Sum Of Nitrate Research Articles

Effects of residence time on summer nitrate uptake in mississippi river flow‐regulated backwaters

AbstractNitrate uptake may be improved in regulated floodplain rivers by increasing hydrological connectivity to backwaters. We examined summer nitrate uptake in a series of morphologically similar backwaters on the Upper Mississippi River receiving flow‐regulated nitrate loads via gated culverts. Flows into individual backwaters were held constant over a summer period but varied in the summers of 2003 and 2004 to provide a range of hydraulic loads and residence times (τ). The objectives were to determine optimum loading and τ for maximum summer uptake. Higher flow adjustment led to increased loading but lower τ and contact time for uptake. For highest flows, τ was less than 1 day resulting in lower uptake rates (Unet < 300 mg m−2 day−1), low uptake efficiency (U% < 20%) and a long uptake length (Snet > 4000 m). For low flows, τ was greater than 5 days and U% approached 100%, but Unet was 200 mg m−2 day−1. Snet was < half the length of the backwaters under these conditions indicating that most of the load was assimilated in the upper reaches, leading to limited delivery to lower portions. Unet was maximal (384–629 mg m−2 day−1) for intermediate flows and τ ranging between 1 and 1.5 days. Longer Snet (2000–4000 m) and lower U% (20–40%) reflected limitation of uptake in upper reaches by contact time, leading to transport to lower reaches for additional uptake. Uptake by ∼10 000 ha of reconnected backwaters along the Upper Mississippi River (13% of the total backwater surface area) at a Unet of ∼630 mg m−2 day−1 would be the equivalent of ∼40% of the summer nitrate load (155 mg day−1) discharged from Lock and Dam 4. These results indicate that backwater nitrate uptake can play an important role in reducing nitrate loading to the Gulf of Mexico. Copyright © 2008 John Wiley & Sons, Ltd.

Trends of nitrogen in air and precipitation: Model results and observations at EMEP sites in Europe, 1980–2003

We analyze trends of some nitrogen compounds using long-term measurements and results from the EMEP (co-operative programme for monitoring and evaluation of the long-range transmissions of air pollutants in Europe) chemical transport model at EMEP sites. We find statistically significant declines at the majority of sites for NH x (sum of ammonia and ammonium) in air and for nitrate and ammonium in precipitation, but only at a few sites for xNO 3 (sum of nitrate and nitric acid) in air. Model calculations and measurements give similar results. We demonstrate that the lack of trends for xNO 3 in air at least partly can be attributed to a shift in the equilibrium between nitric acid and ammonium nitrate towards particulate phase, caused by reductions in the sulfur dioxide emissions.

Long-term Development of Inorganic Nutrients and Chlorophyllαin the Open Northern Baltic Sea

Eutrophication is an ongoing process in most parts of the Baltic Sea. This article reports on the changes during recent decades of several eutrophication-related variables in the open sea areas surrounding Finland (wintertime nutrient concentrations, wintertime nutrient ratios, and summer time chlorophyll alpha concentrations at the surface). The sum of nitrate- and nitrite-nitrogen ([NO3+NO2]-N) was observed to increase nearly fourfold in the Northern Baltic Proper and the Gulf of Finland and almost double in the Bothnian Sea from the 1960s until the 1980s or 1990s. The increase was followed by a decrease, which was modest in the two former subregions. Phosphate-phosphorus (PO4-P) concentrations followed a similar pattern in the Northern Baltic Proper (threefold increase and subsequent slight decrease) and Bothnian Sea (30% increase and subsequent decrease), but increased throughout the study in the Gulf of Finland, with the present concentration being threefold to the measurements made in the early 1970s. The PO4-P concentration decreased throughout the study in the Bothnian Bay. Silicate-silicon (SiO4-Si) concentrations decreased 30-50% from the early 1970s to the late 1990s and increased 20-40% thereafter in the Northern Baltic Proper, the Gulf of Finland, and the Bothnian Sea. Chlorophyll alpha showed an increase of over 150% in the Northern Baltic Proper and the Gulf of Finland from the 1970s until the early 2000s. In the Bothnian Sea the chlorophyll alpha concentration increased more than 180% from the late 1970s until the late 1990s, and decreased thereafter. According to these long-term observations, the Gulf of Finland and Northern Baltic Proper show clear signs of eutrophication, which may be emphasized by hydrographical changes affecting the phytoplankton communities and thus the algal biomass.

