Our reference: DF 09/ 05
Samples supplied by: Dr Ben Diggles
Company : DigsFish Services Pty Ltd
Address
Your reference: ______
Revised version: 25/11/09, groundwater flows for 1 and 24 hour periods recalculated. Water quality at 6.45 am on 25/11/09 included / Sample Description: Water testing – BiggsAveLake, Beachmere, QLD
Sample screening date: 24/11/09, 4.30 pm - 8.50pm, 25/11/09, 6.30am - 7.30 am.
Screening method:water samples taken, water quality measurements made using YSI 85 DO/temperature/salinity/conductivity meter
with a refractive salinometer to double check salinity measurements and thermometer to double check water temperature.
Disclaimer:
DigsFish Services have taken all reasonable steps to ensure the information contained herein is accurate at the time of publication, however sample sizes used were small and less than required to make statistically rigorous conclusions on absence or prevalence of disease agents or pathological conditions. Hence this report can only be offered as general advice onlyand we accept no liability for any loss ordamage that may result from reliance on this information.
CASE REPORT: Fish Kill, BiggsAveLake, Beachmere, QLD, 24 Nov 2009 – preliminary investigation
Gross signs
Sample statistics:
N =not available
Initial inspection
I arrived at the lake at 4.30 pm in time to chat to council workers who were running two large aerators (Figure 2). They commented on the large number of dead fish they had to take away and dump in a local landfill. Mobile phone photographs were shown of milkfish up to approximately 1 meter, large mangrove jack (Figure 4) and many mullet, bream, herring and silver biddy (Figure 5). My inspection of the lake margins found large numbers of dead fish as well as a few moribund fish (mainly mullet and yellowfin bream) displaying abnormal behaviour such as slow swimming near the lake edges with their mouths out of the water. Several large mudcrabs were also observed on the edges of the lake in water less than 10 cm deep. At the southern end of the lake (Site 1) there was a Moreton Bay Regional Council construction site (Figure 3) where effluent groundwater was being pumped from a well through a pipe into the lake at a rate (measured with a bucket and stopwatch) of 8 L per 4 seconds (2L/sec). A large number of dead fish were observed immediately to the west of the effluent pipe, blown there by the prevailing E/NE wind (Figure 1). A water sample was taken and later examined under the light microscope and only few algal cells and ciliates were observed.
Water sampling
Water was sampled at 6 different locations on the edges of the lake bordered by Biggs Avenue and Kunde St, Beachmere (Figure 1) between 8.00 and 8.50 pm on 24 Nov 2009 by Dr Ben Diggles. Results for water samples and the observations of dead fish and fish behaviour taken at the various sites are included in Table 1.
Figure 1. Location of lake bordered by Biggs Avenue and Kunde St, Beachmere Beachmere, and locations where water sampling was undertaken. The arrow denotes direction of the prevailing wind.
Table 1. Water quality parameters taken from the lake from between 8.00 pm and 8.50 pm 29 Nov 2009.
Location / Temperature / salinity / ObservationsSite 1
(Pipe outlet) / 24.2°C / 16.0 ppt / 4 large dead mangrove jack (2-3 kg), 1 dead milkfish, and numerous small dead herring, mullet and bream
Site A / 29.0°C / 26.0 ppt / 3 large dead mangrove jack, 1 live mudcrab on the bank
Site B / 29.3°C / 26.5 ppt / 1 school of small live mullet 6-10 cm on the surface, large numbers of dead bream (15-23cm), 1 dead moses perch,50-60 small herring, silver biddies, mullet, toadfish.
Site C / 29.1°C / 26.0 ppt / 2 dead mullet 30-35 cm, 3 dead herring 6-10 cm, 2 dead bream 10-15 cm, 30 cm mullet gasping at water surface.
Site D / 29.3°C / 28.6 ppt / 3-4 large moribund mullet, several schools of 30 to 80 small (6-10 cm) live mullet on the surface. Mudcrabs (x2) in the shallows
Site E / 29.4°C / 28.6 ppt / Several schools of small (6-10 cm) live mullet on surface
Figure 2. Aerators placed in the lake by the Moreton Bay Regional Council. The aerators were placed in the water early in the afternoon, and were taken out at 5 pm when council staff knocked off Photo taken at 4.30 pm.
Figure 3. Pipe outlet (arrow) at site 1. The pipe originated from a Moreton Bay Regional Council construction site and was pumping ground water from a recently constructed section of sewage infrastructure.
Figure 4. Dead mangrove jack, approximately 2 kg, near site A, together with small mullet, silver biddy and herring.
Figure 5. From largest to smallest, sea mullet, yellowfin bream, whiting and numerous herring near site B.
Figure 6. Ground water parameters and colour taken from the effluent pipe at 6.45 am, 25 Nov 2009. Salinity 18.7 ppt, water temperature 24.2°C.
