Towards a Fundamental Understanding of the Interplay and the Interdependence of Biogeochemistry and Biodiversity in the Subsurface of the Earths Critical Zone.

The Earth’s Critical Zone is the thin veneer that spans vegetation, soils, and rock down into aquifers and provides vital services to humanity. Recent interest in understanding the CZ has provided new infrastructure platforms to study this complex interface and discover how it might be impacted by human activities including land use, pollution, and climate change.  The newly established collaborative research center AquaDiva uniquely seeks to combine CZ research with detailed investigation of the functional biodiversity of the subsurface components of the CZ, those portions below the rooting zone, and extending into the first aquifers.  Key questions about this zone still need to be answered, including: What organisms inhabit it? Where do they derive the energy for their metabolism? To what degree do surface land cover and land management influence the biota and biogeochemical function in the subsurface? and How do extreme events at the surface impact subsurface community structure and function? The newly established Hainich Critical Zone Exploratory in central Germany, installed along a ~6km transect spanning forest, pasture and agricultural land uses in the direction of hydrologic flow through limestone parent material is now available to answer these questions.  Initial results indicate fundamental differences in the biota and biogeochemistry of two shallow aquifers likely related to the land use in their recharge area, and the importance of antecedent conditions on the impact of precipitation events on the flow and chemistry of groundwater.  Future research will expand to a similar transect in sandstone parent rock, to evaluate the relative importance of lithology versus surface conditions for the emergent characteristics of the subsurface CZ and the organisms that inhabit it.