EST/EFB 220 Urban Ecology  Lab 1

Assessment of Water Quality in Onondaga Creek Using Aquatic Invertebrates: A Rural to Urban Gradient Analysis

 

 

INTRODUCTION

 

We will evaluate water quality in Onondaga Creek from its rural origins to its inner city channel using biological indicators to assess water quality.  Bio-indicators are organisms that are used for monitoring environmental pollution because they have a narrow range of tolerance to habitat modification. The bio-indicators of pollution in streams are the aquatic invertebrates or benthic “macro invertebrates” that have varying sensitivity to pollution. They can be thought of as the “canaries of the stream.”  Research on this variation among families of macro invertebrates has shown that they can be lumped roughly into three levels of sensitivity:  Sensitive, Somewhat Sensitive and Tolerant.   Sampling for these organisms in Onondaga Creek will allow us to assess water quality relatively rapidly by examining the community structure using three metrics: EPT Taxa Richness, Percent Composition of Major Groups, and the Major Group (not family-level) Biotic Index.

 

We will collect and identify macro invertebrates along Onondaga creek during the next 2 lab periods at 3-5 locations depending on time available as indicated on Fig 1.    We will begin in the creek’s headwaters near Tully, NY, south of Syracuse, where we will sample above (Tully Farms Road) and below (Otisco Road) the mudboils. The following week we will continue our sampling, downstream, in an increasingly more urban watershed, i.e. more disturbed, more modified from the “natural” landscape.  We will take samples above (Dorwin Avenue) and below (Franklin Square) the Combined Sewer Overflows (CSOs) that discharge raw sewage into Onondaga creek during storm events.

 

We will compare the sites in terms of water quality. Normally three types of assessment are necessary when assessing water quality: Biological, Physical, and Chemical.  You will choose one other chemical or physical factor that you believe may determine why the bug population changes along this gradient and assess that factor as you progress downstream.  You may hypothesize that temperature is the controlling factor, and therefore use the Horiba sonde to measure it at each stop.  Finally you will look for correlation between one or more dependent variables like the % EPT and/or Taxa Richness and the independent variable, e.g. temperature, and be able to state whether the data supports your original hypothesis.

 

Figure 1. Onondaga Creek Watershed, and stream sampling locations

 

OBJECTIVES

 

1)      to learn how macroinvertebrates can be used as bio-indicators to  rapidly assess  water quality

2)      to engage in hypothesis testing and a real scientific inquiry

3)      to learn how to analyze and interpret environmental data by calculating the taxa richness, percent composition of dominant taxa,  number of EPT taxa, and the biotic index.

4)      to become familiar with the ecological concept of the rural to urban gradient as applied to water quality by sampling and analyzing different sites along this gradient.

5)      To compare the results from either the water chemistry analysis or physical analysis with the results from the analysis of macroinvertebrate sampling data.

 

HYPOTHESES (examples)

 

a)      We predict that water quality is higher above the mudboils as indicated by macroinvertebrate community structure and water chemistry data.

 

 

b)       We predict that water quality decreases along a rural to urban gradient as indicated by macroinvertebrate community structure as a function of nitrate concentration.

 

c)      We expect that water quality, in spite of the CSOs in the city does not, vary much from the rural to urban sections, and that stream substrate is a more important factor than ammonia, in explaining the variation in macroinvertebrates.  

 

MATERIALS

 

For rapid bioassessment:

Keys to macroinvertebrates

Dice

Kick nets

White pans

Tweezers

Data sheets

Horiba probe

Velocity Meter

Optional: to be used if bugs are collected and taken to the lab for further analysis

Distilled water

Plastic Ziploc freezer bags

Sharpie markers

            80% ethanol solution

EPA Visual Assessment worksheets

 

Depending on the questions you want to ask, the Hudson Basin River Watch (HBRW) describes at least five kinds of water quality studies:

 

1. Water Quality Standard Survey: determines whether a river meets selected state water quality standards for its designated uses.

2. River Characterization: establishes a profile of a river along its length.

3. Trend Analysis: provides baseline information about how a river changes over time. 

4. Impact or Improvement Assessment: peasures the impact on a river of a particular human alteration or land use, or the improvement from a remediation activity.

