Predicting N transformations from organic inputs in soil in relation to incubation time and biochemical composition

Seventeen different added organic materials (AOM) in a sandy soil were incubated under controlled laboratory conditions (28 °C, 75% WHC), and examined for C and N mineralisation. The transformation of added organics (TAO) model has been presented in previous work for predicting C mineralisation. The two variables (very labile and stable fractions of AOM) used in TAO have been related to the biochemical characteristics of the AOM. The transformed added organic N fraction (TAONF) was estimated from the remaining C_AOM and N_AOM linked by the C-to-N ratios. TAONF was split (P_im parameter) into immobilised N (imN) and inorganic N (inorgN). When necessary, an additional N mineralisation of imN was predicted by first order kinetics (constant k_remin). The TAO version with the two parameters P_im and k_remin allowed us to predict very different dynamics of N mineralisation and N immobilisation from the AOM. In a few cases, another first order kinetic law (constant k_v) was used to predict N volatilisation from inorgN.Biochemical characteristics of AOM were used for predicting N transformations. First, at each incubation date, inorgN was approximated to inorgNa=α(N-to-C_AOM)+β by linear regression. The α, β and −β/α (C-to-N_AOM threshold for mineralisation/immobilisation) were related to time. The TAO expression (1−P_im)TAONF was then replaced by the proposed approximation inorgNa as a function of incubation time and C-to-N_AOM. Secondly, significant relationships were computed between k_remin and organic fibre content of AOM. Finally, a TAO approximation was proposed for predicting the simultaneous transformations of C and N, only using biochemical data (plus the k_v parameter in a few cases of N volatilisation). For all AOMs, the validity of the approximation and its borderline cases were examined by comparing the two TAO versions.     

Macrophyte succession in Swedish lakes caused by deposition of airborne acid substances

Water, Air, & Soil Pollution - Recurrent biological investigations have been made in six lakes in two areas in western Sweden. It has been found that the supply of acid substances induces...     

Current and historical inputs of mercury to high-latitude lakes in Canada and to Hudson Bay

Sediment cores collected from several lakes in northern Canada have been analyzed for mercury and several other chemical contaminants. Sites ranged from the Experimental Lakes Area of northwestern Ontario, north to Cornwallis Island, and west to the southern Yukon. Cores were sliced at sites of collection and individual slices were freeze dried and analyzed for Pb-210 and Cs-137 to estimate average time intervals of deposition. The earliest date estimated by Pb-210 was about 1850, and mercury concentrations in some lakes were clearly increasing before then, assuming no vertical movements of mercury within the sediments. Extrapolation of dates downward to deeper slices, assuming a constant sedimentation rate, indicated that in some lakes mercury inputs increased slowly even in the 1500's, more rapidly after 1750, and more rapidly yet over the current century. These increases are interpreted as increased fluxes of mercury to the lakes as a result of long-range transport of atmospheric mercury, since there are no local industrial sources of mercury. Slices taken near the bottom of a core are taken to estimate the geological component while elevations in excess of that in surface slices are taken to represent contamination from fallout. This partitioning suggests that sediments in the eastern Northwest Territories are dominated by pollution, while those from the western Northwest Territories are influenced more by their geological settings. Two cores from Hudson Bay suggest that mercury is increasing there too, but has not yet exceeded geological sources. Mercury shows little or no tendency to decline in the most recent slices; indicating that inputs of mercury remain at or near their historical maxima. Given relatively high and continuing inputs of mercury to northern lakes it seems likely that some portion of that mercury may find its way into the food chain, hence the long-term prospect is for increasing levels of mercury in northern fish.     

Amino acid composition of ryegrass in relation to nitrogen fertilization and soil water status

In a lysimeter experiment the overall amino acid concentration in dry matter of ryegrass (Lolium perenne) increased in response to nitrogen application. Lack of water reduced the overall concentration of most amino acids in dry matter except proline the concentration of which was increased. Nitrogen application as well as lack of water significantly affected the overall amino acid composition, and in particular the relative concentration of glutamic acid and proline, respectively, which might be attributed to variations in the free amino acid composition, and resulting in a decreasing overall ratio essential/not essential amino acids.     

