1st Order Streams Research Articles

Factors determining occupancy and habitat use by Asian small-clawed otters in the Western Ghats, India

We examined patterns of habitat occupancy and intensity of habitat use by Asian small-clawed otters (Aonyx cinerea) by sampling 59 hill stream segments in the Western Ghats between February and April 2008, using spraints (otter feces) as an indicator. We used an occupancy-based approach to determine the influence of habitat covariates on detection and occupancy. We also used generalized linear models to model encounter rate of spraints as a function of the habitat covariates. Although occupancy of streams was high before summer showers, it declined drastically after the rains. Sampling time, therefore, indicated otter movement across the area. Altitude was the next-best predictor of occupancy. Intensity of habitat use was influenced most by altitude followed by stream type, with pools preferred over cascades and riffles. Second- and 3rd-order streams were used more intensively than 1st-order streams. The study identifies high-altitude areas with stream pools as important prospective otter habitats and demonstrates the applicability of occupancy-based surveys to identify determinants of occurrence and habitat use of otters.

Origins of streamflow in a crystalline basement catchment in a sub-humid Sudanian zone: The Donga basin (Benin, West Africa): Inter-annual variability of water budget

During the last quarter of the 20th century, West Africa underwent a particularly intense and generalized drought. During this period, the biggest drops in streamflow were observed in the Sudanian zone rather than in the Sahelian zone, but the reasons are still poorly understood. In 2000, a meso-scale hydrological observatory was set up in the sub-humid Sudanian zone of the Upper Oueme Valley (Benin). Three embedded catchments of 12-586 km2 located on a crystalline bedrock were intensively instrumented to document the different terms of the water budget and to identify the main streamflow generating processes and base-flow mechanisms at different scales. Geophysical, hydrological and geochemical data were collected throughout the catchments from 2002 to 2006. Crossing these data helped define their hydrological functioning. The region has seasonal streamflow, and the permanent groundwater in the weathered mantle does not drain to rivers, instead, seasonal perched groundwaters are the major contributor to annual streamflow. The perched groundwaters are mainly located in seasonally waterlogged sandy layers in the headwater bottom-lands called bas-fonds in French-speaking West Africa of 1st order streams. During the period 2003-2006, regolith groundwater recharge ranged between 10% and 15% of the annual rainfall depth. Depletion of permanent groundwater during the dry season is probably explained by local evapotranspiration which was seen not to be limited to gallery forests. During the 4-year study period, a reduction of 20% in annual rainfall led to a 50% reduction in streamflow. This reduction was observed in the two components of the flow: direct runoff and drainage of perched groundwater. Thanks to the comprehensive dataset obtained, the results obtained for the Donga experimental catchment are now being extrapolated to the whole upper Oueme valley, which can be considered as representative of sub-humid Sudanian rivers flowing on a crystalline basement, for example, the upper courses of several major West African rivers (Senegal, Niger, Bani, and Volta).

Nitrous oxide (N 2O) in the Seine river and basin: Observations and budgets

In the Seine basin (71 730 km 2) intensive use of N fertilizers in agriculture and the release of reduced N in urban wastewater, not fully eliminated in treatment plants, have deeply perturbed the regional nitrogen cycle, namely by promoting intense nitrification and denitrification, two key microbial processes involved in N 2O emission. Sampling surveys in the whole Seine drainage network have shown that N 2O water concentrations are always far above saturation with respect to atmospheric concentrations. Highest values are found in 1st order streams (1–4 μg N l −1), decrease by out-gazing down to 4th order rivers (0.5 μg N l −1) and increase again in polluted higher order rivers (4 μg N l −1). Calculated values of gas transfer velocities and the observed N 2O supersaturation by stream order was used to estimate N 2O emissions for the whole water surface area of the Seine drainage network to 100–200 × 10 3 kg N-N 2O yr −1. The results show that a major fraction of the emission occurs in head-water streams. On the basis of previous work, the emission by wastewater treatment plants – WWTPs – has been estimated at the scale of the Seine basin, to 150–260 × 10 3 kg N-N 2O yr −1, i.e. to be in the same range as N 2O emissions from the entire water surface. Using an emission factor approach, based on an intensive literature survey considering grassland, cropland and forest soils distribution, the total direct emissions of N 2O of the Seine basin was estimated to 10 400 × 10 3 kg N-N 2O yr −1 among which 2500 × 10 3 kg N-N 2O yr −1 are issued from the forested soils and 7900 × 10 3 kg N-N 2O yr −1 from agricultural land. The latter figure agrees well with the [Intergovernmental Panel on Climate Change (IPCC), 2006. AFOLU, N 2O Emissions from Managed Soils, and CO 2 Emissions from Lime and Urea Application, vol. 4, 54 pp (Chapter 11)] estimate of 8250 × 10 3 kg N-N 2O yr −1. The quantified indirect emissions (from the river-atmosphere interface and from the WWTPs) thus represent 3–6% of the direct agricultural emissions of the Seine basin. However, N 2O indirect emissions from ‘riparian zones’ have only been roughly calculated and, thus, are remaining uncertain. A conservative estimate might increase the indirect emissions to about 13–17% of the direct ones.

