Effects of experimentally enhanced flows on fishes of a small Texas (U.S.A.) stream: assessing the impact of interbasin transfer

1. Completion of a large interbasin water transfer system in northern Texas (U.S.A.) provided the opportunity to test the effects of pre-planned, experimental increases (≈×30) in flow on the fish fauna of a small, low-gradient, natural stream that was included as part of the conveyance system. Water from Lake Texoma (Red River basin) was pumped via a 16-km pipeline to the headwaters of Sister Grove Creek (Trinity River basin), which then carried the donor water 50 km downstream to Lake Lavon.
2. Baseline (pre-transfer) data on the composition of fish assemblages at seven stations on the creek or at its confluence with the receiving reservoir were collected monthly for 3 years, and similar data were collected for 2 years during and after trial flows of Lake Texoma water to Sister Grove Creek. We also documented fish abundance at five creek stations immediately before and after three trial flow periods of 10–14 days each in summer and autumn.
3. Multivariate analysis of all routine monthly samples over the 5-year pre- and post-transfer period showed moderate changes in the fish fauna of the creek after initiation of the trial flows. Samples taken within a week before and after the artificial high flows showed little overall change in abundance of individual fish species, but at some stations the quantitative or qualitative change in composition of the local assemblage was substantial.
4. The trial flows lasted 2 weeks or less. Long-term effects of water transfer on the fish fauna of Sister Grove Creek can only be determined after the conveyance system goes into normal operation, with periods of artificial flow of longer duration.     

Effects of a small dam on freshwater mussel growth in an Alabama (U.S.A.) stream

1. Dams, ubiquitous features in many lotic ecosystems, are believed to have many broad‐ranging and predominantly negative effects on stream biota. Whereas the impacts of larger dams are well studied, few studies have quantified effects of small dams on streams. 2. Recent surveys found numerous locations where mussels were abundant and larger in reaches immediately downstream from small dams. We examined mussel shell growth and resource conditions in Sandy Creek, a small (third‐order) tributary of the Tallapoosa River in east‐central Alabama (U.S.A.), to determine whether larger populations and individuals result from more rapid growth or longer lifespans of mussels downstream from the dam. 3. Growth rates for populations occurring immediately downstream from the dam (mill reach), c. 5 km downstream from the dam (downstream reach) and upstream from the impoundment (upstream reach) were compared with environmental conditions (seasonal measures of nutrient concentrations and water chemistry) and food availability [total suspended solids (TSS)]. Water temperature was continuously monitored using data loggers. 4. Analysis of length‐at‐age data using multiple growth models found that mill reach mussels grew faster than both up‐ and downstream populations. This dam appears to substantially increase water temperatures and may extend the shell growth period in the mill reach. TSS quantity varied seasonally between sites but was generally highest in the impoundment and mill reach during spring and autumn. TSS quality was highest in the upstream reach from spring through autumn but was highest in the impoundment and mill reach during winter. 5. Our data suggest that some small impoundments enhance conditions for freshwater mussel growth in downstream reaches. However, we do not know how far downstream this subsidy extends or how different species respond to mill dam augmentation. Regardless, mounting evidence suggests that this phenomenon is geographically and taxonomically widespread in eastern North America. Heretofore, undocumented positive effects of small dams suggest that some older dams may warrant protection or restoration if downstream reaches support imperilled mussel populations. Further, some small dams may prove useful conservation tools for natural resource managers attempting to identify sites for mussel culture facilities or translocation refugia.     

