Higher Order Streams Research Articles

Chemical and biological trends associated with acidic atmospheric deposition in the Rhode River watershed and estuary

The Rhode River estuarine/watershed system is a tributary of Chesapeake Bay located on the inner Atlantic Coastal Plain. Its soils are fine sandy loams. Bulk precipitation pH in the spring season declined from 4.95 in 1974 to 3.82 in 1981 and was 4.03 in 1985. The changes in pH of a forested primary stream were more related to changes in bulk precipitation pH than were the changes in pH of agricultural streams, reflecting the importance of other major terrestrial sources of acidity on agricultural systems. Surges in acidity and dissolved total Al concentration in primary (first order) streams reached extremes of pH 3.2 and 300 μg Al L−1. Higher order streams were observed to have surges in acidity with pH minima below 5.0. Surges in acidity ocurred during accelerated groundwater percolation following storm events and did not coincide with surface runoff or snowmelt. One of the reasons why groundwater is more acidic than surface runoff is that the vegetation exchanges H30 + for alkaline cations in the soil and translocates these ions to the vegetational canopy. When it rains, subsequently, H30+ in the precipitation displace some of these alkaline cations from the canopy. The end result is that overland flow during storms is enriched in alkaline cations, while groundwater is enriched in H30+. Although the source of dissolved Al is dissolution of clay minerals with atomic ratios of Al to silicate of 1:l, 1:2, or 1:3, this ratio in stream water rapidly declined to 1:1200 due to loss of Al. On average, forest drainage was the most acidic, the highest in dissolved Al, and the lowest in Ca. Surges in acidity were most severe from pastureland, and next most severe from cropland. Total fluoride concentrations were high relative to Al from all three land uses. Rhode River spawning runs of Perca flavescens declined drastically from the early 1970s to essentially zero since 1981. Larval bioassays of acidity indicate negligible toxicity to Hyla crucifer, significant toxicity to Perca flavescens and drastic effects on Morone saxatilis at pH 5.0.

The exopterygote insect community of a mountain stream in North Carolina, USA: Life histories, production, and functional structure

Life histories and production of the Exopterygota inhabiting a first to second order mountain stream in North Carolina, USA, were studied by replicated monthly sampling of three different habitats (BO = boulder‐outcrop, R = riffle, PL = pool). Life histories were diverse, ranging from multi‐voltine (e.g. Baetis) to semi‐voltine (e.g. Leuctra ferruginea, Sweltsa lateralis). Habitat‐weighted annual production was 1862 mg (ash‐free dry weight)/m2 with > 50% being based on four taxa (of 21 considered): Serratella sp. (16%), Peltoperlidae (16%), Leuctra spp. (13%), and Beloneuria spp. (8%). The Odonata, Ephemeroptera, and Plecoptera contributed 36, 760, and 1066 mg/m2 to annual production, respectively. Production was distributed evenly among four functional groups with collector‐gatherers, shredders, scrapers, and engulfing‐predators contributing 21%, 33%, 23%, and 23%, respectively. Production by functional groups followed broad taxonomic categories with the Ephemeroptera, euholognathous Plecoptera, and systellognathous Plecoptera contributing 93%, 90%, and 92% of the scraper, shredder, and engulfing‐predator production, respectively. Serratella sp. contributed 77% of the collector‐gatherer production. Annual production by the Exopterygota was greatest in the BO habitat (2056 mg) > R (1981 mg) > PL (951 mg). Production in the BO was attributable to a unique combination of taxa compared with R and PL. Sixty‐five percent of the BO production was based on Serratella sp., a collector‐gatherer. Collector‐gatherers constituted only 2% and 8% of PL and R production, respectively. The remainder of the PL and R production was generally distributed evenly among scrapers, shredders, and engulfing‐predators. Comparison of the functional structure of the exopterygote communities of headwaters with higher order streams indicated a shift from a dominance of detritivory to predation. In higher order, low gradient streams characterized by limited stable substrate, the majority of the Exopterygota are unable to use entrained food resources directly, and predation upon the filter‐feeding Endopterygota (e.g. Chironomidae) may be the predominant method of feeding.

