Light absorption by phytoplankton and chromophoric dissolved organic matter in the drainage basin and estuary of the Neuse River, North Carolina (U.S.A.)

1. We examined the absorption of solar radiation by phytoplankton and chromophoric dissolved organic matter (CDOM) taking into account riparian shading in the rivers, reservoirs, swamps of the Neuse River Estuary and its drainage basin. 2. In the streams, CDOM typically absorbed 55 and 64% of photons in the spectral range of 400–700 nm (photosynthetically active radiation, PAR) and 500–600 nm, respectively. The large proportion of photons absorbed by CDOM indicates high potential for abiotic photochemial reactions in the 500–600 nm region. 3. Despite the high concentration of nutrients, phytoplankton contributed little (2%) to the total absorption of PAR in the streams. Small (<30 m wide) streams typically received only 7% of incident PAR that impinged onto the more exposed reservoirs and estuary. Riparian shading and the low contribution of phytoplankton to the total absorption resulted in conditions where phytoplankton absorbed nearly two orders of magnitude less PAR in the streams than in the estuary and reservoirs. 4. The results indicated that riparian shading and non‐algal absorbing components can significantly restrict phytoplankton production in nutrient‐rich streams with a high concentration of CDOM flowing throughout forested catchments.     

Distribution of Nitrogen-Fixing Microorganisms along the Neuse River Estuary,North Carolina

Nitrogen fixation genes (nifH) were amplified and sequenced from DNA extracted from surface water samples collected from six stations along the length of the Neuse River Estuary, North Carolina, in order to determine the distribution of nitrogen-fixing organisms in the transition from fresh-to saltwater. Nitrogenase genes were detected in all samples by a nested polymerase chain reaction method, and the amplification products from the upriver, midriver, and downriver stations were cloned, sequenced, and used for phylogenetic analysis. The composition of nifH clone libraries from upriver, midriver, and downriver stations (each composed of 14 randomly selected clones) were very diverse (samples from upriver and midriver stations were composed of 14 unique sequences, downriver station composed of 7 unique sequences) and differed among the stations. Some phylotypes were found at more than one station, but were usually found in the upriver and midriver stations or in the midriver and downriver stations, indicating that the phylotypes were probably transported along the river. Cyanobacterial nifH were not found at the most upriver site, but were a large fraction of sequences (50%) recovered from the downriver station, where nitrate concentration was an order of magnitude lower and salinity was higher. In contrast, γ proteobacteria nifH sequences were much more common at the midriver and upriver sites (58% and 64%, respectively), compared to the downriver site (14%). Results indicate that substantially different nitrogen-fixing assemblages are present along the river, reflecting differential watershed hydrological inputs, sedimentation, and environmental selection pressures, along the salinity gradient.     

Longitudinal and seasonal patterns of stream acidity in a headwater catchment on the Appalachian Plateau, West Virginia, U.S.A.

The chemical composition during baseflow was used to elucidate the fundamental processes controlling longitudinal and seasonal patterns of stream acidity in Yellow Creek, a chronically acidic headwater (pH range 3.7--4.2) on the Appalachian Plateau in northeastern West Virginia. Sulfate concentrations controlled the variability of stream acidity within the Yellow Creek catchment. Decreases in stream free H⁺ acidity with decreasing elevation likely resulted from SO ₄ ^2– retention in riparian wetland areas as well as spatial variation in dominant tree species. Seasonal variations in free H⁺ and inorganic monomeric aluminum (Alⁿ⁺) concentrations appeared related to seasonal fluctuations in baseflow discharge which was controlled by vegetative activity. Baseflow stream discharge, as well as H⁺ and Alⁿ⁺ acidity, gradually declined during the growing season (June through October), likely reflecting microbial SO ₄ ^2– > reduction in saturated anaerobic environments within riparian wetlands. A marked pulse of stream H⁺, Alⁿ⁺, and SO ₄ ^2– coincided with an abrupt increase in baseflow discharge resulting from the cessation of transpiration after leaf-fall in November. This seasonal pattern suggests that autumn may be a critical period for eastern brook trout in streams draining wetlands on the Appalachian Plateau.     

Mallomonas weei (Synurophyceae), a new species from North Carolina, U.S.A.

A new species of Mallomonas, M.weei, is described from North Carolina, U.S.A. Fine structure of scales and bristles has been studied using scanning and transmission electron microscopy. The new species is placed in the section Mallomonas, series Intermediae.     

