Enhancement on the simultaneous removal of nitrate and organic pollutants from groundwater by a three-dimensional bio-electrochemical reactor

To improve denitrification performance and effective degradation of organic pollutants from micro-polluted groundwater simultaneously, a novel three-dimensional (3D) bio-electrochemical reactor was developed, which introduced activated carbon into a traditional two-dimensional (2D) reactor as the third electrode. The static and dynamic characteristics of the reactor were investigated with special attentions paid to the performance comparison of these two reactors. In the 3D reactor both TOC and nitrate removal efficiency were greatly improved, and the formation of nitrite byproduct is considerably reduced, comparing with that of the 2D reactor. The role of activated carbon biofilm was explored and possible remediation mechanisms for the 2D and 3D reactors were suggested. In such a 3D reactor, the denitrification rate improved greatly to 0.288 mg NO₃–N/cm²/d and the current efficiency could reach as high as 285%. Further, it demonstrated good performance stably against variable conditions, indicating very promising in application for groundwater remediation.     

Nitrogen dynamics in the hyporheic zone of a forested stream during a small storm, Hokkaido, Japan

Water and dissolved nitrogen flows through the hyporheic zone of a 3rd-order mountain stream in Hokkaido, northern Japan were measured during a small storm in August 1997. A network of wells was established to measure water table elevations and to collect water samples to analyze dissolved nitrogen concentrations. Hydraulic conductivity and the depth to bedrock were surveyed. We parameterized the groundwater flow model, MODFLOW, to quantify subsurface flows of both stream water and soil water through the hyporheic zone. MODFLOW simulations suggest that soil water inflow from the adjacent hill slope increased by 1.7-fold during a small storm. Dissolved organic nitrogen (DON) and ammonium (NH ₄ ⁺ ) in soil water from the hill slope were the dominant nitrogen inputs to the riparian zone. DON was consumed via mineralization to NH ₄ ⁺ in the hyporheic zone. NH ₄ ⁺ was the dominant nitrogen species in the subsurface, and showed a net release during both base and storm flow. Nitrate appeared to be lost to denitrification or immobilized by microorganisms and/or vegetation in the riparian zone. Our results indicated that the riparian and hyporheic system was a net source of NH ₄ ⁺ to the stream.     

Ciliated protozoan communities and saprobic evaluation of water quality in the hilly zone of some tributaries of the Po River (northern Italy)

Ciliate protozoans were collected from five watercourses belonging to the hydrographic network of the North Apennines (Italy) and flowing into the middle lower section of the river Po from its right bank. Thirteen stations were selected in the meta- and hyporhithron section of the five studied rivers and samples from water–sediment interface were collected during a 1year period. A total of 175 species of ciliates belonging to 97 genera were found, of which 68 were bacterivorous, 58 were algivorous, 26 were omnivorous and 23 were carnivorous. Their distribution varied both with distance along the river and with the time. Community structures were analysed using some statistical methods and this allowed the determination of similarities among stations and relationships between species and stations. The saprobic index and valency methods were used to evaluate the water quality at the 13 stations. Comparisons between the five watercourses indicate that trophic state influences the composition of ciliate communities. The high similarity observed in the unpolluted stations enabled us to define the typical species and the community of the meta- hyporhithron zone. Conversely, polluted stations showed the lowest similarities. Our results confirm that in watercourses the organic load may be the dominating factor able to influence, if not eliminate the diversifying effects of other factors such as those which characterize the longitudinal zonation of the watercourses.     

