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Monitoring urban streams: strategies and protocols for humid-region lowland systems.

Governmental mandates and public awareness have forced progressively smaller and less sophisticated agencies and organizations to initiate stream monitoring programs, particularly in urban and urbanizing areas. Yet many of these monitoring efforts lack either a coherent conceptual framework or appropriately chosen methods, and they rely on monitoring techniques that are simply infeasible for these institutional settings. We propose a monitoring strategy, and specific existing monitoring protocols, that will be useful for the management and rehabilitation of streams in urbanizing watersheds. A monitoring strategy must be developed by 1) identifying the management question(s) being addressed, 2) determining the institional level of effort required (and available) to effectively make particular kinds of measurements, and 3) identifying what specific parameters should and can be measured. Only a limited set of parameters show much utility or feasibility in addressing the most common management questions being faced by municipalities in urbanizing, humid-area regions of the United States. These include measures of riparian canopy, bank erosion and bank hardening, and in-stream large woody debris. With some additional expertise useful data can also be included on channel gradient, substrate composition, and pools. Nearly all of the other myriad parameters that have been measured historically on rivers and streams show little apparent value in these watershed and institutional settings.

Cities↗

Effects of leaf wetting and high humidity on stomatal function in leafy cuttings and intact plants of Corylus maxima.

When rooted cuttings of Corylus maxima Mill. cv. Purpurea are moved from the wet and humid conditions of the rooting environment, the leaves frequently shrivel and die. Since the newly formed adventitious root system has been shown to be functional in supplying water to the shoot, stomatal behaviour in C. maxima was investigated in relation to the failure to prevent desiccation. Stomatal conductance (gs) in expanding leaves (L3) of cuttings increased almost 10-fold over the first 14 days in the rooting environment (fog), from 70 to 650 mmol m-2 s-1. In contrast, gs of expanded leaves (L1) changed little and was in the region of 300 mmol m-2 s-1. Midday leaf water potential was much higher in cuttings than in leaves on the mother stock-plant (-0.5 versus -1.2 MPa) even before any roots were visible. Despite this, leaf expansion of L3 was inhibited by >50% in cuttings and stomata showed a gradual reduction in their ability to close in response to abscisic acid (ABA). To determine whether the loss of stomatal function in cuttings was due to severance or to unnaturally low vapour pressure deficit and wetting in fog, intact plants were placed alongside cuttings in the rooting environment. The intact plants displayed reductions in leaf expansion and in the ability of stomata to close in response to dark, desiccation and ABA. However, in cuttings, the additional effect of severance resulted in smaller leaves than in intact plants and more severe reduction in stomatal closure, which was associated with a 2.5-fold increase in stomatal density and distinctively rounded stomatal pores. The similarities between stomatal dysfunction in C. maxima and that observed in many species propagated in vitro are discussed, as is the possible mechanism of dysfunction.

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The impact of humidity above stratiform clouds on indirect aerosol climate forcing.

Some of the global warming from anthropogenic greenhouse gases is offset by increased reflection of solar radiation by clouds with smaller droplets that form in air polluted with aerosol particles that serve as cloud condensation nuclei. The resulting cooling tendency, termed the indirect aerosol forcing, is thought to be comparable in magnitude to the forcing by anthropogenic CO2, but it is difficult to estimate because the physical processes that determine global aerosol and cloud populations are poorly understood. Smaller cloud droplets not only reflect sunlight more effectively, but also inhibit precipitation, which is expected to result in increased cloud water. Such an increase in cloud water would result in even more reflective clouds, further increasing the indirect forcing. Marine boundary-layer clouds polluted by aerosol particles, however, are not generally observed to hold more water. Here we simulate stratocumulus clouds with a fluid dynamics model that includes detailed treatments of cloud microphysics and radiative transfer. Our simulations show that the response of cloud water to suppression of precipitation from increased droplet concentrations is determined by a competition between moistening from decreased surface precipitation and drying from increased entrainment of overlying air. Only when the overlying air is humid or droplet concentrations are very low does sufficient precipitation reach the surface to allow cloud water to increase with droplet concentrations. Otherwise, the response of cloud water to aerosol-induced suppression of precipitation is dominated by enhanced entrainment of overlying dry air. In this scenario, cloud water is reduced as droplet concentrations increase, which diminishes the indirect climate forcing.

