Effects of macrophyte species richness on wetland ecosystem functioning and services.

Wetlands provide many important ecosystem services to human society, which may depend on how plant diversity influences biomass production and nutrient retention. Vascular aquatic plant diversity may not necessarily enhance wetland ecosystem functioning, however, because competition among these plant species can be strong, often resulting in the local dominance of a single species. Here we have manipulated the species richness of rooted, submerged aquatic plant (macrophyte) communities in experimental wetland mesocosms. We found higher algal and total plant (algal plus macrophyte) biomass, as well as lower loss of total phosphorus, in mesocosms with a greater richness of macrophyte species. Greater plant biomass resulted from a sampling effect; that is, the increased chance in species mixtures that algal production would be facilitated by the presence of a less competitive species-in this case, crisped pondweed. Lower losses of total phosphorus resulted from the greater chance in species mixtures of a high algal biomass and the presence of sago pondweed, which physically filter particulate phosphorus from the water. These indirect and direct effects of macrophyte species richness on algal production, total plant biomass and phosphorus loss suggest that management practices that maintain macrophyte diversity may enhance the functioning and associated services of wetland ecosystems.

Optimal trajectories for the short-distance foraging flights of swans.

Optimal flight theory relates body measurements (wing span, body cross-section, body mass) and aerodynamic variables (air density, drag, profile and induced power ratios) to the most energy-efficient velocity for long distance migration. For short-range (2-10 km) foraging flights the theory is expanded to include non-negligible costs for take-off and energy savings/losses for climbing to altitude (drag decreases with air density and therefore with altitude). The theory predicts clear differences between Tundra and Trumpeter swans. Generally speaking, for flights between 2 and 10 km Trumpeter swans can be expected to fly approximately 5-10 m lower in altitude and 1-2 ms(-1)more slowly than Tundra swans. Moreover, the total energy required for these foraging flights is approximately 150% larger for a Trumpeter than a Tundra swan (80 vs. 120 kJ of direct mechanical energy for a 5 km flight), suggesting that Trumpeter swans may be less inclined to take-off than Tundra swans. These factors indicate that even Trumpeters native to the area (as opposed to recently translocated) would be more vulnerable to hunting than native Tundra swans. The expanded theory is compared to observations made in Utah's Bear River Migratory Bird Refuge.

Work-related musculoskeletal disorders among physical therapists.

BACKGROUND AND PURPOSE: Increasing evidence suggests that musculoskeletal disorders are common in workers in the United States health care industry. Physical therapists, who commonly treat patients with these disorders, are also at risk for work-related musculoskeletal disorders (WMD) in the upper limbs and low back. The purpose of this study was to determine the prevalence of WMD during a 12-month period and the job factors that may be associated with these disorders in physical therapists. SUBJECTS: A four-page questionnaire was mailed to physical therapists (N = 1,160) who attended The University of Iowa between 1943 and 1993. Nine hundred twenty-eight questionnaires were returned (80% response rate) from physical therapists in 46 states. METHODS: Based on a literature review and pilot study of physical therapists, a survey instrument was constructed consisting of a symptom survey, a job-factor survey, and various demographic information. RESULTS: The highest prevalences of WMD among physical therapists were in the following anatomical areas: low back (45%), wrist/hand (29.6%), upper back (28.7%), and neck (24.7%). The job factor rated most likely to contribute to job-related musculoskeletal disorders was "lifting or transferring dependent patients." The prevalence of WMD in physical therapists also was affected by work setting, practice specialty, age of patient, and gender of therapist. CONCLUSION AND DISCUSSION: Specific strategies should be developed to reduce WMD in the practice of physical therapy.