Nitrogen attenuation in the Connecticut River,northeastern USA; a comparison of mass balance and N<Subscript>2</Subscript> production modeling approaches

Two methods were used to measure in-stream nitrogen loss in the Connecticut River during studies conducted in April and August 2005. A mass balance on nitrogen inputs and output for two study reaches (55 and 66 km), at spring high flow and at summer low flow, was computed on the basis of total nitrogen concentrations and measured river discharges in the Connecticut River and its tributaries. In a 10.3 km subreach of the northern 66 km reach, concentrations of dissolved N₂ were also measured during summer low flow and compared to modeled N₂ concentrations (based on temperature and atmospheric gas exchange rates) to determine the measured “excess” N₂ that indicates denitrification. Mass balance results showed no in-stream nitrogen loss in either reach during April 2005, and no nitrogen loss in the southern 55 km study reach during August 2005. In the northern 66 km reach during August 2005, however, nitrogen output was 18% less than the total nitrogen inputs to the reach. N₂ sampling results gave an estimated rate of N₂ production that would remove 3.3% of the nitrogen load in the river over the 10.3 km northern sub-reach. The nitrogen losses measured in the northern reach in August 2005 may represent an approximate upper limit for nitrogen attenuation in the Connecticut River because denitrification processes are most active during warm summer temperatures and because the study was performed during the annual low-flow period when total nitrogen loads are small.     

Different mechanisms of inorganic carbon acquisition in red macroalgae (Rhodophyta) revealed by the use of TRIS buffer

The effects on photosynthesis of acetazolamide (AZ, an inhibitor of the external carbonic anhydrase) and TRIS buffer at pH 8.7 were assessed in 24 species of red macroalgae. Only Palmaria palmata was unaffected by both substances. The rest of species were classified into three groups according to their sensitivity to TRIS and AZ. Photosynthesis of fourteen species was significantly inhibited by both TRIS and AZ. Inhibition by TRIS varied from almost 100% to 25% while AZ produced similar effects. Inhibition by TRIS was completely reverted by increasing the dissolved inorganic carbon concentration (DIC). This species group had half-saturation constants for photosynthesis (K_m(DIC)) ranging from 0.5 to 1.1 mM of DIC. TRIS produced a significant increase of K_m(DIC). Altogether, these results indicate that the algae sensitive to TRIS are capable of using HCO₃⁻ efficiently at pH 8.7. Furthermore, the buffering capacity of TRIS was responsible for its inhibitory effect on photosynthesis suggesting that HCO₃⁻ use was facilitated by excretion of protons outside the plasma membrane, which creates regions of low pH resulting in a higher-than-ambient CO₂ concentration. In contrast, photosynthesis by two Porphyra species analysed was slightly stimulated by TRIS and completely inhibited by AZ, suggesting that the mechanism was different. In a third group of seaweeds, photosynthesis was insensitive to TRIS but it was significantly inhibited by AZ. These species had relatively high values of K_m(DIC) indicating that they relied on purely diffusive entry of CO₂ generated by external carbonic anhydrase activity. Consequently, the results demonstrate that external carbonic anhydrase is widespread among red macroalgae since only P. palmata was insensitive to AZ. The functional significance of this enzyme was quite variable among the tested species.     

Soil and water erosion under different plant species in a semiarid river valley, SW China: the effects of plant morphology

The small-scale effects of plant morphology in improving soil quality and reducing runoff and soil loss have remained unclear, especially in some arid environments with sparse vegetation. We selected three representative species with contrasting morphologies (Artemisia gmelinii; Ajania potaninii; Pulicaria chrysantha) to examine the effects of plant morphology on soil quality, runoff, and soil loss in the dry-warm river valley of the upper reach of Minjiang River, SW China. Runoff events were monitored from July through October 2006 using runoff plots on a micro scale (<40 × 40 cm²) on a south-facing slope. The observation duration for rainfall and runoff events can be divided into two stages. Higher runoff depth, but lower soil loss per event occurred at the second stage as compared with the first stage due to the differences in rainfall, plant, and soil surface characteristics. The two herbs, A. gmelinii and P. chrysantha, had greater improvements on soil quality yielding high soil nutrient content and low soil compactness, while the effectiveness of the small shrub, A. potaninii, was minimal. Relative to bare surface (control treatment), the effectiveness of reducing runoff depth per event was 64.9, 66.6 and 38.0%, and reducing soil loss 65.5, 59.3 and 69.9% for A. gmelinii, A. potaninii, and P. chrysantha, respectively. All three plant species can improve soil quality and reduce runoff and soil loss, but their effects vary, which implies that plant morphology has to be considered while selecting species for ecosystem restoration.     

