Best Hills Ranch Lake Sediment Investigation

Danelle RussellJosh PetersonChris Foster

Sarah Richardson

Objectives

• Percent Water• Rate of Sediment Accumulation• Phosphorus Analysis• Percent Organic Matter

K-B Core Samples

Extruding2 cm layers

Percent of Water in Sediment

• An estimate for amount of sediment to remove by suction dredging

• Weigh 1 tsp. wet sediment from each layer• Dry the sediments at 50ºC for 24 hrs in a oven• Reweigh each dried sample • (wet weight - dried weight) = water content

Sediment Accumulation

• 2 cm / 12 years = 0.167 cm / year• (300 cm = deepest point in pond)300 cm / 0.167 = 1796 years for pond to fill in!

Phosphorus Analysis

• P is often a limiting nutrient in aquatic systems (Shindler, 1977)

• Plants that root in sediment primarily uptake P from the sediments (Bristow, 1975; Gabrielson et al., 2984)

• Combined K persulphate, deionized water, soil, pressure, and heat (autoclaved) to detached P from the sediment and put into solution.

• Measured P from each layer of solution using a light spectrophotometer

Organic Matter in Sediment

• OM includes: plants, algae, fungi• Primary source of nutrients for aquatic

vegetation (Wetzel, 2001).

• Use dry sediment• muffle furnace at 550ºC for 3-4 hours

Dry weight – ash weight = organic matter

Water content of soil

10 20 30 40 50 60 70 80 900

2

4

6

8

10

12

14

Water content western half

Midway Middle of lake

% water content

Dept

h (c

m)

20 30 40 50 60 70 800

2

4

6

8

10

12

Water content Eastern half

House Shore Hill Shore% water content

Sedi

men

t Dep

th (c

m)

Organic Matter Content of soil

0 5 10 15 20 25 30 35 400

2

4

6

8

10

Organic matter eastern half

House shore Hill shore

% organic matter

Sedi

men

t Dep

th (c

m)

2 4 6 8 10 12 14 16 18 200

2

4

6

8

10

12

14

Organic content

Midway Middle of lake

% organic content

Dept

h (c

m)

Phosphorus in the Sediment

0.00 2.00 4.00 6.00 8.00 10.00 12.000

2

4

6

8

10

12

14

Sediment phosphorus profile

Phosphorus concentration (g/L)

Soil

dept

h (c

m)

2 2.5 3 3.5 4 4.50

2

4

6

8

10

12

Average Sediment Phosphorus Profile

Eastern half Western half

Phosphorus concentration (g/L)

Dept

h (m

)

Findings:

0-2 cm 2-4 cm 4-6 cm 6-8 cm 8-10 cm 10-12 cm0.00

10.00

20.00

30.00

40.00

50.00

60.00

Depth in sediment

Sedi

men

t TP

(g/m

2)1. Surprisingly little sediment

2. High Phosphorus content

What can we do?

• Phosphorus loading is the problem1. Deal with the phosphorus in the Lake already2. Manage the source of phosphorus

Some measures of removing phosphorus already within the Lake:

Sediment

Removal

Mechanical Dredging

(Not an option)

Suction dredging

• Controlled Removal of Sediment– High Volume Suction Pump

De-water the lake

•Drain during summer months •Use 3” portable gas pumps (2)

•16 days to de-water lake

• $800 to rent 2 pumps (Sun Rentals)

SweepAfter sediment dries sweep to one end

$50 per day for rental (A-Z Rentals)

Remove Sediment

• Haul sediment away– Cost depends on amount of sediment– Also depends on disposal– Possibly find someone to use sediment

• 300 m³ of sediment if top 2 cm are removed.

• Dried sediment should be less due to water content

Issues

• Waterless lake for an amount of time

• Weather– Depends on how much rain

• Well output– Unknown if well can refill lake alone

Before draining

• Contact landowner below dam

Barley Straw

• Use after sediment removal.• Considered a more natural, organic approach.• Used to decrease the algal growth in water.

– Chemical properties of decomposing barley are thought to inhibit the growth of algae.

– May act as a carbon source for microbes. An increase of microbes causes phosphorus to be limited for algal growth.

Barley Straw

• Barley straw must be installed in March or April, before algal growth occurs.

• Takes approximately 6 weeks to decompose.• Barley stuffed loosely into mesh bags.• Anchored in 2 to 5 feet of water with rocks in

bottom of bags.• Suspended in water column with floats in top

of bags.

Barley Straw

• Distribution of straw must be uniform across the lake.

• Good for about 6 months and is taken out of the system in the fall.

• Taking straw out is crucial so as not to add nutrients to the lake.

Amount and Price– It takes about 225 lbs of straw per acre.– 3.7 acres x 225 lbs = 833 lbs– Average price for ½ ton of barley straw is $22.00

Pros and Cons

• Pros• Inexpensive• Can get high school or

college groups to install/remove it.

• Reduction of algae without chemicals.

• Cons• Could promote

macrophyte growth.

• Labor intensive.• Disposal of used

straw messy.

Questions?