Water-soluble organic matter and biological activity of a degraded soil amended with pig slurry

The effects of pig slurry (PS) addition at rates of 30, 90 and 150 m(3) ha(-1) per year for five consecutive years on total organic C (TOC), water-soluble organic C (WSOC), soil microbial biomass C (MBC), basal respiration (BR) and dehydrogenase (DEH) and beta-glucosidase (GLU) activities of soil were investigated in a field experiment conducted under barley cultivation and semiarid conditions. Cumulative PS addition at 90 and 150 m(3) ha(-1) rates had a significant stimulating effect on MBC content and DEH and GLU activities. In contrast, no significant effect of PS amendment on TOC, WSOC and BR was detected. These results suggest that PS addition revitalizes soil microbial metabolism in transitory form because of the low stability of the added organic matter.     

Influence of a stormwater sediment deposit on microbial and biogeochemical processes in infiltration porous media

The purpose of this study was to test the relative influence of organic matter quantity and quality and the pollutant content of a stormwater sediment deposit on mineralization processes, microbial characteristics, and the release of solutes in infiltration sediment systems. In microcosm experiments, two other natural sediment deposits (one low and one rich particulate organic matter deposits) were studied to compare their effects with those of the stormwater deposit. The results showed that the biogeochemical processes (aerobic respiration, denitrification, fermentative processes), the microbial metabolism (enzymatic activities), and the releases of several solutes (NH(4)(+) and DOC) were stimulated in presence of the stormwater deposit and the natural particulate organic matter (POM)-rich deposit because of the quantity of the POM in these deposits. In the stormwater deposit, the high availability of the POM (indicated by its low C/N ratio and its high P content) produced a higher stimulation of the microbial metabolism than in presence of the POM-rich deposit (with a high C/N ratio). Pollutant (hydrocarbon and heavy metal) contents of the stormwater deposit did not have a significant effect on microbial processes. Thus, main effects of the stormwater sedimentary deposit on infiltration system were due to its organic matter characteristics (quantity and quality). Such organic matter characteristics need to be considered in future studies to determine the contamination potential of stormwater management practices.     

Labile substrates quality as the main driving force of microbial mineralization activity in a poplar plantation soil under elevated CO2 and nitrogen fertilization

Soil carbon (C) long term storage is influenced by the balance among ecosystem net primary productivity (NPP), the rate of delivery of new organic matter to soil pools and the decomposition of soil organic matter (SOM). The increase of NPP under elevated CO(2) can result in a greater production and higher turnover of fine roots or root exudation and, in turn, in an increase of labile C belowground. The aim of this work was to detect if changes in labile C substrates influenced the organic C storage in soils, verifying (i) whether treatments with elevated CO(2) and N fertilization induced changes in the amount and quality of labile C pools and in microbial C immobilization and (ii) whether these changes provoked modifications in the microbial C mineralization activity, and therefore changes in soil C losses. The effect of elevated CO(2) was a significant increase in both seasons (June and October 2004), of all labile C fractions: microbial biomass C (MBC), K(2)SO(4) extractable C (ExC), and water soluble C (WSC). The C/N ratio of the microbial biomass and of the K(2)SO(4) extractable SOM presented a seasonal fluctuation showing higher values in June, whereas the elevated CO(2) increased significantly the C/N ratio of these fractions independent of the season and the N addition, indicating a lower quality of labile SOM. Microbial respiration was more than doubled in October compared to June, confirming that changes in substrate quality and nutrient availability, occurring in the plantation at the beginning and at the end of the vegetative period, influenced the microbial activity in the bulk soil. Furthermore, the microbial respiration response to N fertilization was dependent on the season, with an opposite effect between June and October. The kinetic parameters calculated according to the first-order equation C(m)=C(0)(1-e(-kt)) were unaffected by elevated CO(2) treatment, except C(0)k and MR(basal), that showed a significant reduction, ascribable to (i) a lower quality of labile pools, and (ii) a more efficient microbial biomass in the use of available substrates. The C surplus found in elevated CO(2) soils was indeed immobilized and used for microbial growth, thus excluding a priming effect mechanism of elevated CO(2) on SOM decomposition.     

