**4. Results and discussion**

#### **4.1. Seasonal variability**

In order to characterize the 2006 hydrological year, water levels measured in the St. Lawrence River in 2006 were compared with mean water levels derived for a 20-year period (1990–2010) at the Lanoraie station (**Figure 4**). For the 3 months during which sampling was done, mean water levels were higher than the 20-year calculated mean for the months of May and October 2006 but equal for the month of August.

A comparison of seasonal mean values of physicochemical variables reveals that mean values of temperature and total nitrogen (TN) are significantly different for the three seasons

**Figure 4.** Comparison of daily water levels in the St. Lawrence River measured in 2006 (blue curve) and daily mean values calculated over the period from 1990 to 2010 (red curve) at the Lanoraie station.

(**Table 1** and **Figure 5**). As far as temperature is concerned, it is higher in August (summer) than in May (influence of snowmelt water) and October (effect of fall cooling). In summer, water temperature is roughly twice as high as in the spring or fall due to low water levels (low flow) and the increase in solar energy. TN, for its part, which is mainly derived from farming in Quebec, decreases from spring to fall. In springtime, there is widespread runoff on slopes due to snowmelt, which accounts for the increase in TN concentration in rivers. This concentration decreases in summer as runoff decreases. However, because of the relatively low water levels, the total nitrogen concentration remains higher than in the fall due to limited dilution. In any case, mean TN concentrations during the three seasons are higher than the provincial standard limit value (0.5 mg/L).

**Figure 5.** Comparison of seasonal mean values of temperature and TN.

Diffuse attenuation coefficients (*K*d(PAR)) were calculated by linear regression of the natural

with a C-star transmissometer (Wet Labs Inc., 25 cm path length, λ = 660 nm) to measure

Statistical analysis consisted of comparing seasonal mean values of physicochemical variables measured at the four stations using the analysis of variance approach when the data were normal and the Kruskal-Wallis test when the data were not. The same statistical tests were used to compare mean values of certain characteristics at the decadal scale and those of seasonal water levels. Water level data for the St. Lawrence River, taken from the Environment Canada website (https://eau.ec.gc.ca/download/index\_f.html?results\_type=historical, viewed on September 20, 2017) and measured at the Lanoraie station (ID: 02OB011; 45°57′33" N, 73°15′52"W) since 1990,

In order to characterize the 2006 hydrological year, water levels measured in the St. Lawrence River in 2006 were compared with mean water levels derived for a 20-year period (1990–2010) at the Lanoraie station (**Figure 4**). For the 3 months during which sampling was done, mean water levels were higher than the 20-year calculated mean for the months of May and October

A comparison of seasonal mean values of physicochemical variables reveals that mean values of temperature and total nitrogen (TN) are significantly different for the three seasons

**Figure 4.** Comparison of daily water levels in the St. Lawrence River measured in 2006 (blue curve) and daily mean

values calculated over the period from 1990 to 2010 (red curve) at the Lanoraie station.

depth profiles of the scattering of underwater particles (trans) such as sediments.

are strongly influenced by water masses entering from the Ottawa River.

values correspond to PAR. The Hyperpro was equipped

logarithm of *Ed*

**4. Results and discussion**

2006 but equal for the month of August.

**4.1. Seasonal variability**

versus depth. *Ed*

8 Achievements and Challenges of Integrated River Basin Management

**Figure 6.** Comparison of seasonal mean values of NO<sup>2</sup> , TP and *<sup>a</sup>* CDOM340nm.

Mean values of six physicochemical variables are significantly different during two seasons. Nitrite (NO<sup>2</sup> ), total phosphorus (TP), and chromophoric organic matter (*a*CDOM340nm) concentrations are higher in springtime than in the other two seasons (**Figure 6**). This springtime increase is thought to be due to flushing induced by runoff of snowmelt water and resulting in leaching of terrestrial organic and inorganic material. In the case of nitrate (NO<sup>3</sup> ) and soluble reactive phosphorus (PO4 ), their concentrations are higher in summer than in the other two seasons due to limited dilution during the low-flow period and runoff water during summer storm events (**Figure 7**). These two factors can also account for the high values of suspended particles (trans-variable) observed in summer. As for conductivity, its mean value increases markedly in the fall. As far as total phosphorus is concerned, its spring concentration is much higher than the standard limit set by the Ministère de l'Environnement du Québec [34], whereas NO<sup>3</sup> concentrations exceed the standard limit for all three seasons. Mean values of the two other variables ((*K*d(PAR)) m−1) and TURB) do not show significant seasonal variations (**Figure 8**). Turbidity values are higher than the provincial standard limit (1NTU) for the three seasons.

