A study of hydraulic dynamics in vegetated and non-vegetated biorention mesocosms

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732Bioretention systems are stormwater treatment devices installed to remove both dissolved and particulate pollutants. As stormwater percolates through the bioretention system, dissolved pollutants are removed from solution by chemical and biological processes. In our study, 20 bioretention mesocosms (10 with loamy sand and 10 with sandy loam, half with and half without vegetation) were used to investigate hydraulic behavior. The mesocosms were dosed with 120L to 160L synthetic stormwater over 3h to 5h. The infiltration and percolation rates in the sand was rapid (>15 cm-h-1), while rates in the loam were much less (2-3 cm-h-1). Retention time in the sand was 1.5h while that in the loam was well over 10h. Vegetated systems had better percolation rates than the non-vegetated systems. Constriction of outlets rapidly affected infiltration rates. The infiltration and percolation response of the bioretention systems was evaluated in terms of the Green-Ampt equation, as affected by soil properties and vegetation. Implications for the design of bioretention facilities are then discussed

A study of hydraulic dynamics in vegetated and non-vegetated biorention mesocosms

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732Bioretention systems are stormwater treatment devices installed to remove both dissolved and particulate pollutants. As stormwater percolates through the bioretention system, dissolved pollutants are removed from solution by chemical and biological processes. In our study, 20 bioretention mesocosms (10 with loamy sand and 10 with sandy loam, half with and half without vegetation) were used to investigate hydraulic behavior. The mesocosms were dosed with 120L to 160L synthetic stormwater over 3h to 5h. The infiltration and percolation rates in the sand was rapid (>15 cm-h-1), while rates in the loam were much less (2-3 cm-h-1). Retention time in the sand was 1.5h while that in the loam was well over 10h. Vegetated systems had better percolation rates than the non-vegetated systems. Constriction of outlets rapidly affected infiltration rates. The infiltration and percolation response of the bioretention systems was evaluated in terms of the Green-Ampt equation, as affected by soil properties and vegetation. Implications for the design of bioretention facilities are then discussed

Carbon isotope discrimination in leaves of the common paperbark tree, Melaleuca quinquenervia, as a tool for quantifying past tropical and subtropical rainfall

Quantitative reconstructions of terrestrial climate are highly sought after but rare, particularly in Australia. Carbon isotope discrimination in plant leaves (Δleaf) is an established indicator of past hydroclimate because the fractionation of carbon isotopes during photosynthesis is strongly influenced by water stress. Leaves of the evergreen tree Melaleuca quinquenervia have been recovered from the sediments of some perched lakes on North Stradbroke and Fraser Islands, south-east Queensland, eastern Australia. Here, we examine the potential for using M. quinquenervia ∆leaf as a tracer of past rainfall by analysing carbon isotope ratios (δ13C) of modern leaves. We firstly assess Δleaf variation at the leaf and stand scale and find no systematic pattern within leaves or between leaves due to their position on the tree. We then examine the relationships between climate and Δleaf for an 11 year timeseries of leaves collected in a litter tray. M. quinquenervia retains its leaves for 1-4 years; thus cumulative average climate data are used. There is a significant relationship between annual mean ∆leaf and mean annual rainfall of the hydrological year for 1-4 years (i.e. 365-1460 days) prior to leaf fall (r2=0.64, p=0.003, n=11). This relationship is marginally improved by accounting for the effect of pCO2 on discrimination (r2=0.67, p=0.002, n=11). The correlation between rainfall and Δleaf, and the natural distribution of Melaleuca quinquenervia around wetlands of eastern Australia, Papua New Guinea and New Caledonia offers significant potential to infer past rainfall on a wide range of spatial and temporal scales

REST Regulates Distinct Transcriptional Networks in Embryonic and Neural Stem Cells

The maintenance of pluripotency and specification of cellular lineages during embryonic development are controlled by transcriptional regulatory networks, which coordinate specific sets of genes through both activation and repression. The transcriptional repressor RE1-silencing transcription factor (REST) plays important but distinct regulatory roles in embryonic (ESC) and neural (NSC) stem cells. We investigated how these distinct biological roles are effected at a genomic level. We present integrated, comparative genome- and transcriptome-wide analyses of transcriptional networks governed by REST in mouse ESC and NSC. The REST recruitment profile has dual components: a developmentally independent core that is common to ESC, NSC, and differentiated cells; and a large, ESC-specific set of target genes. In ESC, the REST regulatory network is highly integrated into that of pluripotency factors Oct4-Sox2-Nanog. We propose that an extensive, pluripotency-specific recruitment profile lends REST a key role in the maintenance of the ESC phenotype

The hydraulic efficiency of fringing versus banded vegetation in constructed wetlands

