Thirteen-year survival study of an environmentalEscherichia coli in field mini-plots

A multiple-antibiotic resistantE. coli was applied to rye-grass covered field mini-plots to simulate point-source contamination. Using three mini-plots for testing and a fourth as a control, the ability of the tracer bacterium to survive under field conditions was studied. Three test plots each received separately 10⁷, 10⁸, or 10¹⁰ cfu mL^?1 E. coli grown for 24 h. in 5 L one-third strength Tryptic soy broth. In Phase I of the study, it was determined that the tracer disappeared from leaf surfaces of rye-grass covering the plots after 41 days. In Phase II, determination of the presence of the tracer in the top 2″ (5 cm) of soil after two months elapsed time indicated that tracer cfu/g dry wt. of soil had declined five, three, and three-logs for test plots 1,2, and 3. In Phase III, subsurface soil sampling using a soil auger on the three test minei-plots indicated the tracer had penetrated through the top-soil and into the underlying B horizon (20 to 50 cm down). In Phase IV, detailed sampling by excavation of the subsurface soil Horizons of the third test mini-plot showed that the tracer had also penetrated through the hardpan (C Horizon) located 0.6 m below the surface to enter the groundwater (1.06 m deep) (Phase V).E. coli counts fell precipitously to 10³ cfu g^?1 in soil and then, in the groundwater at the groundwater-soil interface, persisted at a concentration of 10³ cfu 100 mL^?1 for 2 yr. As time past, tracer counts fell to 145 cfu/100 mL in 6 yr. rose to 820 cfu 100 mL^?1 in 1986 (8 yr elapsed time), and then fell to 25 cfu 100 mL^?1 in 1991 after 13 yr. Serotyping of 1986E. coli isolates indicated that 62% were of the original tracer serotype (0.128:B12) while only 43% of the 1991 isolates were of the same serotype. The penetration rate of the tracer down through the mini-plot soil into the groundwater was 0.02 m day^?1 while downslope dispersion occurred at an estimated rate of 1.0 m day^?1. The implications of the above findings are discussed.     

Concentrations and Exports of Fecal Indicator Bacteria in Watersheds with Varying Densities of Onsite Wastewater Systems

The research goal was to determine if onsite wastewater system (OWS) density had an influence on the concentrations and watershed exports of Escherichia coli and enterococci in urbanizing watersheds. Eight watersheds with OWS densities ranging from <?0.1 to 1.88 systems ha^?1 plus a watershed served by sewer (Sewer) and a mostly forested, natural watershed (Natural) in the Piedmont of North Carolina served as the study locations. Stream samples were collected approximately monthly during baseflow conditions between January 2015 and December 2016 (n?=?21). Median concentrations of E. coli (2014 most probable number (MPN) 100 mL^?1) and enterococci (168 MPN 100 mL^?1) were elevated in streams draining watersheds with a high density of OWS (>?0.77 system ha^?1) relative to watersheds with a low (<?0.77 system ha^?1) density (E. coli: 204 MPN 100 mL^?1 and enterococci: 88 MPN 100 mL^?1) and control watersheds (Natural: E. coli: 355 MPN 100 mL^?1 and enterococci: 62 MPN 100 mL^?1; Sewer: 177 MPN 100 mL^?1 and 130 MPN 100 mL^?1). Samples collected from watersheds with a high density of OWS had E. coli and enterococci concentrations that exceeded recommended thresholds 88 and 57% of times sampled, respectively. Results show that stream E. coli and enterococci concentrations and exports are influenced by the density of OWS in urbanizing watersheds. Cost share programs to help finance OWS repairs and maintenance are suggested to help improve water quality in watersheds with OWS.     

