Hysteresis Between Coral Reef Calcification and the Seawater Aragonite Saturation State

Some predictions of how ocean acidification (OA) will affect coral reefs assume a linear functional relationship between the ambient seawater aragonite saturation state (Ωa) and net ecosystem calcification (NEC). We quantified NEC in a healthy coral reef lagoon in the Great Barrier Reef during different times of the day. Our observations revealed a diel hysteresis pattern in the NEC versus Ωa relationship, with peak NEC rates occurring before the Ωa peak and relatively steady nighttime NEC in spite of variable Ωa. Net ecosystem production had stronger correlations with NEC than light, temperature, nutrients, pH, and Ωa. The observed hysteresis may represent an overlooked challenge for predicting the effects of OA on coral reefs. If widespread, the hysteresis could prevent the use of a linear extrapolation to determine critical Ωa threshold levels required to shift coral reefs from a net calcifying to a net dissolving state

Carbon Cycling Hysteresis in Permeable Carbonate Sands over a Diel Cycle: Implications for Ocean Acidification

Dissolved inorganic carbon, dissolved oxygen, H+, and alkalinity fluxes from permeable carbonate sediments at Heron Island (Great Barrier Reef) were measured over one diel cycle using benthic chambers designed to induce advective pore‐water exchange. A complex hysteretic pattern between carbonate precipitation and dissolution in sands and the aragonite saturation state (ΩAr) of the overlying chamber water was observed throughout the incubations. During the day, precipitation followed a hysteretic pattern based on the incidence of photosynthetically active radiation with lower precipitation rates in the morning than in the afternoon. The observed diel hysteresis seems to reflect a complex interaction between photosynthesis and respiration rather than ΩAr of the overlying water as the main driver of carbonate precipitation and dissolution within these permeable sediments. Changes in flux rates over a diel cycle demonstrate the importance of taking into account the short‐term variability of benthic metabolism when calculating net daily flux rates. Based on one diel cycle, the sediments were a net daily source of alkalinity to the water column (5.13 to 8.84 mmol m−2 d−1, depending on advection rates), and advection had a net stimulatory effect on carbonate dissolution. The enhanced alkalinity release associated with benthic metabolism and pore‐water advection may partially buffer shallow coral reef ecosystems against ocean acidification on a local scale

Nitrous Oxide and Methane Dynamics in a Coral Reef Lagoon Driven by Pore Water Exchange: Insights from Automated High‐Frequency Observations

Automated cavity ring down spectroscopy was used to make continuous measurements of dissolved methane, nitrous oxide, and carbon dioxide in a coral reef lagoon for 2 weeks (Heron Island, Great Barrier Reef). Radon (222Rn) was used to trace the influence of tidally driven pore water exchange on greenhouse gas dynamics. Clear tidal variation was observed for CH4, which correlated to 222Rn in lagoon waters. N2O correlated to 222Rn during the day only, which appears to be a response to coupled nitrification‐denitrification in oxic sediments, fueled by nitrate derived from bird guano. The lagoon was a net source of CH4 and N2O to the atmosphere and a sink for atmospheric CO2. The estimated pore water‐derived CH4 and N2O fluxes were 3.2‐fold and 24.0‐fold greater than the fluxes to the atmosphere. Overall, pore water and/or groundwater exchange were the only important sources of CH4 and major controls of N2O in the coral reef lagoon

