NATURAL EROSION RATES AND THEIR PREDICTION IN THE IDAHO BATHOLITH1

ABSTRACT: Natural rates of surface erosion on forested granitic soils in central Idaho were measured in 40 m² bordered erosion plots over a period of four years. In addition, we measured a variety of site variables, soil properties, and summer rainstorm intensities in order to relate erosion rates to site attributes. Median winter erosion rates are approximately twice summer period rates, however mean summer rates are nearly twice winter rates because of infrequent high erosion caused by summer rainstorms. Regression equation models and regression tree models were constructed to explore relationships between erosion and factors that control erosion rates. Ground cover is the single factor that has the greatest influence on erosion rates during both summer and winter periods. Rainstorm intensity (erosivity index) strongly influences summer erosion rates, even on soils with high ground cover percentages. Few summer storms were of sufficient duration and intensity to cause rilling on the plots, and the data set was too small to elucidate differences in rill vs. interrill erosion. The regression tree models are relatively less biased than the regression equations developed, and explained 70 and 84 percent of the variability in summer and winter erosion rates, respectively.     

Organotin pollution in China: an overview of the current state and potential health risk

In recent years, considerable amounts of organotin compounds have entered the environment due to the wide industrial applications in China. Organotins were found in various environmental media. An overview of organotin contamination and distribution in China from various environmental samples, including waters and sediments, is presented to better understand the current state of organotin pollution in China and to improve environmental monitoring and management of organotin contamination. Exposure to organotin contaminated water and sediments induces accumulation of organotins in molluscs and biological effects such as imposex. Potential harmful effects on human health may also result from consumption of contaminated seafoods. Detailed information on distribution, impacts and assessment of risk to human health and marine ecosystems is discussed and monitoring of TBT using biomarkers is described. This review highlights the serious organotin contamination of coastal cities in China and emphasizes the need for long-term monitoring and the development of an effective regulatory program.     

Phosphorus and sediment loss in a catchment with winter forage grazing of cropland by dairy cattle

The loss of phosphorus and sediment to surface waters can impair their quality. It was hypothesized that the practice of winter grazing dairy cattle on cropland of moderate slope (5-20%) would exacerbate the loss of P and suspended sediment (SS) from land to water. In a small (4.3 ha) catchment two flumes were installed, upstream and downstream of one field (about 2 ha) that had been cropped for 2 yr and grazed in winter (June-July) by dairy cattle. Flow proportional samples were taken and measured for dissolved reactive phosphorus (DRP), particulate phosphorus (PP), total phosphorus (TP), and SS. During the 2002 hydrologic year (March-February) loads of SS increased per hectare downstream (1449 kg ha(-1)) compared to upstream (880 kg ha(-1)). The same increase from upstream (873 kg ha(-1)) to downstream (969 kg ha(-1)) happened in 2003. However, while in 2003 TP increased downstream by 1.64 kg ha(-1) compared to upstream (0.24 kg ha(-1)), in 2002 an increase of only 0.006 kg ha(-1) at the downstream flume occurred compared to upstream (0.98 kg ha(-1)). Investigation of P transport pathways suggested that overland flow contributed <0.1 kg P ha(-1) to stream flow, 10 and 5% of TP load in 2002 and 2003, with the greater load in 2002 reflecting more rainfall in that year. The contribution to stream flow by subsurface flow was estimated at 0.3 kg P ha(-1). Stream bed sediments showed an increase in total P concentration in summer when no flow occurred due to the admission by the farmer of 10 cattle upstream of the cropped paddock in summer 2001-2002 and 20 cattle between the two flumes in 2003 to graze stream banks. This action was calculated to contribute via dung at least, the remaining P lost: about 0.5 kg P in 2002 and 1.0 kg P in 2003. Clearly, not allowing animals to "clear-up" stream banks is a priority if good surface water quality is to be achieved. Furthermore, compared to stock access the impact of winter grazing cropland on P losses was minimal, but SS load was increased by an average of 75%.     

