New discoveries about biota and rainwater in the North Burial Ground

Greg Gerritt   July 2018
My work in the Providence’s North Burial Ground started off as a video project to record the tadpoles in the Rainwater Pool, and much of what I see is reported via video, with more than 500 short videos on the Moshassuckcritters Youtube channel . But there is a great deal that I see that is never captured on camera, or is captured on camera in ways that do not transmit enough information, so here is an essay reporting on what I have seen and learned so far this year (2018) that has not fully been conveyed previously.
This past January we had some severely cold weather and Ridge Side Lake, the permanent pond in the North Burial Ground next to the esker, froze solid. Normally when it freezes there are still holes and it does not freeze solid around the shorelines. This year it froze up completely for several days. The problem with freezing up is not the cold water or the ice, there is still water under the the ice. The problem is that the ice cuts off the water from the air, and with no gas exchange the animals living in the water can use up the available Oxygen, similar to what happens when decomposing algae use up all the Oxygen in a water body. The result of the freeze was a massive winter kill in the pond, with many dead tadpoles and fish floating around for a few weeks, with the fish getting refrozen into the surface ice after a thaw. I was unsure of the extent of the winter kill, not knowing what percentage of the vertebrae life in the pond was affected, but it was pretty obvious it was a lot of creatures. I made videos that showed many carcasses of fish and bullfrog tadpoles.
With the spring it became obvious that while severe, the winter kill did not wipe out the pond creatures, so this spring i have regularly seen bullfrog tadpoles, and this week I saw confirmation that the sunfish are still around when I found some newly cleaned out nests next to the peninsula and later saw a sunfish on a nest. There have also been a fair number of fish jumping all spring, and while I rarely catch a glimpse of them, the ones I see look like the catfish that also inhabit the pond, Recently I have been seeing a lot of newly hatched fish as well in the shallows. This week I also got confirmation that a significant class of bullfrog tadpoles survived despite the bodies I found as the tadpoles have turned to frogs and they are as abundant as they usually are in July along the shoreline stretch that I census. It should also be noted that Fowler’s Toads are heard calling at the lake, and occasionally seen in the spring, and tadpoles have been seen occasionally, though none have survived long due to predation. This year, when the Rainwater Pool became dangerously low, Ed Brookner transferred some toad tadpoles to Ridge Side Lake, and the timing was such that they thrived and turned into toadlets.
My understanding of the herons in the Burial Ground increased, with a better understanding of the individuality of each bird. There is no doubt that each species has a different way of reacting to human disturbance, but also that individual Blue Herons react differently, with some flying off from humans at a longer distance than others, and each bird having a particular route it chooses for escape. Night herons are less likely to fly off, Green herons are often very good at hiding in a tree, Blues are most likely to fly away from the pond, when disturbed, needing to get the farthest away.
Continuing along the vein of animals as individuals, there appeared to be a new pair of Red-tailed Hawks breeding in the Burial Ground. This year the hawks used a nest 10 feet lower down in the Pine tree, but what was really different was how the hawks reacted to people. The pair present the last two years would circle and call almost incessantly when I was around, though they reacted less vocally to some people. This year the pair rarely circled and called when people were around, and definitely did not react to me the same way as the pair did the last two years. After the young hawks fledged (and it was fun to watch them grow, develop feathers, and fly off) they continue to hang around sitting in very visible places and calling a lot. Not sure how long it takes them to learn to hunt well enough to feed themselves, but I do not think the young ones I see are there yet.
While the area around Ridge Side Lake may be the most wildlife dense region of the city (including coyotes, muskrats, bats, rabbits, turtles, dragonflies, and a plethora of birds) the real action this year was at the Rainwater Pool a few hundred yards away. In November 2017 Friends of the Moshassuck obtained a wetlands permit to modify the pool so that it would retain water longer and give the breeding Fowler’s Toads and Gray Tree Frogs a better shot at a successful breeding season. The modification took place at the end of March and beginning of April, when the pool had dried out quite a bit after a cold wet winter. As the groundwater dropped during a dry spell, the water level sank below the bottom of the pool, but once we started digging we were right back into the water table. What I learned at this phase was how to remove cattails. Essentially we had to slice the cattail muck, a combination of roots and organic buildup, into small squares with a garden spade and then try to corral the squares onto the spade so they could be lifted out. The pool has a very distinct line between the root mass and muck of the cattails and the sandy and gravely fill that had been dumped into what was once a pond many ears ago.
