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Time and Moisture Effects on Total and Bioavailable Copper in Soil Water Extracts

^a Chemistry Department, Royal Veterinary and Agricultural University, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark
^b Department of Microbiology, Danish Veterinary Institute, Bülowsvej 27, 1790 Copenhagen V, Denmark

View larger version (20K): [in a new window]   Fig. 1. Standard curve of bioluminescence emitted by the Pseudomonas fluorescens DF57-Cu15 Cu reporter strain exposed to increasing Cu concentrations. Bioluminescence is measured as relative light units (RLU) and each point represents a single measurement.

View larger version (14K): [in a new window]   Fig. 2. Change in Cu speciation of Davis Minimal Medium (DMM) soil extract test medium as determined by the percentage of total copper concentration ([Cu]tot) present as Cu–citrate (circles) and Cu–ligand (squares) complexes. (A) The effect of concentration of ligand (L) at fixed [Cu]tot = 0.5 µM and fixed log K(Cu–L) = 5. (B) The effect of log K(Cu–L) value at fixed [L] = 0.2 mM and fixed [Cu]tot = 0.5 µM.

View larger version (20K): [in a new window]   Fig. 3. Concentration and time effects on total copper concentration ([Cu]tot) in water extracts from soil systems. (A) [Cu]tot of soil systems spiked with different levels of Cu after incubation for 1 h (circles), 19 h (squares), 8 d (triangles), 32 d (crosses), and 220 d (diamonds). Fitted linear regression lines for each incubation period are shown. (B) Recovery of amended Cu in water extracts as a function of the incubation time and dose of 100 (squares), 200 (crosses), 400 (triangles), and 800 (diamonds) µmol Cu kg–1 soil. Fitted logarithmic regression lines for each Cu amendment are shown. The data presented are from duplicate soil systems and each point represents a single soil system. One data point (200 µmol Cu kg–1 soil, 8 d) and two data points (800 µmol kg–1 soil, 220 d) are missing due to loss of samples.

View larger version (19K): [in a new window]   Fig. 4. Concentration and time effects on "bioavailable" copper concentration ([Cu]bio) in water extracts from soil systems. (A) [Cu]bio measured with the Cu-reporter strain DF57-Cu15 in water extracts from Cu-amended soils after incubation for 1 h (circles), 19 h (squares), 8 d (triangles), 32 d (crosses), and 220 d (diamonds). Fitted linear regression lines for each incubation period are shown. The data presented are from duplicate soil systems and each point represents a single soil system. (B) [Cu]bio in water extracts in percentage of added Cu, as function of the incubation time and dose of 100 (squares), 200 (crosses), 400 (triangles), and 800 (diamonds) µmol Cu kg–1 soil. Fitted logarithmic regression lines for each Cu amendment are shown. The data presented are from duplicate soil systems and each point represents a single soil system. (C) [Cu]bio as fraction of total copper concentration ([Cu]tot) in water extracts and a dose of 100 (squares), 200 (crosses), 400 (triangles), and 800 (diamonds) µmol Cu kg–1 soil, as function of the incubation time.

View larger version (18K): [in a new window]   Fig. 5. Moisture effects on total copper concentration ([Cu]tot) and "bioavailable" copper concentration ([Cu]bio) in water extracts from soil systems incubated for 28 d. (A) [Cu]tot from Cu-amended soil systems after incubation at different moisture conditions: dry (circles), variable (squares), 80% field capacity (triangles), 100% field capacity (crosses), and water-saturated soils (diamonds). The data presented are from duplicate soil systems and each point represents a single soil system. Fitted linear regression lines for each incubation condition are shown. (B) The [Cu]bio to [Cu]tot ratio in water extracts from Cu-amended soil systems after incubation at different moisture conditions: dry (circles), variable (squares), 80% field capacity (triangles), 100% field capacity (crosses), and soil slurry (diamonds) soils. The data presented are from duplicate soil systems and each point represents a single soil system. Three data points are missing due to loss of samples: dry, 800 µmol Cu kg–1 soil; 100% field capacity, 200 µmol Cu kg–1 soil; and variable, 800 µmol Cu kg–1 soil.