Phosphorus
Retention and Remobilization along Hydrological
Pathways in Karst Terrain
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Abstract
Karst landscapes
are often perceived as highly vulnerable to agricultural
phosphorus (P) loss, via solution-enlarged conduits that bypass P
retention processes. Although attenuation of P concentrations has
been widely reported within karst drainage, the extent to which this
results from hydrological dilution, rather than P retention, is poorly
understood. This is of strategic importance for understanding the
resilience of karst landscapes to P inputs, given increasing pressures
for intensified agricultural production. Here hydrochemical tracers
were used to account for dilution of P, and to quantify net P retention,
along transport pathways between agricultural fields and emergent
springs, for the karst of the Ozark Plateau, midcontinent USA. Up
to ∼70% of the annual total P flux and ∼90% of the annual
soluble reactive P flux was retained, with preferential retention
of the most bioavailable (soluble reactive) P fractions. Our results
suggest that, in some cases, karst drainage may provide a greater
P sink than previously considered. However, the subsequent remobilization
and release of the retained P may become a long-term source of slowly
released “legacy” P to surface waters