Oxygen-18 studies of snowmelt runoff in a small Precambrian shield watershed: Implications for streamwater acidification in acid-sensitive terrain

Oxygen-18 tracer studies of snowmelt runoff in the Turkey Lakes watershed, Ontario, Canada indicate that 50–60% of the peak runoff is derived from premelt groundwater in storage in the surficial deposits. Groundwater in the stream valleys has relatively high alkalinity concentrations from silicate and minor detrital carbonate dissolution which neutralize much of the acidity in the meltwater component of runoff when it is discharged into the stream during meltwater infiltration. However shallow groundwater on the hillslopes is susceptible to acidification from infiltrating meltwater and rapid flushing to small, first-order streams. For this reason first-order headwater streams experience greater pH depression than do higher-order streams in well defined stream channels, despite having similar premelt components.

A soil catena on schist in northwestern California

Soil characteristics in a small steepland watershed underlain by schist in a rainy, tectonically active area in northwestern California show close associations with drainage-basin position and slope characteristics. Five soil-topography units based on these associations are defined in the study watershed. Spatial relationships of soil series, and patterns of soil development as indicated by B-horizon clay content and redness, reflect interactions between pedogenesis and erosion. General soil-topography patterns include: (1) decreases in soil-development moving from low-order to higher-order stream vallyes; and (2) more developed soils on north-facing as opposed to south-facing slopes. Decreases in soil-profile development moving from slopes near low-order streams to slopes near higher-order streams approximately correlate with increases in gradient, vertical relief, and drainage density, and reflect a more vigorous stripping of regolith by erosion on the slopes near the higher-order streams. The larger percentage of area covered by the more developed soils on north-facing as opposed to south-facing slopes appears to reflect a contrast in the way dominant erosional processes interact with pedogenic processes. Roadcuts on middle and upper slopes show soil discontinuities indicative of disturbance by block slides or slumps or both. Roadcuts on lower slopes show disrupted soils in small bedrock hollows that could have been created by rapid, shallow landslides or by the pulled-up root wads of toppled trees. Soil-profile characteristics and soil-topography patterns in the study area demonstrate that both erosional and pedogenic processes need to be considered when interpreting characteristics of hillslope soils.

Effect of a leaf-shredding invertebrate on organic matter dynamics and phosphorus spiralling in heterotrophic laboratory streams.

The effect of invertebrate shredders on organic matter dynamics and phosphorus spiralling was studied over a 30-week period in laboratory streams. The streams were fed by groundwater, layered with cobble and gravel from a natural stream, covered with opaque material to eliminate algal growth, and initially contained 195 g/m2 of autumn-shed leaves. Four weeks after leaf addition, leaf-shredding snails (Goniobasis clavaeformis) were added to each of three streams in densities of 75, 220, and 800/m2. A fourth stream contained no snails and served as a control.Presence of snails increased the loss rates of coarse particulate organic matter (CPOM) and total organic matter (TOM), primarily by increasing leaf fragmentation and seston export. Although snail feeding increased specific metabolism of microbes associated with CPOM and cobble surfaces, it was not enough to compensate for reduction in bacterial cell numbers per unit surface area and in stream TOM. Consequently mineralization of detritus and whole stream phosphorus utilization rate were maximum in the stream with no snails and decreased with increasing snail density. From previous simulations of a stream model based on the nutrient spiralling concept, we predicted that there should be an intermediate shredder density which would minimize phosphorus spiralling length (maximize phosphorus utilization) in a natural stream nearby. Our current results conflict with the model-based predictions primarily because the increase in microbial metabolism was less important than reduction in bacterial cell numbers and total benthic organic matter resulting from snail feeding. Although our results indicate macroinvertebrate shredders reduce phosphorus utilization in headwater streams, shreders may increase nutrient utilization downstream where riparian inputs are lower, thus linking low- and high-order streams.

