Variation i sorption og naturlig nedbrydning af herbicider i kalksten Gry Sander Janniche

Sonnenborg, Kalk på tværs, ATV møde 8. november 2006

Formål Undersøge sorption og mikrobiel nedbrydning ved lav initial koncentration af herbicider i kalksten –Kan simple geokemiske parametre forklarer variation i sorption –Falder nedbrydningen over dybden (1-43 mut) –Betydning af små-skala variationer Mechlorprop Isoproturon Acetochlor

Agricultural catchment of app. 4.5 km 2

Field site Altitude (m) Kalk Kalksten, heterogen (lutetian) Sand - vandførende Ler (sparnacien)

Field site

4 intact cores: –Pz14: 0-60 mbs –Pz17a: 0-13 mbs –Pz17c: 0-22 mbs –Pz18: 0-6 mbs

Delicate handling of sediment samples

Sorption M total = M sediment ·C S + C W ·V 5 g sediment 5 mL water and sorbat (1 or 50 µg/L) 10 samples ~ 180 batches K d = C s /C w

Nedbrydningspotentiale 40 g sediment + 1 µg/kg 14 C-herbicid Opsampling af 14 CO inkubationer 2175 inkubationer 5 fortyndinger af sediment med mineralmedie i 5 replikater + 25 µg/L 14 C-herbicid Opsampling af 14 CO 2 Most-probable-number ( 14 C-MPN) Mineralisering

Vertical small-scale variation in sorption Lille sorption – høj mobilitet Stor variation indenfor få cm Kan geologi forklarer sorption ?

Organic carbon is not controlling sorption Sorption (1 µg/L) A1A2B1B2C1C3D1D2D3D4 n.i.

Sorption (1 µg/L) Sorption høj når TIC er lav og SSA er høj Kalksten med mergel A1A2B1B2C1C3D1D2D3D4 ”urenheder” i kalksten n.i.

Mineralization in limestone - Decreases with depth? Acetochlor Fast at 0-1 mbs Slow at >1 mbs Yes!

Acetochlor mineralization in limestone -Decreases with depth? No link between acetochlor mineralization and depth in limestone from >1 mbs Ialt 34 prøver, men kun 12 prøver med mineralisering

Mecoprop mineralization in limestone from mbs Små-skala variation D1 D2 D3

Mineralization and degraders over depth

Conceptual model – importance of “active” layer in limestone for the GW contamination with the herbicides ρ b : 2 kg/L ε: 0.4 v w : 1 m/y K d and k determined x a depends on scenario: 0, 0.3 or 3 m “Active” layer x a thick 10 m limestone profile

Conceptual model Limited importance if “active layer” is only 30 cm thick,

Conceptual model Limited importance if “active layer” is only 30 cm thick, 3

Conceptual model Limited importance if “active layer” is only 30 cm thick, but notable if ten times thicker… The limestone is up to 42 m thick in the field site… and heterogeneous… Consequently, a very detailed knowledge of the limestone characteristics is paramount - over the hole limestone profile

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