Relationship between the loading rate of inorganic mercury to aquatic ecosystems and dissolved gaseous mercury production and evasion

The purpose of our study was to test the hypothesis that dissolved gaseous mercury (DGM) production and evasion is directly proportional to the loading rate of inorganic mercury [Hg(II)] to aquatic ecosystems. We simulated different rates of atmospheric mercury deposition in 10-m diameter mesocosms in a boreal lake by adding multiple additions of Hg(II) enriched with a stable mercury isotope (²⁰²Hg). We measured DGM concentrations in surface waters and estimated evasion rates using the thin-film gas exchange model and mass transfer coefficients derived from sulfur hexafluoride (SF₆) additions. The additions of Hg(II) stimulated DGM production, indicating that newly added Hg(II) was highly reactive. Concentrations of DGM derived from the experimental Hg(II) additions (“spike DGM”) were directly proportional to the rate of Hg(II) loading to the mesocosms. Spike DGM concentrations averaged 0.15, 0.48 and 0.94 ng l⁻¹ in mesocosms loaded at 7.1, 14.2, and 35.5 μg Hg m⁻² yr⁻¹, respectively. The evasion rates of spike DGM from these mesocosms averaged 4.2, 17.2, and 22.3 ng m⁻² h⁻¹, respectively. The percentage of Hg(II) added to the mesocosms that was lost to the atmosphere was substantial (33–59% over 8 weeks) and was unrelated to the rate of Hg(II) loading. We conclude that changes in atmospheric mercury deposition to aquatic ecosystems will not change the relative proportion of mercury recycled to the atmosphere.     

Epiphytic cyanobacteria maintain shifts to macroalgal dominance on coral reefs following ENSO disturbance

Macroalgal dominance of some tropical reef communities in the Eastern Pacific after coral mortality during the 1997-1998 El Ni?o Southern Oscillation (ENSO) was facilitated by protection from herbivory by epiphytic cyanobacteria. Our results do not support that reduction in number of herbivores was a necessary precursor to coral reef decline and shifts to algal reefs in this system. Rather, macroalgae dominated the community for several years after this pulse disturbance with no concurrent change in herbivore populations. While results of microcosm experiments identified the importance of nutrients, especially phosphorus, in stimulating macroalgal growth, nutrient supply alone could not sustain macroalgal dominance as nutrient-stimulated growth rates in our in situ experiments never exceeded consumption rates of unprotected thalli. In addition, thalli with nutrient-enriched tissue were preferentially consumed, possibly negating the positive effects of nutrients on growth. These tropical reefs may be ideal systems to conduct experimental tests distinguishing phase shifts from alternative stable states. Shifts were initiated by a large-scale disturbance with no evidence of a changing environment except, perhaps, dilution in herbivory pressure due to increased algal cover. Community establishment was most likely stochastic, and the community was likely maintained by strongly positive interaction between macroalgal hosts and cyanobacterial epiphytes that uncoupled consumer control of community structure.     

Habitat-specific impacts of multiple consumers on plant population dynamics

Multiple consumers often attack seeds, seedlings, and adult plants, but their population-level consequences remain uncertain. We examined how insect and small mammal consumers influenced the demography and abundance of the perennial shrub, bush lupine (Lupinus arboreus). In grassland and dune habitats we established replicate experimental lupine populations in 81-m2 plots that were either protected from, or exposed to, herbivorous voles and granivorous mice (via fencing) and/or root feeding insects (via insecticide treatment). Populations were initiated with transplanted seedlings in 1999 and 2000. We followed the demography of these cohorts, subsequent generations, and the seed bank for 5.5 years. Voles and insects killed many seedlings in dune (1999 only) and grassland (1999 and 2000) habitats. After 2000, insects and voles had minimal effects on seedling or adult survival. Seed predation by granivorous mice, however, greatly depressed seedling recruitment, resulting in lower adult lupine abundance in control plots vs. those protected from rodents. In grasslands, initial effects of voles and insects on seedling survival produced large differences among treatments in adult plant density and the cumulative number of seeds produced throughout the experiment. Differences among grassland populations in seed rain, however, had little influence on the magnitude of seedling recruitment into this habitat. Instead, recruitment out of a preexisting seed bank compensated for the lack of seed production in populations exposed to consumers. Shading by dense adults in plots protected from consumers limited seedling establishment within these populations. Although differences among populations in cumulative seed rain did not influence adult establishment, populations protected from consumers accumulated substantially larger seed banks than controls. These results illustrate how density dependence, habitat-specific seed dynamics, and particular demographic impacts of consumers interact to shape plant population responses to consumers.     

