An Integrated Analysis of the Eutrophication Process in the Enxoé Reservoir within the DPSIR Framework

Depth profile of reservoir water quality in the Southwest of Ethiopia

The objective of this research was to investigate the variation of water quality parameters at different depths of the Gilgel Gibe I reservoir in Oromia Jimma zone during wet seasons. Five stations within the reservoir were selected, and water quality parameters were determined at four different depths (surface, 5 m, 10 m, and 15 m). Water quality parameters were analyzed on-site using a HACH, HQ40d portable multi-meter, and turbidity was measured using Wag tech turbidity meter and in the laboratory using the standard method. Comparison of water quality parameters among depths were conducted using one-way ANOVA and Tukey's pairwise comparisons with 5% significance level. The probable contributing source of the investigated physicochemical water quality parameters at different depth was identified using Principal components analysis. The results show that depth wise except for total suspended solids (TSS), total dissolved solids (TDS), total phosphorus (TP) and soluble reactive phosphorus (SRP) the rest showed statistically significant difference at p < 0.05 level. Negative correlations were found between depth and dissolved oxygen (DO), water temperature, pH, nitrate (N0₃^-) and chlorophyll a (Chl.a) while positive correlations were found between electrical conductivity (EC), biochemical oxygen demand (BOD₅), turbidity and N0₃^-. The study revealed that the release of nutrients associated with increased concentration of BOD5 at the bottom depth caused low concentration of dissolved oxygen due to oxygen consumption. This was further aggravated through the decomposition of organic matter, indicating organic pollution resulting from runoff from the catchment. The presence of dense masses of blue-green algae in the pelagic zone of Gilgel Gibe I reservoir suggested the presence of ample nutrients for its blooming and significant reduction of water quality, indicating possible eutrophic conditions. Therefore, catchment management is required to protect aquatic life and the reservoir function as a whole from reservoir water quality degradation.

The Drivers-Pressures-State-Impact-Response Model to Structure Cause−Effect Relationships between Agriculture and Aquatic Ecosystems

Different segments of society have shown interest in understanding the effects of human activities on ecosystems. To this end, the aim of this article is to analyze the scientific literature on the application of the Drivers-Pressures-State-Impact-Response (DPSIR) conceptual model to identify the parameters used to describe the causal interactions that occur between agriculture and aquatic ecosystems at the watershed scale. In this way, descriptive indicators were established for the data of 63 publications collected through Scopus, Web of Science, and Science Direct. The results confirm the great heterogeneity in the interpretation of the pressure, state, and impacts components. Part of this discrepancy can be attributed to the use of different indicators, as the model is flexible and generic. Overall, the DPSIR is a tool used not only in the scientific field, but also has demonstrated its potential to guide public policy formulation, planning, and decision-making in water resource management.

Linking DPSIR Model and Water Quality Indices to Achieve Sustainable Development Goals in Groundwater Resources

The achievement of sustainable development goals in groundwater resources related to water quality issues is a critical question in many regions. This study aims to combine powerful tools for helping stakeholders and policymakers achieve sustainable development goals in groundwater resources of agricultural areas. The DPSIR (Driver–Pressure–State–Impact–Response) model in combination with the Canadian Council of Ministers of Environment Water Quality Index and Groundwater Directive 2006/118/European Community—Threshold Values was applied using a hydrogeochemical dataset derived from the analysis of groundwater samples collected from 31 monitoring sites in an unconfined alluvial aquifer. Elevated Cl− (up to 423.2 mg L−1), NO3− (up to 180.1 mg L−1) concentration and electrical conductivity (up to 2037 μS cm−1) value are observed for groundwater samples of the study area. The outcome of the “One Out-All Out” procedure revealed that the groundwater in 42% of the monitored sites is unsuitable for drinking according to the health-based guideline values established by Directive 98/83/European Community. A difficulty to achieve targets under Sustainable Development Goals 3 and 6 in the study area is revealed. The proposed response actions are reported.

Assessing Water and Nutrient Long-Term Dynamics and Loads in the Enxoé Temporary River Basin (Southeast Portugal)

The Enxoé reservoir has been exhibiting frequent high chlorophyll-a concentrations (reaching a geometric mean six times the national limit for eutrophication of 10 μg L−1) since 2000, and represents the reservoir with the highest eutrophic state in Portugal. Toxic algal blooms have also been observed, which pose serious challenges to water managers, as the reservoir is used for potable water production. In an effort to contribute to the reduction of the reservoir trophic state, the watershed inputs (monthly flows, sediment, nitrogen (N) and phosphorus (P) loads) were characterized with the Soil Water Assessment Tool (SWAT). Field data were collected in the ungauged watershed during 2010 and 2011. Model results were then used to characterize the long-term watershed dynamics in terms of water and nutrients. SWAT estimates of the simulated flow, and the sediment and nutrient loads were in good agreement with field data (R2 between 0.42–0.78; Nash-Sutcliffe efficiencies between 0.19–0.75). The Enxoé River was characterized by a temporary flushy regime where high concentrations were transported in short time periods. As a result, nutrient loads delivered to the Enxoé reservoir were estimated to be 18 tonN year−1 and 0.7 tonP year−1 (30 years’ simulation), reaching the reservoir mainly by runoff. These results were consistent with the gentle slopes, extensive agricultural activities, and low urban pressure observed in Enxoé. The magnitude of the nutrient exports suggests that the reservoir eutrophication may also be linked to the reservoir geometry (average depth of 5 m), which provides high light availability to the bottom sediments. Thus, SWAT results were integrated into a reservoir model to depict the origin of the Enxoé trophic state and test management scenarios that may reduce it.