Spatial variability of macroinvertebrate assemblages and the influence of hydrological and environmental variables along the Sigi River, Tanzania-East Africa

The study of investigating the spatial and temporal variability of macroinvertebrate and their relation to hydrology, hydraulic and environmental factors was done along the Sigi River during two sampling periods in the dry (March) and wet (May) periods of 2012. The river was demarcated based on slope ranges and five river zones were identified as mountains streams (MS), upper foothills (UF), lower foothills (LF), rejuvenated foothills (REJ) and mature lower river (MR). Samples of macroinvertebrate were collected from the five river zones and measurements of hydrological (discharge), hydraulics (Depth, velocity and Froude number) and Environmental (pH, Temperature, substrate, conductivity) parameters were done in each zone. In characterizing the macroinvertebrate assemblages along the Sigi River diversity indices (number of taxa, total abundances, Margalef richness index and ShannonWiener index) were calculated and the most representative species for the spatial and temporal variation were identified. Melanoides and Afronurous showed differences in abundance in two samplings periods while Cleopatra, Potamonautes, Ephemerythus, Neoperla, Caenis, Ceratogomphus and Cheumatopsyche showed significant difference among the river zones. Spearman rank correlation and Distance Linear Model (DistLM) used to revealed physical factors governing the macroinvertebrate assemblages distribution. The study demonstrated that the variation of physical factors like discharge, temperature, conductivity and pH have an important role in the spatial distribution of macroinvertebrate assemblages along the river and the life cycle of macroinvertebrate (Afronurus) is important in determining the temporal variability.O estudo de investigar a variabilidade espacial e temporal de macroinvertebrados e sua relação com a hidrologia, fatores hidráulicos e ambientais foi feito ao longo do Rio Sigi durante dois períodos de amostragem na estação seca (Março) e chuvosa (Maio) de 2012. O rio foi demarcada com base nas taxas de inclinação e cinco zonas do rio foram identificadas como: riachos em montanhas, alto sopé, baixo sopé, rejuvenescente sopé e rio inferior. Amostras de macroinvertebrados foram coletadas a partir das cinco zonas fluviais e medições dos parâmetros hidrológicos (descarga), hidráulicos (profundidade, velocidade e número de Froude) e ambientais (pH, temperatura, substrato, condutividade), foram feitas em cada zona. Ao caracterizar as assembléias de macroinvertebrados ao longo do Rio Sigi, índices de diversidade (número de táxons, abundâncias totais, índice de riqueza de Margalef e ShannonWiener) foram calculados e as espécies mais representativas foram identificadas para a variação espacial e temporal. Melanoides, Amphypsyche, Elminae e Afronurous mostraram diferenças na abundância em dois períodos amostrados, enquanto Cleopatra, Potamonautes, Ephemerythus, Neoperla, Caenis, Ceratogomphus e Cheumatopsyche apresentaram diferença significativa entre as zonas fluviais. Correlação de Sperman e Modelo de Distância Linear foram usados a fim de revelar os fatores físicos que regem a distribuição da comunidade de macroinvertebrados bentônicos. O estudo demonstrou que a variação dos factores físicos, como a descarga, temperatura, condutividade e pH apresentam um papel importante na distribuição espacial na comunidade de macroinvertebrados ao longo do rio e do ciclo de vida dos macroinvertebrados (Afronurus) sendo importante para a determinação da variabilidade temporal

Determination of Environmental Flows in Data-Poor Estuaries—Wami River Estuary in Saadani National Park, Tanzania

Land use changes and mounting water demands reduce freshwater inflows into estuaries, impairing estuarine ecosystems and accelerating coastal seawater intrusion. However, determining minimum river inflows for management guidelines is hampered by a lack of ecosystem-flow link data. This study describes the development of freshwater inflow guidelines for the Wami Estuary, combining scarce river flow data, hydrological modeling, inferring natural salinity regime from vegetation zonation and investigating freshwater requirements of people/wildlife. By adopting the Building Blocks Methodology, a detailed Environmental Flows Assessment was performed to know the minimum water depth/quality seasonal requirements for vegetation, terrestrial/aquatic wildlife and human communities. Water depth requirements were assessed for drought and normal rainfall years; corresponding discharges were obtained by a hydrological model (HEC-RAS) developed for the river channel upstream of estuary. Recommended flows were well within historically occurring flows. However, given the rapidly increasing water demand coupled with reduction in basin water storage due to deforestation/wetland loss, it is critical to ensure these minimum flows are present, without which essential ecosystem services (fisheries, water quality, mangrove forest resources and wildlife/tourism) will be jeopardized. The EFA process is described in painstaking detail to provide a reference for undertaking similar studies in data-poor regions worldwide