Phosphorus sources,speciation and dynamics in the lowland eutrophic River Kennet,UK

This paper examines the behaviour of phosphorus (P) in a lowland chalk (Cretaceous-age) stream, the upper River Kennet in southern England, which has been subject to P remediation by tertiary treatment at the major sewage treatment works in the area. The effects of treatment are examined in relation to boron, a conservative tracer of sewage effluent and in terms of the relative contributions of soluble reactive phosphorus (SRP) loads from point and diffuse sources, and in-stream SRP loads. These results indicate a baseline reduction in in-stream SRP concentrations immediately following P-treatment of approximately 72%. Subsequent high flows result in a greater contribution of diffuse inputs and increases in SRP levels relative to the initial post-treatment period. The dynamics of SRP and particulate phosphorus (PP) are examined under a wide range of river flow conditions. Given the flashy nature of near-surface runoff in the River Kennet, sub-weekly (daily automated) sampling was used to examine the dynamics in SRP and PP concentrations in response to storm events. Simple empirical models linking weekly SRP concentrations with flow were developed. The empirical models were successfully applied to the daily data, to partition TP measurements and provide an estimate of daily SRP and PP concentrations. Mass balance studies were used to examine net gains and losses along the experimental river reach and indicate large net losses (up to 60%) during the extreme low flows and high SRP concentrations prior to P-treatment, which may be linked to extensive epiphytic growth. Phosphorus dynamics and response to P-treatment are discussed in relation to hydrological controls in permeable chalk catchments and wider implications for eutrophication management are examined.     

The phosphorus budget of the Thame catchment,Oxfordshire: 2. Modelling

The phosphorus budget of the River Thame was modelled at a daily time scale, using estimates of diffuse and point source contributions of discharge. The model simulated suspended sediment (SS), soluble unreactive phosphorus (SUP), soluble reactive phosphorus (SRP) and particulate phosphorus (PP) concentrations within the main river and major tributaries. Diffuse source estimates of phosphorus loads were based on characteristic losses from identified main landscape classes, with hydrology described by a simple conceptual storage model. In-stream flow was modelled using a kinematic wave equation. Transfer of suspended sediment and phosphorus components was approximated by advection. In-stream sources and sinks included uptake and release of soluble reactive phosphorus by bed sediment, instant equilibration between SRP and the PP concentration on suspended sediment, and flow-related entrainment and deposition of suspended sediment. Simulations at sites within the catchment were compared with measurements made in 1998–1999. Results showed the P budget is dominated by mixing of diffuse and point source water, but some within-river processes have been shown to be capable of significantly influencing SRP concentrations. The development of a sediment entrainment and deposition component of the model has proved particularly valuable in emulating the hysteretic relationship between discharge and suspended sediment concentration in the river. It also provides a measure of available bed sediment.     

Incidence and variability of some elements in the non tidal region of the River Thames,and River Kennet,U.K.

Element incidence and variability in the soluble and suspended particulate fractions of water taken during an extended period from four sampling locations on the Rivers Thames and Kennet is presented. Neutron activation analysis was used to determine 30 elements in the river water samples. One way analysis of variance was applied to investigate the significant variation in metal concentration between the four sampling stations and correlation analysis was used to study the relationship between elemental concentrations and river water parameters. Dissolved Cr, Fe and Se correlated positively with river flow rate whereas Rb and Zn had a significant negative correlation.     

The effects of sediment size fraction and associated algal biofilms on the kinetics of phosphorus release

