Riverine connectivity modulates elemental fluxes through a 200- year period of intensive anthropic change in the Magdalena River floodplains, Colombia

• Published in: Water research (Oxford) 2025-01, Vol.268 (Pt A), p.122633, Article 122633
• Main Authors: Salgado, Jorge, Jaramillo-Monroy, Camila, Link, Andrés, Lopera-Congote, Laura, Velez, Maria I., Gonzalez-Arango, Catalina, Yang, Handong, Panizzo, Virginia N., McGowan, Suzanne
• Format: Article
• Language: English
• Subjects: Biogeochemistry; Climate Change; Climate variability; Colombia; Environmental Monitoring; Eutrophication; Floodplain lakes; Floods; Geologic Sediments - chemistry; Humans; Lakes; Magdalena River; Metals, Heavy - analysis; Palaeolimnology; River damming; Rivers - chemistry; Sediment pollution; Tropical Rivers; Water Pollutants, Chemical - analysis
• ISSN: 0043-1354; 1879-2448; 1879-2448
• DOI: 10.1016/j.watres.2024.122633

•Multiple human pressures have changed the sources and concentrations of sediment biogeochemistry in Magdalena River floodplain lakes.•River-lake connectivity modulates human-drivers and sediment biogeochemistry.•Connected lakes receive higher fluxes of heavy metals while isolated lakes accumulate more nutrients and OM.•Land-cover change is more important than climate in shaping the composition of lake sediment biogeochemistry. Tropical floodplain lakes are increasingly impacted by human activities, yet their pathways of spatial and temporal degradation, particularly under varying hydrological connectivity regimes and climate change, remain poorly understood. This study examines surface-sediment samples and 210Pb-dated sediment cores from six floodplain lakes, representing a gradient in hydrological connectivity in the lower Magdalena River Basin, Colombia. We analysed temporal and spatial variations in several sediment biogeochemical indicators: the concentration and flux of nutrients, heavy metals, and organic matter (OM), and redox conditions, flooding and erosion. Multiple factor analysis (MFA) of surface-sediments identified redox conditions, OM, flooding, heavy metals and lake connectivity as the main contributors to spatial variability within- and between-lakes sediments, accounting for 48 % of the total variation. Additionally, no clear distinction was found between littoral and open-water sediment characteristics. Isolated lakes sediments exhibited reductive conditions rich in OM and nutrients, whereas connected lakes sediments showed greater heavy metal enrichment and higher concentrations of coarse river-fed material. Generalised additive models identified significant changes in the biogeochemical indicators since the late 1800s, that accelerated post-1980s. Shifts in OM, erosion, flooding, redox conditions, land-cover change, heavy metals and climate were identified by MFA as the main drivers of change, explaining 60 %-71 % of the variation in the connected lakes and 53 %-72 % in the isolated lakes. Post-1980s, connected lakes transitioned from conditions of higher accumulation of OM and little erosion to higher accumulation of heavy metals and river-fed material. Conversely, isolated lakes, shifted from detrital-heavy metal-rich sediments to OM-, and nutrient-rich, reductive sediments. Sedimentation rates also surged post-1980s, particularly in highly connected lakes, from 0.14 ± 0.07 g cm² yr⁻¹ to 0.5 ± 0.5 g cm² yr⁻¹, with elevated fluxes of