Cave and Karst Systems
An understanding of the interplay of hydrology and biogeochemical processes that control transport and processing of nutrients in karst watersheds is critical to the design of sustainable land-use practices over karst terrains. Our understanding of the processes operating in karst systems, however, lags considerably behind that of other aquatic ecosystems (such as marine, riverine, wetlands, and granular aquifers). The availability of dissolved organic matter, a strong control in biogeochemical cycling of nutrients within the karst soil system, is easily altered by agricultural, wastewater treatment outfalls, septic systems, and other activities in the karst watersheds. Whereas karst ground-water movement has recently received focused study, controls on the carbon availability and movement, particularly the DIC-DOC-CO2 (g) dynamics have received little attention. Carbon is the basic substrate which must be available for processing nutrients--and specifically nitrate. Basic geochemical monitoring is being conducted which includes continuous pCO2 measurement and isotopic characterization of DIC and DOC behavior moving through the karst-soil system. These data are facilitating source identification and delineation of the complex interaction between water quality and nutrient cycling in karst. This project will establish controls on the effect of carbon cycling and local hydrology on the effective processing of nutrients in mantled-karst watersheds of the Ozarks.
Currently we are working in a cave system in Madison County to help understand the interplay of climate, hydrology, and nutrient processing. Sampling infrastructure design aims at collection of soil gas, soil water, ground water at various points moving along flow paths including caves, and cave CO2. The data set being accrued will help draw direct correlation between the surface conditions and cave responses and enable elucidation of controls on nutrient processing. Data also will allow for characterization of climate effects with improved understanding of CO2-speleothem dynamics and the development of the archived climate records of the cave system.
|Dr. Phillip D. Hays||GEOS||Associate Research Professor, USGS Liaison|
|Dr. J Van Brahana||GEOS||Emeritus Professor|
|Erik Pollock||UASIL||Instructor/Adjunct Professor|
Use of Phosphate-Oxygen Isotope Ratios as a Tracer for Sources and Cycling of Phosphorus in the Illinois River in AR and OK
|Excess phosphorus in streams causes eutrophication, which diminishes an aquatic system's capacity for supporting a healthy and normal ecosystem and diverse aquatic communities, water supply needs, and aesthetic and recreational value. Phosphorus concentrations and sources are a significant regional concern at the Upper Illinois River Watershed in northwestern Arkansas and northeastern Oklahoma, as well as for streams across the Nation. Recently developed isotopic methods enable determination of oxygen isotope composition of soluble reactive phosphate (SRP), potentially allowing sources of phosphates in aquatic systems to be identified. For this method, phosphate is chelated into a magnesium hydroxide precipitate, reprecipitated as cerium phosphate, and then dissolved and precipitated as silver phosphate which works well for isotopic analysis. We are interested in phosphate isotopic composition because oxygen isotopic ratios reflect those of input sources. As organic phosphorus is oxidized, oxygen is derived largely from water, and d18OP reflects the d18O of local water. Isotopic fractionation of dissolved inorganic phosphate can occur, but only as a result of enzyme-mediated biologic reactions. The expected equilibrium of d18OP has been empirically derived for phosphates produced by microbial cultures and the temperature-dependent fractionation may add insight to the amount of SRP cycling occurring in the river. If PO4 demand is low relative to input, the d18OP will reflect the isotopic signatures of the input sources, allowing sources to be identified and transport of PO4 to be characterized. Input sources such as wastewater effluent (29‰), poultry litter extract (20‰) and commercial fertilizer extract (18‰) have been sampled and analyzed. Water samples from the Illinois River are now being sampled. This method has not been not previously been applied in the central United States, but we hope results will give us better understanding of the sources, transport, and cycling of phosphorus in the Illinois River and similarly impacted streams in the region.|