Pennsylvania Streams Research Articles

Stonefly (Plecoptera) species of an acidic intermittent stream in southwestern Pennsylvania, USA, comparison with a circumneutral perennial stream and consideration of survival strategies

The stonefly fauna of an acidic intermittent unnamed tributary to Indian Creek, southwestern Pennsylvania, is described and compared with the fauna of a nearby circumneutral, perennial stream, Camp Run. The unnamed tributary had a distinctive stonefly fauna comprised of 22 species representing seven families, with the highest species richness and abundance in the families Capniidae, Leuctridae and Nemouridae. Allocapnia nivicola (FITCH) was the dominant species. Ostrocerca albidipennis (WALKER) and Leuctra ferruginea (WALKER) were the secondary dominants. Perlids and pteronarcyids were absent. Camp Run had 22 stonefly species representing all nine North American stonefly families, with the highest species richness or abundance in the Capniidae, Leuctridae, and Peltoperlidae. Thirteen species were found in both the unnamed tributary and Camp Run, including six species of Leuctra. Univoltine and semivoltine species were present in both streams. Published accounts of life history, behavior, and acid tolerance were reviewed to explain presence or absence of stonefly species in the unnamed tributary.

Impacts of Steel Mill Slag Leachate on the Water Quality of a Small Pennsylvania Stream

ABSTRACT Leachate from a 20 million ton steel mill slag dump significantly influenced the chemistry of a small western Pennsylvania stream, Nine Mile Run. Alkalinity, acidity, pH, calcium, and magnesium were significantly altered by the alkaline leachate that seeped from the toe of the 95 hectare slag dump. These leachates increased the mean pH of the receiving stream from 7.7 to 9.3, and the maximum pH measured was 11.1. Alkalinity decreased, and Ca++ and Mg++ came out of solution forming carbonate flowstone-like layers over the streambed.

Correlation between Temperature, Colonization Rate, and Population Density of the Diatom Cocconeis placentula in Freshwater Streams

ABSTRACT We examined the correlation between water temperature, colonization rate, and population density of the freshwater diatom Cocconeis placentula over two complete annual cycles in two southeastern Pennsylvania streams. Previous research in these streams showed that differences in diatom community structure between spring and fall were not explained by day length, so water temperature was investigated as the controlling factor in the density of a single common genus in those communities. During the June 1992 to June 1993 period, the diatom population was monitored continuously at two-week intervals using 14-day colonized glass slides; during 2000–2001, colonization and monitoring was over 28-day intervals. Average monthly temperatures and diatom densities were analyzed with a Spearman rank-correlation test for each stream. There were significant positive correlations between the population density of C. placentula and water temperature at all population sizes in both streams in both years.

Acid Stream Water Remediation Using Limestone Sand on Bear Run in Southwestern Pennsylvania

AbstractInstream limestone sand application is used at many sites in Pennsylvania to neutralize acidic stream water resulting from acid deposition. However, questions remain about the effectiveness of limestone sand in the treatment of acid waters, such as reduced contact time at high flow, remobilization of aluminum, and adverse effects on macroinvertebrates. A 1‐year evaluation of limestone sand application to Bear Run, an acidic stream in southwestern Pennsylvania, was begun in 1999. Another nearby acid stream, Linn Run, served as a control. Water quality during baseflow and episodic acidification events, along with fish and macroinvertebrates, were monitored to evaluate impacts of the sand application. Hydrogen ion (H+) concentration and total dissolved aluminum (TDA) were significantly reduced, and acid neutralizing capacity was significantly increased downstream of the limestone sand application compared with the upstream site on Bear Run. These parameters at the downstream sites were also different (∝ 0.10) from the comparable sites on the control stream. TDA and hydrogen ion concentrations were significantly decreased (∝ 0.10) compared with concentrations before the sand application to Bear Run but not on the control stream. No fish were present upstream of the sand application site, and only a few fish were found downstream at the mouth of Bear Run. Standing crop, number of taxa, and Shannon‐Weaver diversity index values indicated that macroinvertebrate populations were negatively impacted 300 m downstream from the sand application and improved at the site 1,600 m downstream. Although water quality was improved on Bear Run, benefits to macroinvertebrates depended on downstream location, and fish populations did not show improvement.

