Geology topics

Jeannie R.B. Barlow

Publications and source records attributed to Jeannie R.B. Barlow.

5 recordsLinked to original sources

USGS2017

Groundwater quality in the Coastal Lowlands aquifer system, south-central United States

Groundwater provides nearly 50 percent of the Nation’s drinking water. To help protect this vital resource, the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Project assesses groundwater quality in aquifers that are important sources of drinking water. The Coastal Lowlands aquifer system constitutes one of the important areas being evaluated. One or more inorganic constituents with human-health benchmarks were detected at high concentrations in about 12 percent of the study area and at moderate concentrations in about 18 percent. Organic constituents were not detected at high or moderate concentrations in the study area.

Alabama, Florida, Louisiana, Mississippi, Texas↗

USGS2014

Occurrence and transport of nitrogen in the Big Sunflower River, northwestern Mississippi, October 2009-June 2011

The Big Sunflower River Basin, located within the Yazoo River Basin, is subject to large annual inputs of nitrogen from agriculture, atmospheric deposition, and point sources. Understanding how nutrients are transported in, and downstream from, the Big Sunflower River is key to quantifying their eutrophying effects on the Gulf. Recent results from two Spatially Referenced Regressions on Watershed attributes (SPARROW models), which include the Big Sunflower River, indicate minimal losses of nitrogen in stream reaches typical of the main channels of major river systems. If SPARROW assumptions of relatively conservative transport of nitrogen are correct and surface-water losses through the bed of the Big Sunflower River are negligible, then options for managing nutrient loads to the Gulf of Mexico may be limited. Simply put, if every pound of nitrogen entering the Delta is eventually delivered to the Gulf, then the only effective nutrient management option in the Delta is to reduce inputs. If, on the other hand, it can be shown that processes within river channels of the Mississippi Delta act to reduce the mass of nitrogen in transport, other hydrologic approaches may be designed to further limit nitrogen transport. Direct validation of existing SPARROW models for the Delta is a first step in assessing the assumptions underlying those models. In order to characterize spatial and temporal variability of nitrogen in the Big Sunflower River Basin, water samples were collected at four U.S. Geological Survey gaging stations located on the Big Sunflower River between October 1, 2009, and June 30, 2011. Nitrogen concentrations were generally highest at each site during the spring of the 2010 water year and the fall and winter of the 2011 water year. Additionally, the dominant form of nitrogen varied between sites. For example, in samples collected from the most upstream site (Clarksdale), the concentration of organic nitrogen was generally higher than the concentrations of ammonia and nitrate plus nitrite; conversely, at sites farther downstream (that is, at Sunflower and Anguilla), nitrate plus nitrite concentrations were generally higher than concentrations of organic nitrogen and ammonia. In addition to the routinely collected samples, water samples from the Big Sunflower River Basin were collected using a Lagrangian sampling scheme, which attempts to follow a single mass of water through time in order to determine how it changes through processing or other pathways as the water moves downstream. Lagrangian sampling was conducted five times during the study period: (1) April 8–21, 2010, (2) May 12–June 3, 2010, (3) June 15–July 1, 2010, (4) August 23–30, 2010, and (5) May 16–20, 2011. Streamflow conditions were variable for each sampling event because of input from local precipitation and irrigation return flow, and streamflow losses through the streambed. Streamflow and total nitrogen flux increased with drainage area, and the dominant form of nitrogen varied with drainage area size and temporally across sampling events. Results from each method indicate relatively conservative transport of nitrogen within the 160 miles between Clarksdale and Anguilla, providing further validation of the SPARROW models. Furthermore, these results suggest relatively conservative transport of nitrogen from the Big Sunflower River to the Gulf of Mexico and, therefore, imply a fairly close association of nutrient application and export from the Big Sunflower River Basin to the Mississippi River. However, within the Big Sunflower River Basin, two potential nitrogen sinks were identified and include the transport and potential transformation of nitrogen through the streambed and the sequestration and potential transformation of nitrogen above the drainage control structures downstream of Anguilla. By coupling these potential loss mechanisms with nitrogen transport dynamics, it may be possible to further reduce the amount of nitrogen leaving the Big Sunflower River Basin and ultimately arriving at the Gulf of Mexico.

Arkansas;Louisiana;Mississippi↗

USGS2012

Demonstrating usefulness of real-time monitoring at streambank wells coupled with active streamgages - Pilot studies in Wyoming, Montana, and Mississippi

Groundwater and surface water in many cases are considered separate resources, but there is growing recognition of a need to treat them as a single resource. For example, groundwater inflow during low streamflow is vitally important to the health of a stream for many reasons, including buffering temperature, providing good quality water to the stream, and maintaining flow for aquatic organisms. The U.S. Geological Survey (USGS) has measured stream stage and flow at thousands of locations since 1889 and has the ability to distribute the information to the public within hours of collection, but collecting shallow groundwater data at co-located measuring sites is a new concept. Recently developed techniques using heat as a tracer to quantify groundwater and surface-water exchanges have shown the value of coupling these resources to increase the understanding of the water resources of an area. In 2009, the USGS Office of Groundwater began a pilot study to examine the feasibility and utility of widespread use of real-time groundwater monitoring at streambank wells coupled with real-time surface-water monitoring at active streamgages to assist in understanding the exchange of groundwater and surface water in a cost effective manner.

