Rainwater Pool update August 2019

In May 2018, after 6 years of observing and studying the cycles of the rainwater pool and its life in Providence’s North Burial Ground,  Greg Gerritt and some volunteers dug out the 6 inch thick cattail root layer out of a 12’ x 25’ area in the center of the rainwater pool focusing on the parts of the pool that held water the longest as it was drying out. The idea was to increase the hydroperiod of the pool by 3 to 5 days, and thereby increase the odds of a successful toadlet cohort most years without turning it into a permanent pool.  A Fowlers Toad tadpole cohort successfully transformed into toadlets in 2018.  Following the mid to late July exit from the pool by tiny Fowlers Toad toadlets it rained extensively, and started one of the rainiest 12 month periods in RI weather history.  Though most years the rainwater pool will go dry, it only takes 17 days of no substantial rain to dry it out, as of August 1 2019 the pool had not dried out since mid June 2018. There is no way to actually compare what would have happened if we had not excavated the cattail layer in an effort to extend the hydro period of the pool as it has not ever reached a stage in which it would have been dry under the old topography. We are still waiting for a dry spell dry enough to empty the pool or nearly so.  There will be much to learn and do then. Thankfully the permit we received for the project allows continued maintenance, and some leeway to figure out what is most appropriate. 


Most of what I have learned from the long term observations of the pool and the surrounding micro watershed, and the results of the excavation have been reported by video in the Rainwater Pool Series on the Moshassuckcritters   https://www.youtube.com/user/Moshassuckcritters?view_as=public   Youtube channel.  But there are many aspects to this story that have not been recorded on video, sometimes because an absence is hard to video or communicate with pictures, often because the amount of vegetation growing in the pool makes it impossible to see anything.  There are also connections that do not translate to video, especially short videos, but that can be explained in writing.  

The major changes in the pool since May of 2018 include a raised delta continuing to form and thicken near the water entry chute in the northeast corner, the resurgent spread of cattails across the excavated area, and the continued silting of the entire area of the pool.  To reduce siltation, mostly from runoff from the hillside above the site to the east/southeast and from the dirt access road to the southwest, the cemetery crew has been allowing more vegetation to stand in the entry chute.  This is why the delta has built up by about a foot in the last few years. The vegetation captures some silt before it gets to the lower part of the pool.  As the silt builds up the channel from the chute to the pool has changed several times, flowing back and forth across the delta.  The current configuration is that the water channel is at the northern end of the delta, but last year there was a channel flowing southwest to reach the pool.  The channels are about 6 inches wide and several inches deep.  Eventually they clog or get overwhelmed by a flood and the flow of the water finds the next lowest spot to flow through.  Same process as delta formation from the Nile to NOLA.   Someone should use it as a lab because things move quickly so you can see year to year changes. 

RIDEM and I had a bit of a disagreement about putting a liner in the pool.  I am sort of glad I removed the liner knowing how the bullfrogs have thrived in the rainwater pool in the rainiest year in a long time, but I do think it would have been a semi effective barrier against cattail expansion, something that will require a great deal of effort to cut back regularly so that open water can be maintained for tadpoles in the pool.  As soon as it is dry, I will be going back into the pool to remove cattails, and I hope that the dry spell will also cause the bullfrogs to leave.

The rest of the vegetation seems pretty stable, with the cattails not running over the areas of bulrush, arrowhead and pickerel weed, though I think things will change as the pool gets progressively shallower and holds water for shorter and shorter periods.  

In 2018 we had a relatively large cohort of Fowlers Toad toadlets hop away in June and July to spread through the Burial Ground.  Shortly after most of the toads had moved on, the Bullfrogs showed up, as they do towards the end of most Julys. They come over from the mass emergence of bullfrogs in Ridgeside lake that happens around July 1 most years.  In the past they have stayed  in the Rainwater pool until it went dry in the next dry spell.  With no dry spell I wondered what it would look like in the spring of 2019 and whether the bullfrogs might affect the breeding cycle of the toads and treefrogs that use the pool.  I can report that a number (an unknown number over 4) survived the winter at the Rainwater Pool and persist whenever the water is low enough so that I can to get close to the center of the pool. And see them jump.  

Breeding season for the toads, and the Gray Treefrogs began right on schedule in early May, with robust numbers of calling breeders when the nights were over 60 degrees F. Around May 20 there were beginning to be thousands of toad tadpoles, while at the same time, breeding season continued.  For those who have not experienced toad breeding season, check out the videos of toad calls on Moshassuckcritters. The toad tadpoles appeared to be growing nicely, but a dry spell seemed to dramatically reduce their numbers even though there was plenty of water in the center of the pool and it did not appear that many of the toad tadpoles were caught in puddles without outlets, mostly as the siltation in recent years has smoothed the bottom and reduced the size of depressions. .  It is quite possible the bullfrogs ate many many tadpoles, but I just do not know.  In any case when the water rose, a reduced number of tadpoles were spread around the pool, with some local populations seemingly avoiding disaster, while other herds were much reduced or eliminated.  Eventually one localized population turned to toadlets, but I never saw evidence of other or later toadlets.  

As the pool rose with the rains that spread the tadpoles around the pool again, a large new cohort of very small tadpoles emerged, but within 3 days they were gone, something I had never noticed before in 6 seasons of close observation. . It has been suggested to me that that water in the pool may have become too warm, that the bullfrogs ate them, and that there was some sort of toxicity or anoxic periods.  Maybe next year I will find a way to do some water sampling and further observations if I see similar events, but as it surprised me this year, I do not have that data, and can only form hypotheses for later testing.

