Karst terrains, regions of soil overlaying limestone bedrock, comprise nearly a quarter of the Illinois landscape. Over time, calcium carbonate in limestone has been solutionally dissolved via surface water infiltration, leading to a network of horizontal and vertical fissures through which groundwater flows. These fissures harbor unique assemblages of groundwater-dwelling fauna, including many aquatic cave species, including the federally listed Illinois cave amphipod (Gammarus acherondytes). The epikarst is the zone below the soil layer but perched above caves in which percolating groundwater moves from the surface and drips through stalactites and fissures.
We sought to develop appropriate and effective stalactite drip sampling methods while augmenting our understanding of the epikarsts' role in groundwater hydrology and community ecology of Illinois' karst areas.
In Illinois Caverns State Natural Area, we used custom-made drip samplers (constructed from plastic nalgene bottles with a small square cut from the side with fine mesh attached over the hole; bike tubing was attached to the mouth of the bottles and attached to stalactites with zip-ties) to collect the biota that is flushed through the epikarst and normally deposited into cave channels. We also collected high-resolution environmental and hydrologic data via use of a HOBO rain gauge apparatus, conductivity logger, and a temperature/relative humidity logger. Data was collected from June - August 2014.
We collected 128 copepod individuals from 11 drips, comprising 8 genera, though a single genus was much more abundant than any other genus (62%). We also found several aquatic worms, one of which has never before been recorded in Illinois.
Copepod occurrence frequency was 0.011 copepods/L with a daily occurrence rate of 0.41 copepods/drip/day. Stalactites with with faster drip rates were also found to harbor less copepods relative to slower dripping stalactites, perhaps indicative of inhospitable conditions for copepod population growth in fast flowing conduits.