Macro-invertebrate response to in-stream biomass

Sheralynn Bauder

Department of Conservation Social Sciences

University of Idaho, McCall Field Campus, McCall, ID

Abstract

1. The effect of in stream biomass on macro-invertebrate communities was examined by gathering macro-invertebrates at plots with high in-stream biomass and low in-stream biomass.

2. Macro-invertebrates were collected at 3 different sites with two plots at each site, one with high biomass and one with low biomass, for a total of six plots.

3. Statistical analysis of abundance indicated a positive relationship between abundance and biomass, but did not show a statistically significant relationship.

4. Statistical analysis of species richness shows a slight positive relationship, but did not show a statistically significant relationship.

5. Synthesis:

Results are inconclusive.

Key words

Biomass, macro-invertebrate, indicator species, erosion

Introduction

So many rivers and streams in Idaho run through sections of farmland or towns. The effect this has on the stream ecosystem is varies from stream to stream, but often changes the nutrient levels, sedimentation, and kinds of in-stream biomass that create the habitats of benthic macro-invertebrate communities (Doledec). Some of the most sensitive players a stream ecosystem are macro-invertebrates, named for their lack of backbone and their ability to be seen with the naked eye, are a significant source of food for life in and above freshwater streams and ponds. In addition to a source of food they are also key in controlling biomass build-up such as algae, etc. (Weatherhead, et al.) They are indicators of the water quality because of their sensitivity to changes in the water’s turbidity, oxygen levels, pH, and temperature. The health of an ecosystem near streams or ponds is very dependent on macro-invertebrates. In forming this research question the habitats of macro-invertebrates and the effect that larger amounts of biomass in a streambed would have on the population and diversity of macro-invertebrates was considered. This information could give insight into the effect erosion could have or perhaps even the changes that natural disasters would cause when downfall and debris increase.

Materials and Methods

Study Site

This research was conducted in Lake Fork stream located in McCall, ID (see site map), south of Little Payette Lake. This section of Lake Fork is located after the stream has passed through farmland close to Comfort Road. The six plots studied were paired in three sections of the stream 10 feet apart (pics 1 to 6). In each pairing there was a plot low in biomass and a plot high in biomass.

site map

Plot 1Plot 2

Plot 3Plot 4

Plot 5Plot 6

Field Methods

Each plot was marked out by a 2 foot squared pbc structure (see figures). Plots were paired in the same cross-sections of the stream. Plots 1 and 2 were Site A, Plots 3 and 4 were Site B, and Plots 5 and 6 were site C. Percent biomass was determined by sight, and included any biofilm, detritus, algae, or plant life. Macro-invertebrates were collected at each plot by using a kick-net and kicking for a total of ----seconds. In addition 10 rocks within the plot were sampled for macros. The macro-invertebrates were then identified using charts (site the chart source).

Results

Six plots were sampled for macro-invertebrates with abundance ranging from one to 41 and species richness ranging from one to eight (see charts).

site

biomass

abundance

1

90

15

2

10

21

3

90

16

4

5

1

5

70

41

6

20

9

site

biomass

species richness

1

90

2

2

10

6

3

90

4

4

5

1

5

70

8

6

20

5

Statistical Analysis

Two scatter plot graphs were produced using R 2.15.2 software (R Development Core Team, 2012) and two linear regression models were completes to determine the statistical significance of the relationship between biomass and species richness and biomass and abundance. Scatter plot A (fig. 1) indicates a slightly positive relationship between biomass and abundance, however, according to the linear regression model there is no statistical significance because the p-value is greater than 0.05 (p-value = 0.3985). Scatter plot B (fig.2) indicates a positive relationship between biomass and abundance, but again the linear regression model produced a p-value greater than 0.05 (p-value = 0.9134) showing that there is no statistical significant relationship between biomass and species richness.

Fig. 1

Linear Regression Model (R output) for Biomass and Abundance

Call:

lm(formula = abundance ~ biomass, data = Abundance)

Residuals:

1 2 3 4 5 6

-8.276 9.224 -7.276 -10.058 20.599 -4.214

Coefficients:

Estimate Std. Error t value Pr(>|t|)

(Intercept) 10.3390 9.1394 1.131 0.321

biomass 0.1437 0.1522 0.944 0.399

Residual standard error: 13.69 on 4 degrees of freedom

Multiple R-squared: 0.1823,Adjusted R-squared: -0.02218

F-statistic: 0.8915 on 1 and 4 DF, p-value: 0.3985

Fig. 2

Linear regression Model (R output) for Biomass and Species Richness

Call:

lm(formula = species.richness ~ biomass, data = SpeciesRichness)

Residuals:

1 2 3 4 5 6

-2.4910 1.8058 -0.4910 -3.1757 3.5832 0.7687

Coefficients:

Estimate Std. Error t value Pr(>|t|)

(Intercept) 4.157135 1.923882 2.161 0.0968 .

biomass 0.003709 0.032046 0.116 0.9134

---

Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Residual standard error: 2.882 on 4 degrees of freedom

Multiple R-squared: 0.003338,Adjusted R-squared: -0.2458

F-statistic: 0.0134 on 1 and 4 DF, p-value: 0.9134

Discussion/Conclusion

The results of this research study did not yield a statistically significant relationship between biomass and the macro-invertebrate populations in Lake Fork. This result may not be an accurate picture of what could be discovered via these methods.

There were a number of limitations to this study. Determining percent biomass simply by sight was not an effectively accurate measurement. If there had been a way to extract the in-stream biomass and take its weight or determine the amount of light reaching the bottom of the stream (via a water-proof light lux meter) perhaps the amount of biomass could have been better quantified. Choice of location was also limited due to the stream crossing through mostly private land. Time limited the number of plots taken. Had there been more plots, perhaps a statistically significant relationship could have been determined.

Other studies have paired the collection of macro-invertebrates and the study of their habitat with the collection of other more quantifiable data, such as dissolved oxygen, temperature, and pH. These other stream variables have been shown to be more significant in their impact on macro-invertebrate population and diversity. Much of the variety seen in macro-invertebrates may be dependent on the type of biomass in the stream, not simply that it is there. The structure and shape that the biomass provides as a habitat, may have more bearing on a sites attractiveness to benthic invertebrates. In addition the sinuosity and reaches in the stream may effect benthic invertebrate populations (Lamouroux). In conclusion, this investigation could have been more conclusive had the data collected been more extensive and included a comparison to more than just in-stream biomass.

References

Alvarez, M. & Peckarsky, B.L. (2013) The influence of moss on grazers in high-altitude streams: food, refuge or both? Freshwater Biology, 58, 1982–1994.

Dolédec, S., Phillips, N., Scarsbrook, M., Riley, R.H., Townsend, C.R., Dole, S., I, C.B.L. & Riley, R.H. (2006) Comparison of structural and functional approaches to determining landuse effects on grassland stream invertebrate communities Comparison of structural and functional approaches to determining landuse effects on grassland stream invertebrate communities. , 25, 44–60.

Lamouroux, N., Dolédec, S., Gayraud, S. & Biologie, U.R. (2004) Biological traits of stream macroinvertebrate communities : effects of microhabitat , reach , and basin filters Biological traits of stream macroinvertebrate communities : effects of microhabitat , reach , and basin filters. , 23, 449–

Weatherhead, M.A. & James, M.R. (2001) Distribution of macroinvertebrates in relation to physical and biological variables in the littoral zone of nine New Zealand lakes. , 115–129.

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