Evaluating macroinvertebrate responses to recovery from acidification in small lakes in Ontario,Canada

The biomonitoring program of Environment Canada examines food chains in small Ontario lakes to interpret ecological responses of waterfowl and their foods to changing acid deposition. Macroinvertebrates and fish were sampled in three acid-sensitive regions: Muskoka (1991; N=20), Algoma (1992; N=20), and Sudbury (1994; N=22). Small lakes (<11 ha;=" important=" breeding=" habitat=" for=" waterfowl)=" were=" chosen=" to=" cover=" the=" range=" of=" ph=" in=" each=" region,=" and=" include=" those=" with=" and=" without=" fish.=" in=" all=" regions,=" macroinvertebrate=" taxonomic=" richness=" (particularly=" nekton=" and=" benthos)=" was=" greater=" in=" fishless=" lakes=" compared=" to=" lakes=" with=" fish.=" among=" fishless=" lakes,=" taxonomic=" richness=" (especially=" benthos)=" was=" positively=" correlated=" with=" ph,=" although=" regional=" differences=" were=" evident.=" previous=" studies=" near=" sudbury=" have=" shown=" that=" several=" benthic=" groups=" have=" distribution=" and=" abundance=" patterns=" with=" respect=" to=" ph=" (trichoptera,=" ephemeroptera,=" hirudinea,=" amphipoda,=" and=" gastropoda).=" those=" patterns=" continue=" near=" sudbury,=" and=" were=" also=" strongly=" apparent=" in=" algoma.=" in=" all=" regions,=" the=" number=" of=" acid-sensitive=" taxa=" per=" lake=" is=" related=" to=" ph,=" and=" should=" increase=" as=" lakes=" recover=" from=" acidification.=" however,=" predicting=" macroinvertebrate=" responses=" to=" recovery=" must=" consider=" concurrent=" effects=" of=" fish,=" as=" they=" are=" a=" dominant=" factor=" structuring=" these=">     

Contribution of zooplankton to the total cadmium pool in Canadian shield lakes varying in acidity

Crustacean zooplankton >250 m in size contributed 0.002 to 11% (median of 1.3%) of the total Cd in the epilimnia of 39 Canadian Shield lakes that ranged in pH from 4.7 to 8.3. The contribution of zooplankton to the total Cd pool was consistently low (1%) only in clear water lakes with pH < 5.0.=" in=" three=" intensively=" studied=" lakes,=" the=" contribution=" of=" zooplankton=" to=" total=" aqueous=" cd=" varied=" with=" time=" and=" depth,=" the=" maximum=" contribution=" (4=" to=" 6%)=" occurring=" in=" the=" metalimnion=" in=" mid-summer.=" changes=" with=" depth=" and=" time=" were=" principally=" a=" product=" of=" seasonal=" changes=" in=" zooplankton=" biomass=" and=" seasonal=" succession=" of=" species=" with=" inherently=" different=" tendencies=" to=" accumulate=" cd.=" implications=" for=" the=" study=" of=" cd=" cycling=" in=" lakes=" are=">     

Snowpack quality as an indicator of air pollution in Finnish Lapland and the Kola Peninsula,NW Russia