This paper describes a numerical model study that has been undertaken to investigate the effects of emergent fringing and banded vegetation on the hydraulic characteristics of constructed wetlands. The model study demonstrates that poorly designed wetlands with inappropriate layout of wetland vegetation can result in a significant reduction in the hydraulic efficiency of the wetland system. An empirical relationship is developed between the vegetation characteristics, the wetland shape and the hydraulic efficiency of the system. The relationship developed allows wetland designers and managers to combine computationally simple continuously stirred tank reactor models of the wetland system with long-term hydrologic analysis to determine the impacts of different design strategies. This relationship also indicates that the hydraulic efficiency will not be significantly influenced by the length-to-width ratio for heavily vegetated wetlands where short-circuiting occurs. The aim of the study has been to aid designers of constructed wetlands by developing a qualitative understanding of the hydraulic effects of wetland vegetation and wetland shape on the hydraulic efficiency of the system

Seagrasses in tropical Australia, productive and abundant for decades decimated overnight

Seagrass ecosystems provide unique coastal habitats critical to the life cycle of many species. Seagrasses are a major store of organic carbon. While seagrasses are globally threatened and in decline, in Cairns Harbour, Queensland, on the tropical east coast of Australia, they have flourished. We assessed seagrass distribution in Cairns Harbour between 1953 and 2012 from historical aerial photographs, Google map satellite images, existing reports and our own surveys of their distribution. Seasonal seagrass physiology was assessed through gross primary production, respiration and photosynthetic characteristics of three seagrass species, Cymodocea serrulata, Thalassia hemprichii and Zostera muelleri. At the higher water temperatures of summer, respiration rates increased in all three species, as did their maximum rates of photosynthesis. All three seagrasses achieved maximum rates of photosynthesis at low tide and when they were exposed. For nearly six decades there was little change in seagrass distribution in Cairns Harbour. This was most likely because the seagrasses were able to achieve sufficient light for growth during intertidal and low tide periods. With historical data of seagrass distribution and measures of species production and respiration, could seagrass survival in a changing climate be predicted? Based on physiology, our results predicted the continued maintenance of the Cairns Harbour seagrasses, although one species was more susceptible to thermal disturbance. However, in 2011 an unforeseen episodic disturbance - Tropical Cyclone Yasi - and associated floods lead to the complete and catastrophic loss of all the seagrasses in Cairns Harbour

Photosynthetic characteristics of seagrasses (Cymodocea serrulate, Thalassia hemprichii and Zostera capricorni) in a low-light environment, with a comparison of leaf-marking and lacunal-gas measurements of productivity

We describe the photosynthetic characteristics of three seagrasses and the relationship between their production and natural light intensities (photosynthesis-irradiance response, i.e. PI curves). Seagrass production (gross production minus shoot respiration) was measured in the field by the rate of gas release from the lacunal space of whole seagrass shoots and compared with net leaf production. Field work was carried out on the seagrasses Cymodocea serrulata (R. Br.) Aschers. and Magnus, Thalassia hemprichii (Ehrenb.) Aschers., and Zostera capricornia Aschers. in the turbid, warm waters of Cairns Harbour, Queensland, Australia. The photosynthetic efficiencies (the initial slope of the PI curves) of all of the seagrass species were 10 times greater than any previously measured for the same species in higher-light environments. The high compensating light intensities (80-92 µE m s) showed that the plants have high respiration rates that were probably due to the high water temperatures (29-33°C) of the harbour. The seagrasses responded to small increases of light at low light intensities by rapidly reaching saturating light intensities, and the maximum rates of production were between 0-4 and 0-6 mg C h shoot. The average period of exposure to saturating light intensity was 2 h day. One-quarter of the gross production was lost to plant respiration. The net productivity and respiration of all three seagrasses was calculated from this photoperiod. Net leaf production in situ compared well with the seagrass production estimates that were measured with the lacunal-gas technique. Most of the production appeared to be allocated to the above-ground tissue, a feature consistent with seagrasses growing in low-light and terrigenous sediments

Artificial wetlands for wastewater treatment, water reuse and wildlife in Queensland, Australia

Queensland, Australia has a subtropical-tropical climate with dry winters and wet monsoonal summers. Arid climatic conditions prevail inland with hot dry days and cold nights. The climatic conditions are conducive to high plant growth rates and hence offer great potential for constructed wetlands for water pollution control. The water (a scarce resource during the dry season and in arid regions) can also be used to irrigate crops, playing fields, parks and gardens or golf courses. The water discharged from the wetlands is also of an acceptable quality to flow into estuarine and riverine environments. Many natural wetlands are only seasonally inundated and during the dry season wildlife has to seek alternative refuges. Artificial wetlands receiving sewage effluent provide permanent wildlife habitats and improve the landscape amenity. The Queensland government's Department of Primary Industries has initiated an Artificial Wetlands for Water Pollution Research Program. Under this scheme 10 experimental pilot artificial wetlands have been established and a further 6 university research projects are being conducted on various aspects of artificial wetlands including nutrient and heavy metal uptake and bioavailability in wetland plants, sediment biogeochemistry and mass balances. One gold mine rehabilitation project has an artificial wetland to treat mine leachate. This paper presents 3 case studies which include significant results with respect to wastewater polishing and re-use