What is the status of benthic communities in Lake Saint-Pierre? (3rd edition, 2016)

Status: Moderate-Good
Observed change: Deterioration from 2004 to 2006, followed by an improving trend until 2014

Highlight

Benthic macroinvertebrates—insects, worms and molluscs that live on the bottom of lakes and rivers—can be used to determine whether environmental conditions are good or show signs of disturbance. Based on biomonitoring studies conducted by Environment and Climate Change Canada scientists, the status of the benthic communities in Lake Saint-Pierre between 2012 and 2014 was classified as moderate-good; these communities have shown signs of improvement since 2006.

Issue

In natural aquatic ecosystems, benthic organisms are distributed according to their biological needs. Some benthic organisms require oxygen-rich water, while others live in or on soft or rocky substrates. The set of environmental conditions that a species needs in order to complete its life cycle and maintain a stable population is referred to as its “ecological niche.”

Figure 1: Change in indices related to the status of benthic macroinvertebrate communities
Long description

On the left side of the diagram, there is an undisturbed aquatic ecosystem with a healthy benthic community characterized by high richness, low dominance of crustaceans and molluscs, and a large number of pollution-sensitive species. The ecosystem on the right side of the diagram is affected by urban and agricultural pollution and its benthic community is characterized by declining richness, a decreasing number of pollution-sensitive species and an increasing dominance of crustaceans and molluscs.


Over time, changes in environmental conditions lead to changes within the benthic community. Natural factors—including climatic variations (precipitation, temperature), type of wetland sampled (aquatic grass beds vs. low marsh), site elevation or the presence of a competing species—may be involved. Anthropogenic factors may also affect benthic communities. For example, the impacts of urban and agricultural runoff on benthic communities have been observed downstream from the Island of Montreal. Monitoring results for the period prior to 2013 showed a worrisome situation for benthic communities in downstream areas, particularly around the Contrecoeur Islands and the Berthier-Sorel Islands in Lake Saint-Pierre, but this was not the case for communities located upstream (Savage et al., 2013).

Since benthic organisms respond to changes in their environmental conditions, they are useful indicators for aquatic biomonitoring aimed at assessing water quality (presence of nutrients). Certain species are more sensitive than others to various stressors, and may exhibit a decrease in their growth or reproduction (chronic effect) or even mortality (acute effect). Exposure to stressors may result in changes in abundance and benthic community composition.

Key measures

Three indices are used to assess benthic community status, or condition: community (taxa) richness, community composition and number of pollution-sensitive families.

The quality criteria for these three indices were calculated using more than 100 reference sites along the St. Lawrence from Lake Saint-François to Lake Saint-Pierre. Benthic communities can be classified in five categories based on their condition: excellent, enriched, satisfactory, impoverished and degraded.

Community (taxa) richness

The greater the richness of a community, the better its state of health (Gernes and Helgen 1999; U.S. EPA 2002). In benthic communities, the number of genus declines as the level of disturbance increases.

Degraded

Impoverished

Satisfactory

Enriched

Excellent

<14

          14 to 20

>20 to 31

>31 to 38

>38

Long description

The table shows a scale for assessing benthic community status from the standpoint of richness. A benthic community is classified as degraded when the number of genus is below 14; as impoverished when the number is between 14 and 20; as satisfactory when the number is higher than 20 and up to 31; as enriched when the number is higher than 31 and up to 38; and as excellent when the number is higher than 38.

Dominance in macroinvertebrate community composition

The relative abundance of crustaceans and molluscs increases in response to disturbance. Where a community is dominated by a group of species or a given species, this indicates that the biophysical conditions are unfavourable (or too degraded) for other species. The higher the index value, the more a community is considered to be degraded (Gernes and Helgen 1999; US EPA 2002).

DDegraded

Impoverished

Satisfactory

Enriched

Excellent

>57%

>27 to 57%

>18 to 27%

3 to 18%

<3 %

Long description

The table shows a scale for assessing benthic communities from the standpoint of dominance of crustaceans and molluscs. A benthic community is classified as degraded when the proportion of crustaceans and molluscs is higher than 57%; as impoverished when the proportion is greater than 27% and up to 57%; as satisfactory when the proportion is higher than 18% and up to 27%; as enriched when the proportion is between 3% and 18%; and as excellent at a level below 3%.

