Groundwater, Lake Chemistry and Climate

Long term research at the NTL-LTER site, which was established in 1981, provided unexpected insights into the effect of climate shifts on lake-groundwater interactions.  Five years after the site was established, the region experienced a severe 4-year drought.  The availability of continuous, long-term data before, during, and after the drought allowed Anderson et al. (1993) to show that local flowpaths of groundwater to lakes were much more dynamic and transient than previously thought.  Crystal Lake, an NTL-LTER seepage lake located high in the landscape received up to 10% of it's water inputs from groundwater during wet periods, but became totally isolated from groundwater inputs during the drought.  These switches in groundwater inputs have important implications for lake chemistry and biological communities.  In the Northern Highland Lake District, groundwater is the major source of materials that support aquatic life (such as the calcium needed by snails to build shells) and buffer lakes from damage by acid rain.  Long term data on lake chemistry from the NTL-LTER program demonstrated that lakes moderately high in the landscape, where reversals in groundwater inflow are likely, lose cation mass during drought (Webster et al. 1996).  Under the more sustained switch to warmer and drier conditions predicted by climate change models, the concentration of biologically important cations and acid neutralizing substances could substantially decline (Kratz et al. 1997).  No change was observed in lakes that are always hydraulically mounded.  Lakes low in the landscape, however, accumulated cations during the drought because their groundwater inputs are dominated by regional flowpaths, which are less temporally responsive to climate shifts

Without the long-term data record on chemistry and hydrology from a set of lakes ranging across the landscape, these insights into the dynamic nature of lake-groundwater interactions and resultant implications for lake chemistry and biology would have been missed.  Further, because of long-term studies at NTL-LTER, we were able to take advantage of a "natural" experiment - the sustained drought - allowing us to better understand differential lake responses to regional climatic events.

Anderson, M.P. and X. Cheng.  1993.  Long- and short-term transience in a groundwater/lake system in Wisconsin, USA.  Journal of Hydrology. 145:1-18.