#### **4.2. Decadal variability**

Mean values of physicochemical variables measured in 2006 were compared with those measured in 1994–1996 by [12] in waters of the St. Lawrence River influenced by the Ottawa River (**Table 2**). Hydrological conditions are similar for the two periods because mean water levels in the St. Lawrence River from May to October are not significantly different. A clear warming of the water is observed between 1994 and 1996 and 2006, as well as a significant increase in nitrite-nitrate concentrations due to climate warming, increased use of nitrogen fertilizers, spreading of solid and liquid manure, as well as effluent releases. In contrast, the amount of phosphate decreased significantly from 1994 to 1996 to 2006 due to its decreasing concentrations in effluents from water treatment plants [34].

Watershed and water resource management strategies are currently applied in the context of global warming and therefore, cannot be interrupted by the implementation of a new regulation program at the provincial and/or federal level. However, the monitoring of potential negative impacts of global warming on the other components of the river ecosystem (plants, animals, water quality, etc.) would allow the quantification of the environmental damages and the implementation of regulation to protect river ecosystems. Such a regulation would enable the development of appropriate mitigation procedures to minimize dramatic environmental consequences. It is important to note the low number of environmental studies on Québec Rivers and, more specifically, the urgent need for studies devoted to the impacts of global warming on river ecosystems. Without such environmental monitoring, it becomes

**Table 2.** Comparison of mean concentrations of some physicochemical variables in Ottawa River waters in the St.

Seasonal Variation of the Physico-chemical Composition of Ottawa River Waters in the St. Lawrence River

http://dx.doi.org/10.5772/intechopen.74122

11

(mg/L) 0.35 (0.25) 2.75 (2.13)

(mg/L) 0.018 (0.007) 0.0059 (0.0038)

**Figure 8.** Comparison of seasonal mean values of *K*d(PAR) and TURB variables.

Data published by [12].

Lawrence River measured from May to October in 1994–1996 and 2006.

Water levels measured at the Lanoraie station.

NO<sup>2</sup> -NO<sup>3</sup>

PO4

\$

() = standard deviation.\*

**Variables 1994–1996\* 2006** Water level (m)\$ 4.91 (0.39) 4.78 (0.40) Temperature (°C) 13.2 (7.9) 16.7 (4.89) Conductivity (μS/cm) 124 (24) 89.7 (132.46) Light extinction coefficient ((*K*d(PAR)) m−1) 1.80 (0.45) 1.75 (0.68)

**Figure 7.** Comparison of seasonal mean values of NO<sup>3</sup> , PO4 , transmittance and conductivity.

Seasonal Variation of the Physico-chemical Composition of Ottawa River Waters in the St. Lawrence River http://dx.doi.org/10.5772/intechopen.74122 11

**Figure 8.** Comparison of seasonal mean values of *K*d(PAR) and TURB variables.


\$ Water levels measured at the Lanoraie station.

Mean values of six physicochemical variables are significantly different during two seasons.

trations are higher in springtime than in the other two seasons (**Figure 6**). This springtime increase is thought to be due to flushing induced by runoff of snowmelt water and resulting in

seasons due to limited dilution during the low-flow period and runoff water during summer storm events (**Figure 7**). These two factors can also account for the high values of suspended particles (trans-variable) observed in summer. As for conductivity, its mean value increases markedly in the fall. As far as total phosphorus is concerned, its spring concentration is much higher than the standard limit set by the Ministère de l'Environnement du Québec [34], whereas

 concentrations exceed the standard limit for all three seasons. Mean values of the two other variables ((*K*d(PAR)) m−1) and TURB) do not show significant seasonal variations (**Figure 8**). Turbidity values are higher than the provincial standard limit (1NTU) for the three seasons.