Bulk snow samples were collected from the snowpack in open areas along two sampling lines running to the west from the Cu-Ni smelters at Nikel and Monchegorsk, NW Russia, during 1991–1993. The aim of the study was to estimate the area affected by sulphur and heavy metal deposition from the smelters. Snowpack quality was used as an indicator of deposition during winter time. The total sulphur, copper and nickel concentrations in the snowpack decreased significantly (p<0.001) with=" increasing=" distance=" from=" the=" smelters=" along=" the=" sampling=" line=" running=" directly=" to=" the=" west=" from=" monchegorsk.=" the=" deposition=" pattern=" was=" similar=" each=" winter=" during=" 1991–1993.=" the=" ph=" values=" did=" not=" correlate=" with=" the=" corresponding=" sulphur=" concentrations,=" and=" there=" was=" no=" decreasing=" ph=" gradient=" in=" the=" snowpack=" on=" moving=" towards=" monchegorsk.=" the=" effects=" of=" sulphur=" emissions=" from=" monchegorsk=" on=" snowpack=" chemistry=" were=" not=" detectable=" on=" the=" finnish=" side=" of=" the=" border.=" the=" 3-year=" mean=" of=" the=" total=" sulphur=" concentration=" was=" 0.27=" mg/kg,=" and=" of=" the=" ph=" values=" 4.92,=" along=" the=" sampling=" line=" running=" to=" the=" west=" of=" monchegorsk.=" the=" total=" sulphur=" concentrations=" near=" the=" smelters=">< 20=" km)=" varied=" between=" 0.37=" and=" 0.95=" mg/kg.=" the=" effect=" of=" the=" cu-ni=" smelters=" at=" nikel=" on=" snowpack=" quality=" was=" not=" detectable=" in=" northern=" finnish=" lapland.=" the=" 3-year=" mean=" for=" total=" sulphur=" was=" 0.20=" mg/kg=" and=" for=" ph=" 4.96=" along=" the=" sampling=" line=" running=" to=" the=" west=" of=">     

Cadmium bioaccumulation by clams dwelling in different salinity regimes along the Saudi coast of the Arabian gulf

The objective of this study was to investigate Cd bioaccumulation in clams living in different salinities. Several hundred clams (Maritrix maritrix) and sediment samples were collected during 1985–1986 from 12 locations on the Saudi coastal areas of the Arabian Gulf. Soft tissue from each clam was removed and digested in HNO₃. Sediments were also digested in HNO₃. Cadmium in the recently collected seawater samples was extracted using pyrrolidine carbodithioic acid-chloroform system. Cadmium in all the collected samples was determined using an inductively coupled argon plasma analyzer. Concentrations of Cd in the sediments varied insignificantly between 0.1 and 0.22 mg kg^–1. Significant geographical variations in the mean Cd concentrations in clams (P < 0.05)=" were=" found.=" intrastation=" differences=" in=" cd=" bioaccumulation=" were=" also=" significant.=" correlation=" between=" biometric=" observations=" and=" cd=" concentrations=" in=" clams=" was=" not=" significant=" (p=">< 0.05).=" seawater=" salinity=" was=" significantly=" (p=">< 0.05)=" correlated=" to=" the=" mean=" cd=" concentrations=" in=" clams=" and=" seawater.=" cadmium=" accumulation=" in=" the=" clams=" was=" supported=" by=" the=" chemical=" behavior=" of=" cd=" in=">     

Critical loads of acidity to surface waters in the Vosges massif (north-east of France)

Acid clearwater fishless streams have been identified in the Vosges mountains. In order to evaluate the relatipnships between acidifying factors (such as atmospheric deposition), buffering factors (such as bedrock and soil type), and surface water acidity, an exhaustive survey of streamwater acidity in the Vosges mountains (N-E France) was performed. A network of 11 measurement stations of atmospheric deposition was used to estimate and map deposition over the whole massif (total area 5000 km²). Data on bedrock, soil, superficial deposits, and vegetation were collected from published studies. Sensitive areas as well as acidifying environment factors were derived from the corresponding maps. Over the whole massif, 19% of streams showed baseflow alkalinity below 30 eq.r¹ and 7.5 % were identified as acid (pH < 5.4).=" acid=" streams=" occur=" on=" the=" north-western=" side=" of=" the=" massif=" on=" quartzrich=" sandstone=" and=" acid=" granites.=" in=" each=" of=" these=" areas,=" we=" could=" clearly=" point=" out=" on=" one=" hand,=" the=" negative=" influence=" of=" conifer=" vegetation=" and=" glacial=" soil=" abrasion=" or=" induration,=" and=" on=" the=" other=" hand=" the=" buffering=" effect=" of=" moraine=" deposits.=" a=" corresponding=" range=" of=" critical=" loads=">< 0.2=" to=" 2.0=" keq.=">¹ yr¹) for surface water was calculated using the Steady State Water, Chemistry method (SSWC).     

