The Seymour Aquifer PDF Download

Author: R.W. Harden and Associates
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Category : Aquifers
Languages : en
Pages :

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Author: Calvin E. Woods
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Category : Groundwater
Languages : en
Pages : 76

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Author: Texas. Department of Water Resources
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Category :
Languages : en
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Author: Texas Water Development Board
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Category : Groundwater
Languages : en
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Author: HDR Engineering
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Category : Hydrogeology
Languages : en
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Author: Toya L. Jones
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Category : Groundwater
Languages : en
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Author:
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ISBN:
Category : Groundwater
Languages : en
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Author: Monty C. Dozier
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Category : Groundwater
Languages : en
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Author: Jeffrey Jack Olyphant
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Category :
Languages : en
Pages : 192

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Land-use change can greatly impact water resources, both water quantity and water quality, by changing the partitioning of water at the land surface among evapotranspiration, runoff, and recharge. The objective of this study was to evaluate the impact of land-use change on water resources in a semiarid region using the Seymour aquifer in the Rolling Plains of Texas as an example. Historical reports indicate that the aquifer was mostly created as a result of land-use change and nitrate contamination has been recorded since the 1940's. Unsaturated zone profiles (18) drilled under three land-use settings (1 rangeland, 11 rain-fed and 6 irrigated) were used to quantify impacts of land-use on groundwater recharge and subsoil nitrate reservoirs, and to link land surface source data with nitrate levels in the aquifer. It is very difficult to find a site that represents the natural rangeland system because most of the region has been cultivated. Only one profile approximates the natural rangeland ecosystem and it has minimal recharge (6 mm/yr), a moderate chloride inventory (358 kg/ha), and a low nitrate inventory (5 kg/ha N). Rain-fed agriculture has moderate recharge (median: 24 mm/yr) and low to moderate inventories of chloride (median: 123 kg/ha) and nitrate (median: 33 kg/ha NO3-N). Irrigated agriculture has moderate to high recharge rates (median: 70 mm/yr), moderate to high chloride inventories (median: 590 kg/ha), and high nitrate inventories (median: 253 kg/ha). Replacement of natural rangeland ecosystems with rain-fed agroecosystems increased recharge indicating that cultivation induced the median water table rise of 8 m recorded from 1910 to 1934, essentially creating the aquifer. The implementation of irrigation in the region began in the 1950's, tripling the recharge under the irrigated systems. Long-term groundwater hydrographs have remained stable suggesting that current pumpage is balanced by the increased recharge under rain-fed and irrigated agriculture and is sustainable. Many of the profiles under rain-fed agriculture (9 of 11) indicate that increased recharge from cultivation has already flushed accumulated salts and nutrients into the underlying aquifer. One profile shows a displaced nitrate inventory of 272 kg/ha NO3-N that should correspond to initial cultivation based on chloride soil water age dating. This nitrate may be attributed to mineralization and nitrification of soil organic nitrogen during initial cultivation related to increased soil moisture and soil aeration. Mobilization of an inventory of this size to the underlying aquifer would produce an increase in groundwater nitrate concentrations of 12.4 mg/L NO3-N based on a current saturated thickness of 7 m (median 1997) and could explain the elevated nitrate concentrations found throughout the aquifer prior to intensive use of synthetic fertilizers. Inventories under cultivated land (86% rain-fed, 14% irrigated by area) indicate that there is sufficient nitrate in the unsaturated zone to maintain current nitrate levels in the aquifer (median: 15.3 mg/L NO3-N), potentially increasing groundwater concentrations by 2.8 mg/L, with 56% derived from irrigated land. Evaluations of surface inputs indicate that irrigated agriculture represents ~ 74% of the total excess nitrogen in the cultivated system and that fertilizer is the dominant source. Current management strategies in irrigated systems do not take into account nitrate inputs from irrigation water, which alone are sufficient to meet crop nitrogen demands, resulting in a 100% mean annual over application of fertilizer. Best management strategies incorporating nitrate in irrigation water should reduce groundwater nitrate contamination and production costs by mining this free nitrate resource in irrigation water and eliminating unnecessary use of fertilizer. Understanding impacts of land-use change is essential for effective management of sustainable groundwater resources in these semiarid regions.

Author: Franklin Mazac
Publisher:
ISBN:
Category : Groundwater
Languages : en
Pages :

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