Submission to the RIDEM Wetlands Restoration Team from Friends of the Moshassuck
The North Burial Ground a 300 year old cemetery along North Main St in Providence has a small wetland that is fed entirely by the runoff coming from a small watershed that funnels water down 3 roads to the rainwater pool. The pool is in an area that would have been originally part of the wetlands lining the Moshassuck River, but between 300+ years of civilization, and the reshaping the area due to the Blackstone Canal and I-95, the river runs underground, and it is hard to say what is natural and what is not. I have been told that in the past the pond was deeper, more permanent, and had a fountain. The 2016 Rainwater pool video series provides detailed pictures of the site, but I am including aerial photos from google as well as screen shots from videos showing the pond. Currently the pool is completely dependent upon rainwater and the pond levels go up and down pretty consistently with the rains.
I was first attracted to the pool in 2011 when i noticed black tadpoles one spring day. In 2013 the Moshassuckcritters video project of Friends of the Moshassuck started documenting the tadpoles and other NBG wildlife. As I spent more time at the pool and watched it change across the seasons and years, i came to understand the pond as a rainwater system, and studied how the Fowler’s Toads and Gray Tree Frogs interacted with the pond.
The rainwater pool in the NBG is approximately 100 ft from east to west and 60 ft from north to south. The grass is mowed right to the edge of the wetland around most of the pond, with a steep sided section on the north covered in knotweed and vines. The pool is closely abutted on 2 sides by cemetery roads. To the south and west the land rises to the cemetery sand piles and a dirt road providing access to the piles off the route to the main gate. Land management practices around the pond create some erosion, but the dirt road, with its delta reaching on to the tarred road, is the source of most of the silt going into the pool, as silt deposits can be seen all the way from the delta to the pond. It seems like the pond has become shallower and vegetation has taken over more of the bottom of the pond recently.
Recent data suggests strongly that amphibian populations in New England are very dependent upon how long the hydroperiods are of ponds that do go dry and therefore have no fish. I believe that the shallowing of the rainwater pool is reducing its hydroperiod. Over the last few years I have watched the pond go dry with tadpoles in it, and then seen the toads and frogs try again when the rains returned. With a hydroperiod of between 12 and 14 days, and the need to have about an inch of rain each week to maintain water levels, it seems that if the hydroperiod could be extended by 4 to 7 days for a full pond, that it might provide for a much higher percentage of years in which breeding is successful and little toads and tree frogs hop away from the rainwater pool during the summer.
Amphibians, with the need for multiple habitats to complete their life cycles, are vulnerable , and even more vulnerable in civilization and during climate change. Amphibian populations and species are disappearing faster than any other large groups of species on the planet right now. The populations using the rainwater pool for breeding are the only Fowler’s Toad and Gray Tree Frog breeders noted in Providence for 100 years. I know of no other populations, though I know a variety of other amphibian species live in the city. Unlike some of the most vulnerable amphibians, Fowler’s Toads breed over a lengthy breeding season whenever conditions are right, and have further resilience in that they can have a breeding cycle interrupted by several dry weeks and start up again when the rains return. Gray Tree Frogs also breed at the pool over an extended season, but treefrog tadpoles are rarely seen, and only one year have I seen numerous shiny little green frogs come out of the pond. I know less of the conditions necessary for tree frogs, but at least one thing is clear. The pool needs to hold water longer for tree frogs to metamorphose as they mature a bit slower.
The rainwater pool is silting in, reducing the hydroperiod and increasing the odds that the amphibians using the pool will be unable to complete their life cycles. We propose a simple intervention that places essentially no risk on the amphibians using the pond by working on the pond in the off season and doing relatively small amounts of work in a way that simply lengthens the hydroperiod a bit by deepening the pool and possibly lining it so that it holds water better..
The work entails removing 8 to 12 inches of silt from the deepest part of the pool, and smoothly tapering off until at the current edge of the pond the depth remains the same. We shall cut the cattails back about 5 feet and in the course of removing a few inches of sediment in the western part of the pond remove some of the pickerel weed. There is still some discussion among my collaborators as to how wide a swath should be included in the deepening of the western part of the pool. Several other plants with patchy distributions reside in that area. The cattails, pickerel weed, and other plants should return on their own as none of their patches will be completely removed.
