Response of stream macroinvertebrate assemblages to erosion control structures in a wastewater dominated urban stream in the southwestern U.S.

Effects of stream erosion control structures on aquatic macroinvertebrates were studied (2000–2009) in a wastewater dominated drainage (Wash) in Las Vegas, Nevada. Mainstem sites with and without structures, wastewater treatment plant outfalls, a reference site above treatment plant inputs, and tributary sites were sampled. Ordination suggested hydrology and channel characteristics (current velocity, stream depth, and width), and water quality (conductivity) were primary factors in organizing macroinvertebrate communities, with some variables altered at structures. Treatment plant inputs changed hydrology (increased flows), water chemistry (conductivity decreased below treatment plants), and temperature. Assemblages differed between site types, with midges and damselflies important at tributary sites and Fallceon mayflies and Smicridea caddisflies common at erosion control structures. Locally unique communities developed at structures which also may have facilitated exotic species invasions. Analyses showed that taxa richness increased over time at these sites and differed significantly from richness at sites without structures. Structures appeared important in retaining organic matter and, among mainstem sites, coarse particulate organic matter was highest, but variable, at structures and at wetlands above the structures. Erosion control structures, coupled with warm effluent, high baseflows, and altered water quality resulted in development of a macroinvertebrate community that did not trend towards reference or tributary sites. In this case, ecological communities at structures used for river restoration were not on a continuum between disturbed and reference sites. Goal setting of community responses at these structures would have required insight beyond the simple use of reference site attributes.     

Occurrence of a thermocline in two lakes of the semi-arid region in western Rajasthan,India

Water quality samples were obtained monthly or bimonthly 17 times from May 1974 to May 1975 at three stations in Delaware Bay. In addition, two 12-hour cruises were also conducted at one station in February and April 1975. Surface and bottom water samples were taken. Measurements and analyses included temperature, salinity, dissolved oxygen, silicate, nitrate and nitrite, orthophosphate, ammonia, chlorophylls a, b, and c, phaeopigments, and carotenoids. The annual pattern of temperature was typical of an estuary in the mid-Atlantic Bight. Salinity and dissolved oxygen ranged from 22.9 to 29.7‰ and from 4.53 to 8.53 ml/l, respectively. Nutrient and pigment values showed seasonal peaks. Silicate (30.3 μg-at/1) and orthosphate (1.59 μg-at/1) were highest in September. Highest concentrations of ammonia were commonly measured in July (6.80 μg-at/1) and September (5.13 μg-at/1), and peak concentrations of nitrate and nitrite were recorded in January (24.27 μg-at/l), February (18.2 μg-at/1), and May (16.37 μg-at/1). Peak concentrations of chlorophyll a were measured in August (17.2 μg-at/1), October (15.70 μg-at/1), and March (15.33 μg-at/1). In general, the annual pattern for chlorophylls b and c were similar to chlorophyll a. Comparison with other estuaries and bays (Narrangansett Bay, Long Island Sound, Raritan Bay, and Chesapeake Bay) indicated that concentrations of nutrients and pigments in Delaware Bay were generally similar in magnitude and seasonality, These are the first set of seasonal water quality data for lower Delaware Bay.     

Growth and reproduction of three cladoceran species from a small wetland in the south-eastern U.S.A.

SUMMARY 1. Growth, reproduction and life‐history parameters were measured for three cladoceran species from a small south‐eastern wetland, U.S.A. Simocephalus serrulatus, Diaphanosoma brachyurum and Scapholeberis mucronata juveniles were reared at temperatures between 10 and 25 °C on natural food resources. 2. Growth rate increased with temperature and decreased with individual size for all three species. Maximum somatic growth rate was higher for Simocephalus (49–72% day^?1) and Diaphanosoma (21–91% day^?1) than for Scapholeberis (11–45% day^?1). Multiple regression equations were developed which predict temperature‐ and mass‐specific growth rates for each species. 3. Scapholeberis egg production was positively related to temperature; however, maximum egg production occurred at intermediate temperatures for Simocephalus and Diaphanosoma. Mean cumulative egg production was higher for Scapholeberis (28–92 eggs per female) than for Simocephalus (18–25 eggs per female) and Diaphanosoma (1–41 eggs per female), and was related to differences in reproductive strategy and survival. 4. Survival was inversely related to temperature in most cases. For all three cladocerans, the intrinsic rate of increase (r) and net reproductive rate (R₀) increased with temperature, whereas generation time (G) decreased. Greater egg production by Scapholeberis compared with the other two cladocerans was consistent with higher R₀ values for Scapholeberis at any given temperature. Although r was very similar among species, G was typically longer for Scapholeberis than for Simocephalus and Diaphanosoma. 5. This analysis provides basic information about the population parameters of these coexisting wetland species, and the growth rate models can be applied to field data to determine production dynamics.     

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.     

Permian predecessors of the mesozoic pteridosperms in western Angaraland,U.S.S.R.

