How Do Mussels and Nutrient Runoff Impact Lake Michigan’s Food Web?

By Kevin Bunch, IJC

quagga mussels
Quagga mussels have effectively displaced their fellow invasive species the zebra mussel throughout the Great Lakes, and can survive in cooler, deeper water than their counterparts. Credit: US Geological Survey

Scientists have known since the 1972 Great Lakes Water Quality Agreement that nutrient runoff from fertilizer and wastewater is responsible for harmful algal blooms. They’re also aware that invasive quagga mussels are to blame for changes in how nutrients move around the lakes and its food web. Now a recent modeling study has better defined the role quagga mussels play in the use and movement of nutrients within Lake Michigan, which could assist efforts to reduce blooms throughout the Great Lakes.

Quagga mussels are a dreissenid species native to the Ponto-Caspian region of eastern Europe that most likely entered the lakes through ballast water in the 1980s. The tiny creatures form hard shells and latch onto practically any hard surface before filter feeding out plankton in the water column. The mussels thrive in nearshore regions, with quagga mussels outcompeting their fellow invasive zebra mussels in many areas. Quagga mussels also are capable of surviving in deeper water than zebra mussels, pushing the invasion further offshore.

Lake Michigan has seen a decline in offshore primary productivity – essentially the rate of how organisms at the base of the food web convert sunlight and nutrients into biomass energy – for around the past decade, according to Darren Pilcher, research scientist with the Joint Institute for the Study of the Atmosphere and Ocean at the US National Oceanic and Atmospheric Administration’s Pacific Marine Environmental Laboratory. Since these phytoplankton species are eaten by a wide variety of other creatures, including invertebrates and eventually fish, understanding what’s driving that decline is important, he said. There are two major drivers that have been suggested: the decline of nutrient pollution into the lake from runoff since the GLWQA went into force and the growth of the quagga mussel population.

“These mussels are able to just graze and eat the phytoplankton as they grow, and that’s one mechanism showing how productivity has been reduced in the lake,” Pilcher said.

The model Pilcher and his partners built shows representations of the lake’s productivity under different conditions. Researchers can see what the lake would look like with a reduced number of mussels, or with a reduced amount of nutrient runoff (based on the observed decline going back to before the mussels invaded). This allows them to tease out the effect of each process. The model accounts for how water moves throughout the lake and for its ecosystem, particularly phytoplankton and zooplankton – organisms that eat phytoplankton.

Pilcher said they found that the growth of the quagga mussel population and drops in total nutrient runoff have impacted the lake, but at different times and places. Quagga mussels have the biggest impact in the spring and late autumn due to how the water moves within the lake, Pilcher said. The mussels live at the bottom of the lake, while phytoplankton tend to live in the upper layers to soak in the sun’s rays. During spring and late autumn those water layers tend to mix, bringing those plankton down to where the mussels can eat them. In the summer, the water layers stratify and rarely mix, denying quagga mussels that food source outside of the nearshore zone where waters are shallower. The researchers had hypothesized that would be the case, and with the modeling they were able to see how the quagga mussel’s seasonal dependence worked.

“The phytoplankton sit in the top layer (of water) and no mussels are grazing on them, so they’re able to continue as business as usual at that point,” Pilcher said.

cladophora
Cladophora algae mats have surged in nearshore areas where phytoplankton isn’t available to use phosphorus runoff as a nutrient source into the Great Lakes. Credit: Wisconsin Sea Grant

However, since mussels in shallower nearshore zones can continue to feed on phytoplankton, they’re clarifying the water and leaving a niche for other algae and bacterial species to move in and use the phosphorus there to grow and expand into blooms. This also has the effect of shuffling nutrients predominantly to the nearshore zone and processing them into a more bioavailable form, in what’s called the nearshore nutrient shunt. Runoff can exacerbate that, and as a result the impact of the runoff is mostly seen in the summer, when harmful algal blooms can grow and species like Cladophora, a kind of algae that lives on the lake bottom, can spread into large mats.