Metal binding properties of Klebsiella oxytoca

Bacterial surfaces are generally negatively charged in the environmental pH-range and may therefore interact with metal cations, thus influencing the mobility of metals in soil and natural waters. In the present work the acid capacity and metal binding properties of Klebsiella oxytoca have been studied. A total acid capacity of 120 meq kg^–1 was determined from potentiometric titrations of a suspension of starved bacteria in 0.1 M KC1. The adsorption of trace elements (Cs, Sr, Eu, serving as model systems, as well as Hg, Zn, and As) on starved bacteria was determined by a batch technique using radio tracers and with variation of pH (3 to 9). The adsorption followed the order Cs < sr,=" as=">< zn=">< hg=">< eu=" (at=" ph=" 5=" to=" 7).=" the=" uptake=" of=" eu=" was=" drastically=" increased=" when=" ph=" increased=" from=" 3.5=" to=" 4.5,=" indicating=" a=" surface=" complexation=" (with=" carboxylic=" or=" phosphate=" groups).=" a=" desorption=" of=" eu=" at=" ph=" above=" the=" acid=" equivalence=" point=" (ph=" 6.9)=" could=" be=" an=" indication=" of=" the=" release=" of=" a=" metal=" complexing=" exudate=" from=" the=">     

Metal chemistry of irrigation and drainage waters of Al-Ahsa Oasis of Saudi Arabia and its effects on soil properties

Water samples from 18 springs and 13 drainage canals and subcanals were collected from Al-Ahsa Oasis. Concentrations of total dissolved salts, Cl, SO₄ HCO₃, B, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, V, Ti, and Zn were determined. The soil salinity development (SSD), the adjusted Na ratio (adj. SAR), the adjusted Na adsorption ratio (adj. RNa), and exchangeable Na percentage (ESP) were calculated. Sodium was the most abundant cation in all water samples followed by Ca, Mg, Sr, and K in descending order. Concentrations of all other metals were below 0.1 mg L^–1. Chloride was the most abundant anion, followed by SO₄ and HCO₃ in these waters. A significant correlation (P < 0.05)=" between=" na=" and=" cl=" in=" water=" samples=" was=" found.=" thermodynamic=" calculations=" revealed=" that=" an=" appreciable=" fraction=" of=" ca=" and=" mg=" in=" spring=" and=" drainage=" waters=" were=" associated=" with=">₄ and HCO₃ ions. Calcium increased from less than 10 meq L^–1 in spring waters to > 16 meq L^–1, Mg was doubled, and Na and Cl increased several times in the drainage waters. The salinity and sodicity hazards of the spring and drainage waters were classified as C₄S₂ i.e. high salinity with medium sodicity problems.     

N2O, NO, and NH3 Emissions from Soil after the Application of Organic Fertilizers, Urea and Water

Agricultural soil is a major source of nitrous oxide (N₂O), nitric oxide (NO) and ammonia (NH₃). Little information is available on emissions of these gases from soils amended with organic fertilizers at different soil water contents. N₂O, NO and NH₃ emissions were measured in large-scale incubations of a fresh sandy loam soil and amended with four organic fertilizers, [poultry litter (PL), composted plant residues (CP), sewage sludge pellets (SP) and cattle farm yard manure (CM)], urea fertilizer (UA) or a zero-N control (ZR) for 38 days. Fertilizers were added to soil at 40, 60 or 80% water-filled pore space (WFPS). The results showed that urea and organic fertilizer were important sources of N₂O and NO. Total N₂O and NO emissions from UA ranged from 0.04 to 0.62%, and 0.23 to 1.55% of applied N, respectively. Total N₂O and NO emissions from organic fertilizer treatments ranged from 0.01 to 1.65%, and <0.01 to=" 0.55%=" of=" applied=" n,=" respectively.=" the=" lower=">₂O and NO emissions from CP and CM suggested that applying N is these forms could be a useful mitigation option. Comparison of the NO-N/N₂O-N ratio suggested that nitrification was more dominant in UA whereas denitrification was more dominant in the organic fertilizer treatments. Most N was lost from PL and UA as NH₃, and this was not influenced significantly by WFPS. Emissions of NH₃ from UA and PL ranged from 62.4 to 69.6%, and 3.17 to 6.11% of applied N, respectively.     

