scholarly journals Effects of Seasonal Thermal Stratification on Nitrogen Transformation and Diffusion at the Sediment-Water Interface in a Deep Canyon Artificial Reservoir of Wujiang River Basin

Water ◽  
2021 ◽  
Vol 13 (22) ◽  
pp. 3194
Author(s):  
Yongmei Hou ◽  
Xiaolong Liu ◽  
Sainan Chen ◽  
Jie Ren ◽  
Li Bai ◽  
...  
Keyword(s):  
Dissolved Oxygen ◽  
Thermal Stratification ◽  
Nitrogen Transformation ◽  
Water Interface ◽  
Mineralization Rate ◽  
Nitrogen Species ◽  
Seasonal Differences ◽  
Artificial Reservoir ◽  
Significant Difference ◽  
Water Quality Deterioration

Watershed-scale nitrogen pollution in aquatic systems has become a worldwide concern due to its continuous impact on water quality deterioration, while the knowledge of key influencing factors dominating nitrogen transportation and transformation at the sediment-water interface (SWI) remains limited, especially in impounded rivers with an artificial reservoir. Hence, for a better understanding of the effects of thermal stratification on nitrogen transformation, we investigated the nitrogen species and isotopes in the sediment of a deep reservoir in Southwest China. Our results confirmed a significant difference in nitrogen species and isotopic composition in sediment between those in the thermal stratification period and non-thermal stratification period and indicated that the sediment biogeochemical process and transportation were clearly linked to the variations in water temperature and dissolved oxygen dominated by the process of thermal stratification. Significant seasonal differences in NH4+-N and NO3−-N in pore water of the upper layer (0–19 cm) revealed that nitrification exhausted NH4+ in the non-stratified period (NSP), and a potential low mineralization rate appeared when compared with those in the stratified period (SP). Seasonal differences in nitrogen species and isotope fractionation of δ15N-PON (about 2.3‰ in SP) in the upper layer sediment indicated a higher anaerobic mineralization rate of organic matter in SP than that in NSP. The diffusion fluxes of NH4+-N at SWI were 9.48 and 15.66 mg·m−2·d−1 in NSP and SP, respectively, and annual NH4+-N diffusion accounted for 21.8% of total storage in the reservoir. This study demonstrated that the nitrogen cycling processes, especially nitrification, denitrification, and mineralization, have been largely altered along with the changes in dissolved oxygen and that the diffusion of nitrogen species varied with the presence of the oxygen. The results contribute to the future study of watershed nitrogen budget evaluation and suggest that the endogenous nitrogen released from the sediment-water interface should be emphasized when aiming to fulfil water management policies in deep reservoirs.

scholarly journals The Dynamic Response of Nitrogen Transformation to the Dissolved Oxygen Variations in the Simulated Biofilm Reactor

2021 ◽  
Vol 18 (7) ◽  
pp. 3633
Author(s):  
Qianqian Lu ◽  
Nannan Zhang ◽  
Chen Chen ◽  
Miao Zhang ◽  
Dehua Zhao ◽  
...  
Keyword(s):  
Dissolved Oxygen ◽  
Copy Number ◽  
Stable State ◽  
Quantitative Relationship ◽  
Nitrogen Transformation ◽  
Biofilm Reactor ◽  
Short Term ◽  
Nirs Gene ◽  
Biofilm Reactors ◽  
Recovery Times