The Influence of Acidic Runoff Episodes on Slimy Sculpin Reproduction in Stone Run

Abstract Much research has been devoted to the effects of acidic runoff episodes on populations of brook trout Salvelinus fontinalis. Less is known about slimy sculpin Cottus cognatus and why their numbers have declined in acidified streams. Adult tolerance of low pH and aluminum (Al) toxicity is similar in these two species. Slimy sculpin spawn in the spring, when high stream flows elevate concentrations of toxic Al and decrease stream pH in acid-sensitive watersheds. We hypothesized that acidic episodes in spring were a source of stress for slimy sculpin and hindered their reproduction. We tested this hypothesis by examining the mortality, behavior, whole-body sodium concentrations, and spawning among slimy sculpin exposed to ambient conditions during the spring spawning period in two Pennsylvania streams, Stone Run (an episodically acidified stream that formerly contained slimy sculpin) and Benner Run (a stream with slimy sculpin that does not experience severe acidic episodes). Our hypothesis was supp...

Colonization History Masks Habitat Preferences in Local Distributions of Stream Insects

Habitat selection is often viewed as a major process determining the distribution and abundance of animals. If animals have limited control over their dispersal, however, they may sometimes be unable to colonize preferred habitats. In such cases, observed spatial variations in abundance may reflect the vagaries of colonization rather than true habitat preferences. Our study examined whether local variations in the density of stream insects are related to habitat quality or colonization history. We focused on larval black flies (Simulium vittatum), a representative group of suspension feeders that exhibit strong preferences for habitats characterized by high near-bed velocities. Despite these preferences, variations in the density of S. vittatum larvae across benthic substrates within the riffles of a Pennsylvania stream were often weakly related to velocity. Moreover, densities on substrates of similar velocity varied by more than six-fold. We conducted a field experiment to test whether these density differences reflect habitat preferences and employed a short-term behavioral assay based on larval emigration to quantify preference. We used a block design to compare emigration rates from paired substrates that had been colonized by markedly different larval densities despite their similar velocities. After removing these larvae, we added larvae to both substrate types in equal numbers, following which we measured larval emigration. There was no significant difference in emigration between these paired substrates even though statistical power was high, which indicates that the large density differences present at the end of the colonization period on substrates of similar velocity were unrelated to habitat preferences. There were, however, significantly more departures from blocks of substrates in lower velocities than from those in higher velocities, demonstrating that the duration of our experiment was sufficient for black fly larvae to express their habitat preferences. These results are consistent with the hypothesis that dispersal constraints associated with the settlement of drifting larvae limit their ability to reach preferred habitats. In fact, related studies predict that larval settlement rates are lowest in the high velocity habitats preferred by larvae. We conclude that such dispersal constraints may be important for a wide variety of freshwater, marine, and terrestrial organisms that are transported by moving fluids.

COLONIZATION HISTORY MASKS HABITAT PREFERENCES IN LOCAL DISTRIBUTIONS OF STREAM INSECTS

Habitat selection is often viewed as a major process determining the distribution and abundance of animals. If animals have limited control over their dispersal, however, they may sometimes be unable to colonize preferred habitats. In such cases, observed spatial variations in abundance may reflect the vagaries of colonization rather than true habitat preferences. Our study examined whether local variations in the density of stream insects are related to habitat quality or colonization history. We focused on larval black flies (Simulium vittatum), a representative group of suspension feeders that exhibit strong preferences for habitats characterized by high near-bed velocities. Despite these preferences, variations in the density of S. vittatum larvae across benthic substrates within the riffles of a Pennsylvania stream were often weakly related to velocity. Moreover, densities on substrates of similar velocity varied by more than six-fold. We conducted a field experiment to test whether these density differences reflect habitat preferences and employed a short-term behavioral assay based on larval emigration to quantify preference. We used a block design to compare emigration rates from paired substrates that had been colonized by markedly different larval densities despite their similar velocities. After removing these larvae, we added larvae to both substrate types in equal numbers, following which we measured larval emigration. There was no significant difference in emigration between these paired substrates even though statistical power was high, which indicates that the large density differences present at the end of the colonization period on substrates of similar velocity were unrelated to habitat preferences. There were, however, significantly more departures from blocks of substrates in lower velocities than from those in higher velocities, demonstrating that the duration of our experiment was sufficient for black fly larvae to express their habitat preferences. These results are consistent with the hypothesis that dispersal constraints associated with the settlement of drifting larvae limit their ability to reach preferred habitats. In fact, related studies predict that larval settlement rates are lowest in the high velocity habitats preferred by larvae. We conclude that such dispersal constraints may be important for a wide variety of freshwater, marine, and terrestrial organisms that are transported by moving fluids.

