Natural remobilization of multicomponent DNAPL pools due to dissolution

Mixtures of dense nonaqueous phase liquids (DNAPLs) trapped in the subsurface can act as long-term sources of contamination by dissolving into flowing groundwater. If the components have different solubilities then dissolution will alter the composition of the remaining DNAPL. We theorized that a multicomponent DNAPL pool may become mobile due to the natural dissolution process. In this study, we focused on two scenarios: (1) a DNAPL losing light component(s), with the potential for downward migration; and (2) a DNAPL losing dense component(s), with the potential for upward migration following transformation into a less dense than water nonaqueous phase liquid (LNAPL). We considered three binary mixtures of common groundwater contaminants: benzene and tetrachloroethylene (PCE), PCE and dichloromethane (DCM), and DCM and toluene. A number of physical properties that control the retention and transport of DNAPL in porous media were measured for the mixtures, namely: density, interfacial tension, effective solubility, and viscosity. All properties except density exhibited nonlinear relationships with changing molar ratio of the DNAPL. To illustrate the potential for natural remobilization, we modelled the following two primary mechanisms: the reduction in pool height as mass is lost by dissolution, and the changes in fluid properties with changing molar ratio of the DNAPL. The first mechanism always reduces the capillary pressure in the pool, while the second mechanism may increase the capillary pressure or alter the direction of the driving force. The difference between the rate of change of each determines whether the potential for remobilization increases or decreases. Static conditions and horizontal layering were assumed along with a one-dimensional, compositional modelling approach. Our results indicated that for initial benzene/PCE ratios greater than 25:75, the change in density was sufficiently faster than the decline in pool height to promote DNAPL breakthrough into the adjacent porous medium. In contrast, there was no potential for natural remobilization of a PCE-DCM mixture, primarily because the densities of the components are not sufficiently different. Dissolution of a DCM-toluene mixture decreased the density, reducing the tendency for downward displacement. However, the ultimate transformation from a DNAPL to an LNAPL may induce upward displacement. These results suggest that at sites with DNAPL pools containing a mix of components of sufficiently different densities and relative solubilities, natural remobilization may be an active mechanism, with implications for site evaluation and remediation.     

An assessment methodology for successional systems. II. Statistical tests and specific examples

This paper presents a dynamic framework for environmental assessment when the system under study is undergoing successional change. Successional differences between sites for which one wishes to detect a difference because of a treatment are essentially confounding factors. We show how successional changes over the study period or resulting from differences in study site plot ages can be factored out by developing a null model of expected behavior over time. The null model for change in state with time is characterized in terms of a stochastic envelope around a nominal trajectory. Specific tests for the detection of trends associated with succession are described and illustrated on example data. It is concluded that the methods developed work particularly well for laboratory microcosm data.     

Conditional lekking in ruff (Philomachus pugnax)

Summary In our study of ruff, a lekking shorebird, we found that the lek ratio — the proportion of the total population of males occurring on leks was low, averaging 12% over the breeding season (Fig. 1D). Off-lek males spent approximately the same proportion of time as lek males in displaying to females (Fig. 4). We defined three spacing tacties that male ruffs use to position themselves to court females: Following — directly pursuing females, and two types of lekking behavior, Intercepting — waiting for females at resource-rich sites, and True Lekking — waiting for females at places without any resources other than the males themselves. Males switched among these tactics, causing the lek ratio to vary over the season (Fig. 1 D). Lek ratio increased when the number of females present in the study area plummeted at the end of May, and was positively correlated throughout the season with the copulation rate of the preceding day, suggesting that males were tracking the behavior, as well as the number, of females available (Table 1, Fig. 1). Early in the season, males off leks spent most of their time feeding (Fig. 4), and lek ratio was positively correlated with temperature (Table 1), suggesting that some males may have been unable to lek during cold weather. Males on leks mated at significantly higher rates than Followers (Table 4). On average, males at our interception lek were less site faithful and less peristent than males at true leks, and the interception lek itself disappeared after females stopped coming to use its adjacent resource (Table 2, Fig. 5). The most successful individuals in our population were the True Lekking males, rather than the Interceptors.In addition to the conditinal lekking tactics described here, ruff display a dimorphism in behaviorat leks. Independent males defend small courts on leks, while Satellite males share courts and mutually display with independents Both independents and satellites may use all three conditional tactics. We propose that satellites evolved as specialized. Followers, adept at tracking the movements of females among leks.     

The normal fetus of an acardiac twin pregnancy: Perinatal management based on echocardiographic and sonographic evaluation

Experience with three prenatally diagnosed pregnancies complicated by an acardiac twin reveals that ultrasonography and echocardiography are helpful in detecting early signs of in-utero congestive heart failure in the normal twin. The use of Doppler blood flow analysis to determine direction of blood flow, post-mortem placental and fetal angiography, and umbilical cord blood gas determination provided proof that retrograde arterial perfusion occurs in the acardiac fetus. In a fourth pregnancy, an experimental approach to occlude the acardiac twin's umbilical cord was attempted, but was unsuccessful.     

Characterization of in vivo absorption features of chlorophyte,phaeophyte and rhodophyte algal species

Despite the plentiful diversity of macroalgae in coastal environments, few studies have examined the in vivo absorption features of common marine macrophytes. Here we report on results of a survey of 12 central California common intertidal and subtidal taxa, representing Chlorophyta, Phaeophyta and Rhodophyta carried out in the summer of 1988. Computer-assisted analyses were used to obtain fourth-derivative spectra from in vivo absorption spectra determined at room temperature to obtain spectral diagnostics for the different algal divisions and to provide a means to determine whether spectral features could be used to identify stress responses among these plants. Among the Chlorophyta, characteristic maxima for chlorophylls a and b were resolved in all species examined, and a spectral component attributable to siphonaxanthin-like carotenoid(s) was observed in two Ulva species and the coenocytic alga Derbesia marina. Representatives of the Phaeophyta were characterized by similar maxima for chlorophyll a and c, and for fucoxanthin. Among the Rhodophyta, maxima for chlorophyll a, as well as B- and R-type phycoerythrin were resolved. Differences in in vivo absorption features were detected for two tidal populations of Porphyra perforata and Mastocarpus papillatus. High-tidal thalli absorb less green light in regions characterized by phycoerythrin, but have enhanced carotenoid absorption compared with lowtidal thalli. Resolution of spectra by fourth-derivative analysis revealed significant differences in phycoerythrin and carotenoid contents. The spectral changes observed appear to reflect environmental and possibly populational characteristics of these algae. The spectral analyses described here provide robust, non-invasive means to characterize subtle responses of macroalgae to environment in ways not possible previously. Additional merits of these fourth-derivative analyses for use in environmental studies are discussed.This contribution is dedicated to the memory of Professor L. R. Blinks, a pioneer in photosynthesis research and algal physiology