Functional microbial diversity of the railway track bed

Railways constitute relatively unexplored microbial habitats. Little is known about the amounts, activities or distributions of microorganisms and their associated heterotrophic capabilities on railway embankments. The aim of this study was to investigate the microbiology of two Swedish railway tracks in order to fill some of the gaps in the available information. We estimated microbial biomass by means of substrate-induced respiration, microbial activity as basal respiration (BR) and as a kinetically derived parameter (r) hypothesised to correspond to the active fraction of the microbial biomass. It was confirmed that the microbial biomass and activity were low as compared with agricultural soils and that their distributions were distinctly positively skewed. Spatial Kriging revealed that covariance structures were sustained on a scale smaller than the employed sampling grid (<1 m). Substrate richness (SR), as measured with Biolog ECO plates, was used as a quantitative measure of functional diversity. SR correlated to microbial activity and SIR, indicating that functional traits were lacking where the microbial biomass was low or less active. The dependence of microbial activities on basic soil characteristics were inferred by separately designed general linear models. Water content was found to be the most important factor moderating basal respiration and functional diversity, whereas the organic matter content was identified as the most important covariate for SIR. Multivariate analysis of the carbon source utilisation patterns of the Biolog plates with equivalent average well-colour development revealed homogenous substrate utilisation among samples. This indicates that the microbial functional potential is randomly distributed in the railway track bed. In combination, our findings imply that the ecosystem functionality of railway embankments may be seriously hampered as compared with agricultural soils. This has consequences for the risk assessment of herbicides applied to railways.     

A biological quality index for volcanic Andisols and Aridisols (Canary Islands, Spain): variations related to the ecosystem degradation

The aim of this work is to identify indicators of biological activity in soils from the Canary Islands, by studying the variation of selected biological parameters related to the processes of deforestation and accelerated soil degradation affecting the Canarian natural ecosystems. Ten plots with different degrees of maturity/degradation have been selected in three typical habitats in the Canary Islands: laurel forest, pine forest and xerophytic scrub with Andisols and Aridisols as the most common soils. The studied characteristics in each case include total organic carbon, field soil respiration, mineralized carbon after laboratory incubation, microbial biomass carbon, hot water-extractable carbon and carboxymethylcellulase, beta-d-glucosidase and dehydrogenase activities. A Biological Quality Index (BQI) has been designed on the basis of a regression model using these variables, assuming that the total soil organic carbon content is quite stable in nearly mature ecosystems. Total carbon in mature ecosystems has been related to significant biological variables (hot water-extractable carbon, soil respiration and carboxymethylcellulase, beta-d-glucosidase and dehydrogenase activities), accounting for nearly 100% of the total variance by a multiple regression analysis. The index has been calculated as the ratio of the value calculated from the regression model and the actual measured value. The obtained results show that soils in nearly mature ecosystems have BQI values close to unit, whereas those in degraded ecosystems range between 0.24 and 0.97, depending on the degradation degree.     

FACTORS AFFECTING THE SOIL MICROBIAL QUALITY MEASUREMENTS OF BIOMASS QUOTIENT AND RESPIRATION QUOTIENT

The soil microbial biomass quotient (expressed as a percentage of the total soil organic carbon) and the specific rate of carbon-dioxide production by soil microbes (respiration quotient) are often used as indicators of stress on soil microbial populations. A low biomass quotient or a high respiration quotient is considered to be an indication of stress from, for example, toxicity from metals in sewage sludge applied to soils. These metabolic quotients are affected by a wide variety of other factors such as the biodegradability of soil organic-carbon amendments, plant inputs of organic carbon into soils, natural variations in microbial population sizes with depth, and in the rhizosphere of plants. These variations could be sufficiently large to make interpretation of changes in biomass quotient and respiration quotient, as a response to stress, problematical.     

