DYNAMICS OF ADDED NITRATE AND PHOSPHATE COMPARED IN A NORTHERN CALIFORNIA WOODLAND STREAM1

ABSTRACT: Injections of NO₃ and PO₄ were made during September 1975 into Little Lost Man Creek, a small pristine stream in Redwood National Park, California. Chloride, a conservative constituent, was added in a known ratio to the nutrients. Nutrient loss at a downstream point was calculated using concentration of added Cl as a reference. Nitrate nitrogen (NO₃-N), added for 4 h, reached 920 μg/1 (above 5 μg/1 background) just below the injection point, but increased only to 405 μg/1 at 310 m downstream. The concentration decrease was attributed to dispersion and to uptake by stream biota. Percent of NO₃-N lost decreased with increasing concentration of NO₃-N. Phosphate phosphorus (PO₄-P) was added a week after the NO₃-N for 3 h, causing a concentration increase of 296 μg/1 (above 13 μg/1 background) just below the injection point, of 161 μg/1 at 90 m downstream, and of 98 μg/1 at 310 m. Percent loss of PO₄-P at downstream sites increased with increasing PO₄-P concentration and also for a short period after peak concentration occurred, but then decreased as PO₄-P concentration continued decreasing. Differences in stream response to added NO₃-N and PO₄-P are attributed to differing rates of reaction with biota and differing degrees of interaction with abiotic stream solids.     

IMPACT OF A TURFGRASS SYSTEM ON NUTRIENT LOADINGS TO SURFACE WATER1

ABSTRACT: Turfgrass systems are one of the most intensively managed land uses in the United States. Establishment and maintenance of high quality turfgrass usually implies substantial inputs of water, nutrients, and pesticides. The focus of this work was to quantify the concentration and loading of a typically maintained municipal turfgrass environment on surface water. Water quantity and quality data were collected from a golf course in Austin, Texas, and analyzed for a 13‐month period from March 20, 1998, to April 30, 1999. Twenty‐two precipitation events totaling 722 mm, produced an estimated 98 mm of runoff. Nutrient analysis of surface runoff exiting the course exhibited a statistically significant (p < 0.05) increase in median nitrate plus nitrite nitrogen (NO₃+NO₂‐N) concentration compared to runoff entering the course, a statistically significant decrease in ammonia nitrogen (NH₄‐N), but no difference in orthophosphate (PO₄‐P). During the 13‐month period, storm runoff contributed an estimated 2.3 kg/ha of NO₃+NO₂‐N and 0.33 kg/ha of PO₄‐P to the stream. Storm flow accounted for the attenuation of 0.12 kg/ha of NH₄‐N. Baseflow nutrient analysis showed a statistically significant increase in median NO₃+NO₂‐N, a significant reduction in NH₄‐N, and no change in PO₄‐P. Estimated NO₃+NO₂‐N mass in the baseflow was calculated as 4.7 kg/ha. PO₄‐P losses were estimated at 0.06 kg/ha, while 0.8 kg/ha of NH₄‐N were attenuated in baseflow over the study period. Even though nutrient concentrations exiting the system rarely exceeded nutrient screening levels, this turfgrass environment did contribute increased NO₃+NO₂‐N and PO₄‐P loads to the stream. This emphasizes the need for parallel studies where management intensity, soil, and climate differ from this study and for golf course managers to utilize an integrated management program to protect water quality while maintaining healthy turfgrass systems.     