Microdistribution of benthic invertebrates in a rocky mountain (U.S.A.) stream

A study of the benthic invertebrate community inhabiting a small, foothill trout stream in the Rocky Mountains of Idaho was conducted over a two-year period. Monthly Hess samples and short-term experiments using substratum-filled trays were used to describe the spatial dispersion of the benthos and to examine the response of invertebrate populations to substratum and current. A method was devised for measuring available surface area which involved coating individual stones with latex and measuring the area of the print resulting from inking the impression left on the latex mold.The dispersion of all populations was clumped throughout the year. Alteration of the cross-sectional pattern of current velocity and stream bed composition changed the pattern of distribution but not the extent of clumping. Collections made in areas of depositing and eroding substrata revealed a more diverse fauna in the latter. Most groups of organisms found in the riffle were scarcer in the pools or absent from them. The pool fauna contained no important additions over those found in the riffles.After a year's study of invertebrate populations in an otherwise undisturbed riffle, the substratum was altered and the flow made more uniform; an increase in the abundance of most of the benthic invertebrates followed. No single factor was responsible for the increase, but the change in substratum size and degree of compaction accounted for most of the change. Interpretation of the results was aided by findings from experiments using substratum-filled trays.Two series of stream experiments using the trays were conducted: one to test the relative importance of current and substratum and the other to test the effect of particle size on the distribution of the benthic fauna. In the first series, placement of trays of stones in a pool resulted in an increase in numbers of some but not all of the invertebrates over numbers usually occurring in the pool. Trays filled with stones and placed in a riffle supported fewer animals than found on the adjacent stream bed but more than in the pool. Variations are attributed to differences in current velocity and amounts of imported organic and inorganic debris. Three different relationships of population numbers to current velocity were found for different members of the community (direct, indirect, and parabolic) over the range of 10 to 60 cm/sec. The second series of experiments consisted of two sets of trays filled with stones of medium or large pebbles, respectively. Nine taxa, as well as all of the combined taxa, showed a preference for trays of small stones over the natural stream bed. A few taxa were noticeably more abundant on the small substratum than on the large but most of the fauna showed only slight increases in numbers or remained constant on the two substrata. Only three taxa showed a direct relation of numbers to total surface area presented by the stones.Number and kinds of organisms found in trays filled with a uniform size of substratum did not correspond to those taken in Hess samples from the natural stream bed. This has important implications in terms of currently recommended pollution monitoring techniques. However, it is suggested that if the substratum composition of the trays more nearly matched that of the stream, the correspondence would be much better. The results of the present study also throw considerable doubt on the adequacy of generalizations derived from earlier studies of responses to substratum size and suggest several reasons for reevaluating current ideas regarding the influence of substratum on invertebrate distribution.     

The Plecoptera community of a small stream in Oregon,U.S.A. *

The Plecoptera community of a small woodland stream in Oregon was studied by examining density and species composition. Four sites were studied using benthos sampling for larvae and emergence trap collections for adults. Sixteen genera and forty-three species were identified with most species occurring in relatively low numbers. A comparison with the species list from an earlier study suggested that the species composition has not changed markedly in 40 years but there were several changes in relative abundance. Species diversity of stoneflies decreased with distance from the headwaters. These changes were correlated with decrease in habitat complexity, decrease in stability of the substrate, and increase in water depth. Examples of longitudinal succession are given as a method enabling the large number of species to partition the habitat. Concurrent benthos and emergence sampling demonstrated differences in emergence success that were correlated with habitat suitability.     

The effect of permafrost on stream biogeochemistry: A case study of two streams in the Alaskan (U.S.A.) taiga

Understanding interactions between permanently frozen soils and stream chemistry is important in predicting the effects of management, natural disturbance and changing permafrost distribution on stream ecosystems and nutrient budgets in subarctic watersheds. Chemical measurements of groundwater, soil water and stream water were made in two watersheds in the taiga of interior Alaska. One watershed (HiP) had extensive permafrost and the other (LoP) had limited permafrost. Soil water collected within the rooting zone (0.3--0.5 m) in both watersheds was high in dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and dissolved inorganic nitrogen (DIN) but low in dissolved minerals (dominantly Ca, Mg and Na) and conductivity. The reverse was true for groundwater from springs and wells. Permafrost in the HiP basin prevented deep percolation of water and generated stormflows rich in DOC. The presence of permafrost in HiP resulted in higher fluxes of DOC, DON and DIN into stream water from upland soils.     

