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1.
We used ionic tracers to estimate the volume of old (soil and ground) water interacting with snowmelt in eleven Adirondack, NY watersheds. The contribution of old water varied from 66 to 90%, with no general relationship between old water % and soil depth to till. This approach also discriminated between watershed retention and release of particular ions to lake outlet water during snowmelt. Most watersheds released NO3 ? during snowmelt, in addition to the snowpack NO3 ?. Nitrification of snowpack NH4 + explained part of the additional NO3 ? in lake out outlet water, but some NO3 ? was likely mineralized nitrogen from soil organic matter. All watersheds retained NH4 + as well. Nitrogen release was greatest in the acidic watersheds in the southwestern Adirondacks, a region thought to be impacted by anthropogenic deposition. During snowmelt, Ca2+ and Mg2+ ions (presumably from soil exchange sites) were also released from most watersheds. In watersheds with acidic (minimum pH<4.6) lake outlet water, Al was also released during snowmelt. Thus, lake outlet water acidification during snowmelt was both buffered by cation release, and intensified by NO3 ? release. If the soil exchangeable cation pools were not replenished prior to snowmelt, or NO3 ? mobilization were increased, acidification during snowmelt would intensify.  相似文献   

2.
We determined the chemical compositions of acidic stream waters on the rural, mountainous island of Yakushima (YK), and compared them with those of near-neutral stream waters in other mountainous watersheds in Japan. The pH and concentrations of the predominant sea-salt components (i.e., Cl?, Na+, Mg2+) in YK water, particularly in streams with small watersheds, decrease with elevation, while the concentration of Al increases. In contrast, water in northwestern YK contains higher concentrations of non-sea-salt SO42? and NO3? and of rock-derived cations such as Si and Ca2+ than water in eastern to southern YK. This clearly shows that the anthropogenic pollutants on YK are dominantly derived from the northwestern to western Asian continent rather than from Japan's main islands, which lie to the northeast. These pollutants are responsible for stream acidification on YK and for accelerating chemical weathering, mainly of plagioclase, in northwestern YK. Large amounts of acid rain on YK may enhance the formation of secondary minerals that strongly adsorb heavy metals, which can partly account for the low concentrations of heavy metals in YK waters.  相似文献   

3.
The soil nitrogen cycle was investigated for several watershed forests of which stream waters have distinctively different nitrate (NO3 ?) concentrations. In a watershed with stream water NO3 ? of more than 100 µM, soil NO3 ? content increased even beneath the rooting zone, revealing "nitrogen saturation" status. A laboratory soil experiment demonstrated that the proportion of net NO3 ? production to CO2 production was largely regulated by a soil C/N ratio, suggesting a key parameter for NO3 ? abundance. In the respective watershed soils, little nitrogen was actually present as NO3 ? above a soil C/N ratio of 20. The annual mean soil temperature recorded at the sites was correlated with a shift in the C/N ratio in watershed soils (a soil C/N ratio increase of 0.5 per 1°C decrease) along the stream NO3 ? gradient of 30 fold. The results suggest that soil microbial metabolisms affected by C/N ratio may be a direct agent regulating NO3 ? leaching from watersheds under the influence of an atmospheric nitrogen load and climate.  相似文献   

4.
There is considerable interest in the recovery of surface waters from acidification by acidic deposition. The Adirondack Long-Term Monitoring (ALTM) program was established in 1982 to evaluate changes in the chemistry of 17 Adirondack lakes. The ALTM lakes exhibited relatively uniform concentrations of SO4 2?. Lake-to-lake variability in acid neutralizing capacity (ANC) was largely due to differences in the supply of basic cations (Ca2+, Mg2+, K+, Na+; CB) to drainage waters. Lakes in the western and southern Adirondacks showed elevated concentrations of NO3 ?, while lakes in the central and eastern Adirondacks had lower NO3 ? concentrations during both peak and base flow periods. The ALTM lakes exhibited seasonal variations in ANC. Lake ANC was maximum during the late summer or autumn, and lowest during spring snowmelt. In general Adirondack lakes with ANC near 100 Μeq L?1 during base flow periods may experience decreases in ANC to near or below 0 Μeq L?1 during high flow periods. The ALTM lakes have exhibited long-term temporal trends in water chemistry. Most lakes have demonstrated declining SO4 2?, consistent with decreases in SO2 emissions and SO4 2? in precipitation in the eastern U.S. Reductions in SO4 2? have not coincided with a recovery in ANC. Rather, ANC values have declined in some ALTM lakes. This pattern is most likely due to increasing concentrations of NO3 ? that occurred in most of the ALTM drainage lakes.  相似文献   