General soil-landscape distribution patterns in buffer zones of different order streams

Understanding landscape and soil distribution patterns in buffer zones along a stream network in a watershed can improve riparian zone management and the representation of soil-landscape parameters in watershed modeling. We analyzed landscape features and soil properties within a 300-m buffer zone of different order streams in a large agricultural watershed (the East Mahantango Creek Watershed) located in the Ridge and Valley Physiographic Province in Pennsylvania, USA. The mean elevation displays an obvious decreasing trend downstream, and increases gradually with the distance away from the streams. Within the buffer distance of approximately 75 m, buffer zone's mean slope shows a rapid increase regardless of stream order; however, it starts to decrease after 75 m in the 1st to 3rd order stream buffers, but continues to increase in a more gradual manner in the 4th and 5th order stream buffers. Agricultural land area percentage increases by 10–25% from near stream area to about 100 m buffer, and becomes nearly the same in 100–300 m buffer zone. The opposite trend holds for forested land area in all stream buffer zones. The 1st to 2nd order stream buffers have 12–28% greater agricultural land area percentage and 0.45–1 m shallower soil depth than the 3rd to 5th order stream buffers, suggesting that the headwater areas in the study watershed are important in preventing nonpoint source pollution due to the more intensive agricultural land use and potential erosion in headwater catchments. The distributions of soil properties in the buffer zones are consistent with the observed landscape patterns. The top two soil layers (approximately A and B horizons) in the 0–100 m buffer zones of the 1st and 2nd order streams generally display a greater clay content and a higher bulk density, but a lesser organic matter content and a lower available water capacity, than those in the similar buffer zones of the 3rd to 5th order streams. Beyond the 100 m buffer distance and in the third layer of the soil profiles (approximately C horizons), the soil properties examined in all stream buffer zones become less distinguishable. With a few exceptions, soil clay content and bulk density increase with increasing buffer distance (particularly within 0–100 m range), while organic matter content and available water capacity decrease with buffer distance. Such patterns reflect the impacts from the landscape features, fluvial processes, and land use in the Ridge and Valley Physiographic region. The results of this study, though maybe specific to the watershed studied, suggest that soil and landscape distribution patterns along stream networks are helpful to guide riparian zone management and nonpoint source pollution prevention in agricultural watersheds.

Effect of anadromous salmon redd construction on macroinvertebrate communities in a recently formed stream in coastal Alaska

The construction of salmon redds represents a localized but intense disturbance to benthic substrate and associated flora and fauna. Pink salmon (Oncorhynchus gorbuscha) have a fixed 2-y life cycle. Thus, their spawning run in Wolf Point Creek, a 1st-order coastal stream in southeast Alaska, alternates between high-density (odd years) and low-density (even years) returns. During July and August 1996 and 1998, counts of returning fish were low (<2000 fish) with little evidence of streambed disturbance by redd construction, whereas in 1997, counts of returning fish were >10,000 fish, and streambed disturbance was extensive. Coarse particulate organic matter and macroinvertebrate density and taxonomic richness were significantly lower in the main channel in 1997 than in 1996 or 1998. Macroinvertebrate densities and taxonomic richness were similar in all years in areas unsuitable for salmon redds (refugium habitat: margins, boulders, shallows). Macroinvertebrate drift density increased during the 1997 spawning run. Several taxa demonstrated circadian drift behavior, but the peak in redd construction activity coincided with an absence of nocturnal peaks for most macroinvertebrate taxa. Simulation of the abrasion and settling of material excavated during redd construction caused a modest but significant increase in total macroinvertebrate drift density compared with unmanipulated reference sites. Drift density declined after the cessation of experimental disturbance, a result suggesting that entombment and mortality associated with abrasion and settling was high and indicating that excavation, rather than abrasion and settling, was the most important process causing overall increase in drift density during redd construction. River habitat structure is a critical feature mediating the effects of disturbance associated with spawning salmon. Redd construction displaces macroinvertebrates and opens habitable space. Thus, it is an important determinant of community structure and function and could influence the course of community succession.

