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Canaan Valley & Environs
2015 Southeastern Naturalist 14(Special Issue 7):65–86
Terrestrial and Longitudinal Linkages of Headwater
Streams
J. Bruce Wallace1,2,* and Sue L. Eggert1,3
Abstract - Headwater streams are important habitats for aquatic organisms. Within forested
regions, headwater streams and riparian corridors function as zones of deposition,
storage, processing, and subsequent transport of organic matter. In forested streams, organic
matter from the adjacent forest provides the major fuel for the aquatic ecosystem.
Along with habitat, headwater streams perform many valuable ecosystem services such
as nutrient, hydraulic, and sediment retention; provide thermal refuges; and function as
important sites of secondary production for higher animals. Headwater streams are being
subjected to many anthropogenic impacts including dams, urbanization, agriculture,
forestry, and mining. Ecologists should promote the importance of headwater streams, as
well as devote more research to examining entire stream networks, rather than just studying
individual longitudinal linkages.
Introduction
Extensive forest cover, rugged relief, abundant rainfall, and thousands of
small streams characterize the Central and Southern Appalachian Mountains.
These small streams are the headwaters, or portions of headwaters, of many large
rivers including the Alabama, Chattahoochee-Apalachicola, Delaware, James,
Ohio, Potomac, Roanoke, Santee, Savannah, Susquehanna, Tennessee, and
Yadkin-Pee Dee. These rivers represent a critical water resource for many major
downstream cities (Wallace et al. 1992). The proper management of headwaters
is vital to maintaining down-river water quality.
In many respects, Canaan Valley, a high-elevation wetland with many tributary
streams, is an excellent example of the effects of past misuses of our headwaters.
Since the area’s early colonization, these streams have suffered serious
impairments, including those from extensive logging, (especially from 1900 to
the 1920s), mining and acid mine drainage, agriculture, urbanization, and road
construction (Meyer and Wallace 2001).
Our objectives here are to emphasize the linkages between headwater
streams and their terrestrial ecosystems, as well as linkages between headwaters
and downstream reaches. Such linkages are critical for understanding lotic
systems and how impairment in one reach may impact downstream segments.
Here we review the literature regarding how these links have contributed to
our overall understanding of several aspects of ecosystems, including 1) detrital
food webs, 2) biogeochemistry and nutrient dynamics, 3) linkages between
1Department of Entomology, University of Georgia, Athens, GA 30602. 2Odum School
of Ecology, University of Georgia, Athens, GA 30602. 3Current address - USDA Forest
Service, Northern Research Station, 1831 Highway 169, Grand Rapids, MN 55744. *Corresponding
author - bwallace@uga.edu.
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ecosystems, and 4) ecological consequences of exotic species, as well as the
role of the linkages as indicators of ecosystem change.
Headwater, Downstream, and Terrestrial Linkages
Role of invertebrates in detrital processing
Most headwater streams in the Appalachians drain forested or previously forested
watersheds. Even in winter, many of these streams have extensive canopy
cover by a dense riparian understory of evergreen Rhododendron spp. In-stream
primary production tends to be a small fraction of total organic matter available
for heterotrophic organisms such as bacteria, fungi, and invertebrates (Webster
and Meyer 1997, Webster et al. 1995). Most of the energy base of these streams
comes from the surrounding forest in the form of coarse particulate organic matter
(CPOM), which consists of leaves, woody debris, and significant amounts of
dissolved organic carbon (DOC) carried by groundwater (Webster and Meyer
1997). The invertebrates in these streams rely primarily on detritus and its associated
microbial assemblage for most of their secondary production (Hall et
al. 2000, Rosi-Marshall and Wallace 2002). In the process of gleaning their
nutrition from this detritus, invertebrates also play an important role in detrital
processing and upstream-to-downstream linkages.
It has long been known that many invertebrates, primarily insects, readily
consume autumn-shed leaves that fall into streams (e.g., Hynes 1941, Petersen
and Cummins 1974, Wallace et al. 1999). How important are these invertebrates
in processing organic matter at the ecosystem level? On 2 different occasions,
2 headwater streams at the Coweeta Hydrologic Laboratory in western North
Carolina were treated with the insecticide methoxychlor. These treatments
caused 4 effects. First, massive invertebrate drift, primarily of immature insects,
resulted in altered community structure (Lugthart and Wallace 1992, Wallace et
al. 1989, 1991b). Second, the abundance, biomass, and secondary production
of invertebrates were reduced, especially of aquatic insect taxa (Lugthart and
Wallace 1992, Lugthart et al. 1990). There was a corresponding increase in the
abundance of non-insect taxa, primarily oligochaetes, copepods, and turbellarians.
