REGIONAL ASSESSMENT OF NLEAP NO3-N LEACHING INDICES1

ABSTRACT: Nonpoint source ground water contamination by nitrate nitrogen (NO₃-N) leached from agricultural lands can be substantial and increase health risks to humans and animals. Accurate and rapid methods are needed to identify and map localities that have a high potential for contamination of shallow aquifers with NO₃-N leached from agriculture. Evaluation of Nitrate Leaching and Economic Analysis Package (NLEAP) indices and input variables across an irrigated agricultural area on an alluvial aquifer in Colorado indicated that all leaching indices tested were more strongly correlated with aquifer NO₃-N concentration than with aquifer N mass. Of the indices and variables tested, the NO₃-N Leached (NL) index was the NLEAP index most strongly associated with groundwater NO₃-N concentration (r² values from 0.37 to 0.39). NO₃-N concentration of the leachate was less well correlated with ground water NO₃-N concentration (r² values from 0.21 to 0.22). Stepwise regression analysis indicated that, although inorganic and organic/inorganic fertilizer scenarios had similar r² values, the Feedlot Indicator (proximity) variable was significant over and above the NO₃-N Leached index for the inorganic scenario. The analysis also showed that combination of either Movement Risk Index (MIRI) or NO₃-N concentration of the leachate with the NO₃-N Leached index leads to an improved regression, which provides insight into area-wide associations between agricultural activities and ground water NO₃-N concentration.     

EFFECTS OF ARTIFICIAL RECHARGE ON GROUND WATER QUALITY AND AQUIFER STORAGE RECOVERY1

ABSTRACT: Ground water nitrate contamination and water level decline are common concern in Nebraska. Effects of artificial recharge on ground water quality and aquifer storage recovery (ASR) were studied with spreading basins constructed in the highly agricultural region of the Central Platte, Nebraska. A total of 1.10 million m³ of Platte River water recharged the aquifer through 5000 m² of the recharge basins during 1992, 1993, and 1994. This is equivalent to the quantity needed to completely displace the ground water beneath 34 ha of the local primary aquifer with 13 m thickness and 0.25 porosity. Successful NO₃-N remediation was documented beneath and downgradient of the recharge basins, where NO₃-N declined from 20 to 2 mg L^-1. Ground water atrazine concentrations at the site decreased from 2 to 0.2 mg L^-1 due to recharge. Both NO₃-N and atrazine contamination dramatically improved from concentrations exceeding the maximum contaminant levels to those of drinking water quality. The water table at the site rose rapidly in response to recharge during the early stage then leveled off as infiltration rates declined. At the end of the 1992 recharge season, the water table 12 m downgradient from the basins was elevated 1.36 m above the preproject level; however, at the end of the 1993 recharge season, any increase in the water table from artificial recharge was masked by extremely slow infiltration rates and heavy recharge from precipitation from the wettest growing season in over 100 years. The water table rose 1.37 m during the 1994 recharge season. Resultant ground water quality and ASR improvement from the artificial recharge were measured at 1000 m downgradient and 600 m upgradient from the recharge basins. Constant infiltration rates were not sustained in any of the three years, and rates always decreased with time presumably because of clogging. Scraping the basin floor increased infiltration rates. Using a pulsed recharge to create dry and wet cycles and maintaining low standing water heads in the basins appeared to reduce microbial growth, and therefore enhanced infiltration.     

