Australia: The Land Where Time Began

A biography of the Australian continent 

The inhabitants of the hyporheic zone (water below a river bed and below the banks of the river). The 2 main categories are permanent and temporary. The temporary hyporheos are mainly small invertebrates, e.g., insect larvae, that get into the hyporheic zone, often as a result of spates (flash flood or heavy rain).

The permanent hyporheos are of many types of small invertebrate such as crustaceans, segmented worms, flatworms, rotifers and water mites, all being specialised for this particular environment. There is not much knowledge of food webs in this zone, but biofilms appear to be an important food source for a number of organisms that graze them, and it is believed the biofilms benefits from grazing activities of hyporheos. Invertebrates assist the microbes by breaking down the plant material in the sediment which increases the surface area accessible to microbes. The fragmentation of the plant material also helps prevent the clogging up of the system. The activities of the hyporheos have the same physical effect on the structure of the hyporheic zone that soil organisms do in soil. Their activities change pore size, provide a means of dispersal for microbes, are a source of food for predators from the surface and mineralise biological detritus, making it available to be recycled by plants. Some of the larger crustaceans are up to 15 mm long. These organisms move through interstitial spaces which has then effect of providing channels for ventilation and the movement of water currents.

A dramatic demonstration of the interconnectedness of various parts of the biosphere was found when a study was carried out in New Zealand on rivers passing through pasture on cleared land, native forest and through pine forests. The highest level of biodiversity was found in the native forest, a lower level in the river passing through the pasture and the least, much lower level of  biodiversity in the river passing through the pine forest. This study demonstrated that changes in land use led to the same changes in biodiversity in the hyporheic zone that it does in the terrestrial environment affected by the land use change.

In Australia similar effects of land use changes were found in the Never Never River in the Dorrigo National Park. At Bellingen near the headwaters of the river there were 28 species of water mite, at least 11 being previously unknown. Where the river runs through heavily logged valleys, as well as river flats that were heavily grazed by cattle or cropped intensively there were not many invertebrates and the interstitial spaces were clogged with silt. In the down-welling zones oxygen levels were low, indicating water exchange between stream water and subsurface water was disrupted. The connection between surface and subsurface water was further disrupted in the downstream portions of the river by extensive gravel extraction. The loss of most of the hyporheos appears to be the result of large scale clogging of the interstitial spaces with silt.

The health of complete hydrological systems is being severely compromised by many land use practices that lead to siltation.

Sources & Further reading

Mary E. White, Earth Alive, From Microbes to a Living Planet, Rosenberg Publishing Pty. Ltd., 2003

Links

Effects of spates on the vertical distribution of the interstitial community