Distribution of the Family Hydropsychidae (Trichoptera) in the Savannah River Basin of North Carolina,South Carolina and Georgia

Hydropsychids were collected along the length of the Savannah River and its headwaters and tributaries. Species distribution was correlated with chemical and physical properties of water, altitude and stream size. Seven genera and 35 species were found among approximately 100,000 specimens collected. Fourteen species divided into three groups on the bases of altitude and stream size preferences. Turbidity, conductivity, temperature, carbonate, nitrate and nitrite increased along the river's course, whereas maximum velocity and dissolved oxygen decreased. For these factors the maximum value tolerated by a species was associated with the species distribution. The genera Hydropsyche and Cheumatopsyche were the most widely distributed. Several species of these two genera had quite large distributional ranges while others had quite restricted ranges.     

The life history and production of Chaoborus punctipennis (Diptera: Chaoboridae) in Lake Norman,North Carolina,U.S.A.

A study of the life history and production of Chaoborus punctipennis (Say) in Lake Norman, North Carolina, U.S.A. was conducted from February 1978 through January 1979. Four sublittoral (～8 m) and two profundal (～30 m) locations were sampled. Larvae and pupae were collected with a modified Petersen grab and a plankton net, and adults were collected with emergence and light traps. Based on larval, pupal, and adult collections, there appear to be two generations per year — an overwintering spring generation and a summer generation. Annual dry weight standing stock biomass, dry weight production, and P/ B ratio were estimated from each sampling location and depth zone. Production was estimated by the size-frequency method. Standing stock biomass (30.9 mg · m^-2) and production (170.8 mg · m^-2) were highest in the profundal zone. In the sublittoral zone, standing stock biomass and production were 4.7 mg · m^-2, and 29.6 mg · m^-2, respectively. Annual P/ B ratios in the profundal and sublittoral zones were 5.5 and 6.3, respectively.     

Relationships between vegetation patterns and hydroperiod on the Roanoke River floodplain,North Carolina

This study quantified relationships between forest composition and flooding gradients on the Roanoke River floodplain, North Carolina. Because flooding is highly variable in time and space, the research was designed to determine the specific hydrological parameters that control woody species abundance on the landscape scale. I specifically tested the importance of spring vs. yearly flood duration, as well as flood duration during hydrologically wet vs. dry years. Field vegetation samples of woody species composition were integrated with spatial data from a Landsat Thematic Mapper (TM) classification and a flood simulation model derived in part from synthetic aperture radar (SAR) imagery. Flood simulations were output and summarized for the periods 1912–1950 (before dams were constructed on the river) and 1965–1996 (after all of the dams were completed). Tenth percentile (dry), median, and 90th percentile (wet) hydroperiod (flood duration) regimes were generated for the spring and year, both pre- and post-dam. Detrended correspondence analysis (DCA) was used to ordinate the plot data, and correlation/regression between ordination axis scores and the flood variables were used to explore the relationships between flooding and species composition. Nineteenth percentile hydroperiod (i.e., wet conditions) correlated most strongly with DCA axis 1 (r>0.9), indicating that inundation during extremely wet years strongly controls species composition on the floodplain. The results were used to quantitatively determine the niche width for both species and mapped vegetation classes in terms of number of days flooded annually and during the spring growth period. The results suggest that spring hydroperiod is an important mechanism that may drive competitive sorting along the flooding gradient, especially during the early years of succession (i.e., pre-dam, which represents the period during which most of the forests sampled were established), and that annual hydroperiod affects the relative dominance of species as the forests mature.     

The relationship between pH and community structure of invertebrates in streams of the Shenandoah National Park, Virginia, U.S.A.

1. A replicated natural experiment was used to assess the influence of pH and low alkalinity on abundance and richness of invertebrate families in streams draining catchments that receive acid deposition. Individual streams were used as the unit of replication, allowing conclusions to refer to a class of streams rather than to particular streams. 2. We also controlled for several factors other than pH and alkalinity, including flow and temperature, that are recognized as determinants of invertebrate distribution. Samples were from indigenous rocks, standardized for size, surface area, and geology. 3. Repeated measures analyses of variance (ANOVA) revealed that invertebrate abundance and richness were significantly lower at pH 5.8 than at pH 7.1 for the total community. Thirty per cent of the forty-seven families exhibited significantly lower abundance at pH 5.8; thirteen families were absent at pH 5.8. Differences were greatest for Ephemeroptera: species richness was significantly lower at pH 5.8, and 71% of the twenty-four species were either absent (seven) or found in reduced abundance (ten) in the acidic streams. 4. Stream alkalinity is projected to continue to decrease with continued acid deposition in the Shenandoah National Park. Concurrent decreases in pH may lead to the absence or continued numerical decline of certain Ephemeroptera species in streams that acidify to less than pH 6.0 and/or 50μEql^?1 alkalinity.     

