St Louis River Estuary: The stories and the science

  • Ricing
  • The Stories
  • The Science

Food that grows on water

Restoration is on the minds of many

Restoring wild rice to the St. Louis River Estuary will benefit birds, mammals and humans. As it ripens in the fall, wild rice provides feeding and resting areas for migrating waterfowl and local native birds, like the secretive Sora rail (Porzana carolina), as well as habitat for muskrats (Ondrata zibethicus) and other mammals. This traditional and native plant of the estuary is still here, restoration projects are underway, as Amy Elliot describes, and perhaps someday people will once again be seen ‘ricing’, or harvesting wild rice in places such as Allouez Bay.

Wild rice – A traditional food of the region

The search for ‘food that grows on water’ led the Ojibwe (Chippewa) people to the Upper Great Lakes region several hundred years ago. This food, wild rice (Zizania palustris), became a staple item of the Ojibwe diet. “On reaching the mouth of the St. Louis River …we here saw in plenty the folle avoine, or wild rice…” wrote Henry Schoolcraft in 1820 while on an expedition led by Lewis Cass seeking the source of the Mississippi River. As late as the 1930s, local community members like John Turk were actively ricing in the estuary.

We see very little wild rice when we scan the St. Louis River mouth today. Occasional stands of wild rice can be found in the upper reaches of Pokegama Bay, and scattered plants occur in the shallower flats of the upper estuary and small, sheltered bays between Nekuk Island and Stryker Bay. Although thousands of people still harvest wild rice the traditional way (by canoe) in Minnesota and Wisconsin, very little is harvested from the St. Louis River Estuary.

Wild rice grows best in clear, shallow water (1.5 – 3 feet deep) with a little bit of current and a mucky or silty bottom. Changes in the estuary that may have played a role in the decline of wild rice include:

  • Changes in water depth
  • Excessive wave action from water craft
  • Increased sediment in shallow areas
  • Loss of suitable habitat
  • Predation from wildlife

Restoration projects are taking place in the estuary, and it is the hope of Rick Gitar, Fond du Lac Band’s Areas of Concern Coordinator, that the restorations will increase the habitat for wild rice and bring this native grain back to the estuary in abundance.

The Stories

Amy EliotAmy Eliot is an associate researcher at the Lake Superior Research Institute at the University of Wisconsin – Superior. Read Amy's perspective.

John TurkJohn Turk grew up in the village of Oliver, Wisconsin, less than half-a-mile from the St. Louis River. Read John's perspective.

Rick GitarRick Gitar works to remediate damage from industry in the St. Louis River Estuary. Read Rick's perspective.

The Science

ecologyWild rice: botany and ecology. Read more.

rice water qualityWhat's in the water? Nitrogen, Phosphorus, Sulphates and their effect on wild rice. Read more.

Toolbox

Deep Map. Explore the St Louis River Estuary using this interactive GIS Map.

Deep Science. DIg deeper into sample design, water quality, bugs and plants.

Amy Eliot

Amy Eliot

The wild rice of Allouez Bay

audio transcript

Wild rice disappeared after dredging

Amy Eliot is an associate researcher at the Lake Superior Research Institute at the University of Wisconsin – Superior. In 2010 she began a project with Douglas County and the Great Lakes Indian Fish and Wildlife Commission to plant 300 pounds of wild rice as part of a restoration effort in Allouez Bay. Her father remembers when Allouez Bay’s rich wild rice beds began to change. “His memory is that wild rice disappeared from it [Allouez Bay] after they dredged it when Highway 2 went in.”

Can Allouez Bay wild rice be restored?

Regardless of what combination of factors played a role in the loss of wild rice, today Allouez Bay supports only a few plants near the mouth of Bear Creek, and those plants appear to be damaged. The restoration project aims to re-invigorate the wild rice beds and determine whether predation by carp or Canada geese is a significant factor in their limited distribution and poor condition. Exclosures (structures placed in the water to keep out carp and Canada geese) are used to determine whether wild rice populations improve in the absence of predation. In 2011 wild rice did grow in all areas that were seeded, but was most robust in the exclosures, suggesting that conditions in the bay can support wild rice growth in the absence of excessive predation by wildlife and/or fish. Efforts continue in the bay, and in other parts of the estuary, to restore wild rice.

