13.2 The Wallis Lake Estuary Management Committee - Great Lakes ...

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Wallis Lake Estuary Management Plan 2.2.3 Management area C: Muddy Creek (Wallamba Cove), Pipers Bay, Pipers Creek and Forster Keys Management Area C1 (Figure 2.5) encompasses Muddy Creek (Wallamba Cove) and Area C2 (Figure 2.6) the Pipers Bay, Pipers Creek and Forster Keys area. These areas are densely urbanised canal estates (or the receiving areas of these) and experience little flushing. Denitrification efficiency in Muddy Creek (Area C1) is low at 50% during summer (Smith and Heggie 2003). Denitrification is an important natural way for estuaries to cleanse themselves of excess nitrogen. It is a process by which organic nitrogen from plant material is converted to nitrogen gas by bacteria and lost to the atmosphere. If this process is not operating efficiently, the organic nitrogen is instead converted to dissolved inorganic forms (nitrate, nitrite and ammonia) and is available for plant growth. A denitrification efficiency of 40% or less is thought to be a sign of deteriorating water and sediment quality, so the value of 50% measured in Muddy Creek is poor. A phytoplankton bloom caused by Microcystis sp from March until May 2002 is testament to this and a sign that excess nutrients are in the system. To alleviate the nutrient (and sediment) loads entering Muddy Creek an artificial wetland was constructed on Bramble Parade in April 2002. Artificial wetland areas act as filtration systems trapping and absorbing nutrients from stormwater in the native vegetation and allowing sediments to settle out before entering the estuary. These constructed wetlands can reduce nitrogen loads by up to 30%. However, there is limited information available to date on the performance of the artificial wetlands constructed in the Wallis Lake catchment. Pipers Creek and Forster Keys (Area C2) are the receiving area for stormwater from the Forster Keys and Wyuna catchments. The catchment area has largely been cleared for residential and commercial purposes, resulting in significant nutrient inputs and possible faecal pollution entering the estuary particularly after rain (Webb, McKeown & Assoc. 1999). Five artificial wetlands have been constructed in this catchment at Goldens Road north (Dec 2002) and south (Mar 2003), Kularoo Drive (Dec 2003), Boronia Street (2004) and Townsend Street (Nov 2001). Further to this, 1 GPT has been installed at Kularoo Drive. Evidence of nutrient enrichment in Area C2 is a persistent bloom of the green filamentous macroalgae Chaetomorpha sp. This alga has been observed forming large mats in shallower areas of the Creek since December 2000 (S. Moore pers. obs.) and sporadically in the Forster Keys and in Pipers Bay. Further, denitrification efficiency is just 38% in Pipers Creek during summer months (Smith and Heggie 2003). This is less than the 40% value indicating poor water and sediment quality, and means that during summer ammonia (a highly available plant nutrient) is leaching out of the sediments into the surrounding water column and is available for plant growth. SEPP 14 wetland areas are present on much of Big Island and in the upper reaches of Pipers Creek. No public access to the Lake is available in Area C1 at Muddy Creek, however access in Management Area C2 is obtained via the Forster Keys ramp. 12
Wallis Lake Estuary Management Plan Duck Swamp Bramble Parade wetland Muddy Creek Native Dog Island Ohmas Bay Oaky Island [Figure 2.5: Management area C1: Muddy Creek] 13
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