5. Ecological Study: determines the effect that natural variation of river or watershed features has on different parameters, or answers a multitude of other questions.

 

The kinds of questions that might be addressed in each are shown in the HBRW table entitled Study Design Questions and Indicators to Study (http://www.hudsonbasin.org/HBRWGD04.pdf, page 24).  We will conduct a Tier 2 short duration/high intensity river characterization from Onondaga Creek’s upper rural reaches to its urban outlet to Onondaga Lake.  Tier 2, as described by the HBRW, is a preliminary assessment used to document that a river segment has either “No Known Impacts” and is supportive of aquatic life, or that there are “Suspected” water quality problems that may be impacting water body uses/aquatic life support. “Suspected” water quality problems requires verification of those impacts by DEC; this verification may incorporate Tier 3 follow-up.

 

How you will proceed:

 

  1. Form a group of four investigators
  2. Together look at the stream, think about rural versus urban environments and select one physical or biological factor that you think may change along this gradient and that may have the most significant impact on the types of macroinvertebrates (i.e. those that are pollution sensitive and those that are not) that you will find as you move from the country into the city.
  3. Conduct your benthic macroinvertebrate collection as described on the HBRW sheets.
  4. Measure or assess the other factor that you believe is controlling the macroinvertebrate community
  5. Calculate EPT Richness, Major Group Biotic Index, and  Major Group Percent Composition.
  6. Graph your findings as illustrated in Figure 2.
  7. Present your findings to the class on Monday, September 10.
  8. Write a lab report (see attached guidelines) to hand in on Wed., Sept. 12.

 

 

Figure 2. Example of graph showing hypothetical taxa richness as a function of distance from headwaters.  Numbers on x axis represent sample locations moving from headwaters to the inner city.

Metrics to assess water quality:

After macro-invertebrate samples are collected they are either preserved or analyzed live.

A sub-sample of 100 organisms (or the entire sample) is picked and sorted into

major groups. These are identified and counted to calculate certain metrics, which

are values that can be compared on a numerical scale to determine a corresponding

level of impact to stream health.

 

EPT Richness Estimate: An estimate of the number of different kinds of mayfly

(Ephemeroptera), stonefly (Plecoptera), and caddisfly (Trichoptera) The EPT’s tend

to be particularly sensitive to pollution. Therefore, less impacted streams generally

have a higher EPT Richness. The EPT Richness can be a useful indicator of stream

health and a way to compare two or more different sites. In Tier 2, the EPT Richness

you measure is an estimate because you do not identify the taxa to the family level;

instead you simply distinguish between different taxa within each of the three major

groups.

Major Group Biotic Index: This metric takes into account pollution tolerance values

that are specifically assigned to each major group of organisms, along with the

number, or density of organisms found in each major group. Different types of

macroinvertebrates have a different tolerance to pollution. By counting the number

of different types you collect and multiplying by the pollution tolerance of each, it is

possible to arrive at a biotic index. In general, the more pollution intolerant

organisms you find, the higher the biotic index, and the less impacted your stream.

Major Group Percent Composition: Percent Composition is not a single metric that

refers to a certain level of impact. It is calculated for each major group by dividing

the number or density of organisms in each major group by the total number of

organisms in the sub-sample and then multiplying by 100 to convert to percentage.

The relative Percent Composition of organisms in major groups will change with

different sites, habitats, and different water qualities. Calculating Percent

Composition gives you a good picture of the community at a particular site. You can

use this to compare two different sites or to see how the community at a site changes

over time. A higher Percent Composition of pollution tolerant organisms suggests

more impact than a higher Percent Composition of pollution sensitive organisms.

 

 

 

To present in class as a group on Monday, September 10:

 

Explanation of what you observed and why you chose the hypothesis that you did

Your hypothesis

Your results including the 3 metrics above for each site graphed against your independent variable  (hand drawn or using Excel) as in Figure 2.

Your conclusions

 

To hand in by Wednesday, September 12:

 

Lab report following the attached guidelines