Study of Hybrid Photovoltaic Thermal (PV/T) Solar System with Modification of Thin Metallic Sheet in the Air Channel.

The increase of the temperature of PV module gradually decreases the electricity production. To eliminate this problem thermal collector is incorporated with the PV module to allow PV cooling. It has been found that PV cooling increases the electricity production and allows the extra heat to be absorbed by the coolant extracting thermal output. This system is called hybrid PV/T system where water and air can be used as the heat extraction medium. Use of Thin Flat Metallic Sheet (TFMS) in the air channel in PV/T system increase the temperature of the air considerably which has found in several experiments. The comparative performance of PV/T system using four types of shape for thin metallic sheet including flat sheet was investigated. The performance was investigated at Islamic University of Technology in Bangladesh by using an experimental hybrid PV/T system at outdoor .The experiment shows that efficiency of the PV/T system varies significantly with the variation of the shape of the metallic sheet in the air channel. The used shape was flat, saw tooth backward, saw tooth forward and trapezoidal. By the experimental results it is found that the efficiency of the flat metallic sheet is the lowest among the four. Saw tooth backward and saw tooth forward shows the same efficiency and trapezoidal metallic sheet is lower than that

The role of hydraulic failure in a massive mangrove die-off event

Between late 2015 and early 2016, more than 7,000 ha of mangrove forest died along the coastline of the Gulf of Carpentaria, in northern Australia. This massive die-off was preceded by a strong 2015/2016 El Niño event, resulting in lower precipitation, a drop in sea level and higher than average temperatures in northern Australia. In this study, we investigated the role of hydraulic failure in the mortality and recovery of the dominant species, Avicennia marina, 2 years after the mortality event. We measured predawn water potential (Ψpd) and percent loss of stem hydraulic conductivity (PLC) in surviving individuals across a gradient of impact. We also assessed the vulnerability to drought-induced embolism (Ψ50) for the species. Areas with severe canopy dieback had higher native PLC (39%) than minimally impacted areas (6%), suggesting that hydraulic recovery was ongoing. The high resistance of A. marina to water-stress-induced embolism (Ψ50 = −9.6 MPa), indicates that severe water stress (Ψpd < −10 MPa) would have been required to cause mortality in this species. Our data indicate that the natural gradient of water-stress enhanced the impact of El Niño, leading to hydraulic failure and mortality in A. marina growing on severely impacted (SI) zones. It is likely that lowered sea levels and less frequent inundation by seawater, combined with lower inputs of fresh water, high evaporative demand and high temperatures, led to the development of hyper-salinity and extreme water stress during the 2015/16 summer

Investigation of heavy metal contents in Cow milk samples from area of Dhaka, Bangladesh

Background: Cow milk is considered as one of the responsible food sources contaminated with heavy metals. The objectives of the study were to assess the content of selected metals in cow milk and its associated human health risks in the food chain of Bangladesh. A total of 90 cow milk samples of Branded, Dairy and Domestically produced milk were collected randomly from different sources of Savar Upazila in Dhaka area. Cadmium (Cd), chromium (Cr), lead (Pb), manganese (Mn), copper (Cu) and iron (Fe) contents in collected milk samples were determined using Flame Atomic Absorption Spectrometry (FAAS). To ensure quality control, one of the best quality control parameters i.e. recovery test; from eight various sample digestion methods were used. The Hazard Quotient (HQ) and Carcinogenic Risk (CR) values were also calculated. Results: From the results, it was found that, the orders of heavy metal content in brand, dairy and domestic cow milk were Cr > Fe > Cu>Mn > Cd > Pb, Cr > Fe > Mn > Cu > Cd > Pb and Fe > Cr > Mn > Cu > Cd > Pb, respectively. Among the six metals, only Cr showed to exceed the highest Estimated Daily Intake (EDI) rate (for brand cow milk: 0.413 mg/day, dairy farm cow milk: 0.243 mg/day, domestic cow milk: 0. 352 mg/day),and the comparison percentages of calculated values per permeable values were as follows; 206.5 % for brand cow milk,121.5 % for dairy farm cow milk and 176.0 % for domestic cow milk. Hazard Quotients (HQ) values and Carcinogenic Risk (CR) values were found within the acceptable level. Conclusion: Although, the metal content in sampled cow milks were within the safe limit, the potential human health risks cannot be neglected for the regular/long time consumption of heavy metal contained cow milk

Vapour pressure deficit modulates hydraulic function and structure of tropical rainforests under nonlimiting soil water supply

