Comparison of Macroinvertebrate Diversity and Community Structure among Perennial and Non-Perennial Headwater Streams
Anna N. Santos and Robert D. Stevenson
Northeastern Naturalist, Volume 18, Issue 1 (2011): 7–26
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2011 NORTHEASTERN NATURALIST 18(1):7–26
Comparison of Macroinvertebrate Diversity and
Community Structure among Perennial and Non-Perennial
Headwater Streams
Anna N. Santos1,2,* and Robert D. Stevenson1
Abstract - The relationships between stream flow regime and macroinvertebrate diversity,
community structure, and functional feeding groups (FFG) were examined to
determine if the biodiversity and macroinvertebrate fauna of non-perennial streams are
significantly different from those of perennial streams. The study was conducted in northeastern
Massachusetts at headwater stream sites of varying flow permanence (perennial,
intermittent, and ephemeral). ANOVA confirmed no significant difference in Shannon-
Wiener diversity (H') between stream types, demonstrating that non-perennial streams
maintain diverse and even macroinvertebrate communities. Whereas taxa richness was
equal among intermittent and perennial sites, ephemeral richness was lower due to their
significantly lower riffle richness. Qualitatively, two non-perennial sites were higher in
grand total H' diversity and taxa richness than perennial sites. Community structure was
also related to flow regime, as hierarchical cluster analysis (HCA) based on taxa presence
produced three distinct groups consistent with stream type, and FFG analysis provided
further evidence of distinct communities, with a transition in FFGs from perennial to
ephemeral sites. This study concludes that non-perennial streams are biologically diverse
and maintain distinct benthic communities and therefore contribute to stream biodiversity
and river ecosystems.
Introduction
Non-perennial streams form the headwaters of river systems where channels
begin to arise as zero or first order streams and are often referred to as drainages,
springs, seeps, or intermittent channels. Headwater areas comprise a large
portion of river networks and may contribute 70% to 80% of the total catchment
area (Meyer and Wallace 2001, Sidle et al. 2000) or over 40% of an active
river area as defined by Smith et al. (2008). Despite their proportion, they
are only recently becoming more recognized as ecologically significant river
areas. Headwater streams provide habitat for locally adapted species (Lowe
and Likens 2005, Meyer at al. 2007), and the in-stream processing of nutrients
and energy from nearby riparian input is transferred to downstream systems
(Bernhardt et al. 2003, Peterson et al. 2001, Vannote et al. 1980). This vital
land–water interface at the micro-watershed scale contributes to the health and
the biological diversity of the entire river system (Meyer et al. 2007). Unfortunately,
non-perennial streams are generally unaccounted for in river-protection
1Department of Biology, University of Massachusetts at Boston, 100 Morrissey Boulevard,
Boston, MA 02125-3393. 2Current address - Department of Geography, Texas A&M
University, 810 O&M Building, 3147 TAMU, College Station, TX 77843. *Corresponding
author - annasantos@tamu.edu.
8 Northeastern Naturalist Vol. 18, No. 1
legislation, contributing to the poor management of headwater areas (Bond and
Cottingham 2008, Gomi et al. 2002).
Naturally formed non-perennial streams are common in temperate forests
of the eastern US (Kirby et al. 1983) and other biogeographic areas where decreased
precipitation and increased evaporation in summer causes surface flow
to cease. Stream flow also varies annually in response to precipitation events,
and this temporal variability may reduce or halt surface flow of perennial
streams during low-precipitation years, while high amounts of precipitation
may cause continuous flow of intermittent streams. The frequency, timing,
and duration of no-flow or low-flow periods have been criteria for defining
stream type (Fritz and Dodds 2005, Gomi et al. 2002), and in the northeastern
US, intermittent streams may be defined by flow patterns in which they cease
flow in summer (Ward 1992) for three to four months during normal precipitation
years.
A third category of streams that is less popularly examined is generally
termed “ephemeral”. Ephemeral streams are typically defined as streams that
maintain surface flow during spring thaw and rainfall events and for a short
duration thereafter, and is further defined by the United States Army Corps of
Engineers (2002) as being above the water table. However, criteria for ephemeral
streams are ambiguous since in some studies they have been defined as
flowing for only several days (Dieterich and Anderson 2000), whereas others
make the demarcation at up to 4 to 5 months of flow (Gomi et al. 2002). There
is also a classification disparity between intermittent streams that flow for
more than eight but fewer than 12 full months out of the year and ephemeral
streams that are said to flow for five or fewer months of the year. To avoid
confusion with idiom by applying a different term to streams that flow for
fewer than eight months and more than five, the term ephemeral was used in
this study for sites that flow for fewer than eight months. This a priori classification
of non-perennial sites is not only based on commonly used terminology,
but also on summer flow characteristics similarly applied by Bonada et
al. (2007), with intermittent streams having isolated pools during summer and
ephemeral streams having stream-bed drying during summer that persists for
longer periods. Due to their small size and to difficulty with map resolution,
both intermittent and ephemeral streams have been typically excluded from
topographic maps and USGS hydrography data (MassGIS 2010), designating
them as obsolete in watershed management activities (Fritz et al. 2006, Gomi
et al. 2002, Meyer and Wallace 2001).