Taking the Metabolic Pulse of the World\u27s Coral Reefs

Worldwide, coral reef ecosystems are experiencing increasing pressure from a variety of anthropogenic perturbations including ocean warming and acidification, increased sedimentation, eutrophication, and overfishing, which could shift reefs to a condition of net calcium carbonate (CaCO3) dissolution and erosion. Herein, we determine the net calcification potential and the relative balance of net organic carbon metabolism (net community production; NCP) and net inorganic carbon metabolism (net community calcification; NCC) within 23 coral reef locations across the globe. In light of these results, we consider the suitability of using these two metrics developed from total alkalinity (TA) and dissolved inorganic carbon (DIC) measurements collected on different spatiotemporal scales to monitor coral reef biogeochemistry under anthropogenic change. All reefs in this study were net calcifying for the majority of observations as inferred from alkalinity depletion relative to offshore, although occasional observations of net dissolution occurred at most locations. However, reefs with lower net calcification potential (i.e., lower TA depletion) could shift towards net dissolution sooner than reefs with a higher potential. The percent influence of organic carbon fluxes on total changes in dissolved inorganic carbon (DIC) (i.e., NCP compared to the sum of NCP and NCC) ranged from 32% to 88% and reflected inherent biogeochemical differences between reefs. Reefs with the largest relative percentage of NCP experienced the largest variability in seawater pH for a given change in DIC, which is directly related to the reefs ability to elevate or suppress local pH relative to the open ocean. This work highlights the value of measuring coral reef carbonate chemistry when evaluating their susceptibility to ongoing global environmental change and offers a baseline from which to guide future conservation efforts aimed at preserving these valuable ecosystems

Seroprevalence and risk factors of herpes simplex virus type-2 infection among pregnant women in Northeast India

<p>Abstract</p> <p>Background</p> <p>Herpes simplex virus type-2 (HSV-2) is one of the most common sexually transmitted infections that facilitate human immunodeficiency virus (HIV) acquisition by over two fold or more. The development of HSV-2 control methods as a measure to control HIV epidemic in high HSV-2/HIV areas has become a priority. Two out of the six high HIV prevalent states of India are located in the Northeastern region of India. Due to lack of documented HSV-2 studies from this part of the country; there was a need for estimating the seroprevalence and risk factors of HSV-2 infection in this defined population.</p> <p>Methods</p> <p>Pregnant women (n = 1640) aged18 years and above attending antenatal clinics of tertiary referral hospitals in five Northeastern states of India were screened for type specific HSV-2 IgG antibodies. Blood samples were collected from all the participants after conducting interviews. Univariate and multivariate analyses were performed to identify the risk factors associated with HSV-2 seropositivity.</p> <p>Results</p> <p>Overall seroprevalence of HSV-2 infection was 8.7% (142/1640; 95% CI 7.3-10.0) with a highest prevalence of 15.0% (46/307; 95% CI 11.0-19.0) in the state of Arunachal Pradesh. Higher seroprevalence was observed with increasing age (Adj. Odds Ratio [AOR] 1.9 for 22-25 years old, AOR 2.29 for > 29 years old). The risk factors associated with HSV-2 seropositives were multiple sex partners (AOR 2.5, <it>p </it>= 0.04), condom non-user's (AOR 4.7, p <it><</it>0.001), early coitarchal age (age of first intercourse) 'less than 18 years' (AOR 9.6, <it>p = </it>0.04), middle income group (AOR 2.1, <it>p = </it>0.001) compared to low income group and low level of education (AOR 3.7, <it>p = </it>0.02) compared to higher education. HSV-2 seropositivity was higher among Christians (12.6%) compared to Muslims (3.8%). The most frequent clinical symptoms among HSV-2 seropositives were excess vaginal discharge in last one year (53.5%, 76/142) and pelvic pain (26.1%, 37/142). While among subjects with genital ulcers, HSV-2 seroprevalence was 36.8% (7/19).</p> <p>Conclusions</p> <p>Overall seroprevalence of HSV-2 infection among pregnant women of Northeast India is relatively low. The generation of awareness among high risk groups may have played key role to limit the infection. The role of vaccination against HSV-2 in near future and elimination of HSV-2 viral shedding along with genital tract inflammation in high HIV/HSV-2 areas may be an option for initiating successful intervention strategies to reduce the transmission and acquisition of HIV infection in Northeast India.</p

Carbon cycling hysteresis in permeable carbonate sands over a diurnal cycle: implications for ocean acidification

