Moderate Acidification Research Articles

Effects of Estuarine Acidification on an Oyster-Associated Community in New South Wales, Australia

Many of the features that make estuaries among the most productive natural systems on earth also make them prone to acidification. Understanding the effects of estuarine acidification on different components of an ecological community is an important step in identifying indicators of ecosystem degradation. This study examined the impact of estuarine acidification, as a result of acid sulfate soil runoff, on wild Sydney rock oysters Saccostrea glomerata and their associated epifaunal communities in estuaries experiencing acid sulfate soil runoff in New South Wales, Australia. The responses of oysters and their invertebrate epifaunal communities to chronic acidification (greater than 6 mo; represented by oyster source site conditions) were assessed by examining the differences in oyster communities associated with moderate acidification (3.5 km from the source of acidification) or low acidification (8.2 km from the source). Oysters from moderate- or low-acidification sites were transplanted to a site with high exposure to acidification (less than 3 km from the source) or back to their original source sites (control) to mimic episodic acidification (2 wk). Epifaunal mussels Xenostrobus securis and limpets Patelloida mimula showed a negative association with oyster mortality, suggesting that these communities are closely tied to oyster survival. Oyster-associated epifaunal communities exposed to both chronic and episodic acidification were significantly different from communities with low exposure. Epifaunal communities exposed to episodic acidification were significantly less diverse than the control. Spionid and syllid worms were significantly less abundant and the mussel X. securis was significantly more abundant on oysters with moderate exposure or chronic exposure to acidification, as compared with communities from areas with low exposure to acidification. The mussel X. securis and the snail Bembicium auratum were significantly less abundant in oyster communities that were exposed to episodic acidification, as compared with the control. In systems where community composition depends on a single habitat-forming species, maintaining resistance may rely on the ability of that species to persist in the face of environmental stress.

Monitoring key organic indoor pollutants and their elimination in a biotrickling biofilter.

A biotrickling filter was evaluated to treat the air of the interior of a bioprocess research laboratory. Initially, various solid-phase microextraction (SPME) fibers were used to identify and quantify the volatile organic pollutants and hexane, methyl isobutyl ketone, benzene, toluene, and xylene were further selected as indicators due to their prevalence and relative abundance. The system treated organic loading rates between 0.16mgcarbonm-3h-1 and close to 30mgcarbonm-3h-1 achieving removal efficiencies (RE) over 85% during 136 operational days. Respirometry experiments demonstrated that moderate acidification (below 5.0), due to microbial activity, adversely affected biofilter performance and consequently pH control was necessary to maintain performance.

Evaluation for effects of severe acidosis on hemostasis in trauma patients using thrombelastography analyzer