Detection and Classification of Motor Vehicle Noise in a Forested Landscape

Noise emanating from human activity has become a common addition to natural soundscapes and has the potential to harm wildlife and erode human enjoyment of nature. In particular, motor vehicles traveling along roads and trails produce high levels of both chronic and intermittent noise, eliciting varied responses from a wide range of animal species. Anthropogenic noise is especially conspicuous in natural areas where ambient background sound levels are low. In this article, we present an acoustic method to detect and analyze motor vehicle noise. Our approach uses inexpensive consumer products to record sound, sound analysis software to automatically detect sound events within continuous recordings and measure their acoustic properties, and statistical classification methods to categorize sound events. We describe an application of this approach to detect motor vehicle noise on paved, gravel, and natural-surface roads, and off-road vehicle trails in 36 sites distributed throughout a national forest in the Sierra Nevada, CA, USA. These low-cost, unobtrusive methods can be used by scientists and managers to detect anthropogenic noise events for many potential applications, including ecological research, transportation and recreation planning, and natural resource management.     

Accumulation of perchlorate in aquatic and terrestrial plants at a field scale

Previous laboratory-scale studies have documented perchlorate ClO(-)(4) uptake by different plant species, but less information is available at field scale, where ClO(-)(4) uptake may be affected by environmental conditions, such as distance to streams or shallow water tables, exposure duration, and species. This study examined uptake of ClO(-)(4) in smartweed (Polygonum spp.) and watercress (Nasturtium spp.) as well as more than forty trees, including ash (Fraxinus greggii A. Gray), chinaberry (Melia azedarach L.), elm (Ulmus parvifolia Jacq.), willow (Salix nigra Marshall), mulberry [Broussonetia papyrifera (L.) Vent.], and hackberry (Celtis laevigata Willd.) from multiple streams surrounding a perchlorate-contaminated site. Results indicate a large potential for ClO(-)(4) accumulation in aquatic and terrestrial plants, with ClO(-)(4) concentration in plant tissues approximately 100 times higher than that in bulk water. Perchlorate accumulation in leaves of terrestrial plants was also dependent on species, with hackberry, willow, and elm having a strong potential to accumulate ClO(-)(4). Generally, trees located closer to the stream had a higher ClO(-)(4) accumulation than trees located farther away from the stream. Seasonal leaf sampling of terrestrial plants indicated that ClO(-)(4) accumulation also was affected by exposure duration, with highest accumulation observed in the late growing cycle, although leaf concentrations for a given tree were highly variable. Perchlorate may be re-released into the environment via leaching and rainfall as indicated by lower perchlorate concentrations in collected leaf litter. Information obtained from this study will be helpful to understand the fate of ClO(-)(4) in macrophytes and natural systems.     

Kinetics of chromate adsorption on goethite in the presence of sorbed silicic acid

The adsorption of chromate on mineral surfaces has received much attention due to its toxicity in natural systems. Spectroscopic studies have demonstrated that chromate forms inner-sphere complexes on variable-charge surfaces. However, in natural systems chromate has been observed to be fairly mobile, which has been explained by the presence of naturally occurring ligands competing with chromate for mineral surface sites. Silicic acid is a ubiquitous ligand in soil and water environments and also sorbs strongly to variable-charge surfaces. Yet little research has examined its influence on chromate adsorption to variable-charge surfaces such as goethite. This study examined the influence of silicic acid (0.10 and 1.0 mM) on the adsorption kinetics of chromate (0.05 and 0.10 mM) on goethite over a range of common soil pH values (4, 6, and 8). The rate and total quantity of chromate adsorption decreased in all the experiments except at a pH value of 4 and a chromate concentration of 0.05 mM. The inhibition of chromate adsorption ranged from 3.1% (pH = 4, Si = 0.10 mM, chromate = 0.10 mM) to 83.3% (pH = 8, Si = 1.0 mM, chromate = 0.05 mM). The rate of chromate adsorption decreased with an increase in pH and silicic acid concentration. This was attributed to a reduction in the surface potential of goethite on silicic acid adsorption as well as a competition for surface sites. The presence of naturally occurring ligands such as silicic acid may be responsible for the enhanced mobility of chromate in natural systems and demonstrates the importance of competitive adsorption for evaluating the mobility of trace elements.     

Emissions study of co-firing waste carpet in a rotary kiln

Post-consumer carpet represents a high volume, high energy content waste stream. As a fuel for co-firing in cement kilns, waste carpet, like waste tires, has potential advantages. Technological challenges to be addressed include assessing potential emissions, in particular NO emissions (from nylon fiber carpets), and optimizing the carpet feed system. This paper addresses the former. Results of pilot-scale rotary kiln experiments demonstrate the potential for using post-consumer waste carpet as a fuel in cement kilns. Continuous feeding of shredded carpet fiber and ground carpet backing, at rates of up to 30% of total energy input, resulted in combustion without transient puffs and with almost no increase in CO and other products of incomplete combustion as compared to kiln firing natural gas only. NO emissions increased with carpet waste co-firing due to the nitrogen content of nylon fiber. In these experiments with shredded fiber and finely ground backing, carpet nitrogen conversion to NO ranged from 3 to 8%. Conversion increased with enhanced mixing of the carpet material and air during combustion. Carpet preparation and feeding method are controlling factors in fuel N conversion.     

