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Mng'ong'o M, Munishi LK, Blake W, Comber S, Hutchinson TH, Ndakidemi PA. Towards sustainability: Threat of water quality degradation and eutrophication in Usangu agro-ecosystem Tanzania. MARINE POLLUTION BULLETIN 2022; 181:113909. [PMID: 35810649 DOI: 10.1016/j.marpolbul.2022.113909] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2022] [Revised: 06/23/2022] [Accepted: 06/28/2022] [Indexed: 06/15/2023]
Abstract
The agrochemicals and nutrient losses from farming areas such as paddy farming significantly dictate quality and eutrophication of the freshwater resource. However, how farming and land use pattern affect water qualities and eutrophication remain poorly understood in most African agro-ecosystems. The present study characterized how paddy farming influences water qualities and eutrophication in 10 irrigation schemes in Usangu agro-ecosystem (UA). About 42 water samples were sampled from intakes, channels, paddy fields, and drainages and analyzed for EC, Cl, P, NH4-N, NO3-N, TN, Zn, Cu, Ca, and Mg. We observed water pH ranging from 4.89 to 6.76, which was generally below the acceptable range (6.5-8.4) for irrigation water. NH4-N concentration was in a range of 10.6-70.0 mg/L, NO3-N (8.4-33.9 mg/L), and TN (19.1-21,104 mg/L). NH4-N increased along sampling transect (sampling points) from intakes (5.7-29.1 mg/L), channels (19-20 mg/L), fields (12.9-35.8 mg/L), and outflow (10.6-70.0 mg/L), the same trend were found for NO3-N and TN. The TP determined in water samples were in the range of 0.01 to 1.65 mg/L; where some sites had P > 0.1 mg/L exceeding the allowable P concentration in freshwater resource, thus indicating P enrichment and eutrophication status. The P concentration was observed to increase from intake through paddy fields to drainages, where high P was determined in drainages (0.02-1.65 mg/L) and fields (0.0-0.54 mg/L) compared to channels (0.01-0.13 mg/L) and intakes (0.01-0.04 mg/L). Furthermore, we determined appreciable amount of potentially toxic elements (PTEs) such as Cu, Pb, Cd and Cr in studied water samples. The high N, P, and PTEs in drainages indicate enrichment from agricultural fields leading to water quality degradation and contaminations (eutrophication). The study demonstrates that water quality in UA is degrading potentially due to paddy rice farming and other associated activities in the landscape. Thus, the current study recommends starting initiatives to monitor irrigation water quality in UA for better crop productivity, and improved quality of drainage re-entering downstream through the introduction of mandatory riparian buffer, revising irrigation practices, to include good agronomic practices (GAP) to ensure water quality and sustainability.
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Affiliation(s)
- Marco Mng'ong'o
- School of Life Sciences and Bioengineering (LiSBE), Nelson Mandela African Institution of Science and Technology, P.O. Box 447, Arusha, Tanzania; School of Geography, Earth and Environmental Science, University of Plymouth, Drake Circus, PL4 8AA, UK; College of Science and Technical Education (CoSTE), Mbeya University of Science and Technology (MUST), P.O. Box 131, Mbeya, Tanzania.
| | - Linus K Munishi
- School of Life Sciences and Bioengineering (LiSBE), Nelson Mandela African Institution of Science and Technology, P.O. Box 447, Arusha, Tanzania
| | - William Blake
- School of Geography, Earth and Environmental Science, University of Plymouth, Drake Circus, PL4 8AA, UK
| | - Sean Comber
- School of Geography, Earth and Environmental Science, University of Plymouth, Drake Circus, PL4 8AA, UK
| | - Thomas H Hutchinson
- School of Geography, Earth and Environmental Science, University of Plymouth, Drake Circus, PL4 8AA, UK
| | - Patrick A Ndakidemi
- School of Life Sciences and Bioengineering (LiSBE), Nelson Mandela African Institution of Science and Technology, P.O. Box 447, Arusha, Tanzania
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