Lake and pond restoration are broad terms that include multiple techniques aimed at bringing a lake or a pond to previously undisturbed conditions. The undisturbed condition of the lake or pond refers to anthropogenically effects (caused by human action) and not those which are naturally occurring. Restoration usually refers to internal measures (actions done inside the lake), but sometimes, it can also refer to outside measures (actions taking place outside the lake – including the reduction of pollutants that reach a lake or pond or reducing the external nutrient loading by using better water treatment technologies).
The Importance of Lakes and Ponds
Lakes are critically important in modern society. Humans use them as a source of water for drinking, irrigation, industrial activity, transportation, hydroelectric power, recreation, fishing, and aesthetic qualities. Lakes are habitats for important ecosystems and an immense variety of plants and animals. Lakes are often faced with damage caused by excessive urbanization, industrial activity, and disturbed ecology. Urban lakes are some of the most sensitive ecosystems in modern society and are often protected by land restoration trusts.
Major problems lakes and ponds face are:
- Draining and encroachment of lakes and ponds – They are fast becoming a lost heritage
- Loss of biodiversity – loss of both vegetation and animals
- Excessive pollution from industrial and domestic waste – toxic substances are often discharged in lakes, including nitrates, nitrites, phosphates, and other toxic substances
- Impact on human and animal health – lake pollution can cause serious diseases, like jaundice, typhoid, gastroenteritis, and malaria, especially in poorer areas of the world.
When Is Lake and Pond Restoration Used?
Most lake restoration projects are started and developed to combat the process of eutrophication* by multiple land restoration trusts. Lake restoration projects were also directed at reducing the acidification process in soft water lakes and ponds. However, the vast majority of lake restoration projects are focused on eutrophication, which is the paramount environmental problem for ponds and lakes worldwide, especially during the past 50 years.
*Eutrophication – also known as hypertrophication, occurs when a body of water (river, lake, pond or any other body of water) becomes overly enriched with nutrients and minerals. This process induces the excessive growth of algae and results in oxygen depletion. The process, known as an algal bloom, can damage the habitat of other plants and animals present in the water. Eutrophication is often caused by a discharge of excessive amounts of nitrates, phosphate-containing fertilizers, sewage or detergents into the bodies of water.
Lake and pond restoration is a fairly recent activity. The return of a lake or a pond to its original, pristine condition was not the goal of many restoration projects. In fact, many restoration projects were just rehabilitation efforts completed in specific situations, on very few lakes or ponds. The techniques used were minimal and non-invasive, with limited results.
On the other hand, long-term restoration involves multiple techniques and strategies. Here are a few important techniques:
Controlling The Source Of The Problem
Before any restoration process begins, the source of the problem must be identified. After determining the problem, the next step is to control it and reduce its effects. For instance, in the case of eutrophication, the main problem is the number of nutrients and minerals reaching the water. The first approach should focus on decreasing the number of nutrients and minerals, particularly the phosphorus from multiple watershed sources. All sources of organic matter and silt must also be checked and controlled.
Fortunately, in most cases, controlling the source of these pollutants is sufficient to restore the lake or pond. However, some lakes or ponds have been so damaged that in-lake restoration techniques must be employed. These damages include major loss of habitat, major shifts in biota (plants and animals of a region), lake hydrology damage or physical changes in sediments.
Dilution Of Phosphorus
Dilution is a common in-lake procedure to reduce the phosphorus in a lake or a pond. The concentration of phosphorus is reduced by adding water that is very low in phosphorus. This promotes the washout of algae and will increase the total phosphorus loading rate of the lake. However, the concentration of phosphorus is greatly reduced. Also, the flushing rate is increased and the phosphorus sedimentation is decreased. The method is successfully used for lakes with high flushing rates is often employed by land restoration trusts across the country.
Phosphorus Inactivation
By adding various aluminum-based salts, the amount of active phosphorus in a lake or pond is greatly reduced. The additives used are either sodium aluminate or aluminum sulfate. The resulting compound, called aluminum hydroxide will form and appear as a visible floc. It will bind with the active phosphate ions and will form an insoluble element, which cannot be dissolved by oxygen. The phosphate ions are then trapped by the floc, and the inactivation process is complete. This method is successful in shallow, thermally stratified lakes.
Sediment Skimming
This procedure involves the use of a hydraulic dredge to remove the recent phosphorus-rich layer deposited on the surface of the lakebed. This procedure is very invasive and quite expensive, often more expensive than phosphorus inactivation. However, it has good restorative effects and doesn’t require the use of potentially dangerous elements (aluminum). This method works well if the nutrient inflows have been eliminated or greatly reduced.
Sediment Oxidation
The phosphorus deposited on the lakebed can be controlled by accelerating the natural oxidation process. The process is simple: it creates an environment where the phosphorus ion binds up with iron in the top 5 to 10 cm of lake sediment. The technique is still in the testing phase, but it shows good results. The active chemical compound is calcium nitrate, which is injected in the sediments. Once the denitrification process starts, the phosphorus is inactive.
Deep-water Discharge
The phosphorus can be inactivated by siphoning the water near the lakebed. Also, the hypolimnetic water (the bottom water layer) can be discharged via a deep gate in the dam. The “old” water is discharged and replaced with clean water, with a reduced amount of nutrients and minerals. The technique should be employed each summer for the best results.
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