Surface Water Nitrate Research Articles

Atrazine contamination at the watershed scale and environmental factors affecting sampling rates of the polar organic chemical integrative sampler (POCIS)

Polar organic chemical integrative samplers (POCIS) were used to estimate atrazine contamination at 24 stream/river sites located across a watershed with land use ranging from 6.7 to 97.4% annual crops and surface water nitrate concentrations ranging from 3 to 5404 μg/L. A gradient of atrazine contamination spanning two orders of magnitude was observed over two POCIS deployments of 28 d and was positively correlated with measures of agricultural intensity. The metabolite desisopropyl atrazine was used as a performance reference compound in field calibration studies. Sampling rates were similar between field sites but differed seasonally. Temperature had a significant effect on sampling rates while other environmental variables, including water velocity, appeared to have no effect on sampling rates. A performance reference compound approach showed potential in evaluating spatial and temporal differences in field sampling rates and as a tool for further understanding processes governing uptake of polar compounds by POCIS.

From Headwaters to Coast: Influence of Human Activities on Water Quality of the Potomac River Estuary

The natural aging process of Chesapeake Bay and its tributary estuaries has been accelerated by human activities around the shoreline and within the watershed, increasing sediment and nutrient loads delivered to the bay. Riverine nutrients cause algal growth in the bay leading to reductions in light penetration with consequent declines in sea grass growth, smothering of bottom-dwelling organisms, and decreases in bottom-water dissolved oxygen as algal blooms decay. Historically, bay waters were filtered by oysters, but declines in oyster populations from overfishing and disease have led to higher concentrations of fine-sediment particles and phytoplankton in the water column. Assessments of water and biological resource quality in Chesapeake Bay and tributaries, such as the Potomac River, show a continual degraded state. In this paper, we pay tribute to Owen Bricker’s comprehensive, holistic scientific perspective using an approach that examines the connection between watershed and estuary. We evaluated nitrogen inputs from Potomac River headwaters, nutrient-related conditions within the estuary, and considered the use of shellfish aquaculture as an in-the-water nutrient management measure. Data from headwaters, nontidal, and estuarine portions of the Potomac River watershed and estuary were analyzed to examine the contribution from different parts of the watershed to total nitrogen loads to the estuary. An eutrophication model was applied to these data to evaluate eutrophication status and changes since the early 1990s and for comparison to regional and national conditions. A farm-scale aquaculture model was applied and results scaled to the estuary to determine the potential for shellfish (oyster) aquaculture to mediate eutrophication impacts. Results showed that (1) the contribution to nitrogen loads from headwater streams is small (about 2 %) of total inputs to the Potomac River Estuary; (2) eutrophic conditions in the Potomac River Estuary have improved in the upper estuary since the early 1990s, but have worsened in the lower estuary. The overall system-wide eutrophication impact is high, despite a decrease in nitrogen loads from the upper basin and declining surface water nitrate nitrogen concentrations over that period; (3) eutrophic conditions in the Potomac River Estuary are representative of Chesapeake Bay region and other US estuaries; moderate to high levels of nutrient-related degradation occur in about 65 % of US estuaries, particularly river-dominated low-flow systems such as the Potomac River Estuary; and (4) shellfish (oyster) aquaculture could remove eutrophication impacts directly from the estuary through harvest but should be considered a complement—not a substitute—for land-based measures. The total nitrogen load could be removed if 40 % of the Potomac River Estuary bottom was in shellfish cultivation; a combination of aquaculture and restoration of oyster reefs may provide larger benefits.