Nutrient,Sediment, and Bacterial Losses in Overland Flow from Pasture and Cropping Soils Following Cattle Dung Deposition

Abstract

The loss of phosphorus (P), suspended sediment (SS), ammonia (NH₄ ⁺‐N), nitrate (NO₃ ^?‐N), and Escherichia coli in overland flow (OF) from dairy cattle dung can impair surface water quality. However, the risk of P and N loss from grazed pastures varies with time. Current practice in southern New Zealand is to select a field, cultivate, sow in Brassica spp., and graze in winter to save remaining pasture from damage. This deposits dung when soil is wet and OF likely. Hence, we determined P, NH₄ ⁺‐N, NO₃ ^?‐N, and E. coli loss from dung in OF via simulated rainfall from intact grazed pasture and cropland treatments of a soil. Analysis of OF, 0, 1, 4, 11, 24, and 43 days after dung deposition at the upslope end of soil boxes indicated that total P (TP), NH₄ ⁺‐N, and SS concentrations decreased sharply from day zero and leveled out after 11 days. More particulate P and SS were lost from the cultivated than pasture treatment, whereas the reverse occurred for dissolved organic P because of greater sorption of phytase active materials. Escherichia coli losses were high (1×10⁵ 100 mL^?1) in both treatments throughout. Using the equations of fit in an example field site indicated that management of dung deposition could affect up to 25–33% of TP lost in OF.     

Discharge of Escherichia Coli from Agricultural Surface and Subsurface Drainage Water: Tillage Effects

Drainage water from agricultural fields with applied manure can degrade the bacterial quality of surface and groundwater. The impact of conventional tillage (CT) and zero tillage (ZT) practices on Escherichia coli (E.coli) discharge through artificially drained soils is not well understood. Consequently, two field trials were conducted during 2002–2004. The first trial involved fall applications of beef manure while the second involved spring applications of dairy manure. Both surface and subsurface drainage water were monitored in the first trial while only subsurface drainage water was monitored in the second. Under fall applied beef manure (trial 1), no differences (p?>?0.05) were observed in E.coli concentrations (cfu/100 ml) in combined drainage water under both tillage systems. However, during 2003–2004, subsurface drainage water under ZT had higher E.coli concentrations and loads than drainage water under CT. When the combined (surface + subsurface) annual E.coli loads were considered, CT loads were greater than ZT during 2002–2003 with an opposite situation during 2003–2004. Overall, annual E.coli loads were similar under ZT (4.7?×?10¹⁰ cfu/ha) and CT (4.8?×?10¹⁰ cfu/ha). Spring dairy manure application (trial 2) produced significant (p?>?0.03) tillage effect on E.coli loads in subsurface drainage water only during the second year. During the study period, ZT plots (1.55?×?10¹⁰ cfu/ha) discharged 5× more E.coli than CT (0.23?×?10¹⁰ cfu/ha). A longer duration of ZT practices resulted in higher subsurface flow volumes and subsequently greater loads of E.coli discharge in both trials.     

Microbiological Quality Assessment of Watershed Associated with Animal-Based Agriculture in Santa Catarina, Brazil

Environmental problems many times could evolve when manure-containing pathogens are distributed into an open environment with no effort made to reduce the content of pathogens or limit their movement in the environment. Wind, surface flow, and subsurface flow can all carry enough pathogens to receiving waters to exceed water quality standards. This study was conducted to assess the microbiological quality of water associated with animal-based agriculture in the sub-basin of Pinhal River located in the rural area of Concordia, Santa Catarina, Brazil. Six sampling points representing different agricultural land uses (LU1—dairy cattle; LU2—without animals; LU3—dairy + pigs + poultry + crops; LU4—pigs + poultry + crops; LU5—dairy + pigs + poultry + crops + human; and LU6—dairy+pigs+crops) along the Pinhal River sub-basin (north to south) were sampled biweekly from August 2006 to December 2008. Concentrations of fecal coliforms and Escherichia coli varied significantly (p?≤?0.05) with land use (LU), but there was no interaction effect of LU, season, and time. Water samples from the catchment area of LU1 had the highest concentration of fecal coliforms (4,479?±?597 CFU ml^?1) when compared with other catchment areas. Catchment area associated with LU2 (no animal) had the lowest concentrations of fecal coliforms (39.2?±?5.2 CFU ml^?1). With the exception of LU2 (control site), all the maximum concentrations of E. coli exceeded the single maximum allowable concentration for E. coli (100 CFU ml^?1). When LU1 was compared with other catchment areas (LU3, 50%; LU4, 67%; LU5, 58%; and LU6, 44%), it had the lowest counts (39%) of Salmonella sp. Our results suggest that spatial pattern of bacterial water quality is evident, which can be linked to the different land uses and associated practices (present or absent of animal activities). Therefore, varying responses associated with the different land uses would be critical in identifying the importance of different sources of bacteria in the catchment area and the mechanisms transferring them.     