Spatial and temporal patterns in the fish assemblages of individual pools in a midwestern stream (U.S.A.)

Synopsis The composition and consistency of fish assemblages in 14 adjacent pools (6–120 m long) of a clear-water, limestone and gravel creek in midwestern U.S.A. were quantified in eight snorkeling surveys over 19 months, to establish a baseline of natural variation in the system at this scale. The fauna of the stream was dominated numerically by minnows (Cyprinidae), sunfish and black bass (Centrarchidae), and topminnows (Fundulidae). The pool fish fauna of the total 1 km reach (including all 14 pools) was highly consistent throughout the study, despite two major floods. Assemblages in individual pools generally were consistent, but there was more variation within pools than at the scale of the entire reach. Throughout the study, most individual pools remained within discrete subsets of the total occupied multivariate space in a principal components analysis based on fish species abundances. Sunfishes (Lepomis spp.) and bass (Micropterus spp.) were more consistent in their distribution among pools than were minnows (Cyprinidae) or a topminnow (Fundulus). There were 25 significant correlations in occurrence of species pairs among stream pools, out of 91 possible comparisons of the 14 most abundant taxa in the reach. Many pools contained assemblages either dominated by large centrarchids or by abundant cyprinids and juvenile centrarchids, but intermediate assemblages also were observed. The dynamics of distribution of fish species and fish assemblages among individual stream pools are likely influenced by a combination of species-specific behaviors and habitat selection, predator constraints on use of individual pools by small fishes, riffles as size-selective barriers to fish movements between pools, dispersal of young-of-the-year fishes, and abiotic phenomena like floods. Individual stream pools appear to be discrete habitat units for fishes, and do represent an appropriate scale for biologically meaningful studies of fish assemblages or their effects on streams.Department of Zoology, University of Oklahoma     

Factors influencing the longitudinal distribution of larval Hydropsychidae (Trichoptera) in a southern Appalachian stream system (U.S.A.)

The influence of physical habitat variables and suspended particulate organic matter (seston) on the distribution and production of eight species of larval Hydropsychidae was studied along a 6.4 km section of a southern Appalachian stream. Samples were collected at six stations encompassing stream orders 1–4 and an elevation range of 610 m. Multivariate analysis of covariance (using time as the covariable) and discriminant function analysis were used to examine habitat differences between the sampling stations due to the following variables: current velocity; coarse benthic detritus; substrate composition (by particle size); substrate heterogeneity; degree-days; and diel temperature fluctuation. The associations of these variables with the abundance (and production) of larval hydropsychids was also examined using the same statistical procedures. The six sampling stations represented three or four distinct habitats based on patterns of change in the variables along the stream continuum. Diel temperature fluctuation, median substrate particle size, the proportion of sand substrate, and substrate heterogeneity were most closely associated with the overall difference between the sampling stations. Hydropsychid species distribution along the stream system followed subfamily lines, i.e., Arctopsychinae and Diplectroninae were more abundant and productive in the upper 4.5 km of the stream, while Hydropsychinae were dominant in the lower 1.9 km. Diel temperature fluctuation was the habitat variable most highly correlated with patterns of hydropsychid abundance and production. The longitudinal pattern of species distribution, i.e., larger particle feeding Arctopsychinae being replaced downstream by smaller particle feeding Hydropsychinae, also coincided with the distribution of seston particle size classes along the stream. Mean seston particle size generally declined downstream, as particles <42 µm increased in relative abundance while those between 43 µm and 5 mm decreased. Temperature, seston, and substrate composition all undoubtedly exerted an important influence on the distribution and production of Hydropsychidae and other filter feeding insects in this stream. The validity and generality of these results depend upon the scope of the sampling effort. Conclusions drawn from data collected over the entire range (and limits) of a species' distribution are more sound than those based on data from a limited area.     

Palynology of the Dockum group (Upper Triassic), Texas,U.S.A.

