Brown Lake
Bummeria[1]
Brown Lake (North Stradbroke Island).JPG
Brown Lake is located in Queensland
Brown Lake
Brown Lake
LocationNorth Stradbroke Island, Queensland
Coordinates27°29′24″S 153°25′57″E / 27.49000°S 153.43250°E / -27.49000; 153.43250Coordinates: 27°29′24″S 153°25′57″E / 27.49000°S 153.43250°E / -27.49000; 153.43250
TypePerched[2]
Primary inflowsPrecipitation[3]
Basin countriesAustralia
Max. length1 km (0.62 mi)
SettlementsDunwich, Amity, Point Lookout

Brown Lake (Bummeria) is a perched lake on North Stradbroke Island, in South-East Queensland, Australia.[4] The ecosystem is an example of a coastal non-floodplain sand lake[5] and is characterised by acidic water, nutrient-poor and sandy soil, shrub-like vegetation and wet heathland.[3]

Brown Lake is of geographical significance, possessing ecological value.[5] The geomorphology of the ecosystem is representative of the unique parabolic dune ridge systems that formed during the Pleistocene epoch.[6] As a perched lake, the hydrological operations of Brown Lake are highly diverse and complex.[2]

The lake is also of cultural significance to the Aboriginal population of North Stradbroke Island, the Quandamooka people, as they possess a spiritual and physical relationship with the ecosystem.[1] The indigenous population care for and protect the landscape, sharing traditional environmental management knowledge.[7][8]

Brown Lake’s cultural heritage and ecological value, along with the environmental damage associated with tourism, has led to increased conservation.[7] The Queensland Government and the Quandamooka Yoolooburrabee Aboriginal Corporation (QYAC) have proposed an improved environmental management plan, combining traditional and contemporary management practices.[7]

Geography

Brown Lake is 1 km in length and is located 4 km east of Dunwich, a small town on North Stradbroke Island.[4] Brown Lake is in a subtropical climatic region; experiencing a wet season in the winter and a dry season in the summer.[4]The mean daily temperature for the area is "15°–29°C in summer and 9°–20°C in winter"[2] and the average annual rainfall is 1668 mm.[4]

Geologically, Brown Lake exists on a parabolic beach ridge system that formed during the Quaternary glacial and interglacial cycles of the Pleistocene epoch.[6] The cold-climate interval of the epoch caused a periodic lower sea level, which exposed the sea-bed of the coastal heathland to strong south-easterly winds that carried and deposited sediment which eventually accumulated to form the dune ridges on which Brown Lake developed.[6]

Perched lakes are formed via geological processes. They occur in sunken landforms (depressions) when an impermeable layer of sand, combined with decomposed organic material, becomes cemented as precipitates of mineral matter fill in pore spaces; transforming sediment into rock.[3] This cemented layer is known as 'coffee rock' and it prevents rainwater from escaping the depression, percolating through to the regional aquifer, forming a perched lake.[5]

The sand at Brown Lake is quartz sand[6] and the yellow-brown colouring of the sand is caused by the sesquioxide coating on the quartz grains.[9] Podzol soil supports the health and growth of the vegetation at Brown Lake.[6] Developed from quartz-rich sand, podzol soil is sandy in texture and is characterised as a well-aerated, well-drained and acidic soil.[6] The soil is also nutrient deficient, which is largely due to leaching.[6]  

Localities around Brown Lake

Encompassing Brown Lake are three townships; Dunwich,[10] Amity[11] and Point Lookout.[12]

City Population
Dunwich 885[10]
Amity 387[11]
Point Lookout 713
Brownish, tea-colour of Brown Lake's water

As a perched lake, Brown Lake contains high levels of dissolved organic matter, resulting in the water system being acidic in nature; possessing a PH level less than 6.[5] The high level of dissolved organic content contributes to the water colour of Brown Lake; staining the lake a brownish tea colour; characterising the lake as dystrophic.[5]

Water systems receive nutrients from the sediment surrounding the ecosystem and at Brown Lake, the sand and soil that support the ecological community possess a low nutrient supply; characterising the lake as oligotrophic.[5]

Perched lakes are recharged and replenished via rainfall infiltration.[2] Accordingly, pro-longed periods of low rainfall often lead to decreased water levels however, studies show that Brown Lake’s water level has been relatively stable; remaining at a normative level due to the large rainfall infiltration that occurred during the January 1975 cyclonic event.[2] The small fluctuation in water level that does occur at Brown lake is most likely a result of water seeping through the lakebed.[2]

Aquatic fauna

Brown Lake supports a diverse population of aquatic fauna; inhabiting macroinvertebrates, fish and decapod crustacea.[13] The taxa of aquatic biota occupying the ecosystem are of conservation significance, as they are representative of rare acid-adapted marine life existing in humic water systems.[14][13]

Macro-invertebrates

Macro-invertebrates inhabiting the area include:[13]