.e. the estuary is now saline up to the tidal limit during the dry season. Though the estuary is protected by being included in the Saadani National Park, the system is stressed by dry season salinization, which is seriously affecting the freshwater-dependent flora and fauna. This calls for remedial ecohydrology-based measures at both the watershed scale and the local scale.
The need to enforce minimum environmental flow requirements in Tanzania to preserve estuaries: case study of mangrove-fringed Wami River estuary
(Elsevier, 2015-11-01) Kiwango, Halima; Njau, Karoli; Wolanski, Eric
The importance of restoring and maintaining environmental flows for sustaining the ecosystem integrity of rivers has been recognized in policies and legal frameworks in many countries. However this is routinely not implemented in Tanzania as exemplified by the case of the Wami River estuary, which plays a vital role in processing riverine nutrients, trapping sediment, recycling nutrients in the mangroves, and supporting the ecology of the Saadani National Park and the livelihood of the local communities. Our study reveals that currently the estuary is ecologically healthy but it is threatened by both increasing sedimentation and declining freshwater flow caused by decreasing rainfall – possibly linked with climate change – and by increasing water demand in the watershed for artisanal and large scale agriculture and irrigation schemes. Environmental flow assessment for the Wami River (with exclusion of estuary) has been done and the minimum flows were recommended but they are not enforced. We recommend that the responsible authority (Wami-Ruvu Basin Water Office) enforce its own environmental flow recommendations in order to maintain a healthy estuarine ecosystem and regulate water usage in the watershed. A similar recommendation also holds for all other rivers and estuaries in Tanzania.