Denitrification rate determined by nitrate disappearance is higher than determined by nitrous oxide production with acetylene blockage

A mixed beech and spruce forest soil was incubated under potential denitrification assay (PDA) condition with 10% acetylene (C 2H 2) in the headspace of soil slurry bottles. Nitrous oxide (N 2O) concentration in the headspace, as well as nitrate, nitrite and ammonium concentrations in the soil slurries were monitored during the incubation. Results show that nitrate disappearance rate was higher than N 2O production rate with C 2H 2 blockage during the incubation. Sum of nitrate, nitrite, and N 2O with C 2H 2 blockage could not recover the original soil nitrate content, showing an N imbalance in such a closed incubation system. Changes in nitrite and ammonium concentration during the incubation could not account for the observed faster nitrate disappearance rate and the N imbalance. Non-determined nitric oxide (NO) and N 2 production could be the major cause, and the associated mechanisms could vary for different treatments. Commonly applied PDA measurement likely underestimates the nitrate removal capacity of a system. Incubation time and organic matter/nitrate ratio are the most critical factors to consider using C 2H 2 inhibition technique to quantify denitrification. By comparing the treatments with and without an antibiotic, the results suggest that microbial N uptake probably played a minor role in N balance, and other denitrifying enzymes but nitrate reductase could be substantially synthesized during the incubation.

Measurement Uncertainty of Sulphur and Nitrogen Containing Inorganic Compounds By 1-Stage and 2-Stage Filter-pack Methods

The sampling and analysis properties of 1-stage and 2-stage filter-pack methods were studied in detail in monitoring of sulphur and nitrogen containing inorganic gases and particles (sulphur dioxide, sulphate, sum of nitric acid and nitrate and total ammonium). The limit of detection and the limit of quantitation for 24-h samples were estimated using the results of a short-term field experiment completed with available data from long-term monitoring and internal quality assurance. Furthermore, the combined expanded measurement uncertainty including sampling and analysis (Utot) was estimated for filter-pack methods in order to give a tool for distinguishing long-term trends in air quality from the measurement variability. Utot was found to be very near the analytical uncertainty when measuring higher air concentration levels, being ± 4.0% for sulphur concentrations > 1.0 μg m−3, ± 3.0% for sulphate concentrations > 0.5 μg m−3, ± 3.5% for the sum of nitrate and nitric acid concentrations > 0.3 μg m−3 and ± 4.5% for total ammonium concentrations > 0.8 μg m−3. At the lower air concentration range Utot increases significantly due to the field blank values. The precision of the 24-h filter-pack sample results expressed by means of modified median absolute difference (M.MAD) and coefficient of variance (CoV) gave 8.3% for sulphur dioxide and 5.4% for particulate sulphate. For the sum of gaseous nitric acid and particulate nitrate the CoV was 5.5% and for total ammonium 4.3%. In addition the suitability of the 24-h filter-pack methods in weekly sampling was proved.

Spatial and temporal variations in airborne particulate matter (PM 10 and PM 2.5) across Spain 1999–2005

Average ranges of particulate matter (PM 10 and PM 2.5) concentrations and chemical composition in Spain show significant variations across the country, with current PM 10 levels at several industrial and traffic hotspots exceeding recommended pollution limits. Such variations and exceedances are linked to patterns of anthropogenic and natural PM emissions, climate, and reactivity/stability of particulate species. PM 10 and PM 2.5 concentrations reach 14–22 μg PM 10 m −3 and 8–12 μg PM 2.5 m −3 at most rural/regional background sites, 25–30 μg PM 10 m −3 and 15–20μg PM 2.5 m −3 at suburban sites, 30–46 μg PM 10 m −3 and 20–30 μg PM 2.5 m −3 at urban background and industrial sites, and 46–50 μg PM 10 m −3 and 30–35 μg PM 2.5 m −3 at heavy traffic hotpots. Spatial distributions show sulphate and carbon particle levels reach maxima in industrialised areas and large cities (where traffic emissions are higher), and nitrate levels increase from the Atlantic to the Mediterranean (independent of the regional NO x emissions). African dust outbreaks have an influence on the number of exceedances of the daily limit value, but its additional load on the mean annual PM 10 levels is only highly significant in Southern Iberia and Canary and Balearic islands. The marine aerosol contribution is near one order of magnitude higher in the Canaries compared to the other regions. Important temporal influences include PM intrusion events from Africa (more abundant in February–March and spring–summer), regional-scale pollution episodes, and weekday versus weekend activity. Higher summer insolation enhances (NH 4) 2SO 4 but depletes particulate NO 3 − (as a consequence of the thermal instability of ammonium nitrate in summer) and Cl − (due to HCl volatilisation resulting from the interaction of gaseous HNO 3 with the marine NaCl), as well as generally increasing dry dust resuspension under a semi-arid climate. Average trace metal concentrations rise with the highest levels at industrial and traffic hotspots sites, in some cases (Ti, Cr, Mn, Cu, Zn, As, Sn, W, and Pb) exceeding rural background levels by over an order of magnitude.