Growth management of vetiver (Vetiveria zizanioides) under Mediterranean conditions

In spite of the advantages of Vetiver grass in light of environmental aspects, this plant is not used in the Mediterranean region. The objectives of the present study were: (i) to elucidate growth parameters and establishment of Vetiver under Mediterranean conditions suitable for its various environmental applications; and (ii) to develop management practices for growing vetiver under Mediterranean conditions. In greenhouse experiments conducted under controlled conditions it was found that, in general, increasing the minimum/maximum temperatures to 21-29 degrees C significantly increased plant height. In the Mediterranean region, this range of air temperatures is obtained mainly during the summer, from June to September. For air temperatures up to 15-23 degrees C the effect of day length on plant height was insignificant, whereas in air temperature >15-23 degrees C, the plant heights under long day conditions were significantly higher than under short day. The number of sprouts per plant increased exponentially with increasing air temperature, and was not significantly affected by the day length at any air temperature range. In open fields, the heights of irrigated vetiver plants were significantly higher than those of rain-fed plants. It was concluded that, once they were established, vetiver plants could survive the dry summer of the Mediterranean region under rain-fed conditions, but they would be shorter than under irrigation. Cutting or burning of the plant foliage during the spring did not improve the survival of vetiver during the dry summer. In order to obtain fast growth of vetiver and to increase the possibility of its using the rainwater, the plants should be planted in the winter, during February and March. However, under this regime, the vetiver plant cannot be used as a soil stabilizer during the first winter, because the plant is still small. In contrast, under irrigation it is advantageous to plant vetiver at the beginning of the summer; the plant then has sufficient time to grow and develop before the beginning of the winter, so that its effect as a soil stabilizer in the following wet winter could be maximal. It was found that vetiver could grow in a wide range of substrates, such as: sandy soil, loamy sand, clay soil, crushed limestone, sandy clay loam, and tuff/peat mixture.     

Studies on the Drying Characteristics of Zingiber Officinale Under Open Sun and Solar Biomass (Hybrid) Drying

Drying characteristics of Zingiber officinale (Ginger) under the open sun and direct type natural convection solar biomass (hybrid) drying were studied. It has been observed that under open sun drying conditions, the drying rate depends on the product thickness and climatic conditions. The results have been drawn for both the summer (April-May, 2004) and winter (November-January, 2003–04) months of Delhi, in India. In the hybrid drier, the ginger, with a thickness of 0.008 m, dried in 33 hours in comparison to 96 hours in open-sun drying. The overall drying efficiency of the hybrid drier was found to be 18% and 13% under summer and winter climatic conditions respectively. The loss of volatile oil content of the ginger is less in hybrid drier in comparison to open sun drying. It was found that the average drying air temperature of 60°C with average air velocity of 0.6m/sec was sufficient for the drying of ginger in the hybrid drier. Ginger quality after drying is better and drying time is less in the hybrid drier in comparison to open-sun drying. The hybrid drier is a simple device, which can be manufactured with locally available materials and can be used for drying of other spices, vegetables and fruits etc.     

Biological Responses to Contrasting Hydrology in Backwaters of Upper Mississippi River Navigation Pool 25

Water level management in Mississippi River Pool 25 differentially influences off-channel habitats in the mid-pool and lower pool. Hydrologic models indicate lower pool off-channel habitats dry with greater frequency and duration compared to similar habitats at mid-pool. We examined the influence of this contrasting hydrology on substrate characteristics, organic matter, macroinvertebrate, and fish communities in off-channel habitats during 2001–2003. Benthic organic matter standing stocks were stable in mid-pool habitats but lower pool values were variable because of annual differences in moist-soil vegetation production. Generally, small-bodied and multivoltine invertebrate taxa had high community biomass and dominated lower pool habitats, whereas longer-lived and large-bodied taxa were more abundant and had higher community biomass in mid-pool habitats having longer hydroperiods. Fish communities were dominated by cyprinids in both habitats, and mid-pool habitats tended to be higher in overall species richness. Unique fish taxa were collected in each pool, with primarily rheophilic forms in mid-pool habitats and limnophilic forms in lower pool habitats. Results indicate that contrasting hydrology associated with a mid-pool control point directly and indirectly influences biological communities in off-channel habitats. Further, management regimes that promote hydrologic diversity in off-channel habitats may enhance biological diversity at larger spatial and temporal scales.     