Historically, the headwaters of watersheds largely comprised of non-perennial
streams (Fritz et al. 2006) have been the least studied of aquatic systems (Ward
1992). Recent findings suggest that intermittent streams contribute to the biodiversity
of river systems (Gomi et al. 2002, Meyer at al. 2007), and past studies
have demonstrated that the macroinvertebrate community assemblage (Boulton
and Lake 1992, Delucchi 1988, Feminella 1996, Williams 1996) and primary production
(Hill and Gardner 1987) of intermittent and perennial streams are similar.
2011 A.N. Santos and R.D. Stevenson 9
Unlike perennial streams, however, intermittent streams are inhabited by unique
organisms specifically adapted to drying conditions. Behavioral adaptations
include burrowing into the hyporheic zone or migrating to wet areas, while physiological
adaptations include diapause or life cycles that favor spring emergence
(Boulton 1989, Delucchi 1988, Ladle and Bass 1981, Poff and Ward 1989, Williams
and Hynes 1977, Wright et al.1984). Earlier investigations of non-perennial
streams typically explored synergies between macroinvertebrate richness and biotic
assemblage of perennial and intermittent streams (Vinson and Hawkins 1998),
whereas few studies have examined the diversity of ephemeral streams.
To determine if the biodiversity and community structure of non-perennial
streams are significantly different from those of perennial streams, this study
examined the relationships between flow regime and macroinvertebrate diversity,
community structure, and functional feeding groups (FFG) of perennial,
intermittent, and ephemeral stream sites. It was predicted that the macroinvertebrate
diversity of intermittent and perennial sites would be comparable, whereas
ephemeral sites would have much lower diversity because of their extended noflow period, which may wipe out taxa and result in a meager benthic community
(Gomi et al. 2002). It was also predicted that non-perennial sites (both intermittent
and ephemeral) would maintain a slightly different community structure and
FFGs with adapted species.
Methods
Study site selection
This study focused on eight stream sites within six streams in eastern Massachusetts,
three of which were not present in Massachusetts Office of Geographic
and Environmental Information (MassGIS) hydrography data of March 2010 (see
Fig. 1). The streams are headwaters of the Fish Brook subwatershed (drainage
area of approximately 47 km2) of the Ipswich River located in Boxford (Essex
County), MA. The Ipswich River flows into Plum Island Sound in the town of
Ipswich located on the North Shore. Although the Ipswich River has been recognized
for its rich diversity, it is considered one of the most threatened rivers in
the United States due to water withdrawal (American Rivers 2003, Zarriello and
Ries 2000).
The stream sites were chosen for representation of varying stream flow permanence
as was documented in other investigations (Beugly and Pyron 2010,
Boulton and Lake 1992, Brönmark et al. 1984, Closs and Lake 1994, Delucchi
1988, Feminella 1996, Bonada et al. 2007). The stream sites are within a 1-km2
area (Fig. 1) and are low gradient, swampy tributaries that are relatively undisturbed
and located in eastern deciduous forest dominated by Tsuga canadensis
(L.) Carrière (Eastern Hemlock) and Acer rubum L. (Red Maple), with at least
75% shade cover at all sites. The sites were monitored (direct observation; MA
DEP 2008) weekly during summer for three years (2001–2003) prior to the study
period for determination of a priori patterns in flow permanence. The 8 sites were
categorized as perennial (constant flow), intermittent (up to 4 months of no flow),
10 Northeastern Naturalist Vol. 18, No. 1
and ephemeral (4 or more months of no flow), based on summer observations
and normal precipitation for the region. Stream sites 1, 2, and 3 are perennial;
sites 4, 5, and 6 are intermittent; and sites 7 and 8 are ephemeral according to a
priori flow patterns. The selected sites are ideal for examining the relationships
between macroinvertebrate diversity and flow regime since they are within the
same drainage network within a 1-km2 area of stream reaches and share similar
water chemistry but vary in stream morphology and flow permanence.
Figure 1. Stream study sites.