AMMONIA IN TEXAS STREAMS DURING LOW FLOW FROM MUNICIPAL WASTEWATER1

ABSTRACT: An investigation of treated municipal wastewaters discharged into Texas streams was conducted to determine the probable effect of concentrations of ammonia in receiving waters, based on existing data on ammonia levels which are lethal to various species of fish. Recorded data for most Texas cities were analyzed. Based on existing toxicity criteria for ammonia of 1/10 TL_m= 0.31 mg/1 NH₃-N, employing known discharge flow rates, and 7-day, 5-year or 7-day, 10-year low flows in Texas streams, appreciable numbers of sites were found to pose a threat to various species of fish. Using the bluegill (Lepomis macrochirus) as a median tolerance limit species, data from 65 cities which met the aforecited requirements, were analyzed. Those included a total of 92 wastewater effluents. Sixty-nine percent of those cities and 70% of their effluents exceeded the 0.31 mg/1 NH₃-N limit in the stream below the discharge point. Thirty-seven percent of the cities equaled or exceeded the 96-hour TL_m concentration limit of 3.1 mg/1 ammonia. Based on the 10 mg/1 NO₃-N standard for intake water for potable supplies, 32% of the effluents resulted in a stream concentration which exceeded 10 mg/1, assuming a straight conversion of NH₃-N to NO₃-N.     

Water quality indices appraisal and health risk assessment of nitrate,mercury and lead in water distribution network: A case study of Robat Karim in Tehran,Iran

Groundwater is a basic source of drinking water supply for urban and rural areas. This is especially the case for communities located in arid and semi-arid regions that rely on groundwater for drinking purposes. The present study set out to assess the potential health impacts of water impurities and to investigate the qualitative status of drinking water in Robat Karim rural areas, located in southwest Tehran, Iran. A total of 66 samples were collected from the water distribution network of 11 villages (33 sampling points, on two occasions) during September 2020 and were tested in terms of the most common quality parameters such as pH, mercury (Hg), lead (Pb), copper (Cu), zinc (Zn), chloride (Cl^–), chlorate (ClO₃^–), nitrite (NO₂^–), nitrate (NO₃^–), and flouride (F^–). Multiple methods and indexes including water quality index (WQI), hazard quotient (HQ), and hazard index (HI), were worked out to assess the quality of water and health risk assessment of NO₃^– Pb²⁺ and Hg²⁺. The results revealed that 33% and 90% of sampling sites have significantly high nitrate and total hardness (TH) concentrations, exceeding the maximum permissible limits set by World Health Organization (WHO; 50 and 200 mg/L, respectively). Furthermore, five sampling points exhibited poor WQIs mainly related to NO₃^– and TH. HQ values higher than 1 for nitrate were noticed in most sampling locations. Except for one sampling point, the HQ obtained for Pb²⁺ and Hg²⁺ were below 1 indicating no obvious health hazard. This study represents that children and infants are at higher risk of chronic toxicity by excess NO₃^– intake. The health hazard that is yet imposed on the community by NO₃^– necessitates regular monitoring of drinking water, the use of advanced technologies to purify water or otherwise alternative resources should be proposed.     

EFFECTS OF NO-FLOW RIVER CONDITIONS ON THE PLATTE RIVER WELL FIELD1

ABSTRACT: Effects of no-flow river conditions on the quantity and quality of water in the Platte River well field of the City of Grand Island, Nebraska, were examined utilizing a finite-difference computer simulation model specifically developed for this well field. Results suggest that the effects of these no-flow periods on water quality may be most important. In particular, the no-flow periods eliminate the hydraulic barrier between the well field and an area north of the River that is contaminated with nitrate (concentrations in the 20 to 40 mg/1 NO₃-N range). They also change the direction and velocity of movement of the contaminated ground water. Simulation results indicate that contaminated ground water moves toward the well field with a velocity of 0.42 ft/d after 30 days of no-flow and 1.43 ft/d after 180 days of no-flow. Limiting no-flow conditions to 10 consecutive days would protect the well field.     