ObjectiveTo investigate effects of metabolic acidosis on hemostasis function in trauma patients using thromboelastography analyzer. Methods65 critically injured patients and 19 healthy volunteers were enrolled in the study. Three samples of whole blood were collected from each patient or healthy volunteer. These three samples were acidified with 50mmol/l phosphate-buffered saline (PBS) (pH5.8) or a neutral buffer (50mmol/l phosphate, pH7.4) and acidified blood sample with target pH of 6.95, 7.15 or 7.35 was obtained respectively. These three samples with target pH value were added into thrombelastography analyzer (TEG® 5000 Thrombelastograph Hemostasis Analyzers; Haemoscope Corporation, Niles, Illinois, USA) respectively and variables of Clot time (r), Rate of clot formation (α Angle), Clot formation time (K), Coagulation Index (CI) and Maximum strength (MA) were monitored at 37°C. Besides, association between TEG® parameters and clinicopathological features was analyzed by the Pearson χ2 test. ResultsIn trauma patients, all 5 thrombelastographic variables, Clot time (r), Clot formation time (K), Maximum Amplitude (MA), Rate of clot formation (α Angle) and Coagulation Index (CI), were significantly affected by blood acidification, F(1.321,83.213)=88.960, P<0.001, F(2,128)=112.738, P<0.001, F(1.199,76.748)=37.964, P<0.001, F(1.195,76.452)=16.789, P<0.001 and F(2,128)=178.674, P<0.001. Post hoc tests showed that moderate acidosis (pH7.15) significantly elongated K time (from 2.6 to 3.4min, P=0.0013) and increased α Angle (from 51.9°to 52.2°, P=0.0040). r, MA and CI were not markedly influenced under moderate acidification. Comparing to mild acidosis (pH7.15), severe acidosis (pH6.95) induced more serious impairment to hemostasis and all 5 variables was substantially affected, r (from 5.9 to 6.8min, P<0.001), K (from 3.4 to 3.9min, P<0.001), α Angle (from 52.2°to 50.8°, P=0.002), MA (from 52.9 to 51.6mm, P<0.001) and CI (from −2.3 to −4.2, P<0.001). Additionally, higher r elongation under severe acidosis was significantly associated with an increased mortality rate and transfusion requirement (P=0.019 and 0.031). In healthy volunteers, similar effects on hemostasis were detected. Inhibition ratios of thrombelastographic parameters were significantly higher in trauma patients than in healthy volunteers indicating severer impairment of metabolic acidosis to hemostasis in critically injured patients. ConclusionsThe degree of metabolic acidosis in trauma patients is positively correlated to the severity of hemostasis dysfunction. Additionally, acidosis induces more serious impairment to hemostasis in trauma patients than in healthy volunteers. Moreover, acidosis-induced r time elongation is positively related to a higher death rate and increased transfusion requirement and this indicates a predictive role of TEG® variables for prognosis of traumatized patients.

Mussel larvae modify calcifying fluid carbonate chemistry to promote calcification

Understanding mollusk calcification sensitivity to ocean acidification (OA) requires a better knowledge of calcification mechanisms. Especially in rapidly calcifying larval stages, mechanisms of shell formation are largely unexplored—yet these are the most vulnerable life stages. Here we find rapid generation of crystalline shell material in mussel larvae. We find no evidence for intracellular CaCO3 formation, indicating that mineral formation could be constrained to the calcifying space beneath the shell. Using microelectrodes we show that larvae can increase pH and [CO32−] beneath the growing shell, leading to a ~1.5-fold elevation in calcium carbonate saturation state (Ωarag). Larvae exposed to OA exhibit a drop in pH, [CO32−] and Ωarag at the site of calcification, which correlates with decreased shell growth, and, eventually, shell dissolution. Our findings help explain why bivalve larvae can form shells under moderate acidification scenarios and provide a direct link between ocean carbonate chemistry and larval calcification rate.

Extreme ocean acidification reduces the susceptibility of eastern oyster shells to a polydorid parasite

Ocean acidification poses a threat to marine organisms. While the physiological and behavioural effects of ocean acidification have received much attention, the effects of acidification on the susceptibility of farmed shellfish to parasitic infections are poorly understood. Here we describe the effects of moderate (pH 7.5) and extreme (pH 7.0) ocean acidification on the susceptibility of Crassostrea virginica shells to infection by a parasitic polydorid, Polydora websteri. Under laboratory conditions, shells were exposed to three pH treatments (7.0, 7.5 and 8.0) for 3- and 5-week periods. Treated shells were subsequently transferred to an oyster aquaculture site (which had recently reported an outbreak of P.websteri) for 50days to test for effects of pH and exposure time on P.websteri recruitment to oyster shells. Results indicated that pH and exposure time did not affect the length, width or weight of the shells. Interestingly, P.websteri counts were significantly lower under extreme (pH 7.0; ~50% reduction), but not moderate (pH 7.5; ~20% reduction) acidification levels; exposure time had no effect. This study suggests that extreme levels - but not current and projected near-future levels - of acidification (∆pH ~1 unit) can reduce the susceptibility of eastern oyster shells to P.websteri infections.

