- Chromophoric Dissolved Organic Carbon Loading of Five Intermittent Streams Recharging Wakulla Springs, Florida.
Kulakowski, Zoe Pemberton, Kish, Stephen A., Parker, William C., Ye, Ming, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Chromophoric dissolved organic matter (CDOM) was quantified by colorimetric light absorption for five blackwater intermittent streams draining into sinks (swallets) connected to the Floridan Aquifer underlying the Woodville Karst Plain, Wakulla County, Florida. Munson Slough receives drainage from the city of Tallahassee and the other streams; Fisher Creek, Black Creek, Jump Creek, and Lost Creek drain the Apalachicola National Forest. Previously conducted dye trace injections have shown the...
Show moreChromophoric dissolved organic matter (CDOM) was quantified by colorimetric light absorption for five blackwater intermittent streams draining into sinks (swallets) connected to the Floridan Aquifer underlying the Woodville Karst Plain, Wakulla County, Florida. Munson Slough receives drainage from the city of Tallahassee and the other streams; Fisher Creek, Black Creek, Jump Creek, and Lost Creek drain the Apalachicola National Forest. Previously conducted dye trace injections have shown the disappearing waters contribute to the discharge of Wakulla Springs, a first magnitude spring. Stage-discharge rating curves were developed for Black Creek and Jump Creek. Wakulla Springs CDOM was determined using UV-VIS spectrophotometry with a 10 cm path length and correlated to total organic carbon concentrations. The year-long study period included a two-month long baseflow period, followed by 12 inches of precipitation, an increase in discharge from 400 cfs to 1700 cfs, and a 41- day recession curve for Wakulla Springs. The Wakulla Springs 2009 water clarity extremes contained 28 percent (poorest water clarity) to 0.5 percent (best water clarity) stream water. The total CDOM mass associated with the streams exceeds the Wakulla Springs mass following storm events, indicating that some mass bypasses Wakulla Springs or is stored in the matrix/conduit aquifer system to be later released. Total stream mass equals Wakulla Springs mass for low baseflow conditions, but for higher baseflow, Wakulla Springs mass exceeds the total stream mass, indicating Wakulla Springs is still discharging mass from the preceding storm. This delayed mass is either from aquifer matrix/conduit storage or from the slower Lost Creek pathway. The storm mass associated with any one stream exceeds the Wakulla Springs lower baseflow mass by 4 to 9 times (for the two lowest mass streams) and has the ability to affect Wakulla Springs water clarity without contribution from any other stream. All of the water filled caves connected to Wakulla Springs contribute CDOM, with wet conditions contributing 25-67 percent more CDOM. A Wakulla Springs transmittance of 99 percent would have a NAC254nm of 0.1 and a TOC concentration of 0.69 mg/l. With the Wakulla Springs baseflow CDOM mass range of 600-1000 kg/day, this concentration indicates that the Floridan Aquifer clear water baseflow discharge will need to be 350-600cfs (10-17cms) to provide the necessary dilution for the bottom of the Wakulla Springs basin to be viewed with the water clarity of historic times. Investigation of upgradient Floridan aquifer water use indicated no change for the potentiometric surface entering Florida, but declines up to 16 feet were noted for northern Leon County, based on the 2008 potentiometric surface. Groundwater withdrawals by municipalities, Consumptive Use Permits, and private wells totaled 14,500 MGY for Leon and Wakulla counties or 9 percent of the 164,000 MGY discharged by Wakulla Spring in 2009. A decline in precipitation for the most recent decade, 1999-2009, was noted that may contribute, but groundwater use is the most likely cause of the decreased water clarity water. Wakulla Springs has an increasing trend for total dissolved solids and specific conductivity indicating a greater contribution of deep Floridan Aquifer water. More research is needed to understand vertical and lateral upgradient flow within the Floridan Aquifer and the fluctuating controls that either direct creek water to Wakulla Springs or result in it bypassing Wakulla Springs.
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