Coastal ecosystem effects of climate change

Coastal environments are one of the most important habitats, not just for their carbon sequestration but for their protection against oceanic weather events. The exact impacts that climate change will have on these areas is not yet fully understood. However, what we do have are decades of data, collected by a range of actors from governmental bodies to citizen scientists. So scientists at the University of Virginia have been analysing these data to extract the signals that might relate to climate change, so we can work out what the future might hold. Here’s Scott Doney…

Scott - We're trying to figure out how climate change might be changing coastal marshes and the lagoons that surround them. And we had decades worth of water quality data that had been collected but really hadn't been analysed in depth. So, we were trying to dig in and see: can we see a trend in warming because of climate change? Can we see a trend in the biology of the organisms that live in the lagoon? And then: can we start to understand what the implications of those trends are.

Chris - What specific things were you measuring or subjecting to scrutiny to see if you could see a signal in them?

Scott - It's things like the temperature of the water, the salinity because we're in the coastal ocean and so you have freshwater coming from land and seawater coming in from the ocean. Chlorophyll which is a proxy for how much phytoplankton is there. And then also things like nutrients. Nutrient pollution can drive harmful algal blooms for example.

Chris - How do you tease out from what you see though as a genuine signal of climate change versus something which is a normal cycle which might operate over long time scales but would look like it's climate change because it's changing in line with everything else?

Scott - That is the challenge. The simplest thing that we started with was we wanted to see from this long-term several decades of data could we first just pull out something simple like the seasonal cycle. The study was actually done by a graduate student as part of her master's thesis and one of the things that I thought the student did which was really interesting was there are groups that have also put out autonomous instruments that are measuring very high frequency data like every quarter of an hour but those are only in a few locations so she did statistical tests to see - given that we have some high frequency records - can we sample those high frequency records like the way we're sampling this decadal record and recover the same information. So, it's kind of this idea of we can't go back in time to measure things 40 years ago - but can we say if the record looked like it does now with these robotic instruments can we say something about how the past might have evolved?

Chris - And can you? Does it work?

Scott - It seemed to work. We were able to show at least with the statistics that we had collected enough data over 30 or 40 years to be able to resolve the seasonal cycle and in a lot of places we could actually show that the seasonal cycle is you know normal things warm in the summer and they cool in the winter and what she was able to show in this study is that shape of that seasonal cycle was actually changing so in some places it was getting warmer-  but it was also getting warmer earlier in the year and that's what we would expect based on models.

Chris - Is this generalisable? So, could I take your model and take it to the opposite coast of the US or even to a European coastline and apply some of the same techniques in order to ask the same questions there?

Scott - We were hoping to develop a methodology that could be used in other places and one of the really encouraging things - since the paper came out - colleagues at other sites in the US who have this water quality data have applied the same sorts of approaches and are seeing similar results so that's very encouraging.

Chris - And can it capture, because you mentioned we wanted to know what people are doing, the other major dramatic change is in recent decades we've seen the population - the human population - go up by tens of percent. I mean we've got a third more people on earth now than when I was doing my PhD. So does that also get captured by this sort of model and how can we control for that because that must also make quite a considerable impact on a lot of these metrics.

Scott - So, I've worked in other places where there's a big impact from a growing human population one of the biggest signals you see is because of nutrient runoff from fertiliser and from atmospheric pollution and we're trying to use this site in Virginia as sort of a baseline of what signals might look like without that local human factor and then we can then compare that to places that have say a larger input of fertiliser runoff or more atmospheric pollution.

Chris - And when you compare your model with the predictions that other models because other people are doing sort of similar things or they're asking a similar question but in a different way they're approaching it or getting at different outcomes. Does it broadly align with what generally is accepted as the likely trajectory and if so what are the predictions then?

Scott - Our work was consistent in that we expect to see coastal waters warming. The freshwater balance which is really important for the ecosystem is going to vary from place to place. Some places are going to get wetter with more runoff from land and other places are going to get drier so that's going to be pretty site specific.
I think one of the interesting things is we saw at some of the stations that we have data from that when the ocean got warmer there was also more chlorophyll, more phytoplankton and we've seen that in a couple of other places. That's tricky in the models. The models are still kind of looking at that.
There are some places around the globe where we expect the ocean to become more productive and places where we expect productivity to drop off at least where we were looking where we could see what we think is a climate signal we saw warming and increased biological productivity.