Seasonal variations in decomposition processes in a valley-bottom riparian peatland

A year-long field survey was carried out at a valley-bottom riparian peatland site in North Wales, UK from January 2002 to December 2002 to examine the seasonal variation of decomposition processes and dissolved organic carbon (DOC) concentrations. Peat temperature, physicochemistry, organic carbon pools, basal CO(2) respiration and extracellular enzyme activities (beta-glucosidase, phosphatase, sulphatase and phenol oxidase) were monitored monthly. The results of a principle component eigenanalysis of field data show that concentrations of basal CO(2) respiration, soil solution DOC and phenolics were positively correlated to soil temperature (P<0.01, F=12.25; P<0.001, F=59.8; P<0.001, F=141.27) with Q(10) responses of 2.29, 6.42 and 14.42, respectively. Extracellular enzyme activities, however, were more strongly associated with seasonal changes in ion concentrations and did not correspond significantly to temperature alone suggesting limitations attributable to a combination of continuous anaerobiosis and/or the suppressive compounds. Restraints on soil enzyme activities may limit the loss of CO(2) from the microbial community that is dependent on soil enzyme activities for nutrient availability. The seasonal effect of temperature on DOC may be explained by increased plant rhizodeposition and microbial activity. These results do not imply that the long-term increasing trend in DOC export is explainable by temperature increase but suggest that temperature may be a key factor regulating the seasonal variation in DOC concentrations. Thus, seasonal temperature effects on DOC may represent an important component of long-term models of DOC export.     

Rapid and cost-effective multiparameter toxicity tests for soil microorganisms

Three biochemical parameters, DNA quantification in soil samples and two enzymatic activities, beta-galactosidase and dehydrogenase have been assessed as potential end-points for the use in cost-effective toxicity tests on soil microorganisms. The assessment included the development of a classical dose-response 24-h assay and the incorporation of measurements of the effects on microbial activities in soil column leaching studies and multispecies miniaturised terrestrial systems (MTS). Four different chemicals, copper, a new herbicide, thiabendazole and fenthion were studied. A rapid fluorescence DNA quantification technique did not produce adequate responses. The efforts to quantify DNA after extraction and clean-up procedures failed due to the presence of humic acids. From the protocol of the technique one could see that the technical procedure is time-consuming and expensive and, for this reason, not suitable for use as a parameter in rapid and cost-effective tests. However, the enzymatic activities showed their potential as toxicity end-points. Copper produced a concentration/response inhibition of beta-galactosidase and dehydrogenase with EC50 values of 78.39 and 24.77 mg Cu/kg soil, respectively. In the soil column study, these endpoints allowed the measurement of the microbial activities through the column. The effects of the new herbicide on beta-galactosidase and dehydrogenase activities were statistically significant for the highest application dose (40 g/ha). Thiabendazole affected the microbial activity when mixed within the soil, but no effects were observed when this fungicide was applied on the soil surface. Fenthion produced effects when applied either in the soil or on the soil surface. These results can be explained by the low mobility of thiabendazole. The results show the capabilities of these biochemical parameters to be included as endpoints in cost-effective bioassays.     

Using soil biomass as an indicator for the biological removal of effluent-derived organic carbon during soil infiltration

This study investigates the relationship between soil biomass and organic carbon removal during the infiltration of conventionally treated effluents used for groundwater recharge during soil-aquifer treatment (SAT). Investigations were conducted on samples collected from full-scale SAT sites, revealing a positive correlation between biodegradable organic carbon (BOC) concentrations in the recharged effluents and total viable soil biomass concentrations in the infiltration zone of soil samples collected from respective recharge basins. Findings of this study suggest that BOC limits soil biomass growth and was able to support a steady-state concentration of viable soil biomass that is characteristic to BOC concentrations introduced with the recharged effluents. All investigated sites indicate that BOC is primarily removed within 30 cm soil depth leading to a significant increase in soil biomass levels (measured as substrate induced respiration (SIR), total viable biomass, and dehydrogenase activity (DHA)). Controlled biological column studies revealed that the primary components of BOC in domestic effluents are organic colloids. Findings of this study support that hydrophobic acids, commonly believed to be recalcitrant, may also be attenuated by biological processes during soil infiltration.     