Compensation of rodent pests after removal: control of two rat species in an irrigated farming system in the Red River Delta, Vietnam

Rodent pests have a strong capacity to recover rapidly from imposed reductions in abundance, but it is unclear how populations compensate to removal when farmers apply rodent control. The response of two rat species to rodent control was monitored using regular live-trapping in an irrigated lowland mixed rice agroecosystem. Rice field rats, Rattus argentiventer (52% of rodent captures), and lesser rice field rats, Rattus losea (29%), were removed using trap-barrier systems (TBS) at two sites while rice crops were present. The TBS was a plastic fence that enclosed a small field planted 3 weeks prior to the surrounding fields and set with multiple-capture cage-traps to capture rats that were attracted to the early-planted crop. Demographic responses of rats were compared to two untreated sites. There was a reduction in abundance of rodents on treated sites relative to untreated sites during the summer rice crop (by 45% and 28% for R. argentiventer and R. losea, respectively) an increase in abundance during the winter season (31% and 69%), and a mixed response during the spring rice crop (39% decrease and 41% increase). There was an increase in the proportion of juveniles captured on treated sites relative to untreated sites post-treatment (148% and 158%) and the body mass was lower on treated sites post-treatment (males: 13% and 41%; females: 22% and 22%). Older, larger animals were removed by the TBS and the rodent populations were compensating through high recruitment of young and high immigration into treated sites. No clear patterns were observed in the occurrence of adult breeding females for either R. argentiventer or R. losea. Rodent management, should therefore, occur over large areas (> 100 ha) to reduce the chance of reinvasion.     

Ecophysiological characteristics of Avicennia germinans and Laguncularia racemosa coexisting in a scrub mangrove forest at the Indian River Lagoon, Florida

The purpose of this work is to increase ecological understanding of Avicennia germinans L. and Laguncularia racemosa (L.) Gaertn. F. growing in hypersaline habitats with a seasonal climate. The area has a dry season (DS) with low temperature and vapour pressure deficit (vpd), and a wet season (WS) with high temperature and slightly higher vpd. Seasonal patterns in interstitial soil water salinity suggested a lack of tidal flushing in this area to remove salt along the soil profile. The soil solution sodium/potassium (Na⁺/K⁺) ratio differed slightly along the soil profile during the DS, but during the WS it was significantly higher at the soil surface. Diurnal changes in xylem osmolality between predawn (higher) and midday (lower) were observed in both species. However, A. germinans had higher xylem osmolality compared to L. racemosa. Xylem Na⁺/K⁺ suggested higher selectivity of K⁺ over Na⁺ in both species and seasons. The water relations parameters derived from pressure–volume P–V curves were relatively stable between seasons for each species. The range of water potentials (Ψ), measured in the field, was within estimated values for turgor maintenance from P–V curves. Thus the leaves of both species were osmotically adapted to maintain continued water uptake in this hypersaline mangrove environment.     

Evaluation of separation and determination of phytoavailable and phytotoxic aluminium species fractions in soil, sediment and water samples by five different methods

