A drought can be described as being an ecosystem disturbance meteorologically, however hydro logically it’s portrayal misleading (Bond, Lake & Arthington 2008). A universal definition for a drought is not known but a meteorological drought can be defined as a lack of rainfall for an extended period of time whether it is several years or a season relative to the arithmetic mean for that region (Bond, Lake & Arthington 2008). As a drought is able to have a substantial impact on the natural marine ecosystems, the outcomes that come with it are aggravated both by indirect and direct anthropogenic adjustments to hydro areas such as rivers and the catchments (Bond, Lake & Arthington 2008). Major impacts in rivers are generally the decline of the amount of water and habitation accessibility for the surrounding animals (Bond, Lake & Arthington 2008). Droughts are a frequently occurring matter in Australia with it being a regular element on the climate with most said to have had an affect by the El Nino phase (Bond, Lake & Arthington 2008). As a drought is classified as a natural hazard it’s able to cause a great amount of destruction socially and economically (Bond, Lake & Arthington 2008). The millennium drought is sought to be one of the biggest to leave an impact on the environment (Bond, Lake & Arthington 2008).

The millennium drought has had a severe impact on most of the South-Eastern Australia region with most of the rivers undergoing a record low water capacity during this period and in some instances 40% lower than earlier records (Bond, Lake & Arthington 2008). The Southern Murray- Darling Basin is spread around most states of Queensland, New South Wales, ACT and Victoria (Whitworth, Baldwin & Kerr 2012). It lies in a Mediterranean climate zone with a yearly average rainfall of approximately under 500 mm each year (Whitworth, Baldwin & Kerr 2012). The floodplains in the region highly depend on the overbank flows, which generally originate from the winter and spring yearly rainfall for conservation of their ecological atmosphere (Whitworth, Baldwin & Kerr 2012). Due to a mixture of severe climate drought and the development of stream water supplies, majority of the floodplains are experiencing a severe moisture stress throughout the past decade (Whitworth, Baldwin & Kerr 2012). Between the years of 2006-2007 the sever drought conditions resulted in a decline of water flow towards the Murray Darling causing for the lowest levels to be recorded (Adamson, Mallawaarachchi & Quiggin 2009). Many researchers have expressed their thoughts on the severity that the drought has caused and many have come to agree upon that its main cause would have to be the human activity, which leads to climate change (Adamson, Mallawaarachchi & Quiggin 2009). However this problem had come to an end around late 2010, with spring and summer rainfall reaching a near record level hence leading the drought to be broken by the immense amount of rainfall leading to a widespread of flood events (Whitworth, Baldwin & Kerr 2012).

The lowest recorded amount of rainfall since 1990 was observed during October 2001 till September 2008 (Potter Chiew & Frost 2010). Throughout the period of 2006, water inflows in the Murray Darling Basin was of the lowest recorded since 117 years (Potter Chiew & Frost 2010). From November 2008incoming inflows into the Murray Darling Basin were recorded as being below average for a period of 37 consecutive months (Potter Chiew & Frost 2010). Researchers are claiming that inflows into the Murray Darling Basin will generally begin to decline in the future, with rainfall predicted to decrease in 2030 by 2% in the north and 5% in the south (Potter Chiew & Frost 2010). Moreover there is widespread fear the decrease amount of rainfall during the drought season is mainly due to climate change hence this great concern is leading researchers to come up with ways to stop the gradual decline of water inflow through the surface waters (Potter Chiew & Frost 2010).

Following the decade long droughts that occurred in the South-eastern region of Australia, a chain of flood events caused for the Southern Murray-Darling Basin to be affected by a large scale of hypoxic blackwater (Whitworth, Baldwin & Kerr 2012). As a result this had a negative affect on over 2000 km of the inner and surrounding river channels for a period of 6 months (Whitworth, Baldwin & Kerr 2012). Subjective observations and experimental data have indicated that the drought developed a harsh effect on the aquatic ecosystems (Bond, Lake & Arthington 2008). The aquatic inhabitants have dramatically declined and to follow rivers have had a negative impact by the droughts with some even undergoing extinction (Bond, Lake & Arthington 2008). The riparian regions have been worn out of their iconic species, for example the river red gum experiencing destruction across many areas of their habitat (Bond, Lake & Arthington 2008). Moreover changes around the aquatic habitat new biogeochemical processes are seemingly apparent however aren’t quite understood (Bond, Lake & Arthington 2008).

For both hydrological and agricultural droughts there are no clear adopted indications in many parts of the world including Australia (Bond, Lake & Arthington 2008). Therefore the absence of a well- defined universal meaning for hydrological droughts makes it difficult to relate the effects of droughts on a freshwater environment with respect to its time and place quite challenging (Bond, Lake & Arthington 2008). A hydrological drought is classified into two factors, a groundwater drought and a surface water drought whilst having the latter lagging well just behind the surface water droughts both when the process finishes and when it commences (Bond, Lake & Arthington 2008). As the developmental stage of a drought commences, the average anticipated amount of precipitation fails to happen on the estimated season (Bond, Lake & Arthington 2008). The lack of amount of rainfall received results in a decrease of soil moistness, groundwater recharge and surface runoff (Bond, Lake & Arthington 2008). With the streams that were used to seasonal drought, the organisms of that region were well adjusted to the expectable hazard however the biota of that region when exposed to a supra-seasonal drought would suffer a dramatic impact towards their species and maybe even local extinction (Bond, Lake & Arthington 2008). The early phases of supra-seasonal drought whether it be a flowing or standing water lead to a dry up or a develop low water levels of pools (Bond, Lake & Arthington 2008). As the drought further forms, the water and volume levels in naturally recurring water decline (Bond,