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O2 plasma treated polyimide-based humidity sensors.

The effect of non-plasma and plasma treated polyimide-based humidity sensors is presented. Pure oxygen was used to etch polyimide in a plasma etcher. The sensor treated in a plasma exhibited higher sensitivity and faster response speed against moisture. The plasma treated sensor had 3.4 times the sensitivity and responded almost twice as fast as the non-plasma treated sensor. A further comparison of sensor outputs, sensitivity and response speed are presented. Chemical analysis of the polyimide surface was carried out by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (ATR-FTIR). XPS and ATR-FTIR showed the increase in carbonyl carbon bonds, C=O, after the plasma treatment. Geometrical modification was observed by atomic force microscopy (AFM). It showed considerable surface roughness after the plasma treatment. O2 plasma treatment improved the sensitivity, and reduced the hysteresis of the sensor due to the increase in C=O bonds in the polyimide.

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The heterogeneous kinetics of HOBr and HOCl on acidified sea salt and model aerosol at 40-90% relative humidity and ambient temperature.

The HOBr and HOCl uptake coefficient gamma on H(2)SO(4)-acidified submicron salt aerosol of known size distribution was measured in an atmospheric pressure laminar flow reactor. The interaction time of the trace gas with the aerosol was in the range 15 to 90 s and led to gamma values in the range 10(-4) to 10(-2). The acidity of the aerosol is essential in order to enable heterogeneous reactions of HOBr on NaCl, recrystallized sea salt (RSS) and natural sea salt (NSS) aerosols. Specifically, HOCl only reacts on acidified NSS aerosol with a gamma ranging from 0.4 x 10(-3) to 1.8 x 10(-3) at a relative humidity (rh) at 40 and 85%, respectively. Uptake experiments of HOBr on aqueous H(2)SO(4) as well as on H(2)SO(4)-acidified NaCl, RSS or NSS aerosol were performed for rh ranging from 40 to 93%. The gamma value of HOBr on acidified NSS reaches a maximum gamma = 1.9 x 10(-2) at rh = 76 +/- 1% and significantly decreases with increasing rh in contrast to acidified NaCl and RSS aerosols whose gamma values remain high at gamma = (1.0 +/- 0.2) x 10(-2) at rh >/= 80%. An explanation based on the formation of an organic coating on NSS aerosol with increasing rh is proposed.

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Effects of adsorbed water layer structure on adhesion force of silicon oxide nanoasperity contact in humid ambient.

The origin of the large relative-humidity (RH) dependence of the adhesion force in the single-asperity contact between silicon oxide surfaces is elucidated. As RH increases, the adhesion force measured with an atomic force microscopy (AFM) initially increases, reaches a maximum, and then decreases at high RH. The capillary force alone cannot explain the observed magnitude of the RH dependence. The origin of the large RH dependence is due to the presence of an icelike structured water adsorbed at the silicon oxide surface at room temperature. A solid-adsorbate-solid model is developed calculating the contributions from capillary forces, van der Waals interactions, and the rupture of an ice-ice bridge at the center of the contact region. This model illustrates how the structure, thickness, and viscoelastic behavior of the adsorbed water layer influence the adhesion force of the silicon oxide nanoasperity contact.

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Abundance, dispersion and parasitism of the stem borer Busseola fusca (Lepidoptera: Noctuidae) in maize in the humid forest zone of southern Cameroon.

