Carsten Matthai

EFFICIENCY OF A CONSTRUCTED WETLAND IN REMOVING CONTAMINANTS FROM STORMWATER

As in most large capital cities, urban stormwater discharging into Port Jackson (Sydney) is highly enriched in a wide range of contaminants, which has resulted in degradation of the receiving basin waters and bottom sediments. The objective of the current investigation was to determine the removal efficiency of contaminants in urban stormwater by a wetland constructed in the Sydney catchment. The wetland (700 m2) drains a residential urban catchment of about 480,000 m2 comprising predominantly houses, streets, gardens, and street parking areas. Samples of stormwater influent and effluent were obtained during rainfall events between April and June 2000. Eight samples were collected at the inlet and outlet to the wetland during each event and analyzed for nutrients, trace metals, total suspended solids (TSS), and organochlorine pesticides and polycyclic aromatic hydrocarbons (PAHs). Water quality parameters (temperature, dissolved oxygen, pH, turbidity, conductivity) were measured concurrently. The average removal efficiency of trace metals Cr, Cu, Pb, Ni, and Zn was 64%, 65%, 65%, 22%, and 52%, respectively for the six events measured, whereas for Fe and Mn, removal efficiencies were negative for most events (mean—84% and—294%, respectively). The average removal efficiency of NOx and TN was 22% and 16%, respectively. The average removal efficiencies of total Kjeldahl nitrogen (TKN) and total phosphorus (TP) were 9% and 12%, respectively. During four high-flow events, the removal efficiency of TSS in stormwater effluent from the wetland was between 9% and 46%; however, substantially higher TSS concentrations were observed in effluent than influent waters during two very high-flow events (removal efficiency—98% and—67%). Fecal coliform counts in the stormwater in this catchment are high (maximum: 620,000 cfu/100 ml), but mean removal efficiency was 76% (range 26% to 98%) during the four high-flow events monitored. Nevertheless, most samples from the outflow exceeded the Public Health criterion for secondary contact (e.g., boating) of 1000 cfu/100 ml. Concentrations of organochlorine pesticides and PAHs in stormwater were below analytical detection. Although highly variable, lower concentrations of Cr, Cu, Ni, Pb, Zn, NOx, TN, and fecal coliform in the stormwater effluent compared to influent waters indicates that the wetland was moderately efficient in removing contaminants from urban stormwater.

Detection of anthropogenic Cu, Pb and Zn in continental shelf sediments off Sydney, Australia--a new approach using normalization with cobalt.

Concentrations of Co, Cu, Pb and Zn were determined in 107 surficial sediment samples from the continental margin adjacent to Sydney, Australia. The spatial distributions of trace metals in the sediments and the mud content are similar and increase with greater distance from the coast. In contrast, normalization of the concentrations of Cu, Pb and Zn in the total sediment with Co enables a coastal anthropogenic source to be identified. The spatial distribution of Co-normalized concentrations of Cu, Pb and Zn in total sediment is similar to the distribution of these trace metals in the fine fraction of sediment (<62.5 microm), indicating that Co may be used as a normalizing element for determining contaminant sources in the marine environment near Sydney.

Anthropogenic trace metals in sediment and settling particulate matter on a high-energy continental shelf (Sydney, Australia)

The anthropogenic contribution of trace metals to settling particulate matter (SPM) and surficial sediments was determined on the high-energy continental shelf adjacent to Sydney, Australia. Settling particulate matter and surficial sediment was collected in the vicinity of a major sewage outfall and at five control sites on the middle shelf (80-100 m water depth). Sediment traps were deployed on 10 occasions for up to 2 weeks during the summer and winter of 1995 and SPM was analyzed for Ag, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn. Cobalt, Fe, Mn and Ni act conservatively in SPM and in sediments regionally and are used as normalizing elements to determine anthropogenic enrichment. Surficial sediments and SPM are enriched in Ag, Cr, Cu, Pb and Zn near a major ocean outfall and at four of the five control sites, although sewage particles contribute < 5% of trace metals in the total sample. Silver is the most sensitive trace metal tracer for establishing the presence of sewage particulate matter. Sewage particulate matter flux near the outfall was estimated using a two end-member mixing model and is below 0.5 g m(-2) day(-1) during all deployment periods. The mean sewage particulate matter flux at sampling locations 30 km and 60 km north of the outfall are <0.13 g m(-2) day(-1) and <0.01 g m(-2) day(-1), respectively, indicating an efficient dispersal of anthropogenic material on this high energy continental shelf.