Lake & Arthington 2008). Numerous amounts of possible thresholds may be obstructed for flowing water(Bond, Lake & Arthington 2008). For example droughts may lead to a reduction in the moist area of the streambed hence causing detachment for marginal habitats (Bond, Lake & Arthington 2008). Following this is the important brink of cease to flow where the streams develop into chains of pools which themselves may disappear (Bond, Lake & Arthington 2008). As a drought begins to diminish the surface waters, groundwater levels and volume capacity may in time begin to reduce (Bond, Lake & Arthington 2008). Unfortunately groundwater drought is inadequately understood and it is important to apprehend that at times groundwater acts as the base flow of the surface systems and that most wetland species are groundwater reliant (Bond, Lake & Arthington 2008). Consequently as normal rainfall begins to reoccur, the meteorological drought usually appears before surface water drought well before the groundwater drought (Bond, Lake & Arthington 2008). A lack of precipitation can lead to a speedy reduction of the soil moisture, which in return has a negative affect on agriculturalists (Adamson, Mallawaarachchi & Quiggin 2009). Saying this the decline of rainfall would not impact reservoir levels instantly thus only proving to be of an affect after a couple of months (Adamson, Mallawaarachchi & Quiggin 2009).

The Murray Darling Basin ends at Coorong and Lower Lakes that also include Lake Albert and Lake Alexandrina (Wedderburn, Hammer & Bice 2012). Over the last decade extreme drought conditions put these lakes under enormous environmental stress thus leading to a substantial reduction in the quality and water levels of both Coorong and Lower Lake from the years 2003-2009 (Wedderburn, Hammer & Bice 2012). The reduced water levels in the lakes resulted in a rise in salinity levels, declines of vegetation in the aquatic region and an interruption of Coorong from the Lower Lakes (Wedderburn, Hammer & Bice 2012). Consequently the species were affected and

as a result had a negative impact on the fish population with their being a decline in the fish and diadromonous specie and alternatively and an increase of the marine fish population (Wedderburn, Hammer & Bice 2012). The sudden decline of the populations allows us to determine that when the diet or habitat of certain species are being put under a negative stress, in this instance the lack of freshwater that flows because of the increase of salinity levels, the habitual species become more vulnerable hence may cause a population decline (Wedderburn, Hammer & Bice 2012).

A decline of rainfall levels that was comparable to that of the millennium drought period were also observed (Timbal & Fawcett, 2013). From the years 1935-1945, which took place in the time of the World War II, thus called the WWII droughts and the Federation drought that occurred around January 1901, the time that the states of Australia became a federation (Timbal & Fawcett, 2013). Throughout the period of the WWII drought, the average rainfall was 10.8% lower than the average amount of rainfall between the years of 1900-2010, with a rainfall total of 518.9mm (Timbal & Fawcett, 2013). By comparing all three droughts, a difference in characteristics was obvious. The greatest percentage rainfall decline in spring was shown by the federation drought that coherently flowed with the numerous amounts of very strong El Nino occurrences during that period (Timbal & Fawcett, 2013). Hence there were no insignificant changes to autumn and winter (Timbal & Fawcett, 2013). Whereas

the WWII drought displayed a fairly insignificant summer change and a decline during autumn, winter and spring (Timbal & Fawcett, 2013). Moreover the millennium drought proved to have the greatest percentage decline in autumn, similar to the federation droughts spring decline, whilst the remaining seasons displaying a decline of approximately a third to a half of that of autumns percentage decline (Timbal & Fawcett, 2013).

Through many research and observation it can be said that the millennium drought presented a decade of rainfall deficit throughout southeastern Australia. It differentiated itself from other droughts in the sense that rainfall decline would occur in different seasons when compared to the WWII drought or the federation drought. The lack of rainfall received had a stressful affect on the surface waters and reducing the soil moisture of the ground thus also affecting the agriculture. Moreover it can be said that the decrease of rainfall can be linked to climate change.

REFERENCES

Adamson, D., Mallawaarachchi, T. and Quiggin, J. 2009. Declining inflows and more frequent droughts in the Murray--Darling Basin: climate change, impacts and adaptation*. Australian Journal of Agricultural and Resource Economics, 53 (3), pp. 345--366.

Bond, N., Lake, P. and Arthington, A. 2008. The impacts of drought on freshwater ecosystems: an Australian perspective. Hydrobiologia, 600 (1), pp. 3--16.

Potter, N., Chiew, F. and Frost, A. 2010. An assessment of the severity of recent reductions in rainfall and runoff in the Murray--Darling Basin. Journal of Hydrology, 381 (1), pp. 52--64.

Timbal, B. and Fawcett, R. 2013. A Historical Perspective on Southeastern Australian Rainfall since 1865 Using the Instrumental Record. Journal of Climate, 26 (4), pp. 1112--1129.

Wedderburn, S., Hammer, M. and Bice, C. 2012. Shifts in small-bodied fish assemblages resulting from drought-induced water level recession in terminating lakes of the Murray-Darling Basin, Australia. Hydrobiologia, 691 (1), pp. 35--46.

Whitworth, K., Baldwin, D. and Kerr, J. 2012. Drought, floods and water quality: Drivers of a severe hypoxic blackwater event in a major river system (the southern Murray--Darling Basin, Australia). Journal of Hydrology, 450 pp. 190--198.