Optimizing organic fertilizer applications under steady-state conditions

Because organic N fertilizers must be mineralized before they become plant-available, application designs should consider time and temperature effects on N release as well as crop N requirements. This study presents deterministic (DOpt) and stochastic (SOpt) linear optimization models to determine sustainable land application schedules. The easily solved models minimize the amount of N that is applied while assuring than crop N demands are met as they develop. Temperature effects on N mineralization were included by using the Arrhenius equation to create a temperature-adjusted time series. Uncertainties associated with mineralization rates and the temperature-adjustment (Q10) factor are considered by SOpt. Examples are presented for a summer maize (Zea mays L.) and winter triticale (Triticum aestivum L. x Secale cereale L.) rotation operated by a hypothetical dairy operation in Stanislaus County, California. Monte Carlo simulations were used to test the models. A closed-form solution for estimating the time until steady state is presented and steady-state conditions were reached within 7 yr after applications were initiated. Because of temperature effects, DOpt solutions were 12% greater during the winter and 29% lower during the summer than a reference approach that applied liquid manure at 130% of the crop N demand. Stochastic linear optimization values were 1.7% greater than DOpt values in the summer and 6.2% greater in the winter. Surplus N estimates from Monte Carlo simulations averaged 104 kg ha(-1) for DOpt and 126 ka ha(-1) for SOpt, but SOpt was much less likely to result in crop N deficits. Linear optimization is a viable tool for scheduling organic N applications.     

RESPONSE OF PHYSICAL AND CHEMICAL PARAMETERS TO ELIMINATING THERMAL STRATIFICATION IN A RESERVOIR1

ABSTRACT The effects of maintaining a 19 ha Colorado montane reservoir in a thermally destratified condition for one year were evaluated. Water temperatures were kept nearly vertically agd horizontally isothermal throughout the year. The weighted mean temperature of the lake was 1-4°C colder in winter and 1-2°C warmer in summer than normal. Deep water in summer was up to 6°C warmer than typical hypolimnion temperatures, but summer surface temperature was unaltered. Without destratification dissolved oxygen depletion develops in summer and winter, but by eliminating stratification, oxygen was kept near saturation throughout the year. Alkalinity, pH, conductivity, and total residue were not significantly affected. Seston decreased which was probably due to declines in planktonic diatom populations. Increases in iron and manganese did not occur in deep water during destratification. Calcium concentrations increased slightly. Magnesium and most anions (chloride, nitrate-N, and silica) were not greatly altered, but sulfate concentration was reduced. Artificial destratification, as a reservoir management tool, will be very useful in altering chemical problems; particularly increasing oxygen and decreasing iron and manganese concentrations.     

Waterbird Population Changes in the Wetlands at Chongming Dongtan in the Yangtze River Estuary,China