A field trial to evaluate the pollution potential to ground and surface waters from woodchip corrals for overwintering livestock outdoors

Outwintering beef cattle on woodchip corrals offers stock management, economic and welfare benefits when compared with overwintering in open fields or indoors. A trial was set up on a loamy sand over sand soil to evaluate the pollution risks from corrals and the effect of design features (size and depth of woodchips, stocking density, and feeding on or off the corral). Plastic‐lined drainage trenches at 9–10 m spacing under the woodchips allowed sampling of the leachate. Sampling of the soil to 3.6 m below the corral allowed evaluation of pollutant mitigation during vadose zone transport. Mean corral leachate pollutant concentrations were 443–1056 mg NH₄‐N L^?1, 372–1078 mg dissolved organic carbon (DOC) L^?1, 3–13 mg NO₃‐N L^?1, 8 × 10⁴–1.0 × 10⁶Escherichia coli 100 mL^?1 and 2.8 × 10²–1.4 × 10³ faecal enterococci 100 mL^?1. Little influence of design features could be observed. DOC, NH₄ and (in most cases) E. coli and faecal enterococci concentrations decreased 10²–10³ fold when compared with corral leachate during transport to 3.6 m but there were some cores where faecal enterococci concentrations remained high throughout the profile. Travel times of pollutants (39–113 days) were estimated assuming vertical percolation, piston displacement at field moisture content and no adsorption. This allowed decay/die‐off kinetics in the soil to be estimated (0.009–0.044 day^?1 for DOC, 0.014–0.045 day^?1 for E. coli and 0–0.022 day^?1 for faecal enterococci). The mean [NO₃‐N] in pore water from the soil cores (n = 3 per corral) ranged from 114 ± 52 to 404 ± 54 mg NO₃‐N L^?1, when compared with 59 ± 15 mg NO₃‐N L^?1 from a field overwintering area and 47 ± 40 mg NO₃‐N L^?1 under a permanent feeding area. However, modelling suggested that denitrification losses in the soil profile increased with stocking density so nitrate leaching losses per animal may be smaller under corrals than for other overwintering methods. Nitrous oxide, carbon dioxide and methane fluxes (measured on one occasion from one corral) were 5–110 g N ha^?1 day^?1, 3–23 kg C ha^?1 day^?1, and 5–340 g C ha^?1 day^?1 respectively. Ammonia content of air extracted from above the woodchips was 0.7–3.5 mg NH₄‐N m^?3.     

Simulating transport of E. coli derived from faeces of grazing livestock using the macro model

Abstract. Coliforms such as Escherichia coli and E. coli O157 are present in faeces deposited on the ground by grazing livestock, which gives rise to environmental concerns about the consequences of their transport in soil water draining to rivers, lakes, groundwater, water supplies and bathing waters. Following a similar study in relation to slurry spreading (Soil Use and Management 2003; 19, 321–330), a two‐stage approach was adopted to using the dual‐porosity contaminant transport model macro to simulate processes by which E. coli microorganisms from grazing livestock (sheep) pass through the soil to receiving waters via field drains. First, model parameter values were selected to reproduce experimental measurements showing rapid flows of the organisms by macropore flow without trapping in smaller pores. However, because of the large number of parameters and likely experimental errors, the set of values chosen, although plausible, is not necessarily unique and so any predictions should be considered provisional pending validation. Second, a series of predictive simulations was carried out to test the influence of soil and weather conditions on losses to field drains during grazing. These showed that E. coli losses were influenced almost entirely by the soil water content at the time of grazing, rising to a high level during grazing in wet conditions, but low or zero under dry conditions. In contrast, rainfall at the time of grazing had almost no consistent effect, other than large losses on the occasional days with over 20 mm of rain. Overall losses for a period of grazing were generally small during summer, but rose to a high level if grazing continued into autumn, due to the increase in soil water content. This demonstrates that there would probably be substantial reductions in the environmental risks of water pollution by E. coli and other faecal microorganisms if continuous grazing were stopped around early September and replaced by grazing on dry days only.     

