Freshwater Oxygen Research Articles

Gut flora alterations among aquatic firefly Aquatica leii inhabiting various dissolved oxygen in fresh water

Knowledge about the impact of different dissolved oxygen (DO) on the composition and function of gut bacteria of aquatic insects is largely unknown. Herein, we constructed freshwater environments with different DOs (hypoxia: 2.50± 0.50, normoxia: 7.00± 0.50, and hyperoxia: 13.00± 0.50mg/L) where aquatic firefly Aquatica leii larvae lived for three months. Their gut flora was analyzed using the combination of 16S rRNA amplicon sequencing and metagenomics. The results showed no difference in alpha diversity of the gut flora between A.leii inhabiting various DOs. However, the relative abundance of several bacterial lineages presented significant changes, such as Pseudomonas. In addition, bacterial genes with an altered relative abundance in response to various DOs were primarily related to metabolism. The alteration of these functions correlated with the DO change. This is the first to uncover structure of gut flora under various DOs in aquatic insect larvae.

Widespread deoxygenation of temperate lakes.

The concentration of dissolved oxygen in aquatic systems helps to regulate biodiversity1,2, nutrient biogeochemistry3, greenhouse gas emissions4, and the quality of drinking water5. The long-term declines in dissolved oxygen concentrations in coastal and ocean waters have been linked to climate warming and human activity6,7, but little is known about the changes in dissolved oxygen concentrations in lakes. Although the solubility of dissolved oxygen decreases with increasing water temperatures, long-term lake trajectories are difficult to predict. Oxygen losses in warming lakes may be amplified by enhanced decomposition and stronger thermal stratification8,9 or oxygen may increase as a result of enhanced primary production10. Here we analyse a combined total of 45,148 dissolved oxygen and temperature profiles and calculate trends for 393 temperate lakes that span 1941 to 2017. We find that a decline in dissolved oxygen is widespread in surface and deep-water habitats. The decline in surface waters is primarily associated with reduced solubility under warmer water temperatures, although dissolved oxygen in surface waters increased in a subset of highly productive warming lakes, probably owing to increasing production of phytoplankton. By contrast, the decline in deep waters is associated with stronger thermal stratification and loss of water clarity, but not with changes in gas solubility. Our results suggest that climate change and declining water clarity have altered the physical and chemical environment of lakes. Declines in dissolved oxygen in freshwater are 2.75 to 9.3 times greater than observed in the world's oceans6,7 and could threaten essential lake ecosystem services2,3,5,11.

Carbon mineralization and oxygen dynamics in sediments with deep oxygen penetration, Lake Superior

To understand carbon and oxygen dynamics in sediments with deep oxygen penetration, we investigated eight locations (160–318‐m depth) throughout Lake Superior. Despite the 2–4 weight percent organic carbon content, oxygen penetrated into the sediment by 3.5 to > 12 cm at all locations. Such deep penetration is explained by low sedimentation rates (0.01–0.04 cm yr−1), high solubility of oxygen in freshwater, and a shallow (~ 2 cm) bioturbation zone. In response mainly to oxygen variations in the bottom waters, the sediment oxygen penetration varied seasonally by as much as several centimeters, suggesting that temporal variability in deeply oxygenated sediments may be greater than previously acknowledged. The oxygen uptake rates (4.4–7.7 mmol m−2 d−1, average 6.1 mmol m−2 d−1) and carbon mineralization efficiency (~ 90% of deposited carbon) were similar to those in marine hemipelagic and pelagic sediments of comparable sedimentation rates. The reactivity of organic carbon was found to decrease with age similarly to the power‐law documented in marine environments. The burial flux of carbon into the deep sediment (0.7 mmol m−2 d−1) was 2.5% of the previously estimated primary production. Maximum volume‐specific carbon degradation rates were 0.3–1.5 µmol cm−3 d−1; bioturbation coefficient near the sediment surface was 3–8 cm2 yr−1. These results indicate that carbon cycling in large freshwater systems conforms to many of the same trends as in marine systems.

