Aquatox application of clear lake california model calibration on blue-green algae bloom and nutrients
Permanent URL:
http://hdl.handle.net/2047/D20200539
Eckelman, Matthew J. (Committee member)
Notably, Clean Water Act (CWA) and Total Maximum Daily Loads (TMDLs) projects are vital water restoration proposals. Clear Lake watershed was selected as the one that should be paid attention to meet water quality standards. US Environmental Protection Agency (EPA) launched a collection of models called "TMDL Modeling Toolbox" for the purpose of developing TMDLs. Therefore, it is important to use efficient models to make Clear Lake realize water restoration target.
AQUATOX is a comprehensive aquatic ecosystem model with good tested ecological risk methodology. Abundant model studies can be achieved due to the multiple functions in AQUATOX. However, the default Clear Lake study attached in AQUATOX package was roughly calibrated. The main purpose of this paper is to calibrate the AQUATOX Clear Lake model to maximally meet precision under the premise of achieving generality and realism. And then, through in depth study of Clear Lake water quality history and AQUATOX model, this paper proposes possible further studies about model application based on on-processing projects. Through analyses, this paper results as below:
(1) Based on the attached study model of Clear Lake California in AQUATOX, this paper fixed values of site characteristic, boundary conditions and certain important state variables' parameters according to academic references and repeated model tests. The driving variables such as flow, temperature, light and nutrients are important to the precision of simulation. Sediment diagenesis sub model plays an important role on simulating nutrients peaks in the end of summer, especially for phosphate. Plus, cyanobacteria parameters are critical for the new model behavior since cyanobacteria biomass and nutrients are sensitive to that parameter changing.
(2) After calibration, nitrate, phosphate and Blue-Green algae model outputs have great improvements. The modeled nitrate concentration has low values in summer about 0.2mg/l because of algae bloom, and then returns to peaks in winter around 0.6mg/l as the highest. Phosphate output falls close to zero in summer and hits peak at 0.3mg/l in the end of summer 1970, and then repeat similar trend each year. Blue-Green algae output starts to increase in May and keeps in a high concentration from 6 to 8 mg/l dry. The bloom period ends in October. Ammonia output stays at a low concentration under 0.1 mg/l. Bottom dissolved oxygen falls to zero in summer due to seasonal stratification. Both nutrients and algae model predication are in good agreement with observed data.
(3) Multiple sensitivity and uncertainty analyses were run to achieve better parameter calibration results. Overlap test shows the relative bias (rB) value of phosphate and algae are both close to zero, but the one of nitrate hits 1 because of the relatively high nitrate concentration in summer. Nitrate, phosphate and algae all have F value close to 1. The test result with rB close to 0 and F close to 1 shows the modified model has good fitness to observed data. Also, the cumulative distribution test shows both nitrate and phosphate have D-stat value that is less than D-crit, which means these two model distributions are not significantly different with the observed data trend. Precise driving variables data are preferred if better accuracy was needed for the model running. Modeling lake stratification in summer and open the sediment digenesis sub model are essential to phosphorus simulation behavior.
blue-green alage
Clear Lake
model calibration
nutrients
AQUATOX (Computer file)
Water quality -- California -- Clear Lake (Lake County) -- Computer simulation
Cyanobacteria -- California -- Clear Lake (Lake County) -- Computer simulation
Cyanobacterial blooms -- California -- Clear Lake (Lake County) -- Computer simulation
Ecosystem management -- California -- Clear Lake (Lake County) -- Computer simulation
Restoration ecology -- California -- Clear Lake (Lake County)
Lake restoration -- Environmental aspects -- California -- Clear Lake (Lake County)
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