We studied the changes in wetland habitats and waterbird communities between the 1980s and the 2000s at Chongming Dongtan, a Ramsar site in the Yangtze River estuary, an ecologically important region. This region is an important stopover site for shorebirds along the East Asian–Australasian flyway and is extensively used by waterfowl. A net loss of 11% of the wetland area was estimated during study periods at Chongming Dongtan. The change was dependent on wetland types: while the area of artificial habitats such as paddy fields and aquacultural ponds more than doubled, more than 65% of natural habitats including sea bulrush (Scirpus mariqueter) and common reed (Phragmites australis) marshes were lost over the two decades. An exotic plant species introduced from North America, smooth cordgrass (Spartina alterniflora), occupied 30% of the vegetated intertidal zone by the 2000s. Although waterbird species richness did not change between the 1980s (110) and the 2000s (111), 13 species found in 1980s were replaced by 14 newly recorded species. Moreover, there were more species with declining trends (58) than with increasing trends (19). The population trends of species were affected by residential status and habitat types. Transients, wintering migrants, and habitat specialists were more likely to show declining trends compared to those breeding at Dongtan (including year-round and summer residents) and habitat generalists. Furthermore, species associated mainly with natural wetlands were more likely to decline than those associated mainly with artificial wetlands. These patterns suggest that the loss and change of wetland habitats at Chongming Dongtan adversely affected local population dynamics and might have contributed to the global decline of some waterbird species. Because Chongming Dongtan provides stopover and wintering habitats for many migratory waterbirds, protection and restoration of natural wetlands at Chongming Dongtan are urgently needed.     

Monitoring the progress of attempts to reduce nutrient load and inputs of certain compounds in the north sea by 50%

During the winter period an inverse linear relation is found between the concentration of dissolved nutrients (phosphorus and nitrogen) and salinity in the Dutch coastal zone. This indicates a conservative behavior of these compounds from the river, through the estuary to the sea. During summer this relation is much more scattered because of biological processes. The physical and statistical properties of the relationship between salinity and the concentration of dissolved inorganic phosphorus and nitrogen are used to calculate when, where, and how many samples have to be taken in order to monitor a reduction of a compound accurately. It appeared that at any given salinity in the estuary and in the sea, the winter period is the most suitable season to detect a reduction of a given dissolved compound. The higher the salinity in the estuary, the more samples are required to prove the reduction significantly. A reduction of only 10% cannot even be demonstrated by field measurements during summer at salinities above 25. It is concluded that one cruise from the river to the sea, covering the salinities from 0 to 35 during the winter period, aimed at establishing the relationship between the concentration and salinity by taking samples at a salinity interval of for instance 1%, is sufficient to monitor a wide-ranging reduction of 10%–50% in both the fresh water and marine water. This program must be combined with a sampling at a salinity of 0, directed to determine the riverine temporal variability.     

EFFECTS OF CLEARCUTTING AND SLASHBURNING ON STREAM TEMPERATURE IN SOUTHWESTERN BRITISH COLUMBIA1

A paired watershed study was conducted in western hemlock/western redcedar/Douglas fir forests of southwestern British Columbia to assess the effects of clearcutting and clearcutting plus slash-burning treatments on stream water characteristics. In the case of stream temperatures, both treatments increased summer temperatures as well as summer daily temperature fluctuations. These effects lasted for seven years in the case of the clearcut stream but longer in the case of the clearcut and slashburned stream. Clearcutting increased winter stream temperatures whereas slashburning caused a decrease. These changes lasted less than four years. Clearcutting and slashburning had a greater impact on stream temperatures than did clearcutting alone.     

TBT contamination of remote marine environments: ship groundings and ice-breakers as sources of organotins in the Great Barrier Reef and Antarctica

Remote marine environments such as many parts of the Great Barrier Reef (GBR) and the Antarctic are often assumed to be among the most pristine natural habitats. While distance protects them from many sources of pollution, recent studies have revealed extremely high concentrations of organotins in areas associated with shipping activities. Sediments at sites of ship groundings on the GBR have been found to contain up to 340,000 microg Sn kg(-1). Very high concentrations (up to 2290 microg Sn kg(-1)) have been detected in nearshore Antarctic sediments adjacent to channels cut through sea ice by ice-breaking vessels. In both cases, the bulk of the contamination is associated with flakes of antifouling paint abraded from vessel hulls, resulting in patchy but locally intense contamination of sediments. These particulates are likely to continue releasing organotins, rendering grounding sites and ice-breaking routes point-sources of contamination of surrounding environments. While the areas exposed to biologically-harmful concentrations of leached chemicals are likely to be limited in extent (1000-10,000 m(2)), deposition of antifouling paints constitutes a persistent ecological risk in otherwise pristine marine environments of high conservation value. The risk of contamination of GBR and Antarctic sediments by organotins needs to be considered against an important alternative risk: that less effective antifouling of ships hulls may increase the frequency of successful invasions by non-indigenous species. Additional options to minimise ecological risk include accident prevention and reducing organotin contamination from grounding sites through removal or treatment of contaminated sediments, as has been done at some sites in the GBR.     