Evaluation of estimation methods and base data uncertainties for critical loads of acid deposition in Japan

Simplified steady state mass balance model for critical load (CL) estimation was applied to a test area in Japan to evaluate applicability of the model. Three different criteria for acidification limits (1: [Al³⁺]<0.2 eq.=">^–3, 2: Al/BC<1.0 mol=">^–1, 3:Al depletion criterion) were used. Mean values and spatial distribution patterns of CL values calculated by these criteria were extremely different from each other. The first criterion produced much higher CL than the second criterion in the Japanese condition with high annual precipitation. Improvements including definition of the criterion were considered necessary. As quantitative data of the base cation weathering rate (BC_w) was lacking, the rate was specified based on surface geology and the soil type of each site. To evaluate uncertainty of BC_w used for CL calculation, ion content and particle-size distribution were measured for the soils collected from the test area, and BC_w was estimated with PROFILE model based on these measurements. It appeared that BC_w estimates by surface geology were adequate as a mean value, but they had uncertainty of about 50% of the average values due to variability of ion contents within the same surface geology group.     

Response of blue spruce (Picea pungens) to manganese pollution from MMT

The use of methylcyclopentadienyl manganese tricarbonyl (MMT) in unleaded gasoline has become a source of manganese (Mn) contamination to which urban ecosystems are exposed. The potential of coniferous trees as spatial and chronological indicators of Mn pollutation was investigated. Manganese concentrations in xylem from blue spruce (Picea pungens) growing near (high-exposure site) and far (low-exposure site) from a road were measured as a function of the year of wood formation. Exchangeable Mn content, which is the soil fraction most readily available for uptake by trees, was also measured in the soils of both sectors. The results of the soil analysis show that exchangeable Mn concentrations are about 10 times higher in soils exposed to contamination (p<0.0005), in=" comparison=" with=" the=" concentrations=" found=" in=" soils=" weakly=" exposed.=" however,=" the=" mn=" concentrations=" in=" the=" trees=" near=" the=" road=" were=" not=" significantly=" different=" from=" those=" in=" the=" reference=" trees=" (p=">0.05). Therefore, it appears that blue spruce is not sensitive to soil Mn contamination arising from the use of MMT in gasoline.     

Ion mass budgets for small forested catchments in Finland

Ion mass and H⁺ budgets were calculated for three pristine forested catchments using bulk deposition, throughfall and runoff data. The catchments have different soil and forest type characteristics. A forest canopy filtering factor for each catchment was estimated for base cations, H⁺, Cl^? and SO ₄ ^2? by taking into account the specific filtering abilities of different stands based on the throughfall quality and the distribution of forest types. Output fluxes from the catchments were calculated from the quality and quantity of the runoff water. Deposition, weathering, ion exchange, retention and biological accumulation processes were taken into account to calculate catchment H⁺ budgets, and the ratio between external (anthropogenic) and internal H⁺ sources. In general, output exceeded input for Na⁺, K⁺, Ca²⁺, Mg²⁺, HCO ₃ ^? (if present) and A^? (organic anions), whereas retention was observed in the case of H⁺, NH ₄ ⁺ , NO ₃ ^? and SO ₄ ^2? . The range in the annual input of H⁺ was 22.8–26.3 meq m^?2 yr^?1, and in the annual output, 0.3–3.9 meq m^?2 yr^?1. Compared with some forested sites located in high acid deposition areas in southern Scandinavia, Scotland and Canada, the catchments receive rather moderate loads of acidic deposition. The consumption of H⁺ was dominated by base cation exchange plus weathering reactions (41–79 %), and by the retention of SO ₄ ^2? (17–49 %). The maximum net retention of SO ₄ ^2? was 87% in the HietajÄrvi 2 catchment, having the highest proportion of peatlands. Nitrogen transformations played a rather minor role in the H⁺ budgets. The ratio between external and internal H⁺ sources (excluding net base cation uptake by forests) varied between 0.74 and 2.62, depending on catchment characteristics and acidic deposition loads. The impact of the acidic deposition was most evident for the southern Valkeakotinen catchment, where the anthropogenic acidification has been documented also by palaeolimnological methods.     

