Do created wetlands aid amphibian conservation?

Study of created weltands leads to unexpected results...
Scientists published a study in the journal Conservation Biology looking at breeding success of amphibians in created verus natural wetlands in both suburban and nearby forested watersheds in Northern Baltimore County, Maryland. Their concern was that artificial wetlands such as stormwater ponds and other detention basins might create habitat traps for amphibians. Many of these wetlands are established at least in part to collect polluted and silted urban runoff before it can reach rivers. Habitat traps might occur if the attractive characteristics of these wetlands such as long hydroperiod lured amphibians but the harmful poluttants prevented breeding success. The researchers, Adrianne Brand and Joel Snodgrass from Townsend University, were suprised to find that the created wetlands were actually critical for the conservation of amphibians in the area.

Young wood frog. Image credit, Michael Zahniser. The scientists looked at 71 wetlands total - 53 in suburban watersheds versus 18 in forested watersheds. In suburban areas, 30.2% of the wetlands were stormwater ponds, 39.6%, were other artificial wetlands, and 30% were natural wetlands. In forested areas, 72% were natural wetlands versus 28% artificial. Of the wetlands, stormwater ponds on average were larger and held water for longer periods of time.

Durring two breeding seasons, the researchers surveyed amphibian calls, egg masses, and larvae at all wetlands to determine the reproductive effort and success of amphibian species using each wetland type. They looked at egg masses for the wood frog (Rana sylvatica) and the spotted salamander (Ambystoma maculatum).

The researchers found that breeding activity and calling activity primarily occurred in anthropogenic wetlands in both forested and suburban areas. While they found no egg masses for salamander anywhere, egg masses for wood frogs were more common in forested areas than suburban areas and were more comon in anthropogenic wetlands. They also found that larval amphibians occurred only in anthropogenic wetlands.

Conservation recommendations...

"We argue that not only can anthropogenic wetlands be important to amphibian reproductive success, but they may be the only productive breeding habitats that remain in some regions where natural wetland densities are currently low and wetland destruction has been extensive."

In the study area, extensive draining and ditching along with removal of beavers has likely destroyed many of the historically occuring wetlands. Other human factors have likely decreased the hydroperiod of existing natural wetlands.

The authors offer the following recomendation for management of created wetlands,

"In our suburban study watershed, many stormwater ponds are being reconstructed so that they hold water for a short period of time following precipitation events to maximize groundwater recharge and as a means of mosquito control. This pond design, however, only serves to attract amphibians and then compromise embryonic and larval survival when the pond dries quickly...In our study stormwater ponds that held water seasonally or semipermanently provided the best habitat for embryonic and larval survival, so design of the pond was critical to its potential to serve as productive habitat for amphibian populations in suburban areas...We advise against the design of stormwater ponds as permanent water bodies, however, because they can quickly lead to invasion by fish or other potential predators that could preclude use by many amphibian species."

Source:	Conservation Biology
Title:	Value of Artificial Habitats for Amphibian Reproduction in Altered Landscapes
Authors:	Adrianne Brand and Joel Snodgrass
	Towson University