Study of physico-chemical characteristics of the westernmost part of the barrier Lagoon complex, Western Nigeria

Some physico-chemical parameters of Badagry Creek and Ologe Lagoon in the Barrier Lagoon Complex of western Nigerian coastal zone were measured on quarterly basis from June 2011 to May 2012. Water samples were collected and analyzed using standard methods at five stations in each of the two water bodies. A brackish condition was observed in Badagry Creek with salinity range of 2.00 ± 3.8 ‰ to 3.85 ± 4.48 ‰ while entirely freshwater condition was recorded in Ologe Lagoon. Surface water temperature, pH, alkalinity, nitrate and phosphate at every station in the two water bodies were within the normal ranges considered suitable for tropical aquatic life. However, high levels of biochemical oxygen demand (BOD) were recorded at a station in Badagry Creek (8.15 ± 1.66 mg/l) and two stations in Ologe Lagoon (16.9 ± 10.46 and 9.40 ± 7.56 mg/l), where untreated municipal wastes are being discharged into the water bodies. These stations also had relatively low dissolved oxygen (DO) levels (3.30 ± 0.22, 1.08 ± 0.96 and 3.68 ± 3.2 mg/l respectively). Relatively high levels of lead were also recorded at these stations (0.50 ± 0.42, 0.85 ± 0.07 and 0.35 ± 0.35 mg/l respectively). The implications of the physico-chemical conditions on bio-communities as well as the imperativeness of regulating the discharge of untreated wastes into the water bodies for their sustainable management and conservation are discussed.Keywords: Physico-chemical parameters, Badagry Creek, Ologe Lagoon, untreated waste discharge, Organic pollution.

A Review of Removal of Pollutants from Water/Wastewater Using Different Types of Nanomaterials

The rapidly increasing population, depleting water resources, and climate change resulting in prolonged droughts and floods have rendered drinking water a competitive resource in many parts of the world. The development of cost-effective and stable materials and methods for providing the fresh water in adequate amounts is the need of the water industry. Traditional water/wastewater treatment technologies remain ineffective for providing adequate safe water due to increasing demand of water coupled with stringent health guidelines and emerging contaminants. Nanotechnology-based multifunctional and highly efficient processes are providing affordable solutions to water/wastewater treatments that do not rely on large infrastructures or centralized systems. The aim of the present study is to review the possible applications of the nanoparticles/fibers for the removal of pollutants from water/wastewater. The paper will briefly overview the availability and practice of different nanomaterials (particles or fibers) for removal of viruses, inorganic solutes, heavy metals, metal ions, complex organic compounds, natural organic matter, nitrate, and other pollutants present in surface water, ground water, and/or industrial water. Finally, recommendations are made based on the current practices of nanotechnology applications in water industry for a stand-alone water purification unit for removing all types of contaminants from wastewater.

Cell Size Dependent Responses of Phytoplankton Assemblages to Nitrate and Phosphate Additions in Surface Waters of the Northern South China Sea

Bioavailability of nitrogen (N) and phosphorus (P) is known to affect marine phytoplankton physiology, thus influencing their primary productivity; and it’s of general interest to see how the N or/and P additions affect the differently cell-sized phytoplankton assemblages. Data from the northern South China Sea showed that P addition increased up to 6 times of total chl a content within 24 h in the estuarine water; and N+P addition increased more than 20 times of chl a within 144 h in the pelagic water. The P addition powered 18.0% and 149% increase in the carbon fixation of larger (>3 μm) and smaller (

Surface Water Quality Is Improving due to Declining Atmospheric N Deposition

We evaluated long-term surface water nitrate and atmospheric nitrogen (N) deposition trends for a group of nine predominantly forested Appalachian Mountain watersheds during a recent multidecadal period (1986-2009) in which regional NOx emissions have been progressively reduced. Statistical analysis showed unexpected linear declines in both annual surface water nitrate-N concentrations (mean =46.4%) and yields (mean =47.7%) among the watersheds corresponding to comparable declines in annual wet N deposition (mean =34.4%) resulting from U.S. NOx emission control programs during the same time period. Nitrate-N concentration trends were robust across a large geographical region and appeared insensitive to watershed size across several orders of magnitude-suggesting that the improvements in water quality are probably propagated to surface and estuarine waters downstream. Surface waters are thus responding to declining atmospheric N deposition in much the same way they responded to declining sulfur deposition-although only one watershed showed a 1:1 relationship. Application of a kinetic N saturation model indicated that all nine forested watersheds are exhibiting signs of N saturation as evidenced by a limited, but variable, efficiency of demand for N. Further reductions in N deposition would be expected to produce additional reductions in streamwater N loads.

