|Page tools: Print Page Print All RSS Search this Product|
SECTION 3 LANDSCAPE
The ABS has produced land accounts for the GBR Region using the SEEA framework (Land Account: Great Barrier Reef Region, Experimental Estimates (cat. no. 4609.0.55.001)), although the Cape York NRM Region was excluded from those accounts. Table 3.1 below presents data on the opening and closing stocks of land cover in the GBR Region, including net changes.
TABLE 3.1. DYNAMIC LAND COVER, GREAT BARRIER REEF REGION, 2008-09 and 2010-11, Area (hectares)
In 2008-09, Trees-Sparse accounted for 12.4 million hectares of all land cover in the GBR Region. Trees-Open is the second largest type of dynamic land cover at 9.9 million hectares, followed by Tussock Grasses-Closed at 8.5 million hectares. Trees-Sparse reported a net decrease of 3.4 million hectares between 2008-09 and 2010-11, from a total of 12.4 to nine million hectares. This was the largest decrease of any land cover type in the GBR Region. The change was driven by an increase of 3.5 million hectares in the Trees-Open category, making it the most abundant type of land cover in 2010-11.
Suspended solids, nitrogen, phosphorous and photosystem II (PSII) inhibiting herbicides have all been shown to effect negatively the quality of marine environments and represent important indicators on the influence of land based activities on the downstream marine environment. Suspended solids, nitrogen and phosphorous are all naturally occurring river loads, although PSII inhibiting herbicides are of anthropogenic origin. The yield condition provides 'natural state' or ideal reference condition context to the load numbers reported in the tables below.
This section presents load data for indicative river systems for the GBR Region, and as yields of load per square kilometre of catchment compared to a reference condition by NRM Region over the period 2006-07 to 2011-12. Tables 3.2 and 3.3 below provide annual estimates for three types of annual loads: total suspended solids (TSS); total nitrogen (TN); and total phosphorous (TP). Table 3 also provides estimates of PSII inhibiting herbicides (pesticides) for the last two years of the time series; namely, 2010-11 and 2011-12.
TABLE 3.2: RIVER LOADS BY TYPE, BY NRM REGION, GREAT BARRIER REEF REGION, 2006-07 to 2011-12, Weight ('000 tonnes and tonnes)
Table 3.2 above shows that the total amount of river loads varies significantly between consecutive years in the majority of NRM Regions. A key reason for this volatility is the effect of rainfall and subsequent volume of river flow. For example, the 2010-11 flood events in Queensland increased river loads across all NRM Regions. There was a threefold increase in total suspended solids between 2009-10 and 2010-11 for the total GBR Region, and an even larger increase in total nitrogen and total phosphates in the same period. Loads, however, returned to pre-flood levels by 2011-12 in most regions.
The yield for each selected river basin was compared to the estimated pre-European yield in order to measure loads in the context of condition (see Kroon et al.,2012). It is an example of a reference condition not based upon accounting period considerations, but upon the notion of 'a condition reflecting an ecosystem which is relatively undisturbed or undegraded by humans' (SEEA Experimental Ecosystem Accounting, 2012, para. 4.16). This type of measure relates more to the condition of the landscape, its use and its ability to stabilise mass (or mitigate erosion), than to the physical form of the rivers. The resultant data shows how much the landscape has been functionally changed in this respect since European settlement.
The measure remains greatly influenced by rainfall and volume of river flow, but the size of catchment controlled as yield is measured in kilograms, or tonnes per square kilometre of catchment. Table 3.3 below presents yields of total suspended solids, total nitrogen and total phosphorous indexed to the pre-European reference condition. There were no pesticides present before European settlement, and, therefore, it is not possible to construct an index for this measure.
TABLE 3.3: RIVER BASIN YIELD CONDITION, BY NRM REGION, GREAT BARRIER REEF REGION, by Type of Load, 2006-07 to 2011-12, Index (Pre-European Settlement = 100)
Table 3.3 above shows that there is considerable variance in the condition of selected rivers in the GBR Region. The selected river basin yields in the Cape York and Burnett Mary NRM Regions are closer to the reference condition in 2011-12 than other regions. There is a decrease of 49 per cent in the Cape York NRM Region in yield of total suspended solids relative to pre-European yields, and a decrease of 85 per cent in the Burnett Mary NRM Region of the same yield. In 2010-11, all yields were significantly increased by very heavy rainfall (including total suspended solids), to 300 per cent of the pre-European yield in the Cape York NRM Region, and by 2,600 per cent in the Burnett Mary NRM Region.
Increases in yield have been observed for the majority of measures each year in areas between the Cape York and Burnett Mary NRM Regions. The Fitzroy and Burnett Mary NRM Regions recorded the highest index value of all measures in 2010-11 (11,000), when both regions recorded a total phosphorous yield 110 times the pre-European condition. Total phosphorous in the Fitzroy NRM Region recorded the highest index value in 2011-12, with a yield nineteen times (1,900) that of the pre-European condition (100).
NET PRIMARY PRODUCTIVITY
Net primary productivity (NPP) is defined as the net flux of carbon from the atmosphere into green plants per unit time. It is a fundamental ecological variable. It not only measures the energy input into the biosphere and terrestrial carbon dioxide assimilation, but also indicates the condition of the land surface area and the status of a wide range of ecological processes.
