Differentiated free-living and sediment-attached bacterial community structure inside and outside denitrification hotspots in the river–groundwater interface

This study assessed the functional significance of attached and free-living bacterial communities involved in the process of denitrification in a shallow aquifer of a riparian zone (Garonne River, SW France). Denitrification enzyme activity (DEA), bacterial density (BD) and bacterial community composition (BCC) were measured in two aquifer compartments: the groundwater and the sandy fraction of the sediment deposit. Samples were collected in wells located inside (IHD) and outside (OHD) identified hotspots of denitrification. Despite high BD values (up to 1.14 × 10¹² cells m⁻³), DEA was not detected in the water compartment (< 0.32 mg N–N₂O m⁻³ d⁻¹). The sandy fraction showed detectable DEA (up to 1,389 mg N–N₂O m⁻³ d⁻¹) and, consistent with BD pattern, higher DEA values were measured in IHD zones than in OHD zones. The BCC assessed by 16S rDNA polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) partly supported this result: attached and free-living communities were significantly different (< 30% similarity) but patterns of BCC did not cluster according to IHD and OHD zones. Targeting the denitrifying communities by means of a culture enrichment step prior to 16S rDNA PCR-DGGE showed that the free-living and sediment attached communities differed. Most sequences obtained from DGGE profiles of denitrifying communities were affiliated to Proteobacteria and showed low genetic distance with taxa that have already been detected in aquifers (e.g., Azoarcus sp., Acidovorax sp. and Pseudomonas spp.). This study confirms that in the aquifer the sediment-attached fraction exhibits different functions (DEA) from free-living communities and suggests that this functional difference is related to the communities’ structure.     

Flood drift and propagule bank of aquatic macrophytes in a riverine wetland

Abstract. Drift of aquatic macrophyte propagules was investigated in a wetland along the River Rhône, during the first flood after the growing season (i.e. in the winter of 1995–1996). Input and output drift were studied at the beginning, around the top, and at the end of the river overflow in the upper reach of a cut-off channel. The soil propagule bank was sampled along the study area before and after the flood. The amount and composition of viable propagule drift and bank were determined, analysed and compared. Drift densities and richness were on average higher at the outlet of the channel than at the inlet (respectively: 23.2 vs 13.1 viable propagules/100 m³ of water and 8.7 vs 2.6 taxa per sample). Immigrating taxa were mostly in the form of helophyte seeds, whereas numerous resident hydrophyte species left the disturbed area rather as vegetative propagules. Temporal variability in propagule bank structure was weak, and mean bank densities did not change before and after the flood (respectively: 33 047 ± 10 510 vs 35 653 ± 15 070 viable propagules/m² of ground, including Chara). However, the density of Elodea canadensis significantly increased after the flood while that of Eleocharis acicularis decreased. This contrast suggests that flood responses vary among species. Despite a broad overlap in the taxa (18 out of 25 were common both to drift and bank collections), no significant relationship occurred in composition or structural changes between flood drift and propagule bank. Flood acted as a means of distribution of existing propagules and also as a provider of new vegetative dispersal units.     

Chemical and microbial evaluation of in-situ bioremediation of hydrocarbons in anoxic groundwater enriched with nutrients and nitrate

In-situ bioremediation of benzene, toluene, ethylbenzene and the xylenes (BTEX) was carried out in an O₂-poor (approx. 1 mg O₂/l) fuel-contaminated aquifer. Extracted groundwater, enriched with ammonium polyphosphate (nutrients) and KNO₃ (electron acceptor), was piped to an infiltration gallery over the contaminated site. Before, during and after infiltration, BTEX, nitrate and different populations of culturable bacteria were measured. BTEX declined by 78% in water from the monitoring well which was most contaminated initially and by nearly 99% in water from one of the extraction wells. These declines persisted after cessation of nutrient and nitrate addition. During the second half of the nutrient and nitrate addition period (weeks 107 to 160.5), nitrate appeared in the monitoring well, denitrifying bacteria increased about 50-fold and bacteria degrading benzene, toluene and xylenes (BTX) and phenanthrene (enumerated aerobically) increased 16- and 121-fold, respectively. At one of the extraction wells, down-gradient of the monitoring well, nitrate appeared in significant concentrations after week 124; this appearance coincided with a marked decline (> 90%) in BTEX concentration and 21- and 10-fold increases, respectively, in BTX- and phenanthrene-degrading bacteria. Low concentrations of BTEX and nitrate in down-gradient, off-site wells showed that water washing did not mobilize BTEX from the aquifer. The data indicate that the BTEX in this nitrate-enriched aquifer was biodegraded in-situ under denitrifying conditions.     

A suitable extractant for assessing plant-available copper in different soils (peaty,red and alluvial)

Summary Relative efficiency of five chemical extractants for the extraction of available Cu in four different soils and its uptake by rice seedlings was studied in a pot culture experiment. The Cu extracted by 0.1N HCl showed significant relationship with plant uptake whereas the values for other extractants except 0.05M EDTA did not approach the level of significance. Among the soil properties studied, pH and CaCO₃ correlated negatively and organic matter and CEC positively with Cu uptake by rice plants.     