Experiments using flumes containing sediment of three different size fractions, from two sites on the River Tame, investigated the influences of sediment particle size, and an associated biofilm, on sediment-water exchanges in heterogeneous sediment deposits. This is the first study undertaken to understand the kinetics of the release of soluble reactive phosphorus from sediments of natural systems to identify which of the size compartments affected those fluxes most. Samples of fine material (<2 mm), gravel (2-20 mm), and stones (>20 mm) were collected over a period of several weeks and brought to a fluvarium where they were placed in artificial, controlled flow, and flume channels. Synthetic solutions of similar ionic strength to the river were prepared using calcium chloride. Temperature, pH, and dissolved oxygen of the solution overlying the sediment were monitored automatically whilst filtered samples were obtained at 2 h intervals over 48 h. The biomass, expressed as mg m(-2) chlorophyll a, of the algal component of the biofilm from the surface of the sediment was estimated using methanol extraction. Differences in the responses were observed between the sediment size fractions and the two sites, where contaminant concentrations varied. The equilibrium phosphate concentration and a phosphorus transfer index were used to establish that there was a net uptake of phosphorus by all three sediment size fractions, from both sites, at the time of sampling. The kinetic results showed very fast initial reactions of phosphorus release from the larger size fractions with a well-developed filamentous algal growth present implying a different mechanism than diffusion being involved. The stones and associated biofilms also released more phosphorus than the fine fraction, e.g. final release concentrations for the most contaminated site were: fines approximately 2.5 microM, gravel approximately 6.5 microM, and stones approximately 65.0 microM (expressed as soluble reactive phosphorus). Phosphorus fluxes, calculated assuming the concentration of phosphorus in the sediment was less than the equilibrium concentration, were a maximum at the most contaminated site, e.g. fines 6.4 nmol m(-2) s(-1), gravel 27 nmol m(-2) s(-1), and stones 109 nmol m(-2) s(-1) (normalised with respect to the river bed area). These results confirm that sediment having a biofilm and associated particulate material results in a greater flux than fine sediment, which does not support a filamentous biomass. Removal of the fine particulates trapped in the algal growth reduced soluble phosphorus release. These factors demonstrate that both gravel and stone substrates have an important control over the release of soluble reactive phosphorus.     

Dissolved and particulate nutrient export from rural catchments: a case study from Luxembourg

Nutrient enrichment of freshwaters continues to be one of the most serious problems facing the management of surface waters. Effective remediation/conservation measures require accurate qualitative and quantitative knowledge of nutrient sources, transport mechanisms, transformations and annual dynamics of different nitrogen (N) and phosphorus (P) forms. In this paper, nitrate (NO3-N), soluble reactive phosphorus (SRP) and total phosphorus (TP) concentrations and loads are presented for two adjacent rural basins of 306 km2 and 424 km2, and for five sub-basins differing in size (between 1 km2 and 33 km2), land use (extent of forest cover between 20% and 93%) and household pressure (from 0 to 40 people/km2) with the aim of studying the influence of land use and catchment size on nutrient exports. The studied catchments are all situated on Devonian schistous substrates in the Ardennes region (Belgium-Luxembourg), and therefore have similar hydrological regimes. As the study period could not be the same for all basins, annual export coefficients were corrected with the 25 years normalized discharge of the Sure River: two regression analyses (for dry and humid periods) relating monthly nutrient loads to monthly runoff were used to determine correction factors to be applied to each parameter and each basin. This procedure allows for the comparing annual export coefficients from basins sampled in different years. Results show a marked seasonal response and a large variability of NO3-N export loads between forested (4 kg N ha-1 year-1), agricultural (27-33 kg N ha-1 year-1) and mixed catchments (17-22 kg N ha-1 year-1). For SRP and TP, no significant agricultural impact was found. Land and bank erosion control the total P massflow in the studied catchments (0.4-1.3 kg P ha-1 year-1), which is mostly in a particulate form, detached and transported during storm events. Soluble reactive P fluxes ranged between 10% and 30% of the TP mass, depending on the importance of point sources in the basins studied. No relation was found between the size of the basins and the export of nitrate, SRP or TP. Nutrient export, specially for NO3-N and TP, shows significant inter-annual variations, closely linked to inter-annual discharge variations. Flow and load frequency data analysis confirm this association for all the basins on an annual basis. Seasonal or storm specific fluxes strongly deviate from their annual values.     

The phosphorus budget of the Thame catchment,Oxfordshire, UK: 1. Mass balance

The relative magnitudes of annual diffuse and point source loads of phosphorus (P) to the River Thame were estimated from daily and monthly measurements of discharge and concentration. Existing data from gauging and monitoring sites on the river network and at point sources were supplemented by survey data at a range of spatial scales. Results showed that during low flow periods most of the P could be attributed to point sources, while at high flows the figure was less than 10%. The introduction of P stripping at Aylesbury, a major sewage treatment works in the catchment, was estimated to have reduced the annual load of P from the sewage treatment works by approximately 45 t, with a similar reduction in loss from the catchment. This gave a reduction in low flow concentrations of soluble reactive phosphorus (SRP) from 2.5 to 1.7 mg l⁻¹. Concentrations of SRP in river water remain above eutrophication thresholds because of the influence of other STWs in the catchment and insufficient natural discharge to dilute this.     