Trace metals and organochlorines in sediments near a major ocean outfall on a high energy continental margin (Sydney, Australia)

Sewage effluent from a large ocean outfall south of Sydney, southeastern Australia, is efficiently dispersed on this high energy continental margin. An enrichment of Ag, Cu, Pb and Zn is only detectable in the fine fraction (<62.5 microm) of sediment. Ag, Co, Cu, Ni, Pb and Zn in the bulk sample correlate strongly with the mud content of surficial sediment, making an identification of the anthropogenic trace metal source difficult using total sediment analyses. The concentrations of HCB and DDE in the total sediment are also slightly elevated near the outfall. In the vicinity of the outfall, the estimated sewage component in the fine fraction of sediment, using Ag, Cu and Zn in a conservative, two-endmember physical mixing model, is <5% and is <0.25% of the total sediment. A greater anthropogenic Pb component in the fine fraction (mean: 24.8%) of surficial sediment compared to Ag, Cu and Zn may suggest a source other than sewage to Sydney continental margin sediments.

Efficiency of a retention/detention basin to removecontaminants from urban stormwater

Retention/detention basins are commonly used to remediate runoff from road surfaces in an attempt to remove contaminants before these materials enter adjacent waterways. However, the efficiency of such devices in removing contaminants is not well known, especially for Australian conditions. The efficiency of a retention/detention device adjacent to a major motorway in Sydney (Australia) was assessed for total suspended solids (TSS), a suite of trace metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn), nutrients (TP, TKN, NOx, TN) and faecal coliforms. The mean removal efficiency of Cu, Pb, Mn and Zn was 23, 41, 43 and 41%, respectively, whereas the mean reduction in Cr, Fe and Ni concentrations was only 0, 3 and 1%, respectively. TSS in stormwater entering the retention/detention basin was highly variable resulting in large variations in removal efficiencies (range: −12 to 93%; mean: 40%). The mean removal efficiency of Kjeldahl nitrogen (TKN) and total nitrogen (TN) was high (56 and 28%, respectively) in contrast to total NOx and total phosphorus (TP) (−42 and −5%, respectively). Faecal coliform was low to very low (<5000 cfu/100 ml) and removal efficiency was 16 to 68%. Possible leaching of fine terrigenous particles from the gravel bed of the retention/detention basin may have contributed to the increase in Cr, Fe and Ni concentrations in effluent stormwater.

Physical resuspension and vertical mixing of sediments on a high energy continental margin (Sydney, Australia).

Four sediment cores from the continental margin adjacent to Sydney were analyzed for 210Pb, 137Cs, trace metals (Ag, Cd, Co, Cu, Mn, Ni, Pb, Zn), iron, dry bulk density, mud and moisture content. The concentrations of trace metals in the total sediment are low at all sites, although slightly elevated concentrations of Ag, Cu, Pb and Zn are present in the fine fraction of sediment (< 62.5 microns) near a major ocean outfall. Concentrations of trace metals in the fine fraction of sediment are similar in the upper 10-15 cm, indicating strong vertical mixing of the sediments, whereas an upward coarsening grain size in the upper 1-3 cm of sediment supports physical resuspension during storms. Sediment accumulation rates on the middle shelf adjacent to Sydney were estimated from downcore profiles of 210Pb and 137Cs and range between 0.2 and 0.4 cm yr-1. Although the mass fluxes of Cu, Pb and Zn within a distance of 2 km from the outfall (up to 36.1, 30.8 and 86.2 micrograms cm-2 yr-1, respectively) are greater than 20 km north of the outfall (< 23.5 micrograms cm-2 yr-1), the low concentrations of trace metals in sediments near the outfall support an efficient dispersal of anthropogenic contaminants on this continental margin.

The Effect of Grain Size and Element Concentration in Identifying Contaminant Sources

The distribution of metal contaminants between different size fractions of marine sediments is well known. However, the use of size normalization techniques may alter the ability or usefulness in identifying potential sources in complex environments. In a reassessment of metal data from the shelf area of Sydney, Australia, the mud and sand fractions were investigated separately by PCA and PLS methodologies. The analyses were able to produce clear distinctions between industrial/urban sources when based on a suite of metals rather than individual (single-element) concentrations. Signature analysis by PLS with copper, lead, zinc, manganese, chromium, cobalt, nickel, and cadmium demonstrated the dispersion of the fine-grained contaminated material to the south in the East Australian Current. However, due to the commonality between many of the metals, a subset of four metals was used to define the signature. This significantly improved separation, showing clear plumes extending ∼30 km from the source rivers.

Efficiency of a continuous deflective separation (CDS) unit in removing contaminants from urban stormwater

The weighted average concentration (WAC) of total suspended solids (TSS) in stormwater effluent from a continuous deflective separation (CDS) unit in Port Jackson (Australia) catchment was reduced by an average 28% during six high-flow events, but some TSS was released during turbulent, high-flow events. The average removal efficiency of metals Cr, Cu, Pb Mn, Ni, Zn and Fe varied considerably (−49% for Pb and +10% for Mn), whereas Ni and Zn were inefficiently removed by the device. Average concentrations of TKN, NOx and TP were similar at both in- and out-flow points and faecal coliforms counts were slightly reduced.