Sediment Depth Analysis and benthic Macro-invertebrate

Blue Lake R.V. ResortSamuel Torp, Simon

Peterson, and Suzette Frazier

Photo by Steve Johnson

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Outline Objectives Methods and Materials Results Conclusion & Management OptionsLimitations

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Objectives

1) Analyze water and organic content of the sediment at different depths of the lake

2) Analyze benthic invertebrate diversity at different depths of the lake

Hypothesis1)There is higher water and organic content in

the littoral zone due to higher productivity of benthic invertebrates.

2)There is a higher species diversity in the

littoral zone due to higher organic and water content in sediment and river outlet.

MethodsIn order to accurately compare littoral zone with center of lake samples were taken in a transect from the river outlet to the center of the lake:

Transect:A) Littoral

Zone at 10m

B) Mid lake 20m

C) Lake center 30m

Source: Google Maps, http://maps.google.com. Retrieved: 12/06/10

SamplesAt each of the sample site the following measurements were taken:Triplicate samples were taken using

Ekman grab to analyze benthic invertebrates

One core sample from each site A, B, C taken using K-B core sampler

Ekman Grab (Hoskin, 2010)

K-B Core sampler (Hoskin, 2010)

Materials and InstrumentsInstruments:Ekman GrabK-B Core sampler Materials:Bucket (to hold core samples)Sample jars (contain Ekman invertebrate samples)Tape measure (measure out transect)Screen to filter Ekman grab samplesCore tubes Stoppers (for core tubes)Filter Screen (for Ekman samples)Label Tape

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Sample: Lab AnalysisK-B core:The cores were segmented into different layers coinciding with visual layer as much as possibleWet weight was measured as raw sampleDry weight (after 60 ˚c degrees for 24hrs)Ash weight (550˚c for 3hrs)

Wet weight-Dry weight= water content

Dry weight – Ash weight=organic content

Ash weight=mineral content

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Sample: Lab Analysis continue…Ekman Grab samples:Filtered through sieveNumber of macroinvertebrates counted using

microscopeBack-track volumes with numbers found to

indicate invertebrate densities

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Results (Sediment depth)

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Figure 1. Sediment composition near the shoreline (group X), Bonners Ferry, ID, USA, 11/30/10.

0 0.5 1 1.5 2 2.5 3 3.5 40

1

2

3

4

5

6

7

8

9

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Sediment Composition from nearshore

Organic wtMineral wt.

Weight (g)

Sam

ple

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Sediment depth at 20 meters

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Figure 2. Sediment composition at 20 meters from the shore, Blue Lake, Bonners Ferry, ID, USA, 11/30/10.

0 1 2 3 4 5 60

5

10

15

20

25

30

Sediment Composition (20 m from shore)

Mineral WeightOrganic Weight

% of (Total) Wet Weight

Sedi

men

t D

epth

(m

)

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Sediment Compostion at 30 meters, deep lake site

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Figure 3. Sediment composition at 30 meters (deep lake) site, Blue Lake, Bonners Ferry, ID, USA, 11/30/10

0 2 4 6 8 10 12 14 160

5

10

15

20

25

30

35

Sediment Composition (30 m from shore)

Mineral WeightOrganic Weight

% of (Total) Wet Weight

Sed

imen

t D

epth

(m

)

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Results (Macroinvertebrates)

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• We found fresh water clams (Mollusks), abundant snails (Gastropoda), mussel shrimp eggs (Ostracoda) and beetles (Coleoptera).

• Each species has the potential to perform an essential role in the persistence of the community & the ecosystem; some represent a particular functional group (Covich et al. 1999).

• Availability of food materials govern the distribution of benthic communities (Saether O.A 1979)

Fig 10 . Population densities at 10, 20 and 30 meters from the shoreline, Blue Lake, Bonners Ferry, ID, USA, 11/30/10.

0 5 10 15 20 25 300

5

10

15

20

25

30

MollusksGastropodaOstracodaColeoptera

Lake depth in meters

Num

bers

of

spec

ies

pres

ent

in 5

, 20

and

30

met

ers

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Macroinvertebrate T-test

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Species Compared samples t-stat

Gastropoda 5m and 30m 0.034

Ostracoda 5m and 30m 0.023

Molluska 5m and 30m 0.013

A t-test was run against the triplicate samples taken from the 5m and 30m sites. Three of the most abundant species were compared. All of the t-stat values were less than 0.05 indicating a significant difference. Overall the data on macroinvertebrates was insignificant due to the lack of data.

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DiscussionIncorporating phosphorus, nitrogen, and chlorophyll

data would be needed to assess ecosystem health. (Kane et al. 2009)

In freshwater sediments benthic invertebrates are often patchily distributed and relatively difficult to sample especially when they live in deep subsurface sediments.

Shannon – Weaver DiversityThere appears to be a significant difference in the total

number of macroinvertebrates at the three location. However the when comparing the data using t-test this

indicates that the values are insignificant.This may be due to the lack of data

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Conclusion Sediment accumulation could be greatest at

the middle depth (shelf). This might be due to contribution from the piece of land in the middle, in addition to those from the shore

Organic matter is the greatest contributor to the sediment accumulation

Macroinvertebrate community is dominated by Mollusks, Gastropoda, Ostrocoda, and Coleptera.

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Limitations & Options• Further investigation with replicate samples

are needed to insure the precision of the data.

• Labels that resist high temperature are recommended, this limited the reproducibility of our samples.

• The benthic community is a reflection of the biotic/abiotic factors of Blue Lake.

• More samples over a larger area would strengthen the data

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Reference List

Covich A. P.; Palmer M. A.; Crowl T. A. The Role of Benthic Invertebrate Species in Freshwater Ecosystems: Zoobenthic species influence energy flows and nutrient cycling. BioScience, Volume 49, Number 2, 1 February 1999, pp. 119-127.

Saether, Ole A. Chironomid communities as water quality indicators Ecography Volume 2 Issue 2, Pages 65 – 74. Published Online: 30 Jun 2006

Kane, Douglas D et al. The Planktonic Index of Biotic Integrity (P-IBI): An approach for assessing lake ecosystem health. Ecological Indicators; Nov 2009, Vol. 9 Issue 6, p1234-1247, 14p

 

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