John Turk

John Turk

Growing up with wild rice

audio transcript

1930s abundance

John Turk grew up in the village of Oliver, Wisconsin, less than half-a-mile from the St. Louis River. He recalls spending hours on the river trapping muskrat, fishing, and later in life, harvesting wild rice on the St. Louis River. “There were some huge beds of rice on the St. Louis in the early 1930s…all these bays above and below the Oliver Bridge were full of wild rice, Big Pokegama Bay and Allouez Bay had a lot of rice.”

Changes and decline

After the 1950s John notes, wild rice became much less common in the estuary. One possible explanation for this decline, according to John, may have to do with the resurgence of Canada geese, a bird rarely seen in the estuary early in the 20th century.“…years ago you never saw a wild goose on that river. The biggest part of the geese now are hatched on this river, they go all over. You never saw a goose landing on that ball field (Oliver) in the 1950s.”

Early newspaper accounts describe the 1,500 acre upper estuary flats area as being heavily vegetated, making it difficult to find the river channel. That’s not the case today and scientists are trying to understand the changes that have occurred.

Water quality, once a major issue in the estuary, has improved in the last 40 years. “The weeds used to be loaded with slime, probably some type of oily substance. You could see where the water line stopped, where the weeds were green. The water cleaned up a great deal,” says John. With improving water quality, natural resource managers and scientists are working together to identify opportunities to restore wild rice to its rightful place in the estuary.

Rick Gitar

Rick Gitar

Sheltered bays and wild rice

audio transcript

Rick Gitar grew up within sight of Lake Superior and has harvested wild rice in northern Minnesota for most of his life. Henotes that rice still grows in Pokegema Bay, on the Wisconsin side of the estuary. “In many years [the bay] is choked [loaded] with wild rice, unfortunately water levels are often low, and the channel is full of [submerged] logs, making it difficult to pole a boat through.”

As the AOC [Areas of Concern] Coordinator for the Fond du Lac Band of Ojibwe, Rick works to remediate damage and pollution from previous industry in the St. Louis River Estuary. When asked what he would like to see change in the estuary, he responded: “The [St. Louis River Estuary] Habitat Plan has identified a number of sheltered bays that could potentially be choked with wild rice, given the right conditions. But one of the things we think might be a problem is recreational boat activity. Establishing a no-wake zone in these sheltered [shallow] bays might help re-establish wild rice and other sensitive aquatic plants.”

Geese are also a detriment to wild rice. Their populations have grown in the estuary, while wild rice stands have become smaller, making them more susceptible to overgrazing by the geese. In 2004 the St. Louis River Citizens Action Committee (now known as the St. Louis River Alliance) received funding to research different methods for reducing goose predation of wild rice stands in the estuary. The stands were expanded by seeding additional rice in the area, but unfortunately the rice did not come up the next year, ending the study.

Rick’s favorite way to visit the estuary is by canoe. . “Canoeing the St. Louis River Estuary …. I find it’s really cool to view wildlife from on the water. In a canoe you’re not actually noticed [by the wildlife], you’re quiet…and the way you know how special the estuary is … is to spend some time on it yourself.” He recommends using a canoe.

Botany and Ecology of Wild Rice

Wild rice (Zazania palustris L.) is a tall aquatic grass found in rivers and lakes throughout the Great Lakes region. The plant has tremendous ecological, economic and spiritual importance. It provides food and habitat for a wide range of wildlife, and is culturally significant to Native American populations, for both sustenance and spiritual reasons. The interactions among the response of wild rice to changing land use, shifting demographics of rice harvesters, and multiple governance structures form a complex and poorly understood system that poses significant challenges to conservation and decision making (Drewes and Silbernagel 2012).

Wild rice has received considerable recent attention in the St. Louis River watershed due to concerns over the environmental effects of mining on Minnesota's Iron Range, on the northern border of the watershed. Of particular interest is the effect of higher than historical concentrations of sulfate leached into waterways from piles of waste rock and taconite tailings, and potentially from future non-ferrous mining operations.