Influence of Catchment Characteristics and Flood Type on Relationship Between Streamwater Chemistry and Streamflow: Case Study from Carpathian Foothills in Poland

The study aimed to determine the influence of catchment characteristics and flood type on the relationship between streamflow and a number of chemical characteristics of streamwater. These were specific electrical conductivity (SC), pH, the concentrations of main ions (Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO ₃ ^? , SO ₄ ^2? , and Cl^?), and nutrients (NH ₄ ⁺ , NO ₂ ^? , NO ₃ ^? , and PO ₄ ^3? ). These relationships were studied in three small catchments with different geological structure and land use. Several flood types were distinguished based on the factors that initiate flooding and specific conditions during events. Geological factors led to a lower SC and main ion concentrations at a given specific runoff in catchments built of resistant sandstone versus those built of less resistant sediments. A lower concentration of nutrients was detected in the semi-natural woodland catchment versus agricultural and mixed-use catchments, which are strongly impacted by human activity. The strongest correlation between streamflow and the chemical characteristics of water was found in the woodland catchment. Different types of floods were characterized by different ion concentrations. In the woodland catchment, higher SC and higher concentrations of most main ions were noted during storm-induced floods than during floods induced by prolonged rainfall. The opposite was true for the agricultural and mixed-use catchments. During snowmelt floods, SC, NO ₃ ^? , and most main ion concentrations were higher when the soil was unfrozen in the agricultural and mixed-use catchments versus when the soil was frozen. In the case of the remaining nutrients, lower concentrations of NH ₄ ⁺ were detected during rain-induced floods than during snowmelt floods. The opposite was true of PO ₄ ^3? .     

Stream chemistry impacts of conifer harvesting in welsh catchments

Hydrochemical data have been collected for between 6 and 9 years from forest harvesting experiments in small catchments (>10 ha) at Plynlimon and Beddgelert, Wales, UK. Felling resulted in rapid increases in NO ₃ ^? and K⁺ concentrations at both sites. A maximum of 3.2 mg N L^?1 was observed at Plynlimon about one year after the start of felling. Concentrations declined to control stream values (0.5 mg N L^?1) after 5 years. At Beddgelert, NO ₃ ^? concentrations in the manipulated catchments remained above those in the unfelled control catchment for three years, before declining below control values. The NO ₃ ^? pulse was related to increased rates of mineralization and nitrification in the soil after felling. The initial increase in K⁺ concentration after felling at Plynlimon was followed by a slow decline, but concentrations were still above those in the control stream after 5 years. From 4 to 8 years after felling at Beddgelert, K⁺ concentrations fell below and then generally remained lower than control values. The NO ₃ ^? pulse after felling at Plynlimon sustained inorganic anion concentrations above those in the control stream for the first 18 months after felling. As the NO ₃ ^? pulse declined, inorganic anion concentrations decreased to below those in the control stream about 4 years after felling. At Beddgelert, the smaller increase in NO ₃ ^? concentrations had less of an effect on inorganic anion concentrations which decreased after felling relative to values in the control stream. The increase in NO ₃ ^? was associated with temporary streamwater acidification in the felled catchments due to the increased rates of nitrification and nitrate leaching. At Plynlimon, streamwater filterable Al concentrations declined after felling, but controls on Al behaviour are complex and not explained by simple equilibrium relationships with Al(OH)₃ or by variations in inorganic anion concentrations. At Beddgelert, felling had no effect on stream water filterable Al concentrations. Felling at Plynlimon led to a large reduction in streamwater Cl^?, Na⁺ and SO ₄ ^2? concentrations. At Beddgelert reductions in SO ₄ ^2? and ‘sea salt’ ion concentrations were less clear, reflecting the smaller proportions of the catchments which were harvested. Felling had no deleterious effects on water quality, apart from a temporary slight further decline in stream pH at Beddgelert. Increases in NO ₃ ^? concentrations were short-lived and concentrations were well below drinking water standards. Filterable Al concentrations were already higher than statutory standards, but were not increased or decreased through felling.     