Dissolved inorganic carbon, dissolved oxygen, H+, and alkalinity fluxes from permeable carbonate sediments at Heron Island (Great Barrier Reef) were measured over one diel cycle using benthic chambers designed to induce advective pore-water exchange. A complex hysteretic pattern between carbonate precipitation and dissolution in sands and the aragonite saturation state (ΩAr) of the overlying chamber water was observed throughout the incubations. During the day, precipitation followed a hysteretic pattern based on the incidence of photosynthetically active radiation with lower precipitation rates in the morning than in the afternoon. The observed diel hysteresis seems to reflect a complex interaction between photosynthesis and respiration rather than ΩAr of the overlying water as the main driver of carbonate precipitation and dissolution within these permeable sediments. Changes in flux rates over a diel cycle demonstrate the importance of taking into account the short-term variability of benthic metabolism when calculating net daily flux rates. Based on one diel cycle, the sediments were a net daily source of alkalinity to the water column (5.13 to 8.84 mmol m−2 d−1, depending on advection rates), and advection had a net stimulatory effect on carbonate dissolution. The enhanced alkalinity release associated with benthic metabolism and pore-water advection may partially buffer shallow coral reef ecosystems against ocean acidification on a local scale

Seawater carbonate chemistry and calcification and productivity of sporadic coral reef

Estimates of coral reef ecosystem calcification (Gnet) and productivity (Pnet) provide insight into coral community health and functionality in response to short- and long-term stressors such as ocean warming and acidification. Here, we investigate spatial variability in calcification and organic production at One Tree Island (OTI) and compare our new observations to sporadic metabolic rates reported over the previous 50 years on the same reef flat. Gnet and Pnet estimates at the nearshore site were 50% and 166% lower than an offshore site with a shift in organic production from net productive to net respiratory. Contrary to expectations, calcification rates in 2017 (145.7 +- 20.2 mmol/m**2/d) were comparable to the 1970s estimate (125.0 +- 12.5 mmol/m**2/d) and 400% greater than similar observations in 2014. Our results indicate only weak associations between Gnet and aragonite (Omega ar). A local increase in coral cover from 18% in 2014 to 31% in 2017 was the likely driver of increased calcification. A steeper TA–DIC slope in 2017 demonstrates a greater control of calcification on seawater carbonate chemistry than prior years. Overall, these results highlight the importance of site selection and replication when comparing metabolic datasets, and demonstrate major short-term variability in metabolic rates. The predictive capabilities of ecosystem metabolism studies may be constrained by using the available short-term datasets to represent long-term calcification trends

Determining Coral Reef Calcification and Primary Production Using Automated Alkalinity, pH and pCO2 Measurements at High Temporal Resolution

We investigated coral reef carbonate chemistry dynamics and metabolic rates using an automated system that measured total alkalinity (TA, 30 min intervals), pH on the total scale (pHT, 10 min intervals) and the partial pressure of carbon dioxide (pCO2, 1 min intervals) over 2 weeks at Heron Island (Great Barrier Reef, Australia). The calculation of pHT (using the pCO2 and TA pair) and pCO2 (using the pH and TA pair) had similar values to the measured pHT and pCO2 values. In contrast, calculated TA from the pCO2-pH pair showed a large discrepancy with measured TA (average difference between measured and calculated TA = 52 μmol kg−1). High frequency sampling allowed for detailed analysis of the observations and an assessment of optimum sampling intervals required to characterise the net ecosystem calcification (NEC) and production (NEP) using a slack water approach. Depending on the sampling interval (30 min–2 h time steps) used for calculations, the estimated daily NEC and NEP could differ by 12% and 30%, respectively. Abrupt changes in both NEC and NEP were observed at dawn and dusk, with positive NEC during these periods despite negative NEP. Integrating NEC and NEP over a full diel cycle using 1 or 2 h integration time steps resulted in small differences of 2–7% for NEC and 1–3% for NEP. A diel hysteresis pattern rather than a simple linear relationship was observed between the aragonite saturation state (Ωar) and NEC. The observed hysteresis supports recent studies suggesting that short-term observations of seawater Ωar may not be a good predictor of long-term changes in NEC due to ocean acidification. The slope of the DIC to TA relationship was slightly higher (0.33) in 2014 than in an earlier study in 2012 (0.30). The automated, high frequency sampling approach employed here can deliver high precision data and can be used at other coral reef research stations to reveal long-term changes in NEC and NEP potentially driven by ocean acidification, eutrophication or other local changes

