The dynamics of water temperature, dissolved oxygen and total dissolved solids concentrations in Aguamilpa Reservoir was analysed by considering horizontal and water column variations. The reservoir model, CE-QUAL-W2, was used to simulate the temporal variations calibrated with data gathered every 2 months from June 2008 to June 2009. Temperature depth profiles indicated a typical asymmetry of reservoirs exhibiting a large stratification in the lower part near the dam. Dissolved oxygen concentration profiles exhibited some degree of anoxia in the bottom water during the rainy season (May through October). This is most likely due to decomposition vegetation and organic matter via soil erosion and runoff from the basin accumulating at the bottom of the reservoir. The reservoir stratification is clearly seasonal, occurring during the rainy season, especially in the lowest reservoir zones. The CE-QUAL-W2 model results provided a comprehensive understanding of the temporal behaviour of the study variables during the modelling study period. Application of this water quality model is directed to water resource managers to help them better understand the dynamics of physicochemical processes, and how they vary temporally and spatially in the reservoir, and to propose the best management practices for preserving or improving the water quality of the system.

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Twenty-four years of spatial-temporal water quality data from three different sampling points at the surface were evaluated in Deer Creek Reservoir in Utah. The chosen sampling locations represent the lotic, transitional and lentic zones of a typical man-made lake. The time frame included data collected before and after the completion of the Jordanelle Reservoir (1987)(1988)(1989)(1990)(1991)(1992), upstream of Deer Creek. On average chlorophyll-a and phosphorus levels have dropped since 1984 and dissolved oxygen levels have remained the same. We used stepwise variable selection and multivariable regression to fit chlorophyll-a on climatological, hydrological, and water quality parameters. Analyses of variance (ANOVA) were used to quantify spatial and temporal variation. Significant spatial variation in chlorophyll-a concentration was found to be 92% higher on average in the lotic zone than the lentic zone. The regression model was also used to evaluate future water quality effects produced by different climatic change scenarios. Chlorophyll-a concentrations were used as water quality indicators to assess the in-reservoir effects of climate variation produced by meteorological changes. The model predicted an inverse relationship between air temperature and chlorophyll-a concentrations. Our findings were validated with results obtained from a computational water quality model that found that the statistical model showed similar trends of chlorophyll-a.

Deer Creek Reservoir in Utah has a history of high algae concentrations. Despite recent nutrient reduction efforts, seasonal algae continue to present problems. Cost effective, accurate, and comprehensive monitoring is important to understand the reservoir processes driving this problem and characterizing the algae spatial and temporal distributions are an important part of this effort. Current laboratory methods for accurately measuring algae are expensive and time consuming and are based on water samples taken in the field and transported to the laboratory. This approach only provides data for relatively few point samples because of the time and expense of sample collection and analysis. These relatively few samples do not describe the complex spatial and temporal trends in the algal data. Algae exhibit non-uniform distributions, especially in the vertical direction. In situ probes are able to measure chlorophyll-a and provide a less expensive measuring alternative than laboratory methods. These probes provide relatively quick, high resolution vertical profile measurements, which allows for more comprehensive horizontal and temporal sampling. To have confidence in the probe data, good correlations between in situ chlorophyll-a measurements and laboratory algae or chlorophyll measurements are important, but these correlations can be reservoir and time dependant as reservoir conditions change. Therefore, they must be developed for each study site. This study reports on efforts at Deer Creek Reservoir to develop these correlations and provide a general description of the dynamic reservoir algal processes. I found that chlorophylla is weakly correlated to most algae species in the reservoir. However, it correlated well with total phytoplankton biovolume and the dominant algal species, which for this study was the diatom. Variations in correlation strength among the several algae species was assumed to most likely be affected by environmental factors, sample methods, algae species diversity, and the accuracy of the optical chlorophyll-a sensor. The data analysis indicate that the field methods used to obtain laboratory samples may have been a significant source of error because of the difficulty of matching the location of a probe measurement to the location of a sample. Field samples were not taken at the same depths as probe measurements and field samples from two locations were either mixed before laboratory analysis or the sample was a composite over a 2meter range. Based on my observations, I have made several recommendations to improve the accuracy of the correlation between algae and chlorophyll-a.

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This study compared the sensitivity of water quality in tropical Aguamilpa Reservoir, as represented by normalized algae mass and dissolved oxygen, to selected projected changes from global climate change and development. The sensitivity of reservoir stratification as an indicator of reservoir sensitivity also was analysed. Model simulations indicated the reservoir was more sensitive to changes during the warm-dry season than at other times. Both indexes (normalized algal mass and dissolved oxygen mass) were more sensitive to changes in air temperature (climate change) and nitrogen loading (development) than to changes in flow. The sensitivity to air temperature was similar to, but generally less than, the sensitivity to nutrient inflow. At the bounding values for change (3°C for temperature; 50% increase in nitrogen loading), the algae mass sensitivities were 0.15 mg L À1 per 3°C and 0.2 mg L À1 per 50% nitrogen load increase, and the dissolved oxygen mass sensitivities were 0.7 mg L À1 per 3°C and 2.0 mg L À1 per 50% load increase. Changes in air temperature and nitrogen loadings affect the reservoir in different ways, air temperature mostly changing the timing of the algal growth with little change in peak values, while nutrient loadings change the peak values with little change in the timing. While the sensitivities are similar, the total algal mass change is significantly larger for nitrogen loading, compared to air temperature changes. These results imply global climate change effects can be partially mitigated by implementing management measures in the surrounding watersheds to minimize nutrient inflows, especially nitrogen in the case of Aguamilpa Reservoir.

Deer Creek Reservoir, located in Utah, supplies municipal and agricultural water for Utah and Salt Lake counties. During the past four decades the high levels of total phosphorus and dissolved oxygen in the water have introduced both taste and odor problems from algae growth, which have necessitated additional treatment to clean the water. In an attempt to discover why late summer algae blooms continue to persist at Deer Creek, the Brigham Young University Deer Creek Research Group collected data using several water quality laboratory tests on samples from 11 different sampling sites within the reservoir: total solids (TS), total suspended solids (TSS), total volatile suspended solids (TVSS), and phosphate. These tests were performed on samples collected during the summers of 2010 (May through October) and 2011 (April through November). Samples from Secchi depth were used for this analysis because of excessive variability introduced if samples from above and below the thermocline and at bottom layers of the reservoir were included. The purpose of this study is to determine if any correlations exists between these three measurements: solid, phosphate, and Secchi depths. We used total suspended solids as an indicator for algal mass. We suspect that phosphate is being trapped in solid material, specifically sediment, and being released into the reservoir slowly over time. Our analysis shows that solids at Deer Creek do not exhibit significant correlations with phosphate or Secchi depths. We suggest that a different approach to the phosphate problem be used that we should analyze and correlate Deer Creek phosphate with sediment oxygen demand (SOD) measurements taken using SOD chambers to correlate algae with potential phosphate release from sediments.

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