Lab-scale simulated biofilm reactors, including aerated reactors disturbed by short-term aeration interruption (AE-D) and non-aerated reactors disturbed by short-term aeration (AN-D), were established to study the stable-state (SS) formation and recovery after disturbance for nitrogen transformation in terms of dissolved oxygen (DO), removal efficiency (RE) of NH4+-N and NO3−-N and activity of key nitrogen-cycle functional genes amoA and nirS (RNA level abundance, per ball). SS formation and recovery of DO were completed in 0.56–7.75 h after transition between aeration (Ae) and aeration stop (As). In terms of pollutant REs, new temporary SS formation required 30.7–52.3 h after Ae and As interruptions, and seven-day Ae/As interruptions required 5.0% to 115.5% longer recovery times compared to one-day interruptions in AE-D and AN-D systems. According to amoA activity, 60.8 h were required in AE-D systems to establish new temporary SS after As interruptions, and RNA amoA copies (copy number/microliter) decreased 88.5%, while 287.2 h were required in AN-D systems, and RNA amoA copies (copy number/microliter) increased 36.4 times. For nirS activity, 75.2–85.8 h were required to establish new SSs after Ae and As interruptions. The results suggested that new temporary SS formation and recovery in terms of DO, pollutant REs and amoA and nirS gene activities could be modelled by logistic functions. It is concluded that temporary SS formation and recovery after Ae and As interruptions occurred at asynchronous rates in terms of DO, pollutant REs and amoA and nirS gene activities. Because of DO fluctuations, the quantitative relationship between gene activity and pollutant RE remains a challenge.

Analysis of the breeding records of a herd of pigs

1954 ◽  
Vol 45 (1) ◽  
pp. 19-27 ◽  
Author(s):  
R. Braude ◽  
P. M. Clarke ◽  
K. G. Mitchell
Keyword(s):  
Statistical Analysis ◽  
Large White ◽  
Seasonal Differences ◽  
Significant Difference ◽  
The Mean ◽  
The Difference ◽  
Length Of Gestation

1. A survey and. statistical analysis of the records of litters born in the N.I.R.D. herd of Large White pigs over a period of 16 years are presented.2. The mean length of gestation was 114 days for both gilts and sows.3. The mean numbers of pigs born alive and born dead per litter from gilts, 10·0 and 0·2 respectively, were both significantly smaller than the corresponding figures for sows, 11·8 and O·8. No seasonal differences were found.4. The mean total losses of pigs from birth to weaning at 8 weeks were 29·5% of pigs born alive. The losses in litters from gilts, 23·0%, were significantly smaller than in litters from sows, 31·0%. The losses during the winter months both for gilts, 32·5%, and for sows, 35·9%, were significantly higher than during the summer months, 19·4% and 26·7% for gilts and sows respectively.5. Over 50% of the total losses were due to crushing by the dam, 74·1% of the losses from this cause occurring during the first 48 hr. after birth.6. The mean number of pigs weaned per litter was 8·0. The difference between the number weaned per litter from gilts, 7·7, and per litter from number of pigs was weaned per litter from sows during the summer months, 8·7, than during the winter months, 7·4.7. There was no significant difference between the number of male and of female pigs weaned.8. The mean weight at weaning was 29·9 lb., male pigs, 30·3 lb., being significantly heavier than females, 29·51b. Pigs in litters from gilts, 27·81b., were significantly lighter at weaning than those from sows, 30·0 lb., and for both gilts and sows, pigs reared during the summer months, 29·7 and 31·8 lb. respectively, were significantly heavier than those reared during the winter months, 25·9 and 28·2 lb. respectively.

scholarly journals Assessment of the physicochemical variables of a subtropical reservoir in the northwest of Argentina

2014 ◽  
Vol 26 (4) ◽  
pp. 367-380 ◽  
Author(s):  
Beatriz Concepción Tracanna ◽  
Silvia Nelly Martínez De Marco ◽  
María de los Ángeles Taboada ◽  
Virginia Mirande ◽  
María de Lourdes Gultemirian ◽  
...  
Keyword(s):  
Dissolved Oxygen ◽  
Physicochemical Parameters ◽  
Thermal Stratification ◽  
Oxygen Demand ◽  
Limiting Factor ◽  
Alkaline Ph ◽  
A Value ◽  
Sodium Calcium ◽  
Calcium Bicarbonate ◽  
Laboratory Results