5.
Steam chemistry was investigated from May 1991 through April 1992 for 13 Japanese forested watersheds and from May 1990 through August 1994 for two of these watersheds. Nine watersheds were treated over different periods (1983–1991) with different amounts of N (nitrogen) fertilizer as urea and ammonium salts. Total N additions ranged from 20 to 375 kg ha-1. There were no distinct seasonal differences in stream NO3 - concentrations in either the treated or untreated watersheds, but concentrations tended to be somewhat higher during periods of high discharge. The annual average NO3 - concentrations in streams had a significant, positive (p < 0.001, r = 0.84) relationship to the total amount of N applied from 1985–1991. The application of 330 kg N ha-1 raised annual average stream NO3 - concentration to about 300 μeq L-1 compared to less than 160 μeq L-1 in untreated watersheds. The concentrations of K+, Ca2+, and Mg2+ in stream water also increased in those watersheds with high rates of N fertilizer as a result of nitrification that increased the generation of the mobile nitrate anion. The lack of seasonality in stream NO3 - concentrations and the large rates of N loss with N addition both suggest that these watersheds were ‘nitrogen saturated’  相似文献   

6.
Seasonal variation of NO3? concentration in xylem sap of the lower trunk part of beeches (Fagus sylvatica L.) From October 1988 to October 1989 five beech trees from a 35-year-old and a 42-year-old stand were felled in 14 day intervals. Xylem sap was extracted from the lower 100 cm of the trunk by means of liquid displacement. In general there was an increase of NO3? xylem sap concentrations in summer. Higher xylem sap nitrate concentrations were accompanied by an almost equal but opposite pH decrease. It is assumed that the rapid surge in NO3? concentration of the xylem sap was due to summer acidification pushes in the forest soil.  相似文献   

7.
Rain water at two forested sites in Guangzhou (south China) show high concentrations of SO4 2?, NO3 ? and Ca2+ and display a remarkable seasonal variation, with acid rain being more important during the spring and summer than during the autumn and winter. The amount of acid rain represents about 95% of total precipitation. The sources of pollutants from which acid rain developed includes both locally derived and long-middle distance transferred atmosphere pollutants. The seasonal variation in precipitation chemistry was largely related to the increasing neutralizing capacity of base cations in rainwater in winter. Soil acidification is highlighted by high H+ and Al3+ concentrations in soil solutions. The variation in elemental concentration in soil solution was related to nitrification (H+, NH4 + and NO3 ?) and cation exchange reaction (H+, Al3+) in soil. The negative effect of soil acidification is partly dampened by substantial deposition of base cations (Ca2+, Mg2+ and K+) in this area.  相似文献   

8.
Root development responds not only to the quantity of inorganic nitrogen in the rhizosphere, but to its form, NH4+ or NO3?. Root growth of tomato showed a hyperbolic response to soil levels of inorganic nitrogen: very few roots were found in soil blocks depleted in inorganic nitrogen, roots proliferated as soils increased to 2 μg NH4+-N g?1 soil or 6 μg NO3?-N g?1 soil, and root growth declined in soils with the higher levels of inorganic nitrogen. High NH4+ concentrations inhibited root growth, but low concentrations promoted the development of an extensive, fine root system. Supply with NO3? as the sole nitrogen source led to a more compact root system. These differences in root morphology under NH4+ and NO3? nutrition may be mediated through pH. Rice and maize roots absorbed NH4+ most rapidly right at the apex and appeared to assimilate this NH4+ in the zone of elongation. During NH4+ assimilation, root cells must release protons, and the resulting acidification around the walls of cells in this region should stimulate root extension. By contrast, NO3? absorption reached a maximum in the maturation zone of rice and maize roots, and this NO3? was probably assimilated in more basal regions. Absorption of NO3? requires proton efflux, whereas NO3? assimilation requires proton influx. The net result under NO3? nutrition was only subtle shifts in rhizosphere pH that probably would not influence root elongation. The signal through which roots detect changes in rhizosphere NH4+ and NO3? levels is still obscure. It is proposed that a product of nitrogen metabolism such as nitric oxide serves as a signal.  相似文献   