Since those nutrients aren’t making it into the offshore zones in the first place, species in the deep water zones are still out of luck. Pilcher said that some fish in nearshore zones still can conceivably eat algae or the mussels, but those in the offshore regions have a harder time finding food unless they’re willing and able to venture closer to shore. This has been thought to be contributing to the population declines of several fish species in the Great Lakes, such as lake whitefish, as they struggle to find food where they live.

In the future, Pilcher said they’d like to see benthic algae such as Cladophora added to the models to better understand how the mussels are affecting their growth. With the mussels clearing out more desirable phytoplankton in nearshore regions, phosphorus is going unused by those species, giving undesirable algae and bacteria an opening to grow. This information could be helpful as the Great Lakes states and Ontario work on reducing phosphorus loading into the Great Lakes, particularly Lake Erie, by helping refine phosphorus loading targets and expectations. Pilcher added that models using similar parameters could be developed for the other four Great Lakes; they already exist to some degree for Lake Erie.

Kevin Bunch is a writer-communications specialist at the IJC’s US Section office in Washington, D.C.

A New Approach to Stormwater Financing and Management

By Kevin Bunch, IJC

green roof
A ’green roof‘ converts a building rooftop into a garden, which holds in rainfall and allows it to evaporate without running into the stormwater system. Credit: Philadelphia Water Department

With more extreme precipitation taxing existing stormwater infrastructure, municipalities in Ontario, the United States and elsewhere are considering new ways to finance existing systems – and incentives for property owners to reduce loads.

Historically, cities and towns in Canada and the United States have funded stormwater capital and maintenance costs through property taxes, said Ellen Schwartzel, deputy commissioner with the Environmental Commissioner of Ontario (ECO) office. The amount paid was based on how much that property tax was, regardless of the actual runoff volume being produced by that property that enters the water system. With a relatively light rainfall, the system works, but when heavy rains hit in a short period of time, all the excess runoff can lead to flooding and pollution.

“A parking lot, for example, may not have a high property tax base, but it produces a lot of runoff,” Schwartzel said. “Once municipalities began to think that through and realized paved over surfaces are the challenge, then they had to begin thinking of ways to connect the cost that we’re incurring to the fee that the property owner experiences.”

Given that a number of municipalities that responded to an ECO survey about stormwater said they didn’t recoup their costs, this has led to some municipalities charging property owners for the amount of runoff their built-up surfaces are producing – an approach recommended by the ECO in its 2016 Urban Stormwater Fees report. Schwartzel said if a property space has a building or paved surfaces built over the ground, it naturally limits how much absorbent surface area is remaining. Furthermore, those that are left – yards, remnant natural areas, landscaping – aren’t able to soak up all the runoff falling into them before becoming saturated.

groundwater supply storm impermeable concrete
Less water is able to seep into the groundwater supply after a storm with impermeable, concrete surfaces. Credit: Philadelphia Water Department

To encourage property owners to reduce the amount of runoff their properties are causing, these municipalities can offer reduced tax bills in exchange for absorbing more runoff onsite, Schwartzel said. For example, a property owner may use permeable concrete to allow water to seep through into the ground, or install bioswales or rain gardens to capture more water. Business owners also can consider installing a green roof to help retain water in densely built areas where those other options aren’t available, she added. Collectively, these lot-by-lot green measures add up to “green infrastructure,” offering several advantages over traditional end-of-pipe stormwater treatment (such as water treatment costs).

With municipalities and cities continuing to expand, Schwartzel said, runoff issues are continuing to grow alongside them. With less water getting into the groundwater system, it’s possible to see creeks and riverbeds be reduced to small flows or dry up completely until a major storm hits, when the influx of water can lead to erosion and flash flooding.

All of these actions to reduce runoff and manage stormwater onsite can have a positive impact on water quality, too. Runoff tends to pick up pollutants as it heads into the sewer, from sediments to auto fluids to garbage – and in cities with combined sewer overflows, wastewater too. When the water from the sewer systems leaves the pipes, it carries those pollutants along with it.