Species Richness in Streams of Different Size from the Same Drainage Basin

The species richness of stream benthic invertebrates was studied along a longitudinal profile of the Salmon River, Idaho, during spring, summer, and autumn. Sampling was done using replicate rocks and the analytical approach of Stout and Vandermeer (1975) was used to calculate theoretical number of species present, relative immigration rate, and relative spatial heterogeneity. Species richness varied with stream size, being highest in midorder streams and lower in headwater and high order streams. This downstream shift in species richness conforms to the river continuum concept (Vannote et al. 1980). Possible cause is associated with varying temperature regimes in the different-sized streams as well as other factors. Species richness also varied with season depending on stream size. Low order streams were more individualistic, probably because of a greater influence of local (terrestrial) environmental conditions, but showed a higher richness in summer than in autumn. Larger streams were more similar and showed a higher richness in autumn than in summer. Other community-level indicators, such as relative immigration rate and extinction rate, also showed seasonal differences. We conclude that different macroinvertebrate community types having characteristics of either nonequilibrium (density-independent, opportunistic) or equilibrium conditions can be found in streams from the same drainage basin depending on location along the river continuum and time of the year. These findings have important implications for future studies of stream communities as well as for those of predation and competition in streams. Among other things, we propose that the interactive/noninteractive model of Wilson (1969) may be more appropriate for stream invertebrate communities than those assuming strictly nonequilibrium or equilibrium conditions. We further suggest that any attempt to classify or compare stream communities, such as was done for tropical versus midlatitude streams by Stout and Vandermeer (1975), must take seasonality and position along the downstream gradient into account.

Parapatric Crayfishes in Southern Ohio: Evidence of Competitive Exclusion?

ABSTRACT A survey of lotic crayfish distributions in the Brush Creek drainage basin of southern Ohio was undertaken to test the hypothesis that narrowly overlapping distribution patterns of Orconectes rusticus and O. sanbornii sanbornii within streams are determined by substrate lithology (Rhoades, 1962); we found no such relationship. Rather, an essentially parapatric distribution was observed along gradients from headwaters to major streams. In areas of parapatry, O. rusticus occurred in lower reaches of tributaries and in major trunk streams, whereas O. s. sanbornii was restricted to isolated populations inhabiting headwaters. In other parts of the basin, O. rusticus alone occupied habitats ranging from headwaters to high-order streams. We postulate that in the absence of O. rusticus, O. s. sanbornii would likewise occupy the full continuum of lotic habitats (i.e., ecological release). In light of this and recent evidence implicating invasions by O. rusticus in apparent species displacements, we propose that competitive exclusion is an important factor influencing the distributions of these species in southern Ohio.

The Role of Benthic Macroinvertebrates in Detritus Dynamics of Streams: A Computer Simulation

Detritus dynamics in Big Hurricane Branch, a second—order stream at Coweeta Hydrologic Laboratory in the southern Appalachian Mountains, were simulated with a computer model, using data from a variety of Coweeta stream studies. The model was used to evaluate the role of macroinvertebrates in the stream. Macroinvertebrates accounted for only a small portion of the respiration of detritus; their major role was conversion of benthic detritus into transported detritus. Macroinvertebrates were responsible for 27% of annual particulate organic matter (POM) transport, though when they were removed there was only a 10% reduction in POM transport because of a compensatory increase in storm transport. The contribution of macroinvertebrates to POM transport during nonstorm periods was much more significant, as high as 83% in late summer. Based on an annual budget, macroinvertebrates decrease the efficiency of detritus processing in low—order streams, because they increase transport loss. On a longer time scale, however, macroinvertebrates prevent accumulation of large amounts of detritus in the stream and major losses during infrequent large storms. By stabilizing long—term detritus export dynamics, they provide an important link between low—order and higher—order streams.