2011 A.N. Santos and R.D. Stevenson 11
Macroinvertebrate sampling and abiotic assessment
Macroinvertebrate sampling was conducted and abiotic measurements were
taken within a designated 5-m stretch x wetted width area of the particular stream
site for each sampling event. Macroinvertebrate sampling was conducted over 3
seasons (summer, autumn, and spring) as recommended by Minshall et al. (1985)
for an accurate representation of stream macroinvertebrate population. Twentyfour
sampling events took place: 8 sites over 3 seasons. Six samples were taken
from 3 riffles and 3 pools in each of the stream sites, for a total of 48 samples per
season and 144 total samples (8 sites x 2 microhabitats x 3 replicates x 3 seasons).
Samples were taken in July (in that month, ephemeral site riffles had enough water
to allow for macroinvertebrate sampling but were too shallow for measuring
flow) and September of 2004, and April 2005 following sampling protocol of the
US Environmental Protection Agency’s Rapid Assessment Procedures (Barbour
et al. 1999). A D-frame net with 500-μm mesh was placed on the bottom of the
streambed facing upstream and an area of substrate (roughly 0.10 m2) in front
of the net was kicked-up (disturbed) for approximately 15 seconds. Organisms
were removed from the net and from rocks located within the sampling area, and
were hand picked from a plastic tub in the field for a minimum of 20 minutes per
sample, which permitted removal of all individuals in this study. Specimens were
placed in 80% ethanol and identified to genus in the lab using a 50x dissecting microscope
and macroinvertebrate identification keys (Merritt and Cummins 1996,
Peckarsky et al. 1990, Wiggins 1996). Stream flow, pH, and water temperature
were also measured during every sampling event (twenty-four times over three
seasons). Stream flow and water discharge was calculated using the USGS cross
sectional area method, and because most of the streams were very shallow, the
float method was used for measuring flow. Water pH and temperature were measured
using an Oakton pH meter.
Biotic indices
Two measures of biotic diversity of streams were assessed: taxa richness and
Shannon-Wiener index of diversity (H'). Taxa richness is the total number of taxa
(genera in this study) found and is a measure of overall diversity, while the H'
measures taxa richness and evenness. Abundance, which equaled the total number
of individuals sampled from each site, was also measured. The major FFG
using Mandaville’s (2002) categorization were analyzed to detect differences in
macroinvertebrate feeding community between streams types. The five major
feeding groups are collector-filterers, collector-gatherers, predators, scrapers,
and shredders. The proportions of individuals from each group were calculated
for each site.
Statistical analyses
Statistical analyses were conducted using SPSS (version 14.0/ 2005, SPSS
Inc., Chicago, IL). Hierarchical cluster analysis (HCA) derived from similarity
(Pearson’s correlation) and dissimilarity (Euclidean distance) matrices was
12 Northeastern Naturalist Vol. 18, No. 1
applied to detect differences in macroinvertebrate community structure based
on presence-absence data of taxa at stream sites. To test the hypothesis of equal
means of the biotic indices between stream type, parametric general linear model
(GLM) univariate analysis of variance (UNIANOVA) tests were used. Multivariate
GLM was used to examine the differences between FFGs of clusters derived
from HCA analysis. Post hoc tests of pairwise comparisons based on estimated
marginal means with Bonferroni corrections for P values were performed to examine
main effects for all dependent variables of UNIANOVA (taxa richness, H')
and for multivaraite GLM FFGs.
Results
Stream type and abiotic properties
Average stream discharge increased with stream width (average wetted width)
in a log linear relationship (Fig. 2). Linear regression showed three distinct
groupings: perennial (sites 1–3), intermittent (sites 4–6), and ephemeral (sites
7–8) based on flow regime, and was consistent with a priori classification. Higher
than normal precipitation (DCR 2005) prevailed during the study, and in the summer
of 2004, the intermittent sites maintained low flow while the ephemeral sites
were reduced to a series of wet puddles; in previous summers, the ephemeral
Figure 2. Stream water discharge versus wetted width, showing a log linear relationship,
and three categories of stream types with site numbers shown.
2011 A.N. Santos and R.D. Stevenson 13
stream beds were dry. The eight sites’ water pH and temperature were comparable;
pH ranged from slightly acidic to neutral (6.25–7.01), with a mean of 6.56
(SD = 0.186), and temperature ranged from 10.3 to 25.4 °C (Table 1), within
normal seasonal fluctuation of temperate forest streams. The ephemeral streams
maintained lower overall temperatures.
Macroinvertebrate sampling
A total of 1802 individuals in 12 macroinvertebrate orders, 41 families, and
61 genera were found at all sites and included in this study. Two families of
dipterans (Chironomidae and Simuliidae) were also found but excluded from
all analyses because high biomass in streams along with patchiness in occurrence
and disproportionate densities can distort diversity analyses (Huryn and
Wallace 2000). The most abundant orders found were Trichoptera, Plecoptera,
Coleoptera, and Amphipoda, with perennial and intermittent sites dominated
by Trichoptera and ephemeral sites equally dominated by Trichoptera and Plecoptera.
