Disturbance of natural vegetation by camping: Experimental applications of low-level stress

Previously undisturbed sites in four different vegetation types were camped on for one night and for four nights. Changes in vegetation cover and vegetation height were measured after camping and one year later. Results are presented separately for different campsite zones—parts of the site where campers slept, cooked meals, and stored their packs. Just one night of camping was sufficient to cause evident impact in all four vegetation types, although the amount of impact varied significantly between zones and between vegetation types. Vegetation impact on campsites used four nights was generally less than twice as severe as impact on the sites used one night. The effects of camping on vegetation were also predicted for 12 other vegetation types on the basis of vegetational responses to experimental trampling. These results suggest that impact can almost always be minimized by confining camping to a small number of campsites instead of dispersing use across many campsites.     

Odor Control for Land Application of Lime Stabilized Biosolids

Over three million dry metric tons of biosolids produced in the United States are land applied as Class B. Lime stabilization is employed for biosolids treatment at approximately 20% of the wastewater treatment plants because it is a simple and inexpensive process. During lime stabilization, the pH of sewage sludge is raised above 12 for pathogen inactivation and odor reduction. Lime dose and mixing have been found to greatly reduce odor generation from lime stabilized biosolids. A better quality biosolids product is less likely to create public opposition to land application programs. In this study, land application tests using Class B biosolids were conducted in order to determine whether better mixing can reduce odor generation during the land application of lime stabilized biosolids. The mixing quality of a treatment plant’s lime stabilized biosolids was improved by relocating the lime addition point, which prolonged the mixing time and produced a better mixed biosolids product. Based on field observations of land application, the poorly mixed biosolids were more odorous and offensive prior to incorporation. However, once incorporated into the soil, there was no appreciable odor difference between the biosolids. Another land application study was conducted to assess the odor of unincorporated Class A biosolids and compare it with incorporated Class A biosolids with the soil.     

Dissipation of four forest-use herbicides at high latitudes

Background, aim, and scope  Large-scale deforestation is occurring in subarctic North America following clearing by salvage logging or insect attack. Numerous shrubs, herbs, and deciduous tree species tend to dominate areas on which stands of white spruce have grown. In the absence of economically advantageous mechanical methods, several herbicides have value in efforts to reforest by planting white spruce. Glyphosate, imazapyr, triclopyr, and hexazinone are all capable of selectively removing many competing species, but there is concern about whether they would degrade naturally or persist owing to the frigid climate. Materials and methods  We established test plots with all four herbicides in upland and river bottom sites at 65°N and 58°N latitudes. The northern site has extremely cold winters, with soils that freeze to a depth of 1–2 m, and precipitation of 275 mm/year. The southern site has heavy rain and snowfall, amounting to 2,250 mm/year evenly distributed. Soil seldom freezes deeply. On each test plot, one of the four herbicides was applied at twice the normal operational use rate to facilitate detection. They were applied at the normal timing, with hexazinone, imazapyr, and triclopyr applied in June and glyphosate applied in fall. Soils were sampled immediately after treatment and those samples used as references for dissipation data gathered over the next 11–14 months from soil 0- to 15- and 15- to 45-cm depths. Results  Dissipation rates did not follow first-order rates because freezing conditions slowed most microbial activity. All products dissipated to close to or below detection limits within the time of the study. Dissipation from vegetation was substantially more rapid and depended on the nature of the plants treated as well as the product used. While soil residues dissipated more slowly than in temperate regions, they did display consistent dissipation patterns during above-freezing conditions and also the influence of microbial activity. Mobility was very limited with all products but hexazinone. Discussion  These products dissipate during summer in high latitudes much as they would in temperate climates. Winter changes are small, but are not unlike some changes reported elsewhere under freezing conditions. Unlike many other studies, soil water did not influence dissipation heavily, but the high latitude and semi-arid climate also did not create severely droughty soils. Residues in plants were much higher than those in soils, but denatured the vegetation quickly, leading to unsuitability for forage in any case. Conclusions  Low toxicity of these products and their metabolites combined with consistent dissipation and low mobility suggest that toxic hazard of their use at high latitudes need not be a matter of serious concern to humans, terrestrial wildlife, or aquatic systems. They are safe for use in management and rehabilitation of boreal forests when used properly. Recommendations and perspectives  Dissipation at rates approaching those in warmer climates offer a hypothesis that microflora native to high latitudes may be adapted to destruction of such molecules at lower temperatures than may be indicated by experiments with microflora adapted to warmer climates. Residues pose no observable risk to wildlife or humans in the area of use when products are applied properly. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available for authorized users.     

