The Problem: -
The client had a lake of two halves, the bottom half has a tarmac visitor’s path around the marginal edge and with no marginal aquatic plant life at all looked totally un-natural. The top half is very well vegetated with volumes of marginal aquatic and terrestrial plant life making for a much more natural aesthetic view. The lake receives hundreds of thousands of visitors every year; many of them feed the waterfowl population creating an inflated resident population which deposits a high percentage of faeces directly into the water. This creates nutrient rich conditions ideal for regular summer algal blooms and lowered dissolved oxygen levels in warn summer conditions. The lake holds a large population of carp and ornamental carp species which feed heavily on the bottom which stirs up silt making the water very coloured and releases volumes of nutrients into the water column that would have otherwise remained locked in the silt, this also helps create ideal conditions for summer algal growth. The client had experienced summer fish kills in the past. The lake had a large aeration fountain that was too powerful blowing water so high that the lake lost water when it was windy; consequently it had been turned off.
Solution: -
Hydroponic growth of aquatic plants using no growing substrate is possible in nutrient rich conditions. Coir rolls pre-planted with native marginal aquatic plants were fixed in suspension from the bank around the entire bottom half of the lake and approximately 50m of exposed top half lake margin, the roots from these planted rolls hang up to 1.2m below the water level drawing nutrients directly from the water column. The plants are protected by security weld mesh wire to deter vandalism and waterfowl from pulling out and/or eating the main roots. The birds can only browse on leafy foliage growing out of the wire cage and these cages disappear very quickly as the plants grow and establish.
The plants have established extremely well transforming the lakes aesthetics and delighting the clients and the many thousands of site visitors. The water quality will improve with direct uptake of nutrients from the water column increasing the lakes natural filtration capability and a more normal diurnal rhythm may be achieved regarding summer dissolved oxygen levels. The large mixed waterfowl population now has protective marginal cover around the entire lake, food by way of young fresh aquatic plant foliage and a hugely increased volume of invertebrate availability plus natural materials to use for nesting. The fish population is being controlled in the future ensuring that not so many bottom feeding fish are present that they can detrimentally affect their own health and lake water quality. The lake fountain/aeration pump has been reduced in power so water is not blown so high in the air that water is lost and is now generally only running during the evenings and nights of summer when dissolved oxygen levels are usually at the lowest levels (and power costs the least).