Wild rice typically grows in shallow water - 1 to 3 feet in depth on soft organic (mucky) sediments, and prefers flowing water. Unlike many aquatic plants, wild rice is an annual, reproducing from seed each year. The seeds of wild rice require a winter dormancy of about three months, with immersion in water at freezing, or near freezing, temperatures needed to break down the waxy coating that covers the seed. Seeds germinate when water temperatures reach 45 oF (Oelke et al.). After germination, the plant develops a system of spongy white roots that grow horizontally 9-12 inches. Like other grasses, wild rice also produces tillers - underground stems that give rise to other shoots. The number of tillers depends on stem density - sparser stands of wild rice produce more tillers on individual plants. Tillers are important in that they can also produce grain, but they tend to flower later than the source plant, which affects both the length of the harvest season and total yield of grain.

Seedlings have 3-4 leaves that remain underwater, with subsequent leaves reaching to and floating on the surface (Marcum 2007). Wild rice forms characteristic floating mats of ribbon-like leaves during mid-June. At this time, the plant is sensitive to water depth - rising waters will uproot the plants and lower water levels will damage the weak hollow stems. Wind and wave action can also uproot plants, and wakes from recreational watercraft are a persistent management issue on wild rice lakes and rivers.

Aerial shoots emerge from the water in late June and early July. The emergent plants grow 3-6 feet tall, with a central stalk supporting 5-6 elongated ribbon-like leaves ½ to 1 ½ inch in width. Flowers are produced in terminal clusters, with staminate (male) flowers on the lower stalk and upright pistillate (female flowers) on the upper branches. The female flowers emerge before the males, so plants are typically cross pollinated. Wind is the primary means of pollination. The seeds are surrounded by a papery hull with a long terminal awn, both of which are removed when rice is processed as a food source.

Wild rice flower close up image - photo credit UMN Extension. Click to zoom.

Wild rice flower close up image - photo credit UMN Extension.

Seeds of wild rice mature in late August. Like other grasses, an important phase of the life history is the “shattering” of the mature seed, which refers to the seeds dropping off the plant as they ripen. In natural systems, shattering occurs over a period of days to weeks, allowing multiple harvests of the wild rice beds. In cultivated rice paddies, shatter-resistant varieties are used to allow for a single mechanized harvest.

The productivity of wild rice beds varies from year to year. A rule-of-thumb provided by the Great Lakes Fisheries and Wildlife Commission is “a typical four year period will include a bumper year, two fair years and a bust”. Walker et al (2010) have attributed this pattern to the nutrient dynamics of decomposition of wild rice straw - the remains of the parent plants. Following a productive year, microbes in the bottom sediments are thought to take up much of the nitrogen as they begin the initial decomposition of plant litter, making it less available to wild rice plants. After a year or two, the final stages of decomposition occur and nitrogen again becomes available for plant growth. Understanding litter dynamics is important, in that it can lead to more informed decisions on the optimal times for seeding wild rice beds.

Environmental Stressors

The distribution of wild rice has been greatly reduced from its historic range prior to European settlement (Meeker 2000, Vennum 1988). Pillsbury and McGuire (2009) reviewed numerous studies on wild rice decline, which are variously attributed to changes in pH and the presence of heavy metals and acids from copper-zinc smelting, [reduced] sediment nitrogen, [increasing] water level changes, and competition from other plants (i.e. invasives). In their study, Pillsbury and McGuire evaluated 60 wetlands which had historically dense wild rice populations but now vary in wild rice productivity, from high, to moderate to degraded. The study included two sites in the St. Louis River Estuary - Boy Scout landing, which now has low wild rice density, and Skibo Mills, which retains a healthy population. They assessed a range of environmental factors, from water chemistry to sediment type to watershed land use, and found that the strongest declines were associated with increased residential development and increased levels of ammonia-N (NH4+-N). Residential development is a predominant environmental stressor, indirectly resulting in increased stream temperature, sedimentation, and ‘flashiness’ of streams that feed the St. Louis River Estuary. The inverse relationship with NH4+-N is less straightforward, as wild rice is often limited by nitrogen availability, but may be related to increased competition from other plants stimulated by increased nutrient levels.

Wild Rice Conservation

Because of the degradation to natural populations, there are strong interests, particularly among the Fond du Lac Band of Lake Superior Ojibway (FDL), which directly and indirectly manages the wild rice resource in the St. Louis River watershed. The dominant method for managing wild rice is by control of water levels, through water control structures, ditch maintenance and beaver dam maintenance. FDL also has a strong program for removing competing vegetation, particularly the widespread pickerelweed (Pontederia cordata), an invasive species which has extensively colonized Perch and Jaskari Lakes on the reservation (Forbes 2005). The band uses a “Cookie Cutter” - a large platform based aquatic plant harvested that severs the mat of vegetation, which is then removed from the lake. This is often followed by wild rice re- seeding.