NPP is used in this information paper as an indicator for the 'vegetation' characteristic of terrestrial condition. The term 'net' refers to the balance (over time) between the rate of gain of carbon in leaves, stems, and roots by photosynthesis (known as gross primary productivity or GPP) and the rate of loss of biomass via respiration. It is positive in cases where the photosynthetic rate exceeds the respiration rate and negative where the respiration rate exceeds the photosynthetic rate.
The NPP estimates reported in this release are produced from the BIOS2 model developed by the CSIRO.
NPP is also applicable to marine areas, but an analysis of those areas has not been undertaken as part of this release. There are a range of possible derivation methods for estimating changes in area of seagrass, coral and mangrove but the required time series data are not available. Chlorophyll concentration is used in some derivation methods to measure marine NPP, and is included in the water quality indicator in the Seascape section.
Table 3.4 below shows the total amount of NPP in kilotonnes of carbon for each NRM Region for the period, 2000-01 to 2012-13.
TABLE 3.4: NET PRIMARY PRODUCTIVITY, BY NRM REGION, GREAT BARRIER REEF REGION, 2000-01 to 2012-13, Carbon ('000 tonnes)
The GBR Region recorded a small decrease from 291,939 kilotonnes to 289,670 kilotonnes (or 0.8 per cent) between 2000-01 and 2012-13. Variation across years is very large, with a low of 206,696 kilotonnes in 2004-05 (a drought year), and a high of 393,321 kilotonnes in 2010-11 (a high rainfall year).
The Cape York NRM Region recorded a 2.1 per cent decrease over the period, 2000-01 to 2012-13; the Wet Tropics NRM Region recorded a smaller decrease of 1.3 per cent. The Burdekin NRM Region recorded the largest decrease both in percentage and absolute terms, by assimilating 11,888 kilotonnes less in 2012-13 than in 2000-01 (or 13.9 per cent).
Figure 3.1 below highlights the impact of variable rainfall. This map shows the differences in net primary productivity across the terrestrial area of the GBR Region between the very dry year, 2002-03 and the very wet year, 2010-11. The coastal area of Burdekin NRM Region and the inland area of Fitzroy NRM Region show some of the greatest variations in NPP between the two years.
FIGURE 3.1: NET PRIMARY PRODUCTIVITY (NPP), GREAT BARRIER REEF REGION, 2002-03 to 2012-13, Percentage Change (%)
The indicator used to measure vegetation condition is mean grams of carbon assimilated per square metre per day (g C/ m2 / day). Table 3.5 below shows the index values for each NRM Region in the GBR Region.
TABLE 3.5: VEGETATION CONDITION, BY NRM TERRESTRIAL REGION, GREAT BARRIER REEF REGION, 2000-01 to 2011-12, Index (2000-01 = 100)
There are large differences between NRM Regions in terms of the amount of carbon assimilated per square metre. For example, the Mackay Whitsunday NRM Region assimilated more than twice the carbon per square metre than the Burdekin NRM Region in 2000-01. On the one hand, the vegetation condition of the Burnett Mary NRM Region has improved by 25 per cent over the reference period, and the Fitzroy NRM Region by 12 per cent. On the other hand, the condition of the Mackay Whitsunday NRM Region decreased by three per cent in the same period.
LIST OF REFERENCES
CSIRO (2014) Assessment of freshwater ecosystem condition, status and trends in the Wet Tropics region. Supporting study to the Wet Tropics Water Quality Improvement Plan. Canberra: Commonwealth Scientific and Industrial Research Organisation (CSIRO).
DSITIA (2013) Total suspended solids, nutrient and pesticide loads (2010-2011) for rivers that discharge to the Great Barrier Reef Great Barrier Reef Catchment Loads Monitoring 2010-2011. Brisbane: Queensland Department of Science, Information Technology, Innovation and the Arts (DSITIA).
Haverd, V. et al. (2013a) 'Multiple observation types reduce uncertainty in Australia’s terrestrial carbon and water cycles', Biogeosciences, Vol. 10, No. 3 (March), pp.2011–2040.
Haverd, V. et al. (2013b) 'The Australian terrestrial carbon budget', Biogeosciences, Vol. 10, No. 3 (February), pp.851–869.
Joo, M. et al. (2012) 'Estimates of sediment and nutrient loads in 10 major catchments draining to the Great Barrier Reef during 2006–2009', Marine Pollution Bulletin, Number 65, pp.150-166.
Kroon, F.J. et al. (2012) 'River loads of suspended solids, nitrogen, phosphorus and herbicides delivered to the Great Barrier Reef lagoon', Marine Pollution Bulletin, Number 65, pp.167-181.
Turner, R. et al. (2012) Sediment, Nutrient and Pesticide Loads: Great Barrier Reef Catchment Loads Monitoring 2009-2010. Brisbane: Queensland Department of Science, Information Technology, Innovation and the Arts.
Wallace, R. et al. (2014) Total suspended solids, nutrient and pesticide loads (2011–2012) for rivers that discharge to the Great Barrier Reef – Great Barrier Reef Catchment Loads Monitoring Program 2011–2012. Brisbane: Queensland Department of Science, Information Technology, Innovation and the Arts.
These documents will be presented in a new window.