Biophysical Interactions and Human Modifications within the Inter-tidal Ecosystem
Explain the biophysical interactions that occur within the inter-tidal ecosystems and outline the human modifications that may impact upon them
Inter-tidal wetlands are ecosystems that are found in swampy coastal regions, which unlike freshwater wetlands, have water that comes partly from the sea as a result of tidal patterns. These ecosystems occur because of biophysical interactions which occur between the atmosphere, hydrosphere, lithosphere and biosphere. These interactions not only produce the features of the inter-tidal wetlands, but the processes which occur within the ecosystem – geomorphological, hydrological, and biogeographical. These interactions also determine how well the inter-tidal wetlands respond to natural stress and change. But these interactions are under threat from humans, who have modified the wetlands, causing changes in each of the four components of the biophysical environment.
The four components of the biophysical environment interact in a unique way in inter-tidal wetlands. The atmosphere interacts with the hydrosphere by creating humidity levels of up to 90%. It interacts with the lithosphere in creating unusually nitrogen rich soils. It interacts with the biosphere in the way it receives hydrogen sulphide gas from the bacteria which reside in the lithosphere, as well as being effected by the canopy which effects its temperature and hence the amount of water in the soil. The hydrosphere interacts with the atmosphere when it receives gasses from the air, for example dissolved oxygen levels, which are high. It interacts with the lithosphere in creating its turbidity of 19 NTU and with the biosphere in creating nutrients which are formed by organic materials. The lithosphere interacts with the atmosphere through the climate, which effects rainfall, which raises the water table in the lithosphere and increases the salinity of it, hence affecting the plants found in the area. It interacts with the hydrosphere resulting in the damp soils which the native mangroves require and it interacts with the biosphere by creating a habitat for organisms such as bacteria, crabs and snails. The biosphere interacts with the atmosphere when the atmosphere provides a suitable climate for organisms, as well as when the mangrove canopy cools the air under it, which in turn keeps the soil moist.
The climatic conditions experienced in inter-tidal wetlands not only affect, but are a result of the interactions between the four components of the biophysical environment. The distribution of the saltmarsh and mangrove species is determined by the temperature and rainfall levels. In fact, rainfall levels affect the water table levels, affecting salinity, the amount of fresh water, photosynthesis, respiration, growth rates and transpiration, all of which are processes which are vital to the functioning of the inter-tidal wetlands. High amounts of rainfall are also necessary for the growth and spread of inter-tidal wetlands. The inter-tidal wetland’s other plant life is determined by rainfall patterns as well since they require certain amounts of fresh water to survive themselves. The warm eastern maritime climate
experienced by the inter-tidal wetlands also affect the wetlands, producing temperatures which are on average higher than the general Sydney area – 27.7oC, as well as slightly lower rainfall. These factors contribute to the environment that inter tidal wetlands are made up of.
Geomorphologic and hydrological processes also combine to create inter-tidal wetlands. For example, the deposition of 8m of silt from the Parramatta River is vital for the growth of the mangroves of the inter-tidal wetlands. Rising sea levels have drastically changed the look of the New South Wales coast since the last ice age, creating a ria coastline which is now Sydney harbour. It has also become evident that the species of vegetation of inter-tidal wetlands is also affected by rising sea levels in that past land connections with Asia have resulted in similar inter-tidal wetlands on both of our coasts. The process of weathering is also vital to the creation of inter tidal wetlands because the accumulation of silt, along with the organic matter from the mangrove leaves (up to 600 tonnes per km2) provides very nutrient rich soils. The process of erosion is important in that the inter-tidal wetlands slow down the process in order to protect the vegetation that relies on the soil. This is especially important because the salty nature of the soils means that the soils are vulnerable to breaking up in times of heavy rain and wind. The process of deposition of the sediment that is weathered away and eroded is also vital in that only fine sediment is suitable for the successful growth of the mangrove species, hence, actions such as the straightening of Powell’s Creek speed up the water flow causing larger, more unsuitable particles to reach the inter-tidal wetlands. Also, the formation of soils is important to the functioning of inter-tidal wetlands. These soils are generally waterlogged and have little oxygen content. Hence, the mangroves rely on their pneumatophores to obtain oxygen and their extensive root systems to cope with the unstable nature of the soil. Inter-tidal wetlands are good examples of invasion, modification and succession.