Cities in the United States have been working on stormwater management as well, and water quality improvements have been a side effect to the changes Philadelphia has been implementing since 2010. The city considered replacing its meter-based stormwater billing system – where properties were charged based on how much water they used – as far back as the 1990s, according to Erin Williams, director for stormwater billing and incentives at Philadelphia’s Water Department. The city worked with a citizen’s advisory committee from 1994-96 to explore alternative methods of funding its stormwater costs of service, and participants ultimately suggested basing it on runoff and the amount of impermeable surfaces on a property. It took the city another 14 years to update its computer systems and analyze its data before it could implement that, Williams said.

In the early years of the program, Williams said property owners weren’t financially motivated to take advantage of the incentives to reduce the amount of runoff their properties were causing, as the cost of making the changes were so high. In response, Philadelphia started offering grants for retrofit projects like green roofs and porous pavement so those property owners can reduce their stormwater fees. Most recently, she said, the city is developing a new website that can “match” contractors and engineers with projects property owners would like to do.

“It’s like match.com for stormwater,” Williams said.

The water department remained revenue neutral in its transition from meter-based to property-based billing for stormwater, though stormwater fees assist the city’s long-term control plan to reduce combined sewer overflows, Williams said. The city’s program to reduce those overflows has been dubbed the “Green City, Clean Waters” program for its projected impact on water quality.

The ECO is recommending that Ontario get out ahead of climate change-related severe weather and require all municipalities adopt full cost recovery for stormwater management, providing incentives for lot-level measures to absorb and store runoff. Schwartzel said the biggest hurdle can be information – some people look at it as a new tax, when the reality is that it’s replacing a tax they’re already paying, and they could be paying more or less depending on their property. It also allows municipalities to better cover the costs of existing infrastructure and provide a reliable, long-term fund for future maintenance and investments, Schwartzel said.

rain garden
Rain gardens absorb precipitation flowing into it from a rooftop or patio, draining it into the soil. Credit: Philadelphia Water Department

Some large cities, such as Toronto, can afford to build large reservoirs to hold stormwater until it can be treated and released at a slower pace over the course of days, or holding ponds to prevent flooding. Schwartzel said smaller towns and cities are often daunted by the perceived costs and complexities of overhauling systems like stormwater financing. But if the province of Ontario were to take a leadership role and provide a common framework and best practices for municipalities to follow, it could help guide those communities toward more sustainable stormwater management, she said.

Kevin Bunch is a writer-communications specialist at the IJC’s US Section office in Washington, D.C.

One Water: A New Way to Think about Water Systems

By Kevin Bunch, IJC

Rain barrels are a way to capture precipitation and keep it from becoming runoff. Credit: Winooski Natural Resources Conservation District
Rain barrels are a way to capture precipitation and keep it from becoming runoff. Credit: Winooski Natural Resources Conservation District

Cities and other communities tend to disrupt the natural water cycle of an area. In natural environments, water falls as precipitation, seeps into the soil and eventually enters the groundwater system, connecting to surface-level waterways. When an area has been developed, more water runs off of hard surfaces like pavement and roofs into storm sewer systems before being dumped into a river or lake, along with any garbage and contaminants like oil or grease carried along by the water.

A new approach known as One Water is aiming at a more holistic system between standard city development and nature for communities to manage their water, from water withdrawal and use to sewage disposal and stormwater management.

“We have to look at the entire system and the entire way in which we use and move water as one integrated cycle and integrated system,” said John Jackson, projector coordinator for the Greater Lakes project with the Great Lakes Commission. “We’re not doing (water reuse and recycling) so much here in the Great Lakes because we have this myth of an endless supply of water because of the lakes, but it’s still very precious.”

More intense storms due to climate change are expected to exacerbate sewage overflows and stormwater runoff contamination to water systems. In addition, over-pumping underground aquifers pulls water from surface water areas that rely on those aquifers to replenish and recharge. This can destroy habitat for fish, wildlife and plants.

A “Greater Lakes” report by the Great Lakes Commission found that in six Michigan and Ontario communities, outdoor water use has the biggest impact on groundwater recharge rates, since changes in water use restrictions and plumbing codes have already helped conserve water.

Storm drains can lead to major erosion issues along waterways, and can back up if there’s too much water from major storms. Meanwhile, small wastewater lines and too much use can lead to capacity problems at treatment plants.  Jackson said it is “wasteful” to do something like use water once to flush a toilet and then discard it from the system entirely.

