Nitrification,soil acidification and streamwater chemistry following deglaciation,glacier bay national park and preserve

A major tool used in the assessment of anthropic atmospheric effects on aquatic and terrestrial ecosystems is biogeochemical nutrient cycling and budgets. However, to be most effective such study should be done in an ecosystem context. Also some assessment of natural variation in factors affecting nutrient cycling must be in place before trends, often subtle and long-term, attributable to man can be statistically quantified. The input and output balance of chemical species in watershed ecosystems is considerably influenced by ecosystem succession. It is hypothesized that during primary ecosystem succession chemical element output is initially relatively high due to rapid acidification and lack of plant uptake. Outputs decline during the period of high ecosystem productivity and biomass accumulation, and they again rise during late successional stages to approximate inputs from precipitation weathering, and aerosol capture. Glacier Bay provides a unique opportunity to quantify many mechanisms responsible for variation in nutrient cycles without the need for site manipulation. This is especially true for quantifying the rate and magnitude of natural acidification in ecosystems. The park has a spectrum of watersheds differing in stage of primary and secondary succession following deglaciation. These sites are not now subjected to or altered by anthropic atmospheric inputs. The objectives of this research were (1) determine the rate of soil chemical change which occurs following deglaciation, (2) relate soil acidification to presence of organic matter, soil NO _inf3 ^sup- , and total N, (3) estimate the downward movement of ionic species within the soil profiles with increasing acidification from advancing plant succession, and (4) determine if such processes and ionic movements might be reflected in watershed stream ionic outputs. We studied five watersheds ranging from 40–350 years since deglaciation. Soil samples were collected and lysimeters installed in seven vegetation successional stages following deglaciation. An anion of ecological importance and a common air contaminant is NO _inf3 ^sup- , and its discharge in streamflow from early successional ecosystems was found to be high. The terrestrial biota in such systems was dominated by Alnus sinuata, a major nitrogen fixer. Stream discharge of NO _inf3 ^sup- suggested that early successional ecosystem N fixation exceeded biotic uptake. This was confirmed by examining NO _inf3 ^sup- in soil extractions and lysimeters. This process was particularly evident beneath >20-year old Alnus (forty years since deglaciation). concurrent with increased NO _inf3 ^sup- concentrations below the rooting zone was increased H⁺ which increased 100x during 25 years of primary succession. This natural acidification from a mobile NO _inf3 ^sup- ion resulted in an pronounced increase in soil base cation leaching and mobilization of aluminium in the soil profile. The magnitude and short time required for such acidification greatly exceeded anything projected or modeled for systems impacted by anthropic inputs. Stream SO _inf4 ^sup2- concentrations also were high relative to precipitation inputs suggesting mineralization of sulfur within the ecosystem and/or poor soil adsorption of SO _inf4 ^sup2- . This is an important finding in such ecosystems where cation nutrient ion levels are often very low. Should atmospheric inputs of SO _inf4 ^sup2- increase additional loss of cations appears imminent. These data suggest that most early successional ecosystems at Glacier Bay would be sensitive to anthropic inputs of both NO _inf3 ^sup- and SO _inf4 ^sup2- . This is unusual in other ecosystems where many conserve ionic NO _inf3 ^sup- inputs, and older systems have considerable SO _inf4 ^sup2- adsorption capacity. The effect of any increased atmospheric inputs of these ions would be accelerated cation leaching and ecosystem acidification.Contribution from Fourth World Wilderness Congress—Acid Rain Symposium, Denver (Estes Park), Colorado, September 11–18, 1987.     

On density of precipitation chemistry networks

Using Scandinavian precipitation chemistry data the dependence of the accuracy of the interpolation and areal averaging of SO _inf4 ^sup2- , NO _inf3 ^sup- , NH _inf4 ^sup+ , and Ca²⁺ contents of precipitation water on the density of the network and on the size of the area considered is studied. On the basis of the results obtained the density of networks operating with a given accuracy can be determined as a function of the area. As an example the density of the networks determining the annual and monthly areal SO_f4/^p2- deposition as well as the point values of the monthly SO_f4/^p2- concentration with an accuracy of 10%, 25%, and 30%, respectively, is calculated. The accuracy provided by such networks for other components in precipitation water is also studied.     

