Simulating the dynamics of sulfur species and zinc in wetland sediments

In situ measurements comparing vertical SO₄²⁻ profiles in vegetated and non-vegetated sediments showed that SO₄²⁻ concentrations in vegetated sediments increased significantly at the beginning of the growing season and then gradually decreased during the rest of the growing season. Throughout the growing season, SO₄²⁻ concentrations remained higher in the vegetated sediments than in the sediments without plants. The higher SO₄²⁻ concentrations in the vegetated sediments indicate that oxygen release from roots and evapotranspiration-induced advection by plants play an important role in the dynamics of sulfur species in sediments. Since the total pool of solid-phase sulfide is relatively large compared to the mass of SO₄²⁻ in the sediments, the gradual decrease of SO₄²⁻ concentrations may result from limitation of the solid-phase sulfide that is in direct contact with or very close to the roots and rhizomes. This would mean that the main pool of solid-phase sulfide and associated trace metals are not affected by the oxygen release from roots, and the associated trace metals will not become bioavailable during the growing season.     

Mound building in Ilyoplax pingi (Crustacea: Brachyura: Ocypodidae)

The ocypodid crab Ilyoplax pingi, observed in Kanghwa I., Korea in 1992, builds a mound at the burrow entrance, by piling mud dug out from the burrow. The mounds were made by both waving and non-waving males, and by both ovigerous and non-ovigerous females. The burrow diameter at the widest part tended to be larger in crabs with mounds than in crabs without mounds, whereas the burrow depth was not different between them. The mound density increased in the late exposure period, when the crabs' surface activities declined. Mound removal and rebuilding experiments revealed that the presence of the mounds has the effect of keeping neighboring crabs away.     

A simple approach to modeling microbial biomass in the rhizosphere

Microorganisms make an important contribution to the degradation of contaminants in bioremediation as well as in phytoremediation. An accurate estimation of microbial concentrations in the soil would be valuable in predicting contaminant dissipation during various bioremediation processes. A simple modeling approach to quantify the microbial biomass in the rhizosphere was developed in this study. Experiments were conducted using field column lysimeters planted with Eastern gamagrass. The microbial biomass concentrations from the rhizosphere soil, bulk soil, and unplanted soil were monitored for six months using an incubation–fumigation method. The proposed model was applied to the field microbial biomass data and good correlation between simulated and experimental data was achieved. The results indicate that plants increase microbial concentrations in the soil by providing root exudates as growth substrates for microorganisms. Since plant roots are initially small and do not produce large quantities of exudates when first seeded, the addition of exogenous substrates may be needed to increase initial microbial concentrations at the start of phytoremediation projects.     

Choosing rewarding flowers; perceptual limitations and innate preferences influence decision making in bumblebees and honeybees

Flowers exhibit great intra-specific variation in the rewards they offer. At any one time, a significant proportion of flowers often contain little or no reward. Hence, foraging profitably for floral rewards is problematic and any ability to discriminate between flowers and avoid those that are less rewarding will confer great advantages. In this study, we examine discrimination by foraging bees among flowers of nasturtium, Tropaeolum majus. Bee visitors included carpenter bees, Xylocopa violacea, which were primary nectar robbers; honeybees, Apis mellifera, which either acted as secondary nectar robbers or gathered pollen legitimately and bumblebees, Bombus hortorum, which were the only bees able to gather nectar legitimately. Many flowers were damaged by phytophagous insects. Nectar volume was markedly lower in flowers with damaged petals (which were also likely to be older) and in flowers that had nectar-robbing holes. We test whether bees exhibit selectivity with regards to the individual flowers, which they approach and enter, and whether this selectivity enhances foraging efficiency. The flowers approached (within 2 cm) by A. mellifera and B. hortorum were non-random when compared to the floral population; both species selectively approached un-blemished flowers. They both approached more yellow flowers than would be expected by chance, presumably a reflection of innate colour preferences, for nectar standing crop did not vary according to flower colour. Bees were also more likely to accept (land on) un-blemished flowers. A. mellifera gathering nectar exhibited selectivity with regards to the presence of robbing holes, being more likely to land on robbed flowers (they are not able to feed on un-robbed flowers). That they frequently approached un-robbed flowers suggests that they are not able to detect robbing holes at long-range, so that foraging efficiency may be limited by visual acuity. Nevertheless, by using a combination of long-range and short-range selectivity, nectar-gathering A. mellifera and B. hortorum greatly increased the average reward from the flowers on which they landed (by 68% and 48%, respectively) compared to the average standing crop in the flower population. Overall, our results demonstrate that bees use obvious floral cues (colour and petal blemishes) at long-range, but can switch to using more subtle cues (robbing holes) at close range. They also make many mistakes and some cues used do not correlate with floral rewards.     

Dynamics of nitrogen,phosphorus, algal biomass,and suspended solids in an artificial lentic ecosystem and significant implications of regional hydrology on trophic status

Chemical and biological parameters were analyzed to examine how regional hydrological fluctuations influence water quality of a artificial lentic ecosystem over a two-year period The intensity of seasonal monsoon rain accounted for most of annual inflow and discharge and influenced flow pathway (interflow vs. overflow), resulting in a modification of chemical and biological conditions. Sharp contrasting interannual hydrology of intense vs. weak monsoon occurred during the study. The intense monsoon disrupted thermal stratification and resulted in ionic dilution, high TP and high inorganic solids (NVSS) in the headwater reach. The variation of NVSS accounted 75% of TP variation (slope = 4.14, p < 0.01, n = 48). Regression analysis of residual chlorophyll-a (Chl) versus flushing rate indicated that short hydraulic retention time and high mineral turbidity affected algal growth in the headwater reach during summer monsoon. In contrast, severe drought during weak monsoon produced strong thermal stratification, low inorganic solids, high total dissolved solids (TDS), and low TP in the entire system. In addition, Chl concentrations were controlled by phosphorus. Based on the physical, chemical and biological parameters, riverine conditions, dominated during the intense monsoon, but lacustrine conditions were evident during the weak monsoon. The interannual dynamics suggest that monsoon seasonality is considered the main forcing factor regulating overall functions and processes of the waterbody and this characteristic has an important implication to eutrophication of the system.     

