Margaret Greenway

Metal Accumulation in Aquatic Macrophytes from Southeast Queensland, Australia

To determine the extent of metal accumulation in some aquatic macrophytes from contaminated urban streams in southeast Queensland, plants were sampled from six sites, along with contiguous sediments. In all, 15 different species were collected, the most common genera being Typha (Cattails or Bulrushes) and Persicaria (Knotweeds). Before heavy metal analysis, plants were further separated into various morphological tissues, and five selected samples were separated into various physiological tissues. The cadmium, copper, lead and zinc content of the plants were analysed using flames AAS. In general, plant roots exhibited higher metal concentrations than the contiguous sediments. Of the metals of interest, only for zinc was there a relatively clear pattern of increasing accumulation in aquatic macrophytes with increasing sediment metal concentrations. Comparison between morphological tissues of the sampled plants found that roots consistently presented higher metal concentrations than either the stems or leaves, however unlike previous studies, this investigation revealed no consistent trend of stems accumulating more metals than the leaves. For Typha spp., metal concentrations followed the order of roots > rhizomes > leaves, while for Persicaria spp. the order was roots > leaves > stems. The submerged species Myriophyllum aquaticum accumulated the highest levels of metals overall (e.g. Zn 4300 micrograms g-1 dry weight and Cd 6.5 micrograms g-1), and the emergent macrophytes also exhibited relatively high metal contents in their roots. The leaves of the submerged and floating-leafed species collected contained relatively high quantities of the four metals of interest, compared with the leaves of emergent aquatic macrophytes. In the Typha rhizome and Persicaria stem samples analysed for internal variation in metal content, there was a pattern of increasing metal concentrations towards the external sections of the stem, both for subterranean stems (rhizomes) and above-substrate stems. For Persicaria stems, no clear pattern was observed for cadmium and lead, the two metals investigated that are not required by plants for survival.

Constructed wetlands in Queensland: Performance efficiency and nutrient bioaccumulation

Abstract Nine pilot wetlands (eight free water surface and one subsurface flow) have been constructed in Queensland as joint projects between the State and Local Governments, to treat municipal wastewater. The wetlands are in several geographical locations which include tropical, subtropical and arid climates. Each wetland is a different configuration and contains a variety of macrophyte types and species. Most species are native and were collected in the locality or self colonised. This paper examines the performance efficiency of the wetlands and nutrient bioaccumulation in wetland plants. Biochemical oxygen demand concentrations were reduced by 17–89% and suspended solids concentrations by 14–77% to produce wetland effluent with BOD less than 12 mg l−1 and suspended solids less than 22 mg l−1. Reduction in total nitrogen concentrations ranged from 18 to 86%, ammonia nitrogen from 8 to 95% and oxidised nitrogen from 55 to 98%, producing effluent with total nitrogen between 1.6 and 18 mg l−1. Reduction in reactive phosphorus concentration was less than 13% in the free water surface systems with concentration in the effluent exceeding the influent in many of the systems over long term operation. In contrast reduction through the single household subsurface system was 65%. Nutrient bioaccumulation was investigated in 60 species. Submerged (Ceratophyllum) and free floating species (duckweed) had the highest tissue nutrient concentrations, followed by the waterlily (Nymphoides indica), aquatic vines (Ipomoea spp., Ludwigia peploides), and waterferns (Ceratopteris, Marsilea). All these species remove nutrients from the water column. Emergent species had lower nutrient concentrations with the highest nutrients occurring in the exotic sedge Cyperus involucratus. Aquatic grasses including Phragmites had higher nutrient content than the sedges. Nitrogen concentrations were higher in leaf/stem tissue compared to the root/rhizome, whereas phosphorus was higher in root/rhizome tissue. Emergent species had a greater biomass than submerged or free floating species and were therefore able to store more nutrients per unit area of wetland. Cropping the shoots of emergent species increased nutrient content in new shoot growth.

