TECHNICAL


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We don’t need to remind ourselves of the challenges we face in terms of the volumes and quality of water used, even in areas that we believed were immune from shortages. This means, more often, people are turning towards


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unconventional resources such as recycled water


onds and lakes, whether man made or not, have a natural life cycle. Before people began to impact the environment, this progression took hundreds, even


thousands of years. Ponds and lakes now can be created, live, and die within decades. Much of the reason for this lies in the fact that water is one of our most abused and least understood natural resource. We allow our ponds and lakes to be unmanaged and, therefore, they become unmanageable. We don’t need to remind ourselves of the challenges we face in terms of the volumes and quality of water used, even in areas that we believed were immune from shortages. This means, more often, people are turning towards unconventional resources such as recycled water. Recycled water has the advantage of being located close to the places of use, being available in large quantities throughout the year and rich in useful nutrients. In the case of recycled water, there are large quantities that can be utilised to water plants and crops, such as irrigated agriculture or green spaces, instead of releasing the water back into the environment. Recycled water is now becoming an essential part of the pond and lake landscape, due to the very nature of the water chemistry, being that it’s recycled. Any pond or lake used as a reservoir for this type of water will almost inevitably deteriorate into a eutrophic* condition in a short space of time if not properly and proactively managed.


Successful pond and lake management, especially for recycled waters, begins with a basic understanding of how the three mechanisms that operate in a pond or lake, affect its overall condition.


1. Thermal stratification


Temperature layering, or thermal stratification, occurs when the sun warms the pond surface water causing it to become less dense. As the warming process progresses, the water becomes separated, or stratified into layers. Densities, created by the varying water temperatures, cause this layering to occur. Colder water settles on the pond bottom and the water gradually gets warmer in layers as you get closer to the surface. Because the surface layer remains warm, algae growth thrives and oxygen is not retained as well as in cooler water temperatures.


*Definition of eutrophic


Eutrophication is when a body of water becomes overly enriched with minerals and nutrients which induce excessive growth of algae and may result in oxygen depletion of the water body


PC June/July 2019 137


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