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Lac Saint-Pierre integrity workshop

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A St. Lawrence Action Plan (SLAP) event held at Université du Québec à Trois-Rivières,
March 24, 2015

Organization : Serge Hébert, MDDELCC, Christiane Hudon, ECCC, Serge  Villeneuve, ECCC et Étienne Gascon, ECCC

Workshop leader : Jean Burton

Table of content


1. Summary of discussions on decline factors

    1.2 Main factors identified in the plenary session

    1.3 Compilation of individual worksheets

2. Summary of discussions on information gaps and required research and monitoring

3. Summary of discussions on priority actions


The lac Saint-Pierre (LSP) ecosystem integrity workshop was held at Université du Québec à Trois-Rivières on March 24, 2015, under the aegis of the St. Lawrence Action Plan (SLAP), and organized by Christiane Hudon (ECCC), Serge Hébert (MDDELCC) and Serge Villeneuve (ECCC).

The purpose of this event was to bring together researchers and scientific experts to make a comprehensive assessment of the various assumptions that explain the major changes in the lac Saint-Pierre ecosystem. In addition to commonly cited factors such as over-fishing, deterioration of water quality and habitats, cyanobacteria, predation by cormorants and goby competition, the project also sought to evaluate other, underestimated stress factors that might affect the ecosystem’s integrity, such as hydroclimatic conditions, parasites, pesticides and emerging contaminants and stressor interaction.

1. Summary of discussions on decline factors

Questions for the subgroups : Is the current deterioration of the LSP ecosystem the result of a single main factor (which one) or a combination of several factors (which ones)? In the latter case, can these factors be listed in order of importance?

1.1 Crucial factors identified by the subgroups

  • The following factors determine the specificity of the lac Saint-Pierre ecosystem and modulate its reaction to stressors :

Physical characteristics of the LSP

The LSP is unique among river lakes in the size of its floodplain, its wetlands and grass beds, the deep channel that separates the north and south lake basins, the toxic substance and nutrient load from its many tributaries and the urban wastewater flowing into it from the greater Montreal area, its exposure to NE-SW winds and the strong seasonal and annual variations of its water level due to the influence of the Ottawa River and Great Lakes water control measures.

Effect of seasonal variation

The growth period of species such as perch extends over more than one season and is subject to disturbance factors that vary in number and intensity. In spring, the high water level determines the duration and the size of the floodplain as well as the secondary (heterotrophic) production that provides sustenance for perch larva. The summertime productivity, biomass and distribution of submerged grass beds vary extensively from year to year and do not always provide identical habitat and feeding quality for juveniles. The effect of one or more of these factors may explain why year (0+) perch are smaller in size (lower condition index) and experience a high rate of mortality during their first winter.

Simultaneous influence of several stress factors

It is difficult to isolate a sole factor for the decline. Instead, it is probable that several distinct stressors combine to induce potential synergies. Understanding the variations of the characteristics of the ecosystem requires a historical reconstruction or a space-time study. For example, the collapse of the perch populations at the start of the last decade was very likely caused by a set of factors involving a series of events that remain as yet unidentified.

  • The following stress factors were identified by the subgroups and brought by their reporters to the plenary session :

Agricultural activities

Many factors related to agriculture are likely to generate pressure on the lac Saint-Pierre ecosystem (destruction or modification of natural habitats, addition of nutrients, pesticides and sediments and loss of inter-habitat connectivity).

  • Loss of floodplain and littoral aquatic habitats : Habitat loss is a crucial factor, one that affects fish population reproduction, feeding and growth. It results mainly from the expansion of agriculture into floodplains, changes in cultivation methods and shoreline erosion. The change from perennial (fodder) crops to annuals (bare ground in spring) has destroyed the spawning habitats of several species and increased suspended material, nutrients and pesticides in the lake’s waters.
  • Pesticides and nutrients : About twenty pesticides are detected in the lake’s waters during the growth season. Measured levels of atrazine and neonicotinoids occasionally exceed standards required for the protection of aquatic life. The additive or synergistic effects of this chemical cocktail on the lake’s fauna and flora have not been evaluated. In addition, the effect of prolonged exposure to toxic substances such as glyphosate on submerged plant life due to the low level of water mass renewal on the lake’s south shore was not evaluated. The lake’s southern tributaries are responsible for major nutrient loads that could facilitate the proliferation of blue-green benthic algae. The effects on benthic invertebrates, fish populations and grass beds were not evaluated.
  • Drainage : The increase in field drainage also adds phosphorus to waterways. The phosphorus contribution to underground drainage networks complicates the problem since these waters escape field and riparian strip impounding reservoirs.