Changes in amino acid and organic acid composition in tomato and cucumber plants in relation to salinity and nitrogen nutrition

Under conditions of salt stress, plants show qualitative and quantitative alterations in various organic compounds, such as nitrogen (N) compounds and organic acids. In this work, the effect of different saline levels as well as various N levels, supplied as nitrate (NO₃) or as ammonium (NH₄)+NO₃ on the concentration of amino acids and organic acids in the leaves of tomato and cucumber plants has been studied. The effect of the source of N on individual amino acid contents varied with plant species. Most of the amino acids increased when the concentration of N in the nutrient solution was increased, except when N was added as NH₄+NO₃ for tomato. The effect of salt stress depended on which amino acid was considered. The data also indicate that the effect of salinity on each particular amino acid was greatly dependent on the plant species and N source. Organic acids were differently affected by salinity and by the N source, depending on the plant species. In tomato, the concentrations of short‐chain organic acids were 2–3 times higher in NO₃‐supplied plants than in those grown with NH₄+NO₃. Finally, in cucumber, malic acid concentration increased as a function of the saline level in the medium.     

Characterization of Mexican Creole wheat landraces in relation to morphological characteristics and HMW glutenin subunit composition

One hundred lines derived from 14 wheat landraces collected in Mexico were characterized in relation to spike and grain morphology and HMW-glutenin subunit composition. Up to seven botanical varieties were identified among these materials based in four morphological traits. The remaining nine morphological traits showed wide variation. The allelic variation at the Glu-1 loci was wide, although showed a clear risk of genetic erosion due to the low frequency of some alleles. These genotypes could be used as genetic resources to improve important biotic and abiotic traits as well as to widen genetic diversity controlling the HMW glutenin subunit composition of common wheat.     

Composition of the benthos in relation to pH in the LaCloche lakes

In the LaCloche Mountains of Ontario, 11 lakes spanning the pH range 4.8 to 6.7 were sampled for benthic organisms. Sixty sediment cores were collected from each lake, organisms >0.5 mm were separated and 25 taxa were identified. The number of taxa present was correlated negatively with [H⁺]: Y=23.2?4.27 × 10⁵ ×, r²=0.61, p<0.005. The density of all organisms was not correlated with lake pH. Six taxa: gastropods, pelecypods, daphnids, ephemeropterans, amphipods and ceratopogonids, either were reduced in abundance or absent from the more acid lakes. Bosminids and acari were more abundant in lakes of pH 5.0 to 5.5. The densities of the remaining taxa, notably chironomids and oligochaetes, appeared to be independent of pH over the range 4.4 to 6.7. These results are discussed in relation to the hypotheses which have been advanced to explain the differences observed in benthos distribution between lakes in Europe and in North America.     

Development of zooplankton in relation to lime treatment in two acidified lakes

Zooplankton has been studied in Lakes Östra Nedsjön and Ömmern (1974–94), two acidified lakes in South-Western Sweden. The former lake was first limed in 1971–73, and secondly in 1982. The first liming increased the pH-level from ca. 5.3 to 6, and the second one from ca. 5.8 to 7–7.5. The pH-value in Lake Ömmern was about 6.1 in 1973, but decreased to 5.3 in 1981, when liming raised the value to 6.5–7. After the first liming in Lake Ö. Nedsjön, the rotatorians represented in average 1% of the total volume of zooplankton. Among the copepods, which made up ca. 22% of the volume, Cyclops was frequent, and both Eudiaptomus gracilis and Heterocope appendiculata were recorded. After the second liming on the other hand the rotatorians increased to in average 28% of the total volume, while the volume of copepods was only ca. 6%. Heterocope disappeared, and Eudiaptomus and Cyclops, usually favoured by liming, were rare. Consequently the supply of larger forms of crustaceans, suitable as fish food was severely reduced. In Lake Ömmern the effects of acidification within the zooplankton were moderate. The species richness was about the same as in unacidified lakes. After liming the development of zooplankton was similar to that in most other limed lakes, i. e. increased frequency of rotatorians, cladocerans and Cyclops spp. In Lake Ö. Nedsjön, however, the small zooplankton volumes and the elimination of copepods was in contrast to the zooplankton development in other limed lakes and in unacidified ones.     

