The genesis of these sediments has been ascribed to either microbial or chemical processes. Microbially, the flocculates are thought to be formed by acidophilic, autotrophic bacteria that oxidize the reduced iron and sulfur in pyrite (Bechard and others, 1993; Ehrlich, 1990; Ingledew, 1982; Tuttle and others, 1969). Chemically, the flocculates are thought to be formed by oxidation of pyrite by ferric iron (Moses and others, 1987; Singer and Stumm, 1970). The flocs can contain a significant amount of sulfate (Bell and others, 1990; Bigham and others, 1996; Herlihy and others, 1988; Murad and others, 1994; Ross and others, 1982), as well as toxics and trace metals (Norton and others, 1991; Rose and others, 1979; Smith and others, 1993).
Acidic creeks having flocculates and precipitates derived from AMD are typically considered to be sterile habitats because fish and molluscs are absent, as are the aquatic insects that are used as indicators of non-polluted environments (Roback, 1969). However, creeks affected by AMD are not sterile. Instead, insects form the top of the acid-tolerant abbreviated food chain; algae, photosynthetic protozoans, and bacteria form the bottom (Lackey, 1938; Tremaine and Mills, 1989).
Fish disappearance in AMD-affected creeks is ascribed to a variety of biological, chemical, and physical factors. These include direct acid toxicity, mobilization of toxic trace elements, disruption of the food chain, toxic effects of increased soluble aluminum, disruption of fish reproduction and recruitment, and disappearance of fish spawning sites (Burrows, 1977; Burton and Allan, 1986; Hoehn and Sizemore, 1977; and Tremaine and Mills, 1989). To this list should be added the effects of the different AMD sediment types: ferric hydroxide formation may decrease the oxygen available to stream inhabitants; suspended iron-rich particles can inhibit light penetration, reduce photosynthesis, and cause difficulty for stream insects to stay in place in the current; and iron precipitates can coat the stream substrate, cover gills and body surfaces, smother fish eggs, and eliminate hiding places (Kimmel, 1983).
During the course of our individual studies on microbiology, remote sensing, chemistry, mineralogy, and fish and invertebrate community structure in creeks affected by AMD in Virginia and Pennsylvania, we (the ever-expanding "Red Slime Team") have also observed the formation and transport of these new-formed sediment types and suggest that formal study of them should be undertaken. We hypothesize that aquatic insect habitat destruction by these AMD-derived sediments may in some manner be a factor in fish disappearance where toxic metals are not abundant.
A tributary having neutral pH and red-orange flocculates discharges into Contrary Creek in the vicinity of State Highway 522 bridge. Average pH is 6.2; in monthly collections in 1994 and 1995, it varied between 5.6 and 7.0 (Anderson, 1996). Similarly, specific conductivity varied between 40 and 200 uS/cm.
Swatara Creek. Swatara Creek, a tributary of the Susquehanna River, has its headwaters in Schuylkill County in the Southern Anthracite region of Pennsylvania (Figure 2). The creek is degraded by numerous discharges from abandoned coal mines. One of the largest discharges, the Rowe Tunnel, drains an underground mine complex of about 16 km2 and forms the headwaters of Lorberry Creek. Rowe Tunnel has an average discharge of 2,500 gpm (5.6 cfs) and is the predominant source of acidity in the Swatara Creek watershed (Fishel, 1988). The discharge water has pH of 4.5 to 5.5 and iron concentration greater than 5 mg/L (Anthracite Research and Development Company, 1972; Berger and Assoc., 1972; Growitz, 1985).
The foci of upper Swatara Creek studies include chemistry, microbiology, mineralogy, remote sensing, and fish and invertebrate community structure (Cravotta and Trahan, 1996; Fishel, 1988; Robbins and others, 1996; Wood, 1996). Analysis of trace metals and nutrients in dissolved and suspended fractions are currently underway. Preliminary biological surveys of aquatic insects have also been undertaken.
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|Figure 1. Contrary Creek, Southern Virginia (Mineral, VA quad).|
The flocculates are flushed during storms. In a monitored storm during Hurricane Danny, 8-10 cm of oxidized, acid sediment was measured downstream in Lake Anna (Bell and others, 1990).
