Lake Basin Characteristics and Morphometry
13
of percent oflake area which is at a given depth (Fig. 1.6). Plot the area of your lake at each depth
and similarly plot the area at each depth as a percentage of the surface area.
Depth-Volume Curves. The depth-volume curve is closely related to hypsographic curves
and represents the relationship of lake volume to depth. Similarly, the units may be expressed in
volume units against depth or in percent of lake volume above a specific depth (Fig. 1.6). That
depth above which 50% ofthe lake volume occurs approximates the mean depth of the lake. Plot
the accumulated volume of your lake from the surface for each stratum and, for each value,
calculate and plot the volume as an accumulated percent from the surface of the lake (see
Fig. 1.6).
Questions
1. How would multiple depressions influence (a) your calculations of area and volume of
different depth strata, and (b) hypolimnetic structure within the basin as a whole?
2. How would island and subsurface lakemounts influence (a) your calculations of area and
volume of different depth strata, (b) fetch (effective length) in relation to wind exposure and
circulation within the lake basin, and (c) the amount of sediment surface available within the
photic zone for colonization by attached algae and larger aquatic plants?
3. Using data from your lake or from Hypo Lake (Fig. 1.4), approximately how much sediment
surface area would be available to benthic invertebrate fauna requiring:
(a) Large sediment particles? Fine, organic-rich sediment particles?
(b) High oxygen concentrations at all times of the year?
4. How might these parameters change in a lake of greater relative depth (zr)?
5. Assume that the free-floating (planktonic) algae in your lake require at depth at least 0.1 % of
solar irradiance impinging on the surface of the lake to maintain a net positive growth. In your
lake or the example provided, what would be the volume of the stratum in which
photosynthesis could occur (the euphotic, photic, or trophogenic zone) if:
(a) Light were attenuated under very productive conditions to the 0.1 % level at a depth of
2m?
(b) Light at the 0.1 % level were not attenuated until reaching a depth of 5.5 m?
(c) Continual turbidity from silt caused the light to be attenuated to the 0.1 % level at a depth
of 25cm?
6. If a mysid crustacean were adapted to cold temperatures and optically to blue light in deep
water (below 10 m), what volume of water would be available to this organism?
Apparatus and Supplies
1. Plane table and tripod, heavy paper, pins, pencils
2. Alidade (telescopic or open-sight) or transit
3. Rulers
4. Metal measuring tapes (ca. 50 m)
5. Stakes (30 to 100), with numbering and flags
6. Surveyor's or military compass
7. Depth sounding lines, graduated in 0.5-m intervals, with platelike weights
8. Graduated sounding poles and endplates
9. Boats and motors
10. Sonar-type depth sounder, if available
11. Ice augers, if work is done in winter
12. Planimeter(s) or electronic digitizer
13. Protractors
14. Graph paper
13
of percent oflake area which is at a given depth (Fig. 1.6). Plot the area of your lake at each depth
and similarly plot the area at each depth as a percentage of the surface area.
Depth-Volume Curves. The depth-volume curve is closely related to hypsographic curves
and represents the relationship of lake volume to depth. Similarly, the units may be expressed in
volume units against depth or in percent of lake volume above a specific depth (Fig. 1.6). That
depth above which 50% ofthe lake volume occurs approximates the mean depth of the lake. Plot
the accumulated volume of your lake from the surface for each stratum and, for each value,
calculate and plot the volume as an accumulated percent from the surface of the lake (see
Fig. 1.6).
Questions
1. How would multiple depressions influence (a) your calculations of area and volume of
different depth strata, and (b) hypolimnetic structure within the basin as a whole?
2. How would island and subsurface lakemounts influence (a) your calculations of area and
volume of different depth strata, (b) fetch (effective length) in relation to wind exposure and
circulation within the lake basin, and (c) the amount of sediment surface available within the
photic zone for colonization by attached algae and larger aquatic plants?
3. Using data from your lake or from Hypo Lake (Fig. 1.4), approximately how much sediment
surface area would be available to benthic invertebrate fauna requiring:
(a) Large sediment particles? Fine, organic-rich sediment particles?
(b) High oxygen concentrations at all times of the year?
4. How might these parameters change in a lake of greater relative depth (zr)?
5. Assume that the free-floating (planktonic) algae in your lake require at depth at least 0.1 % of
solar irradiance impinging on the surface of the lake to maintain a net positive growth. In your
lake or the example provided, what would be the volume of the stratum in which
photosynthesis could occur (the euphotic, photic, or trophogenic zone) if:
(a) Light were attenuated under very productive conditions to the 0.1 % level at a depth of
2m?
(b) Light at the 0.1 % level were not attenuated until reaching a depth of 5.5 m?
(c) Continual turbidity from silt caused the light to be attenuated to the 0.1 % level at a depth
of 25cm?
6. If a mysid crustacean were adapted to cold temperatures and optically to blue light in deep
water (below 10 m), what volume of water would be available to this organism?
Apparatus and Supplies
1. Plane table and tripod, heavy paper, pins, pencils
2. Alidade (telescopic or open-sight) or transit
3. Rulers
4. Metal measuring tapes (ca. 50 m)
5. Stakes (30 to 100), with numbering and flags
6. Surveyor's or military compass
7. Depth sounding lines, graduated in 0.5-m intervals, with platelike weights
8. Graduated sounding poles and endplates
9. Boats and motors
10. Sonar-type depth sounder, if available
11. Ice augers, if work is done in winter
12. Planimeter(s) or electronic digitizer
13. Protractors
14. Graph paper