9.
Three clear-cuts at the Hubbard Brook Experimental Forest (NH) have resulted in a chronosequence of forest watersheds in close proximity. Following clear-cutting, the stands, now 12, 21, 27, and 78 years old, have different species composition, nutrient capital, and biogeochemistry. In this study, we compared seasonal patterns of NO3 – in streamwater, changes in N capital, and N retention in watersheds of differing stand age. All of the watersheds showed elevated losses of NO3 –, H+ and nutrient cations (Ca2+, Mg2+, K+) during the first few years following clear-cutting. Increased retention of N occurred during vegetation regrowth compared to the reference watershed (W6). Nitrate concentrations were low during the summer growing season, increased in the late fall and peaked in March during spring snowmelt. Concentrations of NO3 – were lower in the regrowing watersheds than in W6 during all months. In W6, there was considerable year-to-year variability in N retention, which was not initially observed in the manipulated watersheds. However, two cut watersheds exhibited higher export of NO3 – in 1989 and 1990, corresponding to a 10-year high value in annual NO3 – loss in W6. These results demonstrate the importance of land use and cutting history in assessments of N saturation and loss from forest watersheds.  相似文献   

10.
Atmospheric loads to dilute lakes in the Sierra Nevada mountains of California are very low, and fall almost entirely as snow. When acidic anions preferentially elute from melting snow, these low loads may nontheless be enough to acidify low ANC lakes. Two of the ten lakes included in the Sierra Episodes Study are discussed here: High Lake, the only lake in the study to become acidic during snowmelt; and Treasure Lake, typical of the remainder of the lakes. All lakes exhibited increases in NO3 ? concentrations during early snowmelt; these were accompanied by increases in base cations, primarily Ca2+. In the first few days of snowmelt, NO3 ? concentrations at High Lake increased more rapidly than concentrations of base cations, resulting in ANC values below zero. Export of both NO3 ? and SO4 2? from the watersheds exceeded the inputs from the snowpack, suggesting that other sources (e.g., watershed minerals, stored inputs from the previous summer, transformations of other inputs) of these anions are important.  相似文献   

11.
A study of inorganic-N concentrations in streams, soil waters, throughfall and rainfall was conducted for one year in five moorland and 20 Sitka spruce plantation catchments in upland Wales. The forest ages ranged from 10 to 55 yr. Highly significant positive relationships with forest stand age existed for inorganic-N concentrations in streamwater, B and O horizon soil waters and throughfall. Inorganic-N in streams and B horizon waters was entirely NO3 ?. Inorganic-N fluxes in throughfall also showed a significant, positive relationship with stand age. Throughfall flux of inorganic-N in the oldest stand was 25.1 kgN ha?1 yr?1, double that in incident rainfall. The older forest stands appear unable to utilise the available N. Nitrification is very active in the soils of these older stands, resulting in significant soil acidification. The processes responsible for the observed NO3 ? leaching losses, and the implications for the debate on Nitrogen Critical Loads are discussed.  相似文献   

12.
This study is the first to report nitrite occurrence and variability in surface water across an agricultural watershed in the province of Quebec, Canada. Nitrite (NO2 ?) concentrations were monitored across a 2.4 km2 watershed during 2 years. Water samples were collected at the outlet from April to November and in three contrasted stream branches (six stations) during three hydrological regimes (summer low water levels, fall recharge, and snowmelt). Our study clearly demonstrates that NO2 ? levels observed at the outlet are not representative of NO2 ? variability across the micro-watershed. Surface water collected in cropped areas presents high NO2 ? concentrations during summer low water levels, often exceeding guidelines for aquatic life, with NO2 ? means ranging from 0.022 to 0.107 mg N L?1 and maximum value reaching 0.156 mg N L?1. Furthermore, the two stream branches in cropped area have demonstrated significant differences in NO2 ? concentrations and other water quality parameters. The importance of groundwater discharge to streams in the micro-watershed Bras d’Henri may potentially generate different in-stream sources of NO2 ? and water quality parameters. However, further studies are essential to determine sources and processes related to in-stream NO2 ? peaks.  相似文献   