Nitrogen budget in a microbial mat in the Camargue (southern France)

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 322:75-84 (2006) - doi:10.3354/meps322075 Nitrogen budget in a microbial mat in the Camargue (southern France) Patricia C. Bonin*, Valerie D. Michotey Laboratoire de Microbiologie, de Géochimie et d’Ecologie Marine, CNRS-UMR 6117, Centre d’Océanologie de Marseille, Campus de Luminy, Case 901, 13288 Marseille Cedex 9, France *Email: pbonin@com.univ-mrs.fr ABSTRACT: The main processes associated with the nitrogen cycle were studied in a microbial mat and in the surrounding water during winter (January), spring (March) and summer (June) in the Camargue (southeastern France). Denitrification, nitrogen fixation, nitrification, dissimilative reduction of nitrate, together with mineralization and ammonium assimilation, were measured under dark and light conditions using inhibitor and nitrogen isotope (15N). All these microbial processes were expressed in the mat. The isotope pairing method allowed the identification of the source of denitrified nitrate. It appeared that a major part of the nitrate formed by nitrification was denitrified and that nitrification was a considerable source of nitrate in spring and summer. From variations in net flux (fixation versus denitrification activities), we conclude that the mat acted as a nitrogen source in summer, but as a sink in winter. KEY WORDS: Nitrogen cycle · Denitrification · Microbial mat Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 322. Online publication date: September 20, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Seasonal variations in nutrients and chlorophyll-a concentrations in the Northern east China sea

Nutrients, chlorophyll-a, particulate organic carbon (POC), and environmental conditions were extensively investigated in the northern East China Sea (ECS) near Cheju Island during three seasonal cruises from 2003 to 2005. In spring and autumn, relatively high concentrations of nitrate (2.6~12.4 μmol kg-1) and phosphate (0.17~0.61 μmol kg-1) were observed in the surface waters in the western part of the study area because of the large supply of nutrients from deep waters by vertical mixing. The surface concentrations of nitrate and phosphate in summer were much lower than those in spring and autumn, which is ascribed to a reduced nutrient supply from the deep waters in summer because of surface layer stratification. While previous studies indicate that upwellings of the Kuroshio Current and the Changjiang (Yangtze River) are main sources of nutrients in the ECS, these two inputs seem not to have contributed significantly to the build-up of nutrients in the northern ECS during the time of this study. The lower nitrate:phosphate (N:P) ratio in the surface waters and the positive correlation between the surface N:P ratio and nitrate concentration indicate that nitrate acts as a main nutrient limiting phytoplankton growth in the northern ECS, contrary to previous reports of phosphate-limited phytoplankton growth in the ECS. This difference arises because most surface water nutrients are supplied by vertical mixing from deep waters with low N:P ratios and are not directly influenced by the Changjiang, which has a high N:P ratio. Surface chlorophyll-a levels showed large seasonal variation, with high concentrations (0.38~4.14 mg m-3) in spring and autumn and low concentrations (0.22~1.05 mg m-3) in summer. The surface distribution of chlorophyll-a coincided fairly well with that of nitrate in the northern ECS, implying that nitrate is an important nutrient controlling phytoplankton biomass. The POC:chlorophyll-a ratio was 4~6 times higher in summer than in spring and autumn, presumably because of the high summer phytoplankton death rate caused by nutrient depletion in the surface waters.