The abundance (# of individuals sampled) ranged from 82 to 447 and
was not correlated with taxa richness, since intermittent sites had the highest
total richness but lower abundances (Table 2). Total taxa richness (accumulated
richness and diversity) ranged from 15–25 for perennial streams, 19–27
for intermittent, and 15–24 for ephemeral. Means of seasonal taxa richness
Table 1. Means and standard deviation (SD) of temperature, pH, wetted width, depth, calculated
velocity, and discharge of stream sites. P = perennial, I = intermittent, and E = ephemeral.
Velocity Discharge
Site Type Temp (ºC) pH Width (cm) Depth (cm) (cm/s) (m3/s)
1 P 17.1 (5.8) 6.56 (0.11) 769 (111.2) 33 (14.3) 25.5 (14.6) 0.759 (0.6)
2 P 16.1 (5.6) 6.37 (0.05) 543 (2.1) 36 (17.0) 47.5 (22.6) 1.030 (0.5)
3 P 18.3 (6.2) 6.55 (0.05) 392 (31.4) 31 (1.6) 14.9 (5.6) 0.185 (0.1)
4 I 16.8 (6.1) 6.46 (0.20) 105 (24.4) 10 (3.6) 18.8 (2.9) 0.022 (0.01)
5 I 16.3 (4.4) 6.50 (0.27) 106 (106) 7 (1.9) 35.0 (7.9) 0.028 (0.01)
6 I 14.1 (2.4) 6.69 (0.13) 100 (49.0) 10 (4.3) 17.2 (4.5) 0.021 (0.02)
7 E 14.1 (3.7) 6.53 (0.04) 54 (2.1) 4 (3.9) 5.02 (3.3) 0.002 (0.00)
8 E 14.2 (3.3) 6.86 (0.14) 101 (49.5) 5 (4.9) 7.63 (0.5) 0.006 (0.00)
Table 2. Stream site grand total abundance taxa richness and H' diversity with standard deviations
(SD).
Total richness and diversity Seasonal means
Site Type Abundance Taxa richness H' diversity Taxa richness H' diversity
1 Perennial 271 25 0.98 (0.04) 14 (2.6) 0.85 (0.10)
2 Perennial 447 22 0.86 (0.04) 15 (2.9) 0.78 (0.05)
3 Perennial 301 15 0.78 (0.05) 10 (1.4) 0.71 (0.05)
4 Intermittent 154 25 1.08 (0.04) 14 (2.1) 0.87 (0.12)
5 Intermittent 264 19 0.97 (0.05) 11 (2.5) 0.82 (0.05)
6 Intermittent 124 27 1.11 (0.03) 12 (2.1) 0.89 (0.13)
7 Ephemeral 159 24 1.16 (0.04) 10 (2.6) 0.83 (0.09)
8 Ephemeral 82 15 0.89 (0.04) 7 (3.3) 0.63 (0.19)
14 Northeastern Naturalist Vol. 18, No. 1
ranged from 10–15 for perennial streams, 11–14 for intermittent, and 7–10 for
ephemeral (Table 2, Fig. 3).
Stream type and biotic indices
The stream types did not differ in H' (P = 0.430), and there were no effects of
type, season, or type-season interactions. However, ANOVA confirmed a relationship
between taxa richness and flow regime (P = 0.032) and yielded significant
results (Table 3, Fig. 3). From pairwise comparison, ephemeral sites had signifi-
cantly lower richness (x̅ = 8.7, SE = 1.19) than perennial (x̅ = 13, SE = 0.972) and
intermittent (x̅ = 12, SE = 0.972) (P < 0.05), while intermittent site richness was
not significantly different from perennial (P = 0.635). From pairwise comparison
of riffle and pool analysis, intermittent and perennial site richness were the same
(P = 1.000), whereas the lower taxa richness of ephemeral sites was due to their
reduced riffle richness (P = 0.003) (Table 3, Fig. 3). Pool richness, however, was
not significantly different between stream types (P = 0.637). Furthermore, there
was no effect of season or type-season interactions on taxa richness or between
stream-type pools and riffles (P > 0.05). Finally, there was no association between
taxa richness and stream area, but abundance did increase with stream area
(P = 0.029) (Table 2).
Figure 3. Seasonal taxa richness and H' diversity of stream types (mean ± 1 SE). Seasonal
riffle and pool taxa richness of stream types (mean ± 1 SE). Riffle richness was signifi-
cantly lower in ephemeral streams (P = 0.005).