Fish species distribution in relation to water chemistry in selected Maine lakes

We examined the possible effects of acidity on the number of fish species in 22 lakes in Maine, ranging in pH from 4.4 to 7.0 (mean values). We caught no fish in three lakes with pH <5.0, but collected 1 to 9 species in the remaining 19 lakes (pH 5.4 to 7.0). Brook trout (Salvelinus fontinalis), golden shiners (Notemigonus crysoleucas), and white suckers (Catostomus commersoni) were ubiquitous, but no common shiners (Notropis cornutus) or creek chubs (Semotilus atromaculatus) were collected from lakes with pH below 6.0 and 5.9, respectively. The fishless lakes differed from the others primarily in water chemistry variables related to acidity, i.e., pH, Al, and concentration of divalent cations. Among lakes that contained fish, the factors related to the number of species collected were lake surface area and maximum depth, which may be related to habitat quantity and diversity. Cluster analysis identified two distinct fish species groups — depauperate and cyprinid-sucker — but multiple comparison analysis failed to relate any measured chemical or physical variable to these two groups, probably because water chemistry was suitable for reproduction by these species.     

Hillslope characteristics and particle size composition of surficial armoring on a semiarid watershed in the southwestern United States

Distributed process-based hydrologic models have been used to describe and predict the movement of sediment on small watersheds. However, to parameterize these models requires an understanding of the spatial variability of erosion processes and the particle sizes of the sediment being moved. In this study, a high resolution digital elevation model (DEM) and detailed sediment particle sampling allowed a comparison of hillslope characteristics and particle sizes of surficial armoring in a semiarid watershed. Individual particle size classes on hillslopes are correlated with the underlying sediment type, local slope, aspect, and area draining through a grid element. The strongest correlations are between the underlying sediment and overlying sediment. However, the distribution of the particle size classes is consistent with a hydrodynamic explanation for sorting. In particular, increased area draining through a grid node and increased slope are correlated with higher concentrations of the 16–64-mm particle size class. Both the coarsest and finest particle size classes are significantly correlated with the aspect of flow from a grid cell, with increased coarse particles and decreased fines on east-facing slopes. These spatial differences with aspect are attributed to dry season prevailing winds. These observations about process and spatial distribution are useful in predicting the spatial distribution of particles on the watershed for applications such as distributed hydrologic models.     

Response of limed lakes to episodic acid events in Southwestern Sweden

Occurrence of stratified acidic water is described for five forest lakes situated in the westcoast region of Sweden. Differentiation between two types of acid events is made related to origin; one is caused by heavy rains and the other associated with snowmelt during winter and spring. Acid events are due to incomplete mixing between lake and inflow water. Both mixing forces like wind and density differences are important factors regulating the actual stratification. As observed in the lakes studied, stratification therefore occurs during periods of ice-cover when wind-induced mixing is impeded and generally results in an acidic surface water of varying depth. However, in this study we also describe the stratification of acidic inflow water at the sediment-water interface. This type of inlayering is presumably less frequent as a complex set of conditions must be satisfied for its occurrence. Our study shows that acid events may cause temporal and spatial water chemistry changes even in lakes and streams with relatively high pH and buffer capacity. Thus, early biotic damages can be expected in neutral and limed (soft water) lakes.     