Long-term impact of acid resin waste deposits on soil quality of forest areas I. Contaminants and abiotic properties

Acid resins are residues characterised by elevated concentrations of hydrocarbons and trace elements, which were produced by mineral oil industries in Central Europe during the first half of the last century. Due to the lack of environmental legislation at that time, these wastes were dumped into excavated ponds in public areas without further protection. In this work, the long-term effects of such resin deposits on soil quality of two forest areas (Bayern, Germany) were assessed. We evaluated the distribution and accumulation of contaminants in the surroundings of the deposits, where the waste was disposed of about 60 years ago. General soil chemical properties such as pH, C, N and P content were also investigated. Chemical analysis of resin waste from the deposits revealed large amounts of potential contaminants such as hydrocarbons (93 g kg(-1)), As (63 mg kg(-1)), Cd (24 mg kg(-1)), Cu (1835 mg kg(-1)), Pb (8100 mg kg(-1)) and Zn (873 mg kg(-1)). Due to the location of the deposits on a hillside and the lack of adequate isolation, contaminants have been released downhill despite the solid nature of the waste. Five zones were investigated in each site: the deposit, three affected zones along the plume of contamination and a control zone. In affected zones, contaminants were 2 to 350 times higher than background levels depending on the site. In many cases, contaminants exceeded the German environmental guidelines for the soil-groundwater path and action levels based on extractable concentrations. Resin contamination yielded larger total C/total N ratios in affected zones, but no clear effect was observed on absolute C, N and P concentrations. In general, no major acidification effect was reported in affected zones.     

Influence of irrigation with lagooned urban wastewater on chemical and microbiological soil parameters in a citrus orchard under Mediterranean condition

The reduced availability of water resources in semi-arid Mediterranean regions requires an efficient use of supply sources. Urban wastewater, after treatment to minimise health hazards, may constitute an important resource for irrigation in areas characterised by intensive agriculture. These considerations have motivated an investigation (during the irrigation season 1996) of the dynamics of microbial biomass in the soil of a citrus orchard in eastern Sicily, which has been irrigated for 15 years with lagooned urban wastewater, to evaluate the effects of this practice on soil fertility. The analyses of parameters regarding soil microbial biomass (microbial carbon and microbial nitrogen, soluble carbon and nitrogen, cumulative respiration, respiratory quotient and enzymatic activity in the soil) have confirmed that the evolution of soil microflora is directly conditioned by the type of water used for irrigation and climatic conditions. Just before the beginning of the irrigation season (May), microbial biomass carbon (MBC), soluble C, cumulative respiration and enzymatic activity were significantly higher in the soil irrigated with wastewater with respect to the same soil irrigated with 'clear' water; the qCO2 was significantly lower. In June, after 1 month of irrigation, both soils showed an increase of all microbial parameters except for enzymatic activity and qCO2 which showed a significant reduction. In September, at the end of the irrigation period, there was a decrease of almost all investigated parameters in both plots, which was more evident in the soil irrigated with 'clear' water. The microbial biomass of the soil irrigated with wastewater, during the irrigation period, did not undergo any negative effects, having an evolution analogous to the plot irrigated with 'clear' water. The use of lagooned wastewater after three lustrums has shown, particularly in the dry season, an increase in quantity of easily available nutrients, with an improvement of the metabolic efficiency of soil microflora coupled with a more marked activity of total hydrolase and phosphatases. The variations of the parameters related to the soil microflora were strongly influenced by the seasonal climatic trend.     