Mississippi;Montana;Wyoming↗

USGS2011

Simulation of water-use conservation scenarios for the Mississippi Delta using an existing regional groundwater flow model

The Mississippi River alluvial plain in northwestern Mississippi (referred to as the Delta), once a floodplain to the Mississippi River covered with hardwoods and marshland, is now a highly productive agricultural region of large economic importance to Mississippi. Water for irrigation is supplied primarily by the Mississippi River Valley alluvial aquifer, and although the alluvial aquifer has a large reserve, there is evidence that the current rate of water use from the alluvial aquifer is not sustainable. Using an existing regional groundwater flow model, conservation scenarios were developed for the alluvial aquifer underlying the Delta region in northwestern Mississippi to assess where the implementation of water-use conservation efforts would have the greatest effect on future water availability-either uniformly throughout the Delta, or focused on a cone of depression in the alluvial aquifer underlying the central part of the Delta. Five scenarios were simulated with the Mississippi Embayment Regional Aquifer Study groundwater flow model: (1) a base scenario in which water use remained constant at 2007 rates throughout the entire simulation; (2) a 5-percent 'Delta-wide' conservation scenario in which water use across the Delta was decreased by 5 percent; (3) a 5-percent 'cone-equivalent' conservation scenario in which water use within the area of the cone of depression was decreased by 11 percent (a volume equivalent to the 5-percent Delta-wide conservation scenario); (4) a 25-percent Delta-wide conservation scenario in which water use across the Delta was decreased by 25 percent; and (5) a 25-percent cone-equivalent conservation scenario in which water use within the area of the cone of depression was decreased by 55 percent (a volume equivalent to the 25-percent Delta-wide conservation scenario). The Delta-wide scenarios result in greater average water-level improvements (relative to the base scenario) for the entire Delta area than the cone-equivalent scenarios; however, the cone-equivalent scenarios result in greater average water-level improvements within the area of the cone of depression because of focused conservation efforts within that area. Regardless of where conservation is located, the greatest average improvements in water level occur within the area of the cone of depression because of the corresponding large area of unsaturated aquifer material within the area of the cone of depression and the hydraulic gradient, which slopes from the periphery of the Delta towards the area of the cone of depression. Of the four conservation scenarios, the 25-percent cone-equivalent scenario resulted in the greatest increase in storage relative to the base scenario with a 32-percent improvement over the base scenario across the entire Delta and a 60-percent improvement within the area of the cone of depression. Overall, the results indicate that focusing conservation efforts within the area of the cone of depression, rather than distributing conservation efforts uniformly across the Delta, results in greater improvements in the amount of storage within the alluvial aquifer. Additionally, as the total amount of conservation increases (that is, from 5 to 25 percent), the difference in storage improvement between the Delta-wide and cone-equivalent scenarios also increases, resulting in greater gains in storage in the cone-equivalent scenario than in the Delta-wide scenario for the same amount of conservation.

Mississippi↗

USGS2010

Unintended consequences of biofuels production?The effects of large-scale crop conversion on water quality and quantity

In the search for renewable fuel alternatives, biofuels have gained strong political momentum. In the last decade, extensive mandates, policies, and subsidies have been adopted to foster the development of a biofuels industry in the United States. The Biofuels Initiative in the Mississippi Delta resulted in a 47-percent decrease in cotton acreage with a concurrent 288-percent increase in corn acreage in 2007. Because corn uses 80 percent more water for irrigation than cotton, and more nitrogen fertilizer is recommended for corn cultivation than for cotton, this widespread shift in crop type has implications for water quantity and water quality in the Delta. Increased water use for corn is accelerating water-level declines in the Mississippi River Valley alluvial aquifer at a time when conservation is being encouraged because of concerns about sustainability of the groundwater resource. Results from a mathematical model calibrated to existing conditions in the Delta indicate that increased fertilizer application on corn also likely will increase the extent of nitrate-nitrogen movement into the alluvial aquifer. Preliminary estimates based on surface-water modeling results indicate that higher application rates of nitrogen increase the nitrogen exported from the Yazoo River Basin to the Mississippi River by about 7 percent. Thus, the shift from cotton to corn may further contribute to hypoxic (low dissolved oxygen) conditions in the Gulf of Mexico.

Open-File Report↗