SUBSURFACE RETURN FLOW AND GROUND WATER RECHARGE OF TERRACE FIELDS IN NORTHERN TAIWAN1

ABSTRACT: This study estimates subsurface return flow and effective ground water recharge in terraced fields in northern Taiwan. Specifically, a three dimensional model, FEMWATER, was applied to simulate percolation and lateral seepage in the terraced fields under various conditions. In the terraced paddy fields, percolation mainly moves vertically downward in the central area, while lateral seepage is mainly focused around the bund. Although the simulated lateral seepage rate through the bund exceeded the percolation rate in the central area of the paddy field, annual subsurface return flow at Pei‐Chi and Shin‐Men was 0.17 × 10⁶ m³ and 0.37 × 10⁶ m³, representing only 0.17 percent and 0.21 percent of the total irrigation water required for rice growth at Pei‐Chi and Shin‐Men, respectively. For upland fields, the effective ground water recharge rate during the second crop period (July to November) exceeded that during the first crop period (January to May) because of the wet season in the second crop period. Terraced paddy fields have the most efficient ground water recharge, with 21.2 to 23.4 percent of irrigation water recharging to ground water, whereas upland fields with a plow layer have the least efficient ground water recharge, with only 4.8 to 6.6 percent of irrigation water recharging to ground water. The simulation results clearly revealed that a substantial amount of irrigation water recharges to ground water in the terraced paddy, while only a small amount of subsurface return flow seeps from the upstream to the downstream terraced paddy. The amounts of subsurface flow and ground water recharge determined in the study are useful for the irrigation water planning and management and provide a scientific basis to reevaluate water resources management in the terrace region under irrigated rice.     

Environmental impact of irrigation in la violada district (Spain): I. Salt export patterns

Salt loading in irrigation return flows contributes to the salinization of the receiving water bodies, particularly when originated in salt-affected areas as frequently found in the middle Ebro River basin (Spain). We determined the salt loading in La Violada Gully from the total dissolved solids (TDS) and flows (Q) during the 1995 to 1998 hydrological years. Since this gully collects flows from various sources, an end-member mixing analysis (EMMA) was performed to quantify the drainage flow from La Violada Irrigation District (VID). Three flow components were identified in La Violada Gully: drainage waters from VID (Qd); tail-waters from irrigation ditches, spill-over, and seepage from the Monegros Canal (Qo); and ground water inflows (Qg) originating in the dryland watershed. Gypsum in the soils of VID was the main source for salts in La Violada Gully (flow-weighted mean TDS=1720 mg L-1, dominated by sulfate and calcium). The contribution of Qg to the total gully flow during the 1996 irrigation season was low (6.5% of the total flow). The 1995 to 1998 annual salt load average in La Violada Gully was 78 628 Mg, 71% of which was exported during the irrigation season. The 1995 to 1998 irrigation season salt load average in Qd was 43 015 Mg (77% of the total load). Thus, irrigated agriculture in VID was the main source of salt loading in this gully, with a yield of 11.1 Mg of salts per hectare of irrigated land for the irrigation season. Efficient irrigation systems and irrigation management practices that reduce Qd are key factors for controlling off-site salt pollution of these gypsum-rich irrigated areas.     

A COMPARISON OF RUNOFF QUALITY EFFECTS OF ORGANIC AND INORGANIC FERTILIZERS APPLIED TO FESCUEGRASS PLOTS1

ABSTRACT: Application of fertilizer can degrade quality of runoff, particularly during the first post-application, runoff-producing storm. This experiment assessed and compared runoff quality impacts of organic and inorganic fertilizer application for a single simulated storm occurring seven days following application. The organic fertilizers used were poultry (Gallus gallus domesticus) litter, poultry manure, and swine (Sus scrofa domesticus) manure. All fertilizers were applied at an application rate of 217.6 kg N/ha. Simulated rainfall was applied at 50 mm/h for an average duration of 0.8 h. Runoff samples were collected, composited, and analyzed for nitrate N (NO₃-N), ammonia N (NH₃-N), total Kjeldahl N (TKN), ortho-P (PO₄-P), total P (TP), chemical oxygen demand (COD), total suspended solids (TSS), fecal coliforms (FC), and fecal streptococci (FS). Application of the fertilizers did not alter the hydrologic characteristics of the receiving plots relative to the control plots. Concentrations of fertilizer constituents were almost always greater from treated than from control plots and were usually much greater. Flow-weighted mean concentrations of NH₃-N, PO₄-P, and TP were highest for the inorganic fertilizer treatment (42.0, 26.6, and 27.9 mg/L, respectively). Runoff COD and TSS concentrations were greatest for the poultry litter treatment. Concentrations of FC and FS were greater for fertilized than for control plots with no differences among fertilized plots, but FC concentrations for all treatments were in excess of Arkansas' primary and secondary contact standards. Mass losses of fertilizer constituents were low (≤ 3 kg/ha) and were small proportions (≤ 3 percent) of amounts applied.     

