Sources of acidity in running waters in central northern Sweden

Factors controlling the acidity of running waters between the coast of the Gulf of Bothnia and the Caledonian mountain range in central-northern Sweden were studied intensively in 8 large streams and in two synoptic surveys of 179 small streams. The bulk deposition of SO₄ ^2? was between 11–22 μeq m^?2 y^?1, of which 93% was nonmarine, with the highest values in the coastal region. Organic anions were the most frequent acid anions in the whole investigation area followed by sulfate. The major portion of SO₄ ^2? was from natural sources in the whole investigation area. The most acidic streams occurred in the hilly wave-washed terrain of the coastal region, because of a high terrestrial export of organic acids and very low neutralizing capacity. It is concluded that most of the acidity in the investigated streams is due to natural sources.     

Sources of sulphate and acidity in wetlands and lakes in Nova Scotia

There is a declining gradient of wet SO₄ deposition from south to north in Nova Scotia with the highest values being in the south, along with a localized increase around the Halifax metropolitan area, due to local SO₄ emission. Edaphic conditions such as drainage from soils containing gypsum or drainage on disturbed rocks containing pyrite, provide additional SO₄ to surface waters.Acidity is usually absent in the former (pH > 7.0) and very high in the latter (as low as pH 3.6). By contrast peaty, organic drainages release water low in SO₄ during the growing season but they release high amounts of organic anions (A?), consequently, these waters maintain decreased pH values, usually < 4.5. A study of over 80 wetlands and lakes during the ice free period in Nova Scotia showed that sea salt corrected SO₄ concentrations range from 45 ueq L^?1 in the south end of the province, ～30 ueq L^?1 in the Kejimkujik area and < 17 ueq L^?1 in the northern areas with values > 85 ueq L^?1 in the Halifax area, reflecting the atmospheric deposition pattern of SO₄ The SO₄ concentrations may be > 2000 ueq L^?1 in drainages containing gypsum, > 700 ueq L^?1 in drainages over pyrite bearing socks but < 20 ueq/L^?1 in streams draining bogs. The SO₄ concentrations change considerably during the non-growing season when the ground is saturated with water or frozen, and the runoff is high (snow and rain often alternate in winter). Under such conditions SO₄ concentration drops in the two former cases and increases in bog drainages, accompanied with a considerable drop in (A?) concentrations. Care should be taken when interpreting SO₄ concentrations in surface waters in Nova Scotia with respect to atmospheric SO₄ deposition.     

Wandering spiders limit densities of a major microbi-detritivore in the forest-floor food web

In a long-term field experiment, densities of wandering spiders (i.e. species that do not build webs to capture prey) were reduced in order to determine whether or not a major group of microbi-detritivores, the Collembola (springtails), would increase in response to lowered spider predation. Thirty 4-m² fenced plots (15 spider-removal, 15 control plots) and 15 unfenced, undisturbed reference areas were established in a deciduous forest. Spiders were taken from the removal-treatment after being collected by periodic trapping with pitfall traps that contained no preservative, and by searching the litter surface. Judging from a comparison of the numbers captured during periodic censuses in spider-removal and control plots (one census period was two consecutive days of pitfall trapping), wandering spiders were rapidly reduced by ca. 50% and were maintained at levels lower than control plots for 1.3 years. The reduction in numbers was greatest for wolf spiders (Lycosidae; ≈90%). Of six families of Collembola abundant in the leaf litter during the experiment, one family, the Tomoceridae, exhibited a significant release from spider predation. Densities of tomocerids, which are the largest and most active springtails on the research site, gradually increased until they were consistently 2× higher in the spider-removal treatment than in either fenced control plots or unfenced, open reference areas.     

Sensitivity of forest-floor mosses in boreal forests to nitrogen and sulphur deposition

The response of forest-floor mosses to deposition of nitrogen (N) and sulphur (S) was examined in field conditions in a 60-year-old Norway spruce (Picea abies Karst.) stand in southern Finland. The experimental plots received nitrogen (25 kg N ha^–1) and sulphur (30 kg S ha^–1) as ammonium sulphate once a year for 4 years.The dominant moss species on the site were Pleurozium schreberi (Mitt.) and Dicranum polysetum (Sw.). The biomass of the dominant moss species was decreased significantly by N and S deposition during the study period. Due to the addition of N and S, the biomass of Pleurozium schreberi was decreased by 60% and the biomass of Dicranum polysetum by 78%.     