An analysis of spatial and temporal properties of daily sulfate, nitrate and chloride concentrations at UK urban and rural sites

Daily measurements of sulfate, nitrate and chloride in PM(10) have been made at three geographically separated UK sites over a three year period. Chloride shows a clear seasonal pattern with highest concentrations in winter, whilst sulfate and nitrate both show highest concentrations in the spring, apparently related to weather patterns. Spatial variability of both sulfate and nitrate is low in comparison to temporal variations, with high correlations of both species between all three sites, London (North Kensington), Harwell and Belfast, despite a geographic separation of 510 km. Both SO/SO(2) and NO/NO(x) ratios are considerably higher in summer than winter, reflecting a greater oxidising capacity of the atmosphere. SO(4)(2-)/NO(3)(-) ratios are higher in summer than winter, suggesting that aqueous phase oxidation of SO(2), expected to be most important in the winter months is not appreciably influencing production of sulfate aerosol, although greater dissociation of ammonium nitrate in summer may also play a role. Regression of concentrations at London, North Kensington with those from the proximate rural site of Harwell is interpreted as showing a similar effect of regional transport at the two sites and a small influence of local formation in the urban atmosphere or primary emissions, averaging 0.46 microg m(-3) of nitrate and 0.22 microg m(-3) of sulfate.

Antiphospholipid antibodies are associated with enhanced oxidative stress, decreased plasma nitric oxide and paraoxonase activity in an experimental mouse model

Oxidative stress contributes to atherosclerosis, and evidence of enhanced oxidative stress exists in antiphospholipid syndrome (APS). In a non-lupus murine model, we evaluated whether anticardiolipin (aCL) antibodies could affect the oxidant/antioxidant balance as an early biochemical step of APS. Hybridomas producing human and murine aCL and anti-beta(2)-glycoprotein I (abeta2-GPI) monoclonal antibodies were injected into three groups of five female BALB/c severe combined immunodeficiency (SCID) mice. Corresponding hybridomas secreting non-antiphospholipid antibodies of the same isotype were employed as controls. Sera and organs were collected after 30 days. Paraoxonase (PON) activity, peroxynitrite, superoxide, nitric oxide (NO) and nitrotyrosine were measured in plasma. Expression of endothelial nitric oxide synthase and inducible nitric oxide synthase (iNOS) was assessed by western blot and immunohistochemistry. PON activity and NO (sum of nitrate and nitrite) levels were reduced in the human aCL IgG group (P<0.002 and P<0.04, respectively), whilst peroxynitrite and superoxide and expression of total antioxidant capacity of plasma were increased (P<0.01). PON and NO were decreased in the murine abeta2-GPI IgG and IgM aCL groups (P<0.03 and P<0.05, respectively). Nitrotyrosine was elevated in the human aCL IgG group (P<0.03). Western blotting showed reduced iNOS expression in the hearts of the IgG aCL group, confirmed by immunostaining. PON inversely correlated with IgG aCL titres (P<0.001), superoxide (P<0.008) and peroxynitrite levels (P<0.0009). Peroxynitrite and total IgG aCL were independent predictors of PON (P<0.0009 and P<0.02, respectively). Superoxide was the only independent predictor of NO (P<0.008) and of nitrotyrosine (P<0.002). aCL antibodies are associated with the decreased PON activity and reduced NO that may occur in the preclinical phase of APS.

High-resolution ice cores from US ITASE (West Antarctica): development and validation of chronologies and determination of precision and accuracy

AbstractShallow ice cores were obtained from widely distributed sites across the West Antarctic ice sheet, as part of the United States portion of the International Trans-Antarctic Scientific Expedition (US ITASE) program. The US ITASE cores have been dated by annual-layer counting, primarily through the identification of summer peaks in non-sea-salt sulfate (nssSO42–) concentration. Absolute dating accuracy of better than 2 years and relative dating accuracy better than 1 year is demonstrated by the identification of multiple volcanic marker horizons in each of the cores, Tambora, Indonesia (1815), being the most prominent. Independent validation is provided by the tracing of isochronal layers from site to site using high-frequency ice-penetrating radar observations, and by the timing of mid-winter warming events in stable-isotope ratios, which demonstrate significantly better than 1 year accuracy in the last 20 years. Dating precision to ±1 month is demonstrated by the occurrence of summer nitrate peaks and stable-isotope ratios in phase with nssSO42–, and winter-time sea-salt peaks out of phase, with phase variation of &lt;1 month. Dating precision and accuracy are uniform with depth, for at least the last 100 years.

