Runoff, river, reef

Tuesday 4th October – Lucas and I got an early start this morning to drive from Mackay to Townsville for a 1pm meeting with environmental scientist Jon Brodie at James Cook University. Jon is the Chief Research Scientist, Centre for Tropical Water & Aquatic Ecosystem Research (TropWATER). He has a long list of research articles to his name and a trove of knowledge about “the sources of pollutants in catchments, transport of pollutants to the marine environment, the dispersal of land-based pollutants in coastal and marine environments and the effects of terrestrial pollutants on marine ecosystems”.

Jon Brodie and Lucas
Jon Brodie and Lucas at James Cook University, Townsville

What follows is my amateur understanding of Jon’s explanation of a complex environmental picture:

Jon is currently advising the Queensland Government on how to best spend the $700 million allocated to fix water quality in the Great Barrier Reef catchments. This money is coming from both Queensland and Federal Governments. In his view, this amount of money falls far short of what is needed – he estimates that $10 billion would fix water quality in 5 years. To date, remediations have had only minor success because successive governments target cheaper options rather than best solutions. One example of this is artificial wetlands, which are constructed with the aim of preventing sediment and fertiliser runoff. According to Jon, it has been proved that constructed wetlands simply don’t work, but they are being promoted because they’re a cheap option.

Different catchments have different primary environmental issues. In the Burdekin, Fitzroy and Normanby catchments, cattle grazing contributes to gully erosion and sediment runoff. In the Pioneer catchment (Mackay), sediment runoff is not such a great problem; the Number 1 issue in Mackay is fertiliser runoff, and the Number 2 issue is pesticide runoff. Pesticide runoff is fairly easily managed by targetted weed spraying instead of blanket spraying – “banded spraying” reduces pesticide losses by 90%. Urea (nitrate) fertiliser is the major runoff problem in the Pioneer catchment.

Jon says that cane farmers generally use too much fertiliser (in the belief that more is better). Farmers are using the biggest crop yields in the district as their benchmark, but what they need to be doing is fertilising for an average crop on their own farm. Less fertiliser means less nitrate runoff (10% of applied nitrogen is lost to the river). Mackay sugarcane farmers are currently using an average of 150kg of nitrogen per hectare annually. An A-class practice would be to reduce nitrogen use to 100kg per hectare – this is risky to crop yield (plants need nitrogen to grow). A safer bet would be to reduce nitrogen input to B-class practice (120kg per hectare). Jon thinks that a better strategy still could be to use slow-release fertiliser, which breaks down differently and requires less volume use (but is more expensive).

So, what is the problem with nitrate runoff from fertilisers?

1. Nitrogen fertilises the algae which larval Crown of Thorns starfish love to eat. The increase in nitrogen in the marine environment therefore creates ideal conditions for the Crown of Thorns to proliferate. Crown of Thorns eat coral. In normal populations, Crown of Thorns starfish help to keep a balance of coral varieties. In plague proportions during an outbreak however, they consume coral faster than it can grow. Scary Statistic #1: one female Crown of Thorns starfish can produce 60,000,000 eggs annually. Crown of Thorns starfish have been recorded to live up to eight years in aquaria.

2. Coral disease is partly caused by nitrogen inputs (and possibly phosphorus too – another fertiliser by-product in runoff).

3. Poor water quality (and hotter water) makes coral more susceptible to coral bleaching.

crown of thorns
Underbelly of Crown of Thorns starfish – Reef HQ Aquarium, Townsville

Jon acknowledges that farming strategies to improve soil health are also part of the solution eg. improving organic matter in the soil through methods such as ‘trash blanketing‘. This view supports the work that some of the sugarcane farmers we’ve met have been doing to improve soil health on their farms.

One final question I posed to Jon: what is the future of the Great Barrier Reef? His answer: at this rate, with the current national and international inaction on climate change, and with our continued expectations of a consumer lifestyle, the reef will not survive. It will be gone, replaced by nothing much. There’ll still be some fish and other animals and lots of seaweed, but little living coral. Is that what we’re all prepared to face? Maybe the future will see us looking at a memory of the Great Barrier Reef in an aquarium.

angelfish in Great Barrier Reef aquarium Townsville
Pomacanthus imperator (angelfish) – Reef HQ Aquarium, Townsville