Racing the next snowstorm, I placed a plastic liner at the bottom of the pool to ensure the pool would hold water longer. RIDEM and I seem to have missed on communication as to whether or not the liner was a good idea, and eventually they told me to remove it. Which Michael and I did by wading, shoveling, and hauling in knee deep water the morning before the breeding season for the Fowler’s Toads was about to begin. After that, May and June were really dry, less than half the normal rainfall between May 1 and June 27, when we got about 2 inches of rain. While the rush job at the end of March produced a pool with imperfections, that will be corrected when the pool is dry in the non breeding seasons, the Rainwater Pool project worked as advertised. That is it held water for 17 days after the last significant rain instead of 12, though this was a year in which even more days would have been very useful.
Fowler’s toads present an interesting dilemma. The really prefer to be in very shallow water during the day, though they do retreat from the shorelines in the evening, but at the same time they need pools that will hold water for two full months at a rather hot and potentially dry time of year. I have not seen enough cycles to again use the pool as a rainwater gauge, the excavation has to have changed that dynamic a bit, it is clear that the pool remains good Fowler’s toad habitat while at the same time having a longer hydroperiod, which was the intent of the whole project, a longer hydro period increasing the odds of the tadpoles surviving to the toadlet stage, while still shallow enough to go dry in a real dry spell.
Tadpoles started to turn into toadlets about June 20, and the last of the tadpoles turned to toadlets by July 4, but the drought caught up to the pool by June 21, 17 days after the last real rain. One of the friends of the Burial Ground has followed the tadpole and rainwater projects closely, and when the pool became so low that it was apparent that by the next day it would be completely dry and all the tadpoles would be lost, Ed Brookner started a 21st century bucket brigade and each day for the next week Ed, Margaret, and I brought 60 to 100 gallons of water to the pool, which was enough to see them through until the big rain of June 27, by which time 80% of the tadpoles had turned to toadlets.
The pool now holds water about 5 days longer than it would have, due to its greater depth, increasing the hydro period from about 12 days to 17. And it has a deep end as the result of a thicker cattail layer in the north, and because of the excavations necessary to remove the liner . Having this deeper end allowed us to use less water to keep a sufficient depth for the Fowler’s toad tadpoles., which seem quite content with 2 inches of water. Most years we shall not need to provide water as in the past the pool stayed reasonably full with an average RI rainfall of .84” a week, as long as it comes as a storm with greater than .5” at a time. So that it can push through the wetland vegetation to reach the open water.
One thing to note is the resilience of the Fowler’s Toad breeding system. Many amphibians species breed on one or two big nights, whereas s Fowler’s toads come back tot he pool repeatedly if the weather is warm and the pool has enough water to give them hope. The rains of June 27 seem to have brought them back and in mid July when this piece is being written, there is a new crop of tadpoles swimming about.
I had not seen any Gray Tree Frog tadpoles in several years, despite breeding Tree Frogs being as common as breeding toads in their pool. I spend as much time as I can during breeding season, and eventually can hear that each frog and toad has a distinctive call, and you can generally localize each call. I think on the biggest nights this May there were about 10 toads and 10 tree frogs calling at the pool. This year though I saw at least 2 Gray Tree Frog tadpoles. Fowler’s Toad tadpoles are small and black, eventually turning to grayish. Tree Frog tadpoles are multicolored, and have a very distinctive gold spot on the belly. For years I have watched the toad tadpoles eat, and have become rather familiar with their feeding behavior. They scrape algae and other small things off of vegetation and other surfaces with the keratin scrappers around their mouths. This year I saw that Tree Frog tadpoles feed at the surface of the pool. Seemingly screening the water for organic matter to ingest. They make some interesting bubbles as they slurp and use their tongue to move sieved food to the mouth. With this behavior, using a vertical position in the water to feed as opposed to horizontal feeding that toad tadpoles use, as well as their much larger size, the tree frog tadpoles need deeper pools that last considerably longer than the toads need to successfully make it to froglets. The tree frog tadpoles may not have made it through the very shallow water phase of the rainwater pool cycle in late June, but if they did I might still not see them in the pool now that it is full. If I am really lucky I may see one of the little green froglets before it heads for the trees.
While learning about the hydroperiod of the modified rainwater pool, and how the amphibians interact with it, i was also learning about the bureaucracy that governs wetlands and how the rules make it difficult to help amphibians. On behalf of the Green Infrastructure Coalition I am focusing on modifying the wetland and stormwater regulations so that they will be more amphibian friendly and the process more friendly to local conservation efforts. I have advocated for these changes in several forums, and written a letter to RIDEM on how the the rules should be modified and offering some suggestions as to how to structure the process so that ecological restorations would not be required to go through the same application process as those seeking to ruin wetlands in the pursuit of real estate profit. I also know, from experience, that it will take at least 2 years to make these changes as the wheels of regulations grind slow. I will keep you updated.
