The management of lakes is facing numerous challenges nowadays, some of them related to natural issues and many others to anthropogenic causes.
Climate change will have particularly serious ramifications for lake environments, whilst the increasing demands of mankind will need an unified approach to lake management, taking into account not only the whole watershed area but also the varying ecological and socio-economic aspects. Any recommended solution will depend upon improvements in ecosystems services, and the improvement of lake ecosystems. Additionally, more information needs to be prepared and shared regarding lake and habitat rebuilding.
Lake ecosystems are a prime examples of lentic ecosystems. Lentic refers to still or relatively still water, from the Latin lentus, meaning sluggish. Lentic waters can vary from ponds to lakes and wetlands. These are diverse systems, ranging from small, temporary rainwater pools just a few inches deep to extremely vast lakes thousands of acres in size
Light produces the solar UV energy needed for photosynthesis, the leading energy source of any lentic system. The light quantity received depends upon several factors. Small ponds may be shaded by surrounding trees and shrubs, whereas larger lakes might not be so shaded. Cloud cover can affect the availability of light in all systems. When it comes to the management of a pond or smaller lake, it is always wise to take into account how much light can get into the water.
Oxygen is essential for all life in a lake or pond, including, animals, plants and organisms. The amount of dissolved oxygen (DO) present in standing waters depends upon;
In plant rich but shallow pools there can be great variations in dissolved oxygen, with incredibly high concentrations during the day due to photosynthesis and incredibly low values occurring at night when respiration is the main process of primary producers. In larger systems, thermal stratification can also affect the level of oxygen present across different zones. The epilimnion is rich in oxygen because it circulates swiftly, obtaining oxygen via connection with the air. The hypolimnion, on the other hand, circulates incredibly slowly, with no atmospheric contact.
Dissolved oxygen is a considerable contributor to water quality. Aerobic bacteria that breathe oxygen will decompose organic matter. When oxygen levels become low, anoxic situations can develop, which lessen the water body’s capability to support life.
Aeration can be achieved through the infusion of air into the base of the lake, pond or lagoon or by agitating the surface using a fountain or spray device to allow for oxygen transfer at the surface and the release of noxious gasses including methane, carbon dioxide, or hydrogen sulphide.
Bacteria are present in all areas of lentic waters. Free-living forms are linked with biofilm on the surfaces of plats and rocks (decomposing organic material) suspended in the water, and in the sediments of the profundal and benthic zones. Other types are also linked with the guts of lentic creatures as parasites or in commensal relationships. Bacteria play an important part in the system of metabolism via nutrient recycling.
Acidification: Nitrogen oxides and Sulphur dioxide are naturally discharged from volcanoes, wetlands, organic compounds in the soil, and marine systems, but most of these compounds come from the combustion of oil, coal, gasoline, and the smelting of sulphur containing ores. These materials dissolve in atmospheric moisture and penetrate lentic systems as acid rain. Ponds and lakes that contain carbonate rich bedrock have a natural buffer, resulting in no change to pH. Systems that do not contain this bedrock, however, are extremely sensitive to acid inputs. This is because they have a low neutralising scope, resulting in pH reductions even with only minute inputs of acid. At a pH of 5-6, algal species diversification and biomass reduce considerably, resulting in an increase in water transparency – a distinctive feature of acidified lakes. As the pH continues to decrease, the diversity of all fauna reduces. The most important feature is the disruption caused to fish reproduction. The population is gradually comprised of a few, elderly individuals who eventually die, leaving the systems without fish. Acid rain has been recorded as being especially harmful to lakes in Scandinavia, western Scotland, west Wales and the north eastern United States.
Eutrophic systems contain a high concentration of phosphorus, nitrogen, or both. Phosphorus infiltrates lentic waters from the effluents from waste water treatments, raw sewage discharge, or from run-offs from farmland. Nitrogen is generally found in agricultural fertilizers from run-off, leaching the ensuing groundwater flow. The increase in nutrients needed for primary producers causes a massive increase in the growth of phytoplankton, termed a plankton bloom. This bloom reduces water transparency, leading to the reduction of submerged plants. The resulting decrease in habitat structure has adverse impacts on the species that use it for spawning, maturation and survival in general. Additionally, the large amount of short-lived phytoplankton, leads to an enormous amount of dead biomass settling in the sediment. Bacteria need massive amounts of oxygen to decompose this material, causing a reduction in the oxygen concentration of the water. This is particularly pronounced in stratified lakes where the thermocline prevents water from the surface that is rich in oxygen mixing with lower levels. Low or anoxic surroundings precludes the existence of numerous taxa that are not physiologically sympathetic to these conditions.
Lentic systems have had invasive species introduced to them on deliberately(e.g. stocking food and game species) as well as having experienced events that were unintentional (e.g. in ballast water). These organisms have the ability to affect native species through competition for prey or habitat, habitat alteration, predation, hybridization, or by the introduction of harmful parasites and diseases. With native species, invaders may cause adjustments in size and age structure, density, distribution, population growth, and could even push populations to extinction. Examples of the leading invaders of lentic systems in the UK are Signal cray fish, Mink, and to some extent Catfish.
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