Growth and chlorophyll,mineral, and total amino acid composition of tomato and wheat plants in relation to nitrogen and iron nutrition II. Chlorophyll content and total amino acid composition

Studies of the amino acids distribution in plants subjected to nutrient regimes are limited. The present study investigated the effect of NO₃‐N and FeSO₄‐Fe regimes on chlorophyll and total amino acids composition of tomato and wheat plants. Also the distribution of 17 amino acids between the different plant parts was studied. Increasing the NO₃‐N level up to 200 mg kg^‐1 greatly increased the total amino acids content of tomato plants. The total amino acids content of wheat plants continued to increase with addition of NO₃‐N up to 400 mg kg^‐1. The response of chlorophyll content to NO₃‐N supply was highly dependent on Fe level both in tomato and wheat plants. The interaction between NO₃‐N and FeSO₄‐Fe had a great effect on the total amino acids content and distribution. Iron increased the translocation of proline from roots to leaves. The overall amino acids contents of leaves was higher than that of stems or roots.     

Sediment acid neutralization in softwater lakes

Acid neutralizing capacities (ANC) of sediments from McCloud Lake, Florida and seven other lakes in Wisconsin and Florida were as high as 10 meq 100 g^?1 over the pH range 4.5 to 5.5 in well-mixed batch experiments. Exchange of Ca²⁺ and Mg²⁺ accounted for over 50% of the neutralizing capacity; Al solubilization and sulfate adsorption were unimportant in neutralizing H⁺ additions. ANC was correlated with sediment volatile solids content. Sulfate reduction occurred in microcosms that simulated lake-water interactions and subsurface seepage;in situ pore water profiles and a whole-lake mass balance confirm the occurrence of this process in McCloud Lake. Sediment neutralization is important for lakes that receive most of their water from precipitation and thus are particularly susceptible to acidification.     

Biology and chemistry of three Pennsylvania lakes: Responses to acid precipitation

The biology and chemistry of three northeastern Pennsylvania lakes was studied from summer 1981 through summer 1983 to evaluate lakes with different sensitivities to acidification. At the acidified lake (total alkalinity ≤ 0.0 μeq L^?1) there were fewer phytoplankton and zooplankton species than at the moderately sensitive lakes. The most numerous plankton species in all three lakes are reportedly acid tolerant. Among the benthic macro- invertebrates (BMI) there were more acid tolerant Chironomidae at the acidified lake, but more acid intolerant Ephemeroptera and Mollusca and a higher wet weight at the least sensitive lake. There were no differences among the lakes' BMI mean total numbers or mean number of taxa. The fish community at the acidified lake was dominated by stunted Lepomis gibbosus, but L. machrochirous were most abundant in the other lakes. Principal component analysis suggested a shift in all three lakes over the sampling period toward combined lower pH, alkalinity, specific conductance, Ca and Mg and higher Al and Mn. Such chemical changes have been associated with acidification. The rate and extent of acidification appeared to be controlled by geological and hydrological characteristics of the drainage basins.     

The sensitivity of ecosystems to acid inputs in the Hunter Valley,Australia

This study assesses the importance of H⁺ generation in the Hunter Valley from land use and coal-fired power stations. The Hunter Valley is a temperate coastal landsystem approximately 150 km north of Sydney. Land uses include forestry and national parks, grazing and farming, coal mining, coal-fired electricity generation and manufacturing. The H⁺ generated from land use is estimated from land suitability classes. Wet deposition is estimated from 10 years' rainwater chemistry data and dry deposition is estimated from modelled SO₂ concentrations and a deposition velocity constant. The pH and pH buffer capacity of 51 soils were measured. H⁺ loads from land use ranged from 0.05 to 12 kmol H⁺/ha/year for forests and prime agricultural land, respectively. Estimated H⁺ deposition ranged from 0.27 to 0.65 kmol H⁺/ha/year, depending on the distance and direction from the power stations. The H⁺ load that will lead to critically low pH values in 50 years is 0.27, 0.60, 1.77 and 2.14 kmol H⁺/ha/year for four broad soil classes. The two most sensitive classes, with target loads of 0.27 and 0.60 kmol H⁺/ha/year, occupy 26% and 56% of the study area respectively. Although the total contribution of H⁺ from land use is larger than from deposition (970 vs. 220 Mmol H⁺/year), H⁺ deposition may be important on low fertility nonagricultural soils with low pH buffer capacity. More detailed study of the areas with sensitive soils is warranted.     

