�

Ecosystem Health and Sustainable Agriculture

Editors: Leif Norrgren and Jeffrey M. Levengood

Ecology andAnimal Health

CSD Uppsala.Centre for sustainable development

2

The North American Great Lakes/St. Lawrence River and Estuary

101

The availability of nitrogen (N) and phosphorus (P) lim-its the growth of aquatic plants and plant-like organisms (macroalgae and phytoplankton, including ‘harmful al-gae’). In freshwater, P is the least abundant (and thus the limiting factor), which would explain why reducing P input alone in lakes could be sufficient to prevent algal blooms whereas in estuarine and marine coastal environ-ments, it is N that is often the least abundant, and thus limiting, factor.

Before extensive urbanisation and agriculture, the Great Lakes (GL) were primarily oligotrophic – they re-ceived only small inputs of N and P from streams and rivers. As a result, GL productivity was largely confined to the extensive system of marshes and estuaries located at their periphery.

Nutrient inputs into the GL increased, albeit modestly, as early as the 18th century as European settlers initiated deforestation, which increased erosion. Increasing human populations and the concomitant industrialisation, agri-culturalisation and inputs of sewage by communities es-tablished on the shoreline injected massive amounts of N and P into the GL. These nutrients led to the overgrowth of phytoplankton and macroalgae, a process termed eu-trophication, which perhaps is the largest, most pervasive global water-quality issue (Diaz and Rosenberg, 2008).

Normally, solar energy drives the growth of phy-toplankton upon which the food chain is based. Under

Eutrophication

Jeffrey M. Levengood University of Illinois at Urbana-Champaign, Urbana, IL, USA

Daniel MartineauUniversity of Montreal, Saint-Hyacinthe, QC, Canada

normal conditions phytoplankton are produced – and die – in moderate amounts because of the limited availabil-ity of N and P. Dead phytoplankton fall to the bottom where benthic animals such as aquatic crustaceans, in-sects and annelids feed on them. In turn these animals transfer this energy to upper trophic levels. When N and P are available in enormous amounts, massive amounts of phytoplankton and macroalgae are produced, die and sink to the bottom where their decomposition by bacteria consumes the oxygen dissolved in water, leading to a to-tal (anoxia) or partial (hypoxia) lack of oxygen. In turn, the absence of oxygen may devastate entire populations of aquatic animals, crustaceans being the most sensitive (Vaquer-Sunyer and Duarte, 2008). In addition, benthic animals are deprived of the solar energy that was previ-ously transferred to them through phytoplankton falling to the bottom. Instead, solar energy is monopolised by the massive bacterial population thriving in the overabundant decomposing algae.

Nowadays, all but the northernmost lake, Superior, have grown progressively more eutrophic since the mid-19th century (Meyers, 2006). It seems that restricting P input alone is sufficient (and economically realistic) to mitigate eutrophication in lakes (in contrast to estuaries where the limitation of both N and P should be consid-ered). In the 1970s, regulations limiting phosphorus in-puts into the GLs such as a ban on phosphate-containing

12

The North American Great Lakes/St. Lawrence River and Estuary

102

detergents and improving waste water treatment greatly reduced blooms of the green macroalgae Cladophora in Lakes Erie and Ontario, although a ‘dead’ zone still de-velops during late summer in Lake Erie, which is now re-garded as mesotrophic with some highly eutrophic areas. In estuaries (such as the St Lawrence) and in the Baltic Sea in contrast, it is argued that restricting both P and N inputs is necessary to stop algal blooms (Conley et al., 2009; Schindler and Hecky, 2009).

Hypoxia occurs naturally in bodies of water in which water circulation is limited by slow flushing or stratifi-cation, the latter occurring when layers of water separate because of their different salt concentration (haloclines) or temperature (thermoclines). Thus, both the BS and GL-SL are naturally vulnerable to hypoxia caused by eutrophica-tion because of slow flushing and the presence of thermo-clines and haloclines (the latter for the SL and BS).

