scholarly journals Nitrogen Cycle Dynamics Revealed Through δ18O-NO3− Analysis in California Groundwater

Geosciences ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 95
Author(s):  
Nate Veale ◽  
Ate Visser ◽  
Bradley Esser ◽  
Michael Singleton ◽  
Jean Moran
Keyword(s):  
United States ◽  
Land Use ◽  
Oxygen Isotope ◽  
Nitrogen Cycle ◽  
The United States ◽  
Nitrate Contamination ◽  
Nitrate Sources ◽  
Oxygen Isotope Fractionation ◽  
Dual Isotope ◽  
Quality Issue

Nitrate is a significant water-quality issue in California, the United States as a whole, and the world. Critical to addressing nitrate contamination is understanding the presence and extent of denitrification, and further refining the techniques used to identify nitrate sources. The use and understanding of nitrate isotopic signatures to identify nitrate sources have advanced tremendously; however, knowledge gaps remain concerning specific fractionation pathways and the role of denitrification in altering source values. Using a large unique database of California groundwater nitrate isotopic compositions, we explored the utility of nitrate–oxygen isotope ratios in determining specific nitrate origins. Lawrence Livermore National Lab (LLNL) samples were supplemented by United States Geological Society (USGS) data to create a dataset of over 1200 dual-isotope results. Methods used at LLNL allowed for the determination of δ15N-NO3−, δ18O-NO3−, δ18O-H2O, δ2H-H2O, excess air, major dissolved gases, and excess N2. Results were examined for the degree to which δ18O-NO3− conforms to the model of nitrification in which two atoms of oxygen are sourced from ambient water and one from the atmosphere. Almost 80% of the results fall within one standard deviation of predicted values. However, 19% of samples had significantly higher values, suggesting the preservation of a synthetic nitrate source signature, mixing of sources, or widespread denitrification. Results were examined with respect to general land-use classifications and, while nitrate concentrations followed the expected pattern of being higher in agricultural settings, δ18O-NO3−patterns are complicated by application of N-fertilizer in various forms, and subsequent N cycling in the soil zone. We found that the current understanding of oxygen isotope-fractionation mechanisms cannot yet explain the prevalence of oxygen-isotope compositions with higher than predicted δ18O values, but when paired with related data such as land use and indicators of denitrification, oxygen-isotope compositions of nitrate can help to assess nitrogen cycle dynamics.

Land Use Policy and Problems in the United States

1964 ◽  
Vol 46 (3) ◽  
pp. 698
Author(s):  
A. Allan Schmid ◽  
Howard W. Ottoson
Keyword(s):  
United States ◽  
Land Use ◽  
The United States ◽  
Land Use Policy

Spatial features of land use/land cover change in the United States

2003 ◽  
Vol 13 (1) ◽  
pp. 63-70 ◽  
Author(s):  
Zhiqiang Gao ◽  
Jiyuan Liu ◽  
Xiangzheng Deng
Keyword(s):  
United States ◽  
Land Use ◽  
Land Cover ◽  
Land Cover Change ◽  
The United States ◽  
Land Use Land Cover ◽  
Spatial Features

Reducing Rural Car Ownership: Cultural Not Policy Changes?

2018 ◽  
Vol 2672 (6) ◽  
pp. 1-10 ◽  
Author(s):  
Emma L. Rearick ◽  
Gregory L. Newmark
Keyword(s):  
United States ◽  
Land Use ◽  
Environmental Sustainability ◽  
Urban Areas ◽  
The United States ◽  
Multiple Regression Model ◽  
Census Bureau ◽  
Matched Pair ◽  
Car Ownership ◽  
Quarter Century

