Energetic Carrying Capacity of Actively and Passively Managed Wetlands for Migrating Ducks in Ohio

ABSTRACT Habitat conservation strategies of the North American Waterfowl Management Plan (NAWMP) are guided by current understanding of factors that limit growth of waterfowl populations. The 1998 implementation plan of the Upper Mississippi River and Great Lakes Region Joint Venture (UMR and GLRJV) assumed that availability of foraging resources during autumn in wetlands actively managed for waterfowl was the primary limiting factor for duck populations during the nonbreeding season. We used multistage sampling during autumn and spring 2001–2004 to estimate energetic carrying capacity (ECC) of actively and passively managed wetlands in Ohio, USA, and examine this assumption. Energetic carrying capacity during autumn was similar between actively and passively managed wetlands each year. Averaged across years, energetic carrying capacity was 3,446 and 2,047 duck energy-days (DED)/ha for actively and passively managed wetlands, respectively. These estimates exceeded the UMR and GLRJV assumption that 1,236 DED/ha were provided by managed wetland habitats. Energetic carrying capacity declined each year by >80% between autumn and spring migration. Consequently, ECC of actively and passively managed wetlands was low during spring ( = 66–242 DED/ha). These results suggested that duck foraging resources in actively and passively managed wetland habitats are abundant during autumn, but overwinter declines may create food-limiting environments during spring.     

Comparison of measured and EF5-r-derived N2O fluxes from a spring-fed river

There is considerable uncertainty in the estimates of indirect N₂O emissions as defined by the Intergovernmental Panel on Climate Change's (IPCC) methodology. Direct measurements of N₂O yields and fluxes in aquatic river environments are sparse and more data are required to determine the role that rivers play in the global N₂O budget. The objectives of this research were to measure the N₂O fluxes from a spring‐fed river, relate these fluxes to the dissolved N₂O concentrations and NO₃‐N loading of the river, and to try to define the indirect emission factor (EF5‐r) for the river. Gas bubble ebullition was observed at the river source with bubbles containing 7.9 μL N₂O L^?1. River NO₃‐N and dissolved N₂O concentrations ranged from 2.5 to 5.3 mg L^?1 and 0.4 to 1.9 μg N₂O‐N L^?1, respectively, with N₂O saturation reaching 404%. Floating headspace chambers were used to sample N₂O fluxes. N₂O‐N fluxes were significantly related to dissolved N₂O‐N concentrations (r²=0.31) but not to NO₃‐N concentrations. The N₂O‐N fluxes ranged from 38 to 501 μg m^?2 h^?1, averaging 171 μg m^?2 h^?1 (±SD 85) overall. The measured N₂O‐N fluxes equated to an EF5‐r of only 6.6% of that calculated using the IPCC methodology, and this itself was considered to be an overestimate because of the degassing of antecedent dissolved N₂O present in the groundwater that fed the river.     

Effects of Glyphosate on Metabolism of Phenolic Compounds

Light enhanced the inhibiting effect of root-fed glyphosate (5 × 10^?4M) on dry weight accumulation of soybean [Glycine max. (L.) Merr.] seedling axes. Inhibition of growth by light was greatest in hypocotyls, whereas by glyphosate it was greatest in roots. A synergistic effect of light and glyphosate on stimulation of phenylalanine ammonia-Iyase (PAL, E.C. 4.3.1.5) activity was also demonstrated. In continuous white light PAL activity increased linearly for 4 days in axes of seedlings exposed to glyphosate. Evidence of phytochrome involvement in the light effect was shown. The stimulatory effect of glyphosate on PAL activity was greater in roots than in hypocotyls. Soluble hydroxyphenolic compound levels were reduced by glyphosate but were increased by light on a per axis basis. On a fresh weight basis, hydroxyphenolics were more concentrated in glyphosate-treated than in control tissues in the light. When compared to other amino acids, disproportionate decreases in free pools of phenylalanine and tyrosine occurred in axes of seedlings treated with glyphosate and light. The effect of light on all measured parameters was mainly in the hypocotyl, while that of glyphosate was primarily in the root. In the light, glyphosate caused increases in levels of glutamine and other amino acids that may be the result of amination reactions, protecting from excess ammonia generated by enhanced PAL activity. These results suggest that PAL has a strong influence on its substrate levels in this system and/or that glyphosate inhibits synthesis of aromatic amino acids.     

Electrical Events Correlated with Contractile Vacuole Activity in the Suctorian, Heliophrya

SYNOPSIS. The surface membrane potentials of suctorian genus Heliophrya were studied with intracellular electrodes. Resting membrane potentials averaged -32 mV, and spontaneous depolarizing potentials occurring at apparently random intervals and having a variety of waveforms were routinely observed. Such spontaneous potentials were correlated in time with visually monitored contractile vacuole activity. Individual contractile vacuoles had unique, although somewhat variable, electrical signatures. In the presence of an intracellular electrode all vacuoles contracted independently, but at approximately the same frequency. The amplitude of the electrical potentials increased when the membrane was hyperpolarized and decreased when it was depolarized. The sign of such potentials reversed at between -10 mV and the zero membrane potential. A 20% decrease in the membrane resistance was measured at the peak of the spontaneous depolarizing potentials.     