Number of organic pollution-sensitive families

As organic pollution increases, the abundance of pollution-sensitive macroinvertebrates decreases. This metric uses the number of families of Ephemeroptera, Trichoptera, Pisidiidae and Anisoptera (ETPA)1. The greater the number of ETPA families, the healthier the benthic community (Gernes and Helgen 1999; U.S. EPA 2002).

1- Formerly called the ETSD index (Ephemeroptera, Trichoptera, Sphaeriidae and Dragonflies [Anisoptera]).

Degraded

Impoverished

Satisfactory

Enriched

Excellent

0 to 1

>1 to 2

>2 to 5

>5 to 6

>6

Long description

The table shows a scale for assessing benthic communities from the standpoint of number of organic pollution-sensitive families. A benthic community is considered degraded when the number of organic pollution-sensitive families is between 0 and 1; as impoverished when the number is higher than 1 and up to 2; as satisfactory when the number is higher than 2 and up to 5; as enriched when the number is higher than 5 and up to 6; and as excellent when the number is higher than 6.

Community (taxa) richness is better than satisfactory

Figure 2: Total number of genus in Lake Saint-Pierre
Long description

This figure illustrates the yearly median values for the total number of genus in Lake Saint-Pierre. From 2004 to 2006, the index value decreased, reaching a low of 15 genus in 2006, which is indicative of an impoverished benthic community. In 2007, the index value began increasing and stabilized around a median value of 35 genus, which corresponds to an enriched community.

The total number of invertebrate genus varies over the years. The number of genus decreased so much from 2004 to 2006 that benthic community richness in Lake Saint-Pierre was degraded in 2006. Beginning in 2007, the number of genus counted steadily increased, reaching 33 to 38 genus in Lake Saint-Pierre from 2012 to 2014, which is indicative of enriched benthic communities (Figure 2).

This index must be interpreted with caution, because a minor disturbance can allow new species to appear in a community, thereby increasing richness. The index value will decrease only in response to a protracted, high intensity disturbance. Therefore, the actual effects of a disturbance can only be assessed in light of the other

A benthic community dominated by crustaceans and molluscs is impoverished

Figure 3: Relative abundance (%) of crustaceans and molluscs in Lake Saint-Pierre
Long description

This figure illustrates the yearly median values for the relative abundance of crustaceans and molluscs in Lake Saint-Pierre. From 2004 to 2006, the index value decreased, reaching a low of 13% in 2007, which corresponds to an enriched benthic community. In 2008, the index value began to increase and eventually stabilized around a median value of 40%, which is indicative of an impoverished community.

The index of the relative abundance of crustaceans and molluscs exhibits large inter-annual variations, making it difficult to identify a clear trend. These inter-annual variations can be explained by such factors as suitable habitat availability, water level fluctuations or food abundance (Brown 2001). From 2012 to 2014, the relative abundance of crustaceans and molluscs in Lake Saint-Pierre ranged from 37% to 71%, which points to an impoverishment of the benthic communities.

In 2013, as in 2004, the relative abundance of crustaceans and molluscs was high, which is indicative of degradation. In contrast, the low relative abundance of crustaceans and molluscs in 2005, 2007 and 2010 points to enrichment (Figure 3). The pulmonate gastropods Ferrissia, Physa, Gyraulus and Planorbidae, known for their tolerance to organic pollution, are the most commonly observed and most abundant molluscs in Lake Saint-Pierre.

The number of organic pollution-sensitive families (ETPA) is considered satisfactory or excellent

Figure 4: Number of organic pollution-sensitive families in Lake Saint-Pierre
Long description

This figure illustrates the yearly median values for the number of pollution-sensitive invertebrate families in Lake Saint-Pierre. From 2004 to 2006, the index value declined slightly, reaching a low of 2 families in 2006, which corresponds to an impoverished benthic community. In 2007, the index values began to increase and eventually stabilized around a median value of 4 families, which corresponds to a satisfactory benthic community.