The Kungurian and Upper Permian beds of western Angaraland yield a number of alleged predecessors of Mesozoic flora including Rhaphidopteris praecursoria sp. nov., the oldest representative of the genus hitherto known from the Jurassic only. R. praecursoria shows remarkably variable frond structures. Possible phyletic links between the Permian Rhaphidopteris, Triassic Corystospermaceae, and Jurassic Pachypteris and Rhaphidopteris are suggested.     

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.     

Catholic social policy and U.S. health care reform: a relationship revisited

The Roman Catholic Church is the single largest denomination in the United States and the one with the most extensive provider stake in health (and related social service) care. As a follow-up to an earlier analysis of the Catholic role in the thwarted health care reform effort of 1993-94, this article looks at the revival of interest in reform and at the rationale behind and strategy of the Catholic Church's current agenda-setting initiative. The emphasis in this article is on the delicate relationship between organized religion and social policy in a society with an officially secular culture.     

Co-occurrence of in-stream nitrogen fixation and denitrification across a nitrogen gradient in a western U.S. watershed

It is frequently assumed that nitrogen (N₂) fixation and denitrification do not co-occur in streams because each process should be favored under different concentrations of dissolved inorganic nitrogen (DIN), and therefore these processes are rarely quantified together. We asked if these processes could co-exist by conducting a spatial survey of N₂ fixation using acetylene reduction and denitrification using acetylene block [with and without amendments of carbon (C) as glucose and nitrogen (N) as nitrate]. Rates were measured on rocks and sediment in 8 southeastern Idaho streams encompassing a DIN gradient of 26–615 µg L^?1. Sampling at each site was repeated in summer 2015 and 2016. We found that both denitrification and N₂ fixation occurred across the gradient of DIN concentrations, with N₂ fixation occurring primarily on rocks and denitrification occurring in sediment. N₂ fixation rates on rocks significantly decreased 100× across the DIN gradient in 1 year of the study, and amended (with N and C) denitrification rates increased 10× across the DIN gradient in both years. Multiple linear regression and partial least squares models with environmental characteristics measured at the scale of entire stream reaches showed that C and phosphorus were positive predictors of amended and unamended denitrification rates, but no significant model could explain N₂ fixation rates across all streams and years. This, coupled with the observation that detectable rates of N₂ fixation occurred primarily on rocks and denitrification occurred primarily on sediment, suggests that microhabitat scale factors may better predict the co-occurrence of these processes within stream reaches. Overlooking the potential co-occurrence of N₂ fixation and denitrification in stream ecosystems will impede understanding by oversimplifying the contribution of each process to the N cycle.     

A case study of nitrogen saturation in western U.S. forests

Virtually complete nitrification of the available ammonium in soil and nitrification activity in the forest floor are important factors predisposing forests in the San Bernardino Mountains of southern California to nitrogen (N) saturation. As a result, inorganic N in the soil solution is dominated by nitrate. High nitrification rates also generate elevated nitric oxide (NO) emissions from soil. High-base cation saturation of these soils means that soil calcium depletion or effects associated with soil acidification are not an immediate risk for forest health as has been postulated for mesic forests in the eastern U.S. Physiological disturbance (e.g., altered carbon [C] cycling, reduced fine root biomass, premature needle abscission) of ozone-sensitive ponderosa pine trees exposed to high N deposition and high ozone levels appear to be the greater threat to forest sustainability. However, N deposition appears to offset the aboveground growth depression effects of ozone exposure. High nitrification activity reported for many western ecosystems suggests that with chronic N inputs these systems are prone to N saturation and hydrologic and gaseous losses of N. High runoff during the winter wet season in California forests under a Mediterranean climate may further predispose these watersheds to high nitrate leachate losses. After 4 years of N fertilization at a severely N saturated site in the San Bernardino Mountains, bole growth unexpectedly increased. Reduced C allocation below- ground at this site, presumably in response to ozone or N or both pollutants, may enhance the bole growth response to added N.     

Greenhouse gas fluxes of grazed and hayed wetland catchments in the U.S. Prairie Pothole Ecoregion

Wetland catchments are major ecosystems in the Prairie Pothole Region (PPR) and play an important role in greenhouse gases (GHG) flux. However, there is limited information regarding effects of land-use on GHG fluxes from these wetland systems. We examined the effects of grazing and haying, two common land-use practices in the region, on GHG fluxes from wetland catchments during 2007 and 2008. Fluxes of methane (CH₄), nitrous oxide (N₂O), and carbon dioxide (CO₂), along with soil water content and temperature, were measured along a topographic gradient every other week during the growing season near Ipswich, SD, USA. Closed, opaque chambers were used to measure fluxes of soil and plant respiration from native sod catchments that were grazed or left idle, and from recently restored catchments which were seeded with native plant species; half of these catchments were hayed once during the growing season. Catchments were adjacent to each other and had similar soils, soil nitrogen and organic carbon content, precipitation, and vegetation. When compared with idle catchments, grazing as a land-use had little effect on GHG fluxes. Likewise, haying had little effect on fluxes of CH₄ and N₂O compared with non-hayed catchments. Haying, however, did have a significant effect on combined soil and vegetative CO₂ flux in restored wetland catchments owing to the immediate and comprehensive effect haying has on plant productivity. This study also examined soil conditions that affect GHG fluxes and provides cumulative annual estimates of GHG fluxes from wetland catchment in the PPR.     