Effects of High-Frequency Pulsed-DC Electrofishing on a Wild Brown Trout Population

Abstract I determined the effects of annual exposure to high-frequency (>800 Hz), pulsed-DC electrofishing on the occurrence of spinal injuries, growth, size structure, and population density of wild brown trout Salmo trutta in a high-alkalinity stream in central Pennsylvania. I compared population statistics of brown trout in a section (section A) of Spruce Creek that was electrofished annually from 1985 to 1996 with those in another section (section B) that was electrofished annually from 1985 to 1991 and again in 1996. The frequency of spinal injuries of brown trout in section A (43.6%) was not significantly higher than that in section B (38.0%). The frequency of spinal injuries in angled brown trout from another section of Spruce Creek that had never been exposed to electrofishing was 15.5%. Median lengths of brown trout (ages 1–3) in section A were greater than those of brown trout in section B. Relative weights of brown trout in section B were higher than those in section A only in 1996, but these d...

Highway Deicing Salt Runoff Events and Major Ion Concentrations along a Small Urban Stream

ABSTRACT Highway deicing activities can influence the quality of waters draining urban areas that experience multiple winter season freeze/thaw cycles. However, because of the flashy hydrology of smaller urban streams, and the unpredictable nature of deicing runoff, these events are difficult to fully document by traditional monitoring approaches. The frequency, duration, intensity and downstream attenuation of highway deicing salt runoff events were captured by remote continuous flow and conductivity monitoring, in combination with dry and wet weather grab sampling, at four stations along a three-kilometer-long unculverted reach of an urban Pennsylvania stream, Nine Mile Run.

Effects of urban runoff from a detention pond on water quality, temperature and caged Gammarus minus (say) (Amphipoda) in a headwater stream.

Thompson Run, a headwater stream in central Pennsylvania (U.S.A.), supports an impaired macroinvertebrate community downstream of the outlet of a detention pond that receives urban runoff. To determine if toxicity from the metals or other pollutants in urban runoff contributed to impairment, we exposed adult, male Gammarus minus to urban runoff during a 42-day in situ bioassay that included 12 rain events. Test animals were collected from a site upstream of the detention pond outlet using two methods: precopula pair separation and sieving. Water quality, temperature and tissue metal concentrations were measured during the bioassay. The survival of precopula G. minus was lower (p=0.048) at a site downstream of the detention pond outlet compared to a site upstream of it, but the survival of sieved G. minus was not different between sites (p=0.803). Large hourly increases in temperature (up to 6.6 °C) and major reductions in water quality including order of magnitude increases in suspended materials (measured as turbidity) and the concentrations of copper, zinc and lead occurred downstream of the detention pond outlet during stormflow (i.e. following rain events). In contrast, changes in temperature and water quality were minor upstream of the pond outlet throughout the bioassay. Copper and cadmium concentrations in leaf samples and copper, zinc and lead concentrations in G. minus samples were significantly higher downstream of the pond outlet than they were upstream of it. Despite harsh conditions downstream of the pond outlet (i.e. metal contamination, inputs of suspended materials and rapid temperature increases), the in situ bioassay did not convincingly demonstrate that urban runoff was toxic to adult, male G. minus.

Are native brook charr and introduced rainbow trout differentially adapted to upstream and downstream reaches?