Third, there were lower rates of leaf-litter processing without reductions in
microbial respiration or fungal diversity (Cuffney et al. 1990, Suberkropp and
Wallace 1992). Fourth, by the end of the 3rd summer of treatment, the leaf litter
standing crop increased 2.5- to 3-fold in the treatment stream compared with the
2 reference streams (Wallace et al. 1991a). Leaf-litter processing rates remained
low throughout the pesticide treatment, but subsequently increased during recovery
(Chung et al. 1993) due to fairly swift recolonization by aerial adults of
several taxa (Wallace et al. 1991b, Whiles and Wallace 1992).
Assimilation efficiency of most leaf-shredding insects is low: ≈10% (Wallace
and Hutchens 2000), with ≈90% of the ingested material egested as fine organic
particles. These small particles are much more easily transported downstream
than is CPOM. Compared to reference streams, reductions in the processing rates
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of organic matter in the treatment stream were followed by a 5-fold reduction in
the export of fine particulate organic matter (FPOM; Cuffney et al. 1990). During
the experiment, the export of FPOM from this small headwater stream was
reduced by ≈170–200 kg ash-free dry mass (AFDM) (Wallace et al. 1991a). Invertebrate
manipulation changed the stream’s seasonal export response to storms
(Wallace et al. 1991a) and reduced export during storms (Cuffney and Wallace
1989). As the invertebrates recovered in the treatment stream, FPOM concentrations
and export increased.
Effects of the insecticide treatments on the stream’s FPOM export were
as great as those produced by a range of discharges encompassing a 57-y record
(Wallace et al. 1991a). Applying the measure of FPOM export per 100 m
of wetted first-order channel during the pesticide manipulation to the 33.3 km of
first-order channels in the 1600-ha Coweeta Basin, we conclude that the macroinvertebrate
activities of the headwaters contribute ≈6 to 7 tons of FPOM to the
basin’s downstream reaches annually. This study demonstrated the importance
of stream biota, particularly invertebrates, on the processing of CPOM and subsequent
export of FPOM. Collectively, these studies emphasize the importance
of maintaining biodiversity in the headwaters as an important consideration in
downstream management (Lugthart and Wallace 1992, Wallace et al. 1991a).
Importance of longitudinal linkages
In addition to local physical gradients, several kinds of large-scale physical
changes occur along stream gradients. These longitudinal changes are
incorporated into a general framework of riverine ecosystems known as the river
continuum concept (RCC) (Minshall et al. 1983, Vannote et al. 1980). Since the
RCC was proposed, the results from a number of studies around the world have
indicated that changes in energy supply and biological communities as proposed
in the RCC are not applicable to all river systems (e.g., Cushing et al. 1995, Meyer
1990, Statzner and Higler 1985). Many biological attributes of streams in the
Little Tennessee River Basin of the Southern Appalachian Mountains are similar
to those proposed in the original RCC, although some exceptions exist (Grubaugh
et al. 1997). Striking differences in the production of invertebrate assemblages
occurred between the headwaters and downstream reaches of the Little Tennessee
(Grubaugh et al. 1997). Shredders, gatherers, and predators dominated the
invertebrate assemblage production in the headwaters, whereas in the larger
downstream reaches of the Little Tennessee River, 80% of the secondary production
was attributed to filter-feeding taxa, which are adapted to remove particles
from suspension. At the large river sites, production per m2 of substrate was 20
times greater than that of the shaded headwater stream (Grubaugh et al. 1997).
The dissimilarities in production and community structure between up- and
down-stream sites of the Little Tennessee River resulted from unequal distribution
of resources along the river gradient (Wallace and Hutchens 2000). Hall et al.
(2000) and Rosi-Marshall and Wallace (2002) used the trophic basis of production
method (Benke and Wallace 1980) to estimate the annual food consumption by
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invertebrates at up- and down-stream sites. Invertebrates in the headwaters consumed
primarily leaf and amorphous detritus stored in the stream, which is easily
obstructed by woody debris and highly retentive of CPOM. In contrast, primarily
amorphous detritus and animal tissue were consumed in downstream areas (Rosi-
Marshall and Wallace 2002). In the headwater stream draining a deciduous forest,
there was an abundant supply of stored benthic organic matter, which was 8 times
greater than that found downstream. In contrast, annual transport of organic matter
per linear meter of stream of the larger river site exceeded that of the headwater
stream by >260 times. Thus, there were large differences in the form of the organic
matter, namely stored vs. transported, that were available to the benthic animal
assemblages, and these were reflected in the functional structure of these assemblages.