The suggested research deals with the separation of phytoavailable and phytotoxic aluminium species fractions in soil, sediment and water samples by five different procedures (single and sequential extractions, membrane filtration, chelating solid phase extraction and kinetic strength discrimination method). The concentrations of Al in studied samples and relevant plant materials were measured by flame atomic absorption spectrometry (FAAS), optical emission spectrometry with inductively coupled plasma (ICP OES) and UV/visible (VIS) spectrophotometry. The used separation procedures can be divided into three groups. The first group is consisting of weakly efficient single extraction procedures by H(2)O, dilute acetic acid, nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), salicylic acid, ammonium salicylate and 8-hydroxyquinoline, chelating solid phase extraction by resins Iontosorb Oxin and salicyl and kinetic strength discrimination method using 8-hydroxyquinoline which release from the samples only small amounts of phytoavailable and phytotoxic Al by ion-exchange or complexation processes. The more efficient extractions with KCl, NH(4)Cl, CaCl(2), BaCl(2), CuCl(2), LaCl(3), NH(4)F and (NH(4))(2)C(2)O(4) leach approximately the same amounts of phytoavailable Al as the total Al concentrations in plant material (grass Festuca rubra) growing on analysed soils and sediments. The third group of separation procedures contains the most aggressive leaching with Na(4)P(2)O(7), dilute HCl, NH(2)OH.HCl in HNO(3) and H(2)O(2)/ammonium acetate in HNO(3). These extractants release the highest amounts of Al from solid samples, approximately 2-4-fold as the total Al concentrations in relevant plant material and they are unsuitable for purpose of this study.     

Effects of sediment removal on nitrogen uptake by riparian plants in the higher floodplain of the Chikuma River, Japan

Riparian plants can use nitrogen (N) from soil and river water, but the use of river water N might be limited in higher floodplain environments of the Chikuma River. The purpose of this study is to reveal the relationship between N uptake by riparian plants and the floodplain topography (relative height and distance from a river channel). We examined the hypothesis that surface sediment removal from the higher floodplain increases river water N uptake by riparian plants by using a stable isotope analysis. The δ¹⁵N value of river water samples (ca. 8‰) were significantly higher than those of the soil extracts (ca. 3‰) in the study area. The δ¹⁵N value of riparian plants increased from +3.0‰ (standard deviation, SD ±2.1‰) before sediment removal to +9.6‰ (±2.1‰) after sediment removal, although there was no significant change in the δ¹⁵N value in N sources of soil and river water. The sediment removal enhanced frequency of flood disturbance, relative ground water level, and river water N uptake by riparian plants on the floodplain.     

In situ measurements of uptake of inorganic carbon and nitrogen by the aquatic liverworts Jungermannia vulcanicola Steph. and Scapania undulata (L.) Dum. in an acid stream,Kashiranashigawa, Japan

In situ uptake of inorganic carbon and nitrogen by the aquatic liverworts Jungermannia vulcanicola Steph. and Scapania undulata (L.) Dum. was measured in an acid stream, Kashiranashigawa, Japan. The uptake activities were similar in the both species. The activities were highest at the tip of shoots, and decreased gradually towards the base. Carbon uptake at the tip in the light was 10.4 × 10^–4 for J. vulcanicola and 8.1 × 10^–4 g C g dry wt^–1 h^–1 1 for S. undulata. Ammonium was effectively incorporated into the shoots, and the uptake activity at the tip was between 1.9 × 10^–5 and 5.8 × 10^–5 g N g dry wt^–1 h^–1. Nitrate uptake was smaller than ammonium uptake. The ratio of dark to light uptake in ammonium uptake experiments was larger than that in carbon uptake experiments. These results suggest that the liverworts use ammonium as a major nitrogen source, and that ammonium uptake was less dependent on light than carbon uptake.     

Availability of water and inorganic nutrients in the persistent leaf bases of the grasstree Kingia australis, and uptake and translocation of labelled phosphate by the embedded aerial roots

Numerous lateral branches of the concealed aerial roots of the grasstree Kingia australis ramify through the persistent leaf bases, suggesting a role in uptake of water and nutrients localed up to 8 m above ground. These leaf bases were shown to hold up to more than three times their weight in water. Water and nutrients (N, P and K) available in the leaf bases may greatly exceed that in an equal volume of surface soil, especially during the dry summer months. At this time, ³²P injected# among the leaf bases is strongly absorbed by the aerial roots and translocated to the meristematic regions of other laterals beneath the point of application, but mostly to the stern and leaves above it. Scattered vascular bundles in the pith are the major routes for the rapid distribution of P up and down the trunk following its departure from the aerial roots. Water and nutrients stored in the leaf bases and their subsequent uptake by the associated aerial roots may therefore contribute significantly to this species' tolerance of long summer droughts and extremely impoverished soils.     

