Science Notebook: Transcript of Interview with Joel Hoffman
I would suspect that for many people the words "coast" or "coastal" bring to mind images of oceans rolling onto sandy beaches or crashing onto rocky shores. But what do you picture when you hear "Great Lakes coastal wetlands"? Aren't the Great Lakes lakes? Don't you have to have an ocean to have a coast?
DMH: I'm talking today with Dr. Joel Hoffman, a researcher at EPA's Mid-Continent Ecology Division lab in Duluth, Minnesota. Joel, you study Great Lakes coastal wetlands. Can you explain how the word coast fits in?
JH: Good question. You're right on - when you think about a lake, you probably think of a shoreline rather than coastline. But the Great Lakes are enormous – in total, they have nearly 11,000 miles of coastline. If you were to dump all the water out of the Great Lakes onto the continental U.S., the water would cover the entire country to a depth of 9.5 feet. Lake Superior, the largest of the lakes, is 350 miles long, has an average water depth of about 480 feet and a maximum depth of 1,332 feet. These lakes are BIG.
Like our ocean coasts, the coasts in the Great Lakes are active environments that are subject to both deposition and erosion, by which I mean the building-up and washing away of geological features such as bluffs and beaches. As a result, the Great Lakes coastline is constantly changing. Along the coast you'll find shifting sand dunes, towering sandstone bluffs and, of course, vast wetlands.
Scientists define Great Lakes coastal wetlands as those wetlands that are directly linked to the Great Lakes. Because of this link, they are tied to the hydrological cycle of the Great Lakes and subject to water-level fluctuations on daily, seasonal and annual time periods. They are also subject to physical processes in the Great Lakes, such as currents and waves. These processes are extremely important in shaping our Great Lakes coastal wetlands.
DMH: Can you describe what a typical coastal wetland look likes? For example, if you blindfolded me and dropped me into the middle of one of these coastal wetlands would I have any idea where I was one the blindfold was taken off? What would I see?
JH: Well, hopefully I would drop you on to the shore J Now, what you would see would depend on the kind of wetland you are in. For example, if you were in a river or delta wetland, you would see a large river with a complex channel that is fringed with vegetation and low-lying wetlands. You could watch the river flow gently out into the Great Lake, mostly likely leaving a muddy plume behind. But, if you were in a lagoon or barrier wetland, you would most likely be looking at a shallow aquatic habitat, fringed with marsh, that is narrowly connected to the lake and protected behind a long sand dune or sand bar, which might be covered in a dune forest.
Some wetlands are largely exposed to the Great Lakes and lay directly along the shore. In that cast, you may be looking out past a narrow band of vegetation into waves and surf. In any case, you would certainly see a diversity of wildlife, particularly birds, which thrive in these wetland environments. You might also see deer, river otters and beavers.
DMH: What makes them different from other types of wetlands in the United States?
JH: One obvious difference is that they are attached to 95% of the United States' fresh surface water supply – the Great Lakes. Another important distinction is that they are subject to a periodic wind-driven wave, which is known as a seiche. Seiches can have periods of hours to days and, like tides in estuaries, cause regular changes in the water height of these wetlands. In fact, some folks call seiches "wind tides".
These changes in the water level influence processes such as wetland succession and sedimentation. By succession, we mean the cycle of pioneering to mature vegetation in these wetlands. Constant water level change continually provides new opportunties for vegetation to colonize new habitats. Sedimentation is the slow building up of the wetland – which is critical to maintaining its existence. For example, the wetlands that used to protect New Orleans were sediment-starved for years and the wetlands slowly disappeared as a result.
Another important difference is that they can exchange aquatic organisms readily with the Great Lakes. In some cases, this is beneficial, such as providing important nursery habitat for fish. In other cases, however, this has proved detrimental to the wetland. For example, exotic species brought to the Great Lakes can gain access to the coastal wetlands. The lower St. Louis River, a coastal river-wetland ecosystem in the western end of Lake Superior, for example, now has a robust population of zebra mussels and round gobies, a small fish – marine invaders that can't live in the harsh Lake Superior environment but can thrive in the warmer, more protected waters of the coastal wetland.
