Responses of Karst Springs to Precipitation Reflect Land Use, Lithology, and Climate
Monday, December 4, 2017: 3:50 p.m.
Numerous studies have documented how discharge (Q), water temperature (Tw), and chemistry of karst springs respond to precipitation (P). Fewer have compared responses between regions with differing land use, lithology, and seasonal precipitation patterns. We monitored Tw, specific conductance (SC), and stage (correlated to Q) at Blue Hole spring in Versailles, Kentucky, for 574 d. Blue Hole drains a gently rolling, primarily urban basin developed on flat-lying limestone; there are no pronounced wet or dry seasons. We monitored Tw and stage at three springs (Zerouka, Sidi Rached, and Ribaa), plus stable isotopes of water at Zerouka, in the Middle Atlas region of Morocco for 423 d. The Middle Atlas plateau consists of tabular, faulted dolomitic limestones. The landscape is forest and rangeland; the climate is Mediterranean with dry summers. Average local P during each study period was similar for Blue Hole (2.15 mm/d) and the Middle Atlas (2.38 mm/d). The number of events (defined as total P ≥ 2.5 mm with gaps ≤ 8 h) and maximum hourly P were greater for Blue Hole, whereas median values of event P and event duration were greater for the Middle Atlas. At Blue Hole, the difference between maximum and minimum Tw values during events (ΔTw) was as much as 5.58°C. Tw responses for Middle Atlas springs were more subdued (maximum ΔTw 0.74°C at Ribaa). For storms at Blue Hole, ΔTw increased and minimum SC decreased as maximum Q increased. Stage at Sidi Rached and Zerouka tended to decline gradually from spring to summer before rebounding. Deuterium and oxygen-18 at Zerouka fluctuated with time but did not show pronounced seasonality. We attribute regional differences to the greater extent of impervious cover in the Blue Hole basin and the lower intensity of storms and the lesser extent of carbonate weathering in the Middle Atlas.