Effects of acid deposition on watershed ecosystems of national parks in the great lakes basin

Legally protected national parks provide an appropriate substrate for essential long-term study of ecosystem structure and function, and for detecting trends in natural and human-induced stress. The absence of unplanned site manipulation in such areas is especially valuable for such research. Our present research has two major components. The first is the long-term ecosystem-level study of the effects of atmospheric contaminants on ecosystem processes. The overall objective is to evaluate ecosystem aquatic/terrestrial linkages and their role in establishing aquatic ecosystem sensitivity to anthropic atmospheric inputs. Four watershed/lake ecosystems, representative of much of the region's diversity, are under study. Two mature boreal sites on Isle Royale are characterized by first-order perennial surface stream input and lake outflow. Two additional mainland northern hardwood sites, one with shallow soils and one with soils derived from glacial till, are characterized by sensitive aquatic systems. One site is in a private reserve and the other in Pictured Rocks National Lakeshore. Surface outflow is gaged by Parshall flume and stage height recorder. Meteorological stations record variables for estimating evapotranspiration. One-tenth ha plots have been established in all watersheds and three sites have had intensive study of precipitation modification by canopy and forest soil. Five-year mean maximum and minimum lake pH varies from 6.85 to 4.94, Ca²⁺ from 1070 to 54 eq l^-1, K⁺ from 5.42 to 8.35 eq l^-1, NH ₄ ⁺ from 10.12 to 3.23 eq l^-1, HCO ₃ ^sup- from 635 to 24 eq l^-1, NO ₃ ^sup- from 3.27 to 1.54 eq l^-1, and SO ₄ ^sup2- from 110 to 52.7 eq l^-1. The relatively high NO ₃ ^sup- values observed in one lake are the result of stream drainage from a watershed dominated by Alnus rugosa, and another has high seasonal NO ₃ ^sup- inputs during spring runoff. However, owing to periodic winter thaws, significant snowpack release of nutrients generally precedes maximum spring stream runoff. Water chemistry in both sensitive and non-sensitive lakes appears to be primarily reflecting how the conterminous terrestrial system is retaining atmospheric inputs more than the quality of direct lake atmospheric input. This is especially evident for H⁺, NO ₃ ^sup- and SO ₄ ^sup2- .The second component is the assessment of watershed acidification, SO ₄ ^sup2- output and soil retention across an input gradient. An anthropic deposition gradient provides the opportunity for intersite time-trend analyses as to the effects of inputs. Our study objective was to see if the decreasing west to east input/output values for SO ₄ ^sup2- , noted in small first-order watersheds in national parks from Minnesota to Ohio, might be related to present atmospheric inputs, potential and total soil SO ₄ ^sup2- adsorption, or soil SO ₄ ^sup2- desorption from earlier higher inputs. Precipitation pH ranged from 5.05 at Fernberg, Minnesota to 4.24 at Wooster, Ohio. Minimum and maximum concentrations of NH ₄ ⁺ , NO ₃ ^sup- , SO ₄ ^sup2- and Cl^- were also found at these stations. Stream water concentrations of NO ₃ ^sup- and SO ₄ ^sup2- increase in a similar but sharper gradient. Streams are well buffered. Cation, HCO ₃ ^sup- , NO ₃ ^sup- and especially SO ₄ ^sup2- output increase west to east, but H⁺ output decreases. At the eastern site stream SO ₄ ^sup2- concentration and output exceed HCO ₃ ^sup- . Potential soil SO ₄ ^sup2- adsorption capacity increases eastward, but this capacity is filled. Crystalline Fe hydrous oxides appear more effective than amorphous Fe hydrous oxides at adsorbing SO ₄ ^sup2- . High anthropic anion inputs, inability of forest soil to adsorb additional inputs and perhaps SO ₄ ^sup2- desorption appear responsible for the replacement of HCO ₃ ^sup- by SO ₄ ^sup2- in stream water. The major cation accompanying SO ₄ ^sup2- is Ca²⁺.Contribution from Fourth World Wilderness Congress—Acid Rain Symposium, Denver (Estes Park), Colorado, September 11–18, 1987.     