A palynofloral assemblage is described from the Upper Triassic Dockum Group of Texas. Forty palynomorph species are recorded and these are correlated with European Upper Triassic assemblages. The Dockum Group assemblage is considered to be of late Karnian age.Two new genera, Tulesporites gen. nov., type species T. briscoensis sp. nov., and Daughertyspora gen. nov., type species D. chinleanus (Daugherty) comb. nov. have been erected; new species are Converrucosisporites matsenii sp. nov., Pyramidosporites traversei sp. nov., Callialasporites triassicus sp. nov., Plicatipollenites minutotriletus sp. nov., Triadispora dockumensis sp. nov., Bhardwajispora jansonii sp. nov., Protodiploxypinus americus sp. nov., P. ujhelyi sp. nov., Klausipollenites gouldii sp. nov., Pityosporites old-hamensis sp. nov., Abietineaepollenites bujakii sp. nov., Falcisporites oviformis sp. nov. and F. tecovasensis sp. nov.     

The effects of hydropsychid colonization on algal response to nutrient enrichment in a small Michigan stream, U.S.A.

1. We tested the hypothesis that the indirect effects of colonization by Hydropsyche spp. (Trichoptera: Hydropsychidae) may be greater than direct effects of nutrients on the benthic algal community growth. Two sets of nutrient-releasing substrates (a total of twenty-four) were deployed into a small pristine stream in northern Michigan. Each set was composed of four treatments replicated three times: (i) no nutrient enrichment (C), (ii) 0.5 M phosphate-P enrichment (P), (iii) 0.5 M nitrate-N enrichment (N) and (iv) 0.5 M phosphate-P plus 0.5 M nitrate-N enrichment (P + N). All hydropsychids colonizing on the substrate in one set (twelve substrates) were removed regularly and the other set (twelve substrates) with undisturbed hydropsychids served as the controls. 2. Algal biomass and gross primary productivity were estimated as chlorophyll a (chl a) concentration, algal biovolume, and carbon fixation rate, respectively. There was a significant interactive effect of hydropsychid colonization and P enrichment on algal biomass measured as chl a concentration. With removal of hydropsychids, chl a concentration increased 11-fold in the P enrichment treatments relative to the controls. The effects of P on chl a was, however, not significant in the presence of hydropsychids. Such interactive effects were not observed when algal responses were measured as biovolume and carbon fixation rate (GPP). 3. It is recommended that algal responses to nutrient enrichment should be measured as biovolume or carbon fixation rate in small streams where hydropsychids are commonly present.     

Shoaling species drive fish assemblage response to sequential large floods in a small midwestern U.S.A. stream

I assessed the short-term impact of two sequential scouring floods on the fish assemblage of a small prairie stream. I tested for changes in fish abundance, fish assemblage composition, and fish-habitat associations within individual pools and across a suite of pools following each flood. Before the second flood, 30–90% of fish were removed by seining in five of eight pools. Overall fish abundance was reduced by approximately 50% following the first flood, but effects varied widely among individual pools. Fish abundance was unaffected by the second flood, despite prior removal of a known proportion of fish, suggesting recolonization of defaunated pools during the flood. Fish assemblage similarity across the entire suite of pools was low following each flood, but varied considerably within individual pools. Defaunated pools were more similar to pre-flood assemblages than control pools, though the mechanism behind this pattern was unclear. Changes in abundance and assemblage composition were driven by interpool movement of two minnow species with the shared behavioral trait of shoaling: bigeye shiner Notropis boops and central stoneroller Campostoma anomalum. Shifts in abundance showed no upstream or downstream pattern, suggesting that flooding allowed fish to move actively among pools that are typically isolated by partial barriers (riffles). This study highlights the importance of considering species’ behavioral traits when assessing the impacts of flooding, and suggests that shoaling behavior may be useful trait for predicting fish assemblage change following flooding.     

Effects of forest fire on headwater stream macroinvertebrate communities in eastern Washington,U.S.A.