AIM: The Escaba dam is located in the south of the Tucumán province, Argentina, at 650 m above sea level. It has an extension of 541 ha. and a depth of 65 m and its tributaries are the Chavarría, Las Moras, El Chorro and Singuil rivers. The climate is mild with dry winters and rainy summers. The objective of this study was to characterize physicochemical parameters in the limnetic zone of the dam and the mouths of the tributaries to determine the water quality. METHODS: Seasonal sampling was carried out between August 2010 and May 2012. Temperature, transparency, pH and electrical conductivity were field measured, whereas dissolved oxygen, biochemical oxygen demand (BOD5), major ion constituents and nitrogen and phosphate compounds were analyzed at the laboratory. RESULTS: The water was classified as sodium-calcium-bicarbonate with neutral to alkaline pH, and thermal stratification during spring and summer. The water assayed was well oxygenated except for the bottom of the limnetic zone during the summer months. Lowest transparency was measured in the El Chorro River in November 2011 (0.12 m) and highest degree of transparency in the Singuil River during the winter of 2010 (4.1 m). The waters assayed showed weak mineralization with conductivities between 83 and 218 µS.cm-1. Maximum BOD5 value (183 mg.L-1) was measured in the Singuil River in spring 2010. Highest values for the different nitrogen compounds were as follows: 7 mg NO3-.L-1 at the bottom of the limnetic zone in August 2010, 0.07 mg NO2-.L-1 in the Las Moras River in May 2011 and 1.8 mg NH4+.L-1 in the Chavarría River in March 2011. During the summer of 2012 orthophosphate reached a value of 0.22 mg.L-1 at the bottom of the limnetic zone. The TN/TP ratio revealed that phosphate was generally the limiting factor and rarely nitrogen. CONCLUSIONS: Considering the TN, TP and transparency parameters the ecosystem was classified as hypertrophic. PCA allowed a seasonal differentiation of the sites, and components 1 and 2 classified the samples according to nutrient gradient, dissolved oxygen, BOD5 and temperature.

scholarly journals Changes in the nitrogen biogeochemical cycle in sediments of an urban river under different dissolved oxygen levels

2018 ◽  
Vol 19 (4) ◽  
pp. 1271-1278 ◽  
Author(s):  
Yaping Zhang ◽  
Xiaohong Ruan ◽  
Wenli Shi
Keyword(s):  
Dissolved Oxygen ◽  
Nitrogen Cycling ◽  
Quantitative Polymerase Chain Reaction ◽  
Nitrogen Transformation ◽  
Urban River ◽  
Ammonia Oxidizing Bacteria ◽  
Urban Rivers ◽  
Ammonium Oxidation ◽  
Microbial Nitrogen ◽  
Concentration Changes

Abstract Urban rivers are considered as a hot spot of microbial nitrogen cycling due to extensive N loading. However, microbial nitrogen transformation dynamics in urban rivers with different dissolved oxygen (DO) conditions are still unclear. This study investigated the effects of DO concentration changes (anaerobic to aerobic) in overlying water on nitrogen-cycling gene abundance in incubation conditions using sediment from a typical urban river in the Yangtze River Delta. Quantitative polymerase chain reaction (qPCR) results revealed that the abundances of the nitrification gene amoA, denitrification gene nirS/K, norB, nosZ, and anammox gene hzo increased by one to two orders of magnitude from anaerobic to aerobic conditions. Ammonia-oxidizing archaea (AOA) predominated the ammonium oxidation microbial populations, about tenfold more than the ammonia-oxidizing bacteria (AOB) populations. Significant correlations were found among the abundances of AOA-amoA, AOB-amoA, nirS, nirK, and hzo genes, implying a close coupling of aerobic ammonium oxidation (AAO), denitrification, and anammox processes at the molecular level. Moreover, the nitrogen transformation rates were calculated using a box model linking the measured dissolved inorganic nitrogen species. The contribution of anammox to N2 production was 85% under saturated treatment, and the AAO rate was significantly positive correlated to the anammox rate. Our results suggested that coupled AAO and anammox might be the dominant pathway for reactive nitrogen removal in urban rivers with elevated DO levels.

