Contrasting land-uses in two small river basins impact the colored dissolved organic matter concentration and carbonate system along a river-coastal ocean continuum

• DOI: 10.1016/j.scitotenv.2021.150435
• Publication Date: 2021-09-21T03:33:25Z
• Authors: Elizabeth D. Curr...; Carlos Lara; Marcela Cornejo-D...; Jorge Nimptsch; Mauricio Aguayo; Bernardo R. Broitman; Gonzalo S. Saldías; Cristian A. Vargas
• Keywords: 06 Clean Water and Sanitation; 06 Agua limpia y saneamiento; 550; Oceans and Seas; Carbonates; Fresh Water; 551; 01 natural sciences; Rivers; 13 Acción por el clima; Mussel-farming activity; Humans; 14. Life underwater; Ecosystem; 0105 earth and related environmental sciences; 13 Climate Action; Colored dissolved organic matter; 15. Life on land; 14 Life Below Water; 6. Clean water; 14 Vida submarina; 13. Climate action; Land use; Carbonate chemistry

Human activities have led to an increase in land use change, with effects on the structure and functioning of ecosystems. The impact of contrasting land uses along river basins on the concentration of colored dissolved organic matter (CDOM) reaching the coastal zone, and its relationship with the carbonate system of the adjacent coastal ocean, is poorly known. To understand the relationship between land use change, CDOM and its influence on the carbonate system, two watersheds with contrasting land uses in southern Chile were studied. The samples were collected at eight stations between river and adjacent coastal areas, during three sampling campaigns in the austral summer and spring. Chemical and biological samples were analyzed in the laboratory according to standard protocols. Landsat 8 satellite images of the study area were used for identification and supervised classification using remote sensing tools. The Yaldad River basin showed 82% of native forest and the Colu River basin around 38% of grassland (agriculture). Low total alkalinity (AT) and Dissolved Inorganic Carbon (DIC), but high CDOM proportions were typically observed in freshwater. A higher CDOM and humic-like compounds concentration was observed along the river-coastal ocean continuum in the Yaldad basin, characterized by a predominance of native forests. In contrast, nutrient concentrations, AT and DIC, were higher in the Colu area. Low CaCO3 saturation state (ΩAr < 2) and even undersaturation conditions were observed at the coastal ocean at Yaldad. A strong negative correlation between AT, DIC and ΩAr with CDOM/fDOM, suggested the influence of terrestrial material on the seawater carbon chemistry. Our results provide robust evidence that land uses in river basins can influence CDOM/fDOM proportion and its influence on the carbonate chemistry of the adjacent coastal, with potential implications for the shellfish farming activity in this region.