Rapid soil organic matter loss from forest dieback in a subalpine coniferous ecosystem

Forest dieback caused by climate-change associated stresses and insect outbreaks has emerged as a global concern, and the biogeochemical consequences of this phenomenon need to be elucidated. We measured biological and chemical traits of soil beneath live trees or trees recently killed by a mountain-pine-beetle outbreak in a subalpine coniferous forest in the Front Range of Colorado. We focused on the top 5 cm of mineral soil just beneath the O horizon and measured microbial biomass, soil invertebrate abundance and composition, and soil chemical characteristics. With the termination of inputs from rhizodeposition, mycorrhizal fungal turnover and fine root turnover, soil total carbon (C) and total nitrogen (N) in the mineral soil at three sites decreased by 38–49% and 26–45%, respectively. Tree mortality was associated with reduced soil microbial biomass but soil nematode and microarthropod densities were unchanged. Nematode trophic structure was altered with an increased proportion of bacterial feeders. Soil inorganic N concentrations were inversely correlated to microbial C:N ratios. Tree death was associated with increased soil pH, a possible loss of calcium (Ca²⁺), but an accumulation of soil inorganic N, largely as NH₄⁺. Our results suggest that forest dieback results in rapid C and N loss from surface mineral soils and that the accumulation of soil inorganic N, the reduction in microbial biomass, and the more bacterial-based soil food web increase the potential of enhanced N loss from affected ecosystems.     

Rapid soil organic matter loss from forest dieback in a subalpine coniferous ecosystem

Forest dieback caused by climate-change associated stresses and insect outbreaks has emerged as a global concern, and the biogeochemical consequences of this phenomenon need to be elucidated. We measured biological and chemical traits of soil beneath live trees or trees recently killed by a mountain-pine-beetle outbreak in a subalpine coniferous forest in the Front Range of Colorado. We focused on the top 5 cm of mineral soil just beneath the O horizon and measured microbial biomass, soil invertebrate abundance and composition, and soil chemical characteristics. With the termination of inputs from rhizodeposition, mycorrhizal fungal turnover and fine root turnover, soil total carbon (C) and total nitrogen (N) in the mineral soil at three sites decreased by 38–49% and 26–45%, respectively. Tree mortality was associated with reduced soil microbial biomass but soil nematode and microarthropod densities were unchanged. Nematode trophic structure was altered with an increased proportion of bacterial feeders. Soil inorganic N concentrations were inversely correlated to microbial C:N ratios. Tree death was associated with increased soil pH, a possible loss of calcium (Ca²⁺), but an accumulation of soil inorganic N, largely as NH₄⁺. Our results suggest that forest dieback results in rapid C and N loss from surface mineral soils and that the accumulation of soil inorganic N, the reduction in microbial biomass, and the more bacterial-based soil food web increase the potential of enhanced N loss from affected ecosystems.     

Vegetation and soil acidity of a mangrove swamp in southeastern Nigeria

Abstract. The relationships between vegetation and acid properties of soils from a mangrove swamp in southeastern Nigeria were examined. Field moist soils were moderately acidic with pH ranging from 5.3 to 6.8. Air dry pH ranged from 2.9 to 4.9 indicating strong acidity; the values increased with profile depth and were related to decreasing fibrous root content. Less acidic conditions (air dry pH 4.3–4.9) were associated with the less fibrous soils under Avicennia africana and Pandanus candelabrum ; more acidic conditions (air dry pH 2.9–3.8) occurred in the more fibrous Rhizophora spp. and Nypa fruticans soils. Species occurrences and levels of aluminium and sulphate in the profiles were related, suggesting that hydrogen ions, aluminium and sulphate were the main contributors to exchangeable acidity. Unless crops are known to tolerate very acidic conditions, the fibrous Rhizophora and Nypa soils should not be drained for cultivation.     

Sediment and Phosphorus Export from a Lowland Catchment: Quantification of Sources

Storm event and annual export of suspended sediment (SS) and particulate phosphorus (PP) was measured during three hydrological years (June 1993 to May 1996) in Gelbæk stream, a Danish lowland stream draining a 11.6 km² arable catchment area. The contribution of subsurface drainage water, surface runoff and stream bank and bed erosion to catchment SS and PP losses was estimated using three different strategies: 1) Simultaneous and comparative monitoring of subsurface water. 2) A mass-balance and budget approach dividing the Gelbæk catchment into two subcatchments. 3) Application of the fingerprinting technique to single storm events. Subsurface drainage water proved to be a significant SS and PP source. Subsurface drainage water from half of the catchment area accounted for 9.8–15% of the total annual SS loss from the Gelbæ catchment and 9.6–18.2%, of the annual PP loss. The mass-balance and budget approach showed stream bank and bed erosion to be the major source of SS and PP in this channelized and highly managed lowland stream. These findings were consistent with the fact that the annual loss of SS and PP from an upper culverted stream sub-catchment was significantly lower than that estimated from a mass-balance for a lower sub-catchment with an open stream channel. Comparison of the tracer content (e.g.¹¹⁷Cs) of SS collected during four storm events with that of topsoil and subsoil using a simple mixing model revealed subsoil to be a major source of SS.     