Pine forest and grassland differently influence the response of soil microbial communities to metal contamination

Metal pollution can affect soil microbial communities, and vegetation potentially influences this relationship. It can, for example, modify the toxicity of metal to soil microbes by controlling its input to the ground or by altering soil physicochemical properties. This study examined metal effects on soil respiration, potentially active microbial biomass (SIR) and catabolic abilities of culturable heterotrophic bacterial communities (Biolog GN) in pine forest and grassland ecosystems developed on soils contaminated with Zn, Pb and Cd. In samples from non-forested areas we found that metal pollution reduced the microbial biomass and functional diversity of bacteria, while increasing the metabolic quotient. In samples from pine forests we found no relationship between metal pollution and microbial parameters. Metals induced changes in soil respiration neither in forest nor in grassland sites. Generally, microbial performance was determined predominantly by soil physicochemical properties (nutrient content, acidity, contamination level). Vegetation type seemed a minor but important factor influencing microbial communities. More work is needed to determine why even relatively high metal concentrations do not significantly affect microbial communities in forest soils.     

Effect of electrokinetic remediation on indigenous microbial activity and community within diesel contaminated soil

Electrokinetic remediation has been successfully used to remove organic contaminants and heavy metals within soil. The electrokinetic process changes basic soil properties, but little is known about the impact of this remediation technology on indigenous soil microbial activities. This study reports on the effects of electrokinetic remediation on indigenous microbial activity and community within diesel contaminated soil. The main removal mechanism of diesel was electroosmosis and most of the bacteria were transported by electroosmosis. After 25 days of electrokinetic remediation (0.63 mA cm^− 2), soil pH developed from pH 3.5 near the anode to pH 10.8 near the cathode. The soil pH change by electrokinetics reduced microbial cell number and microbial diversity. Especially the number of culturable bacteria decreased significantly and only Bacillus and strains in Bacillales were found as culturable bacteria. The use of EDTA as an electrolyte seemed to have detrimental effects on the soil microbial activity, particularly in the soil near the cathode. On the other hand, the soil dehydrogenase activity was enhanced close to the anode and the analysis of microbial community structure showed the increase of several microbial populations after electrokinetics. It is thought that the main causes of changes in microbial activities were soil pH and direct electric current. The results described here suggest that the application of electrokinetics can be a promising soil remediation technology if soil parameters, electric current, and electrolyte are suitably controlled based on the understanding of interaction between electrokinetics, contaminants, and indigenous microbial community.     

The Use of Biosolids and Other Organic Substances in the Creation of Soil-Forming Materials

This paper describes an experiment which was carried out at a landfill site in north Lincolnshire to investigate the use of biosolids and other organic materials in soil formation. The following organic amendments were incorporated into the surface of the on-site geological clay to form 'topsoil'treatments: (i) nil, (ii) biosolids (digested cake), (iii) waste peat/compost, and (iv) composted green waste. The biosolids were applied at a rate of 70 tDS/ha and all the organic materials were incorporated to a depth of 150 mm. The organic amendments reduced the topsoil bulk density and increased plant available water supply and soil water infiltration rates. Topsoil organic matter, total nitrogen and extractable phosphorus concentrations, biomass nitrogen, readily mineralisable organic nitrogen and soil respiration rates were also increased. Additionally, the biosolids application increased topsoil aggregate stability and soil surface strength.     