Seston and Dissolved Organic Carbon Dynamics in a Southern Appalachian Stream

Suspended paniculate matter (seston) and dissolved organic carbon (DOC) were stud- ied along a 6.4-km section of a southern Appalachian headwater stream from July 1978 to August 1979. Samples were collected at six sites encompassing stream orders 1-4 and a 635 m elevation change. Nonstorm concentration of particulate organic matter (POM) measured as ash-free dry mass (AFDM) ranged from 0.53-3.68 mg/L during the study. No significant changes in seston concentration occurred from upstream to downstream sites, and only one site had concentrations significantly different from the others. Significant seasonal trends in seston concentrations existed over all stations, and these were associated with corresponding hydrograph changes. During the first storm following leaf-fall both seston concentration (AFDM 22.5 mg/L) and particle size in transport increased. Non- storm DOC/particulate organic carbon (0.45 x POM) ratios average =1. DOC concentrations (mg/L) increased over the first 2 km of stream but remained relatively constant farther downstream. The increase was largely due to high molecular mass fractions. Seven size classes of seston were measured, and discriminant analysis was used to assess longitudinal changes in particle size distribution. The largest and two smallest size classes increased in relative abundance downstream while the four intermediate classes decreased. Although the mean particle size decreased downstream, the ratio of coarse particulate organic matter (CPOM)/fine particulate organic matter (FPOM) increased down- stream. We suggest that CPOM/FPOM ratios do not necessarily reflect downstream reductions in mean particle size. CPOM/FPOM ratios and downstream changes in mean particle size should be viewed as separate phenomena. The ratio of benthic CPOM/suspended CPOM decreases downstream, which is apparently attributable to the lack of retention devices in higher order streams. Food quality available to collector organisms, as indicated by adenosine triphosphate (ATP) measurements, was highest in the two smallest (0.45-43 /^m) seston size classes. No apparent relationship existed between ATP and percent organic matter in the various seston size classes.

Threshold of critical power in streams

Stream power is the power available to transport sediment load, and it may be defined as γ QS , where γ is specific weight of water, Q is stream discharge, and S is slope. Critical power is the power needed to transport sediment load. The threshold of critical power is where stream power/critical power = 1.0. Where stream power exceeds critical power during long time spans, additional sediment load is obtained by vertical erosion that cuts V-shaped cross-valley profiles in bedrock. The threshold is approached asymptotically during downcutting, and high-order streams approach the threshold more rapidly than do low-order streams. High discharges cause net lateral erosion in reaches near the threshold. Straths and flood plains form under such conditions. Where stream power is less than critical power, selective bedload sedimentation decreases sediment load and size and therefore the critical power. Such deposition is self-enhancing because of concurrent decreases in slope. Thus, it is unlikely that aggrading reaches attain the threshold, but the tendency to attain the threshold may keep stream and critical power roughly the same. Reaches of streams at the critical-power threshold are sensitive to changes in climate, base level, and the impact of humans; these may change stream and/or critical power and result in aggradation or degradation.

Vegetation and Watershed Shape

The length L of vegetated first order watersheds developed by fluvial erosion is related to the width W by L = W2/RU, where R is 3 for converging random walks of step size U, whose observed mean is 3 meters for normal dendritic drainage and 40 meters for basins over 300 meters long that drain directly into third or higher order streams. Bare soil watersheds show the relation L = 0.4 W.