Specifically, shredders and collectors were dominant in upstream reaches,
whereas filter feeders predominated in downstream areas. Filter-feeding organisms
in the Little Tennessee River were supported by the most available resource,
FPOM in transport, which was delivered from upstream areas.
In small headwater streams, where the physical environment stores organic
particles, invertebrate assemblages are dominated by shredders, gatherers, and
invertebrate predators (Wallace and Hutchens 2000). Their feeding actions tend
to decrease the particle size of the organic resources and favor the downstream
export of FPOM, which is more easily transported than the larger CPOM.
In contrast, downstream reaches experience higher discharge, greater stream
power, and less retention, all of which promote the entrainment of organic matter.
Again, the invertebrate assemblage exploits the physical characteristics of the
system, supporting a dominance of filter feeders (Grubaugh et al. 1997), which
promote the retention of entrained organic matter. Thus, in both up- and downstream
reaches, the invertebrate feeding assemblages have evolved to effectively
use the physical characteristics offered by the system. The result is a linkage
between the upstream assemblages that break down and transport organic matter
and the downstream assemblages that feed on the transported material.
Invertebrates are exported from headwater streams via downstream drift and
become important food sources for downstream animals such as fish. Invertebrate
export from fishless headwater streams in southern Alaska was estimated to support
100 to 2000 young-of-the-year salmonids to downstream habitats (Wipfli
and Gregovich 2002).
Terrestrial-aquatic linkages
Forested headwater streams are intimately connected with their adjacent terrestrial
environment (Gomi et al. 2002, Hutchens and Wallace 2002, Richardson
2000). Terrestrially derived inputs of organic matter, leaves, and woody debris
are the fuels that drive productivity within small streams (Fisher and Likens
1973, Richardson 1991, Webster and Meyer 1997). An ecosystem-level manipulation
of organic matter inputs over an 8-y period in the Southern Appalachian
Mountains of western North Carolina provided compelling evidence of the
tight coupling between headwater streams and their riparian habitats. A gill-net
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canopy constructed over a 170-m stream reach, starting at a headwater spring
seep, excluded allochthonous inputs from the surrounding forest (Wallace et al.
1997, 1999). A nearby reference stream served to distinguish the effects of litter
exclusion from natural variation. Most leaf litter disappeared from the exclusion
stream within 6 months. The loss of leaf litter in the stream bottom resulted in
a pulse of organic and inorganic particles as they were flushed from the stream
(Eggert et al. 2012). Then, after 3 years of litter exclusion, all small wood was
manually removed. Two years later, all large woody debris was removed by hand
from the stream channel. The benthic storage of organic material declined further
as the wood was removed from the stream bottom.
Removals of benthic organic matter during the first 4 years of exclusion
resulted in a 78% decline in invertebrate secondary production in the mixed substrates
of the exclusion stream compared to pretreatment years (Wallace 1999).
By the end of the study, secondary production in the exclusion stream was the
second lowest ever measured for a north temperate stream when compared to other
streams (Benke 1993). The shredder and gatherer functional feeding groups,
which depend on organic matter from the terrestrial environment, were impacted
most severely. Some detritivores with flexible feeding habits, such as species
of Tipula spp. (crane flies) and Tallaperla (stoneflies), switched diets from leaf
material to wood prior to wood removal, and then switched to amorphous detritus
after wood removal (S.L. Eggert et al. unpubl. data, Hall et al. 2000). Other
taxa, such as the caddisfly Pycnopsyche gentilis (McLachlan), did not shift their
diets and, consequently, were extirpated from the litter-depleted stream (Eggert
and Wallace 2003). The negative effects of these reduced detrital inputs were
observed up the food chain to invertebrate predators and salamanders, the top
predators in these small streams. Populations of Eurycea wilderae Dunn (Blue
Ridge Two-lined Salamander) were significantly smaller and individuals grew at
slower rates compared to the reference stream (Johnson and Wallace 2005).
The flow of organic materials between terrestrial and aquatic habitats is not
just unidirectional. Rather, organic matter and immature aquatic insects from
the stream bottom can be deposited within the riparian zone during large storms
(Hutchens and Wallace 2002, Wallace et al. 1995). Emerging aquatic insects
travel up into the riparian zone, where they serve as food for terrestrial organisms
(Nakano and Murakami 2001, Sabo and Power 2002, Sanzone 2001).