DMH: Why are these coastal wetlands important?
JH: The Great Lakes coastal wetlands provide key ecological services. Ecological services are resources or functions that ecosystems provide that benefit people. For example, wetlands improve water quality. They act like a sponge, absorbing nutrients and some chemicals that are delivered to the wetland by run-off. They also trap sediment and may even serve as a carbon sink in the fight against global warming. Coastal wetlands also provide critical habitat for fish, birds and other wildlife.
Most of the Great Lakes fishes will use coastal wetland habitat during their lives – many of those fishes use it as a nursery or feeding ground. And migratory birds and waterfowl use these habitats for feeding and staging during their annual migrations. I know I love to spend time in these wetlands. They are wonderful places to recreate and enjoy nature. Great Lakes coastal wetlands are great places for bird-watching, kayaking, fishing and duck hunting.
DMH: We often hear about the need to protect wetlands because of their importance. What are the greatest threats facing the Great Lakes Coastal wetlands?
JH: They are the same threats facing wetlands across our country – pollution, habitat modification, and exotic species invasion. Today, we are still polluting our coastal wetlands by adding nutrients and sediments. The nutrients may come from sewage plants or from run-off from agriculture lands or fertilized lawns. Sediments primarily come from altering the landscape – by urbanizing landscapes and clearing forests, the land loses its ability to retain sediments and these are washed into our rivers. This is a big change from the pollution that happened a few decades ago.
Today, our pollution in the Great Lakes often comes from the landscape. Decades ago, it came from discharge and dumping of toxic materials. Still, we do face problems with pollution that is decades old. Many pollutants were added to our Great Lakes coastal wetlands before the Clean Water Act was implemented. These pollutants are now stored in the sediment, which makes them difficult and expensive to clean-up. The worst locations in the Great Lakes are Superfund sites and identified as Areas of Concern by the EPA.
Habitat modification, as I said, is another major threat. It, too, has many causes. For example, changes to the shoreline by homeowners so they can have a nice view can have a major impact if everybody does it. This reduces habitat, reduces fringing wetlands, and increases pollution. This is why preserving and restoring natural shorelines is so important for the health of our wetlands.
Exotic species also remain a major threat. They are introduced by the shipping trade, by people moving them around accidentally in live wells or bait buckets, and by accidental aquarium release. Once in the environment, they can dramatically alter the ecosystems and it is generally very expensive, and often impossible, to contain these exotic species once established. Zebra mussels, for example, cost us millions of dollars a year in damage and alter ecosystems by filtering much of the algae out of the water.
DMH: I know a lot of your research takes place in these wetlands. What are you working on?
JH: In a nutshell, we are interested in how changes in the watershed, such as increased pollution, alter how coastal wetlands support coastal fish and fisheries. This is critical information if we are going to understand how to protect and restore this important ecosystem service provided by our wetlands. We know that Great Lakes coastal tributaries and their associated vegetated, shallow, protected embayments support fisheries by serving as nursery grounds for migratory fishes – their young rely on these habitats for feeding and refuge – and by supporting a forage base for larger, predatory fishes – the fishes we target as anglers and often eat for dinner. Yet, we don't really understand what happens when these systems are enriched with nutrients or fragmented by development.
Now, in some ways, what we do in our lab is forensic. We are using chemical signatures in the fish tissue to tells us about where that fish's energy came from. Did it, for example, come from aquatic vegetation at the water's edge, from algae in the water column, or from sediments? We look to see how these sources change between different wetlands – say, from a wetland that is heavily impacted by human activities and one that is not - to tease out the changes that have occurred. The chemical signatures we are looking at are called stable isotopes. For example, the amount of the stable isotope carbon-13 that is in the tissue reflects the source of the carbon providing energy to that fish. That's why carbon is important - it is the currency of energy used by life on planet earth.
Not only do we use fish, but we use larval fish. These are fish that have recently hatched from the egg stage – they may be days to weeks old. We call them larvae because they do not look like adult fish – not until the juvenile stage will they metamorphose and fully resemble a miniature version of the adult. We use larval fish because they grow rapidly and therefore acquire chemical information from their environment very rapidly. We also study fish larvae because they are generally key to the population's success – if the larvae do not grow and feed well, the fish population will not reproduce well and may decline over time.