Attenuation of insulin-Mediated pressor effect and nitric oxide release in rats with fructose-Induced insulin resistance

Hyperinsulinemia and insulin resistance frequently coexist and have been implicated in the pathogenesis of hypertension. This study aimed to identify the specific effect of hyperinsulinemia on blood pressure and nitric oxide (NO) release in fructose-induced hyperinsulinemic, insulin-resistant rats. Male Sprague-Dawley rats were fed either standard chow or a 60% fructose-enriched diet for 8 weeks before acute study. After basal period, somatostatin (1.3 microg/kg/min) and a variable glucose infusion (to maintain euglycemia) were given intravenously to all groups of rats. In control rats (C) and fructose-fed rats (F) with insulin infusion, insulin (4 mU/kg/min) was given to create a similar hyperinsulinemic condition. In C and F without insulin infusion, a vehicle instead of insulin was infused to produce a hypoinsulinemic state. In C, somatostatin reduced plasma insulin level but did not alter mean arterial pressure (MAP) and heart rate. Insulin infusion significantly increased MAP and NOx (sum of nitrate and nitrite) levels after 90 min and thereafter the elevated MAP and NOx responses were sustained throughout the study. In the basal period, F exhibited significantly higher MAP and plasma insulin levels than C. The index of insulin sensitivity (M) was significantly lower in F than in C with insulin infusion. Somatostatin significantly reduced plasma insulin level but did not affect MAP and NOx level in F. The stimulatory effects of insulin on MAP and NO levels were significantly smaller in F than in C. In conclusion, acute insulin-induced pressor response and NO release were attenuated in rats with fructose-treated insulin resistance, suggesting that hyperinsulinemia-associated attenuation of NO production contributes, at least partly, to the development of fructose-induced hypertension in rats.

Simple flow-injection system for the simultaneous determination of nitrite and nitrate in water samples

A novel spectrophotometric reaction system was developed for the determination of nitrite as well as nitrate in water samples, and was applied to a flow-injection analysis (FIA). The spectrophotometric flow-injection system coupled with a copperised cadmium reductor column was proposed. The detection was based on the nitrosation reaction between nitrite ion and phloroglucinol (1,3,5-trihydroxybenzene), a commercially available phenolic compound. Sample injected into a carrier stream was split into two streams at the Y-shaped connector. One of the streams merged directly and reacted with the reagent stream: nitrite ion in the samples was detected. The other stream was passed through the copperised cadmium reductor column, where the reduction of nitrate to nitrite occurred, and the sample zone was then mixed with the reagent stream and passed through the detector: the sum of nitrate and nitrite was detected. The optimised conditions allow a linear calibration range of 0.03–0.30 μg NO 2 −-N ml −1 and 0.10–1.00 μg NO 3 −-N ml −1. The detection limits for nitrite and nitrate, defined as three times the standard deviation of measured blanks are 2.9 ng NO 2 −-N ml −1 and 2.3 ng NO 3 −-N ml −1, respectively. Up to 20 samples can be analyzed per hour with a relative standard deviation of less than 1.5%. The proposed method could be applied successfully to the simultaneous determination of nitrite and nitrate in water samples.

Aerosol Ion Characteristics During the Big Bend Regional Aerosol and Visibility Observational Study

The ionic compositions of particulate matter with aerodynamic diameter ≤2.5 μm (PM2.5) and size-resolved aerosol particles were measured in Big Bend National Park, Texas, during the 1999 Big Bend Regional Aerosol and Visibility Observational study. The ionic composition of PM2.5 aerosol was dominated by sulfate (SO4 2−) and ammonium (NH4 +). Daily average SO4 2− and NH4 + concentrations were strongly correlated (R2 = 0.94). The molar ratio of NH4 + to SO4 2− averaged 1.54, consistent with concurrent measurements of aerosol acidity. The aerosol was observed to be comprised of a submicron fine mode consisting primarily of ammoniated SO4 2− and a coarse particle mode containing nitrate (NO3 −). The NO3 − appears to be primarily associated with sea salt particles where chloride has been replaced by NO3 −, although formation of calcium nitrate (Ca(NO3)2) is important, too, on several days. Size-resolved aerosol composition results reveal that a size cut in particulate matter with aerodynamic diameter ≤1 μm would have provided a much better separation of fine and coarse aerosol modes than the standard PM2.5 size cut utilized for the study. Although considerable nitric acid exists in the gas phase at Big Bend, the aerosol is sufficiently acidic and temperatures sufficiently high that even significant future reductions in PM2.5 SO4 2− are unlikely to be offset by formation of particulate ammonium nitrate in summer or fall.