13.
Discharge to concentration relationships for eight streams studied by the U.S. Geological Survey (USGS) as part of the U.S. Environmental Protection Agency's (U.S. EPA) Long-Term Monitoring Project (1983–89) indicate acidification of some streams by H2SO4 and HNO3 in atmospheric deposition and by organic acids in soils. Concentrations of major ions in precipitation were similar to those reported at other sites in the northeastern United States. Average concentrations of SO4 2? and NO3 ? were similar among streams, but base cation concentrations differed widely, and these differences paralleled the differences in acid neutralizing capacity (ANC). Baseflow ANC is not a reliable predictor of stream acidity at high flow; some streams with high baseflow ANC (>150 Μeq L?1) declined to near zero ANC at high flow, and one stream with low baseflow ANC (<50 Μeq L?1) did not approach zero ANC as flow increased. Episodic decreases in ANC and pH during peak flows were associated with increased concentrations of NO3 ? and dissolved organic carbon (DOC). Aluminum concentrations exceeding 300 Μg L?1 were observed during peak flows in headwater streams of the Neversink River and Rondout Creek. Seasonal Kendall Tau tests for temporal trends indicate that SO4 2? concentrations in streamwater generally decreased and NO3 ? concentrations increased during the period 1983–1989. Combined acid anion concentrations (SO4 2? + NO3 ?) were generally unchanged throughout the period of record, indicating both that the status of these streams with respect to acidic deposition is unchanged, and that NO3 ? is gradually replacing SO4 2? as the dominant acid anion in the Catskill streams.  相似文献   

14.
Wet deposition monitoring was conducted at six rural stations in western Japan, during the period from 1987 through 1996. Long-term trends in the concentration of non-sea salt ions were analyzed on the basis of the data obtained. The monitoring results indicated that annual average concentrations of NO3 ? and NH4 + in precipitation significantly increased on the order of 45%, and that of nss-Ca2+ and nss-SO4 2?, concentrations did not change over the past 10 years. The ratio of NO3 ?/nss-SO4 2? in precipitation significantly increased, the ratio of NO3 ?/NH4 + showed no marked fluctuations, and the ratio of [nss-Ca2++NH4 +]/[nss-SO4 2?+NO3 ?] slightly increased during the period. These findings suggested that the wet deposition of NO3 ? and NH4 + in western Japan, particularly that in the winter season, was influenced by the long-range transport of nitrogen oxides and ammonia from the Asian continent.  相似文献   

15.
Excessive nitrogen application has caused serious environmental pollution under high-yield maize system in China. Our objective was to evaluate critical stalk nitrate (NO3?) levels that support high yield (>13 Mgha?1), but are not in excess. Optimal stalk NO3? concentration was determined by conducting seven nitrogen levels experiments in two high yield maize regions: Dongyang County (DY) and Wenshui County (WS). Optimal stalk NO3? concentration category range to obtain maximum yield in DY (sandy loam, higher accumulated temperature and solar radiation compared with WS) was 0.44–1.19, which similar to the criteria of US (0.70–2.0 g kg?1). While for WS (loam soil, lower accumulated temperature and solar radiation compared with DY), optimal stalk NO3? concentration category range to obtain maximum yield was 1.95–4.15, greatly higher than the US criteria. These results suggested thatit is necessary to establish matching optimal stalk NO3? category ranges for different ecological regions in China.  相似文献   

16.
Longitudinal and temporal variations in water chemistry were measured in several low-order, high-elevation streams in the Great Smoky Mountains to evaluate the processes responsible for the acid-base chemistry. The streams ranged in average base flow ANC from ?30 to 28 μeq L?1 and in pH from 4.54 to 6.40. Low-ANC streams had lower base cation concentrations and higher acid anion concentrations than did the high-ANC streams. NO3 ? and SO4 2? were the dominant acid anions. NO3 ? was derived from a combination of high leaching of nitrogen from old-growth forests and from high rates of atmospheric deposition. Streamwater SO4 2? was attributed to atmospheric deposition and an internal bedrock source of sulfur (pyrite). Although dissolved Al concentrations increased with decreasing pH in the study streams, the concentrations of inorganic monomeric Al did not follow the pattern expected from equilibrium with aluminum trihydroxide or aluminum silicate phases. During storm events, pH and ANC declined by as much as 0.5 units and 15 μeq L?1, respectively, at the downstream sites. The causes of the episodic acidification were increases in SO4 2? and DOC.  相似文献   

