Water Quality Status of Tono and Vea Reservoirs for Aquaculture Development in the Upper East Region of Ghana

Abstract

Understanding aquatic ecosystem dynamics is fundamental to sustainable development of aquaculture. This study explores the water quality characteristics over temporal and spatial scale in Tono and Vea Reservoirs in the Upper East Region of Ghana for aquaculture development. Water samples and in-situ measurements were taken for fifteen months, from February 2015 to March 2016. Monthly water quality monitoring were based on stratified sampling from upstream, midstream and downstream zones of these reservoirs. Standard analytical methods for examination of water were employed during sampling and laboratory analysis of reservoir water quality. Phytoplankton analysis was done using light microscopy to obtain phylum abundance. Multivariate statistical methods were used to investigate water quality dataset obtained. Cluster analysis grouped fifteen months of water quality changes into three seasonality regimes (periods) based on temporal variation. Principal component analysis (PCA) reduced eighteen water quality variables into five and three factors with total variance of 88.26 % and 79.30% for Tono and Vea reservoirs, respectively. With pH > 7 and alkalinity > 20 but < 100 mg L-1 CaCO3, both reservoirs have alkaline water. Dissolved oxygen was > 5 mg L-1. Three phyla of phytoplankton were identified with dominant (in abundance) phylum as Chlorophyta (72%) occurring in Tono reservoir. To understand the spatial relationship using correspondence analysis (CA), the first axis of CA explained 84.2% and 64.3% of total variation in relative abundance of phytoplankton phyla for Tono and Vea reservoirs, respectively. Thus, Cyanophyta showed strong positive association with conductivity, total hardness, nitrate, sulphate, turbidity, water depth and dissolved oxygen which were responsive to the midstream and upstream zones of Tono reservoir. Whiles in Vea reservoir, Chlorophyta under same water quality variable showed responsiveness to the midstream and downstream zones. Reservoir water quality studied were within acceptable limits for fish culture but changes could be linked to anthropogenic activities on reservoir catchment area and seasonality regime. Results from this provide a baseline to enable information to enable assessment of aquaculture impact in Tono and Vea reservoirs. The use of multivariate analysis could be a reliable statistical method for assessing water quality on a spatio-temporal scale.