The predicted effect of SO2 emission controls on the water quality of eastern Canadian lakes

Changes in SO _inf4 ^sup2- deposition predicted to occur in response to implementation of announced SO₂ emission control programs in Canada and the U.S.A. have been used as input to water chemistry models thereby giving an estimate of the changes in lake acid neutralizing capacity (ANC) and pH that can be expected from these programs. Eastern Canada has been divided into 22 subregions for the purpose of this analysis. Relative to the current level (1982–86) of SO _inf4 ^sup2- deposition (Scenario 1), the effect of the Canadian SO₂ emission control program alone (Scenario 2) is compared to that obtained when controls are implemented throughout North America (Scenarios 3 and 4). SO₂ emission reduction will effect a shrinkage of the high wet SO _inf4 ^sup2- deposition field in NE North America such that under Scenario 4 conditions, almost no area will remain in Canada that receives >20 kg ha^-1 yr^-1. The greatest decrease in deposition and resulting change in lake chemistry occurs in southern Ontario and southwestern Quebec. ANC distributions shift to higher concentrations and the percentage of lakes having pH<6 decreases in these areas. The Atlantic Provinces will obtain only a minor benefit from the control programs, i.e. experiencing only a small decrease in deposition and improvement in water quality. High sensitivity of the terrain in many parts of Atlantic Canada means that large numbers of lakes will remain acidic (i.e. ANC<0) and/or have pH<6 (an important biological threshold) even after full implementation of the current plans for SO₂ control in Canada and the U.S.     

The characteristics of size distribution of suspended particulates in the air for sulphates and selected metals in different areas and seasons

The characteristics of the distribution of particles by size were investigated for sulphates and selected metals (Pb, Fe, Mn, and Cu) in the air in two urban and an industrial area during the winter and summer periods using an Andersen cascade impactor.In the case of metals, but not sulphates, the character of the area affected the value of mass median diameter. Lowest values were obtained in a sparsely populated urban area, whereas in a densely populated urban area and in the industrial area the values were higher.In the industrial area a high correlation coefficient was found between sulphate and manganese, and between sulphate and lead, as well as a high value of the equivalent Mn²⁺/SO _inf4 ^sup2- ratio for the total sample. It may therefore be assumed that in the industrial area manganese produces a catalytic effect on SO₂ conversion to sulphate. Among the investigated metals lead stands out as a dominant cation which binds to the sulphate ion in the industrial and densely populated areas.     

Detection of sulphur dioxide in the air using Scotch pine needles

Air quality is especially important in surface layers, for it is this layer that provides the living components of environment with the needed oxygen and carbon dioxide. Various air polluting gases penetrate cells affecting and contaminating them. Chloroplast shell of some pine species, for instance, doubles under the impact of carbon dioxide which is followed by tillacoids swelling and reduction.Literature provides opinions of some authors, who consider Scotch pine needle to be a biological indicator of sulphur dioxide. Others object to it basing on the observations of physiological development.The property of a Scotch pine as that of biological indicator manifests in SO₂ absorption by its needles. The analysis of total content of SO₂ in the needles shows an increase of SO₂ concentration.Sulphur in the needles is found in the form of organically bound sulphur, aminoacids, hormones as well as in the form of sulphates.Basing on our previous analysis we have generalized the data on the correlation concentrations of sulphur dioxide in the air and general concentrations of sulphur in the needles. We have supplemented the observations with the analyses of organically bound sulphur and concentrations of nonorganic sulphur. According to research data, needles contain a characteristic and rather stable quantity of organically bound sulphur.So we may state that the SO _inf4 ^sup2– concentration and the amount of SO₂ absorbed from the air are interdependent.Some authors state that SO _inf4 ^sup2– content in the soil doesn't affect sulphur content in pine needles. That is why we studied the affect of SO _inf4 ^sup2– content in the soil on sulphur content in Scotch pine needles.We could prove this statement by means of various kinds of analyses only partially. The ion transport is affected by the presence of other ions, pH and a lot of other factors.What may be said for sure is that different qualities of soils gave only minor and insignificant deviations.Hence our assumption about the SO₂ contamination from air, proved by its effect on the soils, turns to suit approximate measurements.     

In search of a recyclable sulphur dioxide sponge—a new look at an old system

The sulphur dioxide content and thermal stability of the quinol-SO₂ clathrate have been studied by thermogravimetric analysis (TG), its derivative (DTG) and differential scanning calorimetry (DSC). These analyses demonstrated the thermal recoverability of the quinol from the clathrate and hence its potential use as a sponge for SO₂ present in the environment as a pollutant. Similarly, Bu₄N⁺I^- was found to occlude NO₂ and SO₂ at 50°C in solution.     