NITROGEN AND PHOSPHORUS CONCENTRATIONS IN FOREST STREAMS OF THE UNITED STATES1

ABSTRACT: Seventy to eighty percent of the water flowing in rivers in the United States originates as precipitation in forests. This project developed a synoptic picture of the patterns in water chemistry for over 300 streams in small, forested watersheds across the United States. Nitrate (NO₃^?) concentrations averaged 0.31 mg N/L, with some streams averaging ten times this level. Nitrate concentrations tended to be higher in the northeastern United States in watersheds dominated by hardwood forests (especially hardwoods other than oaks) and in recently harvested watersheds. Concentrations of dissolved organic N (mean 0.32 mg N/L) were similar to those of NO₃～, whereas ammonium (NH₄⁺) concentrations were much lower (mean 0.05 mg N/L). Nitrate dominated the N loads of streams draining hardwood forests, whereas dissolved organic N dominated the streams in coniferous forests. Concentrations of inorganic phosphate were typically much lower (mean 12 mg P/L) than dissolved organic phosphate (mean 84 mg P/L). The frequencies of chemical concentrations in streams in small, forested watersheds showed more streams with higher NO₃^? concentrations than the streams used in national monitoring programs of larger, mostly forested watersheds. At a local scale, no trend in nitrate concentration with stream order or basin size was consistent across studies.     

Physico-chemical characteristics of well waters in four urban centers in Southern Nigeria

An ensemble of thirty physico-chemical characteristics was used to assess the quality of well waters in four urban centers in southern Nigeria: Lagos, Benin City, Warri, and Ekpoma. The characteristics investigated include pH; color; turbidity; salinity; electrical conductivity, EC; total dissolved solids, TDS; total suspended solids, TSS; dissolved oxygen, DO; total hydrocarbon, THC; biochemical oxygen demand, BOD; chemical oxygen demand, COD; and nitrate, nitrite, ammonia, sulfate, and phosphate concentrations. Also monitored were the concentrations of sodium, calcium, potassium, magnesium, chloride, bicarbonate, iron, lead, copper, manganese, zinc, chromium, nickel, and cadmium. The results obtained were compared with World Health Organization, WHO, and Nigerian Federal Ministry of Environment, FME, drinking water standards. The results show that with the well water obtained from Lagos, turbidity, 11.80 NTU; pH, 5.68; EC, 1065.55 μS/cm; TDS, 539.00 mg/L; concentrations of iron, 1.83 mg/L; manganese, 0.14 mg/L; and lead, 1.35 mg/L did not meet the WHO standards. In Warri, pH, 5.19; concentrations of lead, 1.35 mg/L; and chromium, 0.10 mg/L in the well water were above the WHO desirable limits. The results also indicated that the well water from Benin City contained concentrations of chromium, 0.18 mg/L; and lead, 0.20 mg/L that exceeded the recommended WHO limits. In Ekpoma, the pH, 6.00; concentrations of chromium, 0.15 mg/L; and lead, 0.44 mg/L were higher than the desirable limits of WHO. Generally, the assessments revealed that the waters were good and fit for drinking and other domestic application without serious threat to public health.     

WATER QUALITY AFTER LOGGING SMALL WATERSHEDS WITHIN THE BULL RUN WATERSHED,OREGON1

ABSTRACT: Road building, clearcutting 25 percent of the watershed, and slash disposal by broadcast burning or by natural decomposition caused changes in water quality of two small streams in the Bull Run Watershed in Oregon, which supplies water to the Portland, Oregon, metropolitan area. Concentrations of suspended sediment increased slightly, primarily owing to construction of a permanent logging road that crossed streams. Changes in nutrient cycling occurred due to logging and slash disposal in both watersheds where cutting was done. NO₃-N concentrations, which increased most where logging residue was left to decompose naturally, increased more than sixfold and commonly exceeded 100 pg/i during the October-June high-flow season for seven years after logging. Where logging slash was broadcast burned, NO₃-N concentrations increased roughly fourfold, but rarely exceeded 50 μg/l, and increases had mostly disappeared six years after slash burning. Changes in outflows of cations and other anions were not apparent. Annual maximum stream temperatures increased 2–3°C after logging, but temperature increases had mostly disappeared within three years as vegetation regrowth shaded the streams.     