Biogeochemistry and nutrient dynamics
Anthropogenic inputs of nutrients from the burning of fossil fuels, wastewater
discharges, fertilizer applications, and urban runoff have altered nutrient cycles
in streams of the Appalachians and around the globe (Carpenter et al. 1998).
Headwater streams are important zones of nutrient uptake and thereby reduce
downstream nutrient loading. In the late 1990s, a team of scientists from a number
of institutions around the US started the Lotic Intersite Nitrogen eXperiment
(LINX), in which they studied the transformation and uptake of nitrogen (N)
in various-sized streams at 12 sites, most of which were long-term ecological
research sites representing a diverse range of biomes.
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To trace the uptake and transformation of N, the LINX team released 15N into
streams. Headwater streams retained >50% of the inorganic N inputs (Peterson et
al. 2001). Nitrogen was transformed or removed quickly from small streams, often
within minutes to hours of its input. The shortest uptake distances of N were in the
smallest streams. There was much less uptake, as indicated by longer distances
traveled by N, in larger streams with higher discharge. These findings suggest that
small streams are more important than large ones in regulating N dynamics.
Small streams are often filled with organic detritus from their riparian habitats
and have small cross-sectional areas that allow maximum interface between
substrates and the flowing water. In conjunction with the litter-exclusion study in
the Southern Appalachians, Meyer et al. (1998) found that the biogeochemistry
of dissolved organic carbon (DOC) was altered after the elimination of leaf litter
inputs. DOC generated from leaf litter that had been deposited in small streams
contributed about 30% of the daily DOC export. Since DOC is an important
source of organic matter in stream food webs, its absence from streams that have
been decoupled from their terrestrial habitats would negatively impact higher
trophic levels (Meyer 1994). The average uptake distance of phosphorus and
ammonium increased following leaf-litter exclusion, and increased even more
after woody debris was removed (Webster et al. 2000). In these small streams,
microbial organisms colonize the surfaces of leaves and small woody debris,
and immobilize dissolved nutrients (Tank and Webster 1998, Tank et al. 1998).
Leaves and wood in small streams also serve to slow the flow of water. The presence
of leaves, wood, and their associated microbes reduces the movement of
nutrients to downstream reaches. In essence, small streams are like the vertebrate
kidney—they clean the system of wastes (Meyer 1990).
As with the flow of organic matter between a stream’s channel and its
terrestrial environment, nutrients likewise can move from stream to land. A wellknown
example of this phenomenon is the transfer of marine-derived nutrients
by salmon in the Pacific Northwest (Gende et al. 2002, Naiman et al. 2002). Nutrients
released from salmon carcasses after spawning stimulate the production
of periphyton and invertebrates in headwater streams (Chaloner and Wipfli 2002,
Wipfli et al. 1998). Bears, birds, and other mammals transport nutrients in the
form of salmon carcasses from streams to the terrestrial environment when they
consume carcasses directly (Hilderbrand et al. 1999), or feed on the increased
invertebrate biomass (Gende and Willson 2001). Salmon-derived nutrients may
also increase the growth of riparian vegetation (Helfield and Na iman 2001).
Problems with assessing small streams
As we have said, small streams are critical to the functions of their larger
drainage network. Unfortunately, the value of small streams is often underappreciated
and underestimated (Meyer and Wallace 2001), in part because the
streams are inadequately mapped. First-order streams make up 48% of the total
river miles in the United States (Leopold et al. 1964). However, maps of basin
networks are usually drawn at a scale of 1:24,000 or larger, which excludes the
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smallest streams (Leopold 1994). In the Coweeta Creek basin for example, >98%
of the total stream length is unaccounted for on 1:500,000-scale maps (Table 1).
Many of the smallest streams do not appear on 1:7200-scale maps. It is ironic
that >190 papers have been published on research in Coweeta headwaters that
do not exist according to USGS maps (Meyer and Wallace 2001). For the Chattooga
River watershed in the Blue Ridge Mountains of Georgia, North Carolina,
and South Carolina, only 50% and 75% of the perennial streams were shown on
1:100,000- and 1:24,000-scale maps, respectively (Hansen 2001). Almost none
of the intermittent and ephemeral streams in the Chattooga basin were drawn on
either map.
The problem exists because there are no hydrologic criteria for mapping
ephemeral (shown as dashed blue lines) and perennial (solid blue lines) streams
on US Geological Survey maps. Most headwater streams are mapped according
to the personal aesthetics of laboratory-bound technicians (Leopold 1994).
