Part 2: The eosFD was voted on the island to measure flux!

Welcome back! Or if you only just finished the first part of this blog post, welcome to Part 2! In part 1 we showed you the beautiful “100 Wild Islands” archipelago that spans part of the Eastern Shore in Nova Scotia. For Part 2, we kayaked to the islands and were lucky enough to get permission from the Nature Trust to carry out a couple non-invasive tests using the Eosense gas monitoring equipment.

Our kayak parked at Harbour Island

To quickly recap Part 1, Nova Scotia’s Eastern Shore is full of small fishing villages, spectacular views, and rocky coastlines. The 100 Wild Islands, which is actually 282 islands and islets, is not only full of pristine beaches with white sand and turquoise water, but it’s home to some of the most unique ecosystems in Canada.

The islands contain over 120 species of birds, numerous endangered species such as harlequin ducks and eiders, an array of marine biota, a few mammals such as deer and seals, and a host of rare plants. They are home to every coastal habitat found in the Maritime provinces – from bogs and barrens, to freshwater lakes and saltmarshes. Harsh coastal climatic conditions in Nova Scotia prevent the development of old growth forests on the islands; however, one of the islands is home to a rare and unique boreal rainforest.

Tree on Harbour Island next to slate rock

The islands were inhabited by the Mi’kmaq people well before European Settlement because of their coastline and sheltered bays. Over the years the islands have been home to fishing villages, school houses and even a few roads until they were largely abandoned in the late 20th century.

We Had to See (and Measure) for Ourselves

On Friday, August 24 we hit the road to the Eastern Shore to see these islands for ourselves. We were lucky that the Nature Trust had given us the go ahead to take eosFDs and an eosGP to do some CO2 flux and concentration measurements on and around Harbour Island.  Harbour Island was home to a fishing lodge, originally built in the 1700s, that still remains on the island today. The island is also surrounded by an underwater garden that grows eel grass.

Fishing hut found on Harbour Island

We had two goals with our eosGP and eosFDs in hand. First, we wanted to monitor CO2 flux at several locations on the island to see if the legacy human impacts could be detected by the flux measurements. Second, we wanted survey the aqueous CO2 concentrations off the island to see if we could detect any difference in the CO2 readings in the near-shore environments versus the offshore environments.

The Island Flux Story
Upon arriving at the island we got to work setting up our first two flux monitoring stations near the small isthmus that connects the two larger portions of the island. This was our initial undisturbed location, far from the fishing lodge, our next target. After we had a few hours of data, we moved the units and performed a gradient-type measurement with the eosFD units leading away from the fishing lodge into more pristine territory. Finally, toward the end of the day we moved two of our eosFD units down to a wall near the fishing lodge to get a baseline for all the units nearer the impacted area.

eosFD measuring CO2 flux in the forest

The fluxes (below) measured near the isthmus were quite high compared to fluxes normally observed in Nova Scotia (typically more in the range of 3-5 micromoles per meter squared per second) but initially we assumed it was due to the installation of the collars.

Data from the island for the three deployment locations.

We also noticed a strong downward trend, but more on that later. When we moved to the fishing lodge and set up we noticed an trend of fluxes being higher up-gradient from the lodge, but with no real difference between the bottom and middle positions. There are a few reasons why we likely saw this trend, one is that years of compaction and human foot traffic near the site have probably made it a bit harder for the decomposers there to degrade the organic C in the soil. Second, since the site is more vegetated the further you get from the fishing lodge, we were probably getting a larger proportion of autotrophic respiration from the local flora. When all of the eosFD units were co-located at the end of the survey they were measuring approximately the same flux, with a bit of lee-way for spatial variability.

eosFD measuring fluxes next to the fishing lodge

While we thought nothing of it at the time, possibly the more interesting part of the data is the consistent downward trend observed at all locations. This trend doesn’t match up with the site temperature, as you might expect, but actually more closely reflects the tide. According to the tide charts for nearby Murphy Harbour, high tide on the day we sampled was at 7:47 in the morning, about 4 hours before we arrived and low tide was around 14:15, or about when we were packing up to go home (also the same time as the smallest fluxes we saw all day). Given the geology of the islands and the altitude its very plausible that tide could exert strong controls on the local ground water table and composition, leading to variation in fluxes. Based on the results here, it might suggest that a rising ground water table during high tides may push CO2 rich air from the soil pores into the atmosphere, resulting in a high apparent flux. We’ll have to go back next summer to test this hypothesis!

What’s Next
We took the eosGP around the island to measure the CO2 concentration in the water where the eel grass was growing. We’ll talk about those results in the next 100 Wild Islands blog post – Part 3.

Related Posts Plugin for WordPress, Blogger...