Lake Tomorata
This recreationally used humic stained lake is surrounded by extensive wetlands and is the only one of its kind in the Auckland region.
It is home to a population of black mudfish, bittern and fairy tern which are threatened/endangered species in New Zealand. This lake is considered culturally and ecologically significant and has a rich biodiversity of at-risk native fauna and flora.
Our efforts at this site focus on high frequency water quality monitoring, pest fish incursion, wetland extent, macrophyte establishment and wider catchment management. We are working with local communities, Iwi and the Auckland Council to monitor ecosystem health and develop a biodiversity restoration plan.
How it started
Lake Tomarata has always been an an interest of ours and as a result of our findings at Lake Rototoa and Pupuke we wanted to see if this lake is experiencing similar issues.
We know the lake is now completely devoid of submerged vegetation and that pest fish are an ever increasing issue. The impacts of these factors and the regular use of motorized craft has not been comprehensively assessed so we set out to establish a baseline ecological assessment.
Through our initial exploratory dives we began to see familiar signs of environmental deterioration.
The Auckland Council has a project that is focusing on the ecological effects of pest fish at Lake Tomarata which presented the perfect opportunity to design a collaborative project that would encompass wider ecosystem health. The over arching goal of this project will be to create a well informed biodiversity restoration plan.
Project overview
This project encompasses several aspects of lake health and is made up of a series of targeted studies, each with their own set of outcomes.
The investigations are centered around the following specific aspects of lake ecosystem health:
Water quality
Freshwater mussel surveys
Impacts of pest fish & management
Macrophyte establishment/restoration potential
Wetland habitat & extent monitoring
Overall ecosystem health & restoration
The outcomes from all these targeted investigations will be used to draft a collaborative lake restoration plan focused on restoring native biodiversity values back to this precious lake.
Targeted Studies
Dissolved oxygen, temperature & pH sensors
Water Quality
We have installed continuous water quality sensors at every meter throughout the water column.
These sensors measure temperature, dissolved oxygen and pH every 15 minutes. These sensors will be deployed for 12 months and the data will provide an understanding of the daily and seasonal water quality fluctuations at various depths.
We will also be using the lab data from the councils monthly water samples, this data will be used to calculate the annual and seasonal nutrient state of the lake.
Mature freshwater mussel
Freshwater Mussels
We recently discovered live mussel beds in the lake and are aiming to survey 3 - 4 representative sites over the year.
These mussels are key indicator species of lake health and provide crucial ecosystem functions necessary to maintain a healthy dune lake.
Freshwater mussels are in decline across the country and Lake Tomarata in the fourth lake in which we are surveying these threatened species.
Common bully under threat from pest fish
Pest Fish
We are providing survey support for an Auckland Council run project working on establishing pest fish management techniques.
Coarse fish are a common pest in most North Island lakes. These fish are more aggressive than our native species and often out compete them for resources and habitat. The lake is home to one of the last remaining populations of threatened black mudfish in Auckland which emphasizes the need for effective pest management.
These fish can drastically alter a lake ecosystem and are one of the biggest concerns at Lake Tomarata.
Lake bed devoid of macrophytes
Macrophytes
The lake once had extensive macrophyte beds and is now completely devoid of submerged vegetation.
We have installed photosynthetically active radiation (PAR) sensors at every meter through the water column to assess seasonal light availability at various depths. This in combination with the water quality data will allow us to understand what environmental factors are limiting macrophyte establishment.
Macrophytes play a critical role in maintaining lake health and the essential for any restorative success at Lake Tomarata.
Drone used for wetland mapping
Wetland Extent
The lake is surrounded by a one of the last large lacustrine wetlands in the region. These wetlands are extremely rare in Auckland and provide habitat for a variety of threatened species including fairy tern, bittern and black mudfish.
The effects of climate change, eutrophication, sedimentation and water abstraction are causing increasing pressures on this valuable wetland.
We are using areal imagery and drones to map the wetland extent and track habitat loss through time.
Mussel & habitat survey
Ecosystem Health
All of the targeted studies provide a piece of the puzzle and we will be using water quality, ecology and meteorology data to model lake dynamics.
This model will be the platform on which we can test various ecosystem management scenarios and develop an effective set of restoration tools.