Photosynthetic use of light and inorganic carbon in air and water by the intertidal alga Petalonia fascia (Scytosiphonales, Phaeophyta)

The photosynthetic performance of the intertidal alga Petalonia fascia (0. F. Muller) Kuntze (Scytosiphona-ceae, Phaeophyta) has been investigated, both in air and water, by analyzing the relationship between apparent photosynthesis rate and photon irradiance and inorganic carbon. In relation to the use of photon irradiance, it was found that the net photosynthetic capacity in water was 5.7 times that in air (fully hydrated thallus). The light compensation point was achieved at 5.9 and 3.0 μmol photons m^?2 s^?1 in air and water, respectively. The light onset-saturation parameter and the photosynthetic efficiency were 77% and 25% greater in water than in air, respectively. The dark respiration rate was one-third greater when emersed in comparison to submersion conditions. These data suggest that the photosynthetic response to irradiance in P. fascia is similar to that in infralittoral species rather than the intertidal species. This assessment can be explained by the winter seasonality of the bladed stage of growth, when storms and waves permit a permanent hydrated status of P. fascia that in the intertidal zone. Moreover, the minimum tissue water content that permitted active photosynthesis in the alga was around 20%. The net photosynthetic capacity as a function of inorganic carbon (C) concentration in water was 1.5 times that in air. Photosynthesis was saturated in both media with respect to the availability of inorganic C in natural conditions. The affinity to inorganic C, and the carbon conductance, were two orders of magnitude higher in air than in water. However, the higher photosynthetic capacity when submerged in comparison to emersion conditions suggests that P. fascia can assimilate the external HCO₃,– or the occurrence of a CO₂ concentrating mechanism in this species.     

The influence of wetlands, decaying organic matter, and stirring by wildlife on the dissolved oxygen concentration in eutrophicated water holes in the Seronera River, Serengeti National Park, Tanzania

The dissolved oxygen concentration (DO) was sampled during a diurnal cycle in three water holes heavily used by wildlife and with distinctive biological features along the Seronera River. The DO fluctuated widely (by up to 11.5 mg l⁻¹) as a function of time, mechanical stirring and aeration by animals, and the presence of fringing wetlands. The DO cycle was successfully modeled (within 0.3 mg l⁻¹) by assuming that the four dominant processes were photosynthesis and respiration by algae near the surface, trapping by wetlands, decomposition of dead organic matter on the bottom, and stirring/aeration by hippos. The rate of DO decline from the decay of dead organic matter was equal to the rate of DO removal by algal respiration at night.     

Regulation of growth, water use efficiency and δ13C by the nitrogen source in Casuarina equisetifolia Forst. & Forst.

Carbon isotope composition (δ¹³C) was measured in a glasshouse experiment with N₂-fixing and NO₃^–- or NH₄⁺-fed Casuarina equisetifolia Forst. & Forst plants, both under well-watered and drought conditions. The abundance of ¹³C was higher (more positive δ¹³C) for NH₄⁺- than for NO₃^– -grown plants and was lowest for N₂-fixing plants. NH₄⁺-fed plants had more leaf area and dry weight and higher water use efficiency (on a biomass basis) than N₂- and NO₃^–-grown plants and had lower water consumption than plants supplied with NO₃^–, either with high or low water supply. Specific leaf areas and leaf area ratios were higher with NH₄⁺ than with NO₃^– or N₂ as the N source. The difference observed in δ¹³C between plants grown with different N sources was higher than that predicted by theory and was not in the right direction (NH₄⁺-grown plants with a more negative δ¹³C) to be explained by differences in plant composition and engagement of the various carboxylation reactions. The more positive δ¹³C in NH₄⁺- than in NO₃^–-grown plants is probably due to a decreased ratio of stomatal to carboxylation conductances, which accounts for the lower water cost of C assimilation in NH₄⁺-grown plants.