Pb contamination and isotopic composition of urban soils in Hong Kong

In the urban environment, intense human activities can lead to degradation of environmental quality and have potential long-term effects on human health. In the present study, Pb contamination of urban soil cores in Hong Kong was investigated using a combination of the 'total' concentration, chemical partitioning and isotopic composition of Pb in the soils. The analytical results showed that urban soil cores in close vicinity to high traffic volumes (> 40000 vehicles per day) were usually contaminated with Pb, suggesting atmospheric deposition of Pb as a consequence of vehicular emissions arising from the combustion of leaded gasoline in the past. Increasing Pb concentrations were generally associated with decreasing 206Pb/207Pb ratios of the contaminated soil cores, offering strong evidence of accumulation of Pb derived from anthropogenic sources. In selected contaminated soil cores, the 206Pb/207Pb ratios tended to increase in the order: carbonate < exchangeable < Fe-Mn oxide < organic < residual fractions. The distribution of the 206Pb/207Pb ratios in the five operationally defined chemical fractions showed that the 206Pb/207Pb ratios generally increased with increasing stability, demonstrating preferential association of anthropogenic Pb with the carbonate, exchangeable, Fe-Mn oxide and organic fractions in the soils.     

Effects of chelates on plants and soil microbial community: comparison of EDTA and EDDS for lead phytoextraction

Most studies on chelate-induced phytoextraction have focused on EDTA-mediated Pb phytoextraction. But EDTA and the formed EDTA-Pb complexes have low biodegradability and high solubility in soil, resulting in an elevated risk of adverse environmental effects. EDDS is an easily biodegradable chelating agent that has recently been proposed as an environmentally sound alternative to EDTA. Consequently, a greenhouse experiment, using a completely randomized factorial design with four replications, was carried out to compare the potential of EDTA and EDDS for chelate-induced Pb phytoextraction with Cynara cardunculus, as well as to investigate the toxicity of these two chelates to both cardoon plants and soil microorganisms. The effects of chelate addition on soil microbial communities were studied through the determination of a variety of biological indicators of soil quality such as soil enzyme activities, basal and substrate-induced respiration, potentially mineralizable nitrogen, and community level physiological profiles. EDTA was much more efficient than EDDS for the enhancement of root Pb uptake and root-to-shoot Pb translocation. In a soil polluted with 5000 mg Pb kg(-1), as a result of the addition of 1 g EDTA kg(-1) soil, a value of 1332 mg Pb kg(-1) DW shoot was obtained. EDDS application resulted in a shoot Pb accumulation of only 310 mg kg(-1)DW. Plants treated with EDDS showed lower values of biomass than those treated with EDTA. EDDS proved to be rapidly degraded, and less toxic to the soil microbial community in control non-polluted soils. Pb-polluted EDDS-treated soils showed significantly higher values of basal and substrate-induced respiration than those treated with EDTA. Although EDDS had a lower capacity to enhance Pb phytoextraction than EDTA, it has the advantage of rapid biodegradation.     

Evaluation of soil biological activity after a diesel fuel spill

Diesel fuel contamination in soils may be toxic to soil microorganisms and plants and acts as a source of groundwater contamination. The objective of this study was to evaluate the soil biological activity and phytotoxicity to garden cress (Lepidium sativum L.) in a soil polluted with diesel fuel. For this, a diesel fuel spill was simulated on agricultural soil at dose 1 l m^− 2. During the experiment (400 days) the soil was not covered in vegetation and no agricultural tasks were carried out. A stress period of 18 days following the spill led to a decrease in soil biological activity, reflected by the soil microbial biomass and soil enzymatic activities, after which it increased again. The n-C₁₇/Pristine and n-C₁₈/Phytane ratios were correlated negatively and significantly with the dehydrogenase, arylsulphatase, protease, phosphatase and urease activities and with the soil microbial biomass during the course of the experiment. The β-glucosidase activity indicated no significant connection with the parameters related with the evolution of hydrocarbons in the soil. Finally, the germination activity of the soil was seen to recover 200 days after the spill.     