Atmospheric conditions are expected to become warmer and drier in the future, but little is known about how evaporative demand influences forest structure and function independently from soil moisture availability, and how fast-response variables (such as canopy water potential and stomatal conductance) may mediate longer-term changes in forest structure and function in response to climate change. We used two tropical rainforest sites with different temperatures and vapour pressure deficits (VPD), but nonlimiting soil water supply, to assess the impact of evaporative demand on ecophysiological function and forest structure. Common species between sites allowed us to test the extent to which species composition, relative abundance and intraspecific variability contributed to site-level differences. The highest VPD site had lower midday canopy water potentials, canopy conductance (gc), annual transpiration, forest stature, and biomass, while the transpiration rate was less sensitive to changes in VPD; it also had different height–diameter allometry (accounting for 51% of the difference in biomass between sites) and higher plot-level wood density. Our findings suggest that increases in VPD, even in the absence of soil water limitation, influence fast-response variables, such as canopy water potentials and gc, potentially leading to longer-term changes in forest stature resulting in reductions in biomass

The contribution of mangrove leaf litter to juvenile shrimp (Penaeus monodon) production in mangrove-shrimp aquaculture systems

Intensification of shrimp farming has been identified as one of the main causes for mangrove destruction in the coastal region of many countries. The idea to develop mangrove-shrimp co-management was developed during the last decades of the 20th century as an effort to help restore the mangrove ecosystem and make shrimp culture sustainable. The present research is part of a broader effort to introduce silvo-aquaculture, combining mangrove and shrimp, to Bangladesh. Mangrove- shrimp co-management has very high potential from an ecological and economical point of view. Mangrove leaf litter are shown to enhance shrimp production by enhancing natural food production. In addition, the nutrient use efficiency of artificial feed is found to be enhanced by providing leaf litter as extra nutrient source, a form of synergism between natural and artificial feed. Therefore the main aim of this thesis is to assess the impact of leaf litter from different mangrove species on pond performance, water quality and natural food availability in mangrove shrimp nursery tanks and ponds. First of all, the nutrient and anti-nutrient content in leaf litter of selected mangrove species and their effect on shrimp performance were determined. The observed effects on post-larval shrimp differed between mangrove species, showing a clear ranking of mangrove species in terms of their ability to enhance shrimp growth. Leaf litter from different mangrove species, not only led to different concentrations of plankton in the PL nursery tank system, but also correlated with shrimp growth performance. Secondly, the effects of interactions between leaf litter from the four chosen mangrove species and pelleted feed on shrimp growth and survival in shrimp PL nursery tanks were explored. Leaf litter and feed combined, resulted in a 21 to 33% higher weight gain of shrimp PL than based on the additive contributions of only leaf litter or only feed, indicating a synergistic effect of the two food sources on shrimp growth. Among the different mangrove species tested, S. apetala (Sa; 23.1%) contributed the most to total weight gain followed by A. officinalis (Ao; 21.6%), S. caseolaris (Sc; 21.6%) and H. fomes (Hf; 10%). The lower feed conversion ratio (FCR) (0.18–0.27) in the treatments combining leaf litter and supplemental feed as compared to the feed-only treatment (0.41) indicated that leaf litter (directly or indirectly by stimulating natural food production) contributed to the nutrition of the shrimp. The observed synergistic effect between supplemental feed and leaf litter is an opportunity for farmers to reduce shrimp production costs and simultaneously raise benefits. Thirdly, effect of different combinations of leaf litter from different mangrove species on shrimp larval performance in tanks and small (mesocosm) ponds were also explored. Three 3-mangrove-species and one 4-mangrove-species combinations of mangrove leaf litter were tested. Under controlled conditions in tanks, mixed leaf litter and feed resulted in 22 to 32% higher weight gain of PL than based on the additive contributions of only leaf litter or only feed, indicating a similar synergistic effect of the two food sources on shrimp growth . Although the nutrient input level and PL stocking density in ponds were less than half the input or density in tanks, the shrimp grew 3.5 times larger in the mesocosm ponds. The different combinations of mangrove leaf litter employed influenced water quality and stimulated the production of phytoplankton and zooplankton food, which allowed greater shrimp weight gain. Then, effect of leaf litter on shrimp growth, color and product appeal to farmers, exporters and local consumers was identified. The body color of shrimp not exposed to leaf litter was lighter than of shrimp grown in tanks receiving leaf litter. The majority of Sa-reared shrimp at harvest were significantly darker (P < 0.05) in body color than larvae reared with leaf litter from other mangrove species. The shrimp body color of shrimp not exposed to any leaf litter at all was lighter than of shrimp reared in presence of all types of leaf litter tested. Within each category of shrimp value-chain actors interviewed, more than 50% of respondents preferred dark colored shrimp, and none preferred pale-colored shrimp. 100% from among exporters and local consumers, respectively, 100% and 60% linked dark body color to higher price, while the opposite was the case among non-mangrove farmers. Aside from production volume, mangrove leaf litter was found to strongly enhance the color properties and hence perceived quality of black tiger shrimp to the consumer. Inclusion of mangroves in and along shrimp culture ponds is recommended as a valuable way of improving both the commercial profitability and sustainability of shrimp aquaculture in Bangladesh and elsewhere.Finally, the effectiveness of mangrove leaf litter application in combination with pelleted supplemental feed in PL nursery systems is reviewed against existing concepts and the functioning of mangrove-shrimp rearing systems.The main identifications are:Application of mangrove leaf litter contributes to individual growth and total production in shrimp nursery systems.When applied at 1 kg m-3 and 0.56 kg m-3 culture volume in tanks and mesocosm ponds, respectively, the anti-nutrient content in leaf litter does not negatively impact shrimp performance.Crude fiber content strongly affects the decomposition rate of mangrove leaf litter.Leaf litter decomposition at the described leaf litter loading rates releases nutrients that stimulate plankton production, which in turn enhance the total system performance of shrimp nursery systems.For the input range and culture duration, applied in this Thesis project, joint application of supplemental pelleted feed and mangrove leaf litter created synergy for a more than additive positive effect on shrimp growth.The traditional shrimp farmers in Bangladesh need to be introduced to and trained in mangrove-shrimp co-management rearing techniques to ensure they benefit from mangrove-shrimp aquaculture.Overall, our results show that inclusion of mangroves in shrimp pond culture has great as yet largely untapped potential to enhance pond productivity and make shrimp farming more environmentally sustainable. A paradigm shift is needed with respect to mangroves vis-a-vis shrimp pond aquaculture. Whereas these areas today are largely denuded of mangrove trees, these should be seen as valuable resource for the shrimp farmer of which the leaves can serves as a healthy and inexpensive source of shrimp food. Proper management of mangrove trees in and around shrimp ponds is an opportunity with which to make shrimp farming more resilient, with important benefits for the coastal communities and the coastal ecosystem