1. Recent increases in fire frequency in North America have focused interest on potential effects on adjacent ecosystems, including streams. Headwaters could be particularly affected because of their high connectivity to riparian and downstream aquatic ecosystems through aquatic invertebrate drift and emergence. 2. Headwater streams from replicated burned and control catchments were sampled in 2 years following an intense forest fire in northeastern Washington (U.S.A.). We compared differences in benthic, drift and emergent macroinvertebrate density, biomass and community composition between five burned and five unburned catchments (14–135 ha). 3. There were significantly higher macroinvertebrate densities in burned than control sites for all sample types. Macroinvertebrate biomass was greater at burned sites only from emergence samples; in benthic and drift samples there was no significant difference between burn and control sites. 4. For all sample types, diversity was lower in the burned catchments, and the macroinvertebrate community was dominated by chironomid midges. 5. Compared to the effects of fire in less disturbed ecosystems, this study illustrated that forest fire in a managed forest may have greater effects on headwater macroinvertebrate communities, influencing prey flow to adjacent terrestrial and downstream aquatic habitats for at least the first 2 years post‐fire.     

Macroinvertebrate assemblages in Pennsylvania (U.S.A.) springs

Five distinct macroinvertebrate assemblages were identified using cluster analysis of the rank-order abundances of 13 orders in 15 freshwater springs of central Pennsylvania, U.S.A. A principal components analysis of 20 environmental factors indicated that an insect-dominated assemblage occurred in low pH, softwater sandstone springs and an amphipod-dominated assemblage was associated with medium to hardwater springs with a silt to gravel substratum. Three other assemblages were found in hardwater limestone springs: the peracaridan-hydrobiid assemblage was characterized by dense macrophyte beds and a silt to cobble substratum, the peracaridan-triclad-glossosomatid assemblage by a rubbly, gravel-cobble substratum and relatively high discharge, and the peracaridan-hydrobiid-oligochaete assemblage by a silty substratum and dense mats of green algae.Most of the common macroinvertebrate species were associated with specific physical, chemical, and (or) vegetational factors, but abundance associations between species pairs were generally lacking. We infer that assemblages are primarily determined by the match between the environmental mosaic of individual springs and the ecological requirements of the available species, rather than by strong interspecific interactions.Species-environment associations were assessed in an additional study of five closely neighboring springs in which some environmental variables of the wider study were nearly constant.     

The biology and ecology of the fishes of a small tropical stream

Many small species of fish are found in the stream/swamp systems that flow into Lake Victoria. One such system, in Uganda, was inhabited permanently by only one species, although others ran into the stream when it was flooded in the rainy seasons. Other fishes were confined to the lower reaches near the mouth, but never moved far upstream.
Studies on the biology of these fishes indicate that reproductive behaviour is generally confined to the rains in all species, the cyprinids using the system especially for breeding purposes at these times. Factors other than sexual state, such as feeding habits, vary little between fish from the river and those from the lake.
Experiments show that there is a change in the sexual state of the females of one species during the journey upriver, indicating the importance of this activity in the life cycle of the migratory fish.
The young of the cyprinids first appear in the up-river swamps. Here they grow, migrating to the river and moving downstream to enter the lake after periods of time that are characteristic for each species. This distinctiveness in timing was also found for the other fishes that inhabit the system, and it suggests that downstream migration is controlled by changes in the physiological state of the fish with age.     

