Stormwater ponds have a conservation role

Posted on June 4, 2011

Although natural wetlands have been largely replaced by stormwater ponds and other artificial water bodies in urban and suburban landscapes, the extent to which artificial wetlands function as breeding refuges for amphibians and other aquatic animals hasn’t received much attention.  While the total area occupied by stormwater ponds in urban environments can be significant, it’s possible that their tendency to accumulate pollutants and to dry out periodically means that they act more like ecological traps than ideal breeding habitats.  To shed light on this issue, 71 suburban and forest wetlands inMaryland,U.S.A.were surveyed repeatedly for amphibian calls, egg masses and larvae over two reproductive seasons in 2007-08.  The wetlands ranged in size from 12 to 59 ha. Six amphibian species – five frogs and one toad – were found.  In both suburban and forested watersheds, most of the sites where amphibian breeding activity was recorded were artificial wetlands, and late-stage larvae were found only in these habitats.  Natural wetlands were relatively small in size and didn’t hold water long enough to support amphibian development.  Urbanisation modifies natural wetlands by increasing the area of impervious surfaces, which reduces rainfall capture, groundwater recharge and thus wetland size.  Although some urban wetlands may act as ecological traps, these results suggest that artificial water bodies can play an important role in amphibian conservation, and therefore that it’s  worth including  ecological considerations in the design and management of stormwater ponds.  Because permanent water bodies are rapidly colonised by fish and other predators, the value of artificial wetlands as amphibian nurseries is likely to be greatest when they retain water on a seasonal, but not a permanent, basis. 

Reference:   Brand, A.B.  & Snodgrass, J.W.  2010.  Value of artificial habitats for amphibian reproduction in altered landscapes.  Conservation Biology 24 (1), 295–301.