NUR and our relationship in BNR processes with sewage at different temperatures and its design application

Denitrification is known as an essential part of a biological nutrient removal (BNR) process to remove nitrogen and it also affects phosphorus removal. However, an accurate prediction of nitrogen removal is extremely difficult because there are too many factors involved. This study was conducted to find a relationship between nitrate uptake rate (NUR) and carbonaceous oxygen uptake rate (OUR) and develop a simple method to predict applicable NUR for the design of various BNR processes. Sewage was subdivided into soluble and particulate organic fractions. NUR/OUR ratios were measured by respirometer with these organic fractions and the test sludges grown at various BNR processes and temperatures. NUR/OUR ratios were varied with the types of organic fractions of sewage and temperature. The NURs predicted from the NUR/OUR ratios and computed OUR based on the total tank volume of anoxic and oxic stages with the influent sewage characteristics were very much comparable with the observed NURs from various BNR processes.     

Phytoplankton,pelagic community and nutrients in a deep oligotrophic alpine lake: ratios as sensitive indicators of the use of P-resources (DRP:DOP:PP and TN:TP:SRSi)

The different use of P-resources between two sites in the deep oligotrophic Traunsee was studied by seasonal and vertical patterns of phytoplankton and nutrients from 12/1997 to 10/1998. The P-resources were evaluated from the proportion between the P-fractions, the dissolved reactive P (DRP), dissolved non-reactive P (DOP) and particulate organic P (PP) and from the stoichiometry between nutrients, the total N (TN), the total P (TP) and soluble reactive Si (SRSi). Significant differences between an inshore site impacted by industrial tailings (Ebensee Bay, EB) and an open water reference site (Viechtau, VI) were evident from vertical profiles of both the P-accumulation (%PP of TP) evaluated by DRP:DOP:PP and the distribution of phytoplankton assessed by Si-exhaustion (TN:TP:SRSi), but not from the seasonal patterns of phytoplankton composition, S:V ratios of the algal community or surface layer nutrient dynamics. Low TP and the stable stratification from May to September triggered the relative accumulation of epilimnetic P at VI as it was evident from both the higher portion of particulate P within TP (%PP of TP) and from the shift towards P-enrichment in nutrient stoichiometry of TN:TP:SRSi. The predominance of around 55-52% algal carbon over bacteria at the surface layer to 20m coincided spatially with the lowest Si content relative to N and P. The disturbances at the impacted site was summarised by: up to 11% less P accumulation by organisms at the surface, no stoichiometric shift towards TP in the epilimnion when compared with deeper layers and a reduction of the trophogenic zone to the top 10m. Reasons for this disturbance are seen in the unstable stratification, turbidity, higher TP and the metazoan dominated food chain. Both triple ratios, DRP:DOP:PP and TN:TP:SRSi, were sensitive indicators of the use of P-resources by plankton communities, while inorganic dissolved fractions (DIN:DRP:SRSi, DIN = dissolved inorganic N) provided only insufficient information on nutrient resources in Traunsee.     

A study of phosphorus partitioning and exchange in a South African impoundment

Radiochemical techniques were used to monitor the short-term exchange of phosphorus between soluble and particulate fractions in the water during enrichment experiments in a South African impoundment. Tracer uptake kinetics were examined under a range of conditions in the water, created by the use of a series of isolation columns. Labeled soluble fractions were separated by gel filtration and their exchange with the particulate fraction and with intact sediment cores were examined independently. Only two distinct soluble fractions were evident using the radiotracer method and their exchange characteristics with suspended particulate material and intact sediment cores differed markedly. Radiotracer partitioning contrasted with the phosphorus partitioning measured with standard chemical methods.     