By managing the system as a whole through water conservation practices (like rain barrels) and replacing infrastructure like combined sewers, cities could be saving money and healing the water cycle. There are other benefits, too – fewer greenhouse gas emissions and less energy used from distributing water for long distances, according to a “Greater Lakes” fact sheet.

A rain garden can help soak up rain and hold onto the water until it seeps into the ground, while also helping plants. Credit: MA Watershed Coalition
A rain garden can help soak up rain and hold onto the water until it seeps into the ground, while also helping plants. Credit: MA Watershed Coalition

For example, one way to make these systems more effective is to reduce the amount of water running off into storm drains, Jackson said. Municipalities can make sure there are drainage ditches alongside applicable roads that will hold onto the water until it can seep into the ground.

Rain gardens can accomplish the same task on residential scales, while using rain barrels and cisterns to capture water from a home’s roof for other uses reduces runoff and the need to use more water from the tap.

Jackson said the barrels are typically used for gardening as an alternative to using a hose, while a cistern can provide water for toilets or washing machines. In either case, such practices reduce the amount of water going into expensive wastewater treatment systems. In some communities in places like Australia, Singapore and California – where water is becoming a scarce resource – water managers have started recycling wastewater to reuse elsewhere in the home, including as drinking water. Jackson notes this already happens for people who live downstream of another community and throughout the Great Lakes – where treated wastewater is put back into the water supply and used again – but the idea makes it a hard public sell.

Retrofitting existing buildings and sewer systems isn’t cheap, though. Jackson said communities replacing aging infrastructure should consider water-saving approaches and new development should automatically use these approaches – communities could even adjust building codes to make them mandatory for new construction.

The Great Lakes Commission’s Greater Lakes project has released a number of tools and informational packets, most notably the Green Infrastructure Optimization Tool, which can calculate the impact of different types of development, soil and rainfall on an area. While these are geared toward governments, Jackson said residents interested in green infrastructure should consider bringing it up to local leaders during planning or infrastructure discussions. In a matter of years, green infrastructure has become more of a mainstream concept, with more civil engineers and officials interested in considering it, and more community residents asking about it.

Permeable pavement, such as porous asphalt on the right side in this photo, allows water to seep into the soil beneath while filtering out pollution. Credit: EPA
Permeable pavement, such as porous asphalt on the right side in this photo, allows water to seep into the soil beneath while filtering out pollution. Credit: EPA

Kevin Bunch is a writer-communications specialist at the IJC’s US Section office in Washington, D.C.

 

Watching Algal Blooms from Space

By Kevin Bunch, IJC

saginaw bay harmful algal bloom nasa
A harmful algal bloom in Saginaw Bay as spotted from space by a NASA satellite. Credit: Jeff Schmaltz, MODIS Land Response Team, NASA

Scientists don’t need to be out on the water collecting jars of algae to help measure a bloom – they can do it from space, too.

A team of scientists was able to use historical data from NASA ocean color satellites to measure the extent of Great Lakes algal blooms back to 1997, even before satellites were actively collecting the data. Michigan Tech Research Institute Co-Director Robert Shuchman said they wanted to answer the question on whether or not harmful algal blooms, or HABs, were getting worse year-to-year, focusing primarily on three areas: the western basin of Lake Erie, Green Bay in Lake Michigan and Saginaw Bay in Lake Huron. Thanks to a grant through the Great Lakes Restoration Initiative, they were able to begin the project about five years ago.

Using the data as a “time machine,” Shuchman said they were able to figure out the average extent of the blooms each year in those three basins. They found that all three locations seemed to behave independently of each other, even though they have similar weather patterns and are relatively near each other. While the extent of algal blooms on Lake Erie has been generally increasing, especially since 2006, Saginaw Bay has been fluctuating year-to-year. Green Bay blooms also fluctuate based on runoff and air temperature in the basin.

Michael Sayers, the researcher in charge of the study, said the lack of perennial HAB trends in those two bays compared to Lake Erie is possibly due to land use and geography. The worst of Lake Erie’s algal blooms is due to agricultural nutrients getting into the Maumee River during the spring, which in turn deposits them into Lake Erie.

