Nutrients’ distribution and their impact on Pangani River Basin’s ecosystem – Tanzania

ABSTRACT

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.

KEYWORDS:

• Nutrients
• variability
• ecosystem health
• human health
• river basin
• hypoxia

Acknowledgements

Authors appreciate to the support of Pangani Basin Water Office and communities around the basin during field work. We thank colleagues from Ocean University of China and East China Normal University for their help during the laboratory work.

Disclosure statement

We acknowledge that there was no financial interest or benefit arising in applications of this research.

Additional information

Funding

The first author would like to thank Chinese Government for offering Fellowship grant 2013–2017 CSC No. 2013GXZ869 for PhD study. Special thank to the Graduate School and State Key Laboratories of Estuaries and Coastal Research (SKLEC) both from East China Normal University for financial support [project number SKLEC-KF201502].