Water quality in the central Columbia Plateau, Washington and Idaho, 1992-95

Williamson, Alex K.; Munn, Mark D.; Ryker, Sarah J.; Wagner, Richard J.; Ebbert, J.C.; Vanderpool, A.M.

doi:10.3133/cir1144

Cited by 34 publications

(27 citation statements)

References 15 publications

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“…The observed probability that nitrate exceeds 4 mg/L is 0.703 for wells in landuse studies of the area, and the median predicted probability is 0.641. Irrigation and high rates of fertilizer application are major contributors to the high nitrate concentration in groundwaters of the area (41). Almost all of the water in the Plateau supports irrigation in arid agricultural areas, greatly increasing the recharge of water and nitrate to shallow groundwater.…”

Section: Recalibration Of Multivariate Logistic Regression Modelmentioning

confidence: 99%

Probability of Nitrate Contamination of Recently Recharged Groundwaters in the Conterminous United States

Nolan

Hitt

Ruddy

2002

Environ. Sci. Technol.

318

204

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A new logistic regression (LR) model was used to predict the probability of nitrate contamination exceeding 4 mg/L in predominantly shallow, recently recharged groundwaters of the United States. The new model contains variables representing (1) N fertilizer loading (p < 0.001), (2) percent cropland-pasture (p < 0.001), (3) natural log of human population density (p < 0.001), (4) percent welldrained soils (p < 0.001), (5) depth to the seasonally high water table (p < 0.001), and (6) presence or absence of unconsolidated sand and gravel aquifers (p ) 0.002). Observed and average predicted probabilities associated with deciles of risk are well correlated (r 2 ) 0.875), indicating that the LR model fits the data well. The likelihood of nitrate contamination is greater in areas with high N loading and well-drained surficial soils over unconsolidated sand and gravels. The LR model correctly predicted the status of nitrate contamination in 75% of wells in a validation data set. Considering all wells used in both calibration and validation, observed median nitrate concentration increased from 0.24 to 8.30 mg/L as the mapped probability of nitrate exceeding 4 mg/L increased from e0.17 to >0.83.

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Section: Recalibration Of Multivariate Logistic Regression Modelmentioning

confidence: 99%

Probability of Nitrate Contamination of Recently Recharged Groundwaters in the Conterminous United States

Nolan

Hitt

Ruddy

2002

Environ. Sci. Technol.

318

204

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“…As apple production in Washington state has intensified to meet market demands over the past decades, concerns in the marketplace and on the farm about the negative impacts of conventional food production practices on human health (Hardell and Eriksson, 1999) and environmental quality Williamson et al, 1998) have also increased. These concerns have led to increased grower interest in developing environmentally sound management practices.…”

Section: Introductionmentioning

confidence: 99%

Systematic method for rating soil quality of conventional, organic, and integrated apple orchards in Washington State

Glover

Reganold

Andrews

2000

Agriculture, Ecosystems & Environment

297

151

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Much remains to be known concerning the complex relationships between specific soil property measurements and overall soil quality. The objective of this study was to advance our understanding of these complex relationships by further developing and applying a systematic method for evaluating the effects of conventional, integrated and organic apple production systems on soil physical, chemical, and biological properties using a modified soil quality index. This index utilizes 1998 soils data from these three treatments. The study used four, 0.14 ha replicates of each of the three treatments in a randomized complete block design. Experimental plots were planted to 'Golden Delicious' apples (Malus domestica Borkh.) in 1994 on a commercial orchard in the Yakima Valley of Washington state. Organic soil management practices included additions of composted poultry manure and bark mulches and the use of mechanical tillage for weed control. Conventional soil management practices included additions of synthetic fertilizers and the use of herbicides for weed control. The integrated system utilized practices from each of the other two systems. Increased aggregate stability, microbial biomass, and earthworm abundance were associated with improved soil quality under integrated management when compared to conventional management in 1998. Organic management resulted in lower soil bulk densities and generally improved biological soil properties compared to conventional management. Few significant differences in soil properties were measured between the integrated and organic systems. The integrated production system received a soil quality index rating of 0.92 (out of 1.00), which was significantly higher than the index rating of 0.78 for the conventional production system; the organic production system received a rating of 0.88, which was not significantly different from the other two systems. The study indicates that a well-developed soil quality index can provide an effective framework for evaluating the overall effects of different orchard production practices on soil quality.

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“…According to the Clean Water Action Plan [U.S. Environmental Protection Agency and U.S. Department of Agriculture, 1998], overenrichment by nutrients is the largest overall source of impairment of the nation's rivers and streams. While overlooked in many nutrient management plans, groundwater discharges of nitrate to streams may contribute the majority of the total amount of stream nitrogen [e.g., Williamson et al, 1998]. …”

Section: Introductionmentioning

confidence: 99%

Mechanism and rate of denitrification in an agricultural watershed: Electron and mass balance along groundwater flow paths

Tesoriero¹,

Liebscher²,

Cox³

2000

Water Resources Research

215

150

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Abstract. The rate and mechanism of nitrate removal along and between groundwater flow paths were investigated using a series of well nests screened in an unconfined sand and gravel aquifer. Intensive agricultural activity in this area has resulted in nitrate concentrations in groundwater often exceeding drinking water standards. Both the extent and rate of denitrification varied depending on the groundwater flow path. While little or no denitrification occurred in much of the upland portions of the aquifer, a gradual redox gradient is observed as aerobic upland groundwater moves deeper in the aquifer. In contrast, a sharp shallow redox gradient is observed adjacent to a third-order stream as aerobic groundwater enters reduced sediments. An essentially complete loss of nitrate concurrent with increases in excess N 2 provide evidence that denitrification occurs as groundwater enters this zone. Electron and mass balance calculations suggest that iron sulfide (e.g., pyrite) oxidation is the primary source of electrons for denitrification. Denitrification rate estimates were based on mass balance calculations using nitrate and excess N 2 coupled with groundwater travel times. Travel times were determined using a groundwater flow model and were constrained by chlorofluorocarbon-based age dates. Denitrification rates were found to vary considerably between the two areas where denitrification occurs. Denitrification rates in the deep, upland portions of the aquifer were found to range from <0.01 to 0.14 mM of N per year; rates at the redoxcline along the shallow flow path range from 1.0 to 2.7 mM of N per year. Potential denitrification rates in groundwater adjacent to the stream may be much faster, with rates up to 140 mM per year based on an in situ experiment conducted in this zone.

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Water quality in the central Columbia Plateau, Washington and Idaho, 1992-95

Cited by 34 publications

References 15 publications

Probability of Nitrate Contamination of Recently Recharged Groundwaters in the Conterminous United States

Probability of Nitrate Contamination of Recently Recharged Groundwaters in the Conterminous United States

Systematic method for rating soil quality of conventional, organic, and integrated apple orchards in Washington State

Mechanism and rate of denitrification in an agricultural watershed: Electron and mass balance along groundwater flow paths

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