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Surface and groundwater from Pangani River Basin (PRB) were sampled in dry and wet seasons,
analysed for dissolved organic and inorganic nutrients (N, P, Si and Urea). There was spatial and
seasonal nutrients’ variability, with enrichment of dissolved inorganic fractions accumulated from
natural and anthropogenic sources. Silicates increased in dry season, whereas nitrate,
ammonium, phosphate and urea increased in wet season; except for phosphate, other nutrients
increased from upstream to the river mouth. High rate of chemical weathering possibly due to
tropical climate and volcanic rocks has caused PRB to have higher concentration of silicates than
average freshwater African Rivers. Contribution of PRB to the coast of Indian Ocean was 2.6, 39.0,
45.2, 67.4 and 5444.8 (mol/km2/yr) for nitrite, phosphate, ammonium, nitrate and silicates,
respectively, which were lower than most of the tropical rivers in the world. Levels of nitrate and
phosphate for most of the stations were higher than recommended levels for aquatic ecosystem
health. Furthermore, observed hypoxia condition in some stations threatens aquatic life. This
study recommends the efficient use of fertilizers to reduce nutrients’ uptake into the lakes and
rivers so as to meet the recommended level for aquatic and human health. |
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