Abstract— Due to species introductions, brook charr (Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss) occur together in many North American streams and typically exhibit a pattern of distribution in which brook charr numerically dominate headwaters and rainbow trout dominate downstream reaches. It has been suggested that 1) the two species compete or 2) the two species do not compete because they are differentially adapted to environmental conditions found in upstream and downstream zones. We assessed whether there were differences in growth and macrohabitat (pool, run and riffle) selection of brook charr and rainbow trout in upper, middle and lower stream zones of a small Pennsylvania stream. Brook charr and rainbow trout placed in replicate paired enclosures set in upstream and downstream reaches showed no significant differences in growth and survival rates upstream, but brook charr had significantly greater growth rates than rainbow trout downstream. Enclosed fish and free‐ranging fish both had negative growth rates during the summer. Enclosed fish lost significantly less weight than free‐ranging fish. Instantaneous growth rates of free‐ranging adult brook charr and rainbow trout from May to August were negative for both species in all stream zones. Underwater observations of adult brook charr and rainbow trout showed both species occurred significantly more often in pool macrohabitats than expected on the basis of macrohabitat availability, except for rainbow trout in the upstream zone. The proportion of pool macrohabitat was not significantly different among stream zones. Brook charr do not appear to be better adapted to upstream environments in Powdermill Run based on growth, survival and macrohabitat selection during summer. Negative biotic interactions acting along with differential environmental adaptations may explain the pattern of distribution of brook charr and rainbow trout in streams, but long‐term transplant experiments with additional life stages will be necessary to examine this hypothesis.

The Impact of Airport Deicing Runoff on Water Quality and Aquatic Life in a Pennsylvania Stream

ABSTRACT The impacts of a large airport on the water quality and aquatic life of a small (94.8 km2 drainage area) western Pennsylvania stream were examined. The principal adverse effects of airport runoff were related to runway deicing operations. Microbial metabolism of glycols and urea utilized as deicing reagents exerted a strong biochemical oxygen demand in receiving waters. Similarly, the breakdown of urea led to elevated concentrations of ammonia. The use of alkaline mill slag as a fill material in the construction of the runways was probably responsible for some elevated alkalinity and pH values from runway leachates. The organic waste load stimulated the growth of dense biological slimes on streambeds. Invertebrate communities in waters influenced by airport runoff were severely stressed and dominated by pollution tolerant Chironomidae and Oligochaeta. The fishery of the watershed was also impaired, although transient fishes from the nearby Ohio River apparently reinvaded the stream at certain times of the year.

Seasonal Variation in the Structure of Diatom Communities in Two Pennsylvania Streams

ABSTRACT Current research has demonstrated that a guild of at least a dozen diatom genera dominates the autotrophic base of the systems in the Perkiomen and Skippack Creeks in Montgomery County, Pennsylvania. Previous research in the Skippack alone demonstrated that the common genera exhibited distinct periodicities and suggested that total diatom densities were similar from sampling dates centered around the autumnal and vernal equinoxes. We investigated the question of whether the diversity, richness, and equitability of the diatom guild were the same or different at the equinoxes. Collections at fourteen day intervals centered around the equinoxes of 1992–3 and 1994–5. Densities per date were determined by Whipple field counts, and analyses of diversity, richness, equitability, and community similarity were made using Simpson's Index of Diversity and Sorensen's Coefficient of Similarity. We found that the diatom communities are not the same at the equinoxes, including their total densities and dominant genera. Generic richness varied little between seasons, but the systems were more diverse at the vernal equinox because of changes in equitability.

Riparian Vegetation Survey of Four Small Streams in Northwestern Pennsylvania

The species composition and richness of the summer riparian vegeta? tion of four small streams in the nonglaciated Allegheny Plateau of northwestern Pennsylvania (Forest, Warren and McKean Counties) were examined. The arboreal stratum (stems > 2.5 cm dbh) of the four streams consisted of twenty species with Fagus grandifolia, Betula alleghaniensis, and Tsuga canadensis dominant (mean number of arboreal species across sites = 9.8 + 0.9 SE). Ninety-nine species were recorded from the ground-layer stratum (all vascular plants < 2 m tall) of the four streams with forbs as the dominant growth form. Four species, Dryopteris intermedia, Maianthemum canadense, Pilea pumila, and Viola blanda, were common to the ground-layer vegetation associated with all streams. Species of upland affinity were more prevalent in the riparian vegetation across streams than werewetland species. Several of the plant species recorded are indicators of rich and/or subacid to circumneutral soils, an edaphic medium of limited occurrence in the region. Mean ground-layer species richness and cover differed significantly among streams and ranged from 3.7 to 10.5 species/m2 (mean number of species/m2 across sites = 7.9 ? 1.5 SE) and 8.3 to 43.0% (mean percent cover across sites = 30.4 + 7.7 SE), respectively. Similarity in ground-layer species composition among streams ranged from 33.3 to 54.1% (mean similarity across sites = 38.9 ? 3.7% SE ). Although compositionally distinct, the small stream riparian flora documented by this study compares favorably in richness to other riparian habitats in northwestern Pennsylvania.