Photo courtesy of Fond du Lac Natural Resources Department.

At the landscape scale, wild rice conservation involves a complex interplay among social values, economy and ecology, all of which have underlying spatial dynamics (Drewes and Silbernagel 2012). Not only are populations and the yield of wild rice reduced from historic numbers, but the number of people participating in wild rice harvest is declining, and the average age of active harvesters is increasing. Moreover, management occurs at the level of individual lakes or individual communities - there are few active regional statewide or broader entities that look at the collective effects of local decisions. Given the current social and ecological trends, a regional perspective that allows for broader conversation and planning is essential to ensure the sustainability of this important species (Drewes and Silbernagel 2012).

Literature Cited

Drewes, A. and J. Silbernagel. 2012. Uncovering the spatial dynamics of wild rice lakes, harvesters and management across Great Lakes landscapes for shared regional conservation. Ecological Modelling 229: 97-107.

Forbes, M. E. 2005. Assessing competitive interactions between wild rice (Zizania aquatica) and pickerel week (Pontedaria cordata) in a disturbed northern Minnesota wild rice lake. M.S. Thesis, University of Minnesota Duluth, Duluth, MN 99p.

Marcum, D.B. 2007. Cultivate wild rice production in California. University of California Agriculture and Natural Resources Publication 21622. 25 p.

Meeker, J. 2000. Ecology of ‘wild’ wild rice (Zizania palustris var palustris) in the Sakagon Sloughs, a riverine wetland on Lake Superior. p 68-84 In L. S. Williamson, L. A. Dlotkowski, and A. P. McCommon-Soltis (eds) Wild rice research and management. Great Lakes Fish and Wildlife Commission publication, Odanah, Wi, USA.

Oelke, E. A., T.M. Teynor, P.R. Carter, J.A. Percich, D.M. Noetzel, P.R. Bloom, R.A. Porter, C.E. Schertz, J.J. Boedicker, and E.I. Fuller. Alternative Field Crops Manual: Wild Rice. http://corn.agronomy.wisc.edu/Crops/WildRice.aspx Accessed 6.6.2013

Orcajada, P. 2012. Harvesting Wild Rice. Dept. of Crop Science, U. of Saskatchewan. http://www.agriculture.gov.sk.ca

Vennum, T. 1988. Wild Rice and the Ojibway People. Minn Historical society Press St. Paul.

Walker, R,. J. Pastor, and B. Dewey. 2010. Litter quantity and nitrogen immobilization cause oscillations in productivity of wild rice (Zizania palustris) in Northerm Minnesota. Ecosystems 13:485-498.

Wild Rice Information Resources

GLFWIC Wild Rice Brochure
http://www.glifwc.org/publications/pdf/Wildrice_Brochure.pdf

Minnesota Wild Rice Management
http://www.dnr.state.mn.us/wildlife/shallowlakes/wildrice.html

Wisconsin Wild Rice Harvest Data
http://glifwc.org/WildRice/wildrice.html

1854 Treaty Authority
http://1854treatyauthority.org/wildrice/

Wild rice grows in shallow lakes, ponds, and wetlands. Click to zoom.

Wild rice grows in shallow lakes, ponds, and wetlands.

What's in the Water?

Nitrogen, Phosphorus, Sulfates and their effects on Wild Rice

Wild rice is an annual aquatic grass whose seeds germinate in the soft, mucky sediments of shallow waters. Seeds typically germinate the year after they mature and fall, but can lie dormant for several years. Annual yields in relatively undisturbed areas can vary dramatically from year to year in response to a variety of factors mostly related to the effects of weather patterns on length of growing season, sunlight, temperature and water level. Sudden increases in water level triggered by storms during critical growth periods can reduce yields. Yields can also be influenced by intentional lake level manipulation or lake-outlet blockages from beaver dams. The Minnesota DNR has shown that development of shorelines has had negative impacts on historical wild rice stands, and the Minnesota counties having the majority of wild rice habitats are expected to increase in population significantly in the next 20 years.