DISSOLVED HEAVY METALS IN SHALLOW GROUND WATER IN A SOUTHEASTERN MICHIGAN URBAN WATERSHED1

ABSTRACT: The occurrence of dissolved heavy metal concentrations in shallow ground water were measured at 126 sites within an urban watershed in southeastern Michigan. A total of 1,140 samples were collected from the first saturated zone, and the mean concentrations of 11 heavy metals (arsenic, barium, cadmium, chromium, copper, lead, mercury, nickel, selenium, silver, and zinc) were obtained and compared to their corresponding mean concentrations within surface soil. The results suggest that former and current land use processes have resulted in significant adverse impacts on the study region. Levels of Cr 20 to 30 times the maximum contaminant level (MCL) have been detected in the ground water beneath industrial sites. In addition, Cd and Pb have been found at levels exceeding their MCLs where surface soils are clay‐rich, and in sandy soils at more than 10 times their MCLs. The high levels of Cr in ground water strongly suggest that the chromium is in a hexavalent form, and this likelihood is supported by current studies. Given the hydraulic connection between the watershed's surface waters and the Great Lakes, these findings raise significant ecological and public health concerns.     

INFLUENCE OF AGRICULTURAL PRACTICES ON WATER QUALITY IN NEBRASKA: A SURVEY OF STREAMS,GROUNDWATER, AND PRECIPITATION1

ABSTRACT Rainfall, stream flow and groundwater have been sampled systematically throughout Nebraska since 1970 and analyzed for mineral N and P and the character of any sediments contained. Fallout N and P in rainfall ranges from 5–14 pounds N and 1 pounds P/A/yr, increasing from west to east across the state with increasing rainfall. The amount of NH4-N is essentially double that of NO₃-N. The mean concentration of 2ppm N in rainfall is four times the mean N concentration of streams, demonstrating a substantial depolluting action of soils and growing crops. Where nutrient levels of streams are elevated, cause can usually be traced especially to industrial, sewage or livestock waste intrusion and not to crop production practices. The only significant quantity of nutrient N and P induced by cultivation is that accompanying sediments from eroded fields. The P content of Nebraska groundwater has remained essentially constant during the past 10 years while average NO₃-N has increased slightly, a period during which farmer fertilizer use quadrupled. During the same time, irrigation acreage has increased by 50%, livestock numbers by 30%, with corresponding growth in human population and attendant industries. Indications are that irrigation practice has contributed more than any other factor to the small increase in groundwater NO3-N recorded. Individual cases do exist where groundwater NO₃-N has increased substantially, especially in areas of intensive irrigation agriculture on very sandy soils and elsewhere with irrigation development in the proximity of ancient NO₃-N deposits in mantlerock above the water table.     

Alfalfa rapidly remediates excess inorganic nitrogen at a fertilizer spill site

By 19%, standard remediation techniques had significantly reduced the concentration of nitrate nitrogen (NO3- -N) in local ground water at the site of a 1989 anhydrous ammonia spill, but NO3- -N concentrations in portions of the site still exceeded the public drinking water standard. Our objective was to determine whether local soil and ground water quality could be improved with alfalfa (Medicago sativa L.). A 3-yr study was conducted in replicated plots (24 by 30 m) located hydrologically upgradient of the ground water under the spill site. Three alfalfa entries ['Agate', Ineffective Agate (a non-N2-fixing elite germplasm similar to Agate), and MWNC-4 (an experimental germplasm)] were seeded in the spring of 1996. Corn (Zea mays L.) or wheat (Triticum aestivum L.) was seeded adjacent to the alfalfa each year. Crops were irrigated with N-containing ground water to meet water demand. During the 3-yr period, about 540 kg of inorganic N was removed from the aquifer through irrigation of 4.9 million L water. Cumulative N removal from the site over 3 yr was 972 kg N ha(-1) in Ineffective Agate alfalfa hay, compared with 287 kg N ha(-1) for the annual cereal grain. Soil solution NO3- concentrations were reduced to low and stable levels by alfalfa, but were more variable under the annual crops. Ground water quality improved, as evidenced by irrigation water N concentration. We do not know how much N was removed by the N2-fixing alfalfas, but it appears that either fixing or non-N2-fixing alfalfa will effectively remove inorganic N from N-affected sites.     

