by Brenda Zollitsch, Policy Analyst
I traveled to Rhode Island this week to spend the day with professionals from a variety of backgrounds talking about the intersection of amphibians, habitat and stormwater wetlands. The meeting I attended was framed as a “Stormwater and Amphibians Roundtable” and drew scientists, regulators, land trust managers, teachers, nonprofits and even a zookeeper. The movement to promote green infrastructure across the nation to manage runoff and reduce nonpoint source pollution creates an opportunity to explore other benefits or challenges that arise from new construction and restoration activities to create more natural-looking stormwater management infrastructure. Here is what I learned from the discussion.
To set the stage for group discussion, the convener of the group, Greg Gerritt, arranged for a number of presentations from several experts. Scientific evidence on a variety of research on amphibians, constructed wetlands and the impact of stormwater pollutants on rare amphibian species was presented by two Providence College professors — Dr. Jonathan Richardson an evolutionary biologist and Dr. Nancy Karraker from the Department of Natural Resources Science, who both conduct research that informed our discussion. The following are interesting tidbits that I learned from these presentations. (Note: If you are interested in getting citations for this research, contact me at and I can send you more information and/or connect you with the presenters directly):
There are limited studies connecting constructed wetlands and amphibians. Those looking at these links have shown that leading predictors of amphibian diversity and persistence are hydroperiod, canopy coverage and the upland habitat surrounding the pond/wetland. Other variables for consideration include depth, log area, and habitat fragmentation.
Creating habitat to equally welcome all amphibian species is not viable. Various amphibian species will thrive in different (and contradictory) conditions. This means that when planning amphibian habitat, decisions need to be made about which amphibian(s) the habitat is being designed for.
Because amphibians have two different phases in their life cycle — one where they live in the water and one on land — the land adjacent to the wetland/pond is critical to their lives as adults. Restoration or planning activities should consider this larger habitat when planning to support amphibian communities.
Studies comparing constructed and natural wetlands have shown that constructed wetlands are more likely to have higher pH, greater presence of invasive species such as Phragmites and Duckweed, and higher levels of light infiltration, all of which are threats to many of the more rare amphibian species.
While connectivity among natural ponds has been shown to be critical for amphibians, little research has been conducted on the role connectivity plays in constructed pond/lake habitats. Connectivity issues should still be considered in constructed habitats.
The most critical challenge of constructed wetlands/ponds that gather stormwater is the presence of toxicants. While some species can evolve and develop tolerance, rarer species such as the spotted salamander and the wood frog have not been found to adapt to these conditions.
Studies have explored the impacts of road generated contaminants including road deicing salts (including MgCl, CaCl, and KCl), metals (copper, aluminum, zinc, lead and cadmium), nitrogen and phosphorus, and polycyclic aromatic hydrocarbons (PAHs). The most impactful of these pollutants for rare amphibian populations has been shown repeatedly in studies to be deicing salts. Chlorides have been found up to 175 meters from their road source, often finding their way into wetlands that are not perceived as impacted. Impacts included degraded water quality in ponds used by amphibians for reproduction, reduced reproductive success, lower survival of eggs into hatchlings, the inability of juvenile amphibians to complete metamorphosis, and negative impacts on growth and development.
Some of the research conducted by Dr. Karraker found (what I would refer to as “disturbing”) common malformations in hatchlings exposed to elevated levels of chloride (high conductivity waters). These included kinked tales, abdominal ademas, and what she called “circle salamanders” — hatchling salamanders misshapen into crescents and only able to swim in circles as the membrane of their eggs did not expand properly due to a lack of absorption of water due to the presence of chlorides. Additionally, egg clutch sizes were smaller when collected near roads where salt was applied. Timing of amphibian species metamorphosis is in the early to mid-summer, when chloride concentrations are highest as water volume lowers.
Dr. Karraker also found that metal pollution impacted amphibian survival to multiple life cycle stages, including hatching, metamorphosis, growth and development.
Despite these findings, some researchers have posited that there may be some role for stormwater basins/wetlands to serve as habitat for amphibians where no habitat at all currently exists, especially in urban settings.
Framed by this background information, the roundtable participants then launched into discussion about the viability of creating amphibian habitat from constructed water bodies. As you can imagine, the dialogue that followed about developing stormwater ponds/wetlands for amphibian habitat was animated. Here are some of my takeaway thoughts from our discussion. Integrating stormwater management with development of habitat for rare species is a laudable aspiration. A presentation at the roundtable by staff involved in Providence College’s stormwater master planning effort shows that the opportunities to create beautiful ponds and wetlands that treat stormwater are both real and cost-effective.
However, there are potential unintended consequences from well-meaning efforts to find breeding grounds in developed areas for these creatures. These may include:
- The inability to protect amphibians (and other organisms) from toxins and other pollutants such as excessive sediment and temperature;
- Challenges in regulatory control since currently constructed wetlands designed for the purpose of stormwater treatment are not regulated by state and federal environmental agencies — but wetland habitat within jurisdictional control is. When a constructed wetland is designed as habitat in addition to stormwater treatment, regulatory waters are muddied; and
- Serving as population sinks for rare amphibian species — stormwater wetlands/ponds, if not placed and constructed taking amphibian populations into consideration, may serve as population sinks for rare species. While intending to serve as habitat to support frogs and salamanders, instead they could be damaging or reducing population numbers.
It is easy to see why it makes sense to explore whether or not there is a way to capitalize on these efforts. With the growth and promotion of green infrastructure, finding ways to create multiple benefits from limited resources is important. However, we must tread carefully.
Next steps include exploring the possibility of inventorying existing populations of amphibians in current stormwater ponds and wetlands; additional research on impacts; and working on identifying examples of demonstration sites or studies where stormwater management and amphibian habitat have been harmoniously created.
Rhode Island’s state regulators and research scientists raised deep concerns about moving too quickly to promote the joining up of these two areas of work that are shared by the Association of State Wetland Managers (ASWM). However everyone around the table, including ASWM, is open to exploring new ideas and finding circumstances where this kind of work would be beneficial. One such possibility is establishing clean or pretreated stormwater wetlands as habitat.
As we explore these engaging and complex topics, we always love to hear your thoughts. If you have any experience, studies, or ideas about this topic, please send them to me at .