Impacts of land disturbance on aquatic ecosystem health: Quantifying the cascade of events

The impacts of land disturbance on streams have been studied extensively, but a quantitative mechanism of stream degradation is still lacking. Small changes in land use result in changes in physical and chemical characteristics in the stream, which significantly alter biotic integrity. The objective of this study was to quantify the mechanisms of aquatic ecosystem degradation in streams impacted by watershed urbanization. By quantifying the development level and the changes in the physical parameters of receiving streams, the effects of land use change can be illustrated in a conceptual model and evaluated using a traditional ecological risk assessment framework. Three 1st-order streams draining catchments undergoing varying stages of land development were examined in the upper Piedmont physiographic province of South Carolina, U.S.A. A disturbance index was developed to quantify the changes in land use on a monthly basis. This normalized disturbance index (NDI) was quantitatively linked to an increase in the percentage of impervious cover, stormwater runoff, storm-event total suspended solid (TSS) concentrations, and the North Carolina biotic index (NCBI). The NDI was inversely related to a decline in habitat, median bed-sediment particle size, and benthic index of biotic integrity (BIBI). Unlike the percentage of impervious cover, the NDI facilitated the development of strategies for multiple scales of regulation. Predictive multivariate regressions were developed for storm-event TSS concentrations, the BIBI, and the NCBI. These regressions can be used to develop improved regulations for the effects of development and can lead to better implementation of best management practices, improved monitoring of land use change, and more sustainable development.

Sampling effort and fish species richness in small terra firme forest streams of central Amazonia, Brazil

Small streams are important components of the landscape in terra firme forests in central Amazonia and harbor a large number of fish species. Nevertheless, the lack of a common sampling protocol in studies of this ichthyofauna hinders comparisons among available results. This study evaluates how the length of stream reach sampled affects estimates of local fish species density in 1st, 2nd, and 3rd order streams, and proposes a mean minimum sampling length that best approximates the absolute number of species in a given stream segment. We sampled three streams in the Biological Dynamics of Forest Fragments Project's study sites, between May and August 2004. At each stream, one 1st order, one 2nd order, and one 3rd order segment was sampled. We sampled five 20-m reaches in each stream segment. Three to four people collected along each reach for 45 to 60 minutes. We used Jaccard's coefficient to estimate the similarity of species composition among stream reaches and segments. Estimates of species richness were obtained with Jackknife 1 and Bootstrap algorithms and species accumulation curves. We used simple linear regressions to look for relationships between species density and fish abundance and between species density and the volume of 100-m stream segments. Species density in 1st order stream reaches was slightly higher than in 2nd and 3rd order stream reaches, whereas fish abundance was apparently higher in 3rd order reaches. Similarity in fish species composition between 20-m reaches was low for all studied streams. Species density values in pooled 100-m stream segments represented 71.4% to 94.1% of the estimated values for these streams. Species density showed a direct relationship both with volume of the sampled stream segment and fish abundance. It seems plausible that larger streams contain a higher number of microhabitat types, which allow for the presence of more fish species per stream length. Based on the values of asymptotes and equations for species accumulation curves, the mean minimum sampling length that best estimates the absolute number of species in a stream segment is 180 m ± 20 sd for 1st order segments; 213 m ± 23 sd for 2nd order segments, and 253 m ± 30 sd for 3rd order stream segments.