DMH: Cool! So it's sort of like EPA CSI?!
JCH: Absolutely. In fact, archaeologist use the same sort of data to identify diets of ancient humans. Here, we use it to identify diets of modern fish. We hope that in the future, we can use this chemical data to rapidly identify wetlands that no longer function as a healthy wetland should.
DMH: All of this sounds like fascinating work but I imagine the weather in your part of the country doesn't always participate. What are some of the typical challenges associated with sampling?
JH: No, it certainly doesn't. Weather is a constant challenge. We start sampling in late-April. In a cool spring, the water will be close to freezing, threatening us with hypothermia. And it may snow. We've had to break ice with our research vessel in order to get out of the harbor so that we can sample. We are often out there wearing multiple layers of clothing, specialized thermal gloves, and snow caps. By early July, the biggest weather concern is squalls. Thunderstorms can move quickly along the coast and we keep a constant eye on the horizon while we are working on the water. Also, these rainstorms can cause dangerously flashy conditions in the rivers. The river may become swollen in a matter of hours, which can present a danger if we are out seining in the river bed.
DMH: Who does most of this sampling? Is it mostly EPA employees or do you work with other federal agencies or states and local agencies?
JH: We are an EPA research lab and do a great deal of our own sampling. We maintain a fleet of small vessels to sample along the coast and in the coastal wetlands. We generally hire undergraduate students during the summer to help with this sampling. If you are a student, information on working for us can be found at www.usajobs.opm.gov/students.asp. We often collaborate with other agencies, as well. In the past few years, for example, we've coordinated activities with the Wisconsin and Minnesota DNRs, the US Geological Survey and the US Fish and Wildlife Service. It benefits everyone if we can coordinate our related research activities.
DMH: Having done all of my research in east coast estuaries, I know I have some stories about my field experiences. Got any good stories to share about life in the field?
JH: During the field season, we are out in the field generally 4-5 days a week for 12 hours a day. Field days are long, hard days. And you often have to go out weather it's raining, snowing or sunny. Our first time out on Fish Creek last year had too many of those elements. It was late April. And it was chilly – I think there were snow flurries. The water was near freezing. And the big spring thaw was on so the river was 3-4 feet above its' normal height. Plus, because it was early spring, the vegetation wasn't out to guide you about where the river channel flows.
We left the dock in a small boat hoping to find our sampling stations we had identified on a map, but quickly got lost among a bunch of small islands. The water was into the trees – we had now idea where we were going. We tried following the river by looking to see where the water was flowing the most. That led us on a meandering path through some low alders, until suddenly the channel just ended and boat suddenly nosed into a forest of alder. Later, we realized we had driven into a marsh meadow – at least, a marsh meadow when the river is at a more normal stage. Needless to say, we waited to sample until the river had dropped a few feet. Sometimes, less exciting is better.
DMH: So given all the physical sampling challenges and complexities associated with the Great Lakes, why or how did you end up doing research here?
JH: It's a good question. In part, it's really the complexity that I love because it means that these sytems are biologically rich – full of interesting and sometime unique plants, animals and fishes. I also grew up on the Great Lakes and I remember when they were in truly poor health. I remember walking on a beach along Lake Michigan when I was a child and seeing dead alewives – a marine fish that invaded the Great Lakes – piled up, perhaps feet deep, along the water's edge. You didn't want to swim at the beach because of all the dead fish.
What happended, we know, is that the predator populations of lake trout in Lake Michigan had collapsed. Alewives, a prey fish, became super-abundant and during hard winter would suffer massive die-offs and wash ashore. The water quality in the Great Lakes have improved, many of the fish have come back. This is good news and we should be proud of the progress we've made. Still, there's much work to be done. What I hope is that our research can help that work proceed by providing the information we need to conserve and restore our Great Lakes coastal wetlands.DMH: Thanks so much for taking the time to chat with me today Joel and for filling us in on Great Lakes Coastal wetlands. It's great to know that EPA scientists are out there making a difference and helping to conserve and restore these amazing inland seas.