Government of Nova Scotia Government of Nova Scotia Nova Scotia, Canada




Vernal Pool Mapping and Monitoring Project

vernal pool Are you aware of any shallow wetland pools in the forests near your home or near places you vacation, hike, hunt or bird watch?

If so, we’d love to hear from you!

Nova Scotia Environment is launching a Vernal Pool Mapping and Monitoring Project in the spring of 2011. Our goal is to develop a database of vernal pools around the province to improve the conservation and understanding status of these fragile and important habitats.

Vernal pools are small, shallow wetlands that lack permanent inlet or outlet streams and often dry out in the summer. They provide critical breeding habitat for frogs, salamanders, insects and fairy shrimp, and feeding and drinking sites for birds, mammals, turtles and otherwildlife.

vernal pool Vernal pools have been defined in quite a few different ways by different people that have studied them, but the definition provided by Elizabeth Colburn in her 2004 book, Vernal Pools: Natural History and Conservation, is practical and comprehensive. Dr. Colburn’s is a five-part definition based on woodland context, isolation, size, hydrology and the biological community that is present.

A summarized and simplified version of her definition is that vernal pools:

  • have a short hydro-period (the number o fdays per year the pool is filled with water); vernal pools fill, dry and sometimes refill seasonally; they dry out completely at least every few years
  • occur next to forests and wooded areas
  • do not have permanent streams flowing inor out of them
  • are usually small (< 0.5 ha) and shallow (<1m deep)
  • are usually deepest in the spring and sometimes again in late fall
  • lack fish and are occupied by animals adapted to vernal conditions (ie. wood frogs, spotted salamanders, fairy shrimp)

Vernal Pools in Nova Scotia

vernal pool Vernal pools are probably the least well understood of all the wetlands in Nova Scotia. Dr. Ron Russell and several of his students from Saint Mary’s University (see Chaisson, 2004; Russell and Collins, 2008; Collins and Russell, 2009) have surveyed a number of vernal pools for amphibian presence and potential limiting factors to amphibians (like chloride contamination and proximity to roads) - but there have been no Nova Scotian studies exclusively focused on vernal pools. We know very little about the overall distribution of vernal pools, the range of types present here, how many we have, how many are being lost to development or what biological communities, physical-chemical conditions or hydro periods are typical.

So, there is much to be learned and we need your help!

In the near future, we plan to ask you for information on the biology of our vernal pools, but to get this project started we are looking for volunteers to provide three kinds of basic information that will help us to begin characterizing distribution of types of vernal pools in Nova Scotia - Vernal Pool Data SheetPDF Download Link (PDF:155k):

  1. The geographic location of any vernal pools you are aware of,
  2. Some basic information on pool size, depth and hydroperiod and,
  3. A digital photo of your pool(s).


Location is most easily characterized by recording the latitude and longitude. You can get latitude and longitude coordinates from the center of the pool with a GPS device, by zooming in to your pool with Google Earth software, or by estimating it from a topographic map.

If you use a GPS device, please provide thename and model of the device, the level of accuracy of your device and the coordinate system in which the latitude and longitude are measured. We prefer that you use the NAD83 UTM Zone 20 CSRS coordinate system if possible.

If you get your information from a topographic map, please send us the map series description (e.g., Halifax 11D/12, 1:50,000 scale) and the year the map was printed.

Once you have determined the location ofyour pool(s) please send an email to and we will send you an invite to add your vernal pools to our Google Map. You can view (but not add to) the website publicly, here.

Pool Size, Depth and Hydroperiod

The more information you can provide on pool size, depth and hydroperiod, the better, but at a minimum, we would like you to record at least one of these measures. It is important to note that because vernal pools dry and refill regularly, area and depth fluctuate. To measure maximum depth and area of a vernal pool take your measurements when the pool is fullest- usually after a heavy rain in early spring.

You can measure the maximum depth in a number of ways, but ideally you will wade through the pool to find the deepest spot as a first step (although you can simply make a visual estimate of depth if you don’t want to get your feet wet).

Once at the deepest spot, an easy way to measure depth is to submerge an upright pole (e.g., tree branch, 2 x 4) and measure the length of wetted surface with a tape measure when you are back on dry land. If your pool is very shallow, simply dipping a metre stick to the bottom at the deepest spot may work just fine. If you are interested in taking repeated depth measurements, you can drive a calibrated pole into the sediments and read the exact water level periodically (e.g., weekly or monthly) using binoculars to see the scale from the edge of the pool if you can’t read it directly. You can use a tape laid along the length of your pole and a waterproof marker to transfer accurate calibration marks to the pole before you drive it in to the bottom of the pool.

You can estimate the maximum area of your pool very simply by measuring the maximum length and width of the pool and multiplying these two numbers together. You can also carefully transfer these measurements to a piece of graph paper scaled to the size of your pond and add a sketch of the remaining boundary to this paper using additional measurements to improve the accuracy of the drawing. Then, you can count the squares inside the sketch of your pool to determine the total area of the pool.

vernal pool Diagram of a vernal pool with graph papergrid underneath. Pool area is approximately 200 squares (200 m2 if each square represents 1 m2).

Most GPS devices also provide a slightly more accurate way of estimating area when you create a shape file by walking the perimeter of the vernal pool along its wetted edge and save the file as an object when you have completely walked the perimeter.  If you are unable to measure your pool, do your best to provide an accurate visual estimate.

You can measure the hydroperiod of your pool in one of two ways:

  1. For a pool you can only visit a few times a year you can use the following scale:
    Short: the pool dries completely before July (it’s ok if it refills againin the Fall)
    Medium: the pool dries completely before October
    Long: the pool dries completely some years, but not every year
  2. For a pool you can visit at least once a week you can record the number of weeks per year the pool has water in it from April to November.

Digital Photo

We would like 2 or 3 digital photos that characterize each pool you want to include in the study taken, at minimum, during the time of maximum water levels. If you have an opportunity, we would also appreciate photos taken at other times of the year that show the pool when it is very low or dry. Photos taken during spring, summer, fall and winter would be ideal.

Optional Biological Observations of Indicator Species

We will be asking for your help with more comprehensive monitoring of the biology of your vernal pools in the near future, but to get things rolling for those of you who are especially interested, we would appreciate it if you could report the presence of the key species that typify vernal pools. These are wood frogs, blue spotted salamanders, yellow spotted salamanders and fairy shrimp. Pictures of adults of each species are included on our data sheetPDF Download Link (PDF:155k) to help with their identification.