Performance monitoring of constructed floating wetlands: Treating stormwater runoff during the construction phase of an urban residential development.

In the context of climate change and global trend towards greenfield urbanisation, stormwater and transported pollutants are expected to increase, impairing receiving environments. Constructed floating wetlands (CFWs) can improve stormwater retention pond performance. However, performance data are currently largely restricted to mesocosm experiments, limiting design enhancement fit for field implementation. The present 12-month field study aims to fill part of these gaps by identifying limitations and necessary design improvements for CFWs on a large retention pond/lake. Water in a 2.6-ha lake receiving stormwater from a 45-ha urban area under development in subtropical Queensland, Australia, was recirculated during dry weather periods to minimise algal growth and the risks of blooms. Pollutant removal efficiencies of two full-scale CFWs were evaluated during storm events and dry weather periods as a function of inlet and outlet pollutant concentrations, flow and rainfall. Inlet TSS and TN concentrations in runoff during the construction phase of the development exceeded required water quality limits while TP inflow concentrations were low and often below the detection limit. Median pollutant load reduction efficiencies during storm-events were - 20 % TSS, -2 % TN and 22 % TP at CFW1 and 51 % TSS, 3 % TN and 17 % TP at CFW2, respectively. TSS and TN concentration removal efficiencies at CFW1 were low and highly variable, partly due to low inlet concentrations, high flow velocities and short hydraulic retention times (<1 day). However, CFW1 significantly reduced TSS concentrations during dry weather periods. In contrast, CFW2 significantly reduced TSS concentrations during both storm events and during inter-event periods. This study highlights treatment limitations associated to the operational conditions of CFWs at field-scale not identifiable in a mesocosm-scale study. Further research is necessary to investigate treatment performance of CFWs during the operational phase of the development with higher nutrient levels.

Rapid plant responses following relocation of a constructed floating wetland from a construction site into an urban stormwater retention pond.

This study compared plant growth, nutrient partitioning and total nutrient uptake by tall sedge (Carex appressa) plants in large-scale Constructed Floating Wetlands (CFWs). Two CFWs with a total area of 2088 m2 were installed in a 2.6 ha man-made urban lake to treat stormwater runoff during the construction phase of a 45-ha residential development. After 12 months of operation, parts of the CFWs, with a total area of 147 m2, were removed from the urban lake and relocated into a well-established 0.127-ha stormwater retention pond at another site. Biomass and nutrient concentrations of C. appressa shoots above the floating mat and roots below the mat were analysed at both sites 12, 16 and 25 months after initial planting. Plants at the urban lake maintained an extensive root network but there was no increase in total plant biomass at 16 and 25 months after planting. In contrast, the relocated plants in the stormwater pond showed extensive shoot growth but a significant decline in root biomass. C. appressa at the urban lake removed and sequestered 1.00 ±â€¯1.04 g m-2 N, 0.11 ±â€¯0.07 g m-2 P and 1.03 ±â€¯0.81 g m-2 K while plants at the pond removed 11.20 ±â€¯2.29 g m-2 N, 1.37 ±â€¯0.26 g m-2 P and 16.13 ±â€¯2.88 g m-2 K during 12 and 25 months after planting. This study demonstrated that C. appressa adapted rapidly to changes in nutrient availability. The implications are interesting as nutrient levels can be low in constructed lakes during the initial phase of urban developments but can increase rapidly as the development progresses. The study demonstrated multiple benefits of CFWs for stormwater treatment during the early construction stages of an urban development and the potential benefits of relocating and establishing CFWs in existing stormwater retention ponds and lakes.

Reforestation of agricultural land in the tropics: The relative contribution of soil, living biomass and debris pools to carbon sequestration.

Tropical regions of the world experience high rates of land-use change and this has a major influence on terrestrial carbon (C) pools and the global C cycle. We assessed land-use change from agriculture to reforested plantings (with endemic species), up to 33 years of age, using 10 paired sites in the wet tropics, Australia. We determined the impacts on 0-50 cm below-ground C (soil organic C (SOC), charcoal C, humic organic C, particulate organic C, resistant organic C), C stored in roots (fine and coarse), C stored in living above-ground biomass and debris C pools. Reforested areas accumulated ecosystem C at a rate of 7.4 Mg ha-1 yr-1. Reforestation plantings contained, on average, 2.3 times more ecosystem C than agricultural areas (102 Mg ha-1 and 233 Mg ha-1, respectively). Most of the C accumulation was in living above-ground and below-ground biomass (60 and 30%, respectively) with a smaller amount in debris pools (16%). Apart from C in roots, soil C accumulation was not obvious across sites ranging from 8 to 33 years since reforestation, relative to the agricultural baseline. Differences in SOC (and associated SOC pools) to a depth of 50 cm, did exist between reforested areas and adjacent agriculture at some sites, however there was not a consistent trend in SOC associated with reforestation. Local site-based factors (e.g. soil texture and mineralogy, land-use history and microbial activity) appear to have a strong influence on the direction of the change in SOC. While reforestation in the tropics has great potential to accumulate C in biomass in living vegetation, and debris pools, it is likely to take approximately 50 years before C stocks of reforested areas resemble natural ecosystems. Accumulation of SOC through reforestation is difficult to achieve, highlighting the need to conserve carbon pools in remnant forests in the tropics.

Evaluation of pathogen removal in a solar sludge drying facility using microbial indicators.

South East Queensland is one of the fastest growing regions in Australia with a correspondingly rapid increase in sewage production. In response, local councils are investing in more effective and sustainable options for the treatment and reuse of domestic and industrial effluents. A novel, evaporative solar dryer system has been installed on the Sunshine Coast to convert sewage sludge into a drier, usable form of biosolids through solar radiation exposure resulting in decreased moisture concentration and pathogen reduction. Solar-dried biosolids were analyzed for selected pathogenic microbial, metal and organic contaminants at the end of different drying cycles in a collaborative study conducted with the Regional Council. Although fecal coliforms were found to be present, enteroviruses, parasites, E. coli, and Salmonella sp. were not detected in the final product. However, elevated levels of zinc and copper were still present which restricted public use of the biosolids. Dilution of the dried biosolids with green waste as well as composting of the biosolids is likely to lead to the production of an environmentally safe, Class A end-product.