Buffalo River Watershed Lakes Eutrophication Modeling - Draft Report

Document
Description
This report summarizes the in-lake water quality modeling efforts for lakes in the Buffalo River Watershed (BRW) as described in Tasks 10 and 11 of the Minnesota Pollution Control Agency (MPCA) contract #B55092: Buffalo River Watershed Approach Plan (WRAP) Phase II. The overall goal of this analysis was to establish the loading capacities to the lakes in the BRW providing information for future management of their water quality. Results of the lake modeling include the predicted average amount of nutrient load reduction required to meet current water quality lake eutrophication standards in each lake. The in-lake water quality modeling utilizes a modified version of the BATHTUB model called CNET. CNET models were created for eighteen individual lakes in the BRW, including a special case of five lakes in the Sand-Axberg Chain-of-Lakes located in the north-central portion of the watershed. In addition, the five "example" lakes developed under Task 9 of this project (HEI 2011a), were also modeled. This report covers the development and use of the CNET models and provides a summary of the predicted distributions of mean annual total phosphorus (TP), chlorophyll-a (Chl-a), and Secchi disk depths in the lakes. The CNET models were calibrated to the assumed average condition in each lake using the average observed in-lake water quality condition and watershed inputs (flow and TP loading) from thirteen years (1997-2009) simulated in the BRW Soil and Water Assessment Tool (SWAT) model. Following calibration, the models were used for stochastic simulations using Crystal Ball, a Monte Carlo simulator. The stochastic simulations result in distributions of inlake eutrophication conditions based on statistical distributions of input parameters. The stochastic modeling approach reflects the variability in model parameters inherent in natural systems (e.g., climate) and allows for a more realistic prediction of long-term water quality condition. Finally, load reduction scenarios were developed for each lake to estimate the required load reduction needed to meet current lake eutrophication water quality standards.
Date Issued
2013
Number of Pages
114
Decade
Rights Holder
Minnesota Water Research Digital Library
Rights Management
Public Domain