NITROGEN DYNAMICS IN KARST GROUNDWATER (Invited Presentation)

Karst groundwater is uniquely vulnerable to contamination from the land surface because of the direct connection of surface and groundwater flow related to focused recharge through fissures, sinkholes, and other karst features. The water quality of the Edwards aquifer in Central Texas, an area undergoing rapid population growth, is controlled largely by the quality of the streams that recharge the aquifer. Increases in population result in increases in wastewater discharge generated and in associated nitrogen (N) species. Mechanisms for disposal of treated wastewater include direct discharge to streams, septic systems, and land application. Other sources of N include atmospheric deposition, livestock, wildlife, soils, and instream sources such as biological activity. N species can be transformed in soils, in streams, and in groundwater through processes such as ammonification, nitrification, and denitrification. In this presentation we will discuss how increased loading of N at the surface and subsurface has affected the quality of groundwater with different flow rates in the Edwards aquifer; tools for investigating short- and long-term N dynamics and transformation; and projections and concerns for karst water quality in areas undergoing population growth.