Sayers said around 70-80 percent of the Maumee watershed is agricultural. In contrast, the Saginaw River and Fox River watersheds are closer to 40 percent agricultural. They also seem to react differently to weather factors like temperature, precipitation and seasonal climate – leading Sayers to believe that these blooms are “locally controlled phenomena.” The US Department of Agriculture’s Natural Resource Conservation Service has held community outreach efforts and directed money to farmers in the Saginaw River system to work with local agricultural producers to reduce sediment getting into the Saginaw Bay, Sayers said, so local factors could be playing a role beyond the weather, such as Michigan’s phosphorus-reduction legislation.

By correlating the satellite data with “resuspension events” involving winds and waves, the researchers found that resuspension of phosphorus into the water column from bottom sediments also does not seem to be the same issue in Green Bay and Saginaw Bay as it is in western Lake Erie. Sayers said looking in the areas where the blooms pop up repeatedly, there were few events that could have caused resuspension. He hypothesized that Green Bay’s narrow and long morphology may help protect the waterway from winds strong enough to cause resuspension, where phosphorus that has settled into the lake floor is churned back up into the water, providing new fuel for algal blooms.

Using satellites allows researchers to see a long-term analysis of the lakes and the blooms, adding some extra information on the cause and effects of HABs. There are some limitations, though. Shuchman said the land adjacent to the narrow Green Bay has a tendency to form cloud cover early in the day that doesn’t always clear up by the time the satellite moves overhead, and extended periods of cloud cover over parts of the lakes effectively blind the satellites from seeing surface conditions. Shuchman said aircraft now fly over Lake Erie once a week during the July-September HAB season, which helps collect data when it’s too cloudy for satellites. In the next few years, he hopes to add lower-flying drones to monitor the lakes on particularly cloudy days.

This information can be helpful from a public health standpoint as well. The toxicity of harmful algal blooms can make humans sick if ingested and cause rashes if touched, while it can outright kill dogs and other animals. Shuchman said the data is already used by water treatment facilities to protect their intake systems, and natural resources departments in each state for public safety regarding fishing and other uses of the water.

nasa aqua satellite
NASA’s Aqua satellite, launched in 2002, is used to observe weather and climate patterns and trends — including algal blooms — alongside another satellite called Terra. Credit: NASA/JPL AIRS Project

Sayers said satellites currently in use are primarily sensitive to plant-like green algae, but going forward researchers should be able to collect what’s known as hyperspectral data that can delve deep into subtle color differences. This would allow them to identify specific phytoplankton species and types, including some blue-green colored cyanobacterial algae like those found in toxic HABs. Sayer said the information would be helpful for resource managers and stakeholders in these areas, to find out what kind of toxicity they can expect from a bloom for planning water treatment and usage advisories. Green algae and blue-green algae species are not closely related, but both use the “algae” name based on being aquatic and being able to manufacture their own food using sunlight and nutrients in the water.

“Field measurements have been going on for a long time, but HABs are a complex issue, and remote sensing has added some information on cause-and-effect of HABs,” Sayers said.

Kevin Bunch is a writer-communications specialist at the IJC’s US Section office in Washington, D.C.

Nitrogen Pollution Concerns in Great Lakes Coastal Wetlands

By Matthew Cooper, Northland College

 When it comes to nutrient loading to the Great Lakes, it’s usually phosphorus that makes headlines. The algal blooms that plague western Lake Erie and the “dead zone” that forms in Green Bay, for example, are linked to excessive phosphorus runoff from agricultural and urban lands. However, our study recently published in the journal Freshwater Science suggests that at least one important Great Lakes habitat may be affected by nitrogen loading just as much as it is by phosphorus.

Coastal wetlands of the Laurentian Great Lakes are critical habitats for many ecologically and economically important plants and animals. And like the rest of the Great Lakes, these habitats are susceptible to nutrient pollution from sources such as agricultural and urban runoff as well as discharges from sewage treatment facilities. Yet, there has been very little research devoted to understanding how coastal wetlands in the Great Lakes actually respond to nitrogen and phosphorus pollution.

