SPATIAL VARIATION IN WATERSHED CHARACTERISTICS ALONG A PERENNIAL STREAM IN AWKA, SOUTH EAST NIGERIA

Author: Ndubuisi Lotanna Joseph
Department: Botany
Affiliation: Nnamdi Azikiwe University

The primary driver of the global decline of biodiversity and spatial heterogeneity is habitat loss and fragmentation and sedimentation of streams resulting from anthropogenic pressures on natural ecosystems. This study examined the spatial variation in watershed characteristics along a perennial stream in Awka, South-East Nigeria. The objectives were to study the watershed hydrological division and aspects in relation to its bio-diversity indices. It was also aimed to evaluate the spatial variation in soil properties along the watershed toposequence and examine the relationship between selected soil properties and biodiversity indices. Lastly it sought to study the land-use pattern and its effects on the watershed characteristics. In the study the watershed was divided into three main segments head, middle and tail (60 m × 50 m each). These segments were further sub divided into three sections (20 m × 50 m each) from both the left (West) and right (East) hand side of the stream. Random sampling method with aid of quadrat was used in analyzing the vegetation samples and also undisturbed soil samples. Two replicates were randomly collected from each section of the segment at both sides of the watershed with the aid of a soil auger and metal cylinder. The results showed that there were more trees and fewer herbs in plots closer to the stream whereas there were fewer trees and more herbs in plots further away the steam. The watershed hydrological division and aspects in relation to its bio-diversity indices and spatial dispersion were dominated by herbs (Andropogon tectrum) rather than trees. The species diversity index of the various segments of the stream showed that the tail segment of the stream had higher species diversity index followed by the middle segment and lastly the head segment of the stream with mean total 0.797, 0.651 and 0.606 respectively. The spatial variation in soil properties along the watershed toposequence showed that mean, % Carbon (35.01), % Nitrogen (1.41) and % clay (27.35) were highest at the head division while the mean soil pH (9.53), % organic matter content (2.89), % sand (63.87) and % silt (38.60) were higher at the middle division than in other division. The mean % phosphorus (76.14) and bulk density (1.71) were higher at the tail division. The regression analysis conducted showed that there was no significant relationship between the soil properties of the watershed and the bio-diversity indices such as species diversity and species count (P<0.005). The land use pattern varied at different divisions and was characterized by slashing, cultivation, deforestation and construction. In this study, stream hydrology and watershed toposequence appeared to pose greater influence on spatial variation in bio-diversity than the soil properties.

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