Phosphorus Retention by Bioretention Mesocosms Using Media Formulated for Phosphorus Sorption: Response to Accelerated Loads

Recent research indicates that phosphorus (P) retention by bioretention systems comprising sandy media may not be effective for even a decade of urban runoff loads. To improve P retention for longer durations, this paper present findings from bioretention mesocosms using media amended with red mud (RM), a by-product of bauxite processing; water treatment residuals (WTRs), a by-product of water treatment; or Krasnozem soil (K), a highly aggregated clay soil. All treatments were vegetated except for one (K20nv). All treatments had outlets to restrict outflows except for one (WTR-Knr). To simulate the effect of long-term nutrient loads, the mesocosms were loaded weekly with secondary treated effluent with P concentrations averaging 3.3  mg-L-1. Over 80 weeks, this comprised hydraulic loads from 24.5 to 29.3  m-year-1 at a flow-weighted average between 2.8 and 3.2  mg-L-1 PO4-P, or mass loads from 1,115 to 1,284  kg-ha-1 PO4-P. These cumulative P loads represent the equivalent of over three decades of runoff ...

Nutrient content of wetland plants in constructed wetlands receiving municipal effluent in tropical Australia

Several pilot wetlands have been constructed in Queensland to treat municipal wastewater. The wetlands are in tropical, subtropical and arid geographical locations. Most wetlands are free water surface and contain a variety of macrophyte types and species. A total of 49 native and 11 exotic species of wetland plants have been identified. This paper examines tissue nutrient content in different species and plant components from 7 wetlands. Most species translocated to the constructed wetlands flourished indicating their ability to tolerate nutrient enriched waters, and tended to have higher tissue nutrient concentrations than their controls in natural wetlands. Submerged and free floating species exhibited higher nutrient concentrations than floating leaved and emergent species. Maximum dry weight nutrient concentrations (mg.g −1 ) were recorded in duckweed 18 mgP.g −1 ; 58 mgN.g −1 ; Ceratophyllum 14 mgP.g −1 , 35 mgN.g −1 ; Monochoria cyanea (a native relative of the water hyacinth) 13 mgP.g −1 , 30 mgN.g −1 ; waterlilies: Nymphoides indica 16 mgP.g −1 , 40 mgN.g −1 ; aquatic vines Ipomoea diamantinensis 10 mgP.g −1 , 53 mgN.g −1 , I. aquatica 9.5 mgP.g −1 , 53 mgN.g −1 ; Ludwigia peploides 10 mgP.g −1 , 52 mgN.g −1 ; and the water ferns Ceratopteris thalictroides 10 mgP.g −1 , 31 mgN.g −1 , Marsilea 10 mgP.g −1 , 43 mgN.g −1 . Emergent species with the highest nutrients (P or N) were Eleocharis sphacelata 9.4 mgP.g −1 , 31.7 mgN.g −1 , Baumea articulata 8.7 mgP.g −1 , 24 mgN.g −1 , Typha domingensis 7.2 mgP.g −1 , 51.8 mgN.g −1 and Cyperus involucratus 7 mgP.g −1 , 44.6 mgN.g −1 . Pooled data showed no significant difference between tissue nutrient content in plant components, though nitrogen was highest in the leaves and phosphorus highest in the roots of most species. There was some evidence of spatial variation in tissue nutrient content between different wetlands but it has not been possible to correlate this with nutrient loadings or removal efficiencies.

Phosphorus removal from secondary sewage and septage using sand media amended with biochar in constructed wetland mesocosms

To improve the performance efficiency of subsurface constructed wetlands (CWs), a variety of media have been tested. Recently, there has been a rising interest in biochar. This research aims to develop the effectiveness of sand media amended with biochar and two plants species (Melaleuca quinquenervia and Cymbopogon citratus) in removing phosphorus from sewage effluent in CWs. The experimental design consisted of vertical flow (VF) mesocosms with seven media treatments based on the proportions of biochar in the sand media which ranged from 0 to 25% by volume. During the first 8months, the mesocosms were loaded with secondary clarified wastewater (SCW) then septage was used for the remaining 8months. Inflow and outflow were monitored for total phosphorus (TP) and PO4-P. Plants were harvested at the end of the experiment and TP biomass was determined. Removal efficiencies of TP in the mesocosms loaded with SCW and septage ranged from 42 to 91% and 30 to 83%, respectively. Removal efficiencies of PO4-P ranged from 43 to -92% and 35 to 85% for SCW and septage, respectively. The results revealed that the sand media performed better than the biochar-amended media; increasing the proportion of biochar in the media decreased removal efficiency of phosphorus. However, after flushing due to major rain event, there was no significant difference between sand and sand augmented with 20% biochar. Total plant P ranged from 1.75g in the 20% biochar mesocosm to 2.10g in the sand only mesocosm. Plant uptake of P, at least in part, may be accredited for the better P removal efficiency in the sand media compared to the biochar-amended media.