Leaf-litter decomposition in an Amazonian floodplain stream: effects of seasonal hydrological changes

AbstractDecomposition of allochthonous material is a central process in organic matter budgets of low-order streams. Shredding invertebrates contribute substantially to the decomposition of leaves in northern-temperate-zone streams, but their role in tropical streams is less clear. Hydrology has an overarching control on ecological processes in streams, especially on floodplains, where flooding of the mainstem river may cause backflooding in the tributaries. Decomposition experiments with leaves of Cecropialatiloba, Tessariaintegrifolia, and Symmeriapaniculata were used to assess the importance of hydrology and benthic invertebrates to decomposition in a neotropical floodplain stream. Leaf breakdown rates and leaf-associated aquatic invertebrate assemblages were compared among leaf types in a typical 1st-order stream of the Amazonian whitewater floodplain forest near Leticia, Colombia. The stream hydrograph was influenced by regular rainfall throughout the year and by seasonal backflooding from the Amazon...

Analysis of storm runoff-sediment yield of a 1st order stream basin in Obafemi Awolowo University, Ile-Ife, southwestern Nigeria

The aim of this study is to examine the relationship between storm flow discharge and storm sediment yield of a 1st order stream basin in the degraded forested part of Obafemi Awolowo University, Ile-Ife. The study was carried out between August and October, 2002 and six storm events that occurred during the day were sampled. The results of this study showed that in some of the storm events observed (storm event 1, 4 and 6), the storm flow discharge correlated significantly with the storm yield (with r-value of 0.743, 0.591 and 0.576 at &alpha; = 0.05, respectively) while in other events such as storm events 3 and 5, the storm runoff/discharge was poorly correlated with the storm yield with r-values of 0.102 and 0.330, respectively. Therefore, these findings indicated that sediment load was not a capacity load and thus should not be expected to increase always with increase in storm flow discharge. The findings of this study will aid programme in soil erosion controls designed by the governments and individuals in forested watersheds. Key Words: Storm flow discharge, storm sediment yield, sediment concentration and land use. Ife Journal of Science Vol.6(2) 2004: 185-190

Hydromorphological and biological factors influencing sediment and phosphorus loss via bank erosion in small lowland rural streams in Denmark

AbstractBank erosion was measured at 91 stream banks located in 15 Danish rural 1st and 2nd order streams over a 2‐year period. Our aims were firstly to examine factors controlling spatial variation in bank erosion, secondly to estimate sediment and phosphorus (P) loss via bank erosion. The overall mean bank erosion rate was 11 mm year−1. Bank erosion rate over the 2‐year period was significantly related to a number of site‐specific characteristics, including bank angle, bank vegetation cover, overhanging bank and estimated stream power. An empirical model for bank erosion based on these descriptive variables yielded a 55% explanation of the observed spatial variation in bank erosion rate. Bank erosion was higher at the lower 50‐cm bank section (20 mm year−1) than at the upper bank (6 mm year−1). Cattle fencing in grazed areas and buffer zones with riparian woodland lowered bank erosion rates. We found that total P content of bank material was high (0·64 g P kg−1) and at the same level as found in agricultural topsoil along the streams. The overall annual catchment loss of bank‐derived clay–silt sediment and total P to streams amounted to 58–72 kg sediment ha−1 and 0·23–0·28 kg P ha−1, respectively. In comparison, the mean annual suspended sediment (SS) and total P losses from 14 similar sized Danish agricultural catchments were 122 kg SS ha−1 and 0·58 kg P ha−1 over the 2‐year study period. Thus, bank erosion seems to be a major contributor of suspended sediment and P in this type of small channelized lowland stream. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Leaf retention in streams of the Agüera basin (northern Spain)

The capacity of stream channels to retain leaf litter (retentiveness) was measured in 21 reaches of the Aguera basin (northern Spain) at different discharges, using plastic strips as leaf analogs. Strips were calibrated against seven local leaf species occurring in the area. Retention was highest for alder, followed by plastic strips, oak, beech, chestnut, eucalyptus, hazel, and sycamore. Inter-specific differences in retention were great, and not clearly related to leaf form or size. This result shows that a great deal of caution is necessary to compare results obtained by authors using different leaf species. The Aguera stream channels were highly retentive, especially in the headwaters. At baseflows, the average travel distance of strips was 3.6 m in 1st-order reaches, increasing to 16.6 m in 3rd-order streams. Travel distances of strips increased twofold in 3rd- and 2nd-order reaches and 5-fold in 1st-order streams during periods of high discharge. Leaf litter retentiveness was related to channel gradient, width, and substrate. Cobbles and wood showed high retention efficiencies, and the role of wood as a retention factor increased at high discharges. Retentiveness enhances storage and subsequent utilization of organic materials in forested streams, and thus should be taken into account when managing streams.