The families considered when calculating this index are known to be sensitive to organic enrichment, particularly phosphorus enrichment. When present at high concentrations in an aquatic ecosystem, this essential nutrient can cause eutrophication. Since 2004, the median values for this index have ranged from two to seven families, which corresponds to a satisfactory or even excellent status. The trend in this index since 2004 is considered stable.

A simultaneous comparison of the three metrics can provide a better assessment of the changes in the benthic community in Lake Saint-Pierre since 2012. Over this time period, two of the three indices maintained a status of at least satisfactory.

Long description

The table shows the year-to-year status of the three indices. In 2012, the richness metric shows an enriched status; the dominance metric an impoverished status, and the metric of number of pollution-sensitive families is excellent. In 2013, the richness metric shows an enriched status; dominance is classified as poor; and the number of pollution-sensitive families is satisfactory. Finally, in 2014 the richness metric remains enriched, dominance is classified as impoverished, and the number of pollution-sensitive families is classified as enriched.

Influence of environmental conditions

Overall, the status of the benthic communities in Lake Saint-Pierre can be classified as moderate-good. The high relative abundance of crustaceans and molluscs in 2013 is nonetheless indicative of both natural and anthropogenic disturbances. Since the period 2004 to 2006, when the number of genus and the abundance of pollution-sensitive families declined, the benthic communities in Lake Saint-Pierre have remained stable in spite of inter-annual fluctuations.

In addition, recent work indicates that the status of benthic communities in the St. Lawrence is linked to various factors, particularly the hydrologic cycle (e.g. the amplitude of water level fluctuations) and habitat characteristics, such as wind exposure and sediment and vegetation type (Tall et al., 2015). A number of earlier studies also identified the important influence of the hydrologic cycle and water quality on benthic community structure and composition in wetlands (Hentges and Stewart 2010; Cooper et al., 2006; McCormick et al., 2004).

Bibliography

Brown, K. M. (2001) Mollusca: Gasteropoda in Thorp, J. H. and Covich, A. P. Ecology and Classification of North American Freshwater Invertebrates. Academic Press, 2nd edition, USA.

Cooper, M. J., Uzarski, D. G., Burton, T. M. and Rediske, R. R. (2006) Macroinvertebrate community composition relative to chemical/physical variables, land use and cover, and vegetation types within a Lake Michigan drowned river mouth wetland. Aquatic Ecosystem Health & Management 9(4): 463-479.

Gernes, M. C. and Helgen, J. C. (1999) Indexes of Biotic Integrity (IBIs) for Wetlands: Vegetation and Invertebrate IBIs. Minnesota Pollution Control Agency, Biological Monitoring Program. St. Paul, Minnesota Hentges, V. A. and Stewart, T. W. (2010) Macroinvertebrate assemblages in Iowa prairie pothole wetlands and relation to environmental features. Wetlands 30(3): 501-511.

McCormick, P. V., Shuford III, R. B.E. and Rawlik, P. S. (2004) Changes in macroinvertebrate community structure and function along a phosphorus gradient in the Florida Everglades. Hydrobiologia 529: 113-132.

Savage, C., Armellin, A. and M. Jean. 2013. Benthic Macroinvertebrate Communities: An indicator of water quality and aquatic ecosystem health in the St. Lawrence River. 2nd Edition. Monitoring the State of the St. Lawrence River collection. Montreal, Quebec. On the St. Lawrence Action Plan web site.

Tall, L., Armellin, A., Pinel-Alloul, B., Méthot, G. and Hudon, C. (2015) Effects of hydrological regime, landscape features, and environment on macroinvertebrates in St. Lawrence River wetlands. Hydrobiologia Published online, 28 October 2015.

U.S. EPA (2002) Methods for Evaluating Wetland Condition: Developing an Invertebrate Index of Biological Integrity for Wetlands. Office of Water, U.S. Environmental Protection Agency, Washington, DC. EPA-822-R-02-019.

Prepared by

Alain Armellin
Fresh Water Quality Monitoring and Surveillance
Water Quality Monitoring and Surveillance
Water Science and Technology
Science and Technology Branch
Environment and Climate Change Canada