Simulating acidification and recovery processes in experimental catchments with the ILWAS model

The Integrated Lake Watershed Acidification Study (ILWAS) model was used to simulate soil discharge chemistry at two neighboring experimental catchments. One catchment underwent deacidification because of the artificial application of deacidified precipitation whereas the other catchment received unaltered acidic precipitation. Simulated results reproduce the observed seasonal dynamics in the concentrations of base cations, NO ₃ ^? , Al, and H₄SiO ₄ ⁰ in soil discharges for both catchments. Simulated results also indicate that the export flux of base cations was decreased by 30% at the deacidification catchment in response to the decrease in acid deposition. However, simulated SO ₄ ^2? concentrations show decreases that are about 40% more rapid than were observed. Simulated organic acid concentrations were also substantially lower than those observed at the deacidification catchment, indicating that organic matter decomposition processes were not correctly simulated. Acid-base budgets for both 5 and 50-yr simulations indicate that acid displacement by base cations through ion exchange is the principal process delaying recovery of runoff alkalinity, whereas SO ₄ ^2? desorption has a minor role. Silicate weathering is the dominant acid-consuming process at both catchments. Criteria proposed here for assessing forecast reliability include reproducing seasonal dynamics in discharge chemistry, providing numerically accurate chemical concentrations when compared to monitoring data, and correctly predicting deacidification rate and extent. The ILWAS model generally meets these criteria, indicating that the model can produce a reliable forecast of the effects of acid deposition on the acid-base chemistry of surface waters given sufficient temporal data for confident optimization of the calibrated variables in the model.     

Iron oxides serve as natural anti-acidification agents in highly weathered soils

Purpose

The effect of Fe oxides on the natural acidification of highly weathered soils was investigated to explore the natural acidification process in variable charge soils

Materials and methods

A variety of highly weathered soils with different Fe oxide contents were collected from the tropical and subtropical regions of southern China to investigate the soil acidity status. Electrodialysis experiments were conducted to simulate natural acidification process and promote accelerated acidification in a variety of systems such as relatively less weathered soils, mixtures of goethite with montmorillonite or kaolinite, an Alfisol, a limed Ultisol, and Fe oxides coated montmorillonite. The objective was to gather evidence for the occurrence of Fe oxide inhibited natural acidification in highly weathered soils.

Results and discussion

Highly weathered soils with free Fe₂O₃?<?100?g/kg (17 soils) had an average pH?=?4.64?±?0.06, while the soils with free Fe₂O₃?>?100?g/kg (49 soils) had an average pH?=?5.25?±?0.04. A significant linear relationship was found between the soil pH and Fe oxide content of these soils. Similar results were obtained in electrodialysis experiments, i.e., in soils that underwent accelerated acidification. A negative correlation was found between the Fe oxide content and exchangeable acidity or effective cation exchange capacity, respectively. In another set of experiments, goethite slowed down acidification in experiments conducted with this Fe oxide and montmorillonite, or kaolinite, or an Alfisol, or a limed Ultisol. The overlapping of the electrical double layers on the positively charged Fe oxide particles and negatively charged minerals may have caused the release and subsequent leaching of the base cations, but inhibited the production of exchangeable acidity cations. In addition, when montmorillonite or Fe oxide-coated montmorillonite were electrodialyzed in another set of experiments, exchangeable acidity of the former was much greater than that of the latter, suggesting that the positively charged Fe oxide coatings on montmorillonite have partially neutralized the permanent negative charge on montmorillonite surfaces, decreasing exchangeable acidity.

