Nitrogen cycling during seven years of atmospheric CO2 enrichment in a scrub oak woodland

Experimentally increasing atmospheric CO2 often stimulates plant growth and ecosystem carbon (C) uptake. Biogeochemical theory predicts that these initial responses will immobilize nitrogen (N) in plant biomass and soil organic matter, causing N availability to plants to decline, and reducing the long-term CO2-stimulation of C storage in N limited ecosystems. While many experiments have examined changes in N cycling in response to elevated CO2, empirical tests of this theoretical prediction are scarce. During seven years of postfire recovery in a scrub oak ecosystem, elevated CO2 initially increased plant N accumulation and plant uptake of tracer 15N, peaking after four years of CO2 enrichment. Between years four and seven, these responses to CO2 declined. Elevated CO2 also increased N and tracer 15N accumulation in the O horizon, and reduced 15N recovery in underlying mineral soil. These responses are consistent with progressive N limitation: the initial CO2 stimulation of plant growth immobilized N in plant biomass and in the O horizon, progressively reducing N availability to plants. Litterfall production (one measure of aboveground primary productivity) increased initially in response to elevated CO2, but the CO2 stimulation declined during years five through seven, concurrent with the accumulation of N in the O horizon and the apparent restriction of plant N availability. Yet, at the level of aboveground plant biomass (estimated by allometry), progressive N limitation was less apparent, initially because of increased N acquisition from soil and later because of reduced N concentration in biomass as N availability declined. Over this seven-year period, elevated CO2 caused a redistribution of N within the ecosystem, from mineral soils, to plants, to surface organic matter. In N limited ecosystems, such changes in N cycling are likely to reduce the response of plant production to elevated CO2.     

Evaluation of the electrochemical behavior of pentachlorophenol by cyclic voltammetry on carbon paste electrode modified by humic acids.

Humic substances, or natural recalcitrant organic matter, have an important role in the environment for their plant nutritional functions or for their capability to control the mobility of xenobiotic substances, such as pesticides. To verify the electrochemical behavior of pentachlorophenol (PCP), cyclic voltammetry was used because of its versatility. The following two different electrodes were used: carbon paste electrode (CPE) and carbon paste electrode chemically modified with humic acid (HACMCPE). The results demonstrated that PCP was better accumulated at the HACMCPE electrode, as a consequence of a larger current signal than at the CPE electrode. Cyclic voltammograms showed oxidation steps of PCP itself and probable production of quinonelike compounds.     

Intragroup dynamics of a cooperative breeder: An anlysis of reproductive roles in the acorn woodpecker

Summary The acorn woodpecker is a cooperative breeder generally thought to breed promiscuously within groups, but alternative patterns of reproductive investment can be expected and remain to be examined. With this feature of mating system in mind, we studied the reproductive roles of individuals in a single group of this species in central coastal California over a three-year period. Particularly detailed observations were made in 1979, when the group consisted of two potentially breeding sibling males and a single breeding female. One male (298) contributed significantly more than 297 in virtually all aspects of nest and fledgling care. These include (1) feeding nestlings, (2) nest sanitation, (3) nocturnal incubation and brooding, (4) feeding fledglings, and (5) escorting fledglings. In the few observed and rarely occurring dominance interactions, 298 prevailed. These results suggest that 298 had a higher probability of fathering the group's two 1979 offspring than did his brother. Thus, the two males differed substantially in their parental roles within the group, and very likely in reproductive roles, also. At present stage of knowledge, monogamy in groups with one female and more than one potential reproductive male is no less likely than promiscuity. These findings are discussed with respect to the evolution of cooperative breeding in this species.     

Integrated mite control in apples in Queensland, Australia

An interdisciplinary team introduced Integrated Mite Control (IMC) to the Queensland apple industry in Australia from 1989 to 1992. Project funding supported the employment of a consultant to monitor mite levels and provide management advice to growers who paid for the service. Interviews at the beginning and end of the project showed widespread adoption of IMC over this period. Overall use of chemicals was not reduced, but the use pattern changed towards wider use of chemicals that are less toxic to predatory mites. The future of IMC in the Queensland apple industry is in doubt because the seasonal nature of apple production does not allow the paid consultancy service to be self-sustaining. Indications are that the integrated approach to pest management may not be generally accepted as a strategic management process while the availability of effective chemicals allows the continuation of a spray routine for mite control. The lack of availability of effective and proven methods of pest control was seen by growers as the major constraint to adoption of IMC.     

Simulated Responses of a Forest-Interior Bird Population to Forest Management Options in Central Hardwood Forests of the United States

I used estimates of carrying capacity, survival, fecundity, and edge effects to simulate the responses of a forest-interior bird population to selection cutting clearcutting, and no timber harvest. I also modeled population sensitivity to changes in fecundity, survival, K , and edge relationships. Because model parameters are based on scant data, results should he regarded as hypotheses to be further investigated or measures of the relative impact or sensitivity (given model assumptions). Simulated population size was greater with no timber harvest than with clearcutting and greater with clearcutting than with group selection when edge effects were included in the model. Without edge effects, population levels were only slightly lower under group selection than under no timber harvest, and greater than clearcutting. Edge effects had only a small impact on population levels under clearcutting. Clearcut size did not have much effect on population levels, but longer and shorter rotation ages resulted in higher and lower population levels, respectively. The model was very sensitive to declines in mean fecundity and survival, suggesting that factors affecting mean demographic rates could be more important than local edge effects. Some methods of timber harvest may be compatible with the conservation of forest-interior birds, but better demographic data and information on habitat suitability of selectively cut forests and young even-aged stands is needed to adequately evaluate management options.     

Using Microsimulation to Maximise Scarce Survey Data: Applications for Catchment Scale Modelling and Policy Analysis

Microsimulation can be used to extend the use of scarce survey resources by creating simulated populations whose characteristics are close to those of the real population. The technique involves merging detailed survey observations with variables from more extensive data sets in order to create a simulated population. We illustrate how microsimulated data enable analysis of the economic and environmental impact of different policies on a catchment for which detailed farm level data was unavailable. Use of microsimulation for agri-environmental policy analysis is applicable to diverse problems from simulation of nitrogen trading to modelling of agent response to policy shocks. Scale flexibility is easily implemented since data can be aggregated or disaggregated to the preferred scale. Simulated catchment data allows better understanding of the effects of policies on different types of farm and should be extremely valuable to organisations that want to minimise the economic impact of environmental policies.     

Disinfection of secondary effluents using tin oxide anodes.

Direct current applied to a tin oxide anode submersed in water has the potential to generate hydroxyl radicals, a strong chemical oxidant. Tin oxide anode systems, which may represent a viable alternative disinfectant, were investigated for the disinfection of secondary effluents. Coliform bacteria in the effluent were effectively inactivated in a bench-scale tin oxide disinfection system. The number of anodes in the tin oxide disinfection system influenced the steady-state concentration of hydroxyl radicals and, consequently, the contact time necessary to achieve a specified dose. The life expectancy of the anodes was greater than 30 days and no appreciable loss of tin was observed over a 5-day period. A preliminary estimate of the capital and operating costs of a pilot- or full-scale tin oxide disinfection system designed to meet a discharge requirement of 23 most probable number/100 mL at a 3 785-m3/d (1-mgd) facility was comparable to UV and chlorination/dechlorination facilities. Based on this preliminary assessment, tin oxide disinfection systems are a promising alternative disinfectant for secondary effluents.