Deep waters of the SL Lower Estuary and Gulf (>275 m), and deep waters of the mouth of the Saguenay River into the SLE, at the centre of the beluga whale’s habitat, up to Anticosti island (Gilbert et al., 2005) are eutrophied and/or hypoxic because, like the GL waters, increased N and P are brought by rivers which carry municipal sew-

age, fertilisers and manure. In addition, warmer water also probably contributes to hypoxia. Indeed over recent years, oxygen-poor warmer water has penetrated the SL Gulf deep waters from the Gulf Stream, possibly because of global warming. The low oxygen levels that have re-sulted (warm water contains less oxygen than cold wa-ter), are lethal to cod, and thus may have contributed to the severe decline in cod populations that has economi-cally devastated entire fishing villages in Newfoundland and the Gaspe Peninsula (Quebec). Cod populations have also dwindled in the Baltic since the 1960s for the same reasons e.g. eutrophication and hypoxia, the latter being permanent in the Baltic deep waters (Conley et al., 2002; Österblom et al., 2007). Hypoxia also has sublethal ef-fects on aquatic animals: under hypoxic conditions, some aquatic animals breathe faster and thus absorb more of some lipophilic contaminants. Certain contaminants that damage gills and red blood cells and/or interfere with glycolytic metabolism may hamper the adaptation of aquatic animals to hypoxia (see review by Couillard et al., 2008).

The 21st century has seen an increase in the number and severity of harmful algal blooms (HAB) worldwide

Figure 12.1. A satellite image showing algal blooms in Lake Erie in August 2009. Note large bloom in the western portion of the basin. Image courtesy of NOAA Great Lakes Environmental Research Laboratory.

The North American Great Lakes/St. Lawrence River and Estuary

103

(Heisler et al., 2008), including in both the Baltic Sea (Vahtera et al., 2007) and the GL (NOAA, 2010). Most HAB are composed of plant-like, photosynthetic algae such as cyanobacteria (or blue-green algae), but some, such as Pfiesteria spp., are animal-like protozoans not equipped for photosynthesis. Most HAB have been asso-ciated to varying degrees with eutrophication (Anderson et al., 2002). In freshwater, high nutrient levels mostly promote the growth of nitrogen-fixing cyanobacteria and thus are responsible for most HAB in freshwater lakes. Some species of cyanobacteria can produce cyanoto-xins (hepatotoxins, neurotoxins, cytotoxins, dermato-toxins and or irritant toxins) that are highly toxic to hu-mans, pets, livestock and wildlife (Mehra et al., 2009). Cyanobacteria can also cause hypoxia on their own, and can disrupt food webs. In addition, by fixing N they make it available for other algae, thus countering the efforts made to reduce the input of external N, as has been docu-mented in the Baltic Sea (Vahtera et al., 2007; Schindler et al., 2008). HAB have also increased in the GL (NOAA, 2010a), especially in the shallower Lake Erie, and Lake Huron’s Saginaw Bay (Vanderploeg et al., 2001). Using satellite and aerial monitoring, the National Centres for Coastal Ocean Science and National Coastal Centre of the National Oceanic and Atmospheric Administration, along with external partners, detect and monitor HAB in coastal regions of the US, including the GL (Figure 12.1; NOAA 2010b). In addition, research in experimental HAB forecasting is underway, to allow prediction of the location and intensity of current and expected HAB.

Evidence has suggested that selective filtration and elimination by the exotic zebra mussels (Dreissena poly-morpha) may be promoting blooms of the cyanobacteria Microcystis aeruginosa, which produces mycrocystins, potent hepatotoxins, in some areas of the GL, by giv-ing unpalatable toxic strains of this species a competi-tive edge (Vanderploeg et al., 2001). Later, Raikow et al. (2004) determined that the presence of zebra mussels promoted Microcystis production in lakes with low nutri-ent levels, whereas cyanobacteria increased in eutrophied lakes in the absence of the mussels.