Colonization of fine particulate organic matter by invertebrates in a Central Florida stream

Abstract. Our study was conducted to determine whether small invertebrates of the shredder and collector feeding guilds would preferentially colonize fine particulate organic matter (FPOM) from fast‐decaying species of leaves in central Florida streams. Bags of FPOM (0.2–1 mm) generated from maple, elm, sweetgum, and water oak leaves, as well as artificial Sty‐rofoam, were suspended at two sites in Poley Creek, a 1st‐order sand‐bottomed stream. Three replicate bags of each type were collected from each site after 7, 14, and 28 d, and bacteria and invertebrates present were counted. Bacteria colonized maple and elm in significantly higher numbers than sweetgum, oak and Styrofoam. The amphipod Gammarus tigrinis accounted for 97% of all shredders in FPOM bags, and 63% of total invertebrates. Deposit‐feeding chi‐ronomids comprised 87% of collectors and 28% of total invertebrates. No other taxon comprised &gt;2% of total invertebrates. Large numbers of invertebrates colonized in the first 7 d, but densities did not increase after Day 7. Both shredders and total invertebrates occurred in significantly greater densities on maple and elm than on sweetgum and oak. Amounts of FPOM remaining in bags after 28 d were significantly smaller for maple and elm (P&lt;.05), suggesting that shredders were eating the FPOM. Collectors occurred in similar densities in all natural FPOM bags. Only a few individuals of either functional feeding group colonized Styrofoam bags, suggesting that FPOM was being colonized for its nutritional value rather than as a refuge from predation.

Effects of Coarse Particulate Organic Matter on Fungal Biomass and Invertebrate Density in the Subsurface of a Headwater Stream

Links between groundwater invertebrates and their potential food resources were examined using biofilm development on fine wood. Little is known about biofilm development and organic matter content of lateral subsurface (i.e., parafluvial) environments and hyporheic habitats (upwelling and downwelling zones). Eighteen experimental baskets containing river rocks were paired by treatment in which 1 basket was supplemented with wood (six 7.2 cm × 12 cm strips of oak wood veneer). Nine pairs of baskets were buried 12 to 15 cm below the surface in Gallina Creek, a 1st-order mountain stream in northern New Mexico in late summer 1997. Three pairs were buried beneath the stream bank (i.e., parafluvial zone) and 6 pairs were buried in the hyporheic zone. Baskets were distributed along upwelling and downwelling reaches to assess the potential hydrologic influence of subsurface-surface exchange. Open baskets of wood veneer were placed on the streambed surface to compare fungal biomass on the surface with the subsurface. Wood in both hyporheic and parafluvial baskets was colonized by fungi, but fungal biomass was significantly greater on wood in surface water than in hyporheic and parafluvial zones. In addition, fungal biomass on hyporheic wood was significantly greater than on parafluvial wood. A similar pattern (i.e., surface > hyporheic > parafluvial) was observed for dissolved oxygen. In contrast, concentrations of retained particulate organic matter were significantly higher in the parafluvial than the hyporheic zone. Invertebrate densities were significantly greater in baskets supplemented with wood and were greater in the hyporheic zone than in the parafluvial zone. Our data suggest that wood and associated microbial biofilms represent an important food resource for interstitial invertebrate communities.

Macroinvertebrate assemblages in perennial headwater streams of the Coastal Mountain range of Washington, U.S.A.