Public Space Management: Present and Potential

This paper explores approaches to the management of external public space, both now and in the future. The paper is in five parts. The discussion begins with an exploration of why public space management is universally an important concern by drawing from literature that argues that the quality of public space has declined, and that a greater engagement of the public sector in its management is required. Next, the research methodology is discussed which sought to investigate the management of public space in England as an example of trends and responses that point to a broader international concern. The approach included both a national survey of the state of play in public space management and a series of case studies that sought to explore innovative practice. Third, the results of a national survey are briefly outlined, with discussion following the same structure as the survey itself. Next, the results of detailed interviews with 20 local authority case studies that exhibited interesting or innovative practice in the local management of public space are presented. In a final part, conclusions are drawn which confirm that this is an area of public sector responsibility in need of significant investment and reform, but also that top-down initiatives from national government are beginning to inspire a burgeoning range of local government initiatives below. Therefore, although public space management remains a fragmented area of local government activity, a number of local authorities are beginning to establish a corresponding bottom-up agenda that seems to map a potential way forward for the future.     

Visible-near infrared reflectance spectroscopy for rapid, nondestructive assessment of wetland soil quality

Recent evidence supports using visible-near infrared reflectance spectroscopy (VNIRS) for sensing soil quality; advantages include low-cost, nondestructive, rapid analysis that retains high analytical accuracy for numerous soil performance measures. Research has primarily targeted agricultural applications (precision agriculture, performance diagnostics), but implications for assessing ecological systems are equally significant. Our objective was to extend chemometrics for sensing soil quality to wetlands. Hydric soils posed two challenges. First, wetland soils exhibit a wider range of organic matter concentrations, particularly in riparian areas where levels range from <1% in sedimentation zones to >90% in backwater floodplains; this may mute spectral responses from other soil fractions. Second, spectral inference of cation concentrations in terrestrial soils is for oxidized species; under reducing conditions in wetlands, oxidation state variability is observed, which strongly affects chroma. Riparian soils (n = 273) from western Florida exhibiting substantial target parameter variability were compiled. After minimal pre-processing, soils were scanned under artificial illumination using a laboratory spectrometer. A multivariate data mining technique (regression trees) was used to relate post-processed reflectance spectra to laboratory observations (pH, organic content, cation concentrations, total N, C, and P, extracellular enzyme activity). High validation accuracy was generally observed (r2(validation) > 0.8, RPD > 2.0, where RPD is the ratio of the standard deviation of an attribute to the observed standard error of validation); where accuracy was lower, categorical models (classification trees) successfully screened samples based on diagnostic functional thresholds (validation odds ratio > 10). Graphical models verified significant association between predictions and observations for all parameters, conditioning on biogeochemical covariates. Visible-near infrared reflectance spectroscopy offers both cost and statistical power advantages; hydric conditions do not appear to constrain application.     

Temporal variability in physical speciation of metals during a winter rain-on-snow event

Particulate matter in urban rivers transports a significant fraction of pollutants, changes rapidly during storm events, and is difficult to characterize. In this study, the physical speciation of trace metals and organic C in an urban river and upstream headwaters site in Torrington, CT, were measured during a winter rain-on-snow event. In addition, a selective fractionation scheme, using membrane and tangential-flow ultrafiltration methods to separate suspended particulate matter into sand, silt, clay, and colloid fractions, was evaluated based on the appropriateness of the chosen size categories. During peak runoff at the urban river site, total-recoverable concentrations of the metals Cu and Pb increased 6- and 13-fold to 16.9 and 9.5 microg L(-1), respectively, compared with baseflow concentrations. Concentrations of Cu and Pb reached only 0.9 and 0.86 microg L(-1) at the headwaters site. For the measured storm event, the majority of metals were transported by the urban river in association with coarse silt (20-80 microm particle diam.) during peak runoff. During peak runoff at the urban site, organic C associated with the large colloid fraction (0.1-1.0 microm) increased from 5% (at baseflow) to 54% of the total C in transport, whereas dissolved organic C and that associated with smaller colloids decreased from 91.5% (at baseflow) to 41% of the total. Other elements that were monitored as part of the study were Na, K, Ca, Mg, Fe, Mn, Al, Cd, Cl-, NO3(-), and SO4(2-). The chosen fractionation scheme was useful to characterize pollutant transport during this event, but further testing should be undertaken to determine the most appropriate size range categories, and to ensure that the sizes measured are comparable to those used in other studies.