Tropical coral reef coral patterns in Indonesian shallow water areas close to underwater volcanic vents at Minahasa Seashore, and Mahengetang and Gunung Api Islands

AbstractCoral community patterns on some Indonesian reefs influenced by CO2 from underwater volcanic vents and nutrients from eutrophication pressures were examined. The overall aim of the study was to provide an insight into the significance of future ocean acidification compared to eutrophication pressures on tropical coral communities. Coral cover and seawater characteristics at acidified sites (with varied levels of eutrophication), i.e., moderate acidification (pH: 7.87 ± 0.04), low acidification (pH: 8.01 ± 0.04) and reference (pH: 8.2 ± 0.02), were observed at reefs associated with Minahasa Seashore, and Mahengetang and Gunung Api Islands. Results showed that coral community patterns varied among locations and acidified sites, e.g., domination of families such as Alcyoniidae, Acroporidae, Poritidae and Heliporidae, and with different levels of abiotic cover. Surprisingly, pH was not detected as the major determining factor. This finding probably relates to tropical seawater temperatures being high enough to still allow for aragonite deposition even at pH values down to 7.8. Nutrients (phosphate and dissolved inorganic nitrogen) were shown to be the main determining factors that influenced community patterns on the observed coral reefs. Overall, the results indicate that tropical coral reef community patterns will continue to vary as pH decreases to the predicted oceanic value of pH 7.8 over the next 100 years, and bio‐geo‐ecological characteristics and anthropogenic pressures will be the major factors determining Indonesian tropical coral community structure, compared to pH.

&lt;b&gt;Reassessment of the suitable range of water pH for culture of Nile tilapia &lt;i&gt;Oreochromis niloticus&lt;/i&gt; L. in eutrophic water

The present work aimed at reassessing the suitable range of water pH for culture of Nile tilapia, Oreochromis niloticus L. juveniles in eutrophic water. Two hundred and forty tilapia juveniles (1.37 ± 0.04 g) were stocked in twenty 250-L polyethylene tanks (12 fish per tank) for eight weeks. In the control tanks, the pH of water was not adjusted at any time, varying freely over the entire study. In the slight acidification treatment, the culture water was acidified daily to reach a water pH between 5.5 and 6.5. In the moderate acidification treatment, there were daily applications of HCl solution to reach a water pH between 4.5 and 5.5. In the alkalinization treatment, tanks received daily applications of Na2CO3 and NaOH to achieve a water pH between 8.5 and 9.5. Acidification of water, regardless the degree, i.e., slight or moderate, was not able to significantly affect final body weight, specific growth rate and yield of fish. It can be concluded that the acidification of water up to pH 5.5 has no negative influence on growth of Nile tilapia fingerlings in eutrophic tanks. Accordingly, the suitable range of water pH for rearing Nile tilapia should be set at 5.5 – 9.0.

PH-sensitive MRI demarcates graded tissue acidification during acute stroke ― pH specificity enhancement with magnetization transfer and relaxation-normalized amide proton transfer (APT) MRI

pH-sensitive amide proton transfer (APT) MRI provides a surrogate metabolic biomarker that complements the widely-used perfusion and diffusion imaging. However, the endogenous APT MRI is often calculated using the asymmetry analysis (MTRasym), which is susceptible to an inhomogeneous shift due to concomitant semisolid magnetization transfer (MT) and nuclear overhauser (NOE) effects. Although the intact brain tissue has little pH variation, white and gray matter appears distinct in the MTRasym image. Herein we showed that the heterogeneous MTRasym shift not related to pH highly correlates with MT ratio (MTR) and longitudinal relaxation rate (R1w), which can be reasonably corrected using the multiple regression analysis. Because there are relatively small MT and R1w changes during acute stroke, we postulate that magnetization transfer and relaxation-normalized APT (MRAPT) analysis increases MRI specificity to acidosis over the routine MTRasym image, hence facilitates ischemic lesion segmentation. We found significant differences in perfusion, pH and diffusion lesion volumes (P<0.001, ANOVA). Furthermore, MRAPT MRI depicted graded ischemic acidosis, with the most severe acidosis in the diffusion lesion (−1.05±0.29%/s), moderate acidification within the pH/diffusion mismatch (i.e., metabolic penumbra, −0.67±0.27%/s) and little pH change in the perfusion/pH mismatch (i.e., benign oligemia, −0.04±0.14%/s), providing refined stratification of ischemic tissue injury.