This study was conducted in the humid forest zone of Cameroon, in 2002 and 2003. The main objective was to investigate the effects of intercropping on infestation levels and parasitism of the noctuid maize stem borer Busseola fusca Fuller. Two trials were planted per year, one during the long and one during the short rainy season. Maize monocrops were compared with maize/legume or maize/cassava intercrops in two spatial arrangements: maize on alternate hills or in alternate rows. Spatial analyses showed that the stemborer egg batches were regularly dispersed in the maize monocrop and aggregated in the intercrops, as indicated by b, the index of dispersion of Taylor's power law. Depending on the crop association and planting pattern, intercrops reduced the percentage of plants with stem borer eggs by 47.4-58.4% and egg densities by 41.2-54.5% compared to monocropped maize. Consequently, larval densities were 44.4-61.5% lower in intercrops compared to monocrops. Intercropping maize with non-host plants did not affect larval parasitism. Up to two-fold higher levels of egg parasitism by scelionid Telenomus spp. were recorded in inter- compared to monocrops during the short rainy seasons of 2002 and 2003. No differences were found among the mixed cropping treatments and parasitism was lower during the long compared to the short rainy seasons. It was proposed that differences in levels of parasitism were due to density dependence effects rather than the effect of the presence of non-host plants in the system.

Agriculture↗

Leaf CO(2) exchange of Erythrina poeppigiana (Leguminosae: Phaseolae) in humid tropical field conditions.

An idealized model was developed to describe leaf CO(2) exchange in the leguminous tree Erythrina poeppigiana (Walpers) O.F. Cook under well-watered field conditions. Photosynthetic rate in mature leaves (p) was modeled as a rectangular hyperbolic function of photon flux density (q) and ambient CO(2) concentration (c(a)), relative photosynthetic capacity (pi) was modeled as a logistic s-function of leaf age (l(a)), metabolic dark respiration rate (r(m)) was modeled as an exponential function of leaf temperature (T(l)), and photorespiration rate (r(p)) was modeled as a hyperbolic function of c(a). Assimilation rate (a(c)) was modeled as the difference between the product of p and pi and the sum of r(m) and r(p): a(c) = p(q,c(a))pi(l(a)) - [r(m)(T(l)) + r(p)(c(a))]. The model parameters were estimated separately for five sources of E. poeppigiana (Clones 2660, 2662, 2687 and 2693 and half-sib Family 2431) from field data measured with a portable closed-loop gas exchange system at a humid tropical site in Costa Rica. The between-source differences in leaf CO(2) exchange characteristics were small, but statistically significant. Aboveground biomass production was highest in sources that maintained high relative photosynthetic capacity throughout the leaf life span. Quantum yield varied between 0.046 and 0.067, and light-saturated assimilation rate (q = 2000 micro mol m(-2) s(-1) and T(l) = 28 degrees C) at natural atmospheric c(a) (350 micro mol mol(-1)) was 16.8-19.9 micro mol m(-2) s(-1). Increasing c(a) to 1000 micro mol mol(-1) resulted in an approximate doubling of the light-saturated assimilation rate. Foliole nitrogen concentration, which was 45.3-51.2 mg g(-1) in mature leaves, was positively correlated with relative photosynthetic capacity. Foliole nitrogen concentration, quantum yield and maximum assimilation rate of E. poeppigiana are among the highest values observed in tropical woody legumes.

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Low humidity can cause uneven photosynthesis in olive (Olea europea L.) leaves.

We examined the photosynthetic responses of olive (Olea europea L.) leaves exposed to either (a) two hours of high leaf-to-air vapor pressure difference (vpd) or (b) four 30-min cycles of high vpd separated by 15-min periods of recovery at low vpd. Neither treatment affected photosynthesis when vpd was less than 3.0 kPa. Photosynthesis by mature leaves was also insensitive to higher vpd, but photosynthesis of young leaves was reduced by both treatments at a vpd higher than 3.2 kPa. This effect of vpd was much smaller under high intercellular CO(2) pressure. Autoradiograms showed that under a vpd of 3.2 kPa, mature leaves photosynthesized uniformly, but patches of reduced CO(2) fixation occurred in the distal part of young leaves. We conclude that heterogeneities in photosynthesis along the length of the leaf caused the apparent reduction of photosynthesis in our experiments. This pattern of patchy photosynthesis was different from that observed in mesophytic herbs, but the effect on gas exchange analysis was the same. In this case, apparent biochemical effects of low humidity on photosynthesis of young olive leaves are likely an artifact.

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Aging in humid granular media.

Aging behavior is an important effect in the friction properties of solid surfaces. In this paper we investigate the temporal evolution of the static properties of a granular medium by studying the aging over time of the maximum stability angle of submillimetric glass beads. We report the effect of several parameters on these aging properties, such as the wear on the beads, the stress during the resting period, and the humidity content of the atmosphere. Aging effects in an ethanol atmosphere are also studied. These experimental results are discussed at the end of the paper.