Hansen (2001) defined perennial, intermittent, and ephemeral streams based on
channel presence, flow duration, stream-bed water level (above channel, near
channel surface, or below channel), aquatic insect presence, material movement,
and channel materials. The state of West Virginia defines “intermittent stream”
as a lotic system draining a watershed of >2.6 km2. West Virginia also uses a
biological criterion in which streams are classified as intermittent if they do not
support species that require a continuous aquatic period of >6 months. Many
small drainages and spring seeps of <20 ha support animals with multiyear life
cycles, but they appear as dashed blue lines on topographic maps. To protect all
of the surface waters of the US under the federal Clean Water Act, biologically
meaningful and hydrologic definitions of the smallest streams must be determined
as soon as possible.
Small streams under assault
Headwater streams in the Appalachians tend to be stenothermal, that is, they
have narrow ranges of temperatures, compared to downstream areas (e.g., Vannote
and Sweeney 1980). They offer thermal refuges to many unique species of
invertebrates and amphibians. Very few taxonomic studies to the species level
have been published about the intermittent and permanent small streams of the
Central Appalachians. However, even given the limited data, Meyer et al. (2007)
and Morse et al. (1993, 1997) point out that much of Appalachia’s biodiversity
Table 1. Stream distances in the Coweeta Hydrologic Laboratory (16.3 km2) in western North
Carolina from maps of various scales.1
Map scale Kilometers of streams
1:500,000 0.8 km
1:24,000 24.4 km
1:7200 56.0 km*
1Data from Meyer and Wallace (2001).
*There are many permanent streams that do appear on the 1:7200 scale maps.
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and unique fauna are found in these headwater streams. Unfortunately, as the latter
authors point out, small headwater streams are under assault from a variety of
anthropogenic disturbances.
Ecological consequences of exotic species
Exotic aquatic species alter the community dynamics of steams and compete
with native species for preferred habitat. With the exception of Oncorhynchus
mykiss (Rainbow Trout) replacing Salvelinus fontinalis (Brook Trout) in secondand
third-order streams of the Southern Appalachians (Larson and Moore 1985),
the headwaters of the Appalachian Mountains have not been tremendously affected
by non-native species. Because Rainbow Trout compete with Brook Trout
for food (Ensign et al.1990), Rainbows may affect the Brook Trout habitat selection
and growth rates (Lohr and West 1992, Whitworth and Strange 1983).
Exotic species also affect the linkage between headwater streams and the
terrestrial environment adjacent to them. Some terrestrial exotics have caused
large changes in headwater stream habitat. For example, outbreaks of terrestrial
non-native invasive species, such as Adelges piceae (Ratzeburg) (Balsam Woolly
Adelgid), A. tsugae (Annand) (Hemlock Woolly Adelgid), and Lymantria dispar
dispar L. (Gypsy Moth), can cause riparian canopy loss, and pesticides used in
eradication protocols enter nearby streams via runoff. Both infestation and treatment
affect stream functions (Griffith et al. 1996, Hutchens and Benfield 2000,
Orwig 2002, Snyder et al. 2002, Webster et al. 2012).
Non-native scales and fungi cause diseases such as dogwood anthracnose
and beech bark disease, which have already invaded forests of the Appalachian
Mountain region. The fungus that causes butternut canker is beginning to spread
rapidly in the region (Ward and Mistretta 2002); another introduced fungus that
causes chestnut blight eliminated Castanea dentata (Marsh.) Borkh. (American
Chestnut) from eastern forests. The blight and resulting eradication of American
Chestnut has had lasting impacts on Appalachian streams including decreased
leaf-litter processing, lower quality of litter inputs, and slower invertebrate
growth rates in headwater streams (Smock and MacGregor 1988, Wallace et
al. 2001). Blight-related Chestnut mortality caused input of large woody debris
into streams between 1934 and the 1950s, before the second logging of the Appalachian
forests. This fortuitous timing facilitated the retention of sediment
and served to stabilize stream channels after subsequent logging (Wallace et al.
2001). Clearly, introduced species within streams and riparian habitats can have
long-lasting effects on the functions of headwater streams.
Agriculture
Filling and tiling of wetlands and headwater streams for agriculture has
greatly reduced the surface area of water in the Appalachians and worldwide.
