Connectivity surrogates

Posted on September 22, 2010

The importance of lateral connectivity between rivers and their floodplains, which plays a key role in nutrient distribution and the growth and dispersal of aquatic organisms, is well recognized.     However, the direct measurement of connectivity by monitoring flood pulses and the resulting  hydrological gradients on floodplains is a complex and expensive business, and this has prompted a search for universal surrogates of connectivity that can be used to compare the responses of different types of organisms to changing conditions across aquatic systems.   Studies of ox-box lakes in the Ebro floodplain in north-eastSpainexamined how well six surrogates of connectivity predicted variations in the species richness and abundance of phytoplankton, zooplankton and macroinvertebrates.  The study lasted for a year and included an extreme flood and a period when the lakes were completely disconnected from the river.  The connectivity surrogates, which were measured using aerial photographs, digital terrain models and water level monitors, were the distance from the river, flood duration, flood height and water level variability.   Different combinations of these variables accounted for up to 65% of the variation in abundance or species richness, depending on the type of organism.  The duration of flooding had the strongest impact on macroinvertebrate abundance, possibly through its effect on habitat recolonisation, while flood magnitude and waterlevel variation had a greater influence on phytoplankton and zooplankton composition.    Connectivity surrogates such as flood duration can be used to set restoration goals.  While species richness for zooplankton peaked with short-duration floods (0-10 days /year), the corresponding peaks for macroinvertebrates and phytoplankton were higher (10-20 and 20-30 days / year respectively).  Therefore, allowing flooding for around 10-40 days/year should help to maximize the diversity ofEbrofloodplain habitats and communities .

Reference:  Gallardo, B., Gascón, S., González-Sanchís, M., Cabezas, A. & Comín, F.A.  2009.  Modelling the response of floodplain aquatic assemblages across the lateral hydrological connectivity gradient.  Marine and Freshwater Research  60, 924–935.