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Observation of all the components of elastic constants using tetragonal hen egg-white lysozyme crystals dehydrated at 42% relative humidity.

Success in measuring transverse sound velocity allowed us to determine, for the first time, all six elastic constants of a protein crystal. An ultrasonic pulse-echo method was used to perform sound velocity measurements on tetragonal hen egg-white (HEW) lysozyme crystals that were partially dehydrated at 42% relative humidity. The measurements were performed using the (110), (101), and (001) crystallographic faces. Thus, all six elastic constants of the dehydrated tetragonal HEW lysozyme crystals were determined: C11=C22=12.44 GPa, C12=7.03 GPa, C13=C23=8.36 GPa, C33=12.79 GPa, C44=C55=2.97 GPa, and C66=2.63 GPa. In addition, for the hydrated crystals, the longitudinal sound velocities along the [110] direction and the direction normal to the (101) face were measured. From these results, all the components of elastic constants in the hydrated crystals were extrapolated.

Animals↗

Circadian Rhythm of Leaves of Phaseolus angularis Plants Grown in a Controlled Carbon Dioxide and Humidity Environment.

Leaf movements of primary leaves of Phaseolus angularis Wight. were studied in an environment with controlled levels of CO(2), relative humidity, temperature, light, nutrient concentrations, and water tension. Rhythmic circadian movements and irregular short period movements were evident as the leaves unfolded and persisted during development of the leaves. The mean period in rhythmic circadian movement was 27.3 hours with no significant differences in period between plants of the same or different experiments. The leaf movements of separate plants were not closely synchronized.A system is described for growing plants for extended periods while collecting data with time lapse photography. The system was developed to minimize disturbances to the plants.The occurrence of leaf movements in plants grown from the time of seeding in an environment free of any recognized fluctuation which could stimulate leaf movements supports the hypothesis that leaf movement rhythms originate spontaneously within the plant.

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Leaf conductance as a function of photosynthetic photon flux density and absolute humidity difference from leaf to air.

FOR AN ENTIRE SEASON OF STOMATAL ACTIVITY, LEAF OR NEEDLE CONDUCTANCE WAS OBSERVED ON FOUR SPECIES, EACH IN A DIFFERENT GENUS: Engelmann spruce (Picea engelmannii Parry ex Engelm.), subalpine fir (Abies lasiocarpa [Hook.] Nutt.), lodgepole pine (Pinus contorta var. latifolia Engelm.), and aspen (Populus tremuloides Michx.). Conductance in the natural environment was described for all species by photosynthetic photon flux density (PPFD) and absolute humidity difference from leaf to air (DAH), as follows: Conductance = b(1) ( radicalPPFD/ radicalDAH) + b(2) ( radicalPPFD/DAH) + b(3) ( radicalPPFD/DAH(2)). The only data not fitting this relationship were conifer data collected after freezing nights or aspen data collected during a short period in August when water stress occurred. In both cases, leaf conductance was reduced. It is proposed that PPFD and DAH are primary factors controlling stomatal function for plants growing in their native range; secondary factors, such as temperature and water stress, affect conductance intermittently, except when plants are growing outside their normal environmental conditions.

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Developing Seeds of Ricinus communis L., When Detached and Maintained in an Atmosphere of High Relative Humidity, Switch to a Germinative Mode without the Requirement for Complete Desiccation.

