What causes black ooze?
Contrary to common perceptions, wrack accumulation on the shores of the lake is not the sole cause of black ooze. Many factors lead to ooze formation and wrack is just one piece in the puzzle.
WRACK ≠ OOZE
This point is illustrated by the fact that there are huge deposits of wrack on the shores at Gorokan (Marks Rd) yet there is no smelly black ooze at this site.
Two important factors that lead to ooze formation are:
1) Proximity to stormwater drains (pollution from the catchment)
2) The shoreline is protected from WAVE and WIND energy
- The rotten-egg smell is hydrogen sulphide gas (H2S) which is produced by anaerobic bacteria in the sediment
- Anaerobic means ‘without oxygen’. Anaerobic bacteria metabolise nutrients without oxygen and produce hydrogen sulphide gas
- Sediments in healthy ecosystems include a balance of aerobic (with oxygen) and anaerobic processes. But in stressed ecosystems with excess nutrients, the faster/more efficient aerobic metabolism can no longer occur
- Pollution from the catchment has led to the organic enrichment of the near shore zone. This has upset the balance of bacterial processes in the sediment so that only the slower/less efficient anaerobic metabolism occurs. This leads to a build-up of organic matter and sulphide gas in the sediment which escapes when the sediment is disturbed
Scientists at OEH have delved deep into ooze to see what it is made of.
Scientists from OEH have developed a conceptual model on how ooze is formed.