Water Quality Conditions Associated with Cattle Grazing and Recreation on National Forest Lands

There is substantial concern that microbial and nutrient pollution by cattle on public lands degrades water quality, threatening human and ecological health. Given the importance of clean water on multiple-use landscapes, additional research is required to document and examine potential water quality issues across common resource use activities. During the 2011 grazing-recreation season, we conducted a cross sectional survey of water quality conditions associated with cattle grazing and/or recreation on 12 public lands grazing allotments in California. Our specific study objectives were to 1) quantify fecal indicator bacteria (FIB; fecal coliform and E. coli), total nitrogen, nitrate, ammonium, total phosphorus, and soluble-reactive phosphorus concentrations in surface waters; 2) compare results to a) water quality regulatory benchmarks, b) recommended maximum nutrient concentrations, and c) estimates of nutrient background concentrations; and 3) examine relationships between water quality, environmental conditions, cattle grazing, and recreation. Nutrient concentrations observed throughout the grazing-recreation season were at least one order of magnitude below levels of ecological concern, and were similar to U.S. Environmental Protection Agency (USEPA) estimates for background water quality conditions in the region. The relative percentage of FIB regulatory benchmark exceedances widely varied under individual regional and national water quality standards. Relative to USEPA’s national E. coli FIB benchmarks–the most contemporary and relevant standards for this study–over 90% of the 743 samples collected were below recommended criteria values. FIB concentrations were significantly greater when stream flow was low or stagnant, water was turbid, and when cattle were actively observed at sampling. Recreation sites had the lowest mean FIB, total nitrogen, and soluble-reactive phosphorus concentrations, and there were no significant differences in FIB and nutrient concentrations between key grazing areas and non-concentrated use areas. Our results suggest cattle grazing, recreation, and provisioning of clean water can be compatible goals across these national forest lands.

무산소/호기생물막반응조와 MF막의 연속처리에 의한 퍼클로레이트와 질산염 제거

This research was conducted to investigate whether sequential anoxic/aerobic biofilm reactors and microfilteration (MF) membrane system can be used as a direct treatment for the removal of perchlorate and nitrate in groundwater. The biofilm process consisted of an anoxic first stage to remove perchlorate and nitrate and aerobic second stage to remove remaining acetate used as a carbon source for dissimilatory reduction of perchlorate and nitrate. In final stage, hollow fiber MF membrane was used to remove turbidity. In this research, perchlorate was reduced from the influent concentration of 102 μg/L to below the IC detection level (5 μg/L) and nitrate was reduced from 61.8 mg/L (14 mg/L NO3-N) to 4.4 mg/L (1 mg/L NO3-N). Acetate used as a carbon source was consumed from 179 mg/L CH3COO to 117 and 11 mg/L CH3COO in effluents from anoxic and aerobic biofilm reactors, respectively. Turbidity was reduced from 3.0 NTU to 1.5, 0.3, and 0.2 NTU in effluents from anoxic/aerobic biofilm reactors and MF membrane, respectively. It is expected that the sequential anoxic/aerobic biofilm reactors and MF membrane system can efficiently remove perchlorate and nitrate in surface water or groundwater.