Studies of the hydrobiology of a tropical lake in north-western Queensland. II. Seasonal changes in thermal and dissolved oxygen characteristics

1980 ◽  
Vol 31 (5) ◽  
pp. 589 ◽  
Author(s):  
CM Finlayson ◽  
TP Farrell ◽  
DJ Griffiths
Keyword(s):  
Dissolved Oxygen ◽  
Water Column ◽  
Environmental Conditions ◽  
Seasonal Changes ◽  
Thermal Stratification ◽  
Oxygen Depletion ◽  
Tropical Lake ◽  
North Western

The stratification characteristics of Lake Moondarra (24�34'S.,139�35'E.), a man-made lake in north- western Queensland, have been studied. Evidence is presented that the lake approximates the warm polymictic type in which no persistent thermal stratification ever develops. During the cooler months, thermal stratification breaks down during the night; in the warmer months, the intense rainstorms prevent the establishment of a persistently stratified water column. The shallowness of the lake relative to its surface areaand the prevailing environmental conditions ensure that extensive periods of oxygen depletion do not develop in the water column. It is concluded that a strong and prolonged period of thermal stratification, with subsequent serious effects of the availability of dissolved oxygen in the deeper layers, would only arise if, in a particular year. there were no significant rainstorms.

scholarly journals Seasonal dynamics of Daphnia laevisBirge, 1878 ephippia in a tropical lake with a description of a new methodology for in situ evaluation

2014 ◽  
Vol 74 (3) ◽  
pp. 642-648 ◽  
Author(s):  
LPM Brandão ◽  
DGF Pujoni ◽  
PM Maia-Barbosa
Keyword(s):  
Water Column ◽  
Seasonal Dynamics ◽  
Thermal Stratification ◽  
Core Sample ◽  
Hatching Rate ◽  
The Core ◽  
Significant Difference ◽  
Chi Squared ◽  
Hatching Rates

The effect of dormancy in zooplankton populations is still unknown, largely because of the lack of methods to estimate hatching and production of the dormant stages. This study aimed to compare the production and hatching rates of ephippia of Daphnia laevis between thermal stratification and mixing periods in Jacaré Lake (Middle Rio Doce, Minas Gerais, Brazil). For this, we collected ephippia on the sediment with core sampler and we created a device called the “Ephippial Collector”. There was a significant difference in ephippia hatching in situ between stratification and mixing periods (Pearson's Chi-squared test p <0.001), being higher in the second one. Significant differences in the hatching rates between periods was observed in the laboratory only for ephippia collected with Ephippial Collectors (Pearson's Chi-squared test p <0.001), being higher during the mixing period (∼8%). The core sample allows the collection of a certain fraction of the sediment that may contain a mixture of ephippia produced in different periods, i.e., may contain old and not viable ephippia, which masks the hatching rate. Thus, seasonality in hatching rates of ephippia was reported only by Ephippial Collectors. The higher hatching rate observed during the mixing period in the lake suggests that individuals hatched from ephippia may contribute to the increase in the population of D. laevis in the water column at this time.

scholarly journals Seasonal Dynamics of the Microbial and Physicochemical Characteristics of Streams and Boreholes in Uzuakoli, Eastern Nigeria

2019 ◽  
Vol 10 (2) ◽  
pp. 17
Author(s):  
Okezie Onyemaechi ◽  
Nwachukwu Ejikeme
Keyword(s):  
Dissolved Oxygen ◽  
Water Samples ◽  
Physicochemical Parameters ◽  
Stream Water ◽  
Oxygen Demand ◽  
Enterobacter Aerogenes ◽  
Physicochemical Characteristics ◽  
Potassium Nitrate ◽  
Significant Difference ◽  
Dry And Rainy Seasons