Alien Fishes in Natural Streams: Fish Distribution, Assemblage Structure, and Conservation in the Cosumnes River, California, U.S.A.

The Cosumnes River is the largest stream without a major dam on its mainstem in the Sacramento–San Joaquin drainage, central California, U.S.A. We studied its fishes over a 3-year period to answer the following questions: (1) Was the native fish fauna still present? (2) Why were alien fishes so abundant in a river system with a 'natural' flow regime, which elsewhere has been shown to favor native fishes? (3) Were there assemblages of fishes that reflected environmental differences created by the underlying geology? (4) Were there features of the watershed that consistently favored native fishes or that could be managed to favor native fishes? Of the 25 species collected, 17 were alien species; 14 species (five native) were abundant or widely distributed enough to use in detailed analyses. Of the native species, only rainbow trout, Oncorhynchus mykiss, still occupied much of its native range in headwater streams. Other native species have been extirpated or persisted mainly above barriers to alien invasions. The most widely distributed alien species was redeye bass, Micropterus coosae, previously unknown from the river, whose abundance was associated with low-numbers of native species. Other aliens were found primarily in low-land habitats on the valley floor or foothills. Canonical Correspondence Analysis indicated that both native and alien species located on environmental gradients determined largely by elevation, temperature, flow, and emergent vegetation, but the associations with these variables were not strong. While most alien fishes were found in lowland sections of river flowing through agricultural regions, the general relationships between species abundance and landscape-level variables were weak. Assemblages of fishes were poorly defined mixtures of native and alien species. The strikingly distinct geological regions of the basin no longer supported distinct fish assemblages. Species distributions were highly individualistic, reflecting dynamic patterns of introductions, invasions, and local extinctions, as well as physiological tolerances and life history patterns. Most native fishes are likely to persist in the Cosumnes River only if summer flows are increased and if populations above natural barriers are protected from further invasions by alien species, especially redeye bass. General conclusions from this study include: (1) altered habitats can support native species under some circumstances; (2) new fish assemblages with characteristics of 'natural' communities are likely to develop in invaded systems; (3) restoring flow regimes to favor native fishes may require restoring minimum summer flows as well as high channel-forming flows. However, reversing or even reducing, the impact of the predatory redeye bass, pre-adapted for California streams, is probably not possible.     

Correlates of habitat favourability for benthic macroinvertebrates at five stream sites in an Appalachian Mountain drainage basin, U.S.A.

SUMMARY.

• 1 Based on monthly samples taken over a 1-year period, average density (individuals m^-2). average standing biomass and annual production of benthic macroinvertebrates were estimated at five sites within an Appalachian Mountain drainage basin. Two sites were on first order streams and differed from the three second order sites: they were smaller and more shallow and they were depressed in pH and chemical richness.
• 2 Patterns of abundance of individual taxa, of higher taxonomic groups and of functional (feeding) groups differed according to whether abundance was measured as density, as standing biomass or as annual production. Standing biomass was chosen as the measure of macroinvertebrate abundance because available evidence indicates that only standing biomass is consistently, positively correlated with survivorship, and thus with habitat favourability.
• 3 Two non-insect taxa (the crayfish Cambarus and the snail Leptoxis carinata) dominated standing biomass at each site. Consequently, differences among sites in total macroinvertebrate standing biomass and differences within and among sites in standing biomass of functional groups were determined by differences in estimated standing biomass of these two taxa. Differences in estimates of crayfish standing biomass were consistent with an explanation based on the availability of refuges created by large substrate particles. The abundance of L. carinata appeared to be controlled primarily by water chemistry and possibly secondarily by predators. A number of insect taxa exhibited patterns of standing biomass consistent with hypotheses based on effects of annual depth-flow regimes. Hypotheses based on differences in food resource and on competition appeared, in general, to be inconsistent with observed patterns of macroinvertebrate abundance.
• 4 Contrary to predictions of the River Continuum Concept, the shredder functional group in the Guys Run drainage and in other temperate woodland streams was found to be a minor part of total macroinvertebrate standing biomass. Further, in a majority of small forested stream sites studied to date, standing biomass of grazers has been determined to be greater than that of shredders.