STREAM NITRATE-N LOADS IN RELATION TO VARIATIONS IN ANNUAL AND SEASONAL RUNOFF REGIMES1

ABSTRACT: The calculation of stream nutrient loads from a sampling period of one year or, at most, a few years may provide an inaccurate estimate of average seasonal or annual loads due to considerable year-to-year variations in hydrological regime. The number of years of record required to give a reliable estimate of long-term average NO₃-N loads was analyzed for E. Duffin Creek and the Nottawasaga River in Ontario, Canada. Nitrate load rating relationships were used in combination with a continuous stream discharge record for 22 years (E. Duffin Creek) and 34 years (Nottawasaga River) to simulate long-term seasonal and annual variation in NO₃.N loads. The errors involved in calculating average loads were examined by comparing the loads derived from sampling periods of one or more consecutive years duration with the estimated long-term average load for the two rivers. Annual NO₃-N loads for a single year deviated from the long-term average load by ± 20 to 53 percent in 8 out of 22 years in E. Duffin Creek and in 13 of 34 years in the Nottawasaga River. Six consecutive years of record would be required for both rivers to ensure that an error of > ± 20 percent would occur in only 5 percent of these observation periods. February-April NO₃-N loads for a single year could deviate by up to +90 percent or -61 percent from the long-term average spring period load for the two rivers. A sampling period of at least 6–7 years would be needed to estimate average NO₃-N loads for the spring runoff season with an error <± 20 percent.     

重庆市城区饮用水源健康风险评价

通过对重庆市8个饮用水源地枯水期水体中NH3-N、CN、As、Hg、Cr^＋6、Pb、Cd、Cu、F和挥发酚的浓度进行了调查研究，应用美国环保局推荐的健康风险评价模型对重庆市饮用水源水中污染物引起的健康风险作了评价。结果表明，污染物平均浓度范围分别为NH3-N：0．119—0.740mg／L，CN：0．002—0．004mg／L，As：0．001—0．007mg／L，Hg：0．000001—0．00005mg／L，Cr^＋6：0．004—0.023mg／L．Pb：0．004—0．053mg／L．Cd：0．00035—0．005mg／L．Cu：0．0005—0．0254mg/L，F：0．140—0．335mg／L，挥发酚：0．001—0．0027mg／L。重庆市通过饮水途径引起的非致癌健康风险中Pb的风险最大，F次之，两者风险水平在10^-8～10^-9／a；Cr^＋6引起的致癌风险最大达到10^-4／a；以长江为饮用水源的人群总健康风险大于嘉陵江，其健康风险达到EPA要求，但高于国际辐射防护委员会（ICRP）的最大可接受风险水平。     

GIS-based spatial regression and prediction of water quality in river networks: A case study in Iowa

Nonpoint source pollution is the leading cause of the U.S.’s water quality problems. One important component of nonpoint source pollution control is an understanding of what and how watershed-scale conditions influence ambient water quality. This paper investigated the use of spatial regression to evaluate the impacts of watershed characteristics on stream NO₃NO₂-N concentration in the Cedar River Watershed, Iowa. An Arc Hydro geodatabase was constructed to organize various datasets on the watershed. Spatial regression models were developed to evaluate the impacts of watershed characteristics on stream NO₃NO₂-N concentration and predict NO₃NO₂-N concentration at unmonitored locations. Unlike the traditional ordinary least square (OLS) method, the spatial regression method incorporates the potential spatial correlation among the observations in its coefficient estimation. Study results show that NO₃NO₂-N observations in the Cedar River Watershed are spatially correlated, and by ignoring the spatial correlation, the OLS method tends to over-estimate the impacts of watershed characteristics on stream NO₃NO₂-N concentration. In conjunction with kriging, the spatial regression method not only makes better stream NO₃NO₂-N concentration predictions than the OLS method, but also gives estimates of the uncertainty of the predictions, which provides useful information for optimizing the design of stream monitoring network. It is a promising tool for better managing and controlling nonpoint source pollution.     