Effect of redox conditions on bacterial and fungal biomass and carbon dioxide production in Louisiana coastal swamp forest sediment

Fungal and bacterial carbon dioxide (CO₂) production/emission was determined under a range of redox conditions in sediment from a Louisiana swamp forest used for wastewater treatment. Sediment was incubated in microcosms at 6 Eh levels (-200, -100, 0, + 100, + 250 and + 400 mV) covering the anaerobic range found in wetland soil and sediment. Carbon dioxide production was determined by the substrate-induced respiration (SIR) inhibition method. Cycloheximide (C₁₅H₂₃NO₄) was used as the fungal inhibitor and streptomycin (C₂₁H₃₉N₇O₁₂) as the bacterial inhibitor. Under moderately reducing conditions (Eh > + 250 mV), fungi contributed more than bacteria to the CO₂ production. Under highly reducing conditions (Eh ≤ 0 mV), bacteria contributed more than fungi to the total CO₂ production. The fungi/bacteria (F/B) ratios varied between 0.71-1.16 for microbial biomass C, and 0.54-0.94 for microbial biomass N. Under moderately reducing conditions (Eh ≥ + 100 mV), the F/B ratios for microbial biomass C and N were higher than that for highly reducing conditions (Eh ≤ 0 mV). In moderately reducing conditions (Eh ≥ + 100 mV), the C/N microbial biomass ratio for fungi (C/N: 13.54-14.26) was slightly higher than for bacteria (C/N: 9.61-12.07). Under highly reducing redox conditions (Eh ≤ 0 mV), the C/N microbial biomass ratio for fungi (C/N: 10.79-12.41) was higher than for bacteria (C/N: 8.21-9.14). For bacteria and fungi, the C/N microbial biomass ratios under moderately reducing conditions were higher than that in highly reducing conditions. Fungal CO₂ production from swamp forest could be of greater ecological significance under moderately reducing sediment conditions contributing to the greenhouse effect (GHE) and the global warming potential (GWP). However, increases in coastal submergence associated with global sea level rise and resultant decrease in sediment redox potential from increased flooding would likely shift CO₂ production to bacteria rather than fungi.     

Tracing the sources of nitrate in the Han River watershed in Korea, using delta15N-NO3- and delta18O-NO3- values

The dissolved nitrate concentrations and their nitrogen and oxygen isotopic ratios were analyzed in seasonal samples from Korea's Han River to ascertain the seasonal and spatial variations of dissolved nitrate and its possible sources. Nitrate concentrations in the South Han River (SHR) were much higher than those in the North Han River (NHR), probably because of the more extensive distribution of agricultural fields, residential areas and animal farms in the SHR drainage basin. The nitrogen isotopic composition of dissolved nitrate indicates that nitrate-nitrogen (NO(3)(-)-N) is derived mainly from atmospheric deposition and/or soil organic matter in the NHR but comes principally from manure or sewage, with only a minor contribution from atmospheric deposition or soil organic matter, in the SHR. The oxygen isotopic compositions of dissolved nitrate suggest that most atmospheric nitrate undergoes microbial nitrification before entering the river.     

An environmental record of changes in sedimentary organic matter from Lake Sattal in Kumaun Himalayas, India

Sattal a small mountainous lake in the Kumaun Himalayas has been impacted by various cultural activities in recent years. We explored the effects of human-induced changes in this lake by using various geochemical proxies. Shifts in TOC and N flux, C/N ratio, stable isotopes (δ¹³C and δ¹⁵N), n-alkane, and pigment concentrations in sediments indicate a steady increase in primary productivity over the last few decades. The trophic status of the lake has changed from mesotrophic to eutrophic condition. The C/N, CPI, and TAR based ratios in sediments indicate accumulation of algal matter derived primarily from in situ production, with limited input of terrestrial organic matter from the watershed. The low (between 0.1 and 1‰) δ¹⁵N values imply N₂-fixation by cyanobacteria, and the decrease in δ¹³C values up-core represent the effect of sewage input and land based runoff, or possible contribution from microbial biomass. The pigments change from non-N₂ fixing cyanobacterial species to the N₂-fixing community, and are consistent with the proxy-based productivity shifts inferred in the lake. The deeper sediments are affected by post-diagenetic changes causing an increase in δ¹³C (and possibly δ¹⁵N) due to mineralization of organic C and N.