Nutrient export from catchments to Singapore’s reservoirs in a changing climate

While surface freshwater (i.e., water in lakes, reservoirs, and rivers) plays an essential role in sustaining human life, both its quantity and quality are increasingly threatened by human activities and climate change. Combining field measurements with a mechanistic model T&C-BG, we investigate nutrient export (dissolved organic carbon (DOC), total nitrogen (TN), and total phosphorus (TP)) from catchments to Singapore’s reservoirs considering six land covers (i.e., forest, grassland, golf courses, agricultural land, bare soil, and impervious surfaces). Results show that the T&C-BG model reproduces well measurements of soil nutrients, soil respiration, and nutrient leakage for different land covers. At the plot scale, DOC export tends to increase in the future for all vegetated surfaces because of stimulated plant photosynthesis by CO₂ fertilization effects. In contrast, TN and TP exports can either increase or decrease depending on land cover. Increases in TN and TP export occur when net primary production is reduced and hence nutrient uptake decreases; the opposite occurs when net primary production increases. While upscaling to the catchment scale, DOC export increases for all reservoirs in the future but TN and TP export trends vary regionally depending on the distribution of land cover types in upstream catchments. Moreover, regardless of the spatial scale, climate internal variability plays an important role in regulating nutrient exports in all experiments. Our findings provide insights for the sustainable management of surface freshwater resources in a changing climate.