Trace Elements in the Sediment of Waikato West Coast Estuaries. Technical Report
- Rumsby, A.
- Journal / Source
- Environment Waikato
- In 2008, as part of the regional estuary monitoring programme, EW undertook testing of the levels of trace elements and organic compounds in sediments of the inter-tidal sand and mudflats from five sites in Whaingaroa (Raglan) Harbour, 19 sites in Port Waikato, nine sites in Aotea Harbour and seven sites in Kawhia Harbour. Analysis undertaken by Pattle Delamore Partners Ltd. Findings: Aotea Harbour: The concentration of trace elements tended to be more elevated in sediments near river mouths than in sediments found in the centre of the harbour or near the harbour mouth. The concentrations of most trace elements were at the lower end of the estimated natural range (as represented by regional soil concentrations) and no trace elements within the sediments were present in concentrations which exceed the ANZECC (2000) ISQG-low guideline values. Trace quantities of hexachlorobenzene were detected in two composite sediment samples, and trace quantities of one polycyclic aromatic hydrocarbon (phenathrene) was detected in one composite sediment sample. All polycyclic aromatic hydrocarbons (PAHs) and organochlorine compounds were below the ANZECC (2000) ISQG-low guideline values. Overall, the sample results show little evidence of anthropogenic effects on the sediment quality of Aotea Harbour. Kawhia Harbour: The concentration of trace elements appeared to be more elevated in sediments near river mouths compared to sediments found in the centre of the harbour or near the harbour mouth. With the exception of arsenic near Kawhia Township, the concentrations of most trace elements were at the lower end of the estimated natural range and no trace elements within the sediments were present in concentrations which exceed the ANZECC (2000) ISQG-low guideline values. The geometric mean concentration of most trace elements was either similar or only slightly higher in Kawhia Harbour than in Aotea Harbour, but the differences for the most part were not statistically significant. The highest concentrations of PAHs were detected near Kawhia township. PAHs were detected in all other composite samples except for samples collected near the harbour mouth. However, the concentrations of PAHs that were detected were below the ANZECC (2000) ISQG-low guideline value. The ratio of anthracene to phenanthrene suggests that these PAHs were formed by petroleum combustion process (e.g. emissions from motor vehicles exhaust). Overall, anthropogenic effects may have resulted in the sediments in Kawhia Harbour being slightly enriched with some trace elements and organic compounds. However the concentrations that have been measured are all below ANZECC sediment quality guidelines (ANZECC,2000). Raglan Harbour: The concentrations of most trace elements were at the lower end of their estimated natural ranges, and no trace elements within the sediments were present in concentrations which exceed the ANZECC (2000) ISQG-low guideline values. The concentrations of trace elements tended to be higher in the samples collected in the southern part of the harbour than in samples from elsewhere in the harbour. Trace quantities of some PAHs (fluoranthrene, phenathrene and pyrene) were detected in the composite sample collected from around Ponganui Creek. This sample is the closest to Raglan township of all samples collected. The PAH results may indicate a minor effect from the township. No organochlorine pesticide residues were detected in Raglan Harbour. Port Waikato: Sediment quality at Port Waikato. In general, the particle size of sediment at Port Waikato was either medium or coarse grain sands. Port Waikato had the coarsest grain sediments of the four estuaries. The concentration of arsenic exceeds the ANZECC (2000) ISQG-low guideline value at most sampling locations but does not exceed the ANZZECC (2000) ISQG-high guideline values. Therefore the detected concentrations may pose a low-to-moderate risk to aquatic organism such as benthic macroinvertebrate communities. The concentration of most trace elements (except for arsenic, antimony and caesium) were within their expected natural background ranges in most samples. It is likely that arsenic, antimony and caesium are elevated at Port Waikato due to the geothermal inputs into the Waikato River. The concentrations of some trace elements (As, B, Ca, Li, Sb and Zn) were elevated in the samples which had the highest percentage of fine particles (less than 63 µm) and may exceed the estimated background concentrations. The distribution of trace elements and nutrients at Port Waikato appears to be strongly correlated to the grain size of the sediments. Trace quantities of dieldrin and hexachlorobenzene were detected at one sampling location. The concentration of dieldrin exceeded ANZECC (2000) ISQG-low guideline value. However the detection limit of the analytical method used to measure organochlorine pesticide residues was higher than the ANZECC (2000) ISQG-low guideline value for dieldrin, and therefore it cannot be concluded that dieldrin did not exceed the guideline for the samples in which dieldrin was not detected. Several PAH compounds were detected at a number of different locations. The ratio of PAHs in the samples suggest combustion processes as the source of these PAHs, however it is unclear from the PAH ratios whether coal/biomass combustion or petroleum combustion (e.g. car exhausts) is the primary source of the PAHs. Purpose: This report provides a description of the sediment quality of four west coast estuaries (Aotea Harbour, Kawhia Harbour, Raglan Harbour and the river mouth of Port Waikato) as well as the water quality of the Waikato River at Port Waikato. Environment Waikato (EW) engaged Pattle Delamore Partners Limited (PDP) to prepare the report based on the results of water and sediment sampling of the estuaries undertaken by EW in 2008. EW commissioned PDP to carry out this project with the following objectives: To compare the concentrations of the various water and sediment sampling parameters with expected background concentrations, and to identify and discuss any levels of enrichment. To compare the results against water and sediment quality guidelines (ANZECC, 2000) where they exist. To comment on the significance of any trace organic compounds detected, their possible sources and future trends in their levels in the environment. To comment on whether there are any discernible spatial trends observed within the concentration data. For the six water samples at Port Waikato, comment on the possible significance of the estrogenic compound results and microbiological load in respect of potential impacts upon marine mammals, in particular upon Maui’s dolphins using the river mouth
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