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From eutrophic to mesotrophic: modelling watershed management scenarios to change the trophic status of a reservoir.

Mateus M, Almeida C, Brito D, Neves R - Int J Environ Res Public Health (2014)

Bottom Line: According to the criteria defined by the National Water Institute (based on the WWTP Directive), the Torrão reservoir is classified as eutrophic.Model estimates show that a 10% reduction in nutrient loads will suffice to change the state to mesotrophic, and should target primarily WWTP effluents, but also act on diffuse sources.The method applied in this study should provide a basis for water environmental management decision-making.

View Article: PubMed Central - PubMed

Affiliation: MARETEC, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001, Lisboa, Portugal. marcos.mateus@tecnico.ulisboa.pt.

ABSTRACT
Management decisions related with water quality in lakes and reservoirs require a combined land-water processes study approach. This study reports on an integrated watershed-reservoir modeling methodology: the Soil and Water Assessment Tool (SWAT) model to estimate the nutrient input loads from the watershed, used afterwards as boundary conditions to the reservoir model, CE-QUAL-W2. The integrated modeling system was applied to the Torrão reservoir and drainage basin. The objective of the study was to quantify the total maximum input load that allows the reservoir to be classified as mesotrophic. Torrão reservoir is located in the Tâmega River, one of the most important tributaries of the Douro River in Portugal. The watershed is characterized by a variety of land uses and urban areas, accounting for a total Waste Water Treatment Plants (WWTP) discharge of ~100,000 p.e. According to the criteria defined by the National Water Institute (based on the WWTP Directive), the Torrão reservoir is classified as eutrophic. Model estimates show that a 10% reduction in nutrient loads will suffice to change the state to mesotrophic, and should target primarily WWTP effluents, but also act on diffuse sources. The method applied in this study should provide a basis for water environmental management decision-making.

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Model results for the reference situation and for the scenario where the point sources of nutrients have been removed. Lower panels show smaller periods to highlight differences in results.
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ijerph-11-03015-f008: Model results for the reference situation and for the scenario where the point sources of nutrients have been removed. Lower panels show smaller periods to highlight differences in results.

Mentions: The simulation for the extreme scenario of removing all point sources (WWTP), accounting for a load decrease of only 41 tonN/year and 7 tonP/year, would result in a reduction in the geometric mean of chlorophyll to approximately 4 µg/L. The significant reduction suggests that WWTP is the most significant source of nutrients that contributes for the trophic state of the reservoir. Nonetheless, land use and land cover have been identified has a major contributor of surface water pollution [34]. Interestingly, this source of nutrients only accounts for ~2% of the total nutrient input, but its contribution to phytoplankton growth seems to be critical, as seen in Figure 7. Most of the nutrients that arrive at the reservoir during the dry season are originated in WWTP (diffuse load is almost inexistent and natural river flow reduced). Despite the lower flow of their effluents, the WWTP discharges have high ammonium concentrations and constitute almost the totality of the river load in the dry season. This input seems to be stimulating and maintaining bloom conditions that occur in late spring and summer months, since the ammonium concentration is significantly lower in the scenario without the contribution of WWTP (Figure 8).


From eutrophic to mesotrophic: modelling watershed management scenarios to change the trophic status of a reservoir.

Mateus M, Almeida C, Brito D, Neves R - Int J Environ Res Public Health (2014)

Model results for the reference situation and for the scenario where the point sources of nutrients have been removed. Lower panels show smaller periods to highlight differences in results.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3987018&req=5

ijerph-11-03015-f008: Model results for the reference situation and for the scenario where the point sources of nutrients have been removed. Lower panels show smaller periods to highlight differences in results.
Mentions: The simulation for the extreme scenario of removing all point sources (WWTP), accounting for a load decrease of only 41 tonN/year and 7 tonP/year, would result in a reduction in the geometric mean of chlorophyll to approximately 4 µg/L. The significant reduction suggests that WWTP is the most significant source of nutrients that contributes for the trophic state of the reservoir. Nonetheless, land use and land cover have been identified has a major contributor of surface water pollution [34]. Interestingly, this source of nutrients only accounts for ~2% of the total nutrient input, but its contribution to phytoplankton growth seems to be critical, as seen in Figure 7. Most of the nutrients that arrive at the reservoir during the dry season are originated in WWTP (diffuse load is almost inexistent and natural river flow reduced). Despite the lower flow of their effluents, the WWTP discharges have high ammonium concentrations and constitute almost the totality of the river load in the dry season. This input seems to be stimulating and maintaining bloom conditions that occur in late spring and summer months, since the ammonium concentration is significantly lower in the scenario without the contribution of WWTP (Figure 8).

Bottom Line: According to the criteria defined by the National Water Institute (based on the WWTP Directive), the Torrão reservoir is classified as eutrophic.Model estimates show that a 10% reduction in nutrient loads will suffice to change the state to mesotrophic, and should target primarily WWTP effluents, but also act on diffuse sources.The method applied in this study should provide a basis for water environmental management decision-making.

View Article: PubMed Central - PubMed

Affiliation: MARETEC, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001, Lisboa, Portugal. marcos.mateus@tecnico.ulisboa.pt.

ABSTRACT
Management decisions related with water quality in lakes and reservoirs require a combined land-water processes study approach. This study reports on an integrated watershed-reservoir modeling methodology: the Soil and Water Assessment Tool (SWAT) model to estimate the nutrient input loads from the watershed, used afterwards as boundary conditions to the reservoir model, CE-QUAL-W2. The integrated modeling system was applied to the Torrão reservoir and drainage basin. The objective of the study was to quantify the total maximum input load that allows the reservoir to be classified as mesotrophic. Torrão reservoir is located in the Tâmega River, one of the most important tributaries of the Douro River in Portugal. The watershed is characterized by a variety of land uses and urban areas, accounting for a total Waste Water Treatment Plants (WWTP) discharge of ~100,000 p.e. According to the criteria defined by the National Water Institute (based on the WWTP Directive), the Torrão reservoir is classified as eutrophic. Model estimates show that a 10% reduction in nutrient loads will suffice to change the state to mesotrophic, and should target primarily WWTP effluents, but also act on diffuse sources. The method applied in this study should provide a basis for water environmental management decision-making.

Show MeSH