As some in the community may be aware there have been a number of trees that have been dying in the Jetty Foreshore area.
Effects first came to Council’s notice following a period of high rainfall associated with king tides a few months ago. High rainfall often results in a raising of the water table. The considered theory was that a raised water table combined with king tides bringing sea water right up into the upper reaches of the drainage channels resulted in a contamination of the water table with sea water (sodium chloride) and therefore those plants that had their roots into areas where the water table rose/spread, were taking up contaminated water high in chloride and sodium.
Meetings have been held on site with Jetty Dunecare, Crown Lands, the State Park Trust and Council staff.
Staff have taken leaf samples of the dying trees and had them tested for salt toxicity. Results of leaf samples from affected plants tested for salt levels have revealed:
- 3,350 mg/kg (or mg/L) of Soluble Chloride. Plants are significantly affected at levels above 1000 mg/kg (mg/L), so 3,350 is significantly high (toxic)
- 1,700 mg/kg (mg/L) of Sodium which is also significantly high. Greater than 600 mg/kg (mg'/L) for highly salt tolerant plants will have a significant impact. At 1700 mg/kg (mg/L) the levels will be highly toxic to salt tolerant plants
These results indicate the cause of decline in the plants affected is chloride & sodium toxicity from sea water mixing with a high water table as a result of high rainfall.
Council has also tested for herbicides such as glyphosate, AMPA (results less than 0.5mg/kg), Atrazine, Hexazinone, Trifluralin, and some 8 other herbicides (results all less than 0.1mg/kg). If poisoning by herbicide was the cause these results would show levels in double figures.
Leaf samples were collected from an area south of the central car park north to the end of affected vegetation. Some 20 + leaf samples were taken from 8 different species showing signs of affect and the test results are from these combined samples hence the recording being labeled “composite”. Photos of the dying plants were taken in March; Council is also plotting the location of the dying trees and has arranged for aerial photos of the foreshore to be taken.
To ensure there are no other issues further tests will be undertaken for:
1. Control sample of healthy leaves for salt levels (comparision)
2. Four other herbicides - Triclopyr & Picloram (Grazon), Metsulfuron-methyl (Brush-Off)& Fluroxpyr-methyl (Starane)
As we know there have been claims made by some groups that herbicides have been responsible for the plants decline. No Council herbiciding has taken place in the locality and staff could find no obvious evidence of herbicides having been used. Visual effects of herbicide vs salt toxicity is not dissimilar to the lay person.
The situation, based on the scientific testing, appears to be an act of nature in this particular area. No evidence has been provided to contest this understanding.
The situation presents a typical catch 22. The more salt (Chloride/Sodium) that accumulates in the soil from a natural occurrence, the more energy plants use to gain water via their roots. This use of energy by the plant takes away from the energy it would use to live and grow and where the salt level exceed a harm level to the plant it is adversely affected as we are witnessing at present. This effect happens over time as we are witnessing (two months).
Excess salt levels can be reduced by irrigation (leaching). In the natural area this can be by rainfall. But as we have seen rainfall can cause a rise in the water table. If this occurs combined with 'low peak' high tides leaching may take place. If prolonged rainfall occurs combined with 'peak' high tides, sodium chloride contamination of the water table may occur again.
The natural event of water table contamination with sea water (sodium chloride) and its affect on vegetation is still playing out and it is too early to predict if all plants affected will eventually die. Some already have (Coastal Banksia) while others are a typical autumnal tone of yellow at present (Three veined laurel).
Council will monitor the situation and address hazards to the public from trees that die in areas the public access. As this is a natural phenomenon, Council is not planning to replant the trees but let nature takes its course. Council will continue to work with groups such as Jetty Dunecare to ensure weeds are kept down in the foreshore area.
Jetty Foreshore Leaf Sample
Report of Analysis