Impacts of climate change on in-stream nitrogen in a lowland chalk stream: an appraisal of adaptation strategies

The impacts of climate change on nitrogen (N) in a lowland chalk stream are investigated using a dynamic modelling approach. The INCA-N model is used to simulate transient daily hydrology and water quality in the River Kennet using temperature and precipitation scenarios downscaled from the General Circulation Model (GCM) output for the period 1961-2100. The three GCMs (CGCM2, CSIRO and HadCM3) yield very different river flow regimes with the latter projecting significant periods of drought in the second half of the 21st century. Stream-water N concentrations increase over time as higher temperatures enhance N release from the soil, and lower river flows reduce the dilution capacity of the river. Particular problems are shown to occur following severe droughts when N mineralization is high and the subsequent breaking of the drought releases high nitrate loads into the river system. Possible strategies for reducing climate-driven N loads are explored using INCA-N. The measures include land use change or fertiliser reduction, reduction in atmospheric nitrate and ammonium deposition, and the introduction of water meadows or connected wetlands adjacent to the river. The most effective strategy is to change land use or reduce fertiliser use, followed by water meadow creation, and atmospheric pollution controls. Finally, a combined approach involving all three strategies is investigated and shown to reduce in-stream nitrate concentrations to those pre-1950s even under climate change.     

Particulate composition and origin of suspended sediment in the R. Don, Aberdeenshire, UK

Characterising the nature and origin of suspended particulate and colloidal matter in surface waters is a necessary first step in determining the role of these materials in the transport of pollutants. With this aim in mind, samples of suspended sediment were collected from the R. Don, Scotland, and analysed by a combination of X-ray diffraction (XRD) and vertically attenuated infrared spectroscopy (VATIR). Additionally, the carbon and nitrogen contents of the sediment were measured. Samples were collected at eight sites along the river from the headwaters to the mouth, twice during periods of base flow, and once during a storm. During the base flows, the amount of suspended solids was typically no more than 1-10 mg l(-1), whereas the high flow samples contained up to 150 mg l(-1). XRD showed that the crystalline component of the high flow samples consisted of the clay minerals illite, chlorite, kaolin, hydroxy-interlayered vermiculite, and a 10/14 A regularly interstratified mica/vermiculite. Non-clay components included quartz, feldspars, amphibole and goethite. Kaolin progressively increased in relative abundance downstream. The clay mineralogy of base flow samples was more or less identical to high flow samples but the non-clay components were reduced and, additionally, talc and calcite were present. The identification of many of the crystalline components was confirmed by VATIR, and amorphous silica was identified, particularly in base flow samples. Organic components were identified as wax, protein, and humate/fulvate. Proportionally more protein and wax components relative to silicates occurred in base flow samples, whereas the humate/fulvate component was most clearly identified in samples from the storm. Organic matter contents ranged from approximately 24% during base flow to 13% during the storm, whilst the C/N ratio showed a progressive decrease downstream, irrespective of flow conditions. Both the characteristics of the mineralogy and the organic matter suggested that topsoils were the primary source of the suspended sediment in the R. Don. However, the presence of talc and calcite were believed to fingerprint ground water sources, which together with the in-stream production of diatoms, may have accounted for a significant mass fraction of the suspended particulate matter during base flows.     

Solid state partitioning of trace metals in suspended particulate matter from a river system affected by smelting-waste drainage

The partitioning of particulate trace metals was investigated during one year of monthly sampling of suspended particulate matter (SPM) at eight sites along the Lot-Garonne fluvial system, known for its polymetallic pollution. The chemical partitioning in five operationally defined fractions (exchangeable/carbonate, Fe/Mn oxides, organic matter/sulfides, acid soluble, residual) was determined using a multiple single extraction approach. This approach showed that Cd, Zn, Pb and Cu were mainly associated with acid soluble phases (84-95%, 65-88%, 61-82% and 55-80% of the respective total metal content), and therefore showed a high mean potential of mobilization and bioavailability. In the Riou-Mort River, draining the smelting-wastes, Zn, Cd and Mn showed high mobility as they were little associated with the residual fraction (1-2%) and mainly bound to the 'exchangeable' fraction of SPM (60-80%), probably weakly adsorbed on amorphous freshly-precipitated sulfide and/or oxide phases. Upstream and downstream of the anthropogenic source of metallic pollution, Mn and Cd, and Zn to a lesser extent, remained highly reactive. The other trace metals were mainly associated with the residual fraction and thus less mobile. However, the multiple single extraction scheme revealed that the most reactive transport phases were non-selectively extracted by the conventional extractants used here. These selectivity problems could not have been observed if sequential extraction was used.     