2011 A.N. Santos and R.D. Stevenson 15
Cluster analysis and site composition
Hierarchical cluster analysis (HCA) produced three main groups distinguishable
from one another based on taxa presence at stream sites. Analyses using
ordinal data (actual abundances) were similar to binary results but did not yield
as clear a resolution; therefore, binary results are presented here. HCA produced
two low-scale clusters (Fig. 4): cluster one is composed of sites 1–5, while cluster
two is composed of sites 6–8. At a finer resolution, the first cluster consists of
stream sites 1–3, which are all perennial sites. The second cluster is of sites 4 and
5 (intermittent). The third cluster is composed of sites 6, 7, and 8, with 6 being
an intermittent site and 7 and 8 being ephemeral.
Qualitative analysis of cluster composition resulted in contrasting levels of
common taxa and taxa dominance among stream types. Cluster one had 9 exclusive
genera, cluster two had 8, and cluster three had 17 (Fig. 5). All three
clusters shared common taxa ranging from 5–7, not including ubiquitous taxa,
while there were only 9 ubiquitous taxa across all three clusters. Taxa dominance
(the proportions of the four most dominant genera) between stream type is as
follows: perennial sites had the highest taxa dominance (78%), with a community
comprised of Chimarra (36.9%), Hydropsyche (19.5%), Stenelmis (12.3%),
Table 3. ANOVA results of effects of stream type, season, and type-season interactions on: taxa
richness and H', and taxa richness of riffles and pools. GLM results of FFG analysis showing HCA
grouping and stream type. For Bonferroni probabilities *P < 0.05, ** P < 0.005.
F P
Taxa richness
Type 4.347 0.032*
Season 0.562 0.581
Type * season 2.411 0.095
H'
Type 1.876 0.187
Season 2.022 0.167
Type * season 0.356 0.836
Taxa richness of riffles and pools
Type Pool 0.465 0.637
Riffle 8.835 0.003**
Season Pool 0.814 0.462
Riffle 1.057 0.372
Type * Season Pool 2.192 0.119
Riffle 2.316 0.105
Functional feeding groups (FFG)
HCA grouping Collector-filterers (c-f) 28.25 0.002**
Collector-gatherers (c-g) 0.13 0.884
Predators (prd) 1.92 0.240
Scrapers (scr) 3.57 0.109
Shredders (shr) 33.77 0.001**
A priori stream type Collector-filterers (c-f) 8.88 0.023*
Collector-gatherers (c-g) 0.70 0.540
Predators (prd) 1.24 0.366
Scrapers (scr) 1.03 0.423
Shredders (shr) 3.22 0.126
16 Northeastern Naturalist Vol. 18, No. 1
Figure 5. Exclusive, shared, and ubiquitous taxa (genera) of stream types based on cluster
analyses of taxa presence. From a priori classification, cluster one is perennial, cluster
two consists of intermittent sites 4 and 5, and cluster three consists of ephemeral sites 7
and 8 and intermittent site 6.
Figure 4. Hierarchical cluster analysis dendrogram using average linkage between
groups (Pearson correlation) showing 2 low-resolution groups and 3 high-resolution
groups, based on taxa presence at stream sites.
2011 A.N. Santos and R.D. Stevenson 17
and Gammarus (9.3%); intermittent site dominants were Diplectrona (14.0%),
Psilotreta (14.0%), Prostoia (12.0%), and Hydrospyche (10.2%), totaling 50.2%
of the community composition; and ephemeral site taxa dominance was lowest
with Gammarus (11.2%), Prostoia (10.8%), Planorbula (10.4%), and Ironoquia
(9.5%), totaling 41.9%.
Functional feeding groups
Functional feeding group analysis resulted in a clear transition in functional
feeding groups consistent with a priori classification of stream type and HCA
(Fig. 6). From multivariate analysis, major differences were found between the
proportions of collector-filterers (c-f) and shredders (shr) (Table 3) of HCA-produced
clusters. Perennial sites were dominated by collector-filterers (x̅ = 60%,
SE = 0.052), significantly higher (P = 0.002) than intermittent (x̅ = 31%, SE =
0.064) and ephemeral (x̅ = 2%, SE= 0.052) sites. The composition shifted in intermittent
sites as they maintained a relatively even number of collector-filterers
and collector-gatherers and other groups, but the number of scrapers was highest
in intermittent sites (x̅ = 33%, SE = 0.080). Ephemeral sites had a significantly
higher (P = 0.001) number of shredders (x̅ = 45%, SE = 0.134), followed by
relatively equal numbers of predators and collector-gatherers, few scrapers, and
almost no collector-filterers (2%).
