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Wet Tropics

The Wet Tropics region covers 22,000 square kilometres. The category five Tropical Cyclone Yasi crossed the coast near Cardwell in February 2011, affecting about 13 per cent of the total reef.  The main agricultural land uses are grazing, sugarcane and horticulture. The 2013 risk assessment rated the Wet Tropics region as presenting a very high risk to water quality with the main pollutants being nitrogen and pesticides from sugarcane.

The Wet Tropics' marine condition declined from moderate to poor. Inshore water quality and seagrass meadows declined from moderate to poor and coral reefs have declined from good to moderate condition

Wet Tropics marine results

On this page:

Marine data (.csv, 1 KB)


Wet Tropics snapshot

Results—colour coding
Very goodGoodModerate
PoorVery Poor 

Management practices

Grazing Sugarcane Horticulture
Proportion of graziers who adopted improved practices between 2009 and 2011. Target: 50 per cent by 2013 Proportion of growers who adopted improved practices between 2009 and 2011. Target: 80 per cent by 2013 Proportion of producers who adopted improved practices between 2009 and 2011. Target: 80 per cent by 2013
Grazing 16% - Moderate result Sugarcane 37% - Good result Horticulture 24% - Moderate result

Catchment indicators

Groundcover Nitrogen Sediment Pesticides
Late dry season groundcover as at 2010-2011. Target: 50 per cent by 2013. Reduction in annual average total nitogren load between 2009 and 2011. Target: 50 per cent Reduction in annual average sediment load between 2009 and 2011. Target: 20 per cent by 2020 Reduction in annual average pesticide load between 2009 and 2011. Target: 50 per cent by 2013
Groundcover 95% - Very good result Nitrogen 4% - Poor result Sediment 3% - Good result Pesticides 10% - Moderate result

Management practices

Sugarcane

Sugarcane 37% - Good resultTarget: 80 per cent by 2013.
From 2009 to 2011, 37 per cent of sugarcane growers (501) adopted improved land management practices.

There are 1343 growers managing 1364 square kilometres of land in the Wet Tropics region.

By June 2011, cutting-edge (A) or best management (B) practice systems were used by 57 per cent of sugarcane growers for nutrients, 18 per cent for herbicides and 20 per cent for soil.

Graph data (.csv, 1KB)

Of the 501 growers who implemented improved practices, 289 completed Reef Rescue Water Quality Grants projects facilitated by Terrain Natural Resource Management:

  • 171 growers implemented improved nutrient management practices
  • 98 growers implemented improved herbicide management practices
  • 144 growers adopted improved soil management practices.

The remaining 212 growers were estimated to have progressed from D level nutrient management systems to C level nutrient management systems through a combination of concerted Reef Rescue program extension efforts from a range of sources (Terrain Natural Resource Management, BSES Ltd and local agronomic services providers) and the introduction of the Queensland Government’s regulations.

Grazing

Grazing 16% -  Moderate resultTarget: 50 per cent by 2013.
From 2009 to 2011, 16 per cent of graziers (152) adopted improved land management practices.

There are 935 graziers managing 6983 square kilometres of land in the Wet Tropics region.

By June 2011, 71 per cent of graziers were using (A or B) practice systems that are likely to maintain land in good to very good condition or improve land in lesser condition.

Graph data (.csv, 1KB)

Forty-four graziers who implemented improved practices completed Reef Rescue Water Quality Grants projects facilitated by Terrain Natural Resource Management. The Reef Rescue program directly supported a further 58 graziers to complete relevant training through the Queensland Government. An additional 50 graziers completed training in grazing management through private sector consultants with the support of the FarmReady program and through extension programs run by the Queensland Government.

Horticulture

Horticulture 24% - Moderate resultTarget: 80 per cent by 2013.
From 2009 to 2011, 24 per cent of horticulture producers (78) adopted improved land management practices.

There are 330 horticulture producers managing 198 square kilometres of land in the Wet Tropics region. Bananas are the dominant sector, with 250 growers accounting for nearly 60 per cent of this total area.

By June 2011, cutting-edge (A) or best management (B) systems were used by 60 per cent of horticulture producers for nutrients, 89 per cent for herbicides and 66 per cent for soil.