Changes in soft coral &lt;em&gt;Sarcophyton&lt;/em&gt; sp. abundance and cytotoxicity at volcanic CO&lt;sub&gt;2&lt;/sub&gt; seeps in Indonesia

This study presents the relationship between benthic cover of Sarcophyton sp. living on coral reefs and their cytotoxicity (an assumption of soft coral allelochemical levels) along acidification gradients caused by shallow water volcanic vent systems. Stations with moderate acidification (pH 7.87 ± 0.04), low acidification (pH 8.01 ± 0.04), and reference conditions (pH 8.2 ± 0.02) were selected near an Indonesian CO 2 seep (Minahasa, Gunung Api Island, and Mahengetang Island). Cover of the dominant soft coral species ( Sarcophyton sp.) was assessed and tissue samples were collected at each site. The cytotoxicity tissue extracts were analyzed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolinon bromide (MTT) method. Levels of cytotoxicity were strongly correlated with Sarcophyton sp. cover ( p 2 = 0.60 at 30 ppm and 0.56 at 100 ppm), being highest at mean pH 8.01 where the soft corals were most abundant. This finding suggests that Sarcophyton sp. can be expected to survive ocean acidification near Indonesia in the coming decades. How the species might be adversely affected by further ocean acidification later in the century unless CO 2 emissions are reduced remains a concern.

The release of phosphorus in alkaline vertic soils as influenced by pH and by anion and cation sinks

Alkaline Vertisols contain calcium phosphate (CaP) minerals that dissolve in response to both acidification and the depletion of concentration of phosphorus (P) or calcium (Ca) in the soil solution, conditions commonly observed within the rhizosphere. In these soils, reserve-P is defined as the difference between the concentrations of P extracted by 0.5M sodium bicarbonate and 0.005M sulfuric acid. To mimic rhizosphere modification we sequentially extracted P from three alkaline Vertisols that contained concentrations of reserve-P ranging from 300 to 6500mgkg−1 using an anion sink, and a combined anion and cation sink. The extractions commenced on untreated soil, and then three target pH regimes were imposed: 1) maintain the initial pH; 2) incrementally acidify to pH6.5 then maintain; and 3) incrementally acidify to pH5.5 then maintain. Extractable P increased with decreasing solution pH in all soils until the acid soluble P was depleted. In each soil and at each pH level, more P was extracted when the combined sink was used compared with the anion sink alone. The release of acid soluble-P in these soils was indicative of CaP minerals of varying thermodynamic stability. In addition to the relatively constant concentrations of P extracted at the initial pH with the anion sink, moderate acidification to pH6.5 released 9% of the reserve-P in the high P soil, but this varied from 18 to 33% in the two other soils containing lower soil P. These findings show that the release of P in alkaline soils beyond that measured by a bicarbonate extractant is influenced by the modification of soil pH and by the removal of Ca from the solution, which has implications for plant availability and response to added fertiliser. Further research is needed to identify the individual species of soil P that are involved in buffering the soil solution, and what their potential availability is to plants via rhizosphere modification.