Automobile use is recognized as affecting public health, environmental sustainability, land use, and household expense. Car use is closely tied to car ownership rates. Most car ownership research focuses on urban areas; however, 97% of the United States’ land area and a fifth of its population remains rural. Factors that affect car ownership in these communities may be different than in more urbanized areas. This research focuses on the 2,285 counties in the continental United States that are defined as entirely rural by the guidelines established in the Agricultural Act of 2014. These counties were grouped by five multi-state regions using U.S. Census Bureau definitions. Their percentage changes in car ownership, as well as other demographic variables, over a quarter century were calculated using data from the 1990 Decennial Census and the 2014 5-Year American Community Survey. A multiple regression model was estimated for each grouping to identify counties with lower-than-expected changes in car ownership. For each grouping, one of these outlying counties was selected and matched with another county whose changes in car ownership were within expected ranges given demographic developments. Local professionals were then interviewed to identify policies possibly responsible for the difference in car ownership trends between the matched-pair counties. The interviews suggested that, contrary to expectation, transportation policies had no discernable effect on rural car ownership, but land use polices and, more often, cultural factors linked to changing populations were associated with reduced rural car ownership.

Nitrate in aquifers beneath agricultural systems

2002 ◽  
Vol 45 (9) ◽  
pp. 19-29 ◽  
Author(s):  
M.R. Burkart ◽  
J.D. Stoner
Keyword(s):  
United States ◽  
Groundwater Vulnerability ◽  
The United States ◽  
Point Sources ◽  
Nitrate Contamination ◽  
Agricultural System ◽  
Agricultural Systems ◽  
Fertilizer Use ◽  
Unconfined Aquifers ◽  
The World

Research from several regions of the world provides spatially anecdotal evidence to hypothesize which hydrologic and agricultural factors contribute to groundwater vulnerability to nitrate contamination. Analysis of nationally consistent measurements from the U.S. Geological Survey’s NAWQA program confirms these hypotheses for a substantial range of agricultural systems. Shallow unconfined aquifers are most susceptible to nitrate contamination associated with agricultural systems. Alluvial and other unconsolidated aquifers are the most vulnerable and shallow carbonate aquifers provide a substantial but smaller contamination risk. Where any of these aquifers are overlain by permeable soils the risk of contamination is larger. Irrigated systems can compound this vulnerability by increasing leaching facilitated by additional recharge and additional nutrient applications. The agricultural system of corn, soybeans, and hogs produced significantly larger concentrations of groundwater nitrate than all other agricultural systems, although mean nitrate concentrations in counties with dairy, poultry, cattle and grains, and horticulture systems were similar. If trends in the relation between increased fertilizer use and groundwater nitrate in the United States are repeated in other regions of the world, Asia may experience increasing problems because of recent increases in fertilizer use. Groundwater monitoring in Western and Eastern Europe as well as Russia over the next decade may provide data to determine if the trend in increased nitrate contamination can be reversed. If the concentrated livestock trend in the United States is global, it may be accompanied by increasing nitrogen contamination in groundwater. Concentrated livestock provide both point sources in the confinement area and intense non-point sources as fields close to facilities are used for manure disposal. Regions where irrigated cropland is expanding, such as in Asia, may experience the greatest impact of this practice.

scholarly journals Century-Long Dynamics of the Land Use Structure in the United States

2020 ◽  
pp. 220-231
Author(s):  
Valerij Minat
Keyword(s):  
United States ◽  
Land Use ◽  
Structural Changes ◽  
The United States ◽  
Structural Features ◽  
Summary Table ◽  
Land Use Structure ◽  
Periodic Dynamics ◽  
Space Dynamics ◽  
American Society

The paper studies the experience of American land use in the twentieth century on the territory of 48 contiguous continental states. Changes in time and space (dynamics) of the main indicators of distribution and use of land resources that form the structural appearance of the U.S. land fund are shown. Based on the analysis of the countrys land use structure, the resulting part of which is a summary table, the periodic dynamics of the land use structure (in twenty-year time intervals) is considered, and the dependence of structural changes in land use on the level and nature of the socio-economic development of American society is shown. The study of the age-old dynamics of structural features of American land use conducted on the basis of scientific materials of American scientists and data from official American statistics makes it possible to draw generalizing conclusions about the nature of land use in the United States, both in the whole country and in the regional aspect. As a result, the author has obtained a generalized scientific picture of how the structure of land use in the continental part of the country (without Alaska) has changed over the course of a century in the direction from maximum to optimal use of natural resources.

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