FLUX, PROFILE and BATHTUB:
Simplified Procedures for Eutrophication Assessment and Prediction

Model Processes:

• Nutrient and water balances in a segmented hydraulic network.
• Nutrient sedimentation.
• Algal (chlorophyll) response to flushing, light and nutrient concentration.
• Hypolimnetic oxygen depletion.

Method/Techniques:

Three interrelated programs (FLUX, PROFILE and BATHTUB) simplify assessments of eutrophication-related processes and effects.

• FLUX - Program allows estimation of tributary mass discharges (loadings) from sample concentration data and continuous (e.g., daily) flow records. Five estimation methods are available and potential errors in estimates are quantified.

• PROFILE - Program facilitates analysis and reduction of in-lake water quality data. Algorithms are included for calculation of hypolimnetic oxygen depletion rates and estimation of area-weighted, surface-layer mean concentrations of nutrients and other eutrophication response variables.

• BATHTUB - Applies a series of empirical eutrophication models to morphologically complex lakes and reservoirs. The program performs steady-state water and nutrient balance calculations in a spatially segmented hydraulic network which accounts for advective and diffusive transport, and nutrient sedimentation. Eutrophication-related water quality conditions (total phosphorus, total nitrogen, chlorophyll-a, transparency, and hypolimnetic oxygen depletion) are predicted using empirical relationships derived from assessments of reservoir data (Walker, 1985; 1986).

Model Limitations:

Applications of BATHTUB are limited to steady-state evaluations of relations between nutrient loading, transparency and hydrology, and eutrophication responses. Short-term responses and effects related to structural modifications or responses to variables other than nutrients can not be explicitly evaluated.

Experiences:

The programs and models have been applied to US Army Corps of Engineer reservoirs (e.g., Kennedy, 1995), as well as a number of other lakes and reservoirs. BATHTUB was recently cited as an effective tool for lake and reservoir water quality assessment and management, particularly where data are limited (Ernst et al., 1994).

Version and System Requirements:

• MS DOS; PC Compatible.

Input Data Requirements:

• FLUX - Requires grab sample concentration data and continuous (e.g., daily) flow records.

• PROFILE - Vertical profiles of water quality data collected at one or more sample stations throughout the period of interest.

• BATHTUB - Requires information describing watershed characteristics, water and nutrient loads, and lake or reservoir morphology. Observed lake or reservoir water quality data are desirable.

Output:

• FLUX - Graphic and tabular displays allow users to evaluate input data and calculation results. Mass loads, and associated error statistics (CV) are provided as input to BATHTUB.

• PROFILE - Graphic and tabular displays allow users to evaluate and summarize lake or reservoir water quality data. Mixed-layer water quality summaries (means) and hypolimnetic oxygen depletion rates, and associated error statistics (CV) are provided as input to BATHTUB.

• BATHTUB - Model outputs include tabular and/or graphic displays of segment hydraulics, water and nutrient balances, predictions of nutrient concentrations, transparency, chlorophyll-a concentrations, and oxygen depletion. Statistics relating observed and predicted values are provided.

References Available:

Ernst, M. R., W. Frossard, and J. L. Mancini. 1994. Two Eutrophication Models make the Grade. Water Environment and Technology, November, 15-16.

Kennedy, R. H., 1995. Application of the BATHTUB Model to Selected Southeastern Reservoirs. Technical Report EL-95-14, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.

Walker, W. W., 1985. Empirical Methods for Predicting Eutrophication in Impoundments; Report 3, Phase III: Model Refinements. Technical Report E-81-9, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.