Characterizing water-extractable organic carbon in grassland soils

Background/Question/Methods

Inland waters have been shown to be important players in the global carbon cycle, particularly by transforming carbon as it moves from terrestrial ecosystems to the ocean.  Despite our increased understanding about the role of inland waters in processing organic carbon, the magnitude and quality of terrestrial carbon inputs into aquatic systems is still poorly understood. We have attempted to address this gap in knowledge by performing organic matter extractions on grassland soils from across the United States. We extracted organic matter in purified water and examined bacterial respiration on this organic matter to better describe the quality of organic matter potentially exported to aquatic systems.

Results/Conclusions

We found that the sites ranged in oxygen consumption from 1.7 to 0.27 mg O₂ L^-1day^-1. These rates of oxygen consumption are comparable to rates observed in bacterial respiration experiments on whole lake water with similar amounts of dissolved organic carbon. This implies that terrestrially-derived carbon could represent a significant percent of bioavailable carbon processed by inland water systems. The differences in oxygen consumption among sites were high and therefore suggest significant differences in lability of the water extractable organic matter among sites. Furthermore, because all of these extractions were from grasslands, it suggests the ecosystem type is not a good predictor of the lability of the carbon.