Removal of fluoride from aqueous solution: status and techniques

Presence of various hazardous contaminants like fluoride, arsenic, nitrate, sulfate, pesticides, heavy metals, and other elements in ground water or surface water make the water unsafe and dangerous for the drinking purpose. The presence of any of these elements in drinking water in excess to the permissible limit is harmful for the human life. Fluoride is one of the elements which is very important for health especially for the children during teeth formation as well as harmful for human health if present in water more than permissible limit. Absence or insufficient amount of fluoride in drinking water causes dental caries during teeth formation of children whereas the presence of excess fluoride in drinking water causes dental and skeletal fluorosis. Therefore, maintaining of fluoride concentration within the safe limits is very important. The presence of excess fluoride in drinking water is a global problem. Excessive fluoride concentrations have been reported in ground waters of more than 27 developed and developing countries including India. In India, about 19 states are facing acute fluorosis problem due to excess fluoride concentration. Fluoride is the major inorganic pollutant of natural origin found in ground water. The excessive fluoride from the drinking water should be reduced to the permissible limit. Various technologies such as coagulation–precipitation, ion exchange, electrocoagulation/electrochemical treatment, membrane processes, nanotechnology, and adsorption are being used to remove fluoride from water. Every method of fluoride removal has its advantages and limitations of operations. The selection of treatment process should be site specific as per local needs and prevailing conditions as each technology has some limitations. The present paper deals with the short review on sources of fluoride, its effects on human health, and the techniques available for removal of fluoride from drinking water.

Comparison of Two Spectrophotometric Techniques for Nutrients Analyses in Water Samples

The aim of this contribution is to compare two common techniques for determining the concentrations of nitrate, nitrite, ammonium and phosphates in surface water and groundwater. Excess of these nutrients in water can directly affect human health (e.g. methemoglobinaemia) or indirectly through the products of secondary pollution - eutrophication (e.g. cyanotoxins, emanation of hydrogen sulphide, mercaptanes, methane...). Negative impact of nutrients excess in surface water often causes the destruction of water ecosystems, and therefore, common substances of these elements must be monitored and managed. For these experiments two spectrophotometric techniques - ultraviolet spectrophotometry and nutrient photometry were used. These techniques are commonly used for quick and simple analyses of nutrients in waste water. There are calibration curves for each nutrient and for determination of their concentration.

Nitrogen and oxygen isotopes in nitrate in the groundwater and surface water discharge from two rural catchments: implications for nitrogen loading to coastal waters

In Prince Edward Island, Canada, widespread intensive potato production has contributed to elevated nitrate concentrations in groundwater and streams, and eutrophic or anoxic conditions occur regularly in several estuarine systems. In this research, the stable isotopes of nitrogen and oxygen in nitrate in intertidal groundwater discharge and stream water were used, in conjunction with water quality and quantity data and land use information, to better understand the characteristics of nitrate delivered to two small estuaries with contrasting land use in their contributory catchments. Most of the water samples collected during the two-year study had isotopic signatures that fell in the range expected for nitrate derived from ammonium-based fertilizers (26.5 % of the samples) or in the overlapping range formed between ammonium-based fertilizers and nitrate derived from soil (64 % of the samples). Overall, isotopic signatures spanned over relatively narrow ranges, and correlations with other water quality parameters, or catchment characteristics, were weak. Nitrate in groundwater discharge and surface water in the Trout River catchment exhibited significantly different isotopic signatures only for the nitrogen isotope, while in the McIntyre Creek catchment groundwater discharge and surface water had similar isotopic signatures. When the isotopic results for the waters from the two catchments were compared, the surface waters were found to be similar, while the isotopic signatures of nitrate in groundwater were distinct only for the nitrogen isotope. Denitrification in the two study catchments was not evident based on the isotopic results for nitrate; however, in the case of the Trout River catchment, where a small freshwater pond exists, an average nitrate load reduction of 14 % was inferred based on a comparison of nitrate loads entering and leaving the pond. Overall, it appears that natural attenuation processes, occurring either in the streams or groundwater flow systems, do not significantly reduce nitrate loading to these estuaries.