To shed some light on this question, we conducted experiments to simulate various nutrient pollution scenarios by adding combinations of nitrogen and phosphorus to small areas (called benthic substrates) within each wetland. We then measured how the algae on these substrates grew in response to the added nutrients. While the simulations were conducted at a small scale within each wetland, they revealed a lot about how these wetland ecosystems might respond to nutrient loading.

algal growth
Experimental nutrient additions. Each round disk is a surface that is treated with a nutrient combination (either nitrogen, phosphorus, a combination of nitrogen and phosphorus, or a control that does not contain nutrients). Algal growth is measured on each disk after three weeks. Credit: Jessica Kosiara

After analyzing results from 54 wetlands of lakes Michigan and Huron we found that nitrogen, not phosphorus, had the greatest effect on wetland algal growth. Forty-three percent of the wetlands tested exhibited a response to the nitrogen treatment alone and an additional 18 percent exhibited a response to nitrogen if phosphorus also was provided. Just two wetlands showed a response to phosphorus alone (36 percent did not respond to any of the nutrient treatments). This differs remarkably from other Great Lakes habitats where phosphorus loading tends to cause the greatest effect.

map great lakes coastal wetlands algae to nutrient additions
Results of experimental nutrient additions in 54 coastal wetlands. Red symbols indicate a response of algae to nitrogen additions, yellow indicates a response to both nitrogen and phosphorus, and blue indicates a response to phosphorus alone. The size of the symbol indicates the magnitude of the response. The largest responses tended to occur in northern wetlands, which were the most pristine wetlands. Credit: Freshwater Science

Perhaps the most interesting result of the study, however, was that the response to our experimental nitrogen additions was greatest in wetlands that were located in the most pristine areas, such as those along the northern shores of Lake Michigan and Lake Huron. The landscape in this region is predominantly forested with little agriculture or urban development. These include some of the highest quality and most “natural” wetlands in the region. Therefore, the response to experimental nitrogen additions in these wetlands demonstrates what appears to be their natural susceptibility to nitrogen loading. In contrast, wetlands that were surrounded by agricultural and developed lands, such as those in Saginaw Bay and southern Lake Michigan, showed much less response to the added nitrogen, presumably because these wetlands already receive a lot of nitrogen runoff from the landscape.

nutrient discs coastal wetland algal growth simulated
Nutrient disks after three weeks in a coastal wetland. The three cups on the left are controls (no nutrients added) and the three on the right contained added nitrogen. Algal growth was stimulated by the experimental addition of nitrogen. Credit: Jessica Kosiara

The types of algae growing within the wetlands also appeared to be affected by nitrogen loading. For example, algae that has special adaptations to allow them to utilize nitrogen from the atmosphere (called nitrogen-fixing algae) were most common in the most pristine wetlands and fewer of these specialized algae were found in the wetlands that receive nitrogen runoff from surrounding agricultural and urban lands. This supports our hypothesis that Great Lakes coastal wetlands are naturally sensitive to nitrogen loading and that nutrient pollution from the landscape can alter algal communities in these habitats.

Algae is an important energy source for much of the food web in Great Lakes coastal wetlands, so effects associated with nitrogen loading may have broad implications. For example, stimulation of excessive algal growth due to nitrogen loading may cause a buildup of organic matter as the algae grow, then die and accumulate on the sediment. As this organic matter decomposes, oxygen in the water is consumed, ultimately making the habitat less suitable for resident fish populations.

Currently, there is very little management focus on human-derived nitrogen loading to the Great Lakes. For example, the Great Lakes Water Quality Agreement between the United States and Canada to restore and protect the waters of the Great Lakes, includes specific phosphorus loading targets for each of the Great Lakes. The Agreement provides an essential framework for implementing programs to maintain or improve water quality. The Agreement does not, however, address nitrogen loading — and nitrogen concentrations continue to increase throughout the Great Lakes. The implications of this nitrogen buildup for the entire ecosystem remain unclear, though negative impacts to coastal wetlands appear to be one risk that warrants further investigation.

Matthew Cooper is from the Mary Griggs Burke Center for Freshwater Innovation at Northland College in Ashland, Wisconsin.