STREAM QUALITY IMPACTS OF BEST MANAGEMENT PRACTICES IN A NORTHWESTERN ARKANSAS BASIN1

ABSTRACT: A variety of management options are used to minimize losses of nitrogen (N), phosphorus (P), and other potential pollutants from agricultural source areas. There is little information available, however, to indicate the effectiveness of these options (sometimes referred to as Best Management Practices, or BMPs) on basin scales. The objective of this study was to assess the water quality effectiveness of BMPs implemented in the 3240 ha Lincoln Lake basin in Northwest Arkansas. Land use in the basin was primarily forest (34 percent) and pasture (56 percent), with much of the pasture being regularly treated with animal manures. The BMPs were oriented toward minimizing the impact of confined animal operations in the basin and included nutrient management, dead bird composter construction, and other practices. Stream flow samples (representing primarily base flow conditions) were collected bi-weekly from five sites within the basin from September 1991 through April 1994 and analyzed for nitrate N (NO₃-N), ammonia N (NH₃-N), total Kjeldahl N (TKN), ortho-P (PO₄-P), total P (TP), chemical oxygen demand (COD), and total suspended solids (TSS). Mean concentrations of PO₄-P, TP, and TSS were highest for subbasins with the highest proportions of pasture land use. Concentrations of NH₃-N, TKN, and COD decreased significantly with time (35–75 percent/year) for all sub-basins, while concentrations of other parameters were generally stable. The declines in analysis parameter concentrations are attributed to the implementation of BMPs in the basin since (a) the results are consistent with what would be expected for the particular BMPs implemented and (b) no other known activities in the basin would have caused the declines in analysis parameter concentrations.     

RISK IN IRRIGATION WATER SUPPLY AND THE EFFECTS ON FOOD PRODUCTION1

ABSTRACT: This paper examines irrigation water supply deficit and associated risk indicators due to random climate events and potential effects on irrigated food production during the period 1996 to 2025 for seven river basins in the USA, China, and India. An integrated water and food model with global scope is applied for the analysis. The global climate regime during 1961 to 1990 is used to generate 30 climatic scenarios for the time period 1996 to 2025, and these scenarios are applied to the model in order to characterize the randomness of precipitation, runoff, and evapotranspiration, which affects both irrigation water supply and demand. The risk with random climate events is represented by reliability, variability, and vulnerability from different perspectives. Regarding irrigation water supply, Colorado will bear an increasingly unstable situation although the average water supply relative to the demand will maintain at a relatively high level; selected basins in China and India indicate that significantly lower levels of reliability and more deleterious affects from drought can be expected, but under a less variable condition due to assumed water storage increase. From 1996 to 2025, the effects of water deficits on irrigated food production are characterized with a nonlinear phenomenon and food production loss will be more sensitive to irrigation water supply deficit in the future. Future work following this paper needs to consider the impact of global climate change and the water quality of the irrigation return flow and result verification by local studies.     