Growth and grazed rates of bacterial communities in a bog as determined by the dilution method using a continuous culture system

The population dynamics of bacterial communities in Matsumi-ike Bog located in the campus of the University of Tsukuba was studied by the dilution method with a chemostat. The apparent growth rates of bacteria (total cells, rods, cocci and commas) was linearly proportional to the dilution factor and the growth and grazed rates could be estimated. The micro-zooplankton grazing impact was 14.6% bacterial standing stock hr^?1 and 19.8% bacterial production hr^?1.     

Modellstudien zur Nitratauswaschung unter beweidetem Grünland

Modeling nitrate leaching from grazed pasture A method for estimating nitrate concentrations in seepage water under pastures using the model WASMOD was developed. Urin-N and dung-N input by grazing cattle was calculated as a function of stocking rate, length of grazing, and amounts of urin-N and dung-N excreted (data from literature). Urin-N was modeled as NH₄⁺-fertilizer, dung-N as fresh organic matter (C/N ratio 18.6:1). The model was tested using average stocking rates on pastures and mowing pastures inside the waterworks ‘Föhr-West’ catchment area and a long-term climate scenario (35 yr). The modeled average nitrate concentration (55.5 mg l⁻¹) agreed well with the average nitrate concentration measured in the public wells (59.5 mg l⁻¹). Model studies indicate that the nitrate concentrations in seepage water can be reduced by 40% if the cattle graze only 9 hours per day and no longer than until mid of September.     

Temporal Oscillation and Losses of Three Carbon Forms in a Microcatchment of NW Spain

Long-term agricultural sustainability and water quality may be threatened by inadequate land management. Carbon (C) losses at the catchment scale largely depend on land use and management practices. In “Abelar” farm (A Coruña, NW Spain), swine slurry was directly discharged during a period of about 30 years onto agricultural maize fields and rangeland under cattle production. In 1998, the agricultural fields and rangeland were planted to stands of Eucalyptus globulus. The purpose of this work was to assess the concentrations and losses of total, inorganic, and organic carbon at the outlet of a small catchment (10.7 ha) in the period from March 2007 to December 2010. Nearly 190 water samples were collected; specifically eleven in 2007, sixty-eight in 2008, fifty-six in 2009, and fifty-three in 2010. Total runoff volumes from the catchment were also measured during the 3.7-year study period. Except for a peak recorded in November 2008, total carbon values (TC) ranged from 1.51 to 6.14 mg L^?1, total inorganic carbon (TIC) varied between 0.54 and 3.30 mg L^?1, and total organic carbon (TOC) was between 0.38 and 2.83 mg L^?1; the exception was due to an occasional pig slurry discharge occurring in 2008, which drove the greatest values of the three carbon forms. The season of the year influenced concentrations of total, organic, and inorganic carbon. Total, organic, and inorganic carbon loads exported at the catchment outlet were estimated at the monthly and yearly time scales. Overall, 10 years after planting to the forest, dissolved and total carbon losses were rather small.     

