How do invasive earthworms impact biogeochemical cycles: Pairing laboratory experiments with field surveys

Background/Question/Methods

Preceding European settlement of North America, earthworms were not present in the hardwood forests on the continent.  Since then, invasive earthworms have rapidly spread across many forest systems throughout the United States.  In Minnesota alone, at least fifteen invasive species have been introduced so far.  By consuming and mixing organic matter that is present in the organic soil horizon, earthworms manipulate soil structure and chemistry, modifying many ecosystem processes like nutrient and water cycling.  Previous research has suggested that earthworms increase nitrogen and phosphorus leaching from soils, which could have major effects on aquatic systems within the watershed, but these effects remain uncertain.  Understanding the effect of invasive species on ecosystem level processes is imperative for predicting how systems will respond post introduction.  We paired mesocosm experiments with field surveys to better understand the role of invasive earthworms in altering the nutrient export potential of impacted soils.

Results/Conclusions

Here we show that in a 6 week mesocosm experiment earthworm impacted soils showed an increase in extractable nitrogen and organic carbon but we saw no significant effect on the extractable phosphorus. This suggests that worms may increase the potential of forest soils to export dissolved organic carbon and nitrogen into nearby aquatic systems and influence both soil and aquatic biogeochemical cycling. Soil moisture was also significantly higher in impacted soils, suggesting that worms had a homogenizing effect in our mesocosms. These data will be put into context with field surveys performed during the 2013 summer field season.