Emission of the greenhouse gases nitrous oxide and methane from constructed wetlands in europe

The potential atmospheric impact of constructed wetlands (CWs) should be examined as there is a worldwide increase in the development of these systems. Fluxes of N(2)O, CH(4), and CO(2) have been measured from CWs in Estonia, Finland, Norway, and Poland during winter and summer in horizontal and vertical subsurface flow (HSSF and VSSF), free surface water (FSW), and overland and groundwater flow (OGF) wetlands. The fluxes of N(2)O-N, CH(4)-C, and CO(2)-C ranged from -2.1 to 1000, -32 to 38 000, and -840 to 93 000 mg m(-2) d(-1), respectively. Emissions of N(2)O and CH(4) were significantly higher during summer than during winter. The VSSF wetlands had the highest fluxes of N(2)O during both summer and winter. Methane emissions were highest from the FSW wetlands during wintertime. In the HSSF wetlands, the emissions of N(2)O and CH(4) were in general highest in the inlet section. The vegetated ponds in the FSW wetlands released more N(2)O than the nonvegetated ponds. The global warming potential (GWP), summarizing the mean N(2)O and CH(4) emissions, ranged from 5700 to 26000 and 830 to 5100 mg CO(2) equivalents m(-2) d(-1) for the four CW types in summer and winter, respectively. The wintertime GWP was 8.5 to 89.5% of the corresponding summertime GWP, which highlights the importance of the cold season in the annual greenhouse gas release from north temperate and boreal CWs. However, due to their generally small area North European CWs were suggested to represent only a minor source for atmospheric N(2)O and CH(4).     

Performance analysis of different orc power plant configurations using solar and geothermal heat sources

ABSTRACT

Energy optimization is performed on hybrid solar-geothermal power plant working according to Organic Rankine Cycle and installed in southern Tunisia. The performances of four different configurations of the power plant are studied. Mass and energy balances are established for the different compounds. The effects of the main operating parameters such as the geothermal water temperature, ambient temperature and direct normal irradiation on the power plant performances are analyzed. A code is established using Engineering Equation Solver software (EES) to perform the required calculations. Obtained results show that the hybrid solar-geothermal power plant with a heat recovery system is the most suitable configuration design giving a better overall energy efficiency of 15.77 and13.11% and a maximum net power of 1089 and 1882 kW in winter and summer, respectively. However, in the summer season, using a heat recovery system can valuable only when the water temperature is higher than 66°C. For air-cooled condenser, the suitable condensing pressure is 1 bar in winter and 1.9 bars in summer.     