A melissopalynological study of 54 Louisiana (U.S.A.) honeys

Pollen analyses were made of 54 commercial Louisiana (U.S.A.) honeys collected during 1967–1968. Fifty-eight different pollen types were identified. A direct correlation was assumed between a plant's pollen quantity and its nectar contribution. On this basis, the major Louisiana honey plants that were determined are: Fabaceae, predominantly Trifolium repens (99%), Rubus, Berchemia scandens, and Salix. Plants established as important for their nectar contributions in isolated samples are: Cephalanthus occidentalis, Sapium sebiferum, miscellaneous Compositae (Asteraceae), Glycine max, and Parthenocissus quinquefolia. Native plants such as Rubus, Berchemia scandens, and Salix contribute more to Louisiana's honey sources than do cultivated plants or introduced plants. Most samples originated from six to fifteen different plant types and thus do not appear to be of particularly diverse botanical origin. The pollen types that indicate late spring, summer, or fall honeys include: Glycine max, Cassia fasciculata, Polygonum, Lagerstroemia indica, Lythrum, Ampelopsis, Trachelospermum difforme, and others. Thirty-one samples could be considered unifloral honeys. Most Louisiana honeys were a clear color and from nectar of flowers and not honeydew.     

Implications of community concordance for assessing stream integrity at three nested spatial scales in Minnesota,U.S.A.

1. Fish and invertebrate assemblage data collected from 670 stream sites in Minnesota (U.S.A.) were used to calculate concordance across three nested spatial scales (statewide, ecoregion and catchment). Predictive taxa richness models, calibrated using the same data, were used to evaluate whether concordant communities exhibited similar trends in human‐induced taxa loss across all three scales. Finally, we evaluated the strength of the relationship between selected environmental variables and the composition of both assemblages at all three spatial scales. 2. Significant concordance between fish and invertebrate communities occurred at the statewide scale as well as in six of seven ecoregions and 17 of the 21 major catchments. However, concordance was not consistently indicative of significant relationships between rates of fish and invertebrate taxa loss at those same scales. 3. Fish and invertebrate communities were largely associated with different environmental variables, although the composition of both communities was strongly correlated with stream size across all three scales. 4. Predictive taxa‐loss models for fish assemblages were less sensitive and precise than models for invertebrate assemblages, likely because of the relatively low number of common fish taxa in our data set. Both models, however, distinguished reference from non‐reference sites. 5. The importance of concordance, geographic context and scale are discussed in relation to the design and interpretation of stream integrity indicators. In particular, our findings suggest that community concordance should not be viewed as a substitute for an evaluation of how assemblages respond to environmental stressors.     

Zoosporic marine fungi from the Pacific Northwest (U.S.A.)

Summary An investigation of the zoosporic fungi in the vicinity of the Friday Harbor Laboratory, San Juan Is., Washington, revealed the presence of great numbers of fungi. With one exception (Olpidium sp.) these were all biflagellate organisms. Predominating were species (11) of Thraustochytriaceae which abounded in water, in association with seaweeds, intertidal sands, and particularly on the surface of bottom samples down to depths of 298 m. A twelfth species of this group has several peculiarities and needs further investigation. Of the algal parasites, one on Polysiphonia and Pterosiphonia is considered new and termed Eurychasma joycei n. sp.The assistance of Drs. R. E. Norris and G. J. Hollenberg in calling my attention to certain algal parasites is gratefully acknowledged. I am also indebted to my colleague Dr. H. C. Whisler, and to Dr. C. Anastasiou for assistance in photographic work.     

Recent geologic development of Lake Michigan (U.S.A.)

The stresses placed on Lake Michigan since the advent of industrialization require knowledge of the sedimentology of the whole lake in order to make informed decisions for environmental planning. Sediment accumulation rates are low: areas of the lake receiving the most sediment average only 1 mm a^?1; deep-water basins average 0.1 to 0.5 mm a^?1; and large areas are not receiving any sediment. Sediment was deposited rapidly (typically 5 mm a^?1), in the form of rock flour, during the deglaciation of both Lake Michigan and Lake Superior Basins. Then the rate of accumulation decreased by 80–90% and has remained relatively constant since final deglaciation. Because active sedimentation occurs mostly in the deep water areas of the lake, the sediment remains undisturbed and contains a record of the chemical history of the lake.     

Climatological correlates of screwworm (Cochliomyia hominivorax) abundance in Texas, U.S.A.