Responses of herbage and cattle tail switch hair δ15N value to long-term stocking rates on a rough fescue grassland

The purpose of this study was to investigate the response of δ¹⁵N in herbage and cattle tail switch hair to long-term grazing pressure on a rough fescue grassland (Festuca campestris Rydb.) near Stavely, Alberta, Canada. Cattle have grazed the paddocks from 15 May to 15 November annually since 1949. Stocking rates were 0, 2.4 and 4.8 animal unit months ha^?1 for non-grazing (Control), moderate grazing (MG) and heavy grazing (HG), respectively. Green standing crop (GSC) was sampled monthly throughout the grazing season in 2007. The GSC was fractioned into neutral detergent fiber (NDF), acid detergent fiber (ADF), and their total nitrogen (TN) concentration and δ¹⁵N values in NDF, ADF and GSC were determined. Tail switch hair samples from cows (>2 years old) and calves (<1 year) were collected at the end of the grazing season in 2007 and 2008 and analysed for δ¹⁵N values. The TN concentrations in NDF and δ¹⁵N values in herbage NDF and ADF fractions were higher (P?15N values in tail hair also decreased (P?15N values in tail hair increased with herbage δ¹⁵N values. The δ¹⁵N values in tail hair were enriched by +5.2‰ compared to herbage δ¹⁵N values in 2007. Changes in δ¹⁵N value in GSC and cattle hair reflect the influence of grazing practices on N cycles through the animal/plant/soil system on this rough fescue grassland.     

Effect of long‐term cattle grazing on seasonal nitrogen and phosphorus concentrations in range forage species in the fescue grassland of southwestern Alberta

Numerous studies have examined the nutritive quality of fodder plants in different seasons but few have related this seasonal response to long‐term grazing intensity. Our objective was to examine the effect of long‐term grazing on the concentrations of total nitrogen, δ¹⁵N, and total phosphorus in selected forage species from the fescue grassland near Stavely, Alberta. Plants were selected from paddocks that had been stocked at 0 (control), 2.4 (moderate grazing), and 4.8 (heavy grazing) animal unit months ha^–1 for 58 years. Plant material from ten species was sampled and analyzed at monthly intervals from May to September in 2007. Total N and P concentrations were not (p > 0.05) affected by grazing for most species, but total N and P concentrations in Poa. pratensis L. were higher (p < 0.05) in grazed treatments than in the control. These results reflect an altered plant phenology through defoliation and illustrate delayed phenology in P. pratensis when grazed. The higher δ¹⁵N concentration for most species in the grazed treatments than the control is an indication of accelerated nitrogen cycling through dung and urine deposition.     

Quantifying farmland shelterbelt impacts on catchment soil erosion and sediment yield for the black soil region,northeastern China

As one part of the ‘Three Norths’ forest protection system, dense farmland shelterbelt networks in northeastern China could greatly modify water and sediment flows. In this paper, catchment soil erosion rate and sediment yield (SY) that are impacted by farmland shelterbelts were estimated using WaTEM/SEDEM model. The shelterbelts reduced catchment soil erosion and SY to some extent. The mean soil erosion rate and specific sediment yield (SSY; defined as the ratio of SY to catchment area; t km^?2 yr^?1) of the 25 reservoir catchments decreased from 351.6 and 93.9 t km^?2 yr^?1 under the supposed scenario without shelterbelts to 331.1 t km^?2 yr^?1 and 86.3% t km^?2 yr^?1 under the current situation with shelterbelts. The sediment trap efficiencies (STEs) varied from 0.01% to 23.6% with an average value of 7.6%. The STEs were significantly correlated with shelterbelt density, catchment perimeter, topographic factors, RUSLEP‐factor and land use patterns including patch density (PD), patch cohesion index (COHESION), Shannon's diversity index (SHDI) and aggregation index (AI). The multiple regression equation involving factors of catchment's topography and morphology and land use pattern has a satisfactory performance, and mean slope gradient (MSG) and AI explained most of the variability of shelterbelts’ STE. This information can help land managers to better design shelterbelts and to reduce water‐derived soil loss at catchment scale.     