Drivers of nocturnal stomatal conductance in C3 and C4 plants

Nocturnal water losses were for long considered negligible, but it is now known that incomplete stomatal closure during the night leads to significant water losses at leaf, plant and ecosystem scales. However, only daytime transpiration is currently accounted for in evapotranspiration studies. Important uncertainties on the drivers of nocturnal water fluxes hinder its incorporation within modelling frameworks because some studies indicate that night-time stomatal drivers may differ from day-time responses. Here, we synthesise the studies on nocturnal stomatal conductance (gn) to determine underlying drivers through a systematic literature review and, whenever possible, meta-analytical techniques. Similar to daytime responses, we found negative effects of vapour pressure deficit, predawn water potential, air temperature, and salinity on gn across the plant species. However, the most apparent trend was an increase of gn from the beginning until the end of the night, indicating significant and widespread endogenous regulation by the circadian clock. We further observed how neither elevated CO2 nor nutrient status affected gn significantly across species. We also did not find any significant associations between gn and elevated ozone or increasing plant age. There was a paucity of studies on climatic extremes such heat waves and also few studies connected gn with anatomical features such as leaf specific area or stomatal density. Further studies are also needed to address the effects of plant sex, abscisic acid concentrations and genotypic variations on gn. Our findings solve the long-term conundrum on whether stomatal responses to daytime drivers are the same as those that during the nighttime

Nutrients and anti-nutrients in leaf litter of four selected mangrove species from the Sundarbans, Bangladesh and their effect on shrimp (Penaeus monodon, Fabricius, 1798) post larvae

The release of nutrients and anti-nutrients from mangrove leaf litter plays an important role in the biogeochemical cycling in aquatic environments and directly or indirectly affects water quality and food availability to shrimp. In this study, we assessed nutrient and anti-nutrient loss during decomposition of leaf litter at a concentration of 1 g/L for four mangrove species (Avicennia officinalis, Heritiera fomes, Sonneratia apetala, Sonneratia caseolaris) to monitor water quality and to estimate how leaf litter influences shrimp post larvae (PL) growth and survival. There were significant differences (P < 0.05) between the studied species in terms of mass loss of the leaf litter during the investigation period. There were also significant differences (P < 0.05) between the studied species in terms of loss of nutrients and anti-nutrients in the shrimp PL rearing tank during the four-week experimental period. Decomposing mangrove leaves stimulated availability of natural food for shrimp PLs. There was a strong positive correlation between mass loss and PL production. At the concentrations of leaf litter used, the anti-nutritional factors did not affect the PLs. PL survival with mangrove leaf litter was 75–82%, whereas all the PL died without any leaf litter. PL weight gain ranged from 0.83–3.33 mg/d where S. apetala leaf litter resulted in the highest PL growth rate, followed by A. officinalis, S. caseolaris and H. fomes, in that order (P < 0.05). Overall, mangrove leaf litter had a positive effect on shrimp performance in terms of growth and survival and this effect was highest for S. apetala leaf litter.</p

Mangrove forest conservation vs shrimp production : Uncovering a sustainable co-management model and policy solution for mangrove greenbelt development in coastal Bangladesh.