Extracellular acidification leads to mitochondrial depolarization with following free radical formation in rat brain synaptosomes

Brain ischemia is accompanied by lowering of pHo and pHi. We investigated an influence of of acidosis on free radical formation in synaptosomes. Three models were used. 1) Strong extracellular acidification down to pHo 6.0. 2) Moderate extracellular acidification down to pHo 7.0 3) Intracellular acidification induced by addition of 1 mM amiloride corresponding to pHi decrease down to 6.65. We have shown that both types of extracellular acidification, but not intracellular acidification, increase DCFDA fluorescence by calcium-independent way that reflects free radical formation. These three treatments induce the rise of the dihydroethidium fluorescence that reports synthesis of superoxide anion. However, the impact of low pHi on superoxide anion synthesis was less than induced by moderate extracellular acidification. Mitochondrial uncoupler CCCP did not inhibit an increase of fluorescence of both dyes at pHo 6.0. In contrast, superoxide anion synthesis at pHo 7.0 was almost completely eliminated by CCCP. Furthermore, using fluorescent dyes JC-1 and rhodamine-123, we confirmed that decrease of pHo leads to mitochondria depolarization. Low pHi was not effective. Iron chelator deferoxamine and antioxidant ionol are inhibits pH-induced increase of DCFDA fluorescence, but does not influenced mitochondria depolarization. We are failed to found sodium influx monitored by fluorescent dye Sodium Green in case of low pHo. Involving of plasma membrane receptor which is distinct from acid-sensitive ion channels (ASIC) and electron transport chain of mitochondria for moderate acidification can be suggested. Action of strong acidification seems to be mediated by release of iron from proteins. We have shown that low pHo led to oxidative stress in neuronal presynaptic endings that might underlie the long term irreversible changing in synaptic transmission.

Effects of extruded whole maize, polydextrose and cellulose as sources of fibre on calcium bioavailability and metabolic parameters of growing Wistar rats

The aim of this study was to evaluate the influence of diets with different types of fibres on Ca bioavailability and metabolic parameters in growing Wistar rats. Twenty four male Wistar rats were fed with 3 different diets: control (C), polydextrose (PD), and extruded whole maize (M) during a 60 day period. Apparent Ca absorption percentage (%Ca Abs), total skeleton bone mineral content (t BMC), total bone mineral density (t BMD), femur (F), spine (S) and tibia (T) BMD, cecum weight, and pH were evaluated. Malondialdehyde (MDA) and lipid (TG and cholesterol) contents in serum and liver were also evaluated. The results showed that rats fed with M and PD had the same cecum weight, but higher than that of C (1.53 ± 0.02 vs. 0.94 ± 0.01). There was moderate acidification of the cecal content in rats fed with M compared to C (pH 5.93 vs. 6.98) and the fecal weight was 1.06 ± 0.02, 3.07 ± 0.03 and 4.81 ± 0.05 for PD, M and C, respectively. There were significant differences in %Ca Abs between PD and C (87.57 ± 1.20 vs. 71.10 ± 1.11). The PD group had the highest values of F-BMD, S-BMD, and T-BMD, but there were no differences between M and C groups. Regarding lipids, there was a significant lowering effect in the M liver triglycerides content. Moreover, liver MDA levels significantly decreased with M and PD diets. The consumption of PD and grain fibres can exert some beneficial gastrointestinal effects such as lowering of the pH, hepatic TG and MDA content related to fibre colon fermentation.

A Discussion of the Compound Sand Control Technique of High Pressure Packing and Moderate Acidification

Acidification can both eliminate formation damage and improve flow passage, which can be good for improving single well productivity. Based on this, the authors bring up the thought of moderate acidification technique for sandstone reservoir, and combine it with high pressure packing technique, and one step further, presents a compound sand control technique of high pressure packing and moderate acidification. At the same time, the authors preliminarily discuss the main points of this technique and analyze its mechanism of sand control and yield increase as well as its adaptability. The main purpose of this technique is to clean out the clay and mud in the immediate vicinity of wellbore, decrease the fine content or the particle size in that area, enlarge the seepage channel, and fill in optimized gravel, so as to make it conducive for transpiring the fine sand in the formation and keeping the gravel layer unblocked, as a result making the sand control life prolonged and single-well productivity raised. The keys of this compound technique are moderate acidification and gravel size optimization.