CUMULATIVE IMPACTS OF LANDUSE ON WATER QUALITY IN A SOUTHERN APPALACHIAN WATERSHED1

ABSTRACT: Water quality variables were sampled over 109 weeks along Coweeta Creek, a fifth-order stream located in the Appalachian mountains of western North Carolina. The purpose of this study was to observe any changes in water quality, over a range of flow conditions, with concomitant downstream changes in the mix of landuses. Variables sampled include pH, HCO₃^2?, conductivity, NO₃^?_?-N, NH₄⁺-N, PO₄^3?-P, C1^?-, Na, K, Ca²⁺, Mg²⁺, SO₄^2?, 5iO₂, turbidity, temperature, dissolved oxygen, total and fecal coliform, and focal streptococcus. Landcover/landuse was interpreted from 1:20,000 aerial photographs and entered in a GIS, along with information on total and paved road length, building location and density, catchment boundaries, hydrography, and slope. Linear regressions were performed to relate basin and near-stream landscape variables to water quality. Consistent, cumulative, downstream changes in water quality variables were observed along Coweeta Creek, concomitant with downstream, human-caused changes in landuse. Furthermore, larger downstream changes in water quality variables were observed during stormflow when compared to baseflow, suggesting cumulative impacts due to landscape alteration under study conditions were much greater during storm events. Although most water quality regulations, legislation, and sampling are promulgated for baseflow conditions, this work indicates they should also consider the cumulative impacts of physical, chemical, and biological water quality during stormflow.     

Simulating Soil Water Content,Evapotranspiration, and Yield of Variably Irrigated Grain Sorghum Using AquaCrop

Use of models to simulate crop production has become important in optimizing irrigation management in arid and semiarid regions. However, applicability and performance of these models differ across regions, due to differences in environmental and management factors. The AquaCrop model was used to simulate soil water content (SWC), evapotranspiration (ET), and yield for grain sorghum under different irrigation regimes and dryland conditions at two sites in Central and Southern High Plains. Prediction error (P_e), estimated as the difference between simulated and measured divided by measured, for SWC ranged from ?17% to 4% in fully irrigated, ?3% to ?10% in limited irrigated, and ?16% to 25% in dryland treatments. The P_e within ±4%, ?5%, and ?17% to 24% were attained for seasonal ET under fully irrigated, limited irrigated, and dryland conditions, respectively. P_e values for grain yield were within those previously reported and ranged from ?10% to 12%, ?12% to 7%, and 9% to 17% for fully irrigated, limited irrigated and dryland conditions, respectively. Overall performance of the AquaCrop model showed it could be used as an effective tool for evaluating the impacts of variable crop and irrigation managements on the production of grain sorghum in the study area. Finally, the application of the model in the study area revealed planting date has a significant impact on sorghum yield and irrigation requirements, but the impact of planting density was negligible. Editor's note : This paper is part of the featured series on Optimizing Ogallala Aquifer Water Use to Sustain Food Systems. See the February 2019 issue for the introduction and background to the series.     

TECHNICAL AND INSTITUTIONAL ASPECTS OF SEWAGE EFFLUENT-IRRIGATION WATER EXCHANGE,TUCSON REGION1

ABSTRACT .Many growing municipalities near irrigated agriculture are advocating a transfer of water now utilized for irrigation to municipal use. Alternatives are presented whereby this water can be transferred to municipal use in exchange for treated sewage effluent. The irrigation water would in effect be cycled through the municipal system prior to use on the farms. A case study of the Tucson region illustrates the relevant legal, economic and technical aspects. Effluent could be delivered to irrigators in Avra Valley at a cost less than that now paid for water pumped from declining water tables. In return the City of Tucson could import ground water now being used for irrigation through an existing pipeline which presently cannot be used because of a court injunction obtained by the irrigators. It appears that such an exchange agreement could be made without modification of existing statutory law. Similar exchange arrangements may prove to be feasible in other regions containing irrigated agriculture. Increased efficiency of water use can be achieved avoiding external effects which commonly arise in a direct transfer and are difficult to evaluate. High quality water is allocated to municipal use whereas nutrient-rich sewage effluent is transferred to irrigation.     