Alexandrium tamarense, a photosynthetic dinoflagel-late, produces saxitoxin, a toxin causing paralytic shell-fish poisoning (PSP). It is a well-known cause of recur-rent toxic blooms in the St Lawrence Estuary (Blasco et

al., 2003); these blooms are usually restricted to brackish water plumes formed by freshwater input from the up-per estuary and rivers in the absence of wind. Both the absence of wind and freshwater diminish the turbulence of water, which in turn favour the growth of A. tamarense growth and toxin production. Humic substances and pos-sibly P and N released into rivers after heavy rains would also increase growth of A. tamarense (Fauchot et al., 2005). In 2008, with weather conditions such as those de-scribed above, a bloom of A. tamarense formed in the St Lawrence Estuary, at the heart of the beluga whale habi-tat. It caused the death of hundreds of fish, birds, dozens of seals and 9 beluga whales (actual mortality was prob-ably much higher), an event previously unheard of in the SL Estuary.

The anticipated effects of global warming on eutrophi-cation are currently of great concern. Higher temperatures are known to favour algal blooms (and thus to increase consumption of oxygen by bacteria decomposing dead harmful algae). Because warmer water can contain less gas than cold water, increasing temperatures will worsen hypoxia induced by eutrophication. Finally, reduced pre-cipitation expected at mid-latitudes under global warm-ing scenarios will decrease the volume of water flowing into the GL, which will increase the retention time of nu-trients, thus exacerbating eutrophication.

References

335

Chapter 11

El-Sabh, M. and Silverberg, N. 1990. The St Lawrence Estuary: Introduction. In: El-Sabh, M. and Silverberg, N. (eds). Coastal and Estuarine Studies. Vol 39. Oceanography of a large-scale estuarine system, The St Lawrence. New York: Springer-Verlag Inc, pp. 1-9.

Government of Canada and U.S. Environmental Protection Agency. 1995. The Great Lakes: An environmental and resource book. 3rd ed. EPA 905-B-95-001, Chicago, Illinois. http://www.epa.gov/glnpo/atlas/

Morin, J. and Leclerc, M. 1998. From pristine to present state: hy-drology evolution of Lake Saint-François, St. Lawrence River. In: Canadian Journal of Civil Engineering 25, pp. 864–879

St. Lawrence Centre. 1996. State of the Environment Report on the State of the St. Lawrence River. Volume 1. The St. Lawrence Ecosystem. “St. Lawrence UPDATE” series. Environment Canada – Quebec Region, Environmental Conservation, and Les Éditions MultiMondes, Montreal.

Vis, C., Hudon, C., Carignan, R. and Gagnon, P. 2007. Spatial analy-sis of production by macrophytes, phytoplankton and epiphyton in a large river system under different water-level conditions. In: Ecosystems, Volume 10, Number 2/March 2007, pp 293-310.

Chapter 12

Anderson, D.M., Glibert, P.M. and Burkholder, J.M. 2002. Harmful al-gal blooms and eutrophication: nutrient sources, composition and consequences. In: Estuaries 25, pp 704-726.

Blasco, D., Levasseur, M., Bonneau, E., Gelinas, R. and Packard, T.T. 2003. Patterns of paralytic shellfish toxicity in the St. Lawrence region in relationship with the abundance and distribution of Alexandrium tamarense. In: Scientia Marina 67, pp. 261–278

Couillard, C.M., Macdonald, R.W., Courtenay, S.C. and Palace, V.P. 2008. Chemical-environment interactions affecting the risk of im-pacts on aquatic organisms: A review with a Canadian perspective - interactions affecting exposure. In: Environmental Reviews 16:1-17.

Conley, D.J., Humborg, C., Rahm, L., Savchuk, O.P. and Wulff, F. 2002. Hypoxia in the Baltic Sea and basin-scale changes in phos-phorus biogeochemistry. In: Environmental Science & Technology 36, pp 5315-5320

Conley, D.J., Paerl, H.W., Howarth, R.W., Boesch, D.F., Seitzinger, S.P., Havens, K.E., Lancelot, C. and Likens, G.E. 2009. Controlling eutrophication. Nitrogen and phosphorus. In: Science 323, pp 1014-1015

Diaz, R.J. and Rosenberg, R. 2008. Spreading dead zones and conse-quences for marine ecosystems. In: Science 321, pp. 926 - 929

Fauchot, J., Levasseur, M., Roy, S., Gagnon, R. and Weise, AM. 2005. Environmental factors controlling Alexandium tama-rense (Dinophyceae) growth rate during a red tide event in the St Lawrence Estuary (Canada). In: Journal of Phycology 41, pp. 263–272.

