Veliidae from Black Jackie pond on Mulloon Creek. [Photo: Dr Paul Cooper, ANU]

Dr Paul Cooper from the Australian National University has now completed analysing the aquatic macroinvertebrates survey data collected in 2019-20, after Covid restrictions delayed earlier identification efforts in the lab.

The survey forms part of the ongoing monitoring for the Mulloon Rehydration Initiative, where the Mulloon Institute is working with 23 landholders in the Southern Tablelands of NSW to rebuild the natural landscape function of the Mulloon catchment and boost its resilience to climatic extremes. This will result in more reliable stream flows, improved ecosystem functioning and enhanced agricultural productivity. Crucial to the MRI is the development and implementation of a comprehensive Integrated Monitoring Plan.

Keeping in mind that the data was collected during the final year of an extreme drought (2017 – Jan 2020), the results are not overly surprising. We had expected the macroinvertebrates to reflect the drop in water quality and quantity (flow) due to the drought conditions, but where leaky weirs were already installed and had been in for longer, there was not as much a drop in principal component analysis. This analysis evaluates and interprets the relationship between water quality and macroinvertebrates and has remained steady between 2015-16 and 2019-2020 at sites where the leaky weirs had already been installed.

Conditions were quite extreme during the drought period and the drop in aquatic macroinvertebrates showed that the ecosystem was really struggling, but the creek didn’t go dry where the leaky weirs were installed, giving the aquatic macroinvertebrates and other creatures somewhere to live while they waited for conditions to improve. Without these remnant pools in place the survey would have been sampling dry creek bed where no aquatic macroinvertebrates could live!

Two Hydroptilidae from Black Jackie pond on Mulloon Creek. [Photo: Dr Paul Cooper, ANU]

Six survey sites were chosen along Mulloon Creek, with invertebrates collected by sweep nets as the creek had no water flow. Monthly samples looked at water temperature, dissolved oxygen, conductivity, pH and water flow.

Overall, 8992 aquatic macroinvertebrates were identified, falling into 30 different taxa. The highest number of individual aquatic macroinvertebrates collected came from Peter’s Pond while Triple Ponds and Reedy Creek had the most diverse taxa collected.

With no water flow in the creek and all the ponds isolated during the survey because of the drought, results revealed that the species which dominated were those that did best when water was not flowing.

The survey suggested that it would be beneficial to see more overhanging vegetation in the riparian zone, to help protect and enliven water conditions. The presence of leaves, wood and rocks contribute to aquatic macroinvertebrate diversity, and various functional groups (e.g. shredders and grazers) use the wood and leaves from surrounding overhanging plants to enhance biodiversity in the creek. The MRI is actively planting native trees, shrubs and vegetation along the creek to help boost this diversity.

Following the recent amazing wet period that has recharged the system over the last two years, we look forward to the next monitoring survey reflecting good results and showing whether the macroinvertebrate populations have really improved or recovered after the end of the drought.

The Mulloon Rehydration Initiative is jointly funded through the Mulloon Institute and the Australian Government’s National Landcare Program. It is also supported by the NSW Government through its Environmental Trust.