Graph data (.csv, 1KB)

All 78 horticulture producers who implemented improved land management practices did so with the support of Reef Rescue Water Quality Grants, facilitated by Terrain Natural Resource Management and the Growcom Farm Management System program. Of these, 58 completed nutrient management projects and 20 completed soil management projects.

Catchment indicators

Groundcover

Groundcover 95% - Very good resultTarget: 50 per cent by 2013.
Late dry season groundcover for the grazing lands of the Herbert catchment was high (95 per cent) in 2011. The 24-year mean groundcover was 88 per cent.

Groundcover results for the Herbert catchment (Wet Tropics region)
Catchment 24-year mean groundcover (%) 2011 mean groundcover (%) Area with less than 50% groundcover averages over past 24 years (%)> Area with less than 50% groundcover in 2011 (%)
Herbert (Wet Tropics Region) 88 95 0.9 0.3

Groundcover changes over time

The Herbert catchment had consistently high mean groundcover from 1988 to 2011 with a mean groundcover level of 88 per cent and a consistently low proportion of grazing lands under the Reef Plan target of 50 per cent groundcover. The minimum mean groundcover for the monitoring period was 76 per cent in 1988.

Graph data (.csv, 1KB)

The highest percentage of area with groundcover below 50 per cent was 3.2 per cent in 1994 and 1995.

Graph data (.csv, 1KB)

The Herbert catchment is the second wettest of the areas reported (1250 millimetres mean annual rainfall).

Graph data (.csv, 1KB)


Catchment pollutant loads

Nitrogen

Nitrogen 4% - Poor resultTarget: 50 per cent by 2013.
The estimated annual average total nitrogen load leaving catchments reduced by four per cent (263 tonnes). Agricultural fertiliser use is a key source of dissolved inorganic nitrogen and phosphorus. The estimated annual average dissolved inorganic nitrogen load leaving catchments reduced by 9 per cent (172 tonnes).

Phosphorus

Phorphorus 6% - Moderate resultTarget: 50 per cent by 2013.
The estimated annual average total phosphorus load leaving catchments reduced by six per cent (59 tonnes).

Pesticides

Pesticides 10% - Moderate resultTarget: 50 per cent by 2013.
The estimated annual average pesticide load leaving catchments reduced by 10 per cent (822 kilograms).

Sediment

Sediment 3% - Good resultTarget: 20 per cent by 2020.
The estimated annual average suspended sediment load leaving catchments reduced by three per cent (21,000 tonnes).

Graph data (.csv, 1KB)

Land management changes in the horticulture and dairy industries have not been modelled.


Marine

Water quality

Inshore water quality in the Wet Tropics region is poor overall and has varied from poor to moderate since 2005-2006, largely driven by total suspended sediment. Scores for chlorophyll a were consistently worse than suspended sediment in all monitoring years.

In 2010-2011, chlorophyll a was rated as very poor with concentrations exceeding the Great Barrier Reef Marine Park Water Quality Guideline for 99 and 63 per cent of the inshore area, in the dry and wet season, respectively. Total suspended solids were rated as good; however, concentrations exceeded the guidelines for 59 and 16 per cent of the inshore area, in the dry and wet seasons, respectively.

Remote sensing of water quality across the region showed a clear gradient of improving water quality from inshore areas more frequently exposed to flood waters to offshore areas.

Graph data (.csv, 1KB)

Site-specific water quality was rated as either good or very good at eight out of 11 sites in the region, three of which are located in the midshelf water body. However, water quality at the three sites close to river mouths draining from highly developed catchments was rated as poor due to high concentrations of particulate phosphorus, chlorophyll and turbidity that exceeded the Great Barrier Reef Marine Park Water Quality Guidelines in 2010-2011. The water quality scores are a long-term integrative assessment based on four indicators of water quality relative to the Great Barrier Reef Water Quality Guidelines (GBRMPA 2009b).

Map: Water quality and pesticide scores for PSII herbicides at fixed monitoring sites in the Wet Tropics region.

