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  Teaching Modeling Water Quality
 

Credits
Cindy Hagley, Rich Axler and George Host

Goals
This exercise has three primary goals:

  1. To teach students the basics of interpreting RUSS temperature and oxygen profile data
  2. To introduce students to Geographic Information Systems (GIS), particularly with respect to interpreting maps
  3. To have students link the GIS information with a model of phosphorus and sediment loadings, and interpret these loadings in light of results from goals 1 and 2.

Introduction
This lesson is consists of three exercises in data analysis and interpretation. The first has the students interpret temperature and oxygen profiles from Lake Independence and Hale Lake, which are located in agricultural and urban-forest watersheds, respectively. The differences in watersheds between the lakes should have an impact on water quality, particularly those factors sensitive to nutrient inputs. The exercises integrate RUSS data interpretation, GIS analyses and modeling exercises.

This lesson assumes some basic knowledge of limnology and builds on density stratification, gas solubility, and other Water on the Web labs. It also incorporates Geographic Information System (GIS) and Phosphorus loading model exercises. The italicized information is provided.

There is also an advanced exercise that allows a comparison of major US Lakes (Tahoe, Lake Erie, Lake Superior) along with the RUSS study lakes to assess their trophic status as a function of mean depth and phosphorus loading.

Outcomes

  1. ability to interpret data from the RUSS units
  2. ability to interpret GIS data
  3. ability to do some simple modeling calculations and interpret the results

Keywords
lake profiles, temperature, oxygen, geographic information systems, modeling, phosphorus loading, sediment

Prerequisites
none

Time Required
1-2 hrs.

WOW Curriculum Links
Embedded in Exercise

Procedure
* The directed study lesson is found in the student section of WOW under the title: "Studying Modeling Water Quality." with Part I: Analysis and Interpretation of RUSS Data, Part II: Using Geographic Information Systems to assess landuse patterns within watersheds, and Part III. Using models to predict sediment and phosphorus loadings.

* The inquiry lesson is found in the student section of WOW under the title: "Investigating Modeling Water Quality."

Teacher version of tables

Figure 3. Vollenweider Loading Plot of Annual Phosphorus Loading versus mean depth. Dashed lines show boundaries of Eutrophic, Mesotrophic and Oligotrophic lakes. Values for US lakes taken from Horne, A.J. and C.R. Goldman.1994. Limnology & Welch, E.B. 1992. Ecological Effects of Wastewater.

Table 4. Lake attributes derived from GIS maps or the Lake Summary Table

 
Ice Lake
Lake Independence

Maximum lake depth (m)

16.1

17.7

Lake area (ha)

16.6

344

Watershed area (ha)

85

1946

Lake volume (m3)

1.16 x 106

1.89 x 106

Mean depth* (m)

7.0

5.5

*Mean depth = V/Ao

Table 5. Watershed to lake area ratio

 

Ice Lake

Lake Independence

Watershed area : lake area ratio (Aw:Ao)

5.1 : 1

5.6 : 1

 

Table 6. Percent landuse from ARC-View analyses

 

Ice Lake (85 ha)

Lake Independence (1946 ha)

Agriculture

0%

72%

Urban

11%

5%

Wet

35%

17%

Forest

54%

6%

Total

100%

100%

 

Table 7. Areas occupied by various landuses (ha)

 

Ice Lake

Lake Independence

Agriculture

0

1401

Urban

9.4

97

Wet

29.8

331

Forest

45.9

117

Total

85 ha

1946 ha

 

Table 8. Sediment and phosphorus loading estimates

 

Default loadings (kg/ha)

Total suspended sediment
(TSS)

Total phosphorus
(TP)

Agriculture

1013

0.9

Urban

200

0.55

Wetland

5

.05

Forest

86

0.11

Grass

346

0.13

Other

50

0.10

 

Table 9. Predicted sediment and phosphorus loadings

 

Predicted TSS (kg/yr)

Predicted TP (kg/yr)

 

Ice

Independence

Ice

Independence

Agriculture

0

1419335

0.0

1261

Urban

1870

19460

5.1

54

Wetland

149

1654

1.5

17

Forest

3947

10041

5.0

13

Grass

0

0

0.0

0

Other

0

0

0.0

0

Total

5966

1450490

11.7

1344

 

Table 10. Morphometry of Ice Lake and Lake Independence
Ice Lake
Lake Independence

Lake area (104 m2)

16.6

344

Volume (106 m3)

1.18

18.9

 

Table 11. Predicted annual loadings for Ice Lake

 

TSS

TP

Areal*

36 (g/m2/yr)

.070 (g/m2/yr)

Volumetric**

5.1 (mg/L)

0.010 (mg/L)

*Annual load per hectare of lake surface
**Annual load per m3 of lake volume

 

Table 12. Predicted annual loadings for Lake Independence

 

TSS

TP

Areal*

422 (g/m2/yr)

0.391 (g/m2/yr)

Volumetric**

77 (mg/L)

0.071 (mg/L)

*Annual load per hectare of lake surface
**Annual load per m3 of lake volume

Table 13. Mean depth (meters) and annual phosphorus
loading (gP/m2/yr) for selected U.S. lakes
LAKE
MEAN DEPTH
(meters)
ANNUAL P-LOADING
(gP/m2/yr)
Western L. Erie
~8
7.0
L. Mendota, WI
13
0.80
L. Ontario
92
0.20
L. Superior
150
0.037
L. TahoeCA-NV
303
0.024
L. Independence
5.5
0.39
Ice Lake
7.0
0.070

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date last updated: Wednesday March 03 2004