Microbiology. Microbial studies have been conducted on flocculates, rock precipitates, and precipitates deposited in situ on microscope slide (Robbins and others, 1996; Mills and Mallory, 1987). In acidic Contrary Creek, loose flocs appear as iron-rich colloids enmeshed with rod-shaped bacteria. Precipitates contain thiobacilli, colorless filaments, pale orange holdfasts of Gallionella ferruginea, and filaments of the green alga, Ulothrix. Slides are colonized by rods, filaments, holdfasts of Leptothrix discophora, and diatoms.
The neutral pH tributary contains flocculates composed of empty sheaths of L. ochracea and holdfasts of L. discophora.
Remote sensing. The spectral characteristics of the flocculates and precipitates were studied by hand-held spectroradiometer and aerial Digital Multispectral Video (DMSV) (Anderson, 1995; Anderson, 1996; Robbins and others, 1995b). The reflectance of the flocs and precipitates is high in the wavelengths 650 to 750 nm. DMSV data show that the loose flocs and other sediment from Contrary Creek enters Lake Anna, travels as a yellow front, and drops out quickly at the mouth of Contrary Creek (Anderson, unpublished data).
Chemistry. The chemistry of flocculates and precipitates has not been studied directly. However, analysis of unfiltered water (laboratory pH 3.1) that carries flocs contained the following metals in mg/L: Cd (0.006), Cu (0.66), Fe (4.2), Mn (2.3), Ni (0.02), and Zn (3.73) (Krishnaswamy, 1996). Analysis of sediment (laboratory pH 2.3) that includes surficial precipitates contained Cu (211), Cd (51.3), Fe (272,000), Mn (87.5), Ni (27.20), and Zn (130).
Mineralogy. Samples of flocculates concentrated from a pool at the discharge of the Sulphur Mine, flocs in Contrary Creek and the neutral seep, and a hard brown crust that was scraped from rip-rap in the stream bed were analyzed by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). All were composed of poorly crystalline ferrihydrite that yielded a single broad peak at 2.5 Å by XRD analysis (see Robbins and others, 1996). Porous zones within the crust are composed of aggregates of microspheres that may be cocci. Energy-dispersive analysis shows the acid flocs are composed of Fe>S>Si>Al.
Aquatic insects. Unidentified odonate nymphs swim in and out of the flocs and attach to the rocks having precipitate. Trichoptera and Dytiscidae have also been collected (Anderson, unpublished data). Along ledges that project into Contrary Creek, abundant tubes of bright red chironomid larvae (Chironomus?) proliferate at the outflow of Sulphur Mine.
The neutral tributary that drains into Contrary Creek contains Dixidae and Oligochaeta (Anderson, unpublished data).
Fish. One dead fish was observed and is considered to have washed into the acidic portion of the creek during a storm.
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|Figure 2. Upper Swatara Creek watershed, east-central Pennsylvania (Headwaters and Zerbe sites on Minersville, PA quad; Orchard Overflow and Rowe Tunnel sites and Lorberry Creek on Pine Grove, PA quad; Good Spring Creek site on Tremont, PA quad)|
Microbiology. Microbial studies have been conducted on flocculates and precipitates at several sites in the watershed. At Rowe Tunnel (pH 5.0), colorless attached and motile bacterial rods were noted. At pH 4.2 Swatara Creek Headwaters, the red floc in the stream contained colorless bacteria (fat hollow spirals), iron bacteria (masses of Gallionella), algae (Ulothrix), and protozoans (big clear motile type). The reddish precipitate on rock ledges contained masses of hollow iron tubes that are characteristic of tubes left by green algae such as Ulothrix that appear to oxidize iron during photosynthesis.
Remote sensing. Spectral reflectance measurements and DMSV images were taken at several sites in the Swatara Creek watershed to test if specific wavelengths discriminate acid from neutral drainage. Point discharges of acid were noted along Orchard Overflow and Rowe Tunnel. Swatara Creek at the Headwaters site is neutral.
Chemistry. The chemistry of Swatara Creek is moderately acidic. Co, Cu, Ni, and Zn are detectable in the tens of mg/L range in filtered water (Wood, 1996).
Aquatic insects. A preliminary benthic invertebrate investigation was conducted in September, 1996, at two sites. After a one hour search, one sialid larva was discovered near Zerbe and one individual chironomid larva was found at Good Spring Creek (Bilger, unpublished data).