Phosphorus dynamics observed through increasing scales in a nested headwater-to-river channel study

The hypothesis that the dynamic patterns of phosphorus (P) transport at plot scale are similar to the patterns that could be observed quasi-simultaneously (i.e., approximately at the same time) at a river basin scale, in terms of inputs and dilution of P, across a range of rainfall and runoff conditions, was tested. From this information, it was hoped to be able to make some simple inferences about the connectivity or mass flux of P transport between the different scales of observation. An intensive study using 30-m2 plots, 1-ha plots and nested river channel sites ranging in scale from 20 ha up to a maximum of 834 km2 in the River Taw basin, South West England, UK, was conducted with three campaigns under differing flow conditions: (1) a zero rainfall base flow period, (2) a 10-mm rainfall residual flow period, and (3) a 42-mm rainfall storm flow period. The mass flux of total P ranged from 49 kg during base flow to 4 tonnes during the storm period at the largest 834 km2 scale. During base flow conditions, total phosphorus (TP) concentrations from diffuse sources were low (26 microg L-1 in the upper catchment) and reactive P forms dominated the fractions filtered <0.45 microm. During storm flow, concentrations of TP increased at all scales within the drainage basin, to a maximum of 500 microg L-1 and were sufficient to override the effect of any point source inputs of P. Unreactive (i.e., mostly 'organic') forms of P dominated the fractions that were >0.45 microm during residual flows and storm flows. Spatially normalised discharge apparently decreased with increasing scale, most notably during storm flow conditions and this implies that there is some storage of water through the catchment and in part may reflect varying velocities of water in different pathways. Most attenuation and dilution of P appeared to occur at larger scales, whilst the hydrological connectivity between source areas and receiving waters was greatest at smaller scales (<20 ha), and during the highest flows. The importance of diffuse agricultural sources in contributing to P export through the basin was dominated by dynamic temporal changes in hydrological activity, with a 'piston pushing' effect of particulate associated P through the basin as it wets up in response to rainfall input. We concluded that the processes of P transfer are different at different scales. However, some uncertainties of spatial heterogeneity around the catchment underlie the difficulties in dealing with scale and thus more data and studies of this nature are required.     

Systematic salt effects in the automated determination of nutrients in seawater

The Bran + Luebbe TRAACS continuous flow analyser, commonly used for the determination of nutrients in seawater, primarily employs standard methods that have been modified and adapted for automated use. The analyser is fitted with self aligning spectrophotometric flow-cells with parallel optical ends of uniform thickness. As the light beam strikes both ends of the flow-cell perpendicularly, there is no refraction therefore no spurious absorbance caused by changes in the refractive index of the flow-cell contents. Investigation of methods for the determination of ammonia, nitrate, nitrite, orthophosphate, soluble reactive silica and urea, using TRAACS, confirmed that this was the case. Also, for the methods assessed, the absorbance signal was not biased by either sample turbidity or wetting agents. Chemical interference from salt was assessed by analysing nutrient spiked solutions, over the 0–35 ppt salinity range, relative to working calibration solutions prepared using demineralised water. A major salt effect which caused an apparent decrease in concentration, was detected over the analytical working ranges in the ammonia and nitrate methods. The salt effect results from a chemical interference which causes the production of reaction products to vary as a function of salinity. The salt effect is totally unrelated to refraction and produces a concentration error in the ammonia and nitrate methods up to 35 and 25% respectively. The degree of salt effect was shown to be dependent on both the salinity and true nutrient concentration of the sample. Over the salinity range 8.75–35.00 ppt, corrective equations were derived for ammonia and nitrate to express the true nutrient concentration in terms of the observed concentration and the salinity of the solution. Within the range 0–8.75 ppt no correction was required for ammonia wheras the nitrate showed a 3.5% increase in apparent concentration at 8.75 ppt. The orthophosphate, soluble reactive silica, urea and nitrite methods showed no significant salt effect as the coefficient of variation (CV) of the observed nutrient concentrations over the 0–35 ppt salinity range was within the accepted CV or analytical precision of the methods. The ammonia and nitrate corrective equations were applied in assessing the true nutrient content of “depleted” or low nutrient seawater, used in the preparation of working calibration solutions, after analysing relative to working calibration solutions prepared in demineralised water.     