     

Organic matter transport in an Appalachian Mountain river in Virginia,U.S.A.

Organic material transport in the New River, Virginia, was investigated over a 12 month period. Collections were made using drift nets and grab water samples from bridges at two sites about 210 km apart. About midway between the two sampling sites is a 1920 ha impoundment used for flood control and power generation. Dissolved organic matter (DOM) ranged 1–50 mg l^–1 at Site 1, upstream from the impoundment, and 11–19 mg l^–1 at Site 2 and was the most abundant form of organic matter at both sites during most periods of the year. Fine particulate organic matter (FPOM) ranged 1–45 mg l^–1 at Site 1 and 1–9 mg l^–1 at Site 2. Concentration of coarse particulate organic matter (CPOM) ranged 0.1–0.7 mg l^–1 at Site 1 and 0.1–0.2 mg l^–1 at Site 2. On an annual basis, the organic matter loads at Site 1 and Site 2 were computed to be 67 000 and 76 800 T y^–1, respectively, suggesting that the impoundment trapped and processed POM, and that municipal and industrial treatment facilities between the study sites supplemented DOM in the river.     

Bartonella and Rickettsia in fleas and lice from mammals in South Carolina, U.S.A.

Species in the genera Bartonella and Rickettsia are vector-borne pathogens of humans and domestic animals. The natural reservoirs and enzootic transmission cycles of these bacteria are poorly known in South Carolina. Thirteen species of lice and fleas were collected from urban animals and screened for the presence of Bartonella and Rickettsia by PCR amplification using genus-specific primers. Bartonella henselae was present in cat fleas (Ctenocephalides felis) from Virginia opossums (Didelphis virginiana) and a novel genotype of Bartonella was detected in Orchopeas howardi from an eastern gray squirrel (Sciurus carolinensis). We detected R. typhi and three novel genotypes Rickettsia in other species of fleas and lice. Rickettsia typhi, the causative agent of murine typhus, was detected in two pools of lice (Enderleinellus marmotae) from the woodchuck (Marmota monax). Cat fleas harbored one of two novel genotypes of Rickettsia. A third novel Rickettsia was detected in Orchopeas howardi from an eastern gray squirrel.     

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.     

Influence of stream geomorphic condition on fish communities in Vermont, U.S.A.

1. Evaluations of stream geomorphic condition may increase our understanding of the composite effects of human‐induced habitat change on fish communities. Using systematic sampling of 44 reaches spread across 26 rivers in Vermont from 2002 through 2004, we tested the hypothesis that stream reaches in reference geomorphic condition would support fish assemblages that differed in diversity and productivity from fish communities found in reaches of poorer geomorphic condition. 2. At each study reach, we sampled the fish community, identified the morphological unit according to common stream classification systems and then evaluated the extent of deviation from reference geomorphic condition using a regionally adapted geomorphic assessment methodology. 3. We used principal component analysis (PCA) and linear regression to build exploratory models linking stream geomorphic condition to fish community characteristics. 4. Our results suggest that geomorphic condition significantly influences fish community diversity, productivity and condition. Geomorphic condition was a significant factor in all of our fish community models. In conjunction with additional reach characteristics, geomorphic condition explained up to 31% of the total variance observed in models for species diversity of fish communities, 44% of the variance in assemblage biomass and 45% of the variance in a regional index of biotic integrity. 5. Our work builds on single‐species evidence that geomorphic characteristics represent important local‐scale fish‐habitat variables, showing that stream geomorphic condition is a dominant factor affecting entire fish communities. Our results enhance our understanding of the hierarchy of factors that influences fish community diversity and organisation and support the use of geomorphic condition assessments in stream management.     

Quantity and quality of seston in an impounded and a free-flowing river in Virginia,U.S.A.

Seston in the impounded North Anna River (NAR) was analyzed and compared to that in the free-flowing South Anna River (SAR) in Virginia, U.S.A. A wet filtration technique was used to separate seston into five size classes. The overall quantity of organic seston was much lower in the NAR than in the SAR. The seston in the NAR was composed of more living organisms, in particular zooplankters in the medium large (234–864 µm) and small (105–234 µm) size classes and diatoms and other algae in the fine (43–105 µm) and very fine (25–43 µm) size classes. The percentage of zooplankton declined sharply before reaching the downstream study site (32 km). The seston in the NAR tended to consist of slightly larger particles, but 80–85% of the seston in both rivers was in the ultrafine (0.45–25 µm) size class, which was almost entirely composed of detritus. One indication of seston food quality, the organic/inorganic ratio, was considerably higher for the medium large and small size classes in the NAR immediately below the dam and for the fine and very fine size classes farther downstream. Another indication of food quality, the usable caloric content, showed that the seston in the NAR contained considerably less total assimilable energy as far as 32 km downstream from the dam, but that the medium large and small size classes were rich in assimilable energy immediately below the dam because of zooplankton released from the reservoir. Thus, the overall quantity and quality of seston was lower in the NAR, but the quality of the seston, for at least a short distance below the dam, was higher in a well-defined size range that can be effectively utilized by certain filter feeders.     