Regulatory issues

Wild rice is an important part of Minnesota’s aquatic plant communities, particularly in the north. It provides food for waterfowl and habitat for fish and wildlife. Several Native American cultures, such as the Ojibwa, consider wild rice to be an important food and a sacred element of their culture. It is also economically important to those who harvest and market wild rice. Although many environmental factors regulate its growth and distribution, evidence has pointed to sulfate (SO4 -2) concentrations greater than 10 ppm (technically 10 milligrams-per-liter, expressed as mg/L) in the water being detrimental to wild rice. Surveys across the state by Minnesota DNR ecologist John Moyle in the 1940s indicated that the rice was more prevalent in the (typically) very low sulfate waters of most of northern Minnesota. This correlation of high sulfate and less wild rice was the major scientific basis for the establishment by the Minnesota Pollution Control Agency of the 10 mg/L sulfate concentration as a regulatory standard to help protect existing wild rice “waters.” The standard could also potentially help identify degraded water bodies so the cause of the problem could be diagnosed accurately and then addressed. This action was approved by the U.S. Environmental Protection Agency as part of the requirements of the U.S. Clean Water Act.

Before taking a closer look at the potential effects of excess sulfate on wild rice, it is helpful to review some basics about wild rice and aquatic vegetation in general in terms of several important water quality parameters.

Minnesota’s sulfate standard to protect wild rice
The MPCA created this website to allow people access to “Wild Rice-Sulfate” information including its historical basis and the science behind this somewhat unique water quality standard. Since 2011, in response to the potential new sources of sulfate from proposed non-ferrous sulfide ore mines (usually just called “Copper” ) mines, MPCA has engaged in a set of field and laboratory studies to better understand the cause of the negative association between wild rice and sulfate, and determine if the 10 mg/L value is appropriate.  These studies were designed with input from a broad community of scientists and carried out largely by scientists from the University of Minnesota. Details of this process, the study designs, and preliminary data and analyses may be found here.  As you can see from the diagram below right, the processes and other water quality parameters that affect sulfur and mercury chemistry and biology in water bodies is extremely complex and dynamic. Note: 10 mg/L can also be expressed as 10 parts-per-million (ppm).

Nutrients

Nitrogen

A four year cycle between peak wild rice production years is frequently observed, recent studies of local wild rice in natural waters and in tank experiments have suggested that nitrogen availability drives this cycle. Most of the nitrogen needed by the plants is taken up from the sediments by plant roots. Decomposing plants from previous years release nitrogen, with stems and leaves decomposing faster than roots. Nitrogen also enters wetlands and shallow waters via soil and plant litter washed in naturally from the surrounding watershed and from stormwater runoff from human activities. These sources vary from year to year, throughout the year, and from watershed to watershed. Organic matter in the sediments also comes from the decomposing remains of algae and from other aquatic plants besides wild rice.

Phosphorus

Phosphorus (P) is another key nutrient that is critical to plant growth and usually is in short supply in northern Minnesota waters unless there are inputs coming from domestic wastewater (i.e., sewage from septic systems or community wastewater treatment plants) or eroded soil from lawn or farm runoff where fertilizer-P was applied. In the absence of such an “unnatural” loading of phosphorus into the water body, there is little information on how natural variations in phosphorus levels might affect annual yields of wild rice 3,4.

Nutrient impacts on Shallow Lake Ecology

Studies of many shallow lakes have shown that when aquatic vegetation (mistakenly called “aquatic weeds” by many lake enthusiasts) reaches its peak in summer, the abundance of algae freely suspended in the water (phytoplankton) declines, and the water actually becomes much clearer. What’s happening is that the aquatic plants are shading the water enough to drastically reduce sunlight available for phytoplankton photosynthesis, thus reducing growth. Also affecting water clarity, the aquatic plants and their roots combine to dampen wave action from the wind. This lets particles in the water drop to the bottom faster and reduces the amount of bottom muck or mud that is stirred up during storms.

However, excess nitrogen and phosphorus can have significant negative impacts on aquatic plant communities by promoting excess algal growth. Human-generated sources of nutrients include seepage from septic systems, lawn fertilizer runoff, erosion, and stormwater runoff. Planktonic (free-floating) algae and attached algae (the scuzzy and often-slippery green and brown slime growing on rocks, plants and other structures along the shoreline) are fertilized by these nutrients, and as their abundance increases, the clarity of the water decreases. This excess growth of algae clouds the water, and if it occurs before aquatic plants have gotten well-established, algal growth can shade the bottom where rooted plants get their start, thus reducing the area of lake bottom where plants can grow.