The trophic basis of production of the macroinvertebrate community of a southeastern U.S.A. blackwater stream

The trophic basis of production of the macroinvertebrate communities at three sites on a second-order, low gradient blackwater stream in southeastern U.S.A. was determined. The sampling sites were located above, within and below a low-flow swamp system. From 47–64% of macroinvertebrate production was supported by FPOM at the three sites, with dependence on FPOM being greatest at the swamp site. Algae (filamentous species and diatoms) supported 15–31% of production, indicating that algae can be of considerable importance even in fully canopied headwater streams. The production of some collector-gatherers including Stenonema modestum (55%), Hexagenia munda (58%) and Baetis spp. (78%), was supported predominantly by algae. Algae also supported 61–79% of Hydropsychidae production and 68% of Simuliidae production. Animal material supported 16–26% of macroinvertebrate production at the three sites. CPOM was of minor direct importance to the macroinvertebrate community of this headwater stream, supporting only 1–3% of macroinvertebrate production. Shredders ingested only 1–3 g m⁻² y⁻¹ of CPOM, or about 1% of the annual direct leaf fall to this stream. Assuming a 10% assimilation efficiency for CPOM, shredders produced <3 g m⁻² y⁻¹ of FPOM through CPOM processing, this being approximately 2 orders of magnitude less than reported for high gradient headwater streams. These results indicate that low-order coastal plain streams vary somewhat from the River Continuum Concept in that they exhibit little utilization of and dependence on CPOM as a direct energy source. Only the smallest first-order streams and especially the extensive floodplains may be the functional headwaters of these stream systems.     

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     

Changes in algal assemblages along observed and experimental phosphorus gradients in a subtropical wetland, U.S.A.

• 1 We wanted to determine if changes in algae in the Everglades were due to increased phosphorus (P) loading. Epiphytic algae, water chemistry, and surface sediment chemistry were characterized from 32 sloughs along a P gradient in the Everglades and changes in the algal assemblages along the P gradient were compared with those along an experimental P gradient of in situ mesocosms. The sloughs are the wettest open water habitats characterized by floating and submerged aquatic plants in the Everglades.
• 2 Algal species composition was much more sensitive to P concentration than algal biomass. The diatom species variance among sloughs, captured by 1st ordination axis, was more highly correlated with total P (TP) in surface sediments (r = ‐ 0.79), than soluble reactive P (SRP) (r = ‐ 0.08) and TP (r = ‐ 0.48) in the water column. Algal biomass (µg chl a cm^‐2) was not significantly correlated with P (SRP: r = 0.22, TP: r = 0.19, sediment TP: r = 0.07) along the P gradient in the Everglades. Cluster analysis classified diatom species assemblages in 32 sloughs into three groups (TWIN I, II, III), which corresponded to three zones along the P gradient. Dominant diatom species shifted from Mastogloia smithii (40.3%), Cymbella scotica (22.3%), and Fragilaria synegrotesca (21.8%) in TWIN I to Nitzschia amphibia (22.4%) and C. microcephala (12.4%) in TWIN III. TP in surface sediments and TP in epiphyton assemblages increased 4‐ and 5‐fold from TWIN I to TWIN III, respectively.
• 3 Patterns in epiphytic assemblages along the experimental P gradient in the mesocosms were very similar to those along the Everglades P gradient. Shannon diversity indices and species richness significantly increased along both P gradients. TN : TP ratio in epiphyton assemblages significantly decreased as sediment TP increased along both P gradient. Ordination analysis showed that diatom assemblages in the impacted zone (TWIN III) were ordinated closely to the assemblages from the highest P treatments in the mesocosms. The assemblages from the less impacted zone (TWIN I) were ordinated closely to the assemblages from controls in the mesocosms.
• 4 Concurrence between results of our survey and experiments suggest that changes in epiphytic assemblages along the P gradient in the Everglades are caused by increases in P concentrations.

     

Resource utilization by bull char and cutthroat trout in a mountain stream in Montana,U.S.A.

Resource utilization of sympatric populations of bull char,Salvelinus confluentus, and west-slope cutthroat trout,Oncorhynchus clarki lewisi, were studied by underwater observations of foraging behaviour and microhabitat use, and dietary analysis in a mountain stream of the Flathead River Basin, northwest Montana, U.S.A. Nearly 70% of bull char were categorized as benthic foragers, which moved constantly and captured prey primarily from the streambed, while all cutthroat trout were drift foragers, which held relatively fixed focal points in the midwater layers of pools during foraging. The composition of stomach contents was markedly different between the two species. Bull char fed primarily on baetid mayflies captured from the benthos or drift, whereas cutthroat trout ate primarily terrestrial invertebrates. The species also used different microhabitats. Bull char held positions close to the streambed and rarely strayed far from overhead cover, whereas cutthroat trout held focal points farther above the bed and far from overhead cover. Dietary segregation between these two salmonids appeared to result not only from differences in foraging tactics but also in the foraging microhabitats. Resource partitioning is considered to be one of important mechanisms allowing coexistence of these two stream salmonids.