Brownie Lake (DNR ID: 27-0038-00)
Sampling Location - GPS Coordinates: Surface Area: 18 acres Max. Depth: 49.9 ft |
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Go east on Minnetonka Blvd and head North on I-494. Take the exit for I-394 E and then take exit 7 for Penn Ave. Merge onto US 12 Service Rd/ S Wayzata Blvd and continue to follow US 12 Service Rd. Turn left on to the ramp to Theodore Wirth Pkwy. Continue on Cedar Lake Pkwy and look for Brownie Lake on the right side of the road.
Brownie Lake is a meromictic lake and is part of the Chain of Lakes. It is protected for aquatic life and recreation and has water quality data going back to 1979. Currently Minneapolis Park and Recreation Board (MPRB) staff monitor the lake on a bi-weekly basis and send MCWD the raw data each fall.
The surface area of Brownie Lake has been decreased by construction of a railroad embankment in 1867 and during the construction of the inter-lake canal between Cedar and Brownie (completed in 1917). Water level was affected by the second construction project lowering the level by approximately 3 m (~ 10 ft). Swain (1984) speculated that these development activities caused the lake to become meromictic. Over the past two centuries, several inputs from multiple sources have altered the lake’s water quality. Currently, stormwater inputs from HWY 394 add pollutants (e.g. chloride) contributing to the stability of the chemocline (MPRB, 2006).
Monitoring season started in early May and ended in late October by MPRB. Hydrolab mini-sonde 5 multi-probe measured dissolved oxygen (DO), temperature (oC), pH, and specific conductivity (µS/cm) at each meter depth from the water surface to the bottom. Surface water samples were a composite of the first two meters below the surface while bottom water samples were collected one meter from the bottom. Additional discrete samples were collected throughout the thermocline mixing zone once stratification developed. Surface sample parameters analyzed are extensive; MCWD is concerned with total phosphorus (TP), total nitrogen (TN), and soluble reactive phosphorus (SRP). Surface concentrations of chlorophyll-a were also analyzed and measurements of Secchi disc depth were recorded. Thermocline and bottom samples were analyzed for TP and SRP.
| 2008 Summer Water Quality Summary |
| Parameters | Range | Mean | TSI Value | Lake Grade |
| Months | June - Sept. | May - Sept. | ||
| Secchi Depth (m) | 0.9 - 2.7 | 1.7 | 52 | C |
| Surface TP (µg/L) | 35 - 41 | 38.3 | 57 | C |
| Chlorophyll-a (µg/L) | 4.5 - 13.6 | 10.9 | 54 | B |
| Overall Score | 54 | C+ |
The following summary refers to the following Figure 2.3 (a-d).
- Secchi disk increased from 0.67 m to 2.7 m from late April to June and then declined by July (standard > 1.2 m). The remainder of the season, secchi disk depth ranged between 1.3 m and 2.2 m.
- Chlorophyll-a concentrations increased from 8.2 µg/L to 17.1 µg/L from late April to May. Concentrations declined in June, then increased to 13.6 µg/L until September. In October, chlorophyll-a concentrations decreased by half (standard < 15 µg/L).
- In general, surface TP concentrations decreased throughout the season with largest change occurring between April and May (standard < 40 µg/L). Surface SRP concentrations ranged between less than 0.005 µg/L to 5 µg/L.
- Bottom TP concentrations ranged between 5520 µg/L and 6000 µg/L. Bottom SRP concentrations were less than 29 µg/L until an increased occurred in October (70 µg/L).
Lake Grades and Historical Monitoring Summaries
When available, previous reports are linked to applicable year. Additional lake data previous to 2007 may be available in the applicable year's hydrodata report. If you have additional questions or you are looking for specific information please contact MCWD's Water Quality Staff.
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