Nutrient retention in tile-fed and non-tile reconstructed oxbows in north central Iowa

Nutrient export from the agricultural Midwest threatens the Gulf of Mexico and new conservation practices are needed to reduce the loss of nutrient from subsurface tile drainage systems. Oxbows are natural waterbodies formed when a river cuts off a meander loop and water quality benefits of reconstructed oxbows are being increasingly recognized. In this study, we monitored four reconstructed oxbow sites (two tile-fed, two non-tile) over a 2-year period in north-central Iowa and assessed their capacity for NO₃-N and dissolved reactive phosphorus (DRP) reductions. Water flow and quality monitoring of tiles, shallow groundwater, oxbow and receiving streams documented that the oxbows were dominated by tile drainage inputs. NO₃-N concentrations were highest in the drainage tiles flowing into the tile-fed oxbows (mean 8–10 mg/L) and much lower in floodplain groundwater (<1–2 mg/L). Annual NO₃-N loads into the tile-fed oxbows were substantially larger than input loads into the non-tiled oxbows. For the two tile-fed oxbows, the 2-year NO₃-N retention efficiencies were very similar (0.76–0.77) and on a monthly basis, greater retention efficiencies were measured in summer and fall. DRP concentrations and loads into the tile-fed oxbows were too low to allow for meaningful estimates of retention. Reconstructing oxbows to receive tile drainage water should be considered a sustainable conservation practice for tile drainage treatment in agricultural areas.     

Effects of inorganic nutrients on the regrowth of heterotrophic bacteria in drinking water distribution systems

Three laboratory-scale water pipe systems were set up to study the effects of adding three inorganic nutrients (ammonium, nitrate or phosphate) on biofilm formation in water pipes. The results showed that the effects of adding ammonium or nitrate on the biofilm formation were insignificant when levels below 0.1 mg N/l were added. Analogous results were observed when phosphate was added at levels below 0.005 mgP/l. However, as the addition of ammonium increased to 0.5 mgN/l, significant effects on biofilm formation were observed. Similar results were obtained phosphate was added at levels above 0.01 mgP/l. Batch tests were also conducted using water samples collected from a Taiwanese drinking water distribution system. The results indicated that the addition of ammonium, nitrate or phosphate to treatment plant effluent stimulates bacterial growth. In the distributed water of an urban area, the addition of nitrate or phosphate stimulated bacterial growth. The bacterial growth in the distributed water of a suburban area was not stimulated by adding any of these three inorganic nutrients.     

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.     

Sample intake position and loading rates from nonpoint source pollution

Paired water samples were simultaneously activated from two different vertical positions within the approach section of a flow-control structure to determine the effect of sample intake position on nonpoint runoff parameter concentrations and subsequent event loads. Suspended solids (SS), total phosphorus (TP) and organic plus exchangeable nitrogen [(Or+Ex)-N] were consistently higher throughout each runoff event when sampled from the floor of the approach section as opposed to those samples taken at midstage. Dissolved molybdate reactive phosphorus (DMRP) and ammonium (NH₄-N) concentrations did not appear to be significantly affected by the vertical difference in intake position. However, the nitrate plus nitrite nitrogen [(NO₃+NO₂)-N] concentrations were much higher when sampled from the midstage position.Although the concentration differences between the two methods were not appreciable, when evaluated in terms of event loads, discrepancies were evident for all parameters. Midstage sampling produced event loads for SS, TP, (Or + Ex)–N, DMRP, NH₄-N, and (NO₃+NO₂)-N that were 44,39,35,80,71, and 181%, respectively, of floor sampling loads. Differences in loads between the two methods are attributed to the midstage position, sampling less of the bed load. The correct position will depend on the objective; however, such differences should be recognized during the design phase of the monitoring program.This work was supported by the Soil Science Department, College of Agriculture and Life Sciences, University of Wisconsin-Madison, and by the U.S. Environmental Protection Agency, Region V., Chicago, Illinois (Grant No. G005139-01).     