Figure 6. Functional feeding group (FFG) composition of stream types (a priori) classifi-
cation and HCA clusters. c-f = collector-filterers, c-g = collector-gatherers, prd = predators,
scr = scrapers, and shr = shredders. Significant differences between c-f and shr of
clusters (P = 0.002, P = 0.001) and c-f of perennial sites (P = 0.023) is shown.
18 Northeastern Naturalist Vol. 18, No. 1
Discussion
Macroinvertebrate diversity and richness of non-perennial streams
Our results indicate that non-perennial streams are as biologically diverse,
if not more so, than perennial streams. The macroinvertebrate diversity (H')
between perennial, intermittent, and ephemeral sites were analogous, and
qualitatively, two unmapped non-perennial streams had the highest grand total
taxa richness and highest grand total H' of all stream sites (Table 2). This
finding implies that the biodiversity of non-perennial streams may be underestimated
because of lack of sampling and their absence from maps (Meyer et al.
2007). An investigation of unmapped non-perennial streams by Stout and Wallace
(2003) and long-term research conducted by the Coweeta Hydrologic Lab
in South Carolina (1985–2000) revealed significant richness of insect taxa in
these streams. Similarly, Dieterich and Anderson (2000) discovered that nonperennial
streams had 20% greater species richness than perennial streams and
reported two intermittent streams with a higher number of taxa than a nearby
perennial one. The high richness and evenness of non-perennial streams,
which was found in this and other studies, may be due to their ebb and flow,
which creates “local habitat variability that favors certain traits” as stated by
Bonada et al. (2007). This environmental variability is favorable to adapted
benthic fauna, but may be inhospitable to many lotic fauna and thus supports
a more even community (Lake 2000). This result is also evident qualitatively
in this study, since perennial sites had high taxa dominance compared to intermittent
and ephemeral.
Although the non-perennial sites showed high evenness compared to perennial
sites, a correlation was confirmed between richness and flow regime consistent
with other studies in which increased richness was related to increased flow
duration (Closs and Lake 1994, Feminella 1996). These studies, however, did not
include ephemeral sites, and further analysis in this study from pairwise comparison
revealed that intermittent site richness was not different from perennial
site richness, whereas ephemeral sites had significantly lower richness. Bonada
et al. (2007) also included ephemeral sites in their study and found no difference
in richness of permanent and intermittent sites while ephemeral was lower. The
inclusion of ephemeral sites created a broader category of flow regime, thereby
facilitating better detection of variation in richness and likely was the reason
these results are different from previous studies that focused only on intermittent
and perennial streams (Vinson and Hawkins 1998).
The lower richness of ephemeral streams is likely due to the extended no-flow
periods that can eliminate taxa (Gomi et al. 2002) or drive them into hyporheic areas
of the streambed (Boulton 1989, Williams and Hynes 1977) just before drying.
Taxa richness has been found to be correlated with riffle permanence (Feminella
1996), and in this study, pairwise comparison confirmed this relationship since it
was the significantly lower richness of ephemeral riffles that was the factor contributing
to the overall lower richness of ephemeral sites. The extremely low flow
of ephemeral sites minimized the formation of riffles, and it can be deduced that the
2011 A.N. Santos and R.D. Stevenson 19
fauna of the ephemeral sites were concentrated in pools because pool richness was
not significantly different between stream type and these fauna contributed to the
overall richness and diversity of these sites. The influence of flow regime on benthic
fauna is also evident at the other extreme, since periods of excessive flow and
spring floods can propel them downstream (Boulton and Lake 1992, Lake 2000)
and significantly reduce richness. The increase in discharge of perennial streams
by almost 60% from fall measures may have temporarily reduced richness of the
perennial sites in the spring, but not to the extent that it reduced the long-term overall
richness of these sites. due to recolonization of fauna.
Community structure of non-perennial streams
Another substantial outcome of this study was the finding of distinct community
structures and FFGs of perennial, intermittent, and ephemeral sites. The HCA
model based on taxa presence-absence data produced uniform results consistent
with the log linear relationship between flow regime and stream type as shown
in Fig. 2. Despite the proximity of the sites and ability of freshwater macroinvertebrates
to rapidly colonize and disperse via drift, migration, and adult flying
(Boulton and Lake 1992, Brönmark et al. 1984, Delucchi 1989) the differences
in community assemblage were discernable, contrary to the findings of other investigations.