Gilbert, D., Sundby, B., Gobeil, C., Mucci, A. and Tremblay, G-H. 2005. A seventy-two-year record of diminishing deep-water oxygen

in the St. Lawrence estuary. The Northwest Atlantic connection. In: Limnology and Oceanography 50:5, pp. 1654-1666

Heisler, J., Glibert, P.M., Burkholder, J.M., Anderson, D.M., Cochlan, W., Dennison, W.C., Dortch, Q., Gobler, C.J., Heil, C.A., Humphries, E., Lewitus, A., Magnien, R., Marshall, H.G., Sellner, K., Stockwell, D.A., Stoecker, D.K. and Suddleson, M. 2008. Eutrophication and harmful algal blooms: A scientific consensus. In: Harmful Algae 8:3-23 (2008).

Mehra, S., Dubey, J. and Bhowmik, D. 2009. Impact of natural tox-ins from cyanobacterial blooms in eutrophic lakes. In: American-Eurasian Jornal of Toxicologic Sciences 1:57-68.

Meyers, P.A. 2006. An overview of sediment organic matter records of human eutrophication in the Laurentian Great Lakes region. In: Water, Air, and Soil Pollution: Focus 6, pp. 453–463

NOAA. 2010a. Harmful algal bloom event response. Centre of Excellence for Great Lakes and Human Health, National Oceanic and Atmospheric Administration (NOAA), http://www.glerl.noaa.gov/res/Centres/HABS/lake_erie_hab/lake_erie_hab.html; last ac-cessed 17 March 2010.

NOAA. 2010b. Harmful algal blooms. National Ocean Service, National Oceanic and Atmospheric Administration (NOAA), http://oceanservice.noaa.gov/topics/coasts/hab/; last accessed 18 March 2010.

Raikow, D.F., Sarnelle, O., Wilson, A.E. and Hamilton, S.K. 2004. Dominance of the noxious cyanobacterium Microcystis aeruginosa in low-nutrient lakes is associated with exotic zebra mussels. In: Limnology and Oceanography 49, pp. 482-487.

Schindler, D.W., Hecky, R.E., Findlay, D.L., Stainton, M.P., Parker, B.R., Paterson, M.J., Beaty, K.G., Lyng, M. and Kasian, S.E.M. 2008. Eutrophication of lakes cannot be controlled by reducing ni-trogen input: results of a 37-year whole-ecosystem experiment. In: Proceedings of the National Academy of Sciences 105, pp 11254-11258.

Schindler, D.W. and Hecky, R.E. 2009. Eutrophication. More nitrogen data needed. In: Science 324, pp. 721-722

Vahtera, E., Conley, D.J., Gustafsson, B.G., Kuosa, H., Pitkänen, H., Savchuk, O.P., Tamminen, T., Viitasalo, M., Voss, M., Wasmund, N. and Wulff, F. 2007. Internal ecosystem feedbacks enhance ni-trogen-fixing cyanobacteria blooms and complicate management in the Baltic Sea. In: Ambio 36, pp. 186-194.

Vanderploeg, H.A., Liebig, J.R., Carmichael, W.W., Agy, M.A., Johengen, T.H., Fahnenstiel, G.L. and Nalepa, T.F. 2001. Zebra mussel (Dreissena polymorpha) selective filtration promoted toxic Microcystis blooms in Saginaw Bay (Lake Huron) and Lake Erie. In: Canadian Journal of Fisheries and Aquatic Sciences 58, pp. 1208-1221.

Vaquer-Sunyer, R. and Duarte, C.M. 2008. Thresholds of hypoxia for marine biodiversity. In: Proceeding of the National Academy of Sciences 105, pp. 15452-15457

Österblom, H., Hansson, S., Larsson, U., Hjerne, O., Wulff, F., Elmgren, R. and Folke, C. 2007. Human-induced trophic cascades and ecological regime shifts in the Baltic Sea. In: Ecosystems 10, pp. 877–889