17.
Plants can play an important role in wastewater treatment and water reuse in terrestrial and space systems. Chive growth in biologically treated graywater, simulating the anticipated early planetary base graywater, was evaluated in this study for NASA. Phytotoxicity due to physiochemical parameters such as ammonium-nitrogen (NH4 +-N), nitrite-nitrogen (NO2 ?-N), pH, and sodium (Na+) was assessed using a series of hydroponic experiments in an environmentally controlled growth chamber. Nitrification in wastewater was observed in all graywater treatments, which converted NO2 ?-N (a toxic form of nitrogen) and NH4 +-N (toxic at high concentrations) to nitrate-nitrogen (NO3 ?-N) (preferred N form for plant uptake). Irrespective of the increase in the NO3 –-N concentration due to nitrification, chives in the wastewater treatments typically had poor or no growth. The high levels of Na+ present in the graywater treatments affected potassium uptake and may have affected other nutrient uptake. The impact of nitrification on wastewater pH and NO2 ?-N toxicity is believed to be the critical factor affecting chive growth and may hinder the use high nitrogen waste streams for plant growth unless NO2 ?-N concentrations are controlled during biological treatment of graywater.  相似文献   

18.
Land development has caused runoff of red soil into the ocean on the north side of Okinawa Island, Japan. In an attempt to clarify the impacts of this “red soil pollution” on the oxidizing power of seawater, we studied the formation of hydroxyl radical (?OH), the most potent oxidant in the environment, in red soil-polluted waters using a 313-nm monochromatic light. ?OH was photochemically formed in the red soil-polluted water samples, and the formation rates of ?OH decreased as salinity increased, i.e., as red soil-polluted river water gets mixed with seawater. The photo-formation rates of ?OH showed good correlations with dissolved Fe concentrations (R 2?=?0.96) and [NO2 ?]?+?[NO3 ?] concentrations (R 2?=?0.87), while a negative and weak correlation was found with dissolved organic carbon concentrations (R?=??0.78). Theoretical calculation showed that direct photolysis of NO3 ?, Fe(OH)2+, and hydrogen peroxide all together accounted for less than 10% of the observed ?OH formation in the red soil-polluted waters. Comparison between filtered and unfiltered samples showed that red soil particles were not the main sources of ?OH, and the photolysis of NO2 ? could account for at most 78% of the observed ?OH formation rates. We found that the Fenton’s reaction (a reaction between Fe(II) and H2O2) could possibly account for the observed formation of ?OH in the red soil-polluted waters.  相似文献   

19.
Atmospheric deposition of N and S on terrestrial and aquatic ecosystems causes effects induced by eutrophication and acidification. Effects of eutrophication include forest damage, NO3 pollution of groundwater and vegetation changes in forests, heathlands and surface waters due to an excess of N. Effects of acidification include forest damage, groundwater pollution, and loss of fish populations due to Al mobilization. Critical loads (deposition levels) for N and S on terrestrial and aquatic ecosystems in the Netherlands related to these effects have been derived by empirical data and steady-state acidification models. Critical loads of N generally vary between 500 and 1500 mol c ha?1 yr?1 for forests, heathlands and surface waters and between 1500 and 3600 for phreatic groundwaters. Critical loads of total acid (S and N) vary between 300 to 500 mol c ha?1 yr?1 for phreatic groundwaters and surface waters and between 1100 to 1700 mol ha?1 yr?1 for forests. On the basis of the various critical loads a deposition target for total acid of 1400 mol c ha?1 yr?1 has been set in the Netherlands from which the N input should be less than 1000 mol c ha?1 yr?1. This level, to be reached in the year 2010, implies an emission reduction of 80–90% in SO2, NO x and NH3 in the Netherlands and of about 30% in neighboring countries compared to 1980 emissions.  相似文献   

20.
Rhizospheric pH changes induced by arbuscular mycorrhiza formation in onion plants fertilized either with NO3? or NH4+ were studied. The pH changes promoted by either mycorrhizal or non-mycorrhizal roots were studied by means of a non-destructive technique using the pH indicator bromocresol purple. Results showed that the pH changes observed depended on i) the symbiotic status of the root and ii) the N form amended to the soil. When growing in a NH4+-supplied soil, mycorrhizal onion roots produced more intense and wider acidification halos than non-mycorrhizal plants did. These differences were maintained throughout the whole experiment (60 days). NO3?-supplied mycorrhizal roots initially promoted a more intense alkalinization on their surface, compared to the control roots (30 days); however, at the end of the experiment (60 days), intense acidification halos were observed in the mycorrhizosphere, whereas this acidification was almost absent in the non-mycorrhizal rhizosphere. The link between these mycorrhiza-induced pH changes in the soil and the higher efficiency in the exploitation of nitrogen in the rhizosphere by the arbuscular-mycorrhizal plants is discussed.  相似文献   

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