Microhabitat Selection by Native Brook Trout and Introduced Rainbow Trout in a Small Pennsylvania Stream

ABSTRACT Due to species introductions, brook trout (Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss) occur together in many North American streams. Some have suggested that the two species do not compete because they select different habitats or are adapted to different environmental conditions. We assessed whether native brook trout and introduced rainbow trout selected different microhabitats in a small Pennsylvania stream. Underwater observations of brook and rainbow trout showed adult fish (≥ 90 mm total length) of both species were found significantly more often in deep water microhabitats than would be expected based on habitat availability. Total depth was the most important microhabitat variable in discriminating between the two species, irrespective of fish size. Adult rainbow trout were found in significantly deeper water than adult brook trout. Adult brook trout also were found significantly farther from cover and closer to the stream bottom than adult rainbow trout. Age-0 brook trout were found in significantly deeper water than age-0 rainbow trout. In small streams during low flow, water depth and distance to nearest cover are likely to be major factors in discriminating between brook and rainbow trout.

Episodic Acidification and Changes in Fish Diversity in Pennsylvania Headwater Streams

Current water chemistry and fish communities in 70 Pennsylvania streams were compared with historical records to determine whether fish species richness had declined and, if so, the possible role of acidification. First-, second-, and third-order streams were selected, and stream sites sampled during the 1961–1971 survey were resampled during May and June 1994 in the Appalachian Plateaus province and during June 1995 in the Valley and Ridge province. Streamflow was measured and a habitat assessment was completed at each site. Dominant bedrock types influencing the stream sampling site were determined for the Appalachian Plateaus streams. Episodic water chemistry was collected for 39 of the 50 Appalachian Plateaus streams and 14 of the 20 Valley and Ridge streams during the winter and spring of 1996. Thirty-eight (76%) streams of the Appalachian Plateaus province and 13 (65%) streams in the Valley and Ridge province had a loss of fish species since the 1961–1971 sampling period. Habitat scores were not related to losses of fish species. Of the 53 streams sampled during runoff episodes 22 (42%) increased in total dissolved aluminum by more than 50 μg/L, and 31 (58%) streams decreased in pH by 0.5 units or more. Minnows (Cyprinidae) and darters (Percidae) are sensitive to acidity and were the species most often lost. Streams draining watersheds of the Appalachian Plateaus province dominated by Pottsville bedrock had more acidic water quality during base flow and storm flow sampling periods than streams dominated by Pocono bedrock. The results of this study indicate that many Pennsylvania streams have undergone an alarming reduction in fish diversity during the past 25–34 years. In many of these streams the loss in fish diversity may be attributed to episodic acidification.

Development of a partitioned-biomass model for rooted macrophyte growth

Many surface waters support excessive growth of several rooted macrophyte species. This paper presents a macrophyte growth model to facilitate modeling the growth of several macrophyte species which exhibit distinct patterns of growth and development. The model partitions the biomass of each species according to the phenological stages of plant development including growth, maturation, senescence, and dormancy. The partitioned-biomass model was demonstrated for the growth of Elodea canadensis Michx. and Potamogeton crispus L. in Spring Creek, a shallow fourth-order stream in central Pennsylvania. The structure of the model could be adapted to a wide variety of macrophytes and aquatic ecosystems.

Relations among riparian grazing, sediment loads, macroinvertebrates, and fishes in three central Pennsylvania streams