SPRING RUNOFF AND DRAINAGE N AND P LOSSES FROM HOG-MANURED CORN1

ABSTRACT: A two-year study was conducted to assess the effect of hog manure on the losses of nitrogen and phosphorus in runoff and drainage from grain-corn (Zea mays L.) plots, and the importance of spring versus annual loads. Treatments consisted of mineral N-P-K fertilizer applied at rates of 152 kg N ha^-1, 35 kg P ha^-1, and 86 kg K ha^-1; and hog (Sus scrofa domestica L.) manure applied preplant or post-emergence (six-to-eight leaf stage), at 152 kg N ha^-1, 39 kg P ha^-1, and 112 kg K ha^-1. The plots were rototilled (7 cm depth) in spring to incorporate fertilizer and preplant hog manure, and fall chisel-plowed (15 cm depth) to incorporate chopped corn residues. They were arranged in a completely randomized plot design. Flow volumes and nutrient levels in runoff and drainage waters were monitored year round but occurred mainly during the snowmelt (March 25-April 9), and post.snowmelt (April 10-May 13) periods. Of the total amount of water lost during snowmelt, 90 percent was in runoff, while 92 percent occurred as drainage in the post-snowmelt period. Sixty-five percent of the total annual volume of water lost was lost during these two periods as runoff and drainage. Treatments did not affect the annual snowmelt or post-snowmelt N and P loads. Total annual loads averaged 8.0 kg TKN ha^-1, 1.8 kg NH₄-N ha^-1, 43 kg NO₃-N ha^-1, 0.4 kg TP ha^-1, and 0.15 kg PO₄-P ha^-1. Spring (snowmelt and ost-snowmelt) runoff and drainage loads averaged 2.9 kg TKN ha^-1, 1.2 kg NH₄-N ha^-1, 18 kg NO₃-N ha^-1, 0.25 kg TP ha^-1, and 0.04 kg PO₄-P ha^-1, which were 40 percent to 70 percent of the yearly nutrient loads. Therefore, the hog manure management systems examined were of no greater threat to the environment than mineral fertilizers. However, spring N and P losses do represent an important part of the annual nutrient loss budget, even with conservation practices.     

Performance analysis of on-farm irrigation tanks on agricultural drainage water reuse and treatment

Water reuse and pollutant removal efficiency analysis of the on-farm irrigation tanks (OFTs) was carried out in rice paddy field region of Zhanghe Irrigation District, Southern China through field experiments during the rice growing season of 2009–2011. Water flow measurements indicate that 20.6–68.9% of drainage water captured by OFTs was reused for supplemental irrigation. Rainfall was the most important factor that determines the water reuse efficiency (WRR) of OFTs, since higher rainfall resulted in higher surplus irrigation water draining out of OFTs without reuse, and thus decreased WRR. Fully using the storage capacity for storing return flow, and releasing totally for supplemental irrigation also enhanced WRR of OFTs. Water quality analysis shows that OFTs removed 47.2% of total phosphorous (TP) and 60.8% of total nitrogen (TN) of inflow and have a great effect on increasing sedimentation for return flow as the mean of removal efficiency of pollutant load (REL) for suspended solids (SS) amounted to 68.4%. For water treatment effectiveness of OFTs, high hydraulic retention time (HRT) is most beneficial to increase REL of TN whereas REL of TP is not sensitive to HRT. These results confirm that OFTs can effectively increase agricultural return flow reuse and remove pollutants. As the cascade OFTs irrigation system recycle return flow for several times, the irrigation water demand from outside of region was reduced significantly for rice production. Coupling with the effect of cyclic irrigation on the nutrients recycling by paddy fields, OFTs irrigation system also considerably mitigate the N and P off-site emission. Therefore, it is advisable to integrate the role of OFTs on water reuse and treatment for water saving irrigation and ecological management of paddy fields landscape.     

ECONOMIC ANALYSIS OF WATER-SAVING TECHNIQUES IN IRAN1

ABSTRACT: The possibility of increasing the water supply for irrigation through adoption of more efficient water-application techniques as an alternative to new irrigation projects was studied in an irrigated region of Iran. Excessive water application at the farm level ranks high among the causes of water shortages in the selected region. An empirical analysis of the effect of water-saving technology on the farm operator's net return was made choosing two farms in the region as a case study. The problems facing these farms are common to most farms throughout the country. The results of the budgeting analysis of the selected farms indicated that an improvement in irrigation technique can result in the expansion of water supply and higher marginal value product for water. Comparing the costs of irrigation systems with the net returns resulting from the higher efficiency showed that such an investment is economically feasible.     

