Riverine dissolved organic matter (DOM) as affected by urbanization gradient

Area of Science:

• Environmental Science
• Biogeochemistry
• River Ecology

Background:

• Rapid urbanization significantly impacts global carbon cycling and river hydrology.
• The effects of urban land use and nutrient pollution on dissolved organic matter (DOM) in rivers remain poorly understood.

Purpose of the Study:

• To investigate how varying urban land use and nutrient enrichment influence DOM characteristics in river systems.
• To test the hypothesis that urbanization alters DOM sources and concentrations in rivers draining urbanized areas.

Main Methods:

• Field sampling of headwater rivers across a gradient of urban intensities in the Three Gorges Reservoir Area (TGRA), China.
• Analysis of dissolved organic carbon (DOC) and chromophoric dissolved organic matter (CDOM) properties, including absorption coefficients and fluorescence indices.
• Seasonal sampling during dry and wet periods to capture temporal variations.

Main Results:

• Positive correlations were observed between the percentage of urban land (%Urban) and DOC concentration, CDOM absorption coefficients (a254, a280, a350), and the fluorescence index (FI370).
• Stepwise regression indicated %Urban predicts DOC and CDOM levels, while riverine nitrogen predicts increased autochthonous DOM sources.
• CDOM concentrations were higher in the wet season, whereas autochthonous DOM signals were stronger in the dry season, linked to high nitrogen loading.

Conclusions:

• Urbanization directly increases DOM levels and influences its sources in river systems.
• Urban-induced nutrient enrichment indirectly enhances autochthonous DOM production, further altering riverine DOM composition.
• Understanding these urbanization impacts is crucial for managing water quality and carbon cycling in urban riverine ecosystems.