Reduced marine survival of hatchery-reared Atlantic salmon post-smolts exposed to aluminium and moderate acidification in freshwater

Short-term Al-exposure and moderate acidification increased initial marine mortality in migrating post-smolts, and can thereby reduce viability of Atlantic salmon stocks. The delayed impact of short-term aluminium (Al) exposure on hatchery-reared Atlantic salmon smolt in moderately acidified freshwater (pH 5.88–5.98) was investigated during the first 37 km of the marine migration. Smolts were tagged with acoustic tags and exposed to low (28.3 ± 4.6 μg l−1 labile Al, 90 h) or high (48.5 ± 6.4 μg l−1 labile Al, 90 or 48 h) Al concentrations within the hatchery. Thereafter their movements, together with a control group, were monitored throughout the marine fjord. Al-exposure resulted in increased gill-Al and compromised hypoosmoregulatory capacity, as shown by elevated mortality in laboratory seawater challenge tests and reduced Na+, K+-ATPase activity levels. Further, Al-exposure resulted in decreased plasma concentrations of growth hormone (GH), while the insulin-like growth factor (IGF-I) was unaffected. There was a significant mortality in the 90 h high-Al group during exposure, and those surviving until release died during the first 3.6 km of the marine migration. Physiological stress and mortality were not only a result of the Al-concentrations, but also dependent on exposure duration, as shown by results from the 48 h high-Al group. Elevated mortality was not recorded in freshwater or after entering the sea for this group, which highly contrasts to the 100% mortality in the 90 h high-Al group, despite both groups having similarly high gill-Al levels. The low-Al group showed a 20% higher mortality compared to the control group during the first 10 km of the marine migration, but during the next 28 km, mortality rates did not differ. Hence, post-smolts surviving the first 10 km subsequently showed no differences in mortality compared to controls. At least one third of the mortality in both the low-Al and control groups were due to predation by marine fishes, indicating that the proximate cause for elevated mortality due to Al-exposure may have been predation. Migration speeds over 3.6, 9.6 or 37.1 km from the release site was not affected by Al-exposure.

Influence of Intra- and Extracellular Acidification on Free Radical Formation and Mitochondria Membrane Potential in Rat Brain Synaptosomes

Brain ischemia is accompanied by lowering of intra- and extracellular pH. Stroke often leads to irreversible damage of synaptic transmission by unknown mechanism. We investigated an influence of lowering of pH(i) and pH(o) on free radical formation in synaptosomes. Three models of acidosis were used: (1) pH(o) 6.0 corresponding to pH(i) decrease down to 6.04; (2) pH(o) 7.0 corresponding to the lowering of pH(i) down to 6.92: (3) 1mM amiloride corresponding to pH(i) decrease down to 6.65. We have shown that both types of extracellular acidification, but not intracellular acidification, increase 2',7'-dichlorodihydrofluorescein diacetate fluorescence that reflects free radical formation. These three treatments induce the rise of the dihydroethidium fluorescence that reports synthesis of superoxide anion. However, the impact of amiloride on superoxide anion synthesis was less than that induced by moderate extracellular acidification. Superoxide anion synthesis at pH(o) 7.0 was almost completely eliminated by mitochondrial uncoupler carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone. Furthermore, using fluorescent dyes JC-1 and rhodamine-123, we confirmed that pH(o) lowering, but not intracellular acidification, led to depolarization of intrasynaptosomal mitochondria. We have shown that pH(o) but not pH(i) lowering led to oxidative stress in neuronal presynaptic endings that might underlie the long-term irreversible changing in synaptic transmission.