For example, the drainage density of the Kävlinge River catchment in Skåna,
a southern province of Sweden, was severely altered for extensive agriculture
(Wolf 1956). Between 1812 and 1953, 96.6% of the original surface water area
in the catchment was lost to channelization and drainage for farming. Along
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with the losses of small streams, intensive agriculture has caused nitrate levels
in water to exceed safe drinking levels. Over-fertilization of agricultural land in
low-order sections of river networks often affects downstream river reaches. David
and Gentry (2000) estimated that agricultural sources in Illinois contributed
10–15% of the nitrogen and phosphorus loads to the Mississippi River. Dramatic
shifts in the invertebrate community associated with increased sedimentation
and temperature have been observed from headwater to downstream reaches of
agriculturally impacted streams (Harding et al.1999). Stream fishes are also susceptible
to sediment inputs from agricultural activities (Walser and Bart 1999,
Waters 1995). Along with sedimentation effects, insecticide runoff from agricultural
fields into headwater streams can have deleterious impacts on stream water
quality (Liess et al. 1999).
In the Appalachians, agricultural activity has the potential to modify and reduce
the diversity of stream biota for many years after reforestation (Harding et
al. 1998). In 1940, a mountain farm experiment began at Coweeta Hydrologic
Lab using standard Southern Appalachian farming techniques (mule and plow).
Initially, increases in neither storm runoff nor soil loss were observed, mainly due
to the presence of organic matter in the soil (Hursh 1951). The disappearance of
organic matter from the soil 3 years after clearing resulted in an average of 354
kg of sediment lost per day during May to September 1943. During one storm in
1949, 68,400 kg of sediment were carried into the stream in a 65-minute period.
The effects of cattle grazing on the headwater streams of a mountain watershed
were also demonstrated at Coweeta. No visible effects on stream water
quality were observed over the first 8 summers of grazing (Hursh 1951). After the
9th summer of grazing, however, the 8 head of cattle had trampled an area large
enough to cause increased storm runoff into stream channels, which flushed leaf
packs from the small stream. Without leaf litter to trap sediment and slow the
stormflow, the maximum effects were finally seen well after the experiment had
begun, demonstrating the unique ecosystem services provided by the accumulations
of organic matter in small streams (Hursh 1951).
Urbanization and roads
Urban-growth scenarios predict substantial (0.5 to >10%) increases in population
and income growth for the Central and Southern Appalachians (Wear 2002).
Losses of forested land are expected to occur in areas of increased urbanization.
Deforestation extent is predicted to be greatest in the Southern Appalachian
Piedmont, the Blue Ridge Mountains, the Ridge and Valley, and the Southern
Cumberland Plateau (Wear 2002). The Canaan Valley has also experienced rapid
growth in the last 30 years due to increases in recreation, tourism, and residential
development (Waldron and Wiley 1996).
The replacement of forested land and riparian habitats with impervious surfaces,
such as roads and rooftops, alters stream hydrology and geomorphology
(Elmore and Kaushal 2008, Finkenbine et al. 2000, Paul and Meyer 2001, Rose
and Peters 2001). Increases in surface runoff associated with storm flow lead to
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declines in water quality, including increased turbidity and bacterial populations
(Bolstad and Swank 1997). Pesticide, herbicide, and fertilizer runoff into nearby
streams during storms increased with urbanization as well (Hoffman et al. 2000,
Winter and Duthie 2000). Increased sediment runoff and erosion from construction
sites causes channel widening (Nelson and Booth 2002, Trimble 1997),
resulting in habitat losses for aquatic life (Waters 1995). Fish species diversity
and abundance declined significantly in Tuckahoe Creek, VA after 32 years of
increased road construction, commercial and residential development, and riparian
losses (Weaver and Garman 1994). In streams of southeastern Pennsylvania,
only pollution-tolerant fish and macroinvertebrate species survive in urbanized
streams (Kemp and Spotila 1997). Urbanization has also been associated with
less-diverse, pollution-tolerant macroinvertebrate assemblages in streams of
southeastern Wisconsin (Stepenuck et al. 2002), south-central Maine (Huryn et
al. 2002), and Georgia Piedmont (Roy et al. 2003).
Measurable aquatic degradation occurs as ~10% of a watershed’s area becomes
impervious area (Booth and Jackson 1997; Wang et al. 2002, 2001).
Construction of impervious surfaces, such as roads, has long been associated
with decreased water quality of nearby streams (Duncan et al. 1987, Forman and
Alexander 1998, Jones et al., 2000, Wemple et al. 2001). Ruth Cooper Allman, a
lifelong resident of Canaan Valley, also wrote of the disappearance of “millions
of Brook Trout in the streams when pioneers came to the valley” (Allman 1976).
The construction of West Virginia Route 32 in 1932 resulted in so much sediment
flowing into nearby streams that residents reported, “the water became so muddy
in the spring that the fish either died or had to leave as they could not live in the
muddy water” (Allman 1976).