Impact of Nitrogen Fertilizer Applications on Surface Water Nitrate Levels within a Kenyan Tea Plantation

Tea production in the Kenyan Rift Valley uses high rates of nitrogenous fertilizer. Nitrates can be discharged to water bodies through leaching and surface run‐off. Nitrate levels above 10 mg/L –N cause methemoglobinemia which is fatal. A study to monitor changes in surface water nitrate levels was carried out in ten rivers within a Kenyan tea plantation for three years. Water samples were obtained before and after fertilizer application in 2004, 2005, and 2006. Nitrate‐nitrogen (–N) was determined colorimetrically by the cadmium reduction method using HACH‐DR 2400 dataloging spectrophotometer. For the three years, the highest nitrate‐nitrogen levels were in river Temochewa in 2005 during the first fertilizer applications (4.9 mg/L to 8.2 mg/L). There was no established trend between surface water nitrate levels and the time of fertilizer applications; however, fertilizer application contributed to an increase in nitrate levels. The initial nitrate‐nitrogen levels in most of the rivers were high, indicating that contamination could have been upstream; hence, further research is required to establish this. Nitrogen‐nitrogen levels in the three years were below the maximum contaminant level of 10 mg/L –N; however, the rivers should be monitored frequently.

Atlas of modern dinoflagellate cyst distribution based on 2405 data points

Dinoflagellate cysts are useful for reconstructing upper water conditions. For adequate reconstructions detailed information is required about the relationship between modern day environmental conditions and the geographic distribution of cysts in sediments. This Atlas summarises the modern global distribution of 71 organic-walled dinoflagellate cyst species. The synthesis is based on the integration of literature sources together with data of 2405 globally distributed surface sediment samples that have been prepared with a comparable methodology and taxonomy. The distribution patterns of individual cyst species are being compared with environmental factors that are known to influence dinoflagellate growth, gamete production, encystment, excystment and preservation of their organic-walled cysts: surface water temperature, salinity, nitrate, phosphate, chlorophyll-a concentrations and bottom water oxygen concentrations. Graphs are provided for every species depicting the relationship between seasonal and annual variations of these parameters and the relative abundance of the species. Results have been compared with previously published records; an overview of the ecological significance as well as information about the seasonal production of each individual species is presented.The relationship between the cyst distribution and variation in the aforementioned environmental parameters was analysed by performing a canonical correspondence analysis. All tested variables showed a positive relationship on the 99% confidence level. Sea-surface temperature represents the parameter corresponding to the largest amount of variance within the dataset (40%) followed by nitrate, salinity, phosphate and bottom-water oxygen concentration, which correspond to 34%, 33%, 25% and 24% of the variance, respectively. Characterisations of selected environments as well as a discussion about how these factors could have influenced the final cyst yield in sediments are included.

Nitrate Reduction by Redox-Activated, Polydiallyldimethylammonium-Exchanged Ferruginous Smectite

AbstractNitrate is linked to chronic human illness and to a variety of environmental problems, and continues to be a contaminant of concern in soils and natural waters. Improved methods for nitrate abatement, thus, are still needed. The purpose of this study was to assess the potential for redox-modified, iron-bearing clay minerals to act as nitrate decontamination agents in natural environments. The model clay mineral tested was ferruginous smectite (sample SWa-1) exchanged with either sodium (Na+) or polydiallyldimethylammonium chloride (poly-DADMAC). Structural iron (Fe) in SWa-1 was in either the oxidized or reduced state. Little nitrate uptake was observed in the Na+-SWa-1, which was attributed to coulombic repulsion between the basal surfaces of the smectite and the nitrate anion. The addition of the DADMAC to the SWa-1 reversed the electrostatic charge manifested at the smectite surface from negative to positive, as measured by the zeta (ζ) potential. The positively charged poly-DADMAC-SWa-1 yielded high nitrate uptake due to coulombic attraction in both the oxidized and reduced states of the Fe in the SWa-1. The presence of reduced structural Fe(II) in the positively charged poly-DADMAC-SWa-1 enabled a chemical reduction reaction with the nitrate to produce nitrite. The amounts of nitrite found in solution, however, failed to account for all of the Fe(II) oxidized, so other N reduction products may also have formed or perhaps nitrite was also present in the adsorbed phase. The effects of other complexities, such as polymer configuration at the surface, also need further investigation. The results do clearly establish abiotic nitrate reduction to nitrite and possibly other reduction products. The combination of bacterial activity in soils and sediments, which is known to reduce structural Fe in smectites, and the abundance of organic cations in soil organic matter creates an environment where reversed-charge smectite could exist in nature. This represents a potentially effective system for mitigating harmful effects of nitrate in soils, sediments, groundwater, and surface water.