Effects of feeding on luminal pH and morphology of the gastroesophageal junction of snakes

At the gastroesophageal junction, most vertebrates possess a functional lower esophageal sphincter (LES) which may serve to regulate the passage of liquids and food into the stomach and prevent the reflux of gastric contents into the esophagus. Snakes seemingly lack an LES and consume meals large enough to extend anteriorly from the stomach into the esophagus thereby providing the opportunity for the reflux of gastric juices. To explore whether snakes experience or can prevent gastric reflux, we examined post-feeding changes of luminal pH of the distal esophagus and stomach, the fine scale luminal pH profile at the gastroesophageal junction, and the morphology of the gastroesophageal junction for the Burmese python (Python molurus), the African brown house snake (Lamprophis fuliginosus), and the diamondback water snake (Nerodia rhombifer). For each species fasted, there was no distension of the gastroesophageal junction and only modest changes in luminal pH from the distal esophagus into the stomach. Feeding resulted in marked distension and changes in tissue morphology of the gastroesophageal junction. Simultaneously, there was a significant decrease in luminal pH of the distal esophagus for pythons and house snakes, and for all three species a steep gradient in luminal pH decreasing across a 3-cm span from the distal edge of the esophagus into the proximal edge of the stomach. The moderate acidification of the distalmost portion of the esophagus for pythons and house snakes suggests that there is some anterior movement of gastric juices across the gastroesophageal junction. Given that this modest reflux of gastric fluid is localized to the most distal region of the esophagus, snakes are apparently able to prevent and protect against acid reflux in the absence of a functional LES.

Cadmium and Zn availability as affected by pH manipulation and its assessment by soil extraction, DGT and indicator plants

Manipulation of soil pH by soil additives and / or rhizosphere processes may enhance the efficiency of metal phytoextraction. Here we report on the effect of nitric acid additions to four polluted soils on Cd and Zn concentrations in soil solution (Csoln) and 0.005M Ca(NO3)2 extracts, and related changes in the diffusive fluxes and resupply of the metals as assessed by diffusive gradients in thin films (DGT). The responses of these chemical indicators of bioavailability were compared to metal uptake in two indicator plant species, common dandelion (Taraxacum officinale F.H. Wigg) and narrow leaf plantain (Plantago lanceolata L.) grown for 75days in a pot experiment.Lowering soil pH increased Csoln, the 0.005M Ca(NO3)2-soluble fractions and the DGT-measured Cd and Zn concentrations (CDGT) in the experimental soils. This was associated with enhanced uptake of Cd and Zn on soils acidified to pH 4.5 whereas plants did not survive at pH 3.5. Toxicity along with decreased kinetics of metal resupply (calculated by the 2D DIFS model) in the strong acidification treatment suggests that moderate acidification is more appropriate to enhance the phytoextraction process.Each of the chemical indicators of bioavailability predicted well (R2>0.70) the Cd and Zn concentrations in plantain shoots but due to metal toxicity not for dandelion. Concentration factors, i.e. the ratio between metal concentrations in shoots and in soil solution (CF) indicate that Cd and Zn uptake in plantain was not limited by diffusion which may explain that DGT did not perform better than Csoln. However, DGT is expected to predict plant uptake better in diffusion-limited conditions such as in the rhizosphere of metal-accumulating phytoextraction crops.