Global Emission of Mercury from Anthropogenic Sources in 1995

An estimate of the global emission of mercury from anthropogenicsources in 1995 has been prepared. Major emphasis is placed onemissions from stationary combustion sources, non-ferrous metalproduction, pig iron and steel production, cement production andwaste disposal. About three quarters of the total emission,estimated to be about 1900 tonnes, was from combustion of fuels, particularly coal combustion in China, India, and South and NorthKorea. In general, the Asian countries contribute about 56% to the global emissions of mercury to the atmosphere. Europe and North America seem to contribute less than 25%. The major chemical form of mercury emitted to the atmosphere is gaseouselemental mercury, contributing with about 53% to the totalemissions, followed by gaseous bivalent mercury with 37%. The Hg emissions on particles contribute only about 10% to the total emissions. Again, Asia contributes about 50% to the totalemissions of all individual chemical forms of mercury.     

Simulated nitrogen deposition affects soil fauna from a semiarid Mediterranean ecosystem in central Spain

Nitrogen (N) deposition is a major threat to the semiarid Mediterranean ecosystems. We simulated a gradient of N deposition (0, 10, 20 and 50 kg N ha^?1 year^?1?+?6.4 kg N ha^?1 year^?1 ambient deposition) in a Mediterranean shrubland from central Spain. In autumn 2011 (after 4 years of experimental duration), soil cores were taken to extract the soil fauna. Acari (45.54%) and Collembola (44.00%) were the most represented taxonomical groups, and their abundance was negatively related to soil pH. Simulated N deposition had an impact on the total number of individuals in soil as well as on Collembola and Pauropoda abundance. Collembola abundance increased with N loads up to 20 kg N ha^-1 year^-1 and then decreased. This response was attributed to soil acidification (between 0 and 20 kg N ha^-1 year^-1) and increased soil ammonium (between 20 and 50 kg N ha^-1 year^-1). Pauropoda were favoured by additions of 50 kg N ha^-1 year^-1, and it was the only taxonomical group whose abundance was exclusively related to N deposition, suggesting their potential as bioindicators. Contrary to predictions, there was a negative relationship between soil faunal abundance and plant diversity. In conclusion, soil faunal communities from semiarid Mediterranean ecosystems in central Spain seem to be primarily influenced by soil chemistry (mainly pH) but are also susceptible to increased N deposition. The main drivers of change under increased N deposition scenarios seem to be soil acidification and increased ammonium in soils where nitrate is the dominant mineral N form.     

Reactions of 15N-labelled urea with jack pine forest-floor materials

Urea, labelled with¹⁵N, was applied, at rates equivalent to 0–400 kg N ha^?1, to mixed L + F horizon soil materials from a jack pine (Pinus banksiana Lamb.) forest. The L + F materials were held at 13°C and 33 kPa moisture in three experiments lasting from 6 to 128 days. In the first experiment the immobilization of fertilizer N was determined, in the second the stimulation of microbial activity was measured, and in the third urea reactions in a forest floor without microorganisms were examined. Urea stimulated microbial activity and microbial mineralization of soil N. Total amounts of N immobilized and recovered as organic N, after 128 days, increased with rate of application from 50 to 400 kg urea-N ha^?1. The pH and C contents of water extracts of soil increased with increasing rates of urea application. Organic matter in a forest floor treated with urea was shown to solubilize after microbial activity was inhibited by gamma radiation, and this suggests that chemical C release was brought on by the urea. Results from this study were consistent with the hypothesis that microbial activity in urea-treated soil is stimulated by increased availability of C in soil.     

Retrogradation of Starches from Different Botanical Sources

Retrogradation in 2% pastes prepared from unmodified commercial starches by cooking at 98–100°C under low shear, then held at 4°C for 56 days, was examined by turbidometric analysis and light microscopy. Turbidometric analysis revealed that retrogradation rates followed the order of wheat, common corn > rice, tapioca, potato ≫ waxy maize. Microstructures of stored pastes were examined both before and after centrifugation. Granule remnant morphologies and fresh and stored paste microstructures were unique to each starch examined. Fresh pastes from amylose-containing starches were dominated by networked amylose that condensed into higher density aggregates upon storage. Unique phenomena seen in some stored pastes included interactions of granular remnants with aggregated amylose, composite networks of co-associated amylopectin and amylose, and slight birefringence regained by granule remnants. Microstructural changes in stored pastes could be related to changes in turbidity and to the results of other methods used to quantitate retrogradation.     