Beugly and Pyron (2010) found no difference in macroinvertebrate
community assemblage between perennial and seasonal (non-perennial) sites;
however, their study focused on agricultural headwater stream sites that had been
channelized or converted to drainage ditches, thereby reducing the habitat heterogeneity
of the streams. High faunal similarity between intermittent and perennial
streams was also found by Feminella (1996) when comparing macroinvertebrate
assemblage with flow permanence, but again, that finding was attributed to the
presence of riffles. Delucchi (1988) found less difference in benthic community
structure between riffles of non-perennial and perennial sites than between nearby
pools and riffles, because riffles and pools tend to be inhabited by different benthic
fauna (McCulloch 1986, Scullion et al. 2006), dependent upon their habitat
and food preferences. As previously mentioned, the inclusion of ephemeral sites
which had low riffle occurrence reasonably affected the results of this study since
these sites had significantly higher numbers of shredders compared to perennial
or intermittent sites.
The feeding strategy of stream organisms, according to Merritt and Cummins
(1996), is a result of long-term temporal adaptation to environmental conditions
and is indicative of the significant role of macroinvertebrates in river systems
from headwaters to larger channels. Functional feeding group composition
analysis provided further evidence of divergent macroinvertebrate communities
in streams of varying flow regime. The transition in FFGs is consistent with the
finding that temperate headwater streams are typically dominated by shredders,
while higher order stream reaches are dominated by collectors (Cummins et al.
1989, Vannote et al. 1980, Wiggins and Mackay 1978). Perennial sites were
dominated by collector-filterers, whose numbers decreased in intermittent sites
20 Northeastern Naturalist Vol. 18, No. 1
and were almost non-existent in ephemeral sites. Intermittent sites consisted of
more scrapers than the other sites and had a more even composition of feeding
groups, while ephemeral sites were composed predominantly of shredders. There
were also a higher number of predators, including Odonata, at ephemeral sites,
which may be attributed to faunal congregation at pools prior to streambed drying
(Lytle and Poff 2004), as was found by Boulton and Lake (1992). The linkage
of headwater streams and riparian input of organic material that produce unique
biological processes is demonstrated here by the different feeding-community
structures of macroinvertebrates in these non-perennial headwater streams (Gomi
et al. 2002, Lowe and Likens 2005).
A glance at life in non-perennial streams
Although it was predicted that ephemeral sites would have lower richness
and diversity in this study because of seemingly adverse physical conditions,
they proved to have greater diversity and higher evenness in community
structure than expected. This result is consistent with Fritz and Dodds’ (2005)
findings of reduced taxonomic richness related to harshness or unfavorable
stream conditions while evenness was not affected. It appears that while
many taxa are wiped out from the extended period of no flow, the taxa that
did remain were adapted to the prolonged lack of flow and contributed to
high evenness; an ephemeral site in this study had the highest grand total H'
(1.16), and overall H' was not significantly different between stream types as
previously mentioned. The lower overall temperature of the ephemeral sites
suggests groundwater upwelling, which is common in spring-fed streams
(Hauer and Hill 1996). They harbored a community typical of spring-fed
streams, including Tipula sp. (cranefly), Limnephilus sp. (northern caddisfly),
Glossosoma sp. (saddle-case caddisfly), Rhyacophila sp. (primitive caddisfly),
and Nemoura sp. (spring stonefly) (Ward 1992) among others, some of which
were not found at the other stream sites. The presence of several early instar
and well-developed Odonata species in these tiny streams suggest that these
ephemeral sites may not only provide refuge for early instar individuals, where
they are safe from floods and fish predators (Pritchard 1996), but are also occupied
by multi-year taxa. Stout and Wallace (2003) also found multi-year
taxa in intermittent streams, which supports the theory of species adaptation to
these dynamic habitats.
Non-perennial streams are prime habitat for unique insect fauna (Meyer at al.
2007). One such Odonata species, which was previously on the Massachusetts
Natural Heritage and Endangered Species Program (NHESP) watch-list, is Cordulegaster
obliqua Say (Arrowhead Spiketail), which was found exclusively in
non-perennial streams (intermittent and ephemeral) in this study and in previous
years of preliminary sampling. While most dragonflies’ life spans can range from
6 months to 3 years depending upon the species, the larval stage of the Arrowhead
Spiketail is longer, similar to its congener Cordulegaster boltonii Donovan
(Golden-ringed Dragonfly) which has a larval stage of 2–5 years dependent upon
2011 A.N. Santos and R.D. Stevenson 21
environmental conditions (Ferreras-Romero and Corbet 1999). Long immature
life phases of Odonata are typically associated with cool and/or harsh conditions
that promote seasonal diapause or delayed development. Ranging in size from
6–27 mm, a total of nineteen individuals of the Arrowhead Spiketail were found
strictly in non-perennial sites, while its congener Cordulegaster maculata Selys
(Twin-spotted Spiketail) was found only in perennial sites. The elusive Arrowhead
Spiketail clearly inhabits intermittent streams, but the question of whether
or not they are obligate non-perennial stream dwellers remains unknown.