Water samples from twenty water sources (fifteen boreholes and five streams) in Uzuakoli, Nigeria were collected for the period of 6 months covering the dry and rainy seasons to assess the level of contamination. The Microbiological characteristics including heterotrophic counts, coliform counts and physicochemical parameters includes pH, turbidity, dissolved oxygen, calcium, potassium, nitrate, magnesium and phosphate were evaluated using standard methods. The total Heterotrophic counts for the borehole during the dry and rainy season were 8.3 x 103 cfu/ ml and 10.8 x 104 cfu/ ml. The Heterotrophic counts for the stream were 12.7 x 104 cfu/ ml and 17.8x 106 cfu/ ml. The frequency of occurrence of the isolates are Staphylococcus aureus 63% in borehole and 85% in streams, Pseudomonas aeruginosa 49% in boreholes and 95% in streams, Proteus sp 52% in boreholes and 97% in streams, Streptococcus sp 46% in boreholes and 53% in streams, Enterobacter aerogenes 33% in boreholes and 63% in streams, Escherichia coli 16% in boreholes and 53% in streams and Salmonella sp no percentage in boreholes and 40% in streams. The result shows a significant difference at (P≤0.05) for the bacterial isolates. The physicochemical parameters of the borehole and stream water samples during the dry and rainy seasons were determined. The temperature ranged from 25oC 32oC; pH ranged from 5.3 8.1; turbidity ranged 0.03 3.23; dissolved oxygen ranged from 3.45–7.40mg/l; biochemical oxygen demand ranged from 1.20–4.32mg/l; chemical oxygen demand ranged from 2.50–5.21mg/l; Calcium ranged from 0.81–5.64mg/l; potassium ranged from 1.01–4.22mg/l; Nitrate ranged from 1.49–4.02mg/l; magnesium ranged from 0.13–2.20mg/l; phosphate ranged from 0.51–2.01mg/l. The water samples were all within the WHO limits apart from sample from Iyi Agbozu that had temperature of 32oC.

Effects of rainfall on thermal stratification and dissolved oxygen in a deep drinking water reservoir

2020 ◽  
Vol 34 (15) ◽  
pp. 3387-3399
Author(s):  
Miao Liu ◽  
Yunlin Zhang ◽  
Kun Shi ◽  
Yibo Zhang ◽  
Yongqiang Zhou ◽  
...  
Keyword(s):  
Drinking Water ◽  
Dissolved Oxygen ◽  
Thermal Stratification ◽  
Water Reservoir ◽  
Drinking Water Reservoir

Timing, cause and consequences of mid-Holocene climate transition in the Arabian Sea

2016 ◽  
Vol 86 (2) ◽  
pp. 162-169 ◽  
Author(s):  
Rajeev Saraswat ◽  
Dinesh Kumar Naik ◽  
Rajiv Nigam ◽  
Anuruddh Singh Gaur
Keyword(s):  
Dissolved Oxygen ◽  
Arabian Sea ◽  
Seawater Temperature ◽  
Subsurface Water ◽  
Water Interface ◽  
Holocene Climate ◽  
Carbon Burial ◽  
Sediment Fraction ◽  
Surface Productivity ◽  
Climate Transition

AbstractWe reconstruct centennial scale quantitative changes in surface seawater temperature (SST), evaporation-precipitation (from Mg/Ca and δ18O of surface dwelling planktic foraminifera), productivity (from relative abundance of Globigerina bulloides), carbon burial (from %CaCO3 and organic carbon [%Corg]) and dissolved oxygen at sediment-water interface, covering the entire Holocene, from a core collected from the eastern Arabian Sea. From the multi-proxy record, we define the timing, consequences and possible causes of the mid-Holocene climate transition (MHCT). A distinct shift in evaporation-precipitation (E-P) is observed at 6.4 ka, accompanied by a net cooling of SST. The shift in SST and E-P is synchronous with a change in surface productivity. A concurrent decrease is also noted in both the planktic foraminiferal abundance and coarse sediment fraction. A shift in carbon burial, as inferred from both the %CaCO3 and %Corg, coincides with a change in surface productivity. A simultaneous decrease in dissolved oxygen at the sediment-water interface, suggests that changes affected both the surface and subsurface water. A similar concomitant change is also observed in other cores from the Arabian Sea as well as terrestrial records, suggesting a widespread regional MHCT. The MHCT coincides with decreasing low-latitude summer insolation, perturbations in total solar intensity and an increase in atmospheric CO2.

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