Nutrient characteristics in the Yangtze River Estuary and the adjacent East China Sea before and after impoundment of the Three Gorges Dam

From November 2002 to 2006, five cruises were undertaken in the Yangtze River Estuary and the adjacent East China Sea to compare the nutrient concentrations, ratios and potential nutrient limitation of phytoplankton growth before and after impoundment (June 2003) of the Three Gorges Dam (TGD). Concentrations of dissolved inorganic nitrogen (DIN), soluble reactive phosphorus (SRP) and total nitrogen (TN) exhibited an increasing trend from 2002 to 2006. In contrast, total phosphorus (TP) concentration exhibited a decreasing trend. The mean concentrations of DIN, SRP, and TN in the total study area increased from 21.4 µM, 0.9 µM, and 41.8 µM in 2002 to 37.5 µM, 1.3 µM, and 82.2 µM in 2006, respectively, while TP decreased from 2.1 µM to 1.7 µM. The concentration of dissolved reactive silica (DRSi) had no major fluctuations and the differences were not significant. The mean concentration of DRSi in the total study area ranged from 52.5 to 92.3 µM. The Si:N ratio decreased significantly from 2.7 in 2002 to 1.3 in 2006, while TN:TP ratio increased from 22.1 to 80.3. The area of potential P limitation of phytoplankton growth expanded after 2003 and potential Si limitation appeared in 2005 and 2006. Potential P limitation mainly occurred in an area of salinity less than 30 after 2003, while potential Si limitation occurred where the salinity was greater than 30. By comparison with historical data, the concentrations of nitrate and SRP in this upper estuary during November 1980-2006 increased obviously after impoundment of TGD but DRSi decreased. Meanwhile, the ratios of N:P, Si:N and Si:P decreased obviously.     

Phosphorus in soils and field drainage water in the Thame catchment,UK

Field drains were sampled at five farms in a catchment in south-central England. The farms were selected to include the main soil types present in the catchment, stagnogleys and pelosols. The phosphorus content of field drainage water was measured on several occasions from 1999 to 2000, under varying flow conditions. The components measured were soluble reactive phosphorus (SRP), total dissolved phosphorus (TDP) and total phosphorus (TP). SRP concentrations in drainage water were lower than in streams in the catchment which had no apparent point source. This indicated that many streams were receiving unidentified point sources of SRP. Measurements of P in field drainage water samples under high flow conditions showed concentrations of particulate phosphorus and SRP up to 1300 and 300 μg l⁻¹, respectively, these being associated with high suspended sediment concentrations. Comparison of field drain and soil phosphorus contents at the locations sampled did not provide evidence of an inter-relationship. The equilibrium phosphorus content (EPC₀) of surface soil was generally higher than the SRP content of drainage water, at one farm by 1 order of magnitude. The variability in measurements suggested a larger-scale and more focussed survey would be required to characterise catchment-scale phosphorus losses from commercial farms by land use and soil type.     

Automated simultaneous monitoring of nitrate and nitrite in surface water by sequential injection analysis

A fully automated procedure based on Sequential Injection Analysis (SIA) methodology for simultaneous monitoring of nitrate and nitrite in surface water samples is described. Nitrite was determined directly using the Griess diazo-coupling reaction and the formed azo dye was measured at 540 nm in the flow cell of the fibre-optic spectrophotometer. Nitrate zone was passed through a reducing mini-column containing copperised-cadmium. After the reduction of nitrate into nitrite the sample was aspirated by flow reversal to the holding coil, treated with the reagent and finally passed through the flow cell. The calibration curve was linear over the range 0.05-1.00 mg N l(-1) of nitrite and 0.50-50.00 mg N l(-1) of nitrate; correlation coefficients were 0.9993 and 0.9988 for nitrite and nitrate, respectively. Detection limits were 0.015 and 0.10 mg N l(-1) for nitrite and nitrate, respectively. The relative standard deviation (RSD) values (n = 3) were 1.10% and 1.32% for nitrite and nitrate, respectively. The total time of one measuring cycle was 250 s, thus the sample throughput was about 14 h(-1). Nitrate and nitrite were determined in the real samples of surface water, and the results have been compared with those obtained by two other flow methods; flow injection analysis based on the same reactions and isotachophoretic determination used in a routine environmental control laboratory.     