A seasonally resolved alpine ice core record of nitrate: Comparison with anthropogenic inventories and estimation of preindustrial emissions of NO in Europe

Continuous high‐resolution records from Col du Dôme (CDD, 4250 m above sea level, French Alps) ice cores were used to investigate the impact of growing NO emissions on the midtroposphere nitrate levels over Europe from 1925 to 1997. The large snow accumulation rate at the CDD site largely minimized diffusional and depositional perturbations of the nitrate record as commonly encountered in ice cores. That permits for the first time examination of the winter and summer trends separately with a high degree of confidence. Being close to 100 ng g−1 in 1925, summer levels increased at a mean rate of 2 ng g−1 per year from 1925 to 1960 and 8.5 ng g−1 yr−1 from 1960 to 1980. These summer nitrate changes follow rather well the course of growing NO emissions from source regions (France, Italy, Spain, and Switzerland, denoted WE4) located 1000 km around the Alps as estimated by NMI and EDGAR‐HYDE inventories. After 1980, the summer nitrate levels continue to increase at a slightly weaker rate than during the 1960–1980 time period. Such a lasting increase of nitrate levels is inconsistent with NO emission estimates, which indicate a decrease after 1993. The nitrate record shows a weaker increase (1 ng g−1 yr−1 from 1930 to 1990) in winter than in summer, corresponding to a lower contamination of the European wide midtroposphere as preferentially recorded in CDD winter samples. Using ice core and emission data, we calculate a preindustrial NO emission (including agricultural and natural emissions) of 0.8 ± 0.2 Mt NO2 per year for WE4 countries, which represents 15–20% of the recent NO emissions. These data would help to reduce existing uncertainties in NO inventories which represent key information to assess past and future ozone changes over Europe.

Changes in the yield of chlorophyll a from dissolved available inorganic nitrogen after an enrichment event—applications for predicting eutrophication in coastal waters

An understanding of the dynamic relationship between nitrogen supply and the formation of phytoplankton biomass is important in predicting and avoiding marine eutrophication. This relationship can be expressed as the short-term yield q of chlorophyll from dissolved available inorganic nitrogen (DAIN), the sum of nitrate, nitrite and ammonium. This paper communicates the results of a continuous culture nitrate enrichment experiment undertaken to investigate the cumulative yield of chlorophyll from DAIN ( q). The purposes of the study were: to acquire a better understanding of the relationship between chlorophyll formation and DAIN; to obtain values that could be used in models for predicting eutrophication. The results of a time series experiment carried out using microplankton (all organisms <200 μm in size) indicate that the parameter q does not have a single value but is affected by the ecophysiological response of phytoplankton to changing nutrient status after an enrichment event. It is also dependent on changes in the allocation of nitrogen between autotrophs and heterotrophs. The value of yield obtained at the height of the bloom can be represented by q (max) (2.35 μg chl (μmol N) −1). The post-bloom, steady state value of q can be represented by q eq (0.95 μg chl (μmol N) −1). The microcosm steady state yield was not significantly different from the median value obtained from synoptic studies of Scottish west coast waters. It is proposed that q eq is the most appropriate value for assessing the general potential for eutrophication resulting from continuous nutrient enrichment into coastal waters. It is further proposed that q (max) be used for cases of sporadic enrichment and where a short burst of unrestricted growth may be detrimental.

Nutrient elimination in pre-dams: results of long term studies

The results of inflow–outflow investigations carried out at the pre-dams of Saidenbach Reservoir (southeast Germany) show that the nutrient elimination in pre-dams is largely controlled by biological processes, mainly by the phytoplankton growth, and strongly depends on the retention time. Average SRP-elimination rates of up to 80% in summer and 60% in the whole year were observed in a pre-dam of `optimum size', which confirms the theory well. However, the mean total P reduction was much lower and did not even exceed 25% in the largest pre-dam in summer, since settling of particulate P (fine disperse suspended matter, phytoplankton) was restricted by the short retention time. The highest average summer nitrate elimination rate of 16% was found in a very shallow pre-dam and was mainly the result of extremely high denitrification at the sediment. Dissolved Si removal was low as well and reached average summer rates of up to 15%. In was correlated to the SRP-elimination in two basins. Fast siltation reduced the retention time and nutrient elimination capacity of the pre-dams. Thus, sediments have to be removed regularly from pre-dams.