We studied headwater streams in 4 watersheds of Washington's Coastal Mountain region from June to August 1998 to establish macroinvertebrate reference conditions and describe variation in macroinvertebrate assemblage structure among stream orders and among substrates. Macroinvertebrates were sampled with mesh baskets (30 × 30 cm) filled with equal volumes of wood (1.5 l) and cobble (1.5 l) that were installed into fifteen 1st-order, six 2nd-order, and three 3rd-order streams. Low taxa richness and low macroinvertebrate densities were found in all streams. Crayfish dominated (92.7%) biomass estimates, with shredders dominating the non-crayfish component of the biomass. The importance of shredders declined from 1st- to 3rd-order streams. An abundance of wood and a lack of algae and non-wood based detritus in the 1st-order streams led us to suspect that food webs were wood based. We tested this hypothesis by comparing macroinvertebrate assemblages in substrate baskets filled with equal volumes (3 l) of naturally conditioned (1) wood, (2) cobble, or (3) wood and cobble (1.5 l of each). Macroinvertebrate richness was higher in wood-only and mixed baskets than the cobble-only baskets (p = 0.0118), and macroinvertebrate biomass was higher in mixed than cobble-only baskets (p = 0.044).

Terminal electron accepting processes in the alluvial sediments of a headwater stream

Chemical fluxes between catchments and streams are influenced by biogeochemical processes in the groundwater–stream water (GW–SW) ecotone, the interface between stream surface water and groundwater. Terminal electron accepting processes (TEAPs) that are used in respiration of organic C in anoxic environments may have a strong effect on nutrient dynamics and water chemistry. Concentrations of oxidized and reduced forms of terminal electron acceptors (dissolved O2, NO3−, Fe2+, SO42−, and CH4) were measured in networks of vertically nested wells installed beneath the surface stream and in the near-stream aquifer of a headwater catchment. Tracer addition experiments were conducted in surface and groundwater environments of a 1st-order montane stream to characterize hydrologic fluxes between the stream and aquifer, and to quantify ecosystem retention of terminal electron acceptors (NO3− and SO42−) in the GW–SW ecotone. Sulfate retention was evident in both hyporheic and groundwater environments. Distribution of important redox sensitive solutes varied predictably with changing hydrologic residence time of water in the GW–SW ecotone. Results suggest a strong hydrologic control of TEAPs and ecosystem retention of biologically important solutes in the GW–SW ecotone related to characteristics of GW–SW mixing and residence time of water in the hyporheic zone.

Nutrient and microbiological characteristics of fine benthic organic matter in mountain streams

AbstractFine benthic organic matter (FBOM) was collected over a 10-mo period from 14 1st-order streams in the Cascade Mountains of western Oregon to investigate 1) relationships between FBOM substrate quality and microbial activity, 2) links between organic matter sources and FBOM substrate quality, and 3) how FBOM is influenced by riparian vegetation, elevation, and season. Streams drained forests in 3 successional age classes: old-growth forest dominated by Douglas-fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla), and young regenerating stands, either 10 y old with a large riparian herbaceous component, or 30 y old and surrounded by deciduous trees such as red alder (Alnus rubra).Seasonal trends showed a major autumn depression in carbon:nitrogen ratios (C:N) and an increase in microbial activities, a likely result of increased leaf inputs after an early fall storm. Decreases in C:N, total C, total N, and organic P were correlated with reciprocal increases in respiration, β–glucosida...

Interactions among sediments, organic matter, and microbial activity in the hyporheic zone of an intermittent stream

Interactions between surface and subsurface water in intermittent streams are poorly understood. We predicted that surface discharge patterns would influence retention and transport of fine sediments and particulate organic matter in a first-order intermittent stream, which in turn would affect microbial activity at different depths in the sediment. We measured sediments, dissolved and particulate organic carbon, and microbial and bacterial biomass and activity at three depths (surface and 20 and 40 cm) over a period spanning low and high flows at five stations on an intermittent stream. Discharge influenced physicochemical and sediment characteristics at the upstream stations with coarse substratum. In the finer sediments of the lower reaches, an active hyporheic microbial assemblage primarily governed sediment and organic dynamics. With decreasing discharge and increasing retention of fine sediments and particulate organic carbon, greater microbial hydrolytic activity in bed-sediments occurred downstream. Dissolved oxygen, organic carbon, fine sediments, microbial biomass, hydrolytic activity, and bacterial biomass declined with depth, and changed over time, apparently in response to varying discharge. We conclude that discharge and substratum particle size may interact to control organic dynamics and hyporheic microbial activity in a 1st order stream.

