A century of human-induced environmental changes and the combined roles of nutrients and land use in Lake Victoria catchment on eutrophication

Dennis M. Njagi, Joyanto Routh, Moses Odhiambo, Chen Luo, Laxmi Gayatri Basapuram, Daniel Olago, Val Klump, Curt Stager

Research output: Contribution to journalArticlepeer-review

Abstract

Lake Victoria, a lifeline for millions of people in East Africa, is affected by anthropogenic activities resulting in eutrophication and impacting the aquatic life and water quality. Therefore, understanding the ongoing changes in the catchment is critical for its restoration. In this context, catchment and lake sediments are important archives in tracing nutrient inputs and their dominant sources to establish causality with human activities and productivity shifts. In this study, we determine the 1) changes in concentrations of total organic carbon (TOC), black carbon (BC), total nitrogen (TN), C/N ratio, and phosphorous (P) fractions in catchment sediments and the open lake, 2) distribution of diatom population in the lake, and 3) land use and land cover changes in the catchment. The distribution of TOC, BC, TN, C/N, and P correlate while showing spatial and temporal variations. In particular, the steady increase in BC confirms atmospheric inputs from anthropogenic activities in the catchment. However, lake sediments show more variations than catchment-derived sediments in geochemical trends. Notably, the catchment has undergone dramatic land use changes since the 1960s (post-independence). This change is most evident in satellite records from 1985 to 2014, which indicate accelerated human activities. For example, urban growth (666–1022%) and agricultural expansion (23–48%) increased sharply at the expense of a decline in forest cover, grassland, and woodlands in the catchment. Cities like Kisumu and Homa Bay expanded, coinciding with rapid population growth and urbanization. Consequently, nutrient inputs have increased since the 1960s, and this change corresponds with the divergence of diatom communities in the lake. In addition, the transition to Nitzschia and cyanobacteria mark increasing cultural eutrophication in the lake. The geochemical trends and statistical data support our inference(s) and provide insights into urban development and agriculture practices, which propelled increased nutrients from the catchment and productivity shifts in the lake.

Original languageEnglish (US)
Article number155425
JournalScience of the Total Environment
Volume835
DOIs
StatePublished - Aug 20 2022

Bibliographical note

Funding Information:
We thank the help extended by M?rten Dario and Lena Lundman with laboratory analyses. Francis Omondi helped with the fieldwork. Martin Karlsson advised us on recreating the land use changes. Devanita Ghosh helped with the SPSS analysis. Finally, we are very grateful to Tom Johnson (University of Minnesota), who provided us with samples from the LV-95 core in Lake Victoria. The project was supported by Vetensakpsr?det (Grant 348 2013 6760) to JR.

Funding Information:
We thank the help extended by Mårten Dario and Lena Lundman with laboratory analyses. Francis Omondi helped with the fieldwork. Martin Karlsson advised us on recreating the land use changes. Devanita Ghosh helped with the SPSS analysis. Finally, we are very grateful to Tom Johnson (University of Minnesota), who provided us with samples from the LV-95 core in Lake Victoria. The project was supported by Vetensakpsrådet (Grant 348 2013 6760 ) to JR.

Publisher Copyright:
© 2022 The Authors

Keywords

  • Black carbon
  • Carbon
  • Diatoms
  • Land use
  • Nitrogen
  • Phosphorous

Continental Scientific Drilling Facility tags

  • VICTORIA

PubMed: MeSH publication types

  • Journal Article

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