Floodplain habitat fragmentation

Posted on September 26, 2009

In arid and sub-arid environments, floodwaters trigger strong pulses in productivity by creating temporary aquatic habitats on the river floodplain and delivering nutrients to stimulate the food web.  After a flood event, water bodies on the floodplain gradually dry out and become more fragmented.  In principle, the resulting mosaic of conditions should lead to wide contrasts between water bodies in terms of the densities of different species.   Support for this prediction has come from a study of a floodplain – wetland complex in theNarranRiverin south-eastAustralia.  During a nine-month period following a flood in February 2004, total zooplankton densities at different sites on the floodplain diverged strongly and    eventually varied over a wide range

(< 30 to >4000 animals / litre).  At some sites plankton communities became distinct within a couple of weeks of the flood event, probably due partly to variations in the emergence of resting stages from the sediment.  While site differences explained most of the variation in the abundance of some plankton groups (water fleas, seed shrimps), the time since flooding was a more important factor for other groups, such as copepods.  Densities of water fleas were highest at the only site with aquatic vegetation, possibly because it helped to protect them from predators.  These findings help to show how the timing of flood events and small-scale floodplain habitat mosaics interact to affect river production. 

Reference:  James, C.S.., Thoms, M.C. & Quinn, G.P.  2008.  Zooplankton dynamics from inundation to drying in a complex ephemeral floodplain-wetland.  Aquatic Sciences. 70, 259 – 271.