Abstract:
Water and microbial mat communities of the ponds in the Victoria Valley was investigated to test the hypothesis that the gradient in climatic severity associated with latitudinal and altitudinal gradients drives a corresponding gradient of biological diversity and productivity. The biological, physical and chemical parameters of three ponds near the outflow from Lake Victoria were sampled in
... mid-January. Although many ponds were present close to the stream connecting the Upper Victoria Lake to Lake Vida, they were very similar in character. Two ponds were sampled with aspects of the water column measured to describe depth related changes in temperature, conductivity, dissolved oxygen, pH and redox potential. A fine scale profile (10cm depth intervals) of water samples to analyse for major ions in relation to changes in conductivity with depth and between ponds. Aspects of biology analysis in water samples were for phytoplankton chlorophyll a, PNPP, PNPC and dissolved nutrients. One pond was seen to be different in colour and chemical characteristics and detailed in situ measurements were made of conductivity, temperature and dissolved oxygen at 2cm intervals. Water samples were collected for later chemical analysis. Sediment samples were also collected from the base of three ponds. Salts were visible in the polygonal frost cracks in the valley floor and a sample of these salts was collected for comparison with the pond salts. Additional samples were collected for biochemistry and biology from sites along the river itself where cyanobacterial mat development was extensive. The following season, the same ponds were sampled in mid-October specifically to collect samples of the highly saline basal brine which occurs below the ice of the predominantly frozen pond over winter. Temperature, conductivity, pH and dissolved oxygen concentration were measured at various depths. Basal brine and melted ice samples were analysed for major ions and nutrients and trace metals. Ice cores were collected from one pond for analysis of salt content, salt inclusion, ice structure and dissolved gases. 