Successional development of wood-inhabiting fungi associated with dominant tree species in a natural temperate floodplain forest

Fungi play a crucial role in dead wood decay, being the major decomposers of wood and affecting microbiota associated with dead wood. We sampled dead wood from five deciduous tree species over more than forty years of decay in a natural European floodplain forest with high tree species diversity. While the assembly of dead wood fungal communities shows a high level of stochasticity, it also indicates clear successional patterns, with fungal taxa either specific for early or late stages of wood decay. No clear patterns of fungal biomass content over time were observed. Out of 220 major fungal operational taxonomic units, less than 8% were associated with a single tree species, most of them with Quercus robur. Tree species and wood chemistry, particularly pH, were the most important drivers of fungal community composition. This study highlights the importance of dead wood and tree species diversity for preserving the biodiversity of fungi.     

Characterization of estrogen-degrading bacteria isolated from an artificial sandy aquifer with ultrafiltered secondary effluent as the medium

This study investigated the aerobic and anoxic biodegradation of four estrogens [estrone (E1), estradiol (E2), estriol (E3), and the synthetic 17α-ethinylestradiol (EE2)] in microcosms constructed with marine sand and ulftrafiltered (UF) secondary effluent. Three estrogen-degrading bacteria, LHJ1, LHJ3, and CYH, were isolated. Based on gram-stain morphology and 16S rRNA sequence homology, LHJ1 and LHJ3 belong to the genus Acinetobacter and Agromyces, respectively; CYH matched to 95% with the genus Sphingomonas. Aerobically LHJ3 degrades E3, CYH degrades E1, and all three isolates oxidize E2 to E1. Under anoxic conditions, CYH degrades E1 and LHJ3 degrades E2, whereas E3 and EE2 were not degraded by the three isolates; EE2 was transformed in microcosms incubated with site ground water. The degradation kinetics of E1 and E2 by CYH and E2 by LHJ3 under aerobic conditions was linearly correlated with the initial concentration, which ranged from 50 to 2,000 μg/l. The degradation of E1 by CYH under anoxic conditions followed Michaelis–Menten kinetics. 16α-Hydroxyestrone was found to be a transient transformation product of E3 under aerobic conditions.     

Depletion of Rice as Food of Waterfowl Wintering in the Mississippi Alluvial Valley

ABSTRACT Waterfowl habitat conservation strategies in the Mississippi Alluvial Valley (MAV) and several other wintering areas assume carrying capacity is limited by available food, and increasing food resources is an effective conservation goal. Because existing research on winter food abundance and depletion is insufficient to test this hypothesis, we used harvested rice fields as model foraging habitats to determine if waste rice seed is depleted before spring migration. We sampled rice fields (n = 39 [winter 2000–2001], n = 69 [2001–2002]) to estimate seed mass when waterfowl arrived in late autumn and departed in late winter. We also placed exclosures in subsets of fields in autumn (n = 8 [2000–2001], n = 20 [2001–2002]) and compared seed mass inside and outside exclosures in late winter to estimate rice depletion attributable to waterfowl and other processes. Finally, we used an experiment to determine if the extent of rice depletion differed among fields of varying initial abundance and if the seed mass at which waterfowl ceased foraging or abandoned fields differed from a hypothesized giving-up value of 50 kg/ha. Mean seed mass was greater in late autumn 2000 than 2001 (127.0 vs. 83.9 kg/ha; P = 0.018) but decreased more during winter 2000–2001 than 2001–2002 (91.3 vs. 55.7 kg/ha) and did not differ at the end of winter (35.8 vs. 28.3 kg/ha; P = 0.651). Assuming equal loss to deterioration inside and outside exclosures, we estimated waterfowl consumed 61.3 kg/ha (48.3%) of rice present in late autumn 2000 and 21.1 kg/ha (25.1%) in 2001. When we manipulated late-autumn rice abundance, mean giving-up mass of rice seed was similar among treatments (48.7 kg/ha; P = 0.205) and did not differ from 50 kg/ha (P = 0.726). We integrated results by constructing scenarios in which waterfowl consumed rice at different times in winter, consumption and deterioration were competing risks, and consumption occurred only above 50 kg/ha. Results indicated waterfowl likely consumed available rice soon after fields were flooded and the amount consumed exceeded our empirical estimates but was ≤48% (winters pooled) of rice initially present. We suggest 1) using 50 kg/ha as a threshold below which profitability limits waterfowl feeding in MAV rice fields; 2) reducing the current estimate (130 kg/ha) of rice consumed in harvested fields to 47.1 kg/ha; and 3) increasing available rice by increasing total area of fields managed, altering management practices (e.g., staggered flooding), and exploring the potential for producing second or ratoon rice crops for waterfowl.     

Iron-phosphorus relationship in the nutrition of tomato seedlings grown on alluvial and calcareous soils

Summary In typical alluvial and calcareous soils of Egypt 5 levels of each of P and Fe were added to study their effect on the dry matter and on their uptake by tomato seedlings in greenhouse. Application of phosphorus significantly increased the dry matter yields and both P and Fe uptake by tomatoes grown on both soils. However, application of Fe had no significant effect on the dry matter and P-uptake by tomatoes grown on alluvial soil while they were significantly increased on the calcareous one.