Human Influence on the Health of the Estuaries

                        

An estuary is defined as a semi-enclosed coastal body of water which has free connection to the open sea. The productivity of estuaries is similar to that of the tropical rain forests. The services of estuaries are not only limited to itself but to whole the earth. Although species richness is less, abundance is high due to the high food availability. Most of seawater species use estuaries as their feeding grounds, nurseries and breeding grounds. The existence of the estuary is affected by the activities in the catchment areas as well as in estuaries.

                          Aquaculture in the estuaries effects the bio-physical environment. Mangroves have to be disrupted in order to construct aquaculture ponds. Water is released back into estuaries without proper treatments. Effluents such as growth additives, insecticide and antibiotics, suspended particles, fecal matter are adversely affected to the health of estuaries.

                          Organic matter increase BOD and decreases DO. Therefore oxygen available for estuarine animals becomes limited. Large suspended particles that are released from aquaculture ponds increase the turbidity.  It restricts the light penetration and decreases the primary productivity. Decreasing primary productivity of estuary affects the food availability and oxygen solubility. As suspended particles also absorb heat other than water, temperature of the water column is increased. It decreases the oxygen solubility.

                          Animals those escape from the aquaculture ponds become threatened to estuarine animals. They compete with native animals for foods, breeding places and hiding places.  Sewage of aquaculture animals contains loads of pathogens which may cause diseases among estuarine animals.

                          Insecticides contain high amount of heavy metals which cause bio magnification and bioaccumulation.  As a result of bioaccumulation, animals in the higher trophic level of the food web are adversely effected .High concentration result in even death.  Nutrients such as P and N accelerated the growth of algal and harmful algal bloom (HAB). Eutrophication restricts the light penetration through the water column. Harmful substance which are produced by

HAB are capable of killing estuarine animals.

                          Aquaculture does not affect only the quality but for also quantity. Large amount of estuarine water is extracted into the ponds. It reduces the water volume of the estuary.

                          Human settlement development along the estuarine bank is one of human influences to convert natural habitats. Mangroves are disrupted to erect houses. It causes loss of habitat and productivity of estuaries. Because decomposition falling leaves and branches adds nutrients into the water column.                            People dispose their waste and sewage directly into the estuary. Pollutants are collected and brought into nearby islands by waves. As some animals attempt to ingest these substances and they’ll die. Most of the pollutants are non-biodegradable and remain for thousand years. Sewage adds pathogens and increases the BOD.

                           Irregular tourism also contributes to reducing the quality of estuary. Mangroves are removed to construct tourist hotels beside the estuary. All effluents from the hotels are released into the estuary aid in pipes. Boats those are involved in tourism effects to the estuarine animals. Boats those are regularly maintained in a proper way cause oil leakage.  Oil spills are difficult to remove and costly. Oil increases the water temperature and reduces the oxygen solubility. Waste from the tourist boast is also directly disposed into the estuaries.

                          Over exploitation of estuarine resources leads extinction of some species. When the extinction rate is higher than breeding rate of animals, it is impossible to recover from extinction.  Although it is prohibited to catch animals during their breeding season, illegal incidences are still reported around the estuaries.

                          Irresponsible fishing in the estuary is also major problem.  Most the fish man stops their boats in the estuary during day time. It reduces the light penetration and primary productivity near bank. It also restricts the available surface for oxygen solubility. It may result in less biodiversity. At night they release oil form those boats into the estuarine water.  Fishing gears and nets are thrown away when they get damaged. They are also non-biodegradable and affect the existence of the estuary. Animals are unable to move when they get trapped within those left overs.  

                          Activates in the catchment area also contribute to the health of the estuary.  Sedimentation is directly affected by riverine flow into the estuary. Activities such as deforestation, construction of houses and roads and agriculture in catchment make the soil bare into the open environment. It increases the probability to wash away the soils by runoff. As the riverine flow rate is slow near the estuary, sediment tends to deposit. Estuarine animals are interfering with respiration because their gills are clogged by sediments.

                      Sediments increase the turbidity of the water column and reduce the light penetration which may result in decreasing primary productivity. Continuous filling of estuarine basin tend to be shallower. It   reduces the space available for life. It restricts the navigation through estuary into upstream areas. 

                          Dam construction across the rivers reduces the freshwater input of the estuary.  Estuary receives less amount of water during dry season. As the freshwater input is less, salinity increases due to the high rate of evaporation. Therefore during dry season, esurient environment is more favorable for eury-saline and hyper saline animals. During rainy season, estuary gets more fresh water than sea water. So salinity is reduced. So that estuarine environment is favorable for steno saline and eury-saline species.

                          Dam construction disturbs the migration of animals. Eels migrate from rivers into sea through estuaries their breeding season. Salmon fish also move from sea to rivers through the estuaries during their spawning season. Amount of nutrients and sediments is also decreased due to the less freshwater input.

                          In most of the areas of the country, water requires for water treatment plant for drinking is also extracted large amount of water from the rivers. It also contribute to the environment of the estuary.