Research suggests that it is possible for two distinct and relatively stable states to exist, one in which most of the vegetative productivity is in the form of higher plants, including wild rice, and one that is dominated by algae. Dominance by algae in the form of phytoplankton productivity can cause the water to become quite green and murky – thus restricting the growth of rooted plants to only the shallowest depths nearshore. further illustrates how these impacts, if large enough, are likely to lead to very different food webs, in addition to decreased plant production – including wild rice, if historically present. In summary, excess inputs of nutrients, along with overharvesting of aquatic plants usually leads to undesirable consequences that can negatively impact many of the beneficial uses of the water body.

Schematic of alternative state food webs in shallow lakes and ponds. Source: www.metrocouncil.org Click to zoom.

Schematic of alternative state food webs in shallow lakes and ponds. Source: www.metrocouncil.org

Bottom sediments

Oxygen, Sulfate, Sulfide, Iron – This is not simple!

Another important part of the ecology of wild rice is the character of the bottom sediments in which the plants grow. Just as water chemistry and quality varies across wetlands and with depth, some critical characteristics of the sediments vary dramatically with depth into the sediment, as well as across different parts of the wetland. The most important factor as we go down into the mucky and sometimes soupy mud of the root zone is the amount of dissolved oxygen (DO). DO is rapidly depleted by all the biological activity in the mud, making it pretty much anoxic (lacking oxygen) except near the water-mud surface. In shallow waters (less than 10 – 15 feet or 3 – 4.5 m deep) oxygen is mostly coming from the air above the water, and when it’s windy and foamy the water is aerated more quickly. Photosynthesis by aquatic plants and algae can also contribute a significant amount of dissolved oxygen to the water during daylight, but at night and on cloudy days, the DO in the water above the sediment may drop to zero because the animals and many groups of bacteria continue to consume oxygen throughout the day and night. Their combined demand for oxygen can exceed the amount diffusing downward from the water. Once you probe down into the mud, beyond the top few centimeters you’ll find no oxygen at all.

Oxygen also regulates the metabolism of many groups of naturally occurring bacteria, and low DO will kill some types of bacteria, while allowing the growth of others. The combined effect is to structure the mud into zones and layers having different amounts and types of nitrogen and phosphorus and chemical forms of iron and sulfur. In well-oxygenated streams (riffles and falls) and the surface waters of most lakes and ponds, the primary form of sulfur is sulfate (SO4-2), which is usually harmless to plants and animals even at very high levels. In fact, the drinking water standard for humans (set to control taste and laxative action, not toxicity) is 200 parts-per-million (200 mg SO4-2 /L), which is 20x higher than the wild rice standard. Preliminary results from past and recent experiments, looking at wild rice from seed germination through the annual growth cycle, have largely confirmed that it’s not the sulfate itself at current levels in the St. Louis River that is toxic to wild rice, but the transformation of sulfate to sulfide that occurs under anoxic conditions. And of course, it’s still not that straightforward.

So what happens in anoxic mud?

If you tried to grow houseplants or vegetables in this zone, the roots would die pretty quickly because they need oxygen. Conditions faced by aquatic plants are similar to those of waterlogged houseplants. But wild rice, bulrushes, reeds, cattails, sedges, irises, and some other rooted plants have special adaptations allowing them to thrive in waterlogged conditions, including hollow stems that can transport oxygen to plant roots from overlying water and emergent leaves exposed to the air. Similarly, bacteria that require oxygen to thrive cannot survive in anoxic sediments, while bacteria that can use other compounds in place of oxygen will grow well. Nitrate and nitrite, oxidized iron and manganese, and sulfate can be used by different groups of bacteria in their metabolism analogously to how plants and animals (including humans) use oxygen to breakdown organic matter (food) and extract energy and other nutrients. When oxygen is used, a final waste product is water vapor (the source of our breath steam in cold weather). When nitrate is used, a final “waste” product is nitrogen gas, which harmlessly dissolves in the water, adding a trivial amount of nitrogen relative to what diffuses in from the atmosphere (which is almost 80% nitrogen gas). But when sulfate is used, the end product is hydrogen sulfide gas (H2S), which not only stinks (think rotten eggs) but is extremely toxic to plants and animals. This appears to be the main culprit for the decline or absence of wild rice in habitats that appear suitable but have elevated sulfate levels.