Halophila tricostata (hydrocharitaceae), a new species of seagrass from the great barrier reef region

Abstract A new species of the seagrass Halophila, H. tricostata, is described from Lizard Island, Great Barrier Reef; it has been placed in a new section: Tricostatae.

An investigation into the effectiveness of sand media amended with biochar to remove BOD5, suspended solids and coliforms using wetland mesocosms.

Constructed wetland ecotechnologies (CWEs) are a promising solution to effectively treat domestic wastewater in developing countries at low cost. This paper reports the findings of the effectiveness of sand media amended with woody biochar and two plants species (Melaleuca quinquenervia and Cymbopogon citratus) in removing biological oxygen demand (BOD5), suspended solids and coliforms. The experimental design consisted of 21 vertical flow (VF) mesocosms. There were seven media treatments using sand amended with varying proportions of biochar. During the first 8 months, the mesocosms were loaded with secondary clarified wastewater (SCW) then septage. The influent had a 4-day hydraulic retention time. Samples were monitored for BOD5, total suspended solids (TSS), total volatile solids (TVS), total coliforms and faecal coliforms. In the first 8 months, there were no significant performance differences between media treatments in the outflow concentrations of BOD5, TSS and TVS. The significant differences occurred during the last 3 months; using septage with biochar additions performed better than pure sand. For coliforms, the significant differences occurred after 6 months. In conclusion, the addition of biochar was not effective for SCW. The VF mesocosms system proved to be more effective in removing BOD5, TSS, TVS and coliforms when septage was loaded into the media.

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

ABSTRACTSeagrass 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.

CONSTRUCTED WETLANDS FOR SEWAGE EFFLUENT TREATMENT AND MOSQUITO LARVAE AT TWO SITES IN SUBTROPICAL AUSTRALIA

ABSTRACT This study of 2 wetlands in subtropical Australia, constructed to treat sewage effluent, examined the relationships between dips positive for mosquito larvae and water quality, operational status of the system, vegetation, and nontarget macroinvertebrates. One site is inland and the other is close to the coast. Larvae of disease vector mosquitoes were present at various times in the wetlands, especially in summer and autumn. The proportion of early instars (1st and 2nd) was greater than that of later ones (3rd and 4th). Dissolved oxygen was negatively, and temperature was positively, associated with the proportion of dips containing larvae. For the coastal site we noted that larvae were more common during draw-down of water for maintenance and also as the system started to come online. Vegetation associated with larvae included dense Typha orientalis and algae. Where there were several types of plants, such as at the coastal site, plant density and water depth were not significantly related to larval presence. Where there were several types of macroinvertebrates there were fewer dips positive for larvae. To provide water treatment capacity and minimal mosquito production we concluded that design should include a variety of plant types, discouraging low dissolved oxygen (for example, by aeration) and ongoing maintenance should be carried out in winter or spring, when mosquitoes are fewer than in summer.

Use of phytocaps in remediation of closed landfills - correct selection of soil materials

AbstractPhytocapping is an emerging technology gaining interest as an alternate capping sys-tem in the management of closed landfills, particularly where leachate production occurs primarily through groundwater intrusion rather than surface infiltration. A field trial was undertaken at a former putrescible landfill to compare the performance of a phytocap and an engineered cap. The engineered cap comprised compacted subsoil, overlain by a gravel drainage layer, overlain by sandy clay loam topsoil. The phytocap comprised a layer of topsoil only. A range of native trees, shrubs and grasses were planted into each cap, and irrigated daily with landfill leachate of varying strength (0, 40 or 100%). Laboratory and field-testing evaluated the effect of leachate on soil physical and chemical properties. Deterioration in the topsoil’s hydraulic properties impaired lea-chate infiltration and encouraged surface erosion for both systems. Laboratory studies found that aggregate instability due to slumping was the major cause for the decline in soil hydraulic properties. The topsoil sorbed appreciable amounts of added ammonium, organic nitrogen and organic carbon, and transformed much of the added ammonium to nitrate within a 14-day period. Thus, the capping system has the potential to remove leachate contaminants if the hydraulic properties of the topsoil can be improved. The trial has shown the importance of correct testing prior to selecting soil materials for use in capping systems where infiltration of leachate and rainwater is encouraged rather than discouraged.Key words: nitrogen, carbon, phytocap, phytoremediation, landfill leachate, capping systems