Respiratory Response to Periodic Emergence in Intertidal Molluscs

SYNOPSIS: The ratio of aerial: aquatic was computed for species of intertidal molluscs.This ratio was <1 for sub- and lower littoral species suggestingpartial anaerobiosis in air and >1 for high littoral archeogastropodssuggesting high metabolic demands in air. ratios were near unity for meso- and neogastropodspecies regardless of zonation. Littoral fringe mesogastropodshad ratios <1 reflecting reduced activity on emergence. Amajor gastropod adaptation to increasing emergence is reductionof ctenidium surface area and formation of a mantle cavity lung.Mid- and high littoral pulmonates with both a mantle cavitylung and secondary gills have ratios near unity. In contrast, littoral fringe pulmonates withoutsecondary gills are partially anaerobic in water. Emerged lowand mid-littoral bivalves close the valves, are almost entirelyanaerobic, have ratios 0.14:1and conserve energy by greatly reducing metabolic demand inair. In contrast, emerged high littoral bivalves remain aerobicby periodic gaping and mantle cavity ventilation. Such behaviorssupport an aerobic metabolism while minimizing evaporative waterloss. Aerial gas exchange prevents anaerobic end-product accumulationand, with a reduction in energy demand, allows efficient energystore utilization during prolonged emergence.     

Microbial enzyme activities as indicators of organic matter processing rates in a Lake Erie coastal wetland

1. Particulate organic material (POM) is an important source of energy and nutrients in aquatic ecosystems. The decomposition of this material is typically studied using the litter bag technique. However, this method has inherent limitations that can preclude the estimation of in situ decomposition rates, especially for fine particles. In this study, we tried to circumvent these limitations through the use of enzymatic decomposition models (EDMs), which relate mass loss rates to lignocellulase activities. With this approach, we investigated the in situ processing of three size ranges of detritus in a Typha wetland. 2. Litter was collected, dried and sorted into three size ranges [coarse (C) > 4, medium (M) 0.5–4 and fine (F) 0.063–0.5 mm] and placed in litter bags that were attached to the sediment surface at two sites in a Typha wetland in May 1994. Over a 7-month period, litter bags were collected and analysed for mass loss and the activities of six extracellular enzymes involved in the degradation of lignocellulose. In situ POM was collected concurrently, sorted into the same three size ranges and assayed for the same suite of enzymes. Additional cores were taken for the determination of organic matter standing stocks and particle size distribution. 3. Mean mass loss rates for CPOM, MPOM and FPOM were -0.139, -0.073 and -0.053% day^?1, respectively. Only CPOM rates were significantly different between sites. For CPOM and FPOM there were strong linear relationships between mass loss and cumulative enzyme activities; the mass loss data for MPOM were erratic and precluded the development of reliable enzyme models. EDMs for CPOM and FPOM were constructed from regressions relating mass loss to average cumulative lignocellulase activity, and used to estimate instantaneous in situ decomposition rates. These rates varied by site and throughout the year but averaged -0.204 and -0.045% day^?1, respectively. Based upon measurements of OM standing stock and particle size distributions, POM processing rates of 1100–1400 g m² yr^?1 were calculated. These rates are near the upper end of the range for net annual production in Typha wetlands, suggesting that there is little net accumulation of POM. 4. Despite some problems, the EDM method has the potential to facilitate studies of detrital dynamics in large, heterogeneous systems.     

Disease and the abundance and distribution of bird populations: a summary

Over the past few years, I have written several reviews about the effects of infectious diseases upon the distribution and abundance of their host populations. One general review and synthesis is in the fmd chapter of a book whose earlier chapters focus mainly on human diseases (Anderson & May 1991). A bird-specific discussion, with particular reference to conservation issues, is given by Dobson and May (1991). Broadly related questions about the invasion, persistence and spread of infectious diseases within animal communities are explored by Anderson and May (1986) and with emphasis on bird populations by Dobson and May (1986). Also relevant are a set of papers from the Society for Conservation Biology's first-ever symposium on Conservation and Disease (for an overview, see May 1988, Scott 1988).
Rather than burdening the literature with a recapitulation of these existing reviews, this paper gives a sign-posted guide for those who are not familiar with this particular literature. I first sketch reasons for believing that infectious diseases play an important part in the life history of birds. Next I point towards an analytic framework for understanding the dynamics of host-pathogen associations. Finally I list some of the implications for the conservation biology of bird populations.