Immature seeds of castor bean (Ricinus communis) removed from the capsule at 25 to 40 days after pollination (25-40 DAP) and placed in an atmosphere of high relative humidity undergo limited water loss, and germinate upon subsequent return to full hydration. This switch from a developmental to a germinative/growth mode at 40 DAP is reflected in a change in the types of proteins being synthesized in the endosperm; after partial drying, developmental protein synthesis ceases and germinative/growth-related proteins are produced. The nature and timing of these protein synthetic changes elicited upon imbibition are identical to those following premature desiccation/rehydration of 30 and 40 DAP seeds and upon imbibition of the mature dry seed. Enzymes involved in postgerminative reserve mobilization (l-leucyl-beta-naphthylamidase and isocitrate lyase) are induced upon imbibition, following partial drying at 40 DAP, to levels attained in the endosperms of germinated mature, and prematurely dried/rehydrated, seeds. The changes in protein synthesis resulting from partial drying are effected at the transcriptional and post-transcriptional level. Upon return to full hydration some new (i.e. germination and growth-related) mRNAs are synthesized, while others (associated with development) present in the partially dried endosperm decline. Thus developing seeds of castor bean do not have to experience substantial (whole seed) water loss to acquire the ability to germinate and grow upon subsequent imbibition. Seed detachment from the mother plant alone is not sufficient to elicit a switch to germination and growth processes. However, the length of time of detachment from the mother plant, in combination with some water loss may interact to elicit the "switch" from development to germination.

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The magnitude of the stomatal response to blue light : modulation by atmospheric humidity.

The effect of leaf-air vapor pressure difference (VPD) on the magnitude of the stomatal response to blue light was investigated in soybean (Glycine max) by administering blue light pulses (22 seconds by 120 micromoles per square meter per second) at different levels of VPD and temperature. At 20 degrees C and 25 degrees C, the magnitude of the integrated conductance response decreased with increasing VPD (0.4 to 2.6 kiloPascals), due to an earlier onset of stomatal closure that terminated the pulse response. In contrast, at 30 degrees C this magnitude increased with rising VPD (0.9 to 3.5 kiloPascals), due to an increasing maximum excursion of the conductance response despite the accelerated onset of stomatal closure. When the feedforward response of stomata to humidity caused steady state transpiration to decrease with increasing VPD, the magnitude of the pulse-induced conductance response correlated with VPD rather than with transpiration. This suggests that water relations or metabolite movements within epidermal rather than bulk leaf tissue interacted with guard cell photobiological properties in regulating the magnitude of the blue light response. VPD modulation of pulse magnitude could reduce water loss during stomatal responses to transient illumination in natural light environments.

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Effects of Mild Water Stress and Diurnal Changes in Temperature and Humidity on the Stable Oxygen and Hydrogen Isotopic Composition of Leaf Water in Cornus stolonifera L.

In this paper we make comparisons between the observed stable isotopic composition of leaf water and the predictions of the Craig-Gordon model of isotopic enrichment when plants (Cornus stolonifera L.) were exposed to natural, diurnal changes in temperature and humidity in a glasshouse. In addition, we determined the effects of mild water stress on the isotopic composition of leaf water. The model predicted different patterns of diurnal change for the oxygen and hydrogen isotopic composition of leaf water. The observed leaf water isotopic composition followed qualitatively similar patterns of diurnal change to those predicted by the model. At midday, however, the model always predicted a higher degree of heavy isotope enrichment than was actually observed in leaves. There was no effect of mild water stress on the hydrogen isotopic composition of leaf water. For the oxygen isotopic composition of leaf water, there was either no significant difference between control and water-stressed plants or the stressed plants had lower delta(18)O values, despite the enriched stem water isotopic composition observed for the stressed plants.

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Water-dependent domain motion and flexibility in ribonuclease A and the invariant features in its hydration shell. An X-ray study of two low-humidity crystal forms of the enzyme.

The crystal structures of 88 and 79% relative humidity forms of ribonuclease A, resulting from water-mediated transformations, have been refined employing the restrained least-squares method using X-ray data collected on an area detector to R = 0.173 for 15 326 observed reflections in the 10-1.5 A resolution shell and R = 0.176 for 8534 observed reflections in the 10-1.8 A shell, respectively. The comparison of these structures with those of the native, the phosphate-bound and the sulfate-bound forms demonstrates that the mobility of the ribonuclease A molecule involves hinge-bending movement of the two domains and local flexibility within them, particularly at the termini of regular secondary structures and in loops. The comparison also leads to the identification of 31 invariant water molecules in the hydration shell of the enzyme, many of which are involved in holding different parts of the molecule together and in stabilizing local structure. The conformational changes that accompany the partial removal of the surrounding water, particularly those observed in the 79% form, could be similar to those that occur during enzyme action.

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