Losing Function Through Wetland Mitigation in Central Pennsylvania,USA

In the United States, the Clean Water Act requires mitigation for wetlands that are negatively impacted by dredging and filling activities. During the mitigation process, there generally is little effort to assess function for mitigation sites and function is usually inferred based on vegetative cover and acreage. In our study, hydrogeomorphic (HGM) functional assessment models were used to compare predicted and potential levels of functional capacity in created and natural reference wetlands. HGM models assess potential function by measurement of a suite of structural variables and these modeled functions can then be compared to those in natural, reference wetlands. The created wetlands were built in a floodplain setting of a valley in central Pennsylvania to replace natural ridge-side slope wetlands. Functional assessment models indicated that the created sites differed significantly from natural wetlands that represented the impacted sites for seven of the ten functions assessed. This was expected because the created wetlands were located in a different geomorphic setting than the impacted sites, which would affect the type and degree of functions that occur. However, functional differences were still observed when the created sites were compared with a second set of reference wetlands that were located in a similar geomorphic setting (floodplain). Most of the differences observed in both comparisons were related to unnatural hydrologic regimes and to the characteristics of the surrounding landscape. As a result, the created wetlands are not fulfilling the criteria for successful wetland mitigation.     

Perceived Effects of Setting Attributes on Visitor Experiences in Wilderness: Variation with Situational Context and Visitor Characteristics

Understanding how setting attributes influence the nature of the visitor experience is crucial to effective recreation management. Highly influential attributes are useful indicators to monitor within a planning framework, such as Limits of Acceptable Change. This study sought to identify the setting attributes perceived to have the most profound effect on the ability to have “a real wilderness experience” and to assess the degree to which attribute importance varied with situational context and visitor characteristics. To this end, exiting hikers were surveyed at moderate and very high use trailheads in Alpine Lakes Wilderness, WA (USA), and Three Sisters Wilderness, OR (USA). They were asked about the degree to which encountering varying levels of different setting attributes would add to or detract from their experience. Attributes with the largest range of effect on experience, based on evaluations of different levels, were considered most important. The most influential attributes were litter and several types of campsite interaction—people walking through camp and number of other groups camping close by. The perceived importance of setting attributes did not vary much between wilderness locations with substantially different use levels, suggesting that conclusions are robust and generalizable across wilderness areas. There also was little difference in the perceptions of day and overnight visitors. In contrast, we found substantial variation in the perceived importance of setting attributes with variation in wilderness experience, knowledge, attachment, and motivation. Our results validate the emphasis of many wilderness management plans on indicators of social interaction, such as number of encounters.     

Trace Element Concentrations and Bioindicator Responses in Tree Swallows from Northwestern Minnesota

Extremely high concentrations of cadmium (3.5 μg/g dry wgt.) and elevated concentrations of chromium (>10 μg/g dry wgt.) and mercury (1.6 μg/g dry wgt.) were reported in waterbird tissues at Agassiz National Wildlife Refuge in northwestern Minnesota in 1994. Tree swallows (Tachycineta bicolor) were studied during 1998–2001 at three drainages into the Refuge, two pools on the Refuge, and at a nearby reference location to document whether high levels of contaminants were still present, and if so to quantify the source and severity of the contamination. Trace elements were measured in tree swallow eggs, livers, and diet. Reproductive success and bioindicator responses were monitored. In 2000, water was drawn down on Agassiz Pool, one of the main pools on the Refuge. This presented an opportunity to evaluate the response of trace element concentrations in the diet and tissues of tree swallows after reflooding. High concentrations of trace elements were not detected in swallow tissues, nor were there differences among locations. Less than 20% of swallow samples had detectable concentrations of cadmium or chromium. Mercury concentrations were low and averaged <0.25 μg/g dry wgt. in swallow tissues. Trace elements, including mercury, did not increase in tree swallows following the 2000 drawdown at Agassiz Pool. Hatching success and survival of nestlings to 12 days-of-age for tree swallows on the Refuge were similar to the national average and consistent with background trace element concentrations. Bioindicator measurements were within the normal ranges as well.     

Gonadal structure and population characteristics of the protogynous goby Coryphopterus glaucofraenum

Protogynous hermaphroditism has been reported in two gobiid species within the genus Coryphopterus, including C. nicholsi from the temperate northeastern Pacific and C. personatus from the Caribbean. In a third species from the Caribbean, C. glaucofraenum, experimental groups were established and gonad structure of experimental individuals (collected off the southwest coast of Puerto Rico between February 1985 and June 1987) was subsequently examined histologically to determine the sexual pattern. Protogyny was confirmed in C. glaucofraenum. Sex change was either initiated or completed, typically by the largest female, in all-female groups held for 10 to 40 d. Ovarian, transitional, and testis structure were similar to that of C. nicholsi and C. personatus. No preformed testicular tissue was evident in the ovary proper and ovarian features were not retained in the sex-changed testis beyond the newly transformed stage. Secretory accessory gonadal structures associated with the testis and which develop at the time of sex change arose from precursive tissue masses associated with the ventral portion of the ovarian wall in the region of the common genital sinus. The rapid development and onset of function in these structures, generally preceding that of the associated developing testis, suggest that they may play an important role in sex change events and in advertising new male status. Based on observed similarities of ovarian, transitional and secondary testis structure in three protogynous Coryphopterus species, including one species isolated since the last closing of the American landbridge, it is probable that protogyny is an ancestral condition in this genus.