Skid trails and logging roads are often major sources of sediment in streams
located in logged watersheds, and their presence has significant effects on
aquatic organisms (Tebo 1955). Soil erosion from logging roads has been studied
extensively at the Coweeta Hydrologic Laboratory (Swift 1988) and Fernow
Experimental Forest (Trimble 1977). Guidelines for building environmentally
friendly and low-cost forest roads have been pioneered through demonstration
projects at both sites (Kochenderfer and Helvey 1987; Swift 1984a, b). Longterm
monitoring at one of these demonstration projects (Watershed 7 at Coweeta)
showed that copious sedimentation occurred only during storms immediately
following road construction (Swank et al. 2001).
Forestry practices
Most Appalachian headwater streams were exposed to a major disturbance
around the turn of the 19th–20th century with the widespread logging of the eastern
deciduous forest. An excellent and informative account of the early logging
in West Virginia, including the Canaan Valley and surrounding area, can be found
in Clarkson (1964). Early logging obviously degraded streams as the logs were
often floated downstream with the aid of splash dams, thereby scouring stream
beds. Based on photographs (Clarkson 1964), it is evident that many log slides
were constructed in the channels of small headwater streams.
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In addition to habitat alteration due to stream scour by floating logs, logging
also causes other problems for streams and headwater biota. These effects
include changes in stream temperature regimes (Swift 1983); greater discharge
and altered hydrology (Bormann and Likens 1979, Swank et al 2001); increased
levels of nutrients (Swank et al. 2001), solar radiation, and primary production
(Duncan and Brusven 1985, Noel et al. 1986, Webster et al. 1983); more sediment
export (Gurtz et al. 1980, Swank et al. 2001, Webster and Golladay 1984); and
changes in the kinds and amounts of dissolved organic matter from the adjacent
terrestrial ecosystem (Meyer and Tate 1983). These changes can be accompanied
by large changes in the energy base of the stream, with a shift from allochthonous
detritus to autochthonous production (Webster et al. 1983).
The physical and energy-base changes can lead to large shifts in the structure
of the macroinvertebrate community (Gurtz and Wallace 1984, Newbold et al.
1980, Noel et al. 1986, Stone and Wallace 1998). Invertebrate taxa with short life
cycles and the ability to exploit increases in primary production greatly increase
in population abundance, biomass, and productivity (Wallace and Gurtz 1986).
Studies in the Central (Griffith and Perry 1991) and Southern Appalachians (Benfield
et al. 2001) show that long-term patterns of leaf litter breakdown can be
altered for many years after logging. However, depending upon the extent of terrestrial
succession, invertebrate assemblages can revert toward their pre-logged
and forested reference stream condition in about 15 y, although differences remain
between reference and logged streams (Stone and Wallace 1998).
Most of the studies cited above were performed in Southern Appalachian
streams at the Coweeta Hydrologic Laboratory in western North Carolina. However,
the data clearly show that logging causes an array of physical and biotic
disturbances to streams draining logged catchments. The logging effects that
probably cause the largest changes in benthic assemblages include increased solar
radiation, altered thermal regimes, greater sediment with associated physical
disturbance of the substrate, and increased water yield and sto rmflow.
Dams and impoundments
Dams and impoundments alter the ecology, geomorphology, temperature,
and hydrology of river networks (Chin et al. 2002, Nislow et al. 2002, Stanford
and Ward 2001). Alterations of flow regimes and stream network fragmentation
that accompany impoundment lead to direct habitat loss, water quality
degradation, and decreased biodiversity of aquatic species (Bunn and Arthington
2002, Dynesius and Nilsson 1994).
Small impoundments are common in higher elevations in the Central and
Southern Appalachians (Menzel and Cooper 1992, Merrill 2001). The number of
these small impoundments, mostly in the form of ponds <10 ha in area, is staggering.
In one northern Georgia Piedmont watershed, 46% of 6167 headwater
streams have been impounded (Merrill 2001). Over 5400 of these small ponds
had inundated 8% of the total stream length; the many dams severely fragmented
the river network. Approximately 31% of the stream length had a downstream
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impoundment within 5 km. Because 1:24,000 maps were used in this analysis,
these values are most certainly underestimates due to streams and impoundments
unmapped at this scale. Dam-building and feeding activities by Castor canadensis
Kuhl. (Beaver) can also negatively affect the quantity and quality of headwater
streams. In portions of the Canaan Valley, increasing Beaver populations have converted
17% of the total stream length to pond habitat and may contribute to lower
dissolved oxygen levels in downstream reaches (Synder et al. 2006).
