Dynamics of critical source areas: does connectivity explain chemistry?

Area of Science:

• Environmental science
• Hydrology
• Soil science

Background:

• Critical source area (CSA) approaches are vital for managing sediment and nutrient transfer in catchments.
• These methods often assume hydrological connectivity drives environmental risk, an assumption requiring empirical testing.

Purpose of the Study:

• To test the critical source area hypothesis by examining overland flow generation and nutrient transfer dynamics.
• To assess the influence of storm characteristics on hydrological connectivity and nutrient export.

Main Methods:

• High-resolution monitoring of 14 rainfall events with varying intensities on a grassland hillslope.
• Detailed analysis of spatial and temporal dynamics of overland flow and nutrient (phosphorus) transfer.
• Comparison of nutrient export coefficients calculated using plot size versus contributing area.

Main Results:

• Total and soluble phosphorus loads correlated significantly with the overland flow contributing area (P<0.05).
• Near-linear relationships (R²=0.86) were found between contributing area size and total overland flow volumes.
• Nutrient concentration dynamics were complex and storm-dependent, indicating limitations in simple contributing area models.
• Export coefficients based on plot size underestimated annual total phosphorus losses by a factor of 17 compared to those using the contributing area.

Conclusions:

• Current critical source area definitions may be insufficient for effective catchment management as they overlook storm-specific characteristics.
• Understanding storm dynamics is essential for accurately assessing nutrient transfer and implementing targeted mitigation strategies.
• The study highlights the need for more dynamic approaches to critical source area identification in hydrological risk assessment.