HORTON'S LAW OF STREAM NUMBERS FOR TOPOLOGICALLY RANDOM CHANNEL NETWORKS

HORTON‘S LAW OF STREAM NUMBERS FOR TOPOLOGICALLY RANDOM CHANNEL NETWORKS CHRISTIAN WERNER University of California, Irvine ACCORDING to Horton’s law of stream numbers, the bifurcation ratio in a drainage network is fairly constant with an average value between 3.5 and 4, so that the stream numbers tend to form a geometric progression. This paper investigates drainage net- works whose structure is controlled by chance only. The mathematical analysis shows that the expected stream numbers also approach a geometric progression, and that the corresponding bifurcation ratios approximate the value 3.6 18. INTRODUCTION A scientific investigation of real world phenomena usually concentrates on selected properties and disregards all others. An example is the sequential pattern of merg- ing rivers in a drainage network. The apparent hierarchy of their mergers can be studied disregarding all other components (topography, hydrology, morphometry). What remains is the information regarding the number of tributaries the system contains, and how they are interconnected, i.e., the topological structure of the net- work. This structure is the subject of Horton’s famous law. To understand its content, a few network parameters have to be defined. Since the original concept of stream order introduced by Horton (1945, p. 281) still contains a geometrical element (angles), the refined version of Strahler (1952, p. 1120) will be used here. The stream segments starting from a source are called streams of first order, and the stream segments starting from the confluence of two streams of ith order are called streams of order i + 1 . The end of each stream is defined as the point where a higher-order stream starts. The bifurcation ratio of streams of order m is defined as the ratio between the number of streams (stream numbers) of order m and the number of order m + 1 . An example is shown in Figure 1. To avoid the problem of ambiguity, only rivers with a “mature” topography will be considered here; i.e., rivers with lakes and islands are excluded. We further assume that no more than two rivers merge in one point. FIGURE 1. Stream orders in a river net- work (after Strahler, 1952). XIV, 1, 1970 CANADIAN GEOGRAPHER,

Stream Order, Morphometry, Physico-Chemical Conditions, and Community Structure of Benthic Macroinvertebrates in an Intermittent Stream System

ABSTRACT: Morphometry, physico-chemical conditions, and community structure of benthic macroinvertebrates were quantitatively related to stream order in a 6th order, intermittent stream system located in north-central Oklahoma. Number of species and individuals, and species diversity and heterogeneity indices were used as measures of community structure. Average drainage area and average lengths of streams increased, and stream numbers and average gradient decreased exponentially as stream order increased. Physico-chemical fluctuations, mean annual turbidity and water temperature decreased, while mean annual flow, alkalinity, and conductivity increased as stream order increased. Numbers of individuals were maximum in 4th order streams throughout the year. Minimum numbers occurred in the 6th order stream during periods of stream flow, and in 3rd order streams during drought. Annual numbers of species and total community species diversity (H) increased in 3rd, 4th, and 5th order streams and decreased in the 6th order stream. Diversity per individual (H) increased and redundancy (R) decreased as stream order increased. Species diversity was significantly different between and within stream orders at the 75% confidence level, diversity per individual at the 95% level, and redundancy at the 90% level. During autumn, winter, and spring diversity per individual increased and redundancy decreased as stream order increased. Diversity per individual was significantly different at the 95% confidence level during autumn and the 90% level during winter and spring. Significance of redundancy increased from the 25% level during summer and autumn to the 90% level during spring. Annual ranges of species diversity, diversity per individual, and redundancy decreased as stream order increased, indicating more uniform community structure in the higher stream orders. Mean annual heterogeneity (IH) decreased as stream order increased, indicating that similarity of community structure and faunal assemblages increased progressively with stream order. A station located in a 3rd order adventitious stream that flowed directly into the 6th order stream had a community structure and faunal assemblage more similar to stations in higher order streams than to other 3rd order stations. Drought and seepage of oil-field brines upset the stream ordercommunity structure relationship. During drought community structure was similar in all stream orders. Influx of low concentrations of oilfield brines caused diversity per individual to increase and redundancy to decrease, indicating improved stream conditions and more random distribution of individuals into species. More concentrated brines caused diversity per individual to decrease and redundancy to increase, denoting less random distribution and greater repetition of selected species.