Periphyton productivity and radionuclide accumulation in the Columbia River,Washington, U.S.A.

Summary An investigation of the periphyton of the Columbia River below the Hanford Atomic Works, Washington, was conducted to study the relationships between productivity, radionuclide uptake, and environmental influences.Best correlations between the four biomass measurements were between dry weight, ash weight, and chlorophyll a. Net Production Rate varied from 0.005 to 0.070 mg dry weight/cm²/day and was closely related to chlorophyll a and also to solar energy.The accumulation of ³²P and ⁶⁵Zn was highly related to dry and ash weight and chlorophyll a. Low correlations were found between radionuclide accumulation and the radioisotope burden of the river. The data suggest that adsorption was the dominant mode of uptake.This paper is based on work performed under United States Atomic Energy Commission Contract AT(45-1)-1830.     

Dynamics and predictive modelling of Vibrio spp. in the Neuse River Estuary, North Carolina, USA

Vibrio spp. are naturally occurring bacteria in marine and estuarine environments around the world. The genus includes several human and animal pathogens that can negatively impact human health, seafood and aquaculture. Vibrio spp. populations are capable of rapid adaptation in response to changing environmental conditions, making them dynamic over short-term and seasonal scales. Temperature, vertical mixing, tidal flushing, climate, precipitation and nutrient loading can change the estuarine environment and subsequently alter microbial community structure, including Vibrio spp., affecting estuarine water quality and public health. To describe these dynamics, Vibrio spp. concentrations and a range of microbial, physical and chemical measures were monitored every 2 weeks and after storm events for 19 months in the Neuse River Estuary (NRE). Results showed clear seasonal and geographic trends in Vibrio spp. abundance. Multiple regression analysis revealed a strong relationship to temperature and salinity, with additional minor influences of chlorophyll a and dissolved organic carbon. Similar models based on easily measured environmental parameters should be pursued for individual Vibrio species in the NRE and other estuarine environments. Predictive models provide useful information for managers, researchers and modellers of estuarine ecosystems.     

Composition of inorganic and organic nutrient sources influences phytoplankton community structure in the New River Estuary, North Carolina

The New River Estuary, NC, is a nutrient-sensitive, eutrophic water body that is prone to harmful algal blooms. High annual loading from the watershed of varying nutrient forms, including inorganic phosphorus and inorganic and organic nitrogen, may be linked to the persistence of algal blooms in the estuary. In order to evaluate phytoplankton response to nutrient inputs, a series of in situ nutrient addition experiments were carried out during June 2010 to July 2011 on water from an estuarine site known to support algal blooms. Estuarine water was enriched with nutrients consisting of individual and combined sources of dissolved inorganic nitrogen, orthophosphate, urea, and a natural dissolved organic nitrogen (DON) addition derived from upstream New River water. The combined inorganic N and P addition most frequently stimulated phytoplankton biomass production as total chlorophyll a. The responses of diagnostic (of major algal groups) photopigments were also evaluated. Significant increases in peridinin (dinoflagellates), chlorophyll b (chlorophytes), and myxoxanthophyll (cyanobacteria) were most frequently promoted by additions containing riverine DON. Significant increases in zeaxanthin (cyanobacteria) were more frequently promoted by inorganic nitrogen additions, while increases in fucoxanthin (diatoms) and alloxanthin (cryptophytes) were not promoted consistently by any one nutrient treatment. Evaluating the impact of varying nutrient forms on phytoplankton community dynamics is necessary in order to develop strategies to avoid long-term changes in community structure and larger-scale changes in ecosystem condition.     

Differences in Species Composition and Feeding Ecology of Catostomid Fishes in Two Distinct Segments of the Missouri River, North Dakota, U.S.A.

In 1997 and 1998, we sampled the Missouri River, North Dakota to determine if anthropogenic disturbances had influenced catostomid species composition and feeding ecology. We compared two distinct river segments