We assessed relations among riparian grazing, sediment loads, macroinvertebrates, and fishes in three streams in adjacent catchments in central Pennsylvania. The catchments consisted mostly of agricultural and forest lands. Lengths of streams subjected to riparian grazing were 2.5 km along Cedar Run and 4.1 km along Slab Cabin Run; there was no riparian grazing along Spring Creek. Median daily discharge and temperatures during summer and winter were significantly different among streams. Annual sediment yields were 113, 255, and 273 t in Spring Creek, Cedar Run, and Slab Cabin Run, respectively. Substrate permeability of potential spawning sites for brown trout ( Salmo trutta), and densities of benthic macroinvertebrates were significantly higher in Spring Creek than in the other streams. Densities of wild brown trout were 5-23 times higher in Spring Creek than in Cedar Run and Slab Cabin Run. Although there were marked differences among streams with and without riparian grazing, other watershed attributes could have had some influence on these streams. Resume : Nous avons evalue les relations existant entre le broutage riverain, la charge de sediments, les macro-invertebres et les poissons, dans trois petits cours d'eau de bassins-versants voisins, dans le centre de la Pennsylvanie. Ces bassins-versants etaient principalement recouverts de terres agricoles et de forets. Le broutage riverain touchait 2,5 km du Cedar Run et 4,1 km du Slab Cabin Run, alors que les berges du ruisseau Spring n'etaient soumises a aucun broutage. Le debit quotidien moyen ainsi que les temperatures estivales et hivernales etaient sensiblement differents selon les cours d'eau. La production annuelle de sediments etait de 113 t pour le ruisseau Spring, de 255 t pour le Cedar Run et de 273 t pour le Slab Cabin Run. La permeabilite des substrats pouvant servir de frayeres a la truite brune ( Salmo trutta) et la densite des macro-invertebres benthiques etaient significativement plus elevees dans le cas du ruisseau Spring que dans celui des deux autres cours d'eau. De meme, la densite des truites brunes sauvages etait 5-23 fois plus elevee dans le ruisseau Spring que dans le Cedar Run et le Slab Cabin Run. Il existe donc des differences marquees entre les cours d'eau soumis et non soumis au broutage riverain, mais il est possible que d'autres caracteristiques des bassins-versants aient eu une incidence sur ces cours d'eau. (Traduit par la Redaction)

Episodic Acidification of Small Streams in the Northeastern United States: Ionic Controls of Episodes

As part of the Episodic Response Project (ERP), we intensively monitored discharge and stream chemistry of 13 streams located in the Northern Appalachian region of Pennsylvania and in the Catskill and Adirondack Mountains of New York from fall 1988 to spring 1990. The ERP clearly documented the occurrence of acidic episodes with minimum episodic pH ≤ 5 and inorganic monomeric Al (Alim) concentrations &gt; 150 μg/L in at least two study streams in each region. Several streams consistently experienced episodes with maximum Alim concentrations &gt;350 μg/L. Acid neutralizing capacity (ANC) depressions resulted from complex interactions of multiple ions. Base cation decreases often made the most important contributions to ANC depressions during episodes. Organic acid pulses were also important contributors to ANC depressions in the Adirondack streams, and to a lesser extent, in the Catskill and Pennsylvania streams. Nitrate concentrations were low in the Pennsylvania streams, whereas the Catskill and Adirondack study streams had high NO3‐ concentrations and large episodic pulses (≤ 54 μ eq/L). Most of the Pennsylvania study streams also frequently experienced episodic pulses of SO42‐ (≤ 78 μ eq/L), whereas the Adirondack and Catskill streams did not. High baseline concentrations of SO42‐ (all three study areas) and NO3‐ (Adirondacks and Catskills) reduced episodic minimum ANC, even when these ions did not change during episodes. The ion changes that controlled the most severe episodes (lowest minimum episodic ANC) differed from the ion changes most important to smaller, more frequent episodes. Pulses of NO3‐ (Catskills and Adirondacks), SO42‐ (Pennsylvania), or organic acids became more important during major episodes. Overall, the behavior of streamwater SO42‐ and NO3‐ is an indicator that acidic deposition has contributed to the severity of episodes in the study streams.

Accumulation of aluminum and iron by bryophytes in streams affected by acid-mine drainage

Accumulation of two heavy metals (Al and Fe) by bryophytes was examined in a northern Pennsylvania stream system affected by acid-mine drainage. Four sites within one watershed were selected on the basis of their pH and dissolved metal concentrations. Significant differences among sites were found with regard to bioaccumulation of Al and Fe. A negative relationship between pH and Fe concentrations in bryophyte tissues was found, with the highest accumulation of Fe observed at the most acidic site (pH 3.5), whereas accumulation of Al was highest at a site with an intermediate pH of 5.2. Bryophytes transplanted from a circum-neutral site to acidic sites showed highly significant increases in Fe and Al concentrations in tissues after 6 weeks, and transplants from more acidic sites to a circum-neutral site generally showed highly significant declines in Fe and Al concentrations in tissues after the incubation period.