Real-time contaminant detection and classification in a drinking water pipe using conventional water quality sensors: Techniques and experimental results

Accurate detection and identification of natural or intentional contamination events in a drinking water pipe is critical to drinking water supply security and health risk management. To use conventional water quality sensors for the purpose, we have explored a real-time event adaptive detection, identification and warning (READiw) methodology and examined it using pilot-scale pipe flow experiments of 11 chemical and biological contaminants each at three concentration levels. The tested contaminants include pesticide and herbicides (aldicarb, glyphosate and dicamba), alkaloids (nicotine and colchicine), E. coli in terrific broth, biological growth media (nutrient broth, terrific broth, tryptic soy broth), and inorganic chemical compounds (mercuric chloride and potassium ferricyanide). First, through adaptive transformation of the sensor outputs, contaminant signals were enhanced and background noise was reduced in time-series plots leading to detection and identification of all simulated contamination events. The improved sensor detection threshold was 0.1% of the background for pH and oxidation–reduction potential (ORP), 0.9% for free chlorine, 1.6% for total chlorine, and 0.9% for chloride. Second, the relative changes calculated from adaptively transformed residual chlorine measurements were quantitatively related to contaminant-chlorine reactivity in drinking water. We have shown that based on these kinetic and chemical differences, the tested contaminants were distinguishable in forensic discrimination diagrams made of adaptively transformed sensor measurements.     

FATE OF NITROGEN AND PHOSPHORUS ENTERING A GULF COAST FRESHWATER LAKE: A CASE STUDY1

ABSTRACT: Nitrogen and P fluxes, transformations and water quality functions of Lake Verret (a coastal Louisiana freshwater lake), were quantified. Ortho-P, total-P, NH₄⁺-N NO₃ -N and TKN in surface water collected from streams feeding Lake Verret averaged 104, 340, 59, 185, and 1,060 mg 1^?1, respectively. Lake Verret surface water concentrations of ortho-P, total-P, NH⁺-N, NO₃^?_-N and TKN averaged 66, 191, 36, 66, and 1,292 μg 1^?1. The higher N and P concentrations were located in areas of the lake receiving drainage. Nitrification and denitrification processes were significant in removing appreciable inorganic N from the system. In situ denitrification rates determined from acetylene inhibition techniques show the lake removes 560 mg N m^?2 yr^?1. Laboratory investigations using sediment receiving 450 μg NH⁺₄-N (N-15 labeled) showed that the lake has the potential to remove up to 12.8 g N m^?2 yr^?1. Equilibrium studies of P exchanges between the sediment and water column established the potential or adsorption capacity of bottom sediment in removing P from the overlying water. Lake Verret sediment was found to adsorb P from the water column at concentrations above 50 μg P 1^?1 and the adsorption rates were as great as 300 μg P cm^?2 day^?1 Using the ¹³⁷C s dating techniques, approximately 18 g N m^?2 yr^?1 and 1.2 g P m^?2 yr^?1 were removed from the system via sedimentation. Presently elevated nutrient levels are found only in the upper reaches of the lake receiving nutrient input from runoff from streams draining adjacent agricultural areas. Nitrification, denitrification, and adsorption processes at the sediment water interface over a relatively short distance reduces the N and P levels in the water column. However, if the lake receives additional nutrient loading, elevated levels will likely cover a larger portion of the lake, further reducing water quality in the lake.