Mean values of physicochemical variables measured in 2006 were compared with those measured in 1994–1996 by [12] in waters of the St. Lawrence River influenced by the Ottawa River (**Table 2**). Hydrological conditions are similar for the two periods because mean water levels in the St. Lawrence River from May to October are not significantly different. A clear warming of the water is observed between 1994 and 1996 and 2006, as well as a significant increase in nitrite-nitrate concentrations due to climate warming, increased use of nitrogen fertilizers, spreading of solid and liquid manure, as well as effluent releases. In contrast, the amount of phosphate decreased significantly from 1994 to 1996 to 2006 due to its decreasing concentra-

, PO4

, transmittance and conductivity.

leaching of terrestrial organic and inorganic material. In the case of nitrate (NO<sup>3</sup>

), total phosphorus (TP), and chromophoric organic matter (*a*CDOM340nm) concen-

), their concentrations are higher in summer than in the other two

) and soluble

Nitrite (NO<sup>2</sup>

NO<sup>3</sup>

reactive phosphorus (PO4

**4.2. Decadal variability**

tions in effluents from water treatment plants [34].

10 Achievements and Challenges of Integrated River Basin Management

**Figure 7.** Comparison of seasonal mean values of NO<sup>3</sup>

**Table 2.** Comparison of mean concentrations of some physicochemical variables in Ottawa River waters in the St. Lawrence River measured from May to October in 1994–1996 and 2006.

Watershed and water resource management strategies are currently applied in the context of global warming and therefore, cannot be interrupted by the implementation of a new regulation program at the provincial and/or federal level. However, the monitoring of potential negative impacts of global warming on the other components of the river ecosystem (plants, animals, water quality, etc.) would allow the quantification of the environmental damages and the implementation of regulation to protect river ecosystems. Such a regulation would enable the development of appropriate mitigation procedures to minimize dramatic environmental consequences. It is important to note the low number of environmental studies on Québec Rivers and, more specifically, the urgent need for studies devoted to the impacts of global warming on river ecosystems. Without such environmental monitoring, it becomes difficult to predict the evolution of river ecosystems in the context of global warming. The observed increase in nitrites-nitrates in the last 10 years reinforces the need for the Québec Government to develop an efficient management program which would significantly reduce the massive nitrogen fertilizer inputs in agriculture. In addition, this management program should include the respect of legal water quality standards for nitrogen wastes in rural and city areas. These standards already exist but are barely applied.

**Author details**

**References**

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Jean-Jacques Frenette and Ali A. Assani\*

Trois-Rivières, Québec, Canada

\*Address all correspondence to: ali.assani@uqtr.ca

Environmental Sciences Department, University of Quebec at Trois-Rivières,

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#### **5. Conclusion**

As already pointed out by Hudon [12], flow variations exert a strong influence on the physicochemical characteristics of Ottawa River waters. This influence was observed in St. Lawrence River waters affected by the Ottawa River. However, this influence does not affect all characteristics in the same way. Depending on this influence, these characteristics may be grouped into three categories. The first category comprises water temperature and total nitrogen, the values of which vary seasonally as a function of water levels. The second category comprises variables that vary significantly over a single season, resulting in marked increases in the spring (NO<sup>2</sup> , TP, *a*CDOM340nm, and suspended particles), summer (NO<sup>3</sup> and PO4 ), or fall (Cond). Finally, the third category comprises variables whose mean values do not change significantly as a function of water levels ((*K*d (PAR)) m−1 and TURB).

Comparison of data at the decadal scale revealed a clear warming of waters, a significant increase in nitrite-nitrate concentrations, but a significant decrease in phosphate concentrations. These changes confirm the trend observed since 1979 in many Quebec Rivers [34]. Mean concentrations of these chemical parameters in 2006 were higher than standard limits set for river waters by the Ministère de l'Environnement du Québec as compared to those measured in 1994–1996. In order to assess the ecological integrity of rivers in Québec, there is an urgent need for the implementation of a monitoring program which would allow for the development of solutions to reduce the negative impacts of global warming on the functioning and evolution of river ecosystems. We also recommend reinforcing the strict application of existing water quality laws for nitrogen wastes in rural and city areas.

#### **Acknowledgements**

We gratefully acknowledge Captain François Harvey and the crew of the RV *Lampsilis* for their invaluable support during the expedition on the St. Lawrence River. We thank A.-L. Larouche, J.-F. Lapierre, C. Martin, D. M'Radamy, P. Thibeault, and A. Veillette for help in the field and in the laboratory. This research was funded by the Natural Sciences Research Council of Canada (NSERC ship time and discovery programs) and the Fonds Québécois de la Recherche sur la Nature et les Technologies (FQRNT) to J.-J.F. Québec-Océan's logistical support during sampling is greatly acknowledged. This is a contribution of the Groupe de Recherche Interuniversitaire en Limnologie (GRIL).
