THE PROBLEM: Odor pollution, sludge formation, oxygen depletion, threat of fish kills — Home to many waterfowl, ponds can be particularly susceptible to algae growth, sludge formation, oxygen depletion and fish kills. The reason? Feeding the birds, while well-intentioned, causes a greatly increased intake of phosphate and, in addition to waste, leaves and plant residue, leads to more and more organic matter being deposited on the bottom of the pond. Nearby residents, not to mention the local press, are very sensitive to such issues affecting their ponds, meaning that municipal administrators and their policies quickly come under fire. This was the case as a foul odor and the beginnings of a fish kill were noticed in the Schwanenweiher pond in Ostpark, a small park east of the town center of Landau.

Project Overview:

Background:
The total depth of the pond was only one meter (39.37 in), yet the sludge in the pond had already reached an average depth of 55 cm (21.65 in). This meant that more than half of the precious water volume was no longer available. The evaporation losses from the approximately one-hectare (2.47 acre) pond are offset by a freshwater inlet, which renews the total amount of water once over the course of a year. However, this inlet is very rich in phosphates, which further reduced the water quality. The increasingly poor water quality could be clearly seen and smelled. The local press started to take notice when dead fish were occasionally seen floating on the surface. Action had to be taken quickly – there was no alternative. Ralf Bohde from the town’s environment office described the goal succinctly: “Remove the sludge and improve the quality of the water.”

Treatment:
The first priority was to remove the sludge. Dredging the pond seemed unavoidable, but the costs would have gone into six figures, in addition to further six-figure costs for the disposal of organic material. But then the responsible parties came across an innovative and quick alternative, which also happened to be 80- to 90-percent cheaper: OASE water therapy with SchlixX Plus. The mineral-rich powder with an oxygen source and highly active microorganisms binds phosphate from the sediment, thus preventing the formation of algae. The microorganisms also significantly reduce organic sludge. A tonne (1.1 US tons) of SchlixX Plus was added into the Schwanenweiher pond from a small rowing boat.

The active ingredient release of SchlixX Plus is usually scheduled to take place over eight to twelve weeks – however, this was not the case with the Schwanenweiher pond, as it was on the brink of becoming a dead zone. The eutrophication process was already too advanced: A few days after use, the weather became cooler and darker after a heat wave. While sunlight penetrates the pond, its algae perform photosynthesis and supply oxygen. However, a lack of light stops this process, leading plants to use up the remaining oxygen. Consequently, the onset of darkness and the associated increase in oxygen consumption by algae had an unfortunate impact on the Schwanenweiher pond: Several hundred fish perished overnight due to lack of oxygen. OASE PeriDox was immediately used as an acute measure, to great success: The oxygen content in the water quickly increased, successfully preventing the water from becoming a dead zone.

Results:
Of an estimated 150,000 to 250,000 fish in the Schwanenweiher pond, the application of PeriDox kept the deaths down to just a few hundred. The follow-up measures a few months later resulted in a 55-percent reduction in sludge. The remaining sludge is no longer black and foul-smelling, but has a healthier, brighter colour and an earthy smell.

The critical state of Landau’s Schwanenweiher pond and the beginning of fish kill had attracted a lot of attention in the local press and in municipal politics. OASE’s innovative water technology solutions enabled the town’s council and environment office to counter the alarming state of the Schwanenweiher pond quickly and cost-effectively, ensuring that the pond can continue to serve as a place of recreation for residents for years to come. Its fish stocks and water values remain stable to this day.