Aquatic ecology and Biodiversity

Unit 10- Coastal ecosystems

10.3.2. Characteristics of estuary
These biotic and abiotic factors play an important role on the distribution and diversity of organisms in the estuary.
Salinity: Variations in salinity are affected by temperature, dissolved gases, density and viscosity. Salinity in the estuary varies with depth, flux of fresh water, and changes with the tide. Floods result in reduced salinity and drought can result in higher salinity.
Temperature: Shallow estuarine waters exhibit great temperature changes. The sun heats up the estuary during the day and cools at night due to influx of water from rivers and the sea. Tides also affect estuarine temperatures at high tide, the deeper, lower reaches of the estuary remain cool, and only the top layers are heated by the sun.
Oxygen: Some estuaries have very low oxygen levels. In highly stratified estuaries, the level of biological activity in the lower levels can deplete oxygen levels. When mixing is low and tidal effects are minimal, replenishment of oxygen in the estuary may be minimal.
Sediment: Particle size and chemistry of estuarine sediments can make a difference in the organisms that can survive. Infiltration of the estuarine sediments by nutrients, trace elements, sewage and industrial waste can influence the productivity of the estuary.
Wave action: This effect is very minimal in estuaries and hence more amounts of sediments are settled along the bottom of the estuaries. This reduced wave action in turn promotes the deposition of sediments and development of rooted plants in the estuarine regions.
Turbidity: As this region is having good amounts of fine sediments or particles, turbidity of the estuarine waters is very high in most of the periods. The highest turbidities are known to occur during the maximum freshwater discharge into the estuaries.