Nitrat‐Austräge auf intensiv und extensiv beweidetem Grünland,erfasst mittels Saugkerzen‐ und Nmin‐Beprobung II Variabilität der NO3‐ und NH4‐Werte und Aussagegenauigkeit der Messmethoden

Nitrate leaching from intensively and extensively grazed grassland measured with suction cup samplers and sampling of soil mineral‐N II Variability of NO₃ and NH₄ values and degree of accuracy of the measurement methods Data from a grazing experiment — comparison of mean values, see Anger et al. (2002) — were used to estimate within‐field variability to asses the accuracy of two frequently used methods of estimating NO₃ leaching on pastures: (1) the ceramic suction cup sampling (with 34 cups ha^—1 minimum, calculated climatic water balance, 4 leaching periods) and (2) using the soil mineral‐N method (vertical soil NO₃ and NH₄ content in 0—0.9 m (N_min) measured at the beginning and end of two winters on a minimum of 10 different areas of 50 m² each with a minimum of 7 different sample cores). These methods were used on two permanent pastures with high mean stocking density of cattle of 4.9 LU ha^—1 on 1.3 ha with N‐fertilization of 250 kg N ha^—1 (= intensive [I]) and 2.9 LU without N fertilization on a 2.2 ha pasture (= extensive [E]). The results show that NO₃ leaching on pastures was largely due to few selectively extremely high NO₃ amounts under a few excrement spots — mainly urine spots — which would not be sampled representatively with an acceptable effort in a conventional grazing experiment. In both grazing treatments, very large spatial variation occurred. This was greater between the different suction cups than between the compound mineral N samples of each area. Therefore, a marked skewness and kurtosis demonstrated a non‐normal distribution of samples from suction cups, while mineral N values did not show this effect consistently. Sampling selected mostly spots without noticeable influence of excrement, but a few samples with very high values identified evidently urine spots from summer or autumn grazing. The differences in mean coefficient of variation (CV) between the grazing treatments and estimation methods were mainly based on the stocking rate and the density of excrement spots. CV values were 131 % [I] / 242 % [E] for NO₃ leaching measured with suction cup samplers and of 71 % [I] / 116 % [E] for soil NO₃ values and 24 % [I] / 34 % [E] for soil NH₄ values in 0—0.9 m according N_min‐method. Results of the N_min method are obviously inaccurate even with a sampling intensity much greater than 70 cores ha^—1; and so making an estimation of NO₃ leaching by this method is unsatisfactory for pastures. Compared to this, the results of suction cup sampling are more convincing; but even with a tolerated deviation of ± 20 % from the empirically estimated average and with a 95 %‐confidence interval, the calculated mean minimum number of samples in our experiment should be increased to 146 and 265 suction cups ha^—1 for the intensively and extensively grazed treatments, respectively. This requirement would be prohibitive for many field experiments.     

夏季休牧对高寒矮嵩草草甸温室气体排放的影响

以高寒矮嵩草草甸为研究对象，利用密闭箱－气相色谱法，对夏季休牧8a的围栏草地(休牧草地)和全年放牧的草地(放牧草地)的温室气体排放通量、土壤特性和生物量进行了对比研究。结果表明：与放牧草地相比，休牧草地植被盖度较之高41％，单位面积生物量较之高53％。同时，土壤特性也有较大不同；休牧草地的植被－土壤系统CO₂排放通量比放牧草地低20.7％，测定期间两者CO₂排放通量以每天每公顷排放C的质量计分别为30.7和38.7 kg·(hm²·d)^-1；试验期间高寒矮嵩草草甸植被－土壤系统是大气CH₄的弱汇，休牧后草地土壤对CH₄的吸收能力增强，休牧和放牧草地CH₄的平均吸收强度分别为28.1和21.9 g·(hm²·d)^-1；休牧草地土壤N₂O排放通量比放牧草地低，两者排放通量分别为4.5和7.6 g·(hm²·d)^-1。可见，夏季休牧措施降低了草地对大气中温室气体浓度增加的贡献。     