Fish studies. A fish community investigation was conducted at 6 sites in the watershed in September, 1996. Approximately 1,200 individuals were collected, representing 25 species (Bilger, unpublished data). In general, abundances and numbers were inversely correlated with pH. Trout have been found in upstream reaches of Swatara Creek and downstream of its junction with Lorberry Creek (Cravotta, unpublished data).
Our studies have elucidated several potential directions for future collaborative work. These include sediment characterization and mapping, characterization of regional variability of benthic invertebrate community structure and composition in AMD streams, experiments aimed at understanding the relationship between microbially-generated sediment and aquatic communities, and experiments testing fish survival and growth in AMD water from which Al has been removed. Collaborative experiments such as these might prove useful in the establishment of cause and effect relationships between sediments in AMD environments and the major aquatic communities.
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ELEANORA I (NORRIE) ROBBINS,USGS-Geologic Division, National Center, Reston, VA: As an economic bio-geologist/microbiologist in the Eastern Energy Resource Surveys Team, supported by the Energy Program, current responsibilities include identifying biological/chemical process that eliminate metallic products from acidic coal-mine drainage. Remote sensing techniques to discriminate between acid and neutral drainage are used in conjunction with a large team of other federal and state agencies and university students. Research conducted during the past 27 years has dealt with prospecting for economic accumulations of titanium for the SST, assessing the petroleum potential of the Atlantic Outer Continental Shelf, linking the deposition of coal, petroleum, and ore deposit precursors in modern and ancient rift valleys, analyzing the past histories of modern Great Lakes wetlands, and developing microbial ecology methods for geologists and hydrologists.
CHARLES A. CRAVOTTA III,USGS-Water Resources Division, Hydrologic Investigations Section, Lemoyne, PA: As a hydrologist/geochemist, current responsibilities include field and laboratory studies on geochemical controls and treatment of drainage from coal mines in Pennsylvania. Hydrology, chemistry, mineralogy, and microbiology of subsurface and surface water environments are emphasized in studies of acid-forming/-neutralizing and transport processes. During the past 10 years studies have evaluated effects on limestone dissolution from metal hydrolysis and biofilms; on microbial pyrite oxidation from nutrients in sewage sludge and fertilizer used for reclamation; reduction of pyrite oxidation by alkaline addition and selective handling of pyritic materials at surface mines; and on water chemistry considering water-rock interactions along flow paths.
GREGORY B. DESMOND, Cartographer,USGS-National Mapping Division, National Center, Reston, VA: Team Leader for the Geometronics Team within the Mapping Applications Center. He is working on the USGS South Florida Ecosystem Program and coordinates remote sensing applications and surveying projects.
ROBERT R. (BOB) SEAL, II,USGS-Geologic Division, Eastern Mineral Resource Surveys Team (EMRST), National Center, Reston, VA: Bob's main activities center around his duties as Lab Chief for the EMRST Stable Isotope Lab and as Project Chief for the EMRST Environmental Behavior of Mineral Deposits Project. Current research activities include stable isotope studies (H, C, N, O, S) of (1) waters and solids from mine drainage from massive sulfide deposits in the eastern US, (2) the origins of base and precious metal massive sulfide deposits in Maine, (3) the origins of gold deposits in the Carolina Slate Belt in SC, and (4) the sources of sulfate in the south Florida ecosystem. Past studies have included lake and pore water stable isotope characteristic of Lake Baikal (Siberia), Russia.
CRAIG D. SNYDER, Research Ecologist,USGS-Biological Resources Division, Leetown Science Center, Kearneysville, WV: Current research efforts center on evaluating the significance of recent landscape changes on aquatic communities. Recent studies include a watershed study designed to assess linkages among upland, riparian, and instream habitat and their respective influence on fish community structure; a survey of aquatic habitats and species in the Canaan Valley Wildlife Refuge with the goal of determining the relative importance of local- and landscape-level habitat measurements to the distribution of aquatic species; and a comparative study of aquatic biodiversity in streams draining different forest types in two National Parks to evaluate the potential importance of eastern Hemlock to park-wide diversity. Past work has included the study of acid mine drainage, measuring long-term effects of chronic exposure to heavy metals, and the effects of natural disturbances on aquatic invertebrate species.