Conclusions

Fe oxides may function as natural ??anti-acidification?? agents through electric double-layer overlapping and coating of phylliosilicates in highly weathered soils.     

Aquatic Ecosystem Degradation of High Conservation Value Upland Swamps,Blue Mountains Australia

Temperate highland peat swamps on sandstone (THPSS) are unique state and federally protected ecological communities. THPSS is a higher level classification which is comprised of multiple swamp communities which include Blue Mountains Swamps and Newnes Plateau Shrub Swamps. The Blue Mountains has a string of urban settlements surrounded by large expanses of undisturbed natural vegetation which have varied degrees of protection ranging from state forests to World Heritage national parks. This study investigated aquatic invertebrates from seven THPSS within the Greater Blue Mountains area. Four swamps drain catchments with varying degrees of urban development and associated impervious surfaces, and three swamps have non-urban, naturally vegetated catchments. Water chemistry of non-urban swamps was acidic (mean pH 4.70) and dilute (mean EC 26.7 uS/cm) and dominated by sodium and chloride ions with most other major ions at low concentrations often below detection limits (Belmer et al. 2015). In contrast, urban swamps had higher pH (mean 6.60) and salinity (mean 153.9 uS/cm) and were dominated by calcium and bicarbonate ions (Belmer et al. 2015). Aquatic macroinvertebrate abundance, family richness and % EPT taxa were all found to be lower within urban swamps when compared to non-urban swamps. These results support the hypothesis of Belmer et al. (2015) that urban runoff within THPSS catchments is affecting the condition of their aquatic ecosystems.     

Export of Dissolved Inorganic Nitrogen in a Partially Cultivated Subtropical Mountainous Watershed in Taiwan

A spatial and temporal investigation of dissolved inorganic nitrogen (DIN; NO₃, NO₂ and NH₄) was conducted under various water discharge conditions in Lanyang-Hsi, a subtropical mountainous stream, which drains through distinct degrees of agriculture-influenced sub-watersheds. In both the cultivated and non-cultivated sub-watersheds, NO₃ was the most abundant species accounting for >80% of total DIN, while NH₄ and NO₂ accounted for <15% and=" 5%=" of=" din,=" respectively.=" agricultural=" activities=" along=" the=" riverbank=" led=" to=" significantly=" higher=">₃ concentrations (13–246 M) and DIN yields (1300–3800 kg N km^–2 yr^–1) in main channel when compared to those of non-cultivated tributaries (9–38 M for NO₃ and 550–740 kg N km^–2 yr^–1 for yield). The much lower and less variable DIN yields observed in tributary stations (mean = 660 ± 120 kg N km^–2 yr^–1) are considered as the present day background of DIN yield, which is significantly higher than those of most natural watersheds in other regions. Elevated atmospheric DIN deposition is likely the cause for the high background DIN yield. Human activity within the watershed results in additional DIN yield, which accounted for 49% of total N export. However, the reported atmospheric DIN input in northern Taiwan (1800 kg N km^–2 yr^–1) is much higher than the background DIN yield implying that a major fraction (70%) of atmospheric inputs are retained or processed within the watershed. A dilution pattern occurred in the main channel where high NO₃ concentrations from the upstream sources decreased significantly in downstream direction due to inputs of NO₃-diluted water from non-cultivated areas. We adopted a two-source mixing model to predict the NO₃ dilution pattern. This model revealed a third yet not recognized N source in the lower part of watershed. Model results also indicated the importance of water discharge rate in regulating the relative contribution to total DIN export among these sources.     