Mangrove forests are remarkably diverse and productive ecosystems, with distinctive biophysical environments in intertidal coastal regions of the tropics and subtropics. In these regions, shrimp cultivation is identified as a profitable business and one of the main reasons for clearing of mangroves to construct shrimp farms. Against this backdrop and based on the first author's previous PhD research and other relevant scholarly works, in this commentary we discuss the aspects and contexts of the mangrove-based integrated shrimp farming system. Then, we recommend a model of co-management and a set of policy option towards sustainable silvo-aquaculture to protect/restore the mangrove forests and sustain shrimp production in coastal areas of Bangladesh. Mangrovesand shrimp culture are not necessarily incompatible. Many mangrove species have been identified as beneficial for shrimp culture for a number of possible reasons. Most importantly, the nutrients in the leaf litter of several mangrove species have been found to enhance natural food production for shrimp. Besides the nutrient input, the leaf litter also provides surface area for biofilm development, on which different life stages of shrimp can graze. In addition, the combination of mangrove leaf litter and feed has been shown to enhance shrimp productionsynergistically. Additional economic benefits from mangrove-shrimp co-management include the production of timber (e.g. buildings, boats and fuel woods) and non-timber products (e.g. fruits, honey, fibers, firewood, resinsand bark). Thus, mangrove-based aquaculture or silvo-aquaculture system can be considered as a nature-based solution to sustainably revitalize the economy in coastal areas where shrimp has been the economic mainstay. Though there are positive effects, we point out some potential negative impacts of mangrove-based shrimp culture, like the anti-nutrients content in the leaf litter, which might impact shrimp production. In addition, the long term use of mangrove leaf litter might degrade the water quality. Therefore, the co-management policyrecommends a controlled practice of mangroves in shrimp culture to balance conservation of mangrove-based ecology and profitable shrimp production. The approach promotes nature-based solutions and fosters sustain-able pathways for food production, considering socio-economic and environmental dynamic

Synergistic effects of mangrove leaf litter and supplemental feed on water quality, growth and survival of shrimp (Penaeus monodon, Fabricius, 1798) post larvae

Shrimp based mangrove-aquaculture (silvo-aquaculture) is practiced in many countries of the world and leaf litter of different mangrove tree species is a potential nutrient source in these systems. The present study evaluated the effects of mangrove leaf litter from four mangrove species (Sonneratia apetala, S. caseolaris, Avicennia officinalis and Heritiera fomes) on the production of juvenile shrimp (Penaeus monodon) with and without supplemental feed. Fifteen-day-old post larvae (PL15) with an average weight of 0.01 g were reared in 1100 L fibre-reinforced polyethylene tanks containing 1000 L of 10 ppt saline water and a water depth of 0.9 m. Leaf litter with or without supplemental feed was applied to the tanks according to a 4 × 2 factorial design. The PLs were stocked at a density of 100 per tank and the experiment was conducted for 4 weeks without any exchange of water. Both mangrove species and feed application affected shrimp performance and water quality parameters except dissolved oxygen (DO), chemical oxygen demand (COD) and zoo-plankton concentration. The average survival rate of juvenile shrimp ranged from 86 to 94% in the treatments with both leaf litter and feed, 75–82% in the treatments with only leaf litter and 88% in the treatment with only feed. However, 100% mortality was observed in the treatment without any leaf litter or supplemental feed. Combined, leaf litter and feed resulted in 21 to 33% higher weight gain of shrimp PL than based on the combined contributions of leaf litter only or feed only, indicating synergism. Among the different mangrove species, S. apetala (23.1%) contributed the highest to total weight gain followed by A. officinalis (21.6%), S. caseolaris (21.6%) and H. fomes (10%). The lower feed conversion ratio (FCR) (0.18–0.27) in the treatments combining leaf litter and supplemental feed as compared to the feed-only treatment (0.41) indicated that leaf litter (directly or by stimulating natural food production) contributed to supplemental feeding. The growth of phytoplankton also appeared to contribute in low FCR as evidenced by a positive correlation (P < 0.001, r = 0.681⁎⁎) between phytoplankton concentration and shrimp weight gain. The synergistic effect between leaf litter and supplemental feed can help the farmer to minimize the shrimp production cost by lowering the feed input and enhancing mangrove three coverage on pond dikes as an inexpensive source of natural food