This is illustrated through the differing placements and diversities of the mangrove species as a result of different biogeographical processes. There is a succession both within and between each of the seagrass, mangrove and salt marsh species of intertidal wetlands. The diversity and number of species using the intertidal area hence changes. The succession of intertidal areas to one of the later stages of the salt marsh is validated by the fact that there is greater species diversity, nutrient recycling and niche specialisation in this area. Thus, because of its high level of nutrient recycling, salt marshes are described as one of the most productive ecosystems on earth.
Intertidal wetlands must adjust to stresses, including salinity and tidal movements. Intertidal wetlands are located in parts of the coastal environment that receive both fresh and salt water. They must, therefore, be able to survive extreme conditions. The salt water is a very difficult condition for plants to survive in. The mangroves can survive because its root structure lets it filter out salt. The saltmarsh must be able to
survive the salinity levels of both the water and soil. Plants near the water must be able to cope with salt water. This area is inundated during higher tides. Hence it is vulnerable to the stress factors associated with pollution because it can accumulate pollutants with the water. The changes and stress caused by tidal movements are great and the inter-tidal wetland has very specific responses. The grey mangrove has a root system that includes pneumatophores. However, this natural response to the stress of tidal inundation can fail if the magnitude or frequency of inundation is changed by increased runoff or altered drainage, and the roots are submerged for too long. The mangroves can be pushed beyond their threshold levels if the water quality is changed and substances such as oil cover the root’s lenticels because this impedes their ability to take in air. The locations of intertidal wetlands mean that even healthy ecosystems are vulnerable to changes within the catchment. Parts which are vulnerable are humidity, phosphate concentrations, soil pH and the existence of monocultures.
Unfortunately, humans have impacted upon the inter-tidal wetlands in negative ways. Impacts on the atmosphere include the production of wind tunnels as a result of building straight paths through the mangroves; hence walkways such as the one we were on during the field trip are made in a zigzag pattern as not to create wind tunnels. Alterations to water flow such as the re-structuring of Powell’s Creek affect humidity levels, which since the 1950’s have slipped slightly. Humans have also affected the hydrosphere. Urban and industrial land uses within the Powell’s Creek catchment have contributed to increased levels of turbidity. Chemicals from rubbish and industrial uses are also detrimental to the quality of the water, hence affecting the living elements of the ecosystem, for example pneumatophores, which become smothered in the case of an oil spill. Humans have affected the lithosphere by building bund walls. This has re-directed the flow of water, and has affected the amount of soil moisture for the mangroves. This has the potential to elevate levels of acid sulphate, damaging the health of the mangroves and adversely affecting decomposer organisms that recycle minerals essential to the functioning of the ecosystem. Just about every impact that humans have eventually leads to an impact on the biosphere. For example, the dumping of toxic chemicals into the water has obvious effects on aquatic life. Also the creation of bund walls has altered the tidal flow and has introduced weeds into the fragile environment, forcing competition.
Inter-tidal wetland ecosystems occur because of biophysical interactions which occur between the atmosphere, hydrosphere, lithosphere and biosphere. These interactions not only produce the features of the inter-tidal wetlands, but the processes which occur within the ecosystem – geomorphologic, hydrological, and biogeographical. These interactions also determine how well the inter-tidal wetlands respond to natural stress and change. But these interactions are under threat from humans, who have modified the wetlands, causing changes in each of the four components of the biophysical environment.
© 2016 Billy Zhang