Spatial variation of aerosol properties over Europe derived from satellite observations and comparison with model calculations

Abstract. Aerosol optical depths (AOD) and Angström coefficients over Europe were retrieved using data from the ATSR-2 radiometer on board the ESA satellite ERS-2, for August 1997. Taking advantage of the nadir and forward view of the ATSR-2, the dual view algorithm was used over land to eliminate the influence of the surface reflection. Over sea the AOD was retrieved using only the forward observations. Retrieved aerosol optical properties are in good agreement with those from ground-based sunphotometers. The AOD and Angström coefficients together yield information on the column integrated effective aerosol distribution. Observed regional variations of the AOD and Angström coefficient are related to anthropogenic emissions of aerosol precursors such as SO2 and NOx in the major European industrial and urban areas, and their subsequent transformation into the aerosol phase. The influence of anthropogenic aerosols such as ammonium sulphate and ammonium nitrate on the total AOD is estimated using a regional chemistry transport model. Sulphate is estimated to contribute from 15% in very clean areas to 70% in polluted areas, the contribution of nitrate is between 5% and 25% over most of Europe. This paper shows the great importance of nitrate in summer over The Netherlands.

GROUND WATER NITRATE REDUCTION IN GIANT CANE AND FOREST RIPARIAN BUFFER ZONES1

ABSTRACT: Ground water contamination by excess nitrate leaching in row‐crop fields is an important issue in intensive agricultural areas of the United States and abroad. Giant cane and forest riparian buffer zones were monitored to determine each cover type's ability to reduce ground water nitrate concentrations. Ground water was sampled at varying distances from the field edge to determine an effective width for maximum nitrate attenuation. Ground water samples were analyzed for nitrate concentrations as well as chloride concentrations, which were used as a conservative ion to assess dilution or concentration effects within the riparian zone. Significant nitrate reductions occurred in both the cane and the forest riparian buffer zones within the first 3.3 m, a relatively narrow width. In this first 3.3 m, the cane and forest buffer reduced ground water nitrate levels by 90 percent and 61 percent, respectively. Approximately 40 percent of the observed 99 percent nitrate reduction over the 10 m cane buffer could be attributed to dilution by upwelling ground water. Neither ground water dilution nor concentration was observed in the forest buffer. The ground water nitrate attenuation capabilities of the cane and forest riparian zones were not statistically different. During the spring, both plant assimilation and denitrification were probably important nitrate loss mechanisms, while in the summer nitrate was more likely lost via denitrification since the water table dropped below the rooting zone.

Nutrient utilization ratios in the Polar Frontal Zone in the Australian sector of the Southern Ocean: A model

To investigate the non‐Redfield N/P depletion ratio in the Polar Frontal Zone (PFZ) of the Southern Ocean, we simulated the seasonal nitrate, phosphate, and silicate cycle in the upper ocean with a biophysical model. Total phytoplankton biomass was prescribed from the Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) estimates, and we included two phytoplankton types, diatoms and nondiatoms. We set the nondiatoms N/P uptake ratio to 16 while the diatoms N/P and N/Si ratios were determined by fitting the observed seasonal nitrate, phosphate, and silicate cycle in the mixed layer. The best model fit to the observations required an annual N/P utilization ratio of 13.2, but this low N/P ratio still overestimated the nitrate utilization during the summer. We considered three mechanisms for improving the simulated nitrate cycle: (1) seasonal variation in the N/P ratio of the horizontal nutrient supply to the PFZ, (2) different remineralization length scales for particulate organic nitrogen (PON) and particulate organic phosphorus (POP), and (3) seasonal accumulation and decomposition of labile dissolved and suspended organic matter (OM). Model simulations showed that the seasonal variability in the N/P ratio of horizontal supply failed to reduce the simulated excess nitrate utilization in summer. Preferential recycling of PON compared to POP below the mixed layer degrades the simulation and cannot produce results that satisfy both the observed seasonal nitrate and phosphate cycle in the mixed layer. The most realistic model simulation was obtained with preferential recycling of POP over PON, but this mechanism alone was incapable of satisfying the summer nitrate and phosphate data. With the inclusion of an OM pool in our model we were able to reproduce the observed seasonal mixed layer nitrate and phosphate cycles. Satisfactory results can be achieved through various combinations of the N/P ratio of OM and the lifetime of the OM. Seasonal observations of dissolved and suspended organic phosphorus, nitrogen and carbon are needed to confirm their role. The important conclusion of our model study is that in the PFZ the annual nutrient utilization ratio of nitrate to phosphate is considerably less than the classical Redfield value of 16.