Time-course uptake and elimination of benzo(a)pyrene and its damage to reproduction and ensuing reproductive outputs of Pacific oyster, <Emphasis Type="Italic">Crassostrea gigas</Emphasis>

The time-course of uptake and elimination of benzo(a)pyrene (BaP) for the Pacific oyster, Crassostrea gigas and reproduction damage and reproductive outputs were studied. Sexually immature C. gigas broodstock were fed for 28 days with live algae grown in four BaP solutions of 0, 50, 500, and 5,000 μg L⁻¹ (hereafter, control, 50, 500, and 5,000 oysters) and were subsequently conditioned to maturation by a feeding with BaP-free live algae under temperature manipulation for another 28 days. The 5,000 μg L⁻¹ oysters gained a steady state concentration, around 30,000 ng g⁻¹ d.w. for digestive gland, a week earlier compared to the 500 μg L⁻¹ oysters. The earlier gain or longer persistence of the steady state concentration influenced elimination of BaP, with an eliminating trend for 500 μg L⁻¹ oysters, while no elimination for 5,000 μg L⁻¹ oysters. The maternal persistence of the steady state concentration resulted in significant damages in the reproductive success and their reproductive outputs in terms of the hatching rate and larval growth, survival, and settlement. The 50 μg L⁻¹ oysters remained far below the steady state concentration, and showed a manifest eliminating behavior during the subsequent BaP-free 28 day maturation period. The reproductive success and initial larval events of 50 μg L⁻¹ oysters were comparable to those of control. However, the damage potential of the 50 μg L⁻¹ oysters might be more significant if their maternal exposure continued beyond 28 days, since the accumulation profile at this dose was linear.     

Removal characteristics of trace compounds of landfill gas by activated carbon adsorption

The removal characteristics of trace compounds and moisture in raw landfill gas (LFG) were studied. The LFG from the extraction well was saturated with water and moisture was eliminated by physical methods including cyclone-type dehydrator and compressor. The moisture removal efficiency of dehydrator and compressor was above 80%. As the moisture contents of LFG decreased, the toxic compounds like aromatics and chlorinated compounds were effectively removed by using the granular activated carbon. The breakthrough time and adsorption capacity of benzene, toluene, and ethyl benzene decreased rapidly when the relative humidity is over 60%. The effect of moisture was more pronounced at lower adsorbate concentrations tested than at higher concentrations. The breakthrough curves for multi-component mixtures show displacement effects. In the course of competing adsorption, adsorbates with strong interaction force to displace weakly bounded substances. Adsorption by activated carbon is in descending order of xylene, ethylbenzene, toluene, tri or tetrachloroethylene, benzene, carbon tetrachloride and chloroform in LFG, respectively.     

Removal of ammonia by biofilters: a study with flow-modified system and kinetics

The characteristics of ammonia removal by two types of biofilter (a standard biofilter with vertical gas flow and a modified biofilter with horizontal gas flow) were investigated. A mixture of organic materials such as compost, bark, and peat was used as the biofilter media based on the small-scale column test for media selection. Complete removal capacity, defined as the maximum inlet load of ammonia that was completely removed, was obtained. The modified biofilter showed complete removal up to 1.0 g N/kg dry material/day. However, the removal capacity of the standard biofilter started to deviate from complete removal around 0.4 g N/kg dry material/day, indicating that the modified biofilter system has higher removal efficiency than the standard upflow one. In kinetic analysis of the biological removal of ammonia in each biofilter system, the maximum removal rate, Vm, was 0.93 g N/kg dry material/day and the saturation constant, Ks, was 32.55 ppm in the standard biofilter. On the other hand, the values of Vm and Ks were 1.66 g N/kg dry material/day and 74.25 ppm, respectively, in the modified biofilter system.     

PCDDs, PCDFs, and PCBs concentrations in breast milk from two areas in Korea: body burden of mothers and implications for feeding infants

We determined breast milk concentration of polychlorinated dibenzo-p-dioxins (PCDDs)/polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) in 24 mothers living in Korea, and assessed the maternal body burden based on PCDDs/PCDFs and PCBs concentrations in breast milk and an infant intake rate through breast-feeding based on their concentration in breast milk. PCDDs/PCDFs and PCBs levels in breast milk from primipara mothers were found to be higher than those from multipara mothers. For total PCDDs/PCDFs TEQ level, 2,3,4,7,8-PeCDD was the predominant congener, and the proportion of 2,3,7,8-TCDD was less than 3% of total PCDDs/PCDFs TEQ level. For PCBs TEQ level, PCB-126 was the predominant congener. Maternal body burden levels of PCDDs/PCDFs and PCBs based on their concentrations in breast milk were 268-622 TEQ ng. The daily dioxin intakes of mothers were predicted to be 0.78-2.18 TEQ pg/kg/day for PCDDs/PCDFs and 0.34-0.66 TEQ pg/kg/ day for PCBs. For the first year, the body burden of an infant was predicted to be 212 TEQ ng and the daily intake of an infant was predicted to be 85 TEQ pg/kg/day, assuming the mean dioxin-related compounds concentration (27.54 TEQ pg/g fat).