Phosphorus Retention and Remobilization along Hydrological Pathways in Karst Terrain

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

Phosphorus Retention and Remobilization along Hydrological Pathways in Karst Terrain

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

Change in neonicotinoid residues in honey pre- and post-moratorium.

<p>The first graph (<b>A</b>) shows the change in average (±SE) combined (clothianidin, thiamethoxam and imidacloprid) residues found in honey over time. Due to the limited number of samples the pre-moratorium period is combined into a single value. The second graph (<b>B</b>) shows how the proportion of honey samples containing neonicotinoid residues changed over time. Note that residues of more than one neonicotinoid type may appear in a single honey sample. As such the proportion of samples containing either clothianidin, thiamethoxam or imidacloprid has been scaled so that when combined it does not exceed the proportion of honey samples containing neonicotinoid residues of any type. Where N = the number of honey samples for a particular time period.</p

Summary of neonicotinoids residues found in honey pre- and post the EU moratorium.

<p>Summary of neonicotinoids residues found in honey pre- and post the EU moratorium.</p

Response of combined neonicotinoid residues in honey to land use.

<p>The graphs show the back transformed model predictions (±SE) for the response of combined neonicotinoid residues found in honey to (<b>A</b>) oilseed rape cover, (<b>B</b>) winter sown cereals and (<b>C</b>) total arable cover. All honey was collected in 2015 during the first year where the use of neonicotinoids seed treatments had been banned on mass flowering crop in the EU. All percentage covers are within 2 km radii of individual hives. Neonicotinoid residues represent the combined concentration of imidacloprid, thiamethoxam and clothianidin.</p

Location of UK honey samples.

<p>The two maps show the location of honey samples collected in 2014–15 superimposed over the cover of all arable crops (A) and oilseed rape (B).</p