The causes of screwworm (Cochliomyia hominivorax) outbreaks in North America are not well understood, but the literature suggests that climate was historically important. Screwworm case incidence in each of seven climatological divisions of Texas was examined for the years 1962-83, the period when sterile-male releases were made. Weak but statistically significant correlations were found between winter and summer cases and mean winter and summer rainfall and temperature when the independent variables were examined one at a time. Multiple regression of log case incidence on previous quarterly cases and current rainfall and temperatures showed a significant, negative effect of temperature on summer cases. Lagged screwworm cases accounted for most of the variation in quarterly cases. No climatic effects were detected in the other seasons. Rainfall was statistically unrelated to screwworm abundance in any season even in an arid region. The analysis does not support a climatic genesis of screwworm outbreaks or eradication. The sterile-male method is a credible explanation for screwworm disappearance.     

Nitrogen uptake and transformation in a midwestern U.S. stream: A stable isotope enrichment study

This study presents a comprehensive analysis ofnitrogen (N) cycling in a second-order forestedstream in southern Michigan that has moderatelyhigh concentrations of ammonium (mean,16 g N/L) and nitrate (17 g N/L). Awhole-stream ¹⁵NH₄ ⁺ addition wasperformed for 6 weeks in June and July, and thetracer ¹⁵N was measured downstream inammonium, nitrate, and detrital and livingbiomass. Ancillary measurements includedbiomass of organic matter, algae, bacteria andfungi, nutrient concentrations, hydrauliccharacteristics, whole-stream metabolism, andnutrient limitation assays. The resultsprovide insights into the heterotrophic natureof woodland streams and reveal the rates atwhich biological processes alter nitrogentransport through stream systems.Ammonium uptake lengths were 766–1349 m anduptake rates were 41–60 g N m^–2min^–1. Nitrate uptake could not bedetected. Nitrification rates were estimatedfrom the downstream increase in¹⁵N-enriched nitrate using a simulationmodel. The ammonium was removed bynitrification (57% of total uptake),heterotrophic bacteria and fungi associatedwith detritus (29%), and epilithic algae(14%). Growth of algae was likely limited bylight rather than nutrients, and dissolvedO₂ revealed that the stream metabolism washeterotrophic overall (P:R = 0.2). Incubationsof detritus in darkened chambers showed thatuptake of ¹⁵N was mostly heterotrophic.Microbial N in detritus and algal N inepilithon appeared to reach isotopic steadystate with the dissolved ammonium, but theisotopic enrichment of the bulk detritus andepilithon did not approach that of ammonium,probably due to a large fraction of organic Nin the bulk samples that was not turning over. The actively cycling fraction of total N inorganic compartments was estimated from theisotopic enrichment, assuming uptake ofammonium but not nitrate, to be 23% forepilithon, 1% for fine benthic organic matter,5% for small woody debris, and 7% for leaves. These percentages agree with independentestimates of epilithic algal biomass, whichwere based on carbon:chlorophyll ratios in bulksamples and in algal fractions separated bydensity-gradient centrifugation in colloidalsilica, and of microbial N in the detritus,which were based on N released by chloroformfumigations.     

Temperature-dependent growth rates of larval midges (Diptera: Chironomidae) from a southeastern U.S. stream

Inland aquatic ecosystems and their biodiversity in Asia represent a wide spectrum along a complex continuum of interacting ecological, economic, socio-cultural and political gradients all of which determine their present and future. Whereas the diversity of biophysical environments ensures a rich inland aquatic biodiversity, their present status has been greatly influenced by human societies that have depended on them for millennia. Besides high population densities and developmental pressures, socio-cultural factors, economic considerations and various policies concerning land and water resources are major factors responsible for the degradation of habitats and loss of biodiversity. The looming global climate change may only worsen the situation unless remedial measures are taken on a large scale and urgently. The future of aquatic biodiversity in Asian countries will depend upon a radical change in national policies on water, and upon research that can support the development of appropriate policies.