Removal of nitrite interference in the Winkler determination of dissolved oxygen in seawater

Nitrite is a well recognized interference in iodometry. However, while steps for its removal are part of the routine practice in the standard methods for the determination of dissolved oxygen in freshwater and wastewater when the iodometric Winkler method is used, they are not included in any of the widely used standard procedures for seawater analyses. In de-ionized reagent-grade water, artificial seawater and natural surface seawater, the concentration of apparent oxygen increased linearly with increasing concentrations of added nitrite, indicating that the presence of nitrite does lead to an over-estimation. The average ratio of increase in apparent oxygen to nitrite added was 0.4±0.1mol mol−1. At the widely claimed accuracy and precision in the determination of dissolved oxygen in seawater of ±0.1 to ±0.3%, the interference of nitrite may be safely ignored only when the concentration of nitrite is below about 0.3μM. At higher concentrations, such as those found at the nitrite maxima and in coastal waters, it should be taken into account. Since nitrite can be easily and readily removed by the addition of azide, such a step should be incorporated into the standard procedures for the determination of dissolved oxygen in seawater.

Phosphorylation in crayfish ( Procambarus clarkii) eggs during hatching

1. 1.|The high-energy phosphorylation metabolism in crayfish, Procambarus clarkii eggs during brooding and juvenile crayfish after hatching was studied by in vivo 31P nuclear magnetic resonance ( 31P NMR) spectroscopy. 2. 2.|Inorganic phosphoric acid (Pi) and adenosine-5′-triphosphate ATP(γ-,α-,β-) were detected in the dark brownish red eggs after oviposition. 3. 3.|In orange unhatched eggs, only sugar phosphate (SP), Pi and resolved phosphometabolite from ATP were observed. 4. 4.|Peaks of SP, Pi, arginine phosphate (Arg-P), and ATP (γ,α,β) appeared in larvae of crayfish after hatching (nauplius, zoea and juvenile crayfish). 5. 5.|The high-energy phosphorylation metabolism changed to an anaerobic condition along with a decrease in the concentration of dissolved oxygen in fresh water.

The concentration and isotopic fractionation of oxygen dissolved in freshwater and seawater in equilibrium with the atmosphere1

Previous work on the solubility of oxygen in freshwater has been extended to seawater. Measurements of the Henry coefficient in the ranges 0° < t < 45°C and 0< S < 50 fit the Setschenow relationship for the variation with salinity. The temperature dependence of the Setschenow coefficient for oxygen is found to be K = 0.0225034 ‒ 13.6083/T + 2,565.68/T2. The equation for the Henry coefficient as a function of temperature and salinity is used to calculate values for unit standard atmospheric concentrations (USAC) in freshwater and seawater in equilibrium with air at a total pressure of 1 atmosphere. It is estimated that the possible error in the new USAC values is no greater than ±0.1% and probably less. Tables and equations are presented for obtaining accurate USAC values in the ranges 0° < t < 40°C and 0 < S < 40. Simple procedures are given for calculating standard atmospheric concentrations at pressures different from 1 atm. The presence of sea salt has a negligible effect on the fractionation of the oxygen isotopes during solution.

Stress Corrosion Cracking of Aluminum Brass in Fresh Water (III)

The stress corrosion cracking of aluminum brass in fresh water has been investigated. Specimens used are aluminum brass plates (BsTF3) and are stressed by the application of bending. The corrosion medium was 30ppm NaCl aqueous solution, to which are added ammonium ion (1.44ppm as NH4+), oxygen (saturated) and hydrogen sulfide. The anodic polarization test method was used.The results obtained in this study are summarized as follows;(1) Stress corrosion cracking of aluminum brass in fresh water did not occur in the medium free from dissolved oxygen, even if ammonium ion existed and neither in the medium free from ammonium ion, even if dissolved oxygen is saturated. Co-existence of ammonium ion and dissolved oxygen in fresh water resulted in stress corrosion cracking.(2) Stress corrosion cracking of aluminum brass also occured in fresh water containing hydrogen sulfide.

The Relative Atomic Weight of Oxygen in Water and in Air II. A Note on the Relative Atomic Weight of Oxygen in Fresh Water, Salt Water and Atmospheric Water Vapor

Purified Lake Michigan water appears to be nearly exactly intermediate in density between purified Atlantic Ocean water and water condensed from the atmosphere. Within the experimental error the entire difference in density between fresh and salt water appears to be due to differences in the oxygen isotopic ratios. The bearing of these results on theories explaining the relatively large concentration of O18 in the atmosphere is discussed.