Dr. Brian LAPOINTE Nutrient Monitoring in the Florida Keys

Dr. Brian LAPOINTE Nutrient Monitoring in the Florida Keys


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Thank you, Megan, and thank you Josh. That was a great lead in talk to my talk, which
will show you that water from Lake Okeechobee — it can go East, it can go West, and it
can go South. And that’s really what I’ll be talking about. How we’ve seen the impacts
of freshwater coming down through the Everglades at Looe Key, the Crown Jewel of the Florida
Keys Reefs. I’ll also be talking about Upper Harbor Key, a tidal flat in the back country
about 12 miles north of Looe Key. I’ll show you some pictures of that in a second. But
the objectives of this project — this was a small project — but was to go out and track
dissolved nutrients and chlorophyll-a in the water, at Looe Key and Upper Harbor Key over
a year cycle. And to really tie this in to the Harmful Algal Blooms that are developing
in these communities, and we did that by also measuring the algae, carbon-nitrogen-phosphorous
content and stable nitrogen isotopes. All this being done quarterly. We also looked
at the community of the algae and the primary producers, both at Looe Key and Upper Harbor
Key quarterly through this study. This shows you the location of the two study sites. Again,
Looe Key about four miles offshore of Big Pine. Upper Harbor Key, near the Content Keys,
in the back country and you can see Shark River up there just under the study sites.
This is the major source of freshwater discharge from South Florida. These are high nitrogen
discharges coming out. It drains not just the Everglades but the Everglades agricultural
area, at the very northern part of the Everglades. Like our other studies, it involves a lot
of intensive field work. Laura Herren, up top left panel, my dive buddy, there quarterly
diving, collecting samples at Looe Key. Macroalgae and water. We come back to the lab, we process
these, filter the water samples. We clean up and dry the macro algae and analyze these
for nutrients and isotopes. OK. This is a Google Earth image, just to show you a little
bit more about the Upper Harbor Key site. The back country guides have been complaining
about these algal blooms on these tidal flats for many years now. No one has really looked
at these. They’re kind of difficult areas to get to because they’re very shallow. Upper
Harbor Key is the Mangrove Island. You can see our innermost site was at the shore. We
had a middle site along the transect and we had a channel site, along Upper Harbor Key
Channel. That connects with the Gulf of Mexico. This is what the site actually looks like
on the ground. This is an ebbing tide. You can see these turtle grass communities and
you can see that kind of yellow stuff. That’s macroalgae growing at epiphytes on these turtle
grass communities. Through the course of the study, we saw dissolved inorganic nitrogen
generally decrease through the study. Soluble reactive phosphorus increased. Typically what
you see when you get a big injection of nitrogen the plants take up the phosphorus to balance
their growth. You can see these red lines are what we have established as thresholds
for concentrations that support very rapid growth in bloom development, you know, these
benthic algal blooms. OK. If we look at chlorophyll-a in the water, again Upper Harbor Key, it goes
from high values in the beginning of the study in Summer of 2011, to lower values which tracks
the total nitrogen, total phosphorus ratio, so this tells us a lot about the source of
the water. This high N-to-P water is what’s coming out of Shark River, out of the Everglades.
That water has an N-to-P ratio of about 150 or so, or more, and so whenever we see this,
and we can see there was a lot of green water, a lot of chlorophyll coming with these discharges
early in the study. We collected a lot of different types of macroalgae for analysis
during this study, and they told us quite a bit about nutrients across these tidal flats.
Looking at the stable nitrogen isotope, at the shore site, these brown bars, are right
around plus 3 parts per mil — that’s the effect of the bird guano coming off that — these
are bird islands, and you can see how those values drop off as you come across the flat
to lower values that are actually characteristic of agricultural nitrogen from Everglades peat
and fertilizers. Carbon-to-phosphorus ratio down here tells us a very similar story. We
have very low values at the shore site, compared to the middle transect and channel site. Again
showing the phosphorus enrichment around the island, from the birds. Now, if we look at
the communities over the course of the study, this goes back to a point Dennis made. This
plant, Halodule, which is more of a stress-tolerant seagrass, we see it growing in these higher
nutrient halos throughout this study, it dominated that inshore shore site compared to the middle
site and the outer site that were dominated by turtle grass and to a lesser extent Syringodium,
and what was really most interesting is to see the onset of this bloom in the Winter
of the study right here, and extending up into the Spring. This was a bloom of an epiphyte
of a macro alga that you can see accounted for upwards of 80% or more of the bottom and
this is what it was, and this was what the back country guides have been seeing fouling
these tidal flat communities. This is Spyridia filamentosa literally covering just hundreds
and hundreds of acres of these flats these days. OK, moving offshore to Looe Key. These
are three of our long term monitoring sites that we began looking at way back in 1984
with Mark and Diane Littler. Looe Key, the Mid-Fore Reef in the middle of the spur and
groove zone. The West Fore-Reef and the Rubble zone in the back. So, quarterly, just like
Upper Harbor Key, we went out and collected our samples. Again, you see the one micromolar
threshold, so there’s a lot of nitrogen in the water out there, especially around the
Mid-Fore Reef area, so you’re in the middle of the reef. There’s a concentrating effect
there of the reef. As you go toward the side of the reef, or the back it drops off a little
bit. Soluble reactive phosphorus, again you see the threshold, we’re pretty much right
there, a lot of phosphorus in the water as well. We do see kind of a shift over time
through the study of increasing phosphorus. Those green bars kind of increasing in all
cases. Chlorophyll I kind of tracked the phosphorus. You can see through the study just like phosphorus
we saw increasing chlorophyll at Looe Key which is opposite what we saw at Upper Harbor
Key. I wanted to also point out this .1 micromolar threshold for chlorophyll-a is what we saw
historically at Looe Key and this goes back to the point Dennis made earlier that we’re
really working in impacted systems, so this is very much a eutrophic condition having
this much chlorophyll-a at Looe Key. These are some of the algae we collected for analysis.
I’m not going to talk about that today, given the time. So, what I want to share is the
long-term data from Looe Key. This is dissolved inorganic nitrogen in the water column of
Looe Key going from 1984 to 2012. You can just see how relatively clean that reef was
back in the 80s when we really still had haystacks of Elkhorn coral high coral cover for some
of you that knew that. Look at the flow rate: that’s Shark River slough, and so Mark, I
wanted you to see this because you keep saying “Move that water south.” This is what happens
down in the Keys when that water goes south. You can see [laughs] the whole system went
south, and the point is it has not come back. Even though the flows of the Shark River have
come down, the nitrogen has built up in the system. Everyone asked me what happened there
to make that happen? Ironically, that is when the Florida Keys National Marine Sanctuary
lobbied actually to have that water put into the system. The neat thing about long term
data sets, patterns emerge and we now know whenever they put water in there, we get a
rise in the nitrogen-to-phosphorus ratio, because the high nitrogen in that water — this
correlates directly, these two big releases with the two major coral bleaching events
that we’ve seen in the Keys. We know this condition stresses corals and it reduces their
temperature threshold for bleaching by several degrees. This is some of the bleaching of
the two major events, ’87 and then again in ’97. Chlorophyll-a over time, just showing
you again, how clean that reef was back in the 80’s. Again, it has not returned to its
original condition. So, this is my summary. I just want to maybe make that final point
on the bottom that this is a really great example of a shifting baseline, not one necessarily
caused by over-fishing but one caused by water quality shifts over time. And I just want
to acknowledge all the help. Laura Herren, David Debortoli, many other people and especially
the Foundation and the Save Our Seas Plate Funds.
Thanks. [applause]
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