No other vertebrates use the rainwater pool regularly, with ducks using it when it is very high and leaving as soon as it shrinks, though there are a variety of insects that use it as well as microscopic pond fauna. Doing the work in the off season, and only when the pool has gone dry will prevent most harm to the fauna.
There are some things that would be very good to know before moving any dirt. The first is a need to actually look at the soils in the bottom of the pool and understand their water holding capacity. It has been suggested to me that it is likely the soils are rather sandy, after all it is a burial ground, places chosen due to droughty soils that made for poor agriculture but easy digging. That might mean adding something to the bottom of the pool once the extra silt is removed, either a layer of clay or some sort of liner. First step is to get a professional to look at the soils.
The way the work could be done is with a crew of volunteers with shovels, possibly supplemented by something on the order of a bobcat for removal of cattails, and we are not removing much soil, probably an area of 30 by 50 and no more than a foot deep at the most, and much less most places as it slopes to the current shoreline.
About two inches of the top layer of pond bottom should be removed and kept separately. When done this should be returned to the pond to seed flora and fauna. If the soil has sufficient water holding capacity, then simply deepening the deepest hole by 8 to 12 inches and sloping it smoothly to the shoreline will be sufficient. If the soils are not tight enough, it will mean digging a bit deeper to put in some sort of impermeable layer and then backfilling to a depth 8 to 12 inches deeper than the current situation.
Friends of the Moshassuck is a regular partner with the City of Providence Parks Department on this and other sites in the watershed. The city is most willing to let FOTM do this project and believes that the project should simply be considered routine maintenance of rainwater infrastructure. It is likely that the actual work will be done by a crew of volunteers with shovels and wheelbarrows, though we are not currently ruling out using small motorized digging machinery to remove the cattails.
It has also been suggested that some sort of silt filter be installed where the rainwater funnels into the pool basin in the northeast corner. That is a project for another year.
The Green Infrastructure Coalition is interested in the idea of creating amphibian habitat in those places where it makes sense and to include this in the standard manual of practices for increasing resilience in our communities. Friends of the Moshassuck is pushing the envelope.
Beyond simply preventing flooding,and reducing pollution in our waters, it also behooves us to find beneficial ways to use our cleaner storm water and improve community resilience. One use for this water could be as breeding habitat for amphibians such as frogs, toads, and salamanders. Amphibians are a bellwether. They tell us if our community is healthy as they are sensitive and need a variety of habitats to insure their survival. In the North Burial Ground runoff from 3 roads ends up in a depression that can hold water or a week or 4 months, depending upon how much it rains. Fowler’s Toads and Gray Tree Frogs breed there. I have seen toadlets the last 5 years. But due to siltation from upstream, it is filling in fast and changing its characteristics. If it fills in too much it will not hold water long enough most years for metamorphosis to take place.
In some ways this is routine maintenance, but as it has never been done, I am engaged in a discussion with the various authorities about what to do and how to do it. With the understanding that there are other places in Rhode island and beyond, which might be able to use stormwater to aid amphibians, and therefore we need to think carefully about regulations and see if they can be a bit more amphibian friendly. Friends of the Moshassuck is partnering with the City of Providence on this, as the site is in a city burial ground. To explain and clearly demonstrate how the rainwater pool functions and what lives there, I am producing a series of short (2 to 5 minutes) that show the ups and downs of the pool for each month of a year. Beyond education, one of the purposes of the video series is to have evidence available so that RIDEM can decide what is proper at the site, And then hopefully to document the work we do to keep amphibians hopping in Providence.
The 2016 Rainwater Pool Series
January 2016 https://www.youtube.com/watch?v=EESIJfo8w1I
February 2016 https://www.youtube.com/watch?v=Drl6zu_1Ejw&t=8s
March 2016 https://www.youtube.com/watch?v=Y9wr5DR3O7o
August 2016 https://www.youtube.com/watch?v=op-YI8bGsJI
September 2016 https://www.youtube.com/watch?v=MT6IE1X0Kjk
October 2016 https://www.youtube.com/watch?v=nyPPsIQ8tNU
November 2016 https://www.youtube.com/watch?v=cjisDrf36OU
December 2016 https://www.youtube.com/watch?v=7-5uUV4xhsk