Evaluation of a second derivative UV/visible spectroscopy technique for nitrate and total nitrogen analysis of wastewater samples

A method for nitrate analysis based on second derivative UV/Visible spectroscopy was developed by Simal et al. (1985: Simal J., Lage M. A., and Iglesias I. (1985) Second derivative ultraviolet spectroscopy and sulfamic acid method for determination of nitrates in water. J. Assoc. Analyt. Chem. 68, 962-964) and Suzuki and Kuroda (1987: Suzuki, N. and Kuroda R. (1987) Direct simultaneous determination of nitrate and nitrite by ultraviolet second-derivative spectrophotometry. Analyst 112, 1077-1079), and later modified for the analysis of total nitrogen in aqueous samples of varying nitrate:organic nitrogen ratios (Crumpton et al., 1992: Crumption W. G., Isenhart T. M. and Mitchell P. D. (1992) Nitrate and organic N analyses with second-derivative spectroscopy. Limnol. Oceanogr. 37, 907-913). The procedure uses the second derivative of the absorption spectrum for nitrate (NO3-), which has a peak at approximately 224 nm that is proportional to the NO3- concentration. Samples for total N analysis are first oxidized to NO3- by persulfate digestion. The objectives of this study were to: (1) test the accuracy and precision of the second derivative method through the use of NIST-traceable wastewater check samples; (2) determine whether the second derivative method for nitrate analysis can be used for wastewater samples and whether the method compares favorably with other currently used nitrate analysis methods; and (3) use the method to analyze wastewater samples containing a range of nitrate and total nitrogen concentrations. Our results indicated that the method needed to be modified to include a longer digestion time (60 min) and dilution of samples prior to digestion (if needed). With the modified method, nitrogen recoveries were not significantly different (P > or = 0.05) from samples with known N concentrations. In addition, nitrate concentrations in constructed wetland and wastewater samples analyzed by both second derivative spectroscopy and ion chromatography were not significantly different. Total nitrogen concentrations in wastewater samples also compared favorably to the same samples analyzed by Kjeldahl digestion. The method is faster, simpler, requires smaller sample volumes, and generates less waste than many EPA-approved methods of N analysis, and may offer a suitable alternative to current methods for analysis of nitrate and total N in wastewater samples.     

Relative importance of wastewater treatment plants and non-point sources of perfluorinated compounds to Washington State rivers

Perfluorinated compounds (PFCs) were measured in 10 Washington State rivers and 4 wastewater treatment plants (WWTPs) under periods of low and high flows to investigate the relative importance of point and non-point sources to rivers. PFCs were detected in all samples with summed values ranging from 1.11 to 74.9 ng/L in surface waters and 62.3-418 ng/L in WWTP effluent. Concentrations in 6 of the 10 rivers exhibited a positive relationship with flow, indicating runoff as a contributing source, with PFC loads greatest at all 10 waterbodies during high flows. Perfluoroheptanoic acid:perfluorooctanoic acid homologue ratios suggest atmospheric contributions to the waterbodies are important throughout the year. Principal component analysis (PCA) indicated distinct homologue profiles for high flow, low flow, and effluent samples. The PCA demonstrates that during the spring when flows and loads are at their greatest; WWTP discharges are not the primary sources of PFCs to the river systems. Taken together, the evidence provided signifies non-point inputs are a major pathway for PFCs to surface waters in Washington State.     

Transport of polycyclic aromatic hydrocarbons and pesticides during snowmelt within an urban watershed

During snowmelt events in urban watersheds large amounts of organic contaminants are mobilized, potentially affecting the quality of surface and groundwater resources. The transport of polycyclic aromatic hydrocarbons (PAHs) and two pesticides in the highly urbanized Highland Creek watershed within the city of Toronto, Canada, was investigated by sampling river water during two snowmelt periods. The dissolved and the particulate fractions were separately extracted and analyzed. While during normal flow conditions levels of the sum of nine PAHs including phenanthrene, anthracene, fluoranthene, pyrene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, indeno(1,2,3-c,d)pyrene, and benzo(ghi)perylene ranged between 18 and 45 ng/L, concentrations at the onset of melting varied from 550 to 4500 ng/L. Considering enhanced stream discharge rates during snowmelt the contaminant flux in the river increased by three orders of magnitude. The intensity of the melt event largely determined the extent of the PAH concentration increase in the river. The relatively water soluble pesticides chlorothalonil and lindane (γ-HCH) also tended to appear early during melting. Their enrichment in river water may be influenced by the thickness of the snow pack at the onset of melting, and the mode of melt water ablation from the snow pack to the stream, i.e. whether it occurs by overland or sub-surface flow.