Our hypotheses are:
1) Land-use affects aquatic biota in adjoining fluvial systems and responses are proportional to degree of disturbance (length and intensity).
2) The impact of land-use on aquatic diversity results from sediment inputs.

Changes in land-use practices that increase sedimentation in streams cause greater shifts in species composition and ecological function than do changes that stabilize or reduced sediment input. We have broken down the focus into four research approaches.

For more information:
IIB1. Faunal assemblages and ecosystem function in streams draining regions of different land-use
IIB2. Interactions among biota and sediments in streams draining regions of different land-use
IIB3. Long-term patterns of change in aquatic biota
IIB4. Experimental manipulation of sediment inputs

An integrative ecosystem function is one that involves interaction over several trophic levels. Organic matter decomposition in streams is an example of this interaction because it may involve fungi, bacteria, and macroinvertebrates. By measuring stick decomposition as an integrated functional response to land-use, we can achieve an indication of the allochthonous organic matter that contributes to stream energetics (Benfield et al. 1991, Tank et al. 1993). Stream biota are also particularly vulnerable to sediment moving along the bottom as bedload. Seasonal bedload movement is accounted for by using deadfall traps (Shen and Julien 1993).

We synthesized breakdown and transport of allochthonous detritus from many Coweeta stream studies, and demonstrated that leaves generally break down near where they enter streams at a rate predicable from litterbag measurements (Webster et al. 2000). Fine particles of organic matter, however, travel long distances before being metabolized (Webster et al. 1999). We also found that small streams are very efficient in retaining dissolved inorganic nitrogen (Tank et al.2000, Peterson et al. 2001). Flood entrainment of floodplain detritus is a measurable source of organic matter in the middle reaches of the Little Tennessee River, but is nevertheless small compared to leaf fall and in-stream primary production (Neatrour 1999).

P-IIB2. Interactions among biota and sediments in streams of different land-use
Summary:   In southern Appalachian streams, the interactions among macro biota (fish, crayfish), sediments, and algae are not known, but are likely influenced by changes in land-use because of its impact on both light regime and sediment delivery to the channel; this research seeks to understand these interactions.

Increased sedimentation is a primary cause of biodiversity changes in streams (Waters 1995). Sediments and macro biota (fish, shrimp) interact to influence standing crop and composition of algal periphyton assemblages in tropical streams of Puerto Rico and Costa Rica (Pringle et al. 1993, Pringle and Blake 1994, Pringle in press, Pringle and Hamazaki in review). In these streams, macro biota remove sediments and associated algae from benthic surfaces, often reducing total algal standing crop but enhancing the bio-volume of understory algal taxa. In southern Appalachian streams, the interactions among macro biota (fish, crayfish), sediments, and algae are not known, but are likely influenced by changes in land-use because of its impact on both light regime and sediment delivery to the channel. This project investigates these interactions by excluding macro biota from small (~0.5 m2) patches of stream bottom using an electric exclusion technique (Pringle and Blake 1994) that excludes macro biota via continuous, non-lethal, electric pulses produced by 6-volt, solar-powered electric fences.

In year 1 exclusion experiments were done at the nine sites in Little Tennessee Basin (LT). The interactions among sediments, macro biota, and periphyton may vary depending on current regime; therefore, in year 2 we did an exclusion experiment in each of three habitats [pool (0 cm/s), riffle (25-35 cm/s), and run (2-5 cm/s)] in 3 streams draining pasture in the French Broad (FB) basin. In year 3, we experimentally altered sediment load in Coweeta Creek to examine its interaction with macro-consumers and algae. In each of 3 runs, 3 replicates of each of the following treatments were installed in a randomized block design: macro biota present or absent in treatments with natural sedimentation, artificial sediment removal, and sediment augmentation. In years 4, 5, and 6 we assess the interactive effects of nutrient enrichment, sediments, and macro-consumers in pasture or suburban streams in the LT and FB basins by combining electric exclosure experiments with an algal bioassay technique that employs nutrient-diffusing substrata (Tate 1990, Pringle and Triska in press).

The 6-year plan of experiments is summarized

 Chlorophyll A and ash free dry mass were higher, and aquatic insect larvae were larger (>4 mm) in exclusion than control areas of both streams. We concluded that macrobiota influence the structure of southern Appalachian benthic communities by (a)decreasing the amount of organic matter (algae and detritus) available for other consumers, and (b) preferentially preying on certain sizes and taxa of invertebrates (Schofield 2001).

P-IIB3. Long-term patterns of change in aquatic biota
Summary:  We are tracing changes in land-use over time to see if changing land-use is important in determining biodiversity (macroinvertebrate and fish species composition and function) in streams.

 Using watersheds that have been stable over the last 50 - 100 years (as pasture, row crops, and/or forest) we have established what appears to be characteristic, baseline communities to compare to streams that have undergone radical land-use change. In addition, we are addressing the question of how long an area has to be subjected to a particular land-use type for changes in species or functional group composition to occur by re-sampling sites that were sampled decades ago and catalogued in museums or other collections.  Using collection data bases from 9 museums, we have located over 30 collection locales (including species lists and relative abundances) in 2 counties that go back as far as 1888, with more frequent records from 1934 to the present. By assimilating these records into a data base that can be combined with land-use records, fauna is then re-sampled  at sites showing both little and extensive land-use change over the intervening period.

The current invertebrate and fish diversity of aquatic communities is best predicted by land use in the 1950s, indicating that past land use and in particular agriculture produces long term modifications in aquatic systems regardless of reforestation. Land use in the 1970s explains
the current ratios of endemic to cosmopolitan species (Scott and Helfman 2001) while fish density and diversity are affected by upstream than streamside deforestation (Jones et al. 1999). The "legacy effect" and upstream effects point to the importance of large-scale and long-term
restoration, and suggest that localized efforts may contribute little (Harding et al. 1998). A surprising finding was that upland areas of high fish endemism are being invaded, displaced, and homogenized by native species, not by exotics. Native invaders capitalize on habitat degradation from changes in land use. Since traditional metrics of stream integrity overlook native invasion, the early signs of stream ecosystem deterioration may be similarly overlooked (Scott 2001, Scott and Helfman 2001, Scott et al. in review).

P-IIB4. Experimental manipulation of sediment inputs
Summary:  To understand underlying mechanisms creating patterns of diversity and distribution, we are experimentally manipulating  the influence of sediment load on life history and reproductive characteristics of LT fishes (Burkhead and Walsh 1995, Buckley and Bart 1995).

In 2000 and 2001, we tested a representative benthic species native to the area that responds to differences in sediment load (e.g. Etheostoma chlorobranchium ). Three paired channels were constructed  (0.5 m wide x 4 m long) in a Coweeta stream, and used in experiments with added sediment. We hypothesized that sediment reduces growth and reproductive rates of darters ( a native fish species) through 3 major effects:

1) an energy cost by filling in refuge sites, forcing animals to expend more energy to maintain position in the stream,
2) a feeding cost by reducing the amount of available habitat for stream invertebrates, and
3) a reproductive cost such as silting of spawning sites.


Investigators and Collaborators:
Fred Benfield
Gene Helfman
Judy Meyer
Katherine Pringle

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