Adsorptive Removal of Nitrate and Phosphate from Water by a Purolite Ion Exchange Resin and Hydrous Ferric Oxide Columns in Series

Elevated concentrations of nitrate and phosphate in surface and ground waters can lead to eutrophication, and nitrate can also cause health hazards to humans. The adsorption process is generally considered to be an efficient technique in removing these ions provided that the adsorbent is highly selective for these ions. Removal of nitrate and phosphate from a synthetic water (50 mg N/L as nitrate, 15 mg P/L as phosphate) and a wastewater (12.9 mg N/L as nitrate, 5.9 mg P/L as phosphate) using a Purolite A500P anion exchange resin and a hydrous ferric oxide (HFO) columns (60 cm height, 2 cm diameter, flow rate 1 m/h) in series containing 1–10% (w/w) of these adsorbents and the remainder anthracite (90–99%) were studied. Data from batch adsorption experiment at various concentrations of adsorbents satisfactorily fitted to Langmuir adsorption isotherm for nitrate and phosphate on Purolite with adsorption maxima of 64 mg N/g and 7 mg P/g and only for phosphate on HFO with adsorption maxima of 14 mg P/g. Both batch and column experiments showed that Purolite selectively removed nitrate and HFO selectively removed phosphate. The Purolite column BTC time was greater for nitrate than for phosphate. At the highest percentage by weight of Purolite almost all nitrate was removed in batch study and up to 1000 min in column study, but it was not able to remove a comparatively high percentage of phosphate. However, when the effluent from the Purolite column was passed through the HFO column almost all phosphate was removed. The two columns when set up in series also removed almost all nitrate and phosphate from the wastewater.

Restoration of ponds in rural landscapes: Modelling the effect on nitrate contamination of surface water (the Seine River Basin, France)

Ponds were ubiquitous features of the traditional rural waterscape in the Seine watershed, as shown by the 18th century Cassini map. Using the result of a water quality survey at the entrance and the outlet of a small pond receiving agricultural drainage water, the Seneque/Riverstrahler biogeochemical model was shown to accurately simulate the observed 30% reduction in nitrogen fluxes crossing this pond. The model was then used to simulate the effect of various scenarios of pond restoration (inspired by their 18th century geographical distribution as revealed by the Cassini map) on surface water nitrate contamination at different spatial scales. In regions with an impermeable lithological substrate, the restoration of ponds at a density of 5% of the agricultural area would reduce the riverine nitrogen export by up to 25% on an annual basis. It is suggested that such waterscape management, used in conjunction with more preventive measures, can be a useful means to reduce nitrate contamination of water resources.

Copepoda Harpacticoida community of a rocky shore under the influence of upwelling (Arraial do Cabo, southeastern Brazil)

Upwelling can determine important changes in community structure on rocky shores. However, studies on the meiofauna in areas of upwelling are scarce and do not include analysis on the species level for Copepoda Harpacticoida. The present study aimed to describe the Harpacticoida community in a region under the influence of coastal upwelling (Arraial do Cabo, Rio de Janeiro, Brazil). The hypothesis tested was that temporal differences in the fauna would be greater at the rocky shore more affected by upwelling. Samples were collected from the sublittoral of two rocky shores: Sonar, which is more exposed to upwelling, in January and June 2004; and Pedra Vermelha, which is a sheltered shore, in March and September 2002. Each sample consisted of four replicates collected by scraping epilithic algae along with the associated sediment. Weekly data on surface water temperature and nitrate content denoted stronger upwelling in 2002 compared to 2004. Nine genera of Copepoda Harpacticoida are reported for the first time for the Brazilian coast. Univariate indices identified no differences between rocky shores or seasons, whereas multivariate analysis indicated significant differences in assemblages between shores and between seasons. The strong variation in physicochemical conditions associated with upwelling favoured the dominance of opportunistic species, such as Parastenhelia spinosa. At the Sonar rocky shore, temporal differences were significantly stronger than at Pedra Vermelha, thereby confirming the initial hypothesis. These results indicated that the occurrence of upwelling had a very important role structuring the Harpacticoida assemblage at the species level.