An evaluation of two bacteriophages as sewage tracers

Two bacteriophages — phage 80 of Staphylococcus aureus and a P2-like phage (?MWD 1) of Escherichia coli (H₂S + ) — were evaluated as sewage tracers. Background plaque concentrations on the S. aureus host were < 1100 mL^?1 in seven (raw and treated) effluents tested but, on E. coli (H₂S +), they ranged from < 1100 mL^?1 in oxidation pond effluents to 1.1 × 10³ 100 mL^?1 in primary treated meatworks effluent. Thus, phage 80 appears to be a suitable tracer for both raw and treated sewage but ?MWD 1 may only be suitable for use in secondary treated effluent. In frozen samples, concentrations of both tracer phages were reduced by 90% within 2 days, but decreased more slowly over the following 68 days to around 5% of the original (unfrozen) titre. In a field test, the two phages were used simultaneously to trace the movement of oxidation pond effluents down a river system. Timing of assay of frozen samples and the advantages and limitations of bacteriophages as sewage tracers are discussed.     

Interactive influence of livestock grazing and manipulated rainfall on soil properties in a humid tropical savanna

Purpose

The effect of uncontrolled grazing and unpredictable rainfall pattern on future changes in soil properties and processes of savanna ecosystems is poorly understood. This study investigated how rainfall amount at a gradient of 50%, 100%, and 150% would influence soil bulk density (ρ), volumetric water content (θ_v), carbon (C), and nitrogen (N) contents in grazed (G) and ungrazed (U) areas.

Materials and methods

Rainfall was manipulated by 50% reduction (simulating drought—50%) and 50% increase (simulating abundance—150%) from the ambient (100%) in both G and U areas. Plots were named by combining the first letter of the area followed by rainfall amount, i.e., G150%. Samples for soil ρ, C, and N analysis were extracted using soil corer (8 cm diameter and 10 cm height). Real-time θ_v was measured using 5TE soil probes (20 cm depth). The EA2400CHNS/O and EA2410 analyzers were used to estimate soil C and N contents respectively.

Results and discussion

The interaction between grazing and rainfall manipulation increased θ_v and C but decreased N with no effect on ρ and C:N ratio. Rainfall reduction (50%) strongly affected most soil properties compared to an increase (150%). The highest (1.241?±?0.10 g cm^?3) and lowest (1.099?±?0.05 g cm^?3) ρ were in the G50% and U150% plots respectively. Soil θ_v decreased by 34.0% (grazed) and 25.8% (ungrazed) due to drought after rainfall cessation. Soil ρ increased with grazing due to trampling effect, therefore reducing infiltration of rainwater and soil moisture availability. Consequently, soil C content (11.45%) and C:N ratio (24.68%) decreased, whereas N increased (7.8%) in the grazed plots due to reduced C input and decomposition rate.

Conclusions

The combined effect of grazing and rainfall variability will likely increase soil θ_v, thereby enhancing C and N input. Grazing during drought will induce water stress that will destabilize soil C and N contents therefore affecting other soil properties. Such changes are important in predicting the response of soil properties to extreme rainfall pattern and uncontrolled livestock grazing that currently characterize most savanna ecosystems.

     

Influence of pH on the elimination of fecal coliform bacteria in waste stabilization ponds

From the results of in vitro studies carried out on wastewater from a stabilization pond it can be concluded that pH values close to 9, as a single factor, do not play any essential role in the die-off of fecal coliform bacteria. The percentage of elmination that occurs in pond water inoculated with 1.1×10¹⁰ cells of E. coli mL^?1 where the pH is maintained at 8.2 (original pH) is 99.997%, a much greater reduction than that observed (94.1%) in distilled water inoculated with the same concentration of E. coli and where pH is increased up to 9.     

