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Lower Mississippi-Gulf Water Science Center - Mississippi
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Phosphorus Occurrence and Extent in the Mississippi River Valley alluvial aquifer
Concentrations of dissolved phosphorus in groundwater typically are low because phosphorus tends to sorb to soil and aquifer sediments and is not readily transported in groundwater. A recent summary of phosphorus data for water from the Mississippi River Valley alluvial aquifer showed median concentrations of phosphorus well above the background concentration of 0.02 mg/L. Two subunits of the alluvial aquifer, the Holocene alluvium and the Pleistocene valley trains, had median concentrations of 0.65 and 0.11 mg/L, respectively. The widespread occurrence of elevated phosphorus in these two subunits suggests either a natural source in the soils or aquifer sediments, or a nonpoint sources such as fertilizer and animal waste, or a combination of natural and human sources. Additionally, there is a concern that irrigation return flow from groundwater high in phosphorus will cause surface water to exceed nutrient criteria currently being developed by the state and U.S. Environmental Protection Agency. The objective of this study is to characterize the occurrence of phosphorus in groundwater of the Mississippi River Valley alluvial aquifer throughout the Delta. A random selection of irrigation wells located throughout the Mississippi Delta will be selected for sampling. Approximately 50 wells will be sampled for selected major inorganics, iron, manganese, nutrients, and field parameters (pH, specific conductance, temperature, and dissolved oxygen). Data collected will be plotted on a map and contours will be drawn to illustrate phosphorus concentrations in the study area.
USGS employee processing samples in the field.
USGS employee sampling ground water.
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