Intermittently Closed and Open Lakes and/or Lagoons (ICOLLs) as groundwater-dominated coastal systems: Evidence from seasonal radon observations

Intermittently Closed and Open Lakes or Lagoons (ICOLLs) are dynamic coastal systems that may be vulnerable to changes in catchment hydrology. However, little is known regarding the role of groundwater on the hydrological cycles of ICOLLs. Groundwater discharge in two ICOLLs (Welsby and Mermaid) and a nearby wetland (South Welsby Lagoon) located on Bribie Island (Australia) was quantified using radon (222Rn, a natural geochemical groundwater tracer) during four seasonal surveys. The distribution of radon revealed temporal and spatial changes over the study period with higher surface water radon concentrations found in winter for Welsby ICOLL and in autumn for Mermaid ICOLL. The average estimated groundwater discharge rates from a radon mass balance were 3.4 ± 2.1, 7.3 ± 8.9 and 2.6 ± 1.1 cm d-1 in Welsby, South Welsby and Mermaid Lagoons, respectively. These values are at least 8-fold greater than the average annual precipitation that falls directly over the ICOLLs (1420 mm per year, or 0.4 cm d-1), which, coupled with minimal surface water runoff due to the permeable sandy soils, demonstrates that these systems are groundwater-dominated. Overall, groundwater discharge rates in these ICOLLs were much larger than has been reported in other lake systems which is most likely due to the high permeability of regional sandy soils and their large shoreline to volume ratio

Discrete nutrient and greenhouse gas (carbon dioxide, methane, and nitrous oxide) measurements in the Great Barrier Reef lagoon, Australia

This dataset provides discrete nutrient, dissolved and greenhouse gas samples collected during ship-based cruises in the southern Great Barrier Reef lagoon, Australia. Here we sampled the greenhouse gases of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) with time matched (georeferenced samples) discrete nutrient measurements (dissolved organic carbon, ammonium, nitrate, dissolved inorganic nitrogen, total nitrogen and phosphate) collected from the lagoon. Nutrient concentrations remained low overall, while the lagoon was oversaturated in CO2 and CH4 despite highly oxygenated waters that are normally unconducive for CH4 production. N2O was also undersaturated in the oligotrophic conditions. Dissolved greenhouse gases were measured with a Picarro G2201-i Cavity Ring Down Spectrometer for CO2 (200 ppb ±0.05%) and CH4 (5 ppb ± 0.05%) and a Picarro G2308 Cavity Ring Down Spectrometer for N2O concentrations (<3.5 ppb ± 0.008%). Both Cavity Ring Down Spectrometer instruments were connected in a closed loop with twin showerhead exchangers and a gas drying agent (Drierite). The showerhead exchangers received seawater from the vessel cold water intake. Both instruments averaged 300 measurements over a five-minute cycle for each greenhouse gas sample. Salinity and temperature were recorded at the inlet of the seawater intake system with a Seabird SBE 21 (salinity ± 0.005 psu, temperature ± 0.002 °C). Dissolved oxygen was also recorded using a Hydrolab MS5 (dissolved oxygen 0.1 ± 0.02 mg L-1) fitted with an inline flow cell. Discrete nutrient and dissolved organic carbon (DOC) water samples were collected along survey transects using Niskin bottles from a depth of ⁓3 m. Dissolved nutrient samples were collected by filtering sample water through cellulose acetate syringe filters (0.45 µm) into sample rinsed 12 mL polypropylene vials before immediate freezing until laboratory analysis. Nutrient concentrations were determined using a Lachat QuickChem 8500 Flow Injection Analyser [Detection limits were 0.07 μmol ± 0.3% for nitrate (NOx-) and 0.35 μmol ± 5% for ammonium (NH4+)]. DOC samples were collected by filtering sample water through Whatman G/FF syringe filters (0.7 μm) into 40 ml pre-treated (100 μL mercuric chloride) VOC vials before immediate refrigeration until laboratory analysis. DOC concentrations were determined with OI Aurora 1030 W TOC Analyzer