A Census of Stream Macroinvertebrates on the Mount Holyoke College Campus
BIO 100B - Biodiversity and Conservation
Fall Semester, 2000
Kirt Moody, Sara Al-Saman, Daisy Carrington, Jeanie Curry, Heather Grant,
Devon Hill, Kasey Kathan, Bekka Lee, Danielle Lewis, Maggie Meehan,
Adrienne Pope, Lisa Roberge, Wesley Robert, Jennifer Roth, Alyssa Veralli,
Claire Yunker, Victoria Stepanenko, Annie Hill, Diana Preziosa
Abstract
Using kick seines, we sampled two shallow water stream sites on the Mount Holyoke
College Campus (one above and one below the lakes) for stream macroinvertebrates.
Thirty species, based on morphological distinctions, were identified, with eleven
species present in densities greater than 1/m2 in at least one of the sites. The results
were analyzed with calculations of a diversity index and a water quality index based on
the relative presence of bioindicator taxa. While both sites exhibited comparable
diversity and “excellent” water quality, the site below the lakes was uniquely dominated
by grazing crustaceans (isopods and gammarid amphipods). This difference may be
the result of nutrient enrichment from run-off, leading to the presence of a notable
filamentous algal turf on the benthic substrate.
Introduction
Over the past decade, biodiversity has become an important focus of scientific
research and a foundation for conservation policy and practice. Today, surveys of
biodiversity are useful tools in the identification and assessment of environmental
degradation. Measures of diversity made in closely associated sites can provide an
indication of relative health and stability of local ecosystems. Aquatic systems are
particularly important as early indicators of ecological decline. One group of aquatic
organisms that exhibits measurable variation in diversity, and is easy to sample, is the
community of benthic macroinvertebrates. The census of these species has been
practiced to the point that indices of water quality based on the presence or absence of
pollution tolerant taxa are commonly calculated.
With the creation of the Center For Environmental Literacy, ecological awareness
has recently become more of an academic priority at Mount Holyoke College. As a
result, students in classes across the curriculum are taking part in projects designed to
expand awareness of the campus environment. Among the features of the campus
landscape, the stream and lake system is of primary ecological importance. To
contribute to environmental awareness, explore patterns in biodiversity, and assess
stream water quality on the Mount Holyoke College Campus, we surveyed two stream
sites for the presence and abundance of macroinvertebrate species.
Methods
Samples were collected from two sites along the streamway that runs through the
Mount Holyoke College Campus (Fig. 1). The sites were chosen for their relative
positions (upstream vs. downstream) with respect to the primary area of human impact
- an area marked by the presence of two artificially created lakes surrounded by paved
roads, campus buildings, and intensively maintained landscapes. A visual inspection
of the sampling sites confirmed that they were characterized by similar depth (5080cm), bottom substrate (rocky “cobble” and larger flattened stones and mixed coarse
sediment), water temperature (15-18oC ), flow rate (.20-.30m/s ), and tree cover (See
photos). Therefore, it was assumed that differences in the biota of the sites could be
largely attributed to human impacts.
The samples were taken on two consecutive days in the first week of November.
Four samples were taken at each site. Each sample consisted of a haphazardly
chosen 1m2 quadrat ( at least 3m away from any other sample position). At each
quadrat position, a 2mm mesh kick seine was held in place on the downstream edge
while the substrate was disturbed so as to dislodge any epifaunal organisms present.
Movable stones in the quadrat were lifted from the bottom, manually brushed off in front
of the seine, and placed outside of the sampling area. Once the stones had been
processed, the remaining sediment and rock surfaces in the quadrat were also
manually brushed and subsequently subjected to 3-minutes of foot-shuffling in order to
complete the exhaustive sampling. Each sample took approximately 10 minutes to
complete, after which, the contents of the seine net were washed into a 500 ml sample
bottle.
The macroinvertebrates in each sample were examined under a dissecting scope
and sorted into a series of morphological types that are referred to here as species.