Evaluation of the effects of acid precipitation in eastern Canada using the raison system

Evaluations have been made of the key chemical factors in the aquatic effects upon surface waters due to acidic precipitation in eastern Canada. The region of Canada east of the Manitoba/Ontario border was divided into 22 aggregates and assessments of inorganic and organic ion chemistry appraised relative to sulphate deposition rates and distributions. Aquatic sensitivity is largely dominated by the concentration, distribution and magnitude of SO _inf4 ^sup2- (sulphate) deposition and by the prevalent geology and derived soils found in each aggregate. The RAISON system provided an adaptable and highly flexible platform to evaluate interactively, multiple data sets of divergent characteristics. Attributes usually associated with geographical information systems are significantly augmented by quantitative numerical and stochastic capabilities that were used extensively in this study.     

Gastro-enteric methane versus sulphate and volatile fatty acid production

The breakdown of low digestible components present in food during passage through the human and animal gastro-intestinal (GI) tract is performed by the highly diverse microbial community present in this ecosystem. Fermentation of these substances yields, besides CO₂ and volatile fatty acids, H₂, which is used as a substrate by three different H₂-consuming bacteria. Sulphate-reducing bacteria (SRB) use H₂ to reduce SO _inf4 ^sup2- to H₂S, hydrogenotrophic methane-producing bacteria (MPB) use H₂ to reduce CO₂ to CH₄ and reductive acetogens (RAC) use H₂ to reduce CO₂ to CH₃COOH. A competition between these three bacterial groups exists for the common H₂ substrate. This results generally in the dominance of one group above the other two.     

Evaluating the Applicability of Regulatory Leaching Tests for Assessing Lead Leachability in Contaminated Shooting Range Soils

The toxicity characteristic leaching procedure (TCLP) is the current US-EPA standard protocol to evaluate metal leachability in wastes and contaminated soils. However, application of TCLP to assess lead (Pb) leachability from contaminated shooting range soils may be questionable. This study determined Pb leachability in the range soils using TCLP and another US-EPA regulatory leaching method, synthetic precipitation leaching procedure (SPLP). Possible mechanisms that are responsible for Pb leaching in each leaching protocol were elucidated via X-ray diffraction (XRD). Soil samples were collected from the backstop berms at four shooting ranges, with Pb concentrations ranging from 5,000 to 60,600 mg kg⁻¹ soil. Lead concentrations in the TCLP leachates were from 3 to 350 mg l⁻¹, with all but one soil exceeding the USEPA non-hazardous waste disposal limit of 5 mg l⁻¹. However, continued dissolution of metallic Pb particles from spent Pb bullets and its re-precipitation as cerussite (PbCO₃) prevented the TCLP extraction from reaching equilibrium at the end of the standard leaching period (18 h). Thus, the standard one-point TCLP test would either over- or under-estimate Pb leachability in shooting range soils. Lead concentration in the SPLP leachates ranged from 0.021 to 2.6 mg l⁻¹, with all soils above the USEPA regulatory limit of 0.015 mg l⁻¹. In contrast to TCLP, SPLP leaching had reached equilibrium, with regard to both pH and Pb concentrations, within the standard 18 h leaching period, and the analytical SPLP results were in good agreement with those derived from modeling. Thus, we concluded that SPLP is a more appropriate alternative than TCLP for assessing lead leachability in range soils.     

The influence of pH on trace element uptake by an alga (Scenedesmus pannonicus subsp. Berlin) and Fungus (Aureobasidium Pullulans)

Experiments were carried oud in order to obtain information on the uptake characteristics of metals in the algal and fungus components of lichens. The uptake of ¹¹⁵Cd, ⁶⁵Zn, ⁶⁴Cu, ¹⁴⁰La, ¹⁸⁷W, ⁷⁵Se, and ⁷⁶As in the alga Scenedesmus pannonicus, subsp. Berlin and the fungus Aureobasidium pullulans was determined during 11 days of incubation at pH 5 and pH 7. The results indicate different acid-sensitivity of the alga and the fungus. The metal uptake in the alga was generally faster at pH 7, in the fungus uptake rates were higher at pH 5. In both the alga and the fungus for different pH-values hardly any differences in ultimate metal levels could be observed for Cd²⁺, Zn²⁺, La³⁺, and SeO _inf3 ^sup2- . In algae, the ultimate levels of the accumulated anionic forms of W and As appeared to be independent of pH; in the fungi the ultimate W and As levels were higher at pH 5. No differences could be observed in the Zn²⁺ accumulation capacities of both organisms. The As accumulation capacity of the alga was estimated to be about 10 times the As uptake capacity of the fungus. The results indicate the component-specific uptake and accumulatiom behaviour in intact lichens.     