Nutrient transport through a Vegetative Filter Strip with subsurface drainage

The transport of nutrients and soil sediments in runoff has been recognized as a noteworthy environmental issue. Vegetative Filter Strips (VFS) have been used as one of the best management practices (BMPs) for retaining nutrients and sediments from surface runoff, thus preventing the pollutants from reaching receiving waters. However, the effectiveness of a VFS when combined with a subsurface drainage system has not been investigated previously. This study was undertaken to monitor the retention and transport of nutrients within a VFS that had a subsurface drainage system installed at a depth of 1.2 m below the soil surface. Nutrient concentrations of NO₃-N (Nitrate Nitrogen), PO₄⁻ (Orthophosphorus), and TP (Total Phosphorus) were measured in surface water samples (entering and leaving the VFS), and subsurface outflow. Soil samples were collected and analyzed for plant available Phosphorus (Bray P1) and NO₃-N concentrations. Results showed that PO₄⁻, NO₃-N, and TP concentrations decreased in surface flow through the VFS. Many surface outflow water samples from the VFS showed concentration reductions of as much as 75% for PO₄⁻ and 70% for TP. For subsurface outflow water samples through the drainage system, concentrations of PO₄⁻ and TP decreased but NO₃-N concentrations increased in comparison to concentrations in surface inflow samples. Soil samples that were collected from various depths in the VFS showed a minimal buildup of nutrients in the top soil profile but indicated a gradual buildup of nutrients at the depth of the subsurface drain. Results demonstrate that although a VFS can be very effective in reducing runoff and nutrients from surface flow, the presence of a subsurface drain underneath the VFS may not be environmentally beneficial. Such a combination may increase NO₃-N transport from the VFS, thus invalidating the purpose of the BMP.     

Irrigated mountain meadow fertilizer application timing effects on overland flow water quality

Nonpoint-source pollution from agricultural activities is currently the leading cause of degradation of waterways in the United States. Applying best management practices to flood-irrigated mountain meadows may improve agricultural runoff and return flow water quality. Prior research has focused on fertilizer use for increased hay yields, while few studies have investigated the environmental implications of this practice. We examined the effects of fertilizer application timing on overland flow water quality from an irrigated mountain meadow near Gunnison, Colorado. Application of 40 kg phosphorus (P) and 19 kg nitrogen (N) ha(-1) using monoammonium phosphate (11-52-0, N-P-K) fertilizer to plots in the fall significantly reduced concentrations of reactive P and ammonium N in irrigation overland flow compared with early or late spring fertilization. Reactive P loading was 9 to almost 16 times greater when fertilizer was applied in the early or late spring, respectively, compared with in the fall. Ammonium N followed a similar trend with early spring loading more than 18 times greater and late spring loading more than 34 times greater than loads from fall-fertilized plots. Losses of 45% of the applied P and more than 17% of the N were measured in runoff when fertilizer was applied in the late spring. These results, coupled with those from previous studies, suggest that mountain meadow hay producers should apply fertilizer in the fall, especially P-based fertilizers, to improve hay yields, avoid economic losses from loss of applied fertilizers, and reduce the potential for impacts to water quality.     

CLIMATE CHANGE,IRRIGATION, AND CROP RESPONSE1

ABSTRACT: A set of simulation models consisting of a weather generator, and irrigation supply, soil moisture and crop growth components was used to evaluate the impacts of climate change on irrigated corn in locations near Albany, New York, Indianapolis, Indiana, and Oklahoma City, Oklahoma. The models evaluated the combined effects of modified water demand, supply and crop management (planting date, cultivar selection, irrigation). Simulations were duplicated for 100-year weather sequences based on current (1961–1988) weather statistics, and statistics modified by outputs from the GFDL GCM runs showing the effects from doubling of atmospheric CO₂. Climate impacts differed greatly with location and management. Effects were most adverse in New York and least damaging in Indiana. At all sites, the beneficial effects of longer growing season and increased water supply were generally overcome by the detrimental impacts of increased evapotranspiration and reduced solar radiation during plant maturing stages. Adverse impacts of climate change can be substantially reduced by irrigation and appropriate selection of planting dates and cultivars.     