The upper boundary of the St. Louis River watershed, of course, is defined by the Mesabi Iron Range, which supplied iron ore to Midwestern steel mills for over 50 years. But the taconite tailings resulting from open pit mining have been a long-term source of elevated sulfate levels (Lindgren et al 2006). This increase in sulfate levels in the St. Louis River and other water bodies over the past 40 or more years from iron mining activities has the potential to negatively impact wild rice by enhancing the amount of sulfate that reaches bottom water and sediment, where naturally occurring anaerobic bacteria convert it into toxic H2S. You can read summaries of the lab experiments and field studies that MPCA and UMD scientists have been conducting for the past few years here . These recent studies are currently being evaluated by MPCA in the context of the validity of the current 10 mg/L sulfate standard.

Other factors that affect the amount of H2S in the water and root zone

The biogeochemistry of the root zone is even more complicated than described above because if there is enough dissolved iron in the root zone mud, the iron can react and bind some of the H2S to form iron sulfide. Iron sulfide is very insoluble in water, forming patches of black mud that might act to delay or decrease the toxicity of the sulfide. Finally, there can be additional reactions between phosphate and iron in the mud that further modify the net amount of sulfide available to impact aquatic plants.

Climate change and wild rice

Our climate has been changing, and current understanding of its likely impacts in northern Minnesota suggests that there will be an increase in severe storms and droughts. This would likely add additional stress to wild rice stands because the plant is very sensitive to water depth, i.e., rising waters can uproot the plants and lower water levels can damage the weak hollow stems. Wind and wave action can also uproot plants, adding to other stresses such as the damage that can result from the wakes created by recreational watercraft, which are a persistent management issue on wild rice lakes and rivers.

Invasive species and wild rice

Invasive and exotic species of aquatic plants are thought to benefit from disturbances to natural habitats. Mechanically harvesting aquatic “weeds” or dosing aquatic plants with herbicides creates open areas, which can increase the likelihood of an invasive plant species gaining a toehold that later leads to its spread. Research suggests that a healthy and diverse native assemblage of aquatic plants has a better chance of resisting the invasion of an exotic plant or animal. It may not completely exclude invaders but they are much less likely to completely dominate the near shore zone. In general, “weedy” species (think dandelions on lawns, fields, and vacant lots) are excellent colonizers and well adapted to exploiting disturbed and open bottom sediments, particularly when nutrients are abundant. This, along with their importance as habitat for fish and wildlife, is an important reason that lake managers and educators emphasize the importance of maintaining a healthy aquatic plant community in your lake.

Additional information on the ecology of wild rice

References

  1. Walker, R. D., J. Pastor, and B. Dewey. 2010. Litter quantity and nitrogen immobilization cause oscillations in productivity of wild rice (Zizania palustris L.) in northern Minnesota. Ecosystems 13: 485-498.
  2. Walker, R. D., J. Pastor, and B. Dewey. 2006. Effects of wild rice (Zizania palustris L.) straw on biomass and seed production in northern Minnesota. Canadian Journal of Botany 84: 1019-1024.
  3. Sims, L., J. Pastor, T. Lee, and B. Dewey. 2014In press. Nitrogen, phosphorus, and light effects on growth and allocation of biomass and nutrient in wild rice. Oecologia. Pastor, J. and R. D. Walker. 2006. Delays in nutrient cycling and plant population oscillations. Oikos 112: 698-705.
  4. MPCA Wild Rice Literature Holdings (Last Update: 12/31/2013)
  5. Moss, B., J. Madgwick and G. Phillips. 1996. A guide to the restoration of nutrient enriched shallow lakes. Environment Agency, Broads Authority & European Life Programme. Norwich, England. Natural History Book Services, Totnes, Devon, UK. 180 p.
  6. >Moss, B. 2003. Cinderella goes to the ball: A story of shallow lakes. Lakeline (a publication of the North American Lake Management Society, http://www.nalms.org) 23 (1): 11-16 (Spring 2003).
  7. Lindgren J., Schuldt, N., Borkholder, B., Howes, T., Levar, A., Olson, C., Tillma, J. and Vogt, D. (2006) A Study of the St. Louis River. Minneosta Department of Natural Resources Division of Fisheries Report, Duluth, MN, 48 p. plus figures, tables, and appendicies.

Maps