Moderate acidification affects growth but not survival of 6-month-old oysters

Oyster populations periodically exposed to runoff from acid sulfate soils (ASS) are of depressed abundance and have fewer smaller individuals than unaffected populations, despite having similar recruitment levels to unaffected sites during dry periods. We examined how the timing and duration of exposure to ASS runoff influences the growth and survival of successfully settled oysters. We predicted that among 6-month-old oysters, growth and survival would be (1) lower among individuals continuously exposed to ASS-acidified waters than those that are episodically exposed, and (2) most negatively affected during rainfall events, which enhance transport of ASS runoff to estuaries. Six-month-old Sydney rock oysters, Saccostrea glomerata, were deployed at ASS-affected and unaffected sites within each of two south-east Australian estuaries. After 10 weeks, oysters were transplanted within and across sites in an estuary and maintained in situ for another 10 weeks. Oysters that remained for 20 weeks at ASS-affected sites grew at just over half the rate of oysters at reference sites. Oysters transplanted from acidified to reference sites grew more than oysters transplanted from reference to acidified sites or oysters that remained at reference sites. Unexpectedly, overall oyster mortality was low. Greater rainfall, and hence a lower pH, is likely to have accounted for the greater impact of acidification on growth during the second 10 weeks. Where oysters recruit to a 6-month age cohort, they may be able to tolerate subsequent, moderate, acidification events. Reduced growth during acidification periods may be offset by positive growth during intervening dry periods.

Effects of fishing and acidification‐related benthic mortality on the southeast Australian marine ecosystem

AbstractOceanic uptake of anthropogenic carbon dioxide (CO2) is altering the carbonate chemistry of seawater, with potentially negative consequences for many calcifying marine organisms. At the same time, increasing fisheries exploitation is impacting on marine ecosystems. Here, using increased benthic‐invertebrate mortality as a proxy for effects of ocean acidification, the potential impact of the two stressors of fishing and acidification on the southeast Australian marine ecosystem to year 2050 was explored. The individual and interaction effects of the two stressors on biomass and diversity were examined for the entire ecosystem and for regional assemblages. For 61 functional groups or species, the cumulative effects of moderate ocean acidification and fishing were additive (30%), synergistic (33%), and antagonistic (37%). Strong ocean acidification resulted in additive (22%), synergistic (40%), and antagonistic (38%) effects. The greatest impact was on the demersal food web, with fishing impacting predation and acidification affecting benthic production. Areas that have been subject to intensive fishing were the most susceptible to acidification effect, although fishing also mitigated some of the decline in biodiversity observed with moderate acidification. The model suggested that ocean acidification and long‐term fisheries exploitation could act synergistically with the increasing sensitivity to change from long‐term (decades) fisheries exploitation potentially causing unexpected restructuring of the pelagic and demersal food webs. Major regime shifts occur around year 2040. Greater focus is needed on how differential fisheries exploitation of marine resources may exacerbate or accelerate effects of environmental changes such as ocean acidification.

Modulatory effects of neuropsychopharmaca on intracellular pH of hippocampal neurones in vitro

The intracellular pH (pHi) of neurones is tightly regulated by, for example, membrane-bound acid-exchangers and loaders. Nevertheless, excessive bioelectric activity lowers steady-state pHi. In turn, even a moderate acidification can inhibit neuronal activity, a process believed to be part of a negative feedback loop controlling neuronal excitation. As moclobemide, an antidepressant, and also some antiepileptic drugs can reduce neuronal pHi in hippocampus slices in vitro, we screened a panel of currently used neuropsychopharmaca for comparable effects. BCECF-AM loaded hippocampal slices were superfused with 16 different neuroleptics, antidepressants and antiepileptics under bicarbonate-buffered conditions. Changes in steady-state pHi of CA3 neurones were measured fluorometrically. The antipsychotics haloperidol, clozapine, ziprasidone, and the antidepressants amitriptyline, doxepin, trimipramine, citalopram, mirtazapine, as well as the anticonvulsive drug tiagabine reversibly reduced the steady-state pHi by up to 0.35 pH-units in concentrations of 5-50 microM. In contrast, venlafaxine, the anticonvulsants carbamazepine, clonazepam, gabapentin, lamotrigine, zonisamide, and the mood stabilizer lithium had no effect on neuronal pHi. These data substantiate the view that clinically relevant concentrations of neuroleptics and antidepressants can mediate changes in neuronal pHi, which may contribute to their pharmacological mode of action. Effects on pHi should be taken into account when therapeutic or even harmful effects of these drugs are evaluated.