Redistribution of zinc, cadmium, and lead among soil fractions in a sandy calcareous soil due to application of poultry litter

This study was conducted to evaluate, using soil columns, the mobilization and redistribution of heavy metals (Zn, Cd, and Pb) among different soil fractions by soluble organic ligands within poultry litter. Uncontaminated soil was amended with Zn, Cd, and Pb to achieve concentration levels of 400, 8, and 200 mg kg⁻¹ soil, respectively. Columns repacked with this amended soil were leached with distilled water, 0.01 M EDTA, 0.01 M CaCl₂, or poultry litter extract (PLE) solutions. After leaching, the soil samples in the columns were sequentially extracted for exchangeable (EXC), carbonate (CARB) organic matter (OM), Mn oxide (MNO), Fe oxide (FEO), and residual (RES) fractions. Considerable mobilization of Zn, Cd, and Pb occurred in soil during EDTA leaching. Leaching with PLE and CaCl₂ solutions significantly decreased Zn and Cd concentrations in the EXC, CARB, and OM fractions. These solutions significantly decreased Pb concentration in the EXC fraction, while PLE solubilized more Pb from EXC fraction than CaCl₂. Thus, the applied poultry litter may change Zn, Cd, and Pb fractions in metal-amended soil and possibly enhance metal mobility.     

The effects of salinity,temperature and sediment on the toxicity of copper to juvenile Hediste (Nereis) diversicolor (O. F. Muller)

Without sediment, increasing salinity (7.3 to 29.2) and increasing temperature (12 to 22 °C) reduced the toxicity of copper to juvenile Hediste diversicolor. The LC₅₀ values ranged from 357 gL^-1 in 7.3 to 513 g L^-1 in 29.2 at 12°C and from 247 to 500 g L^-1 at 22°C. In deionized water all the juvenile were dead in all solutions to which copper was added (100 to 600 g L^-1). Dead worms were swollen and everted their pharynxs. In higher doses of copper (500 to 600 g L^-1) the worms were abnormal in behaviour in all salinities (0 to 29.2). The ability to swim or crawl was disturbed.With sediments increasing temperature and increasing salinity increased the toxicity of copper to the worms. The LC₅₀ values ranged from 3200 to 4100 g L^-1 at 22°C. The response of the juvenile to copper was antagonistic to increasing temperature and salinity and synergistic to increasing salinity and increasing temperature without and with the sediment respectively.     

MODELING NITROGEN UPTAKE AND POTENTIAL NITRATE LEACHING UNDER DIFFERENT IRRIGATION PROGRAMS IN NITROGEN-FERTILIZED TOMATO USING THE COMPUTER PROGRAM NLEAP

Readily available nitrogen (N) sources such as ammonium nitrate with excessive irrigation present a potential hazard for the environment. The computer program Nitrate Leaching and Economic Analysis Package (NLEAP) is a mechanistic model developed for rapid site-specific estimates of nitrate-nitrogen (NO₃-N) moving below the root zone in agricultural crops and potantial impacts of NO₃-N leaching into groundwater. In this study, the value of NLEAP was tested to simulate N uptake by crops and NO₃-N leaching parameters in large lysimeters under the tomato crop. Three seedlings of tomato variety of H-2274 (Lycopersicum esculentum L.) were transplanted into each lysimeter. N fertilizer at the rate of 140 kg N ha^–1 was sidedressed in two split applications, the first half as ammonium sulphate and the second half as ammonium nitrate. The lysimeters were irrigated based on programs of C 0.75, 1.00, 1.25 and 1.50, C referring to class A-Pan evaporation coefficients. Parameters such as leaching index (LI), annual leaching risk potential (ALRP), N available for leaching (NAL), amount of NO₃-N leached (NL) and amount of N taken up by the crops (NU) were estimated using the NLEAP computer model. To test the ability of model to simulate N uptake and NL, measured values were compared with simulated values. Significant correlations, R² = 0.92 and P < 0.03 for the first year and R² = 0.86 and P < 0.06 for the second year, were found between measured and simulated values for crop N consumption, indicating that the NLEAP model adequately described crop N uptake under the varied irrigation programs using an optimal N fertilization program for the experimental site. Significant correlations, R² = 0.96 and P < 0.01 for the first year and R² = 0.97 and P < 0.01 for the second year, were also found between measured and simulated values of NL, indicating that the NLEAP model also adequately predicted NL under the varied irrigation programs. Therefore, this computer model can be useful to estimate the NO₃-N moving beyond the root zone under conditions in which the present experiment was carried out. Also, the NLEAP-estimated NAL values and other parameters can also be used to improve N management practices and N fertilizer recommendations that will help to decrease the adverse effect of N fertilizer on groundwater quality and farm profitability.     