A range of herbicides were detected in the Wet Tropics region including diuron, atrazine and its breakdown products hexazinone, simazine and tebuthiuron. Diuron was present at the highest concentrations. Concentrations of photosystem II (PSII) herbicides were above those known to affect photosynthesis in diatoms (Category 4) at Green, Fitzroy and Normanby Islands. The highest PSII herbicide equivalent concentration in flood waters (Category 3) was detected in grab samples collected near the Tully River mouth and around Bedarra Island following a flow event.

Long-term monitoring of pesticides shows evidence of an increasing trend in the detection of herbicides at some sites in the Wet Tropics since 2005. In 2010-2011, the higher concentrations typical of the wet season were sustained for longer periods of time as evidenced by an increase in average PSII herbicide concentrations by 1.5 to 3.4 times.

Seagrass

The overall condition of inshore seagrass in the Wet Tropics region is poor and has been poor since 2005-2006. This is due to complex interactions between the three indicators of seagrass condition: abundance, reproductive effort and nutrient status which are highly variable between years and habitats. Cyclone Yasi had an impact on the south of the region with abundance and meadow extent declining until only a few isolated shoots remained.

Graph data (.csv, 1KB)

Inshore seagrass were monitored in coastal and reef habitats in the Wet Tropics and were in very poor or poor condition, respectively. Dominant influences on seagrass communities in the region include elevated temperatures, seasonal run-off and disturbance from wave action and associated sediment movement. In 2010-2011, seagrass meadows at Yule Point and Green Island in the north remained relatively stable. However, the effects of Cyclone Yasi were apparent in the south, and seagrass meadows at Lugger Bay and Dunk Island were either completely lost or reduced to scattered isolated shoots by the physical disturbance and deposition of sediments. The reproductive effort of inshore seagrass in the Wet Tropics was very poor in five of the six monitoring years which may indicate a low potential of meadows to recover from disturbances. Leaf tissue nutrient ratios were rated poor overall with a site in the north showing signs of light limitation and poor water quality.

Graph data (.csv, 2KB)

Graph data (.csv, 1KB)

Graph data (.csv, 1KB)

Graph data (.csv, 1KB)

Coral

The overall condition of inshore coral reefs in the Wet Tropics remained moderate; however, there were differences between northern and southern parts of the region and the underlying scores decreased markedly from 2010. Coral reef communities in the Barron Daintree and Johnstone Russell-Mulgrave areas in the northern Wet Tropics were downgraded from good to moderate condition, while those in the more southerly Herbert Tully area were in poor condition.

Graph data (.csv, 1KB)

Coral cover of inshore reefs in the Wet Tropics varied with reefs in the north in better condition than those in the south. Prior to 2010-2011, coral communities were recovering from the impact of past disturbances; however, Cyclones Tasha and Yasi had a negative impact on coral cover and the density of juvenile corals across the region.

Average cover of hard corals, cover of macroalgae and density of hard coral juveniles in the Wet Tropics region from 2005 to 2011.

Graph data (.csv, 1KB)

Graph data (.csv, 1KB)

Graph data (.csv, 1KB)

Coral cover at sites in the Barron to Daintree area remained very good. However, coral cover at reefs in the Johnstone Russell-Mulgrave area declined to moderate condition as a result of acute disturbances from cyclones Tasha and Yasi. Macroalgae cover was higher at some locations in 2010-2011 and the density of coral juveniles declined to very poor. Coral disease also contributed to declines in coral cover and the moderate condition assessment of reefs in the northern Wet Tropics.

In contrast, coral cover in the Herbert Tully area was still very poor, reflecting the severity of Cyclone Larry in 2006 and Cyclone Yasi in 2011 and the subsequent negative impacts on the density of juvenile corals. As well as reducing coral cover, Cyclone Yasi also reduced the cover of macroalgae resulting in a good score overall for the Wet Tropics region. However, macroalgae cover is likely to increase rapidly as occurred following Cyclone Larry. Reefs in the region were recovering at a moderate rate prior to the extreme weather of 2010-2011, which may indicate some resilience to disturbance and a capacity for recovery.

Last updated:
27 August, 2014
Last reviewed:
4 December, 2013

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