Wood bison population recovery and forage availability in northwestern Canada

Forage availability was assessed to determine sustainable stocking rates for eight broadly defined vegetation types (Treed Uplands, Treed Lowlands, Mixed Tall Shrub/Sedge, Closed-canopied Willow, and Open-canopied Willow, Meadow, Wetland Grass, Wetland Sedge) for use by wood bison (Bison bison athabascae), a threatened subspecies, in the Canadian boreal forest of northern Alberta. Clip plots (n=108) were used to sample peak availability of herbs and current annual growth of Salix spp. in late summer. Graminoid wetlands dominated by Carex atherodes, Carex aquatilis, Carex utriculata, Scolochloa festucacea, or Calamagrostis stricta produced 1975-4575 kg ha(-1) of fair to good quality forage, whereas treed stands produced < 250 kg ha(-1) of forb-dominated forage (>85% content), which was below a published 25% foraging efficiency threshold of 263 kg ha(-1) for bison. Upland forests that dominate the region produced < or = 1 animal unit day (AUD) of forage per hectare in summer. Most forest understory plants were of poor forage value, suggesting the potential sustainable stocking rate of such areas was actually < or = 0.3 AUD ha(-1), with even lower rates during winter due to snow cover. Herbaceous wetlands contained approximately 78 AUD ha(-1) of forage, but were considered largely unavailable in summer because of flooding and soft organic soils that make access difficult. Conversion of prime foraging habitat to agricultural land, forest expansion due to fire control, and a warmer and wetter climatic regime after the mid-1900s likely contributed to a regional reduction in carrying capacity. It is hypothesized that substantial recovery of the wood bison population toward historical levels will be constrained in northern Alberta by the availability of summer forage, and the limited extent of graminoid wetlands that provide winter foraging habitat.     

Seasonal food use by white-tailed deer at Valley Forge National Historical Park,Pennsylvania, USA

Food habits of white-tailed deer (Odocoileus virginianus) were examined from January to November 1984 via fecal-pellet analysis at Valley Forge National Historical Park (VFNHP), which represents an island habitat for deer surrounded by extensive urbanization, in southeastern Pennsylvania. In addition, use of fields by deer was compared to food habits. Herbaceous vegetation (forbs, leaves of woody plants, and conifer needles) was the predominant food type in all seasons except fall. Acorns and graminoids (grasses and sedges) were important food resources in fall and spring, respectively. Use of woody browse (twigs) was similar among seasons. Field use was relatively high during fall, winter without snow cover (<20 cm), and spring when food resources in fields were readily available. In contrast, use of fields was lowest in summer when preferred woodland foods were available and in winter with snow cover when food in fields was not readily accessible. Patterns of food-type use by deer at VFNHP indicate the year-round importance of nonwoody foods and field habitats to deer populations on public lands such as national parks in the northeastern United States.     

Ammonia emissions from field-simulated cattle defecation and urination

Atmospheric ammonia (NH(3)) is a concern because of its environmental impact. The greatest contribution to atmospheric NH(3) comes from agricultural sources. This study quantified NH(3) volatilization from cattle defecation and urination on pasture under field conditions in Auburn, Alabama. Treatments consisted of beef feces, dairy feces, dairy urine, and a control. The experiment was conducted during four seasons from June 2003 to April 2004. Fresh feces or urine was applied onto grass swards, and NH(3) volatilization was measured up to 14 d after application using an inverted chamber method. Dairy urine was the only significant source of NH(3). Ammonia nitrogen (N) loss differed among seasons, ranging from 1.8% in winter to 20.9% during the warmer summer months. Cumulative volatilization was best described in this experiment by the equation % NH(3)-N loss = N(max) (1 - e(-ct))(i). The highest rate of NH(3) volatilization generally occurred within 24 h. This study suggests that NH(3) volatilization from cattle urine on pasture is significant and varies with season, whereas NH(3) volatilization from cattle feces is negligible.     

Evolution of a Mediterranean Coastal Zone: Human Impacts on the Marine Environment of Cape Creus