There have been Killdeer, a small shorebird related to plovers, in the North Burial Ground for as long as I have been walking there. Living near the Rainwater Pool. I have noticed them for years, but rarely did they seem to spend time along the pool. This year, I saw two Killdeer regularly, and often saw them down along the shoreline, especially in the areas that were impacted by the spring excavation., I could not get it on film, but they very definitely appeared to be hunting and eating tadpoles in the very shallow water in places with limited vegetation, and often the tadpoles seemed diminished when i returned the next day, a phenomena that seems related to predation as unless they pool goes dry, there is little tadpoles mortality from other causes. One highlight was that I saw a miniature killdeer one day, obviously a young one in adult plumage, but half the height and still unable to fly. It went and hid in the cattails, so I headed out to let it relax. I think the excavation opened up some unvegetated habitat right next to the water, and the Killdeer were using the vegetation free zones for hunting.
Currently the funding for this project comes primarily from grants to the Green Infrastructure Coalition from the Rhode Island Foundation and the Pisces Foundation. So lets close this essay with a bit on the management of stormwater using nature based solutions. The goal of nature based stormwater management is to prevent high volumes of water from instantly entering streams and rivers when it rains which causes flooding, and to reduce the pollution in runoff by filtering it before it gets to rivers and streams. Usually this is done by creating ways to slow water down, filter it, and infiltrate it into the ground with constructed rain gardens and swales. ( An aside is that during the course of writing this essay I saw an article about a new type of filter being developed to capture airport deicer fluid from rainwater before it goes into a stream or river, and that that work is leading to advances is filters to clean rainwater in streets as well. While infiltration of the water is appropriate in most places, it is interesting to ponder how we might manage runoff in ways that enhance habitat for wild creatures, in other words can we find places to keep the filtered water around so that vertebrates: amphibians, reptiles, birds, and mammals can use it. Amphibians are among the most endangered taxa on the planet, with a lifestyle that requires both clean water and upland hunting grounds. They mostly breed in temporary pools, and temporary pools are always a target for the real estate industry to turn into house-lots. The loss of habitat, along with new diseases and climate change, mean that often we discover new species of frogs just as they are about to get wiped out by the new mine, forest concession, or suburb. In a place like Rhode Island, it means that small temporary wetlands get very limited protection when profits are at stake. And that any place where upland habitat is separated from breeding habitat by roads, populations are even more fragile.
The Rainwater Pool seems to provide excellent habitat for Fowler’s Toads, an amphibian found in small populations throughout Rhode Island and up and down the East Coast. It is a temporary pool that holds water for months on end in wet years, but does go dry nearly every year, which keeps out toad predators for the most part. As noted in its name, it is entirely fed by rainwater, which enters through a chute after running along cemetery roads in a small watershed. If the pool was not a recipient of this rainwater, it would rush directly to the Moshassuck River via the cemetery stormwater system, contributing to the rapid ups and down of the Mighty Mo as it runs in its very channelized system on its way to meet the sea in downtown Providence. What also makes it good Fowler’s Toad habitat is that no cars drive in the cemetery at night, which means toads going to the breeding grounds are not getting squished, and the soil is sandy, so the Fowler’s Toads can easily burrow into it. In New England ofter sandy spots are used for cemeteries as often the soils are too droughty for growing corn and the digging is easy. Cemeteries also often have little ponds or wetlands, so more attention should be paid to them as amphibian habitat.
The Rainwater Pool in the NBG shows that a place that can or could hold onto water for a few weeks after a rain, but does go dry occasionally, if surrounded by sufficient habitat to support amphibians in the non breeding times of the year, may be made into more useful habitat when trying to manage the stormwater in the neighborhood. On a recent trip to Virginia for a conference, the conference center was next to a park that primarily was a stormwater management system to manage the water from suburban development grafted onto a lowland forest, protecting the river, but in several places in the area I saw little ponds that were created to manage stormwater and they were full of life, frogs in one, fish and herons in another so I am not the only one thinking about this. Rhode Island stormwater regulations primarily push for rapid infiltration, so we need to find a path into the regulations that allows for temporary breeding pools, or even pools that can be drained in the off season in places with sufficient habitat. It has been said to me that places in the Northeast without pools that had some constructed saw an influx of amphibians breeders including species that had not previously been documented in the area. The flip side of that is that the regulations and the application requirements for work in wetlands are tailored to the needs of the real estate industry, and are an expensive and frustrating process for efforts to restore habitat. I am also working with the State of RI to create a new category in the regulations with a process specifically for approving small scale restorations that will be much more friendly to low budget operations. I hope my work at the Rainwater Pool has helped start that process, and I expect to continue to learn new things that help me see that process through.