Dinitrogen fixation by biological soil crusts in an Inner Mongolian steppe

Eurasian steppe ecosystems are nitrogen-limited and suffer additionally from high grazing intensities in many areas. Soil surface-bound cyanobacteria are able to fix nitrogen and can be the major source of plant available nitrogen in such ecosystems. In this study, the abundance and dinitrogen fixation capacity of the most common soil surface-bound microbial and lichen species were determined at an ungrazed, a winter-grazed, and a heavily grazed steppe site in the Xilin River catchment, Inner Mongolia, People’s Republic of China. The microorganisms were identified as Nostoc spec. and the lichen species as Xanthoparmelia camtschadalis (Ach.) Hale by a combination of classical light microscopy, confocal laser scanning microscopy and molecular analysis of the internal transcribed spacer (ITS1) region of ribosomal RNA. Both species were found exclusively at grazed steppe sites, with a clear difference in abundance depending on the grazing intensity. At the winter-grazed site, Nostoc was more abundant than Xanthoparmelia; for the heavily grazed site, the opposite was found. N₂ fixation was quantified with both the acetylene reduction method and ¹⁵N₂ incubation. Cyanobacterial colonies of Nostoc fixed N₂ vigorously, whereas X. camtschadalis did not at all. The fraction of nitrogen derived from the fixation of molecular nitrogen in Nostoc was 73%, calculated from ¹⁵N natural abundance measurements of Nostoc with X. camtschadalis as reference. The conservatively calculated N₂ uptake by Nostoc was 0.030–0.033 kg N ha⁻¹ for the heavily grazed site and 0.080–0.087 kg N ha⁻¹ for the winter-grazed site for the growing seasons of 2004 and 2005, respectively. Together with previous findings, this study demonstrates that N₂ fixation by Nostoc can potentially replace significant amounts, if not all, of the nitrogen lost in the form of N₂O and NO soil emissions in this steppe ecosystem.     

Nitrat‐Austräge auf intensiv und extensiv beweidetem Grünland,erfasst mittels Saugkerzen‐ und Nmin‐Beprobung I Einfluss der Beweidungsintensität

Nitrate leaching from intensively and extensively grazed grassland measured with suction cup samplers and sampling of soil mineral‐N I Influence of pasture management Leaching of nitrate (NO₃^—) from two differently managed cattle pastures was determined over four winters between 1993 and 1997 using ceramic suction cup samplers (with min. 34 cups ha^—1); additionally, vertical soil mineral‐N content in 0—0.9 m (N_min) was measured at the beginning and end of two winters (with min. 70 different sample cores ha^—1). The experimental site in the highlands north‐east of Cologne, Germany, is characterized by high annual precipitation (av. 1,362 mm between 1993 and 1996). An intensive continuous grazing management (1.3 ha, fertilized with 250 kg N ha^—1 yr^—1, average stocking density 4.9 LU ha^—1, = [I]) was tested against an extensive continuous grazing system (2.2 ha, av. 2.9 LU ha^—1; no N‐fertilizer but an estimated proportion of Trifolium repens up to 15 % of total dry matter in the final year, = [E]). The results can be summarized as follows: (1) Mean leaching losses of NO₃‐N, estimated from suction cup sampling and balance of drainage volume, were 85 kg NO₃‐N ha^—1 [I] and 15 kg NO₃‐N ha^—1 [E] during three wet winters with drainage volumes between 399 and 890 mm; in a dry winter with 105 mm calculated percolation, nitrate leaching decreased by a factor of 5 for both grazing treatments. (2) Although the amount of mineral N in soil (N_min) sampled in late autumn showed differences between intensive and extensive grazing, the N_min method permits no certain indication of the risk of NO₃ leaching. For example, during the winter period 1994/95 a reduction of mineral N in the soil (0—0.9 m) in both grazing treatments was found (—33 [I] / —8 [E] kg NO₃‐N ha^—1 and —26 [I] / —21 [E] kg NH₄‐N ha^—1) whereas during the winter 1996/97 an increase in almost all mean mineral N values occurred (+10 [I] / +2 [E] kg NO₃‐N ha^—1 and +10 [I] / —10 [E] kg NH₄‐N ha^—1). (3) In spite of the differences between both methods, the experiment shows that NO₃‐N leaching under extensive grazing could be reduced almost to levels close to those under mown grassland.