This study presents an integrated analysis of the evolution of the marine environment and the human uses in Cape Creus, a Mediterranean coastal area where intense commercial fisheries and recreational uses have coexisted over the last fifty years. The investigation synthesizes the documented impacts of human activities on the marine environment of Cap de Creus and integrates them with new data. In particular, the evolution of vulnerable, exploited species is used to evaluate the fishing impacts. The effects of area protection through the establishment of a marine reserve in the late 1990s and the potential climate change impacts are also considered. The evolution of the human uses is marked by the increasing socioeconomic importance of recreational activities (which affect species and habitats) in detriment to artisanal and red coral fisheries (which principally affect at a species level). Overall, populations of sedentary, vulnerable exploited species, hard sessile benthic invertebrates, and ecologically fragile habitats, such as seagrass meadows, the coralligenous and infralittoral algal assemblages have been the most negatively impacted by anthropogenic activities. Albeit human uses currently constitute the largest negative impact on the marine environment of Cap de Creus, climate change is emerging as a key factor that could have considerable implications for the marine environment and tourism activities. The establishment of the marine reserve appears to have had little socioeconomic impact, but there is some evidence that it had some positive biological effects on sedentary, littoral fishes. Results demonstrate that the declaration of a marine reserve alone does not guarantee the sustainability of marine resources and habitats but should be accompanied with an integrated coastal management plan.     

Ecological effects after an alum treatment in Spring Lake, Michigan

A whole-lake alum treatment was applied to eutrophic Spring Lake during October and November 2005. Eight months later, an ecological assessment of the lake was performed and compared with data collected in 2003 and 2004. Field measurements showed reduced soluble reactive phosphorus (SRP) and total phosphorus (TP) concentrations in the water column the summer after the alum application, but chlorophyll levels and irradiance profiles were not significantly affected. Total macroinvertebrate density declined significantly in 2006 compared with 2004, with chaoborids and oligochaetes experiencing the greatest reductions. Internal phosphorus release rates, measured using sediment cores incubated in the laboratory, ranged from -0.052 to 0.877 mg TP m(-2) d(-1) under anaerobic conditions. These internal loading rates were significantly lower than those measured in 2003 at three out of four sites. Mean porewater SRP concentrations were lower in 2006 than in 2003, but this difference was statistically significant only under aerobic conditions. The NaOH-extractable SRP fraction in the sediment was also significantly lower in 2006 compared with 2003, whereas the HCl-extractable SRP sediment fraction showed the opposite pattern. Overall, these results indicate that the alum treatment effectively reduced internal P loading in Spring Lake. However, water column phosphorus concentrations remain high in this system, presumably due to high external loading levels, and may account for the high chlorophyll levels. An integrated watershed management approach that includes reducing internal and external inputs of P is necessary to address the cultural eutrophication of Spring Lake.     

Season and bedding impacts on ammonia emissions from tie-stall dairy barns

Federal and state regulations are being promulgated under the Clean Air Act to reduce hazardous air emissions from livestock operations. Few data are available on emissions from livestock facilities in the USA and the management practices that may minimize emissions. The objective of this study was to measure seasonal and bedding impacts on ammonia emissions from tie-stall dairy barns located in central Wisconsin. Four chambers each housed four Holstein dairy heifers (approximately 17 mo of age; body weights, 427-522 kg) for three 28-d trial periods corresponding to winter, summer, and fall. A 4x4 Latin Square statistical design was used to evaluate four bedding types (manure solids, chopped newspaper, pine shavings, and chopped wheat straw) in each chamber for a 4-d ammonia monitoring period. Average ammonia-N emissions (g heifer(-1) d(-1)) during summer (20.4) and fall (21.0) were similar and twice the emissions recorded during winter (10.1). Ammonia-N emissions accounted for approximately 4 to 7% of consumed feed N, 4 to 10% of excreted N, and 9 to 20% of manure ammonical N. Cooler nighttime temperatures did not result in lower ammonia emissions than daytime temperatures. Ammonia emissions (g heifer(-1) d(-1)) from chambers that contained manure solids (20.0), newspaper (18.9), and straw (18.9) were similar and significantly greater than emissions using pine shavings (15.2). Chamber N balances, or percent difference between the inputs feed N and bedding N, and the outputs manure N, body weight N, and ammonia N were 105, 90, and 89% for the winter, summer, and fall trials, respectively. Relatively high chamber N balances and favorable comparisons of study data with published values of ammonia emissions, feed N intake, and manure N excretion provided confidence in the accuracy of the study results.