重金属迁移与土壤性质的关系

Cu, Zn, Pb and Hg runoff from yellow limestone soil and purple soils and the relationships between the mobility of the heavy metals and the soil characteristics were studied in laboratory using a rainfall simulator. The results showed that the concentrations of soluble Zn in surface runoff were significantly negatively correlated with the contents of < 0.002 mm particles and CEC of the soils, indicating that Zn was mostly adsorbed by clays in the soils. The contents of Cu and Hg in surface runoff were positively related to their contents in the soils. The amounts of Cu, Zn, Pb and Hg removed by surface runoff were influenced by the amounts of soil and water losses and their contents in the soils, and were closely related to the contents of soil particles 1~0.02 mm in size.     

Spatial variability of infiltration patterns related to site characteristics in a semi-arid watershed

Preferential flow may strongly affect hydrology at different scales. Measurement of preferential flow however remains very difficult. Tracer-infiltration profiles are often used to measure the degree of preferential flow at plot scale. These experiments are time-consuming, costly and destructive. As a result existing dye-tracer studies are often based on a limited number of profiles. The aim of this study is therefore to select a limited number of soil and landscape characteristics with high predictive value for the degree of preferential flow. 18 rainfall simulations with a dye-tracer and additional site measurements such as soil type, vegetation type and soil physical parameters were performed in a 1 km² catchment in the Dehesa (Extremadura, Spain). A stepwise multiple regression procedure was used to select variables with a high predictive value for the degree of preferential flow.     

Potassium-supplying power of some northern-Greece soils in relation to clay-mineral composition

The correlation between the content of the clay minerals, mica, montmorillonite or vermiculite, and the logarithmic form $\text{pK-}\text{1}\text{2}\text{p (Ca + Mg)}$ of the activity ratio (K)/√(Ca + Mg) was highly significant for 23 soils from northern Greece. The correlation was negative with mica and positive with montmorillonite and vermiculite. A free-energy term, ΔF¹, necessary to bring the activity ratio of each soil equal to the lowest value encountered, using the concentrations of soluble and exchangeable K and Ca + Mg in the equilibrium systems, was also calculated. The relationship between the content of the three clay minerals and ΔF¹ was the same as when $\text{pK-}\text{1}\text{2}\text{p (Ca + Mg)}$ was used except that the correlation coefficient was greater in all cases, being significant at P_0.001 with each of the clay minerals. The regression of ΔF¹ on each of the clay mineral contents was also much greater than the corresponding ones with $\text{pK-}\text{1}\text{2}\text{p (Ca + Mg)}$.     

Gradual reduction and extinction of fish populations in acid lakes

Fish communities in four lakes sampled over several years were compared against a reference data set of forty-nine lakes in south-central Ontario. Two of the temporal-comparison lakes (Crosson and Grindstone) exhibit significant changes in their fish communities relative to the reference set. This was due to the extirpation of various fish species (white sucker Catostomus commersoni, lake trout Salvelinus namaycush, and blacknose shiner Notropis heterolepis) during the intervening years. A control lake in the temporal comparison (Poorhouse) showed little change in species composition over time and no loss of species. The fourth temporal lake, Plastic Lake, also showed little change likely as a consequence of the previously documented extinctions in this lake. White suckers within Crosson Lake have demonstrated intermittent recruitment and a 89% reduction in population abundance due to acid-induced reproductive constraints in their spawning stream. Similar conditions contributed to the loss of sucker populations and additional species in Grindstone and Plastic Lakes also. Various species in many of the lakes represent metapopulations. Given the barriers imposed by outflow drainage conditions, these accelerated rates of local extinctions have not been balanced by colonizations from other lakes within the watershed. As a consequence the underlying fish communities have been changed and will remain so without active rehabilitation.