Threats to non-perennial streams and conservation implications
Freshwater systems are among the most biodiverse and threatened ecosystems
in the world (Allan and Flecker 1993, Master et al. 1998, Saunders et al. 2002). In
particular, the aquatic biota of headwater streams are among the most imperiled
species, as small streams are more sensitive to disturbance and anthropogenic
impacts than larger streams and often they have been heavily altered (Gomi et al.
2002, Lowe and Likens 2005, Meyer and Wallace 2001, Meyer et al. 2007). Landsacpe
alterations including deforestation, urbanization, and water withdrawal have
been the main threats to lotic habitats, and still continue to degrade water quality
and habitat (Meyer and Wallace 2001, Naiman et al. 1995, Richter et al. 1997).
In Massachusetts (MA), non-perennial streams, despite their contribution
to stream biodiversity, have been more vulnerable than their perennial counterparts.
Historically, they have been explicitly excluded in stream protective
regulations such as the MA Rivers Protection Act (St. 1996, c. Chapter 258; MA
DEP 1996) and the Wetlands Protection Act 1997 (M.G.L. c. 131, § 40; MA DEP
1997). Models were also developed to distinguish perennial from non-perennial
streams for the purpose of prioritizing protective status (Bent and Archfield
2002. These outdated regulations and models either stated that streams must
maintain perennial flow to be explicitly protected as lotic waters or that intermittent
streams could be designated as perennial if perennial macroinvertebrate
species were found in them. The latter criteria completely disregarded the fauna
unique to non-perennial streams.
More recently, however, the MA Department of Environmental Protection
(DEP) has appropriately addressed the disparities relative to stream flow
criteria, and the Wetlands Protection Act Regulation 310 CMR 10.00 (2009)
states, in defining streams, “… such a body of running water which does not
flow throughout the year (i.e., which is intermittent) is a stream except for
that portion upgradient of all bogs, swamps, wet meadows, and marshes.”
This advancement is greatly warranted and shows progress in headwater
stream management that has historically been criticized as outdated (Gomi et
al. 2002) and failed to recognize the ecological significance of streams (Allan
and Flecker 1993). Improved environmental management and regulations that
recognize non-perennial streams is advantageous, and perhaps even necessary,
for headwater systems and their inhabitants to adapt to climate change.
It has been projected that climate change effects may alter macroinvertebrate
22 Northeastern Naturalist Vol. 18, No. 1
assemblage and reduce species richness in headwater streams (Durance and
Ormerod 2007), and severe weather and increased precipitation is predicted
for temperate regions due to climate change (IPCC 2007), which will further
alter hydrologic regimes. A more holistic approach is necessary to successfully
manage and conserve river ecosystems and biodiversity in their entirety.
Implications for future studies
This study underestimates the true biodiversity of non-perennial streams since
it not only excluded two families of Dipterans from analysis, but also excluded
sampling of hyporheic zones and sampling of organisms such as amphibians,
bryophytes, diatoms, and nematodes, among others. Most taxa were identified
only to genera due to time constraints, and the study does not determine if there
are obligate species of non-perennial streams, a research question we highly
recommend pursuing in future studies. Non-perennial streams should be further
explored within and across drainage basins, with more sampling replicates and
analyses at the species level for finer resolution. Notwithstanding these limitations,
the study was rigorous since sampling effort was rigorous and consistent
and, as previously mentioned, all stream sites are within the same drainage
network, minimizing differences in most abiotic conditions while maximizing
dispersal of aquatic fauna. Finally and more importantly, ephemeral sites were
included in this study, allowing for a more comprehensive comparison of the
streams, in contrast to most other studies to date, which focused only on perennial
and intermittent streams.
Conclusion
This study demonstrated key points that support the significance of non-perennial
streams. First, it confirmed that non-perennial streams are just as biodiverse,
if not more so, than perennial streams. Second, it verified that non-perennial
streams maintain distinct biological communities with adapted species. Finally, it
stipulated that non-perennial streams should be recognized under environmental
legislation for stream protection as they do contribute to the biological diversity
and ecological function of river ecosystems.
Acknowledgments
Gratitude is given to Robert Chen and the Watershed Integrated Sciences Partnership
(WISP) Program funded by NSF (DGE-0231638, DGE-0538445) at the
University of Massachusetts at Boston (UMASS Boston) for financial support during
the study. This study was also supported in part by NSF grant DBI-0416835. Special
thanks to Betsy Colburn of Harvard Forest, John Ebersole and Richard Kesseli of
UMASS Boston, and Fred SaintOurs for their comments and review, and support and
enthusiasm for this study.
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