Relationships between buffer acidity and exchangeable acidity in lime trials with Ultisols and Histosols

Abstract

Lime requirements ordinarily are based on buffer methods but could be based on unbuffered salt‐exchangeable acidity. The relationships between exchangeable acidity (EA) and buffer acidity (BA) were studied across a range of pH levels established through lime trials in four Ultisols and one Histisol in North Carolina Coastal Plain and Piedmont regions. Buffer acidity was proportionately higher than EA in all soils at any pH level. Linear regression slopes between either BA or EA and pH, within each soil, were not significantly different when the latter relationship included samples with pH less than or equal to 5.4. Variations in EA accounted for by BA ranged from 41 to 67% among the soils investigated. Buffer acidity alone accounted for 64% of the variation in EA for samples from all soils with pH less than or equal to 5.4. Including a squared BA term and either HM or CEC increased the R² to 0.79 and 0.86, respectively, but neither equation provided a completely suitable prediction of EA across all five soils investigated.     

Impacts of Pollution from Different Sources on Ecological Quality of a Multiple-use Coast

Investigation of pollution sources and their impacts on ecosystems is important, not only for better understanding the responses of an ecosystem to pollutants, but also for making practicable prevention and control plans. In this study, ecological quality of three areas which received different source pollutants in Shanghai coast were evaluated and compared in four seasons using Shannon–Wiener index (H′), a benthic diversity index as an indicator of ecological quality of coastal waters. The genotoxicity and physical-chemical variables of water samples were also analyzed. The H′ value indicated the ecological quality of Shanghai coastal waters was seriously impacted, and the ecological quality of two areas receiving waste discharges were significantly worse than that of the natural protection zone but not significantly different in four seasons. The positive genotoxic response was detected in most samples from two discharge zones but not detected in the samples from the natural protection zone. However, no significant difference was observed in water quality variables in the different coastal areas. Our study suggested that the point source pollution had significantly contributed to the genotoxicity of the coastal waters and impaired benthic assemblages, while the deterioration of ecological quality status was also critically impacted by the stressors from other sources.     

Sources of nitrite in a permanent grassland soil

The objective of this study was to separate the observed nitrite (NO₂^–) concentration in a permanent grassland soil into process‐specific subpools. A laboratory experiment was carried out where either the nitrate and/or ammonium pool was labelled with ¹⁵N at 60 atom % excess. The main N transformations that occurred in this experiment were analysed with a ¹⁵N tracing model extended with a NO₂^– submodel. Techniques that have been used to date have been only able to identify NO₂^– subpools related to nitrification (NO₂^–_nit) and denitrification (NO₂^–_den). With the analysis presented here, we were able to quantify the size of an additional NO₂^– pool in the soil related to organic N turnover (NO₂^–_org). All transformations related to NO₂^– turnover of the three subpools occurred simultaneously. After non‐linear parameter optimization the model predicted that on average NO₂^–_den, NO₂^–_nit and NO₂^–_org pools contributed 57, 33 and 10% to the total soil NO₂^– concentration. The finding that heterotrophic processes can contribute to the NO₂^– dynamics in permanent grassland soils might also have important implications for the understanding of gaseous N production that are tightly linked to NO₂^– turnover. Further work is needed to find out how important the conversion of organic N to NO₂^– is in other soil‐based ecosystems and to identify the microbial groups responsible for this process.     

Effects of altered precipitation and wolf spiders on the density and activity of forest-floor Collembola

A 2×2 factorial field experiment was conducted in a deciduous forest to determine how changes in moisture and numbers of a common wolf spider, Schizocosa, affect Collembola abundance and activity. Each of four 4-m² fenced, roofed plots was divided into eight 0.5-m² fenced subplots, and each subplot was assigned a rainfall treatment (drought or high-rainfall) and a Schizocosa treatment (Schizocosa-removal or Schizocosa-addition). Water was sprayed on the high-rainfall subplots weekly from 7 August to 1 October 2003 at a rate of roughly 2× the long-term mean, while the drought subplots received no water. In order to increase the probability of uncovering possible effects of Schizocosa, predatory arthropods (Schizocosa, other spiders, and centipedes) were first removed from all subplots; Schizocosa-addition subplots were then stocked with five juvenile Schizocosa on 19 August, with additional Schizocosa added throughout the experiment. An index of relative Collembola activity was calculated by comparing the number captured in pitfall traps (activity-density) with absolute density (no./m²) measured by extracting Collembola from litter samples. Decreased moisture reduced overall Collembola density, but led to increased Collembola activity. This response to rainfall was exhibited by the families Entomobryidae, Tomoceridae, and Hypogastruridae. The presence of Schizocosa had no impact on overall Collembola density, nor did spider presence affect Collembola activity, with the possible exception of the Hypogastruridae, for which there was an interaction between rainfall and Schizocosa presence. Hypogastrurid Collembola were more active in the drought subplots and exhibited the same level of activity in the presence or absence of Schizocosa under drought conditions. However, in the high-rainfall treatment, the presence of Schizocosa increased hypogastrurid activity.