Characterisation, potential toxicity and fate of storm water run-off from log storage areas of the Port of Tauranga.

Abstract

Stormwater run-off from industrial sources can impact the receiving environment by the discharge of toxic substances, nutrients, sediments or fresh water (in marine environments). The Port of Tauranga is New Zealand’s largest by cargo volume with untreated logs being one of the major exports. The port stores logs totalling up to 300,000 m3 with an average residency time of 18 days. Runoff from log storage areas can cause toxicity to aquatic life due to low pH, high organic solids content and associated BOD, and chemicals leached from timber such as resin acids. Metals and PAH’s from heavy vehicles and other machinery can also be present. At the port, stormwater collects from the storage areas into slot drains and is screened for larger particulates in screening chambers before discharging into Tauranga Harbour. Large rainfall events produce a visible, highly coloured plume extending across the main harbour channel. This study looks at compounds within the stormwater runoff and associated marine water samples and the toxicology of the effluent. It then focusses on the gradients of compounds found in sediments and biota in relation to the main discharge sources. This is followed with a more specific investigation of the bioaccumulation of resin acids in resident and transplanted mussels. It concludes with a comparison of low intertidal species assemblages within and outside the influence of the stormwater plume. Findings indicate that there are high levels of wood derived chemicals in the stormwater runoff and a gradient of quantities of these can be detected in nearby sediments, decreasing with distance from the discharge point of the effluent. Those compounds, such as metals, able to be quantified against national and international guidelines were well within acceptable levels. Others, such as resin acids, were found in lower quantities than in a previous study. A correlation between organics related to leachate from the logs, inorganic compounds found in the effluent and sediment grain size, indicates that some elements of the runoff may reach further into the harbour. The influence of dredging and disturbance of the seabed by shipping movements is considered in relation to this. Levels of organic compounds, related to the log storage in transplanted mussel populations, were not detected spatially or temporally and no evidence of bio-accumulation of resin acids was found. Based on the combined findings there are very low detectable effects on the marine environment from the runoff of the Port of Tauranga log storage areas. These come in the form of a gradient in chemical compounds related to the runoff and are well within the ANZECC (2000) Interim Guideline Levels. This study adds to the limited knowledge on log storage runoff into the marine environment and incorporates elements which can be applied to many areas of research related to stormwater discharge. It uses the Port of Tauranga runoff as a relevant example of issues and environmental responses related to urban and industrial stormwater runoff.