Effect of Temperature on Absorption Efficiency of NO2 in Arsenite Method

The sodium arsenite method developed by Jacobs andHochheiser is one of the most widely used manualmethods for nitrogen dioxide (NO₂) monitoring inambient air, particularly in developing countries. Asreported, the method gives 82% NO₂ absorptionefficiency (NAE) in the concentration range from 40 to750 g/m³, when only one impinger tube isemployed in the sampling train at a flow rate of 0.2lpm and for 24 h sampling duration. Accordingly,a uniform correction factor (0.82) is used indenominator to calculate the ultimate concentration ofNO₂ in ambient air.In the present investigation, the effect oftemperature on absorption efficiency of NO₂ isstudied employing four impinger tubes in series tocollect the maximum NO₂ generated in the gasstream. The study conducted at 16, 26 and 36 °Ctemperatures shows maximum absorption efficiency(average) of 87.8% at 26°C in 1st impingertube. At lower and higher temperatures, it is foundconsiderably less. A suitable correction factor,therefore, must be applied to estimate actual NO₂concentration in ambient air using arsenite method, intropical countries like India, where atmospherictemperature variations are large (less than 5°Cin winter and more than 45°C in summer).     

Assessment of Temporal and Spatial Variation of Nitrate Removal in Riparian Zones

The aim of this study was to monitor long-term temporal and spatial groundwater NO₃^- removal efficiencies in different riparian zones via a limited number of sampling wells. Groundwater NO₃^- concentrations were measured fortnightly or monthly over a period of two years using transects of ground water sampling wells. Depending on the level of the NO₃^- load (up to 120mgNL^-1 at the input side of the riparian zone a distance of 10 to 30m was needed to remove NO₃^- from the groundwater below 11.3mgNL^-1. Considering all seasons, the mixed vegetation and grass riparian site succeeded to remove groundwater NO₃^- efficiently (92—100% within a distance of 30m. The forested riparian zone removed 72—90% of the total NO₃^- input within a distance of 30m. Evidence emerged that NO₃^- could also be removed actively at depths up to 2m, due to the presence of organically enriched layers of alluvial deposits or roots. Our four dimensional approach (three dimensional space and time), in combination with a limited number of sampling wells, was shown to be a useful monitoring tool to assess the variability of NO₃^- removal in riparian zones.     

An overview of the acidification of lakes in Atlantic Canada

Analysis of water chemistry from a sample of lakes (1300) in Atlantic Canada has indicated that lakes in geologically sensitive portions of Nova Scotia and Newfoundland have been acidified due to the combined effects of natural organic acids and anthropogenically derived mineral acids. Principal component analysis of six measured variables (pH, Ca, Conductance, SO _inf4 ^sup* , Alkalinity, Colour) and one computed variable (Alk/Ca^*+Mg^*) for each province result in four components which retain at least 89% of the original variability. Cluster analysis of the four principal components resulted in 6 lake groups for New Brunswick and 8 groups for Nova Scotia and 7 groups for Newfoundland. Geographic ordination of these clusters indicates that there is good correspondence between cluster group and the underlying bedrock geology of the region.     