ON THE NECESSARY AND SUFFICIENT CONDITIONS FOR A LONG-TERM IRRIGATED AGRICULTURE1

ABSTRACT. Salinization and water logging have been the nemesis of irrigated agriculture societies since Babylonian times. Low quality water substitutes for high quality water for irrigation at an increasing rate up to the limits of the soil's ability to transmit the additional water and remove excess salts from the root zone. Soil transmissibility can be increased by additional investment in drainage ditches and underground tile. Low valued-high salt tolerant crops can be substituted for higher valued-salt sensitive crops to maintain production in areas served by irrigation water sources of deteriorating quality. Thus physical factors specify the necessary conditions for survival of an irrigated agriculture. The sufficient conditions for survival must be in terms of a positive net income in each subplanning period discounted to its present value.     

A PRELIMINARY STUDY OF THE EFFECTS OF DRAINAGE AND HARVESTING ON WATER QUALITY IN OMBROTROPHIC BOGS NEAR SEPT-ILES,QUEBEC1

ABSTRACT: Runoff and ground-water samples were collected from four ombrotrophic bogs, representing undisturbed and drained/harvested conditions, at two-week intervals during the summer of 1984. Analyses of samples for water quality parameters revealed significant (P < 0.05 level) increases in specific conductance, NH4⁺-N, total dissolved P, Mg, K, and Na and a decrease in the E₄:E₆ ratio (suggesting increased proportions of humic acid) associated with drainage. There were no significant changes in dissolved organic carbon, Ca concentrations, or pH. Comparison of samples collected before, during, and after ditching showed increases in the dissolved organic carbon, NH₄⁺-N, total dissolved P, K, and Na and a decrease in the E₄:E₆ ratio, but these changes were short lived; water quality returned to preditching values after about a week. The observed changes in water quality are small, probably because the peat is very acid (pH 3.0 to 4.5).     

USING INFILTRATION ENHANCEMENT AND SOIL WATER MANAGEMENT TO REDUCE DIAZINON IN RUNOFF1

ABSTRACT: Pesticide runoff from dormant sprayed orchards is a major water quality problem in California's Central Valley. During the past several years, diazinon levels in the Sacramento and San Joaquin Rivers have exceeded water quality criteria for aquatic organisms. Orchard water management, via post‐application irrigation, and infiltration enhancement, through the use of a vegetative ground cover, are management practices that are believed to reduce pesticide loading to surface waters. Field experiments were conducted in Davis, California, to measure the effectiveness of these management practices in reducing the toxicity of storm water runoff. Treatments using a vegetative ground cover significantly reduced peak concentrations and cumulative pesticide mass in runoff for first flush experiments compared with bare soil treatments. Post‐application irrigation was found to be an effective means of reducing peak concentrations and cumulative mass in runoff from bare soil treatments, but showed no significant effect on vegetated treatments.     

SOIL CHANGES CAUSED BY MUNICIPAL WASTEWATER APPLICATIONS IN EASTERN SOUTH DAKOTA1

ABSTRACT: Wastewater from a municipal treatment plant was applied in rapid infiltration basins for four years to determine a poorly drained soils effectiveness in removing influent N and P and the soil changes that might limit their removal. About half the total PO₄-P lost from the influent was sorbed in the upper 91 cm of the soil and the other half was sorbed by the soil below the perforated pipe, which was used to drain the basins and collect the effluent for analysis. Drying of the basin soils converted more sorbed PO₄-P to Ca phosphates but the total sorbed was about the same. The in. fluent N decreased, probably by volatilization, because the two basins with surface soil lost soil N rather than gained soil N. The soil total Ca, Mg, and K contents did not change significantly but Na increased slightly. Changes in the physical characteristics of the soils were slight and would have little effect on the longevity of a rapid infiltration basin.