The role of nitrogen deposition in the recent nitrate decline in lakes and rivers in Northern Italy

Deposition of inorganic nitrogen (N) in north-western Italy is around 20–25kgNha−1y−1, and has remained constant during the last 30years. This flux of N caused saturation of terrestrial catchments and increasing levels of nitrate (NO3) in surface waters. Recently, monitoring data for both rivers and lakes have shown a reversal in NO3 trends. This change was widespread, affecting high-altitude lakes in the Alps and subalpine lakes and rivers, and occurred at almost the same time at all sites. The seasonal pattern of NO3 concentrations in running waters has shown a change in the last few years, with a tendency towards slightly lower leaching of NO3 during the growing season. Atmospheric input of N has also shown a recent decrease, mainly due to decreasing emissions and partly to the lower amount of precipitation occurring between 2003 and 2009. Surface waters are probably responding to these changing N inputs, but a further decrease of N deposition, especially reduced N, will be required to achieve full recovery from N saturation.

Groundwater and Surface-Water Exchange and Resulting Nitrate Dynamics in the Bogue Phalia Basin in Northwestern Mississippi

During April 2007 through September 2008, the USGS collected hydrogeologic and water-quality data from a site on the Bogue Phalia to evaluate the role of groundwater and surface-water interaction on the transport of nitrate to the shallow sand and gravel aquifer underlying the Mississippi Alluvial Plain in northwestern Mississippi. A two-dimensional groundwater/surface-water exchange model was developed using temperature and head data and VS2DH, a variably saturated flow and energy transport model. Results from this model showed that groundwater/surface-water exchange at the site occurred regularly and recharge was laterally extensive into the alluvial aquifer. Nitrate was consistently reported in surface-water samples (n = 52, median concentration = 39.8 μmol/L) although never detected in samples collected from in-stream piezometers or shallow monitoring wells adjacent to the stream (n = 46). These two facts, consistent detections of nitrate in surface water and no detections of nitrate in groundwater, coupled with model results that indicate large amounts of surface water moving through an anoxic streambed, support the case for denitrification and nitrate loss through the streambed.

Simulation of 1D surface and 2D subsurface water flow and nitrate transport in alternate and conventional furrow fertigation

Increasing water and fertilizer productivity stands as a relevant challenge for sustainable agriculture. Alternate furrow irrigation and surface fertigation have long been identified as water and fertilizer conserving techniques in agricultural lands. The objective of this study was to simulate water flow and fertilizer transport in the soil surface and in the soil profile for variable and fixed alternate furrow fertigation and for conventional furrow fertigation. An experimental data set was used to calibrate and validate two simulation models: a 1D surface fertigation model and the 2D subsurface water and solute transfer model HYDRUS-2D. Both models were combined to simulate the fertigation process in furrow irrigation. The surface fertigation model could successfully simulate runoff discharge and nitrate concentration for all irrigation treatments. Six soil hydraulic and solute transport parameters were inversely estimated using the Levenberg–Marquardt optimization technique. The outcome of this process calibrated HYDRUS-2D to the observed field data. HYDRUS-2D was run in validation mode, simulating water content and nitrate concentration in the soil profiles of the wet furrows, ridges and dry furrows at the upstream, middle and downstream parts of the experimental field. This model produced adequate agreement between measured and predicted soil water content and nitrate concentration. The combined model stands as a valuable tool to better design and manage fertigation in alternate and conventional furrow irrigation.