Headwater streams flowing into impoundments have lower biological integrity
than free-flowing streams (Merrill 2001). Fortunately, much of this impact
can be reversed with dam removal, although responses vary between up- and
down-stream areas, which proceed at different rates (Bednarek 2001, Hart et al.
2002). Longitudinal linkages are reestablished after dam removal, and mobile
organisms, such as fish, can respond relatively quickly (Bushaw-Newton et al.
2002). Changes in channel geomorphology, and in sediment and nutrient transport,
may take longer to respond to dam removal (Doyle et al. 2002, Hart et al.
2002, Pizzuto 2002, Stanley and Doyle 2002).
Mining
About 2017 km2 of the Central and Southern Appalachians were surface
mined for coal between 1930 and 1971. Some 32% to 48% of this mined area
was not reclaimed, and abandoned mines represent an on-going problem (Samuel
et al. 1978). Invertebrate and fish populations were reduced for >20 years after
mining operations ended. Odonata (Dragonflies and Damselflies), Ephemeroptera
(Mayflies), Megaloptera (Alderflies, Dobsonflies and Fishflies), and Diptera
(True Flies) were severely affected (Roback and Richardson 1969). Some of
West Virginia’s rivers have been so severely degraded by coal mining, stream
acidification, and industrialization, especially chemical plants, that only the more
tolerant species of benthic organisms can inhabit them (Pond et al. 2008, Snyder
et al. 2006, Tarter 1976). Selenium concentrations in mining effluent can reach
levels 15 times the threshold for toxic bioaccumulation in aquatic organisms
(Lemly 2008). These concentrations have caused teratogenic deformities and
reproductive toxicity in fish of the Mud River ecosystem, WV (Lemly 2008).
In recent years, heated controversy has developed around the practice of
mountaintop removal and valley-fill coal mining (Palmer et al. 2010). As of 1998,
some 1450 km of streams, primarily in West Virginia, Kentucky, Tennessee, and
Virginia had been permanently buried by overburden from mining operations
(USFWS 1998). Since these estimates of filled streams were made from a USGS
1:24,000-scale map, there is no doubt that the estimate of 1450 km is a significant
underestimate. This continues to be one of the most important environmental
concerns facing headwater streams in West Virginia.
Conclusions
Research has yielded much data and increased our knowledge of functional
aspects of headwater streams. In the last 3 decades, we have studied stream
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segments along longitudinal reaches spanning multiple stream orders (Grubaugh
et al. 1997, Vannote et al. 1980). We have also made progress toward understanding
how physical factors, such as local geomorphology and discharge, influence nutrient
uptake, retention, and transformation, as well as how they affect detritus
retention, food webs, and the functional structure of biota. However, we need to
apply what we know about individual streams and longitudinal linkages to entire
stream networks (Fisher 1997, Meyer and Wallace 2001).
Such applications would inform the debate about mountaintop mining and
the burial of small streams during that process. Studies of streams as entire networks
are especially important because we are currently burying steams without
knowing the basin-wide consequences of these practices. Headwater streams
are exceptionally valuable sites of nutrient uptake and retention. Research had
already demonstrated many biotic and abiotic effects of stream alteration. Science
can help the public and policy-makers to answer several questions that have
arisen: How much of an increase in downstream nutrients, as well as harmful
chemicals in our water supplies, are we willing to accept as a result of buried
headwater streams? Are we willing to accept the altered hydrology with the propensity
to raise downstream flood peaks? These floods are associated with the
flushing of organic matter, scouring of algal food resources, and enhanced drift
of aquatic animals.
The burial of headwater streams eliminates the linkages among forests, headwaters,
and downstream segments. Complete biotic inventories are required for
most, if not all, of the buried streams. It is obvious that, based on their invertebrate
assemblages, some streams destined to be buried are currently of excellent
quality. How much concern do we place on the loss—in perpetuity—of this biotic
diversity and habitat? How many long-term, irrevocable cumulative effects to
downstream rivers is the public willing to accept? Finally, once the environment
has been degraded and the resources are diminished, can we maintain a reasonable
quality of life? These important questions directly affect a substantial area
of the Central Appalachians, and in many instances, decisions are being made
without considering the consequences of our actions.
Acknowledgments
We appreciate the efforts of Dr. George Constantz and Mr. Ron Preston in organizing
the Canaan Valley and its Environs Celebration and this special issue. We thank the
editors and reviewers for editorial comments that improved this manuscript. Much of the
information reported here was supported by grants from the National Science Foundation
(Ecosystems Studies Program and Long-term Ecological Research) and the US Department
of Agriculture Forest Service. We thank these agencies for their continued support
of research on headwater streams.
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