Influence of acid rain on CO2 consumption by rock weathering: Local and global scales

Sulphuric and nitric acids, which are supplied by acid precipitation, take over from carbonic acid in weathering reactions, which induced a decrease of the atmospheric/soil CO₂ consumption by weathering (WCO₂). In order to quantity this disturbance, one has compared the bicarbonate fluxes determined at the outlet of 2 small catchments (one is substantially disturbed and the other is is weakly disturbed by acid precipitation). Our study shows that, under the influence of acid precipitation, bicarbonate fluxes (i.e. WCO₂) are decreased by about 73%. It has also been attempted to simulate at the continental scale, the influence of acid precipitation on WCO₂, using a Global Erosion Model (GEM-CO₂) recently developed. Several simulations have been performed corresponding to different realistic scenarios of global acid precipitation. In the most pessimistic of these scenarios, the GEM-CO₂ simulation shows that the global WCO₂ would be decreased by no more than 10%.     

Weathering rates in catchments calculated by different methods and their relationship to acidic inputs

The sensitivity of catchments to acidification is often assessed by calculation of weathering rates for comparison of the rates of release of base cations with the measured acidic inputs. Methods of calculation of weathering rates include (1) long-term rates from elemental depletion in soil profiles; (2) current rates from input-output budgets; (3) strontium isotope ratios to modify current rates for calcium; (4) modelling using PROFILE or MAGIC; (5) laboratory experimental methods. Not all these methods can be applied in any one situation and when more than one method can be used, there are often discrepancies in the resulting figures. Comparison of long-term and current rates with acidic inputs are often consistent with the known acidification status of some Scottish catchments, but in others it is often difficult to establish a relationship. In some catchments where acidification only occurs under high-flow conditions, for example, long-term rates (12–24 meq m^?2a^?1) are an order of magnitude lower than current rates (185–340 meq m^?2a^?1). In seven Scottish catchments on four rock types, weathering rates calculated by PROFILE are of the same order of magnitude as long-term rates calculated for the same soil profiles. Current rates, on the other hand, are always higher than the long-term rates, sometimes by a factor as high as 22, and although this could indicate that release of base cations from these soils has increased in recent times, possibly due to anthropogenic inputs, the comparisons may not be valid.     

Effects of nitrogen fertilizer on the acidification of two typical acid soils in South China

Purpose

A laboratory incubation under constant temperature and humidity was conducted to estimate the impacts of nitrogen (N) fertilizers on the acidification of two acid soils (Plinthudult and Paleudalfs) in south China.

Materials and methods

The experiment had three treatments, i.e., control (CK), addition of urea (U), and addition of ammonium sulfate (AS). We measured soil pH, nitrate (NO₃ ^?), ammonium (NH₄ ⁺), exchangeable hydrogen ion (H⁺), and aluminum ion (Al³⁺) concentrations at various intervals during the 90 days of incubation. Soil buffering capacity (pHBC) was also measured at the end of the experiment.

Results and discussion

The application of N fertilizers resulted in soil acidification. The U treatment caused greater acidification of the Plinthudult soil than the AS treatment, while there were no differences between U and AS treatments on the acidification of the Paleudalfs. At the end of the trial, the pHBC of Plinthudult in AS treatment was greater than that in CK and U treatments, which may be due to the buffering system of NH₄ ⁺ and NH₄OH. However, the pHBC of Paleudalfs was unchanged between treatments. The dynamics of exchangeable H⁺ and Al³⁺ corresponded to that of soil pH. Correlation analysis showed that both soil exchangeable H⁺ and soil exchangeable Al³⁺ were significantly related to soil pH.

Conclusions

Application of urea and ammonium sulfate caused acidification in both soils and increased soil exchangeable Al³⁺ and H⁺ concentrations in the Paleudalfs. The application of urea increased exchangeable Al³⁺, and ammonium sulfate increased pHBC in the Plinthudult.