Each species was identified taxonomically at least to the Order level. (Table 1). In
cases where morphological variation suggested separate species, but the available
taxonomic references were not detailed enough to make distinctions, the species were
given numerical designations and categorized separately (eg. mayfly 1, mayfly 2, etc).
It is our hope to eventually see these assumptions resolved through further taxonomic
assessment.
When all samples had been sorted and all specimens classified, the average
abundance (density) of each species was calculated for each site. In addition, a
Shannon Diversity Index (for all species with a mean density greater than one
individual per square meter) and a water quality index, based on the presence of
bioindicator species (Izzak Walton League - Save Our Streams Program 1996), were
generated for each site.
Results
A total of 865 macroinvertebrate specimens were collected from the two sites - 490
from the Lower Lake Stream site, and 375 from Stony Brook. The Lower Lake Stream
samples contained 21 species with 9 occurring in densities greater than one individual
per square meter. The Stony Brook samples contained 22 species, with 6 occurring in
densities greater than one individual per square meter. The Shannon diversity indices
calculated for the two sites were 1.51 and 1.71 respectively. Of the more abundant
species, four were found at both sites, occurring in the same order of abundance:
Mayflies (1), Caddisflies (1), Midge larvae, and Stoneflies (1) (Fig. 2). Among the
remaining higher density species were four that were found in only one of the two sites:
isopods, amphipods, and mussels at the Lower Lake Stream site, and oligochaetes at
the Stony Brook site.
The bioindicator water quality indices calculated were 29 for the Lower Lake Stream
and 25 for Stony Brook. Both of these values are indicative of an “excellent” water
quality state. The logic of this water quality assessment technique is illustrated in the
high overall diversity of the two sites and in the high abundance of larval mayflies,
caddisflies, and stoneflies; which are all classified as pollution sensitive taxa.
Discussion
The use of a kick seine as a sampling device limits the precision of this type of
survey. As a result, interpretation of these data should be restricted to the clearest of
distinctions between the two sites. In this light, the diversity indices and water quality
classifications determined in this survey are too similar to provide for a comparative
analysis. However, a primary difference between the sites can be seen in the
distribution of species. At Site 1, the Lower Lake Stream, 237 isopods were collected,
representing almost half of all of the specimens gathered there. In contrast, the Stony
Brook samples did not contain any isopods at all. Similarly, gammarid amphipods and
unionid mussels were found only in the Lower Lake Stream (albeit at much lower
densities). Conversely, the Stony Brook samples contained a number of oligochaete
worms, while the other Lower Lake samples did not.
These differences in species distribution may reflect environmental variation,
including human impacts. For instance, the abundance of grazing isopods and
amphipods in the Lower Lake site could suggest the availability of a unique trophic
resource there. Although we did not collect any information about plant or algal
species during this project, it was noted more than once that the Lower Lake Stream
site was a more challenging sampling environment, due to “slippery rocks”. This
observation would be consistent with a well-developed algal film or turf on the benthic
substrate. If so, then it may explain the dominance of the benthic grazing crustaceans
at this site. Artificial nutrient enrichment due to run off around the Lower Lake could be
a likely contributing factor in the promotion of algal productivity. Similarly, the presence
of large (5-15cm shell length) filter-feeding unionid mussels at the Lower Lake site
could reflect a higher level of suspended algal biomass. Water quality characteristics,
including higher nitrate (nutrient) concentrations, higher dissolved oxygen levels, and
higher concentration of chlorophyll a at the Lower Lake site (Table 2) support these
suppositions. An alternative explanation could be the observed periodic reductions in
flow that some areas of Stony Brook experience. These types of disturbances could
restrict the distribution of wholly aquatic macroinvertebrates such as the benthic
crustaceans and bivalves.