Spatial Variation and Historical Change in Fish Communities of the Schuylkill River Drainage, Southeast Pennsylvania

The use of fish communities to evaluate stream habitat typically requires that the community at a target site be compared with concurrently or recently sampled reference communities at nearby sites. For this approach to be effective, spatial and temporal variation in the reference communities of a region must both be known. This study relates 307 recent (1976–1994) fish survey records in the Schuylkill River drainage, southeastern Pennsylvania, to four concurrent measures of water chemistry (pH, conductivity, alkalinity, hardness), two measurements of stream size (stream order, stream width) and three variables describing site position within the drainage network (elevation, link number and C-link number defined herein). Based on canonical correspondence analysis, stream size and position within the watershed influenced fish species composition more strongly than did water chemistry. Species richness, dominated by the families Cyprinidae (minnows) and Centrarchidae (sunfishes), increased from a median of four species in 1st-order streams to 21 species in 5th-order streams. Secondly, recent frequencies of occurrence are compared to frequencies inferred from historical collections using log-linear analysis. Nine species have increased in frequency, while the frequencies of eight species have declined. Eighteen species, or about ⅓ of the recent community, have been introduced. All but three of these introduced species were absent from collections before 1931, and many are now widespread. Several previously common species associated with clear, vegetated streams are now uncommon or rare (e.g., Esox americanus americanus, Notropis bifrenatus); one species, N. chalybaeus, was not found in the recent dataset. Substantial historical changes in the fish community thus accompany the influences of stream habitat and location in determining species composition at sites within the drainage.

Fungal Biomass of 3 Leaf Litter Species during Decay in an Appalachian Stream

Leaf decay and fungal biomass accrual was measured for maple (Acer rubrum), tulip-poplar (Liriodendron tulipifera), and rhododendron (Rhododendron maximum) leaf packs in an Appalachian stream over 8 mo. Packs were placed in 2 stream sites along a longitudinal gradient at the Coweeta Hydrologic Laboratory in North Carolina: a 1st-order headwater stream and a 4th-order stream. Decay was measured as percent mass loss over time, and fungal biomass was estimated using ergosterol. Tulip-poplar decayed faster than maple, and rhododendron decayed the slowest of the 3 in both sites. Decay was faster in the 4th-order stream for tulip-poplar and rhododendron leaves, largely because of differences in stream geomorphology. Fungal biomass showed no trend along the longitudinal gradient. Average fungal biomass (as dry mass [DM] per ash free DM [AFDM]) of aquatic hyphomycetes during the study period was 42 mg DM/g AFDM on tulip-poplar and 11 mg DM/g AFDM on maple leaves in these streams. These estimates are on the lower ...

Transient Storage in Appalachian and Cascade Mountain Streams as Related to Hydraulic Characteristics

Hydraulic characteristics were measured in artificial streams and in 1st- to 5th-order streams in the Appalachian and Cascade mountains. Appalachian Mountain stream sites at Coweeta Hydrologic Laboratory, North Carolina, were on six 1st-order streams and a 1st- through 4th-order gradient of Ball Creek-Coweeta Creek. Cascade Mountain sites were located on constrained and unconstrained reaches of Lookout Creek, a 5th-order stream in H. J. Andrews Experimental Forest, Oregon. At each site, a tracer solution (chloride or rhodamine WT) was released for 30-180 min and then discontinued. At the downstream end of the release site, the resulting rise and fall of the tracer concentration was measured. These data, along with upstream concentration and measured widths and depths, were used in a computer model to estimate several hydraulic parameters including transient storage and lateral inflow. Estimated transient storage zone size (A_s) ranged from near zero in artificial streams to 2.0 m² in 5th-order streams. A_s was largest relative to surface cross-sectional area (A) at 1st-order sites where it averaged 1.2 × A, compared with 0.6 × A and 0.1 × A in unconstrained and constrained 5th-order sites, respectively. Where measured, lateral discharge inputs per metre of stream length ranged from 1.9% of instream discharge in 1st-order streams to 0.05% of instream discharge at 5th-order sites. Our results show that surface water exchange with storage zones is rapid and extensive in steep headwater streams and less extensive but still significant at 3rd- through 5th-order sites. An understanding of relationships between stream morphology, storage zone size, and extent of interactions between surface and subsurface waters will assist comparisons of solute dynamics in physically diverse streams.