Nutrient Source Evaluation using Stable Isotopes

We used the natural abundance of stable isotopes to trace nitrogen inputs to Belongil Creek from a wastewater treatment plant, a piggery and a poultry processing plant. This allowed us to evaluate the important contributors to nutrient enrichment of the Belongil Creek.

Skennars Head Wastewater. Client: Ballina Shire Council
Wastewater from the Skennar Head treatment plant is discharged into the ocean at Skennars Head, but it cannot be detected using traditional water quality monitoring due to rapid dilution in the ocean. We undertook a survey of natural abundance stable isotope signatures in algae and snails along the rocky shores adjacent to the wastewater discharge to determine the extent of the wastewater plume. δ15N values showed that there was clear uptake of wastewater-derived nitrogen by algae and that this nitrogen was passed to first- and second-order consumers (grazing and carnivorous snails, respectively). Enriched δ15N values were found in all algal and consumer species within 10m of the discharge point and remained enriched, relative to control values, up to 150m away from this point. We are undertaking further work to determine if use of the wastewater nitrogen is impacting on the ecological communities.
Client outcome: This study provided our client with information about the extent of the influence of the wastewater plume. Future monitoring of stable isotopes will determine how much wastewater nitrogen is being used by the ecological communities along the rocky shores, allowing our client to evaluate the effectiveness of current wastewater treatment upgrades.

Macleay Arm Client: Kempsey Shire Council
Septic tank seepage had long been suggested as a possible source of nutrients to the Macleay Arm, but this could not be demonstrated using traditional water quality monitoring techniques. We undertook a survey of natural abundance stable isotope signatures in seagrass to determine in septic tank effluent was be being biologically used along the Macleay Arm. The technique uses the ratio of 15N to 14N in dried plant material, compared to a worldwide standard, to determine the delta 15N in the plant. As sewage effluent decomposes in the septic tank bacteria have a preference towards 14N over 15N, making the effluent enriched in 15N. When plants such as seagrass utilize this sewage nitrogen they become enriched in15N resulting in a distinct 15N signature in these plants.
Client Outcome: This study identified septic tanks as a possible source of nutrients entering the Macleay Arm allowing out clients to take action to manage this problem.

Lower Richmond River Client: Ballina Shire Council
Wastewater from the West Ballina treatment plant is discharged into Fisheries Creek. Stable isotope signatures of seagrass, mangroves and sediments were used to trace the extent of nitrogen in the effluent plume.
Client outcome: This study provided our client with information about the extent of the influence of the wastewater plume. Future monitoring of stable isotopes will determine how much wastewater nitrogen is being used by the ecological communities in the lower Richmond River, allowing our client to evaluate the effectiveness of current wastewater treatment upgrades.

Belongil Creek Piggery Effluent Client: Byron Shire Council
We used the natural abundance of stable isotopes to trace nitrogen inputs to Belongil Creek from a wastewater treatment plant, a piggery and a poultry processing plant. This allowed us to evaluate the important contributors to nutrient enrichment of the Belongil Creek.
Client outcome: This study allowed our client to identify the sources of nutrients entering Belongil Creek so management actions could be undertaken to decrease loads.

Updated: 16 December 2010