Comparisons of Geochemical Signatures of Biotransformation of Fuel Hydrocarbons in Groundwater

Biotransformation processes play an active role in reducing the environmental impact of fuel hydrocarbon releases to groundwater. Because monitoring data at release locations are typically sparse, spatial variations in geochemical indicator parameters are often called upon as indirect evidence of biotransformation. These parameters include concentrations of electron acceptors (O₂, NO₃ ^-, SO> ₄ ^2- , reduced redox reaction by-products (Fe²⁺, Mn²⁺, CH₄), as well as bicarbonate alkalinity, pH and E_h. However, background variability in a number of these parameters complicates the task of data interpretation, particularly in the case of small data sets. In this study, correlation analyses are applied to geochemical indicator data at six hydrocarbon groundwater contamination sites in California to identify which parameters are the most reliable indicators. The results of the analyses suggest that the most direct indicators of the local redox environment – Fe²⁺, Mn²⁺, CH₄, E_h – yield the most consistent evidence of hydrocarbon biotransformation. Indicators which rely largely on mass balance – O₂, NO ₃ ^- , SO ₄ ^2- , alkalinity – appear to be less reliable. These findings may provide guidance in both the collection and interpretation of groundwater monitoring data at hydrocarbon contamination sites.     

Leaching behavior of nitrogen in a long-term experiment on rice under different N management systems

The leaching behavior of nitrogen was studied in single rice paddy production ecosystems in Tsukuba, Japan after 75 years of consistent fertilization regimes (no fertilizer, ammonium sulfate, a combination of composted rice straw with soybean cake, and fresh clover). During the 75-year period, management was unchanged with respect to rice planting density, irrigation, and net N fertilization for each field to which an N-source was added. Percolation water was collected, from May 2001 to April 2002, using porous suction cups installed in the fields at depths of 15, 40, and 60 cm. All water samples were taken to the laboratory for the measurement of both NH₄ ^?+??CN and NO₃ ^????CN concentrations using a continuous-flow nitrogen analyzer. The result indicated that there were significant differences in N leaching losses between treatments during the rice growing season. Total N leaching was significantly lower with the application of composted rice straw plus soybean cake (0.58 kg N ha^???1) than with ammonium sulfate (2.41 kg N ha^???1), which resulted in N leaching at a similar level to that with the fresh clover treatment (no significant difference). The majority of this N leaching was not due to NO₃ ^????CN loss, but to that of NH₄ ^?+??CN. The mean N leaching for all fertilizer treatments during the entire rice growing season was 1.58 kg N ha^???1. Composted rice straw plus soybean cake produced leaching losses which were 65?C75% lower than those with the application of fresh clover and ammonium sulfate. N accumulation resulting from nitrification in the fallow season could be a key source of nitrate?CN leaching when fields become re-flooded before rice transplanting in the following year; particular attention should be paid to this phenomenon.     

Spatial and seasonal distribution of nitrogen in marsh soils of a typical floodplain wetland in Northeast China

Horizontal and profile distributions of nitrogen in marsh soils in different seasons were studied in a typical site within the Erbaifangzi wetland in Northeast China. Results showed that there was higher spatial heterogeneity for nitrate nitrogen (NO₃^--_{3}^{-}-N) and ammonium nitrogen (NH₄⁺_{4}^{+}–N), as well as available nitrogen (AN), in surface soils in July compared to that in September. Relative to July, the mean nitrogen contents in surface soils were slightly higher in September; however, in November, soils contained significantly lower NO₃^--_{3}^{-}-N and NH₄⁺_{4}^{+}–N, higher AN, organic nitrogen (Org-N), and total nitrogen (TN). Except for mineral nitrogen, no significant differences were observed between Org-N and TN contents in September and November. Nitrogen contents generally declined exponentially with depth along soil profiles in three sampling dates (July, September, and November), except for a significant accumulation peak of NO₃^--_{3}^{-}-N at the 20–30 cm depth in September. However, NH₄⁺_{4}^{+}–N contents showed a vertical alternation of “increasing and decreasing” in both July and September, while nearly kept constant with depth in November. The depth ranking of nitrogen showed the shallowest distribution for AN, followed by Org-N and TN, while deeper distributions for NO₃^--_{3}^{-}-N and NH₄⁺_{4}^{+}–N. TN, Org-N, and AN were significantly correlated with soil organic matter and total phosphorus. Soil pH values were significantly correlated with TN and AN contents in surface soils. Clay contents showed significant correlations with nitrogen contents except for NO₃^--_{3}^{-}-N in surface soils and NH₄⁺_{4}^{+}–N in profile soils. However, soil moisture was not significantly correlated with nitrogen contents among all soil samples.