I also visited the fish kill site early this morning at 6.30 am. More dead fish were evident along the shorelines and the remaining live fish, mostly small mullet, were swimming with their heads out of the water along the entire margins of the lake. Early morning water parameters, taken 6.30 am on 25 Nov 2009, showed that salinity at sites A to D was similar, between 28.2 and 28.3 ppt, while at site E, salinity was slightly higher at 28.6 ppt. Water temperatures at 6.30 am were 28.2°C at all sites. The wind had dropped off overnight which may explain the more homogeneous results with regard to temperature and salinity in the lake. Readings of the effluent ground water at site 1 showed slightly elevated temperature (24.3°C) and salinity (18.4-18.7 ppt) compared to the previous night (Figure 6). A strong smell of hydrogen sulphide was particularly noticeable in the still morning air in the region where the groundwater was being pumped. The water flow rate at 6.45 am filled a 20 L bucket with 16 L of water in 8 seconds, suggesting that the groundwater flow rate remained at 2L/sec. for the 10.75 hours between the two water samples, meaning that a further 7200 x 10.75 = 77400 Litres of ground water had entered the lake overnight. Council workers arrived at around 7 am and began to aerate the water again, and around 7.45 am I noticed that the groundwater was no longer flowing into the lake and was informed by a council spokesman on site that the water was now being diverted down into the sewage system.
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COMMENTS:
This fish kill is considered suspicious and is certainly not a “natural event”. The various species of fish and crabs observed were displaying behavioural signs typical of aquatic animals suffering from oxygen deprivation – ie. Erratic swimming near the surface with mouths at the air/water interface, congregation near the waters edge and jumping out of the water onto the bank. One moribund mullet that jumped out onto the bank was grossly examined for ectoparasites and a negative result was obtained. In the absence of a functioning calibrated oxygen meter I was unable to confirm the actual oxygen levels in the lake water or in the water coming from the pipe originating from the construction site. The water colour, in the lake was dark, but this is not unusual in coastal lakes in this area where a certain amount of tannin staining can occur. Low algal cell counts in water samples taken from the lake suggest that while algae are undoubtedly present, it appears unlikely that a significant algal bloom is occurring at this time. However, the behaviour of the surviving fish observed between 8.00 pm to 8.50 pm is notable. There were no live fish moving in the area immediately adjacent to site 1 where the water from the construction site was entering the southern end of the lake. Instead, the vast majority of the surviving small mullet were congregated further north along the eastern bank at sites D and E, where water temperatures and salinities were actually higher (29.3°C, 28.6 ppt). This strongly suggests that high water temperatures are not the primary cause of the kill, as the effluent ground water coming out of the pipe at site 1 was only 24.2°C, markedly cooler than the rest of the lake, and its salinity was only 15 ppt. Physical parameters of water dictate that cooler, less saline water can hold more oxygen than warm, salty water. But the surviving fish were avoiding the cooler, less saline water in this lake.
Fish when presented with temperature , salinity and oxygen gradients will move to areas most favourable to their survival. If warm water was the problem, the fish would be expected to avoid the hottest water, and instead would be expected to prefer the south end of the lake where the water is cooler and less saline (both conditions would favour higher oxygen levels under normal conditions). Instead, it was apparent that the surviving fish were avoiding the area surrounding the pipe outflow and actually preferred the hotter upwind (eastern) side of the lake further north. Theprevailing east north east wind was pushing the effluent groundwater along the west side of the lake, as evidenced by the lower temperature and salinity readings on the west side. These physiochemical data and observations of behavior of affected fish strongly suggest the effluent groundwater is toxic to aquatic life and/or devoid of oxygen, the latter possibility supported by the pungent and distinctive hydrogen sulphide odour that is emanating from the effluent water from the pipe.
Hydrogen sulphide (H2S) is produced by bacteria in oxygen depleted (anoxic) conditions. It is particularly common in groundwater and can be very toxic to fish. Hydrogen sulphide is commonly found in mangrove muds and when disturbed will become oxidized. The consequent drop in pH can lead to the mobilization of heavy metals. Recommended guidelines for H2S in water used for rearing fish is less than 0.003 mg/L., with detection of any level of H2S considered highly undesirable (Australian and NZ National water quality guidelines, 2000)
While algal blooms (and associated algal toxins) due to nutrient enrichment from the effluent groundwater must be considered in the differential diagnosis as to the cause of the kill, I suggest that around 2 weeks (based on testimony of local residents) of draining ground water from the adjacent construction site into the southern area of the lake at a rate of 2 litres per second (7200 L/hr or 172,800 L/day) has introduced significant amounts of highly toxic H2S into the small, relatively shallow, but previously highly productive lake. The presence of the H2S (as indicated by its distinctive smell, which has been identified by local residents whohave probably mistaken the rotten eggs smell for sewage), strongly suggests that the groundwater itself is anoxic, and probably toxic to aquatic life. This appears a more plausible explanation for the fish kill than high water temperatures and/or an algal bloom, considering the relatively low algal cell count in the water and especially considering that the surviving fish are actively avoiding the cooler southern area of the lake where the ground water inflow is occurring.
Ben Diggles, PhD.