Every spring the Gray Treefrogs congregate at the pool and call, adding their voices and swimming to the breeding frenzy.  In 2018 I saw treefrog tadpoles for the first time in several years, but only once in 7 years have I seen treefrog tadpoles turn into little green frogs and that was the first year of the study.  Clearly the treefrog tadpoles are present in lower numbers, with fewer eggs laid by each female, and fewer calling at the pool than the 17 Fowlers Toads I counted on the biggest night this year.  They also feed differently, and Treefrog tadpoles are larger, so they need deeper water to thrive for longer periods as they take longer than the little toads  to become air breathers. 

My guess is that the delta below the chute has been building up for several years, but it is only in the last couple of years I have paid attention to it.  It would be a great place to hold a workshop on delta formation as it is building right before our eyes. I know it has taught me much hydrology and geology.  I am also pretty sure that if the silt was not building up in the delta, but was instead spreading through the whole pool, the area we excavated would fill even faster and the whole pool would get shallower faster, reducing the odds of a successful toad cohort emerging after breeding season.  

There are a lot of things I still want to know.  I suppose it might be useful to know the water temperature and find out if Fowlers Toads and Gray Treefrogs have temperature limits that are being exceeded, though since both are more common to the south of Rhode Island, that is not likely.  Oxygen levels and tadpole requirements might be useful to study, especially given the interesting behavior or bullfrog tadpoles in Ridgeside Lake, some years regularly breeching like little whales for reasons unknown, but possibly related to low oxygen levels in the pond.  

It would be interesting to tag newly emerging frogs at Ridgeside Lake to see if we could identify an individual that actually makes the trek and prove provenience, but there really is no other place around that could produce migrants. 

Besides impacting the North Burial Ground ecosystem, the Rainwater Pool project, has changed how we think about stormwater and what to do with it in Rhode Island. RI is becoming a little more amphibian conscious.  I did not invent the idea that people could modify rainwater infrastructure to better suit amphibian breeding, or that they could create new wetlands of any type specifically for amphibians, but I did have something to do with popularizing it among people in a position to do something.   When the Green Infrastructure Coalition formed in 2016 and I started to ponder the rainwater pool in the NBG as both amphibian habitat and rainwater infrastructure I started to look into the research and figured out a small intervention at the rainwater pool might be useful. I spent several years of investigation to back up that suggestion and determine what to do.  I began by conversing with Jim Caratolo and Thomas R. Biebighauser who were well into the process of creating amphibian breeding pools by digging shallow ponds in rural areas.  Biebighauser makes a living by going around the country and helping people and non profits create pools for amphibian breeding.  I convened a stormwater and amphibian conference at Providence College to discuss the ideas I had been reading about, my observations, and what others were doing and seeing.  20 people, mostly from RI, attended and a good discussion ensued.  The fruit was slow to ripen, but following the May 2018 Rainwater Pool deepening in the NBG, I have heard about two specific cases of organizations in RI creating breeding habitat for spadefoot toads on lands managed by the Richmond Land Trust and on land managed by the Barrington Land Trust.  In both cases the people involved were part of the convening I did in 2016.  And both hired Biebighauser to manage the projects.  Glad Friends of the Moshassuck and the Green Infrastructure Coalition have been able to help move the agenda of amphibian restoration forward in Rhode Island with our advocacy and a successful project. 

A side note is that at the Northeast Natural History Conference in spring 2019 Michael Graziano presented on

Amphibians and Vernal Pools: Seeing the Forest for the Trees 

A presentation about creating small amphibian breeding pools in Ohio to test whether the specific tree cover in an area affected which amphibians were able to breed.  There were slight differences in species found under different canopies, but the  real take away was that multiple species of amphibians found all of the pools within months and successful breeding was noted in most of them from the first spring on.  I am thinking this should be standard practice wherever practical.  

Intertwined in all of this is the permitting process for the modification of wetlands.  The laws and regulations governing wetlands are a strange amalgamation of the understanding that protection of wetlands offers big benefits to communities and the desire to profit in real estate that calls for nearly unlimited ability to fill wetlands and alter bodies of water to suit profit.  It is basically a negative system that allows the death by a thousand cuts approach for the waters of RI.  And it seemed to have no rules aiding and abetting the restoration of wetlands for habitat, which in an age of ecological collapse, and the terrible extinction plagues being visited on amphibians, it would seem that DEM/the state of RI,  should be going all out to help restore wetlands and habitat, or at least would be facilitating community efforts instead of throwing up expensive obstacles.  There has been some progress, but with the understaffing of DEM in the name of neoliberalism’s attacks on regulations and taxation so the rich can steal more, and the political contributions of the real estate and construction industries, progress will be slow.  

But obviously DEM is starting to at least get the idea that restoration is a good thing and they should cooperate, so when the land trusts in Richmond and Barrington, in conjunction with the professionals, decided to do this, there seem to have been fewer regulatory hurdles.  Maybe some day creating amphibian habitat will be  a regular part of how we create beneficial uses for stormwater.  

The Green Infrastructure Coalition has continued to push forward with stormwater research centers, stormwater utility districts, and helping put more projects in the ground to collect water with every conceivable mix of partners.   The  concept of modifying the planet to aid amphibian populations has now been proven in Rhode Island, and is being adopted by others.  Creating amphibian habitat by better utilizing stormwater is not going to lead the grant proposals of the Green Infrastructure Coalition, there are bigger battles to fight right now. It was always a sidebar, but it does give us a larger range of earth healing options as we do the work of turning stormwater in ever more dangerous quantities into an agent of ecological restoration.