Table 1
Mean density (#/m2) of shallow stream macroinvertebrates at two sites
on Mount Holyoke College campus
Site 1: Lower Lake Stream – below Lower Lake bridge/dam
Site 2: Stony Brook – adjacent to horse crossing at Long Farm
"Species" identified (listed in order of overall mean density) are morphologically distinct
types. Numbers are used (eg. Mayfly 1, 2…) to distinguish types that are assumed to
represent distinct species, but have not been identified beyond the taxonomic level
indicated.
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
AA
BB
CC
DD
"Species"
Mayfly 1
Isopod
Caddisfly 1
Midge larva
Stonefly 1
Caddisfly 2
Amphipod
Crayfish
Damselfly
Mussel
Oligochaete
Mayfly 2
Mayfly 3
Water penny
Caddisfly 3
Riffle beetle 1
Hydra
Leech
Beetle larva 1
Stonefly 2
Cranefly
Flatworm
Aquatic mite
Spider
Fly larva 1
Fly larva 2
Riffle beetle 2
Clam
Beetle larva 2
Beetle larva 3
Taxonomy
Site 1 Site 2
Order Ephemeroptera
38.75 46.75
Order Isopoda
59.25
0
Order Trichoptera
5.75
16
Family Chironomidae
3
9
Order Plecoptera
2.5
8
Order Trichoptera
0.25
5.25
Suborder Gammaridae
3.75
0
Family Astacidae
1.75
0.75
Suborder Zygoptera
2
0.25
Family Unionidae
1.75
0
Suborder Lumbricina
0
1.75
Order Ephemeroptera
0.25
0.75
Order Ephemeroptera
0.5
0.25
Family Psephenidae
0.25
0.5
Order Trichoptera
0.5
0
Family Elmidae
0.5
0
Suborder Anthomedusae
0.5
0
Class Hirudinea
0.25
0.25
Order Coleoptera
0.25
0.25
Order Plecoptera
0
0.5
Family Tipulidae
0
0.5
Order Catenulida
0
0.5
Order Acari
0
0.5
Family Argyronetidae
0
0.5
Order Diptera
0
0.5
Order Diptera
0
0.5
Family Elmidae
0.25
0
Family Pisidiidae
0.25
0
Order Coleoptera
0.25
0
Order Coleoptera
0
0.25
Table 2
Water quality characteristics from two shallow stream sites
on the Mount Holyoke College campus
From data compiled by the Center for Environmental Literacy - Mount Holyoke College
Site designations as in Table 1
o
C
water temperature in degrees centigrade
DO% dissolved oxygen expressed as percent of saturation level
NO3 Nitrate concentration in milligrams/liter
Chl a Chlorophyll a concentration in micrograms/liter
Date
Site
8/11/00 1
8/11/00 2
o
C DO% NO3 Chl a
26.27 105.6 27.8 16.9
23.59 74.6
6.4 7.9
9/8/00
9/8/00
1
2
19.05 100.4
15.73 85.4
18.1
13.8
6.7
5.9
9/21/00
9/21/00
9/21/00
9/21/00
9/21/00
9/21/00
1
1
1
2
2
2
20.66 103.6 21.12
20.67 101.4 21.39
20.67 105.8 22.64
18.84 75.2 14.67
18.83 77.5 14.5
18.82 78.1 14.53
5.1
7
5.1
6
5.8
5.9
Figure 1
Map of sampling sites - Mount Holyoke College campus
Adapted from a map prepared by the Center for Environmental Literacy - Mount
Holyoke College. Site 1 (Lower Lake Stream) is shown to the left, below the Lower
Lake Dam. Site 2 (Stony Brook) is shown to the right, adjacent to Morgan Street. The
direction of flow is from Site 2 to Site 1.
Figure 2
Rank / Abundance charts for stream macroinvertebrate species
collected from two sites on the Mount Holyoke College campus
Species labels by letter refer to designations in Table 1. Note the use of the log scale
on the Y axes. Additional species indicated in Table 1 were present in densities lower
than one individual per square meter.
Lower Lake Stream
100
10
1
B
A
C
G
D
E
I
Stony Brook
100
10
1
A
C
D
E
F
K
H
J
Photographs