Hydrology and climate change

LSP water level has undergone significant annual variability in recent years, which could be related to climate change. Major variation in water level fosters erosion and turbidity. Extreme low levels are unfavorable to healthy grass beds in the littoral zone.


High turbidity levels have been measured along the lake’s shorelines, especially downstream from its tributaries. High turbidity leads to weaker light penetration and primary production, and possibly exerts downward pressure on the size of grass beds that constitute the basic habitat structure for many faunal species. An increase in lake water turbidity has been observed since 2002.

Ice regime change

The effects of ice are limited to the littoral but could in part explain wetland size loss and structural changes as well as increased turbidity and shoreline erosion.

Emerging contaminants

Many so-called “emerging” contaminants (personal care and pharmaceutical products, flame retardants, etc.) have been detected in the LSP and/or its tributaries, but their effects on the lake’s resources have not been systematically evaluated. Their individual and synergistic effects are both little known and of concern.

Invasive species

During the last hundred years, the LSP has been invaded by many animal and plant exotic species which, however, were not flagged as being among the most significant decline factors during subgroup discussions. Environmental monitoring of these species is not systematic (German carp, goby, tench, Chinese mitten crab, water reed, loosestrife, reed canary grass, water chestnut, rush, algae, cyanobacteria, etc.).

1.2 Main factors identified in the plenary session

In an effort to prioritize the factors involved in the decline of the integrity of the LSP ecosystem, the plenary session decided on the preponderance of the following factors :

  • Agriculture in the floodplain : Annual crops grown on bare ground and underground drainage are likely the most important factors that explain habitat loss and determine local nutrient and pesticide contributions.
  • Seasonal variation in water level and flow : Anthropic regulation and climate change could have consequences for grass bed and wetland dynamics, as well as impacting the resources to which they are home. Recurrence levels (0-2, 0-10, 0-20 years) need to be specified in order to facilitate better governance (conservation policies and/or regulatory measures).
  • Tributary contributions : Added nitrogen, phosphorus and pesticides, as well as increased turbidity and suspended material were deemed major stressors; the synergy effect here could amplify individual negative consequences for the LSP.
  • Reduced aquatic grass bed size : The abovementioned stress factors could reduce the size of the lake’s grass beds and affect related invertebrate and fish populations, leading to loss of integrity of the LSP ecosystem.

1.3 Compilation of individual worksheets

At the beginning of the workshop, each participant received a sheet listing factors that were potentially responsible for the decline of the LSP ecosystem integrity (Appendix 4). At the end of the day, participants were to identify the five factors that in their expert opinion were the most likely to explain the ecosystem deterioration. A compilation of individual sheets recorded the concerns of the researchers and experts in regard to the independent factors of decline(Figure 1).

Figure 1. Pincipal stressors identified by participants

Longue description

The figure highlights the factors that could potentially be responsible for the decline of the lac Saint-Pierre ecosystem integrity. The factors identified by participants as the most likely to explain the ecosystem deterioration are:
• the agriculture in floodplain, for 89 % of the participants;
• the water level and flow, for 60 % of the participants;
• the turbidity and suspended matters, for 60 % of the participants;
• the pesticides, for 49 % of the participants;
• the extreme weather (flooding, drought), for 34 % of the participants;
• the synergetic effects, for 29 % of the participants;
• the change in hydrological regime of tributaries, for 29 % of the participants; and
• the nitrogen and the phosphorus, for 26 % of the participants.

2. Summary of discussions on information gaps and required research and monitoring

Questions for subgroups: What information is missing to enable us to understand the causes of the LSP ecosystem decline? What monitoring and research activities need to be implemented to fill the gaps?

  • The following were identified during subgroup and plenary discussions as being required for research and monitoring to mitigate lack of information (order of presentation does not indicate order of priority):

Agricultural in the floodplain and watershed

  • Prepare a current and historical portrait of abutting agriculture (pesticides, crops, fertilization, beneficial practices, etc.)
  • Map pesticide spreading, soil fertilization levels, land use and tenure and sectors subject to erosion
  • Establish the relationships between field practices in the watershed and contributions to the lake’s tributaries
  • Evaluate the effect of the elimination of various practices and/or crops

Ecosystem and biocenosis

Submerged grass beds:

  • Map the distribution, abundance and space-time evolution of macrophytes and their physiological status based on the physicochemical properties of the water mass (turbidity, contaminants, temperature, etc.), hydrology and weather conditions
  • Benchmark and monitor the evolution of grass bed health status
  • Compare LSP sectors with other river lakes that have undergone pressures of different types
  • Reconstitute the evolution of the grass beds and the drop in the perch population in parallel with the evolution of floodplain farming and observed changes in the ecosystem (contaminants, hydrology, etc.)
  • Study the growth of the grass beds as a function of the lake’s sedimentary dynamics

Fish and zooplankton communities:

  • Analyze data provided by the Réseau de suivi ichtyologique (biomass, density, distribution)
  • Establish at what stages of development the perch growth deficit appears
  • Investigate the fish growth indicators
  • Measure the productivity of the various fish guilds
  • Check the selection hypothesis of a perch population that is different from other river lake populations
  • Analyze the possibility of other species of commercial cultural value collapsing
  • Study the lake’s zooplankton based on season and wetland connectivity
  • Document the quality of the alimentary bolus available to fish larva and fry

Trophic network:

  • Document the base of the trophic chain
  • Quantify the trophic role of the floodplain
  • Prepare a current portrait of the trophic network and its evolution after the disappearance of certain migratory and predatory fish and their replacement by opportunistic species that are resistant to environmental stresses (benthivore, omnivore and invasive)
  • Study the historical changes in the trophic networks using stable isotopes

Assessment of ecosystem services:

  • Assess the value of LSP ecosystem services and the economic impact of the loss of other species with commercial and cultural value.

Contaminants and water quality

  • Document the synergistic effect of pesticides (neonicotinoids and glyphosate in particular) and nutrients on the biocenosis (grass beds, benthic organisms and fish)
  • Conduct biological testing for water toxicity in the lake’s lesser tributaries
  • Set up a water quality monitoring program in the LSP littoral zone
  • Measure herbicide and nutrient contributions from the floodplain
  • Characterize and map water masses (physicochemical parameters, contaminants)
  • Study the effects of the N/P ratio on aquatic plants
  • Document the impact of floodplain crop choice on near-shore turbidity and its effects zooplankton, perch larva and grass bed productivity

Hydrology and habitats

  • Improve the method used for incorporating plants into hydrological modeling
  • Make existing data and hydrological models available and simplify their use
  • Determine the extent of the floodplain based on (0-2, 0-10, 0-20 year) recurrence and study the impact of its variability on the LSP grass bed as a function of various land uses and crops
  • Evaluate the impact of climate change on water levels and the floodplain
  • Document the effects of dredging, the navigation channel and wave action from passing boats
  • Study the impact of river mouth ice management on shallow marshes

Management and coordination

Access to data :

  • Ensure the permanence of data in well-documented databases (adequate metadata)
  • Make the State of the St. Lawrence Monitoring Program data available
  • Pool LSP information from various sources into a geographic information system

Development of indicators :

  • Develop indicators to measure contaminant and biocenosis distribution, composition and abundance changes
  • Develop eutrophication indicators
  • Develop habitat quality indicators

Several participants suggested the usefulness of a multidisciplinary study requiring across-the-board participation and data pooling, aimed at lake-wide macrophyte size and density mapping and the identification of key determinant vegetation variables (underwater and surface plants and aquatic grass beds).

3. Summary of discussions on priority actions

Question to the subgroups: What priority actions need to be implemented to restore the integrity of the LSP ecosystem?

During the plenary session, the following were identified as being priority actions to restore the integrity of the LSP ecosystem (order of presentation does not reflect order of priority):

  • Regulation and regulatory compliance : Prohibit annual crops in the floodplain and ensure compliance with current regulations, in particular the Protection Policy for Lakeshores, Riverbanks, Littoral Zones and Floodplains
  • Relocation and repurchase of floodplain farmlands : Promote the relocation and repurchase of floodplain farmlands
  • Improve farming practices and the shift to agroforestry : Improve farming practices by moving agriculture away from waterways, setting up effective riparian strips, reducing runoff and treating drainage water
  • Reduction at source : Reduce the contributions of nutrients, pesticides and suspended materials in the littoral zone and the main and secondary tributaries
  • Ecological management of water level : Manage the St. Lawrence River water level by taking account of the LSP ecological needs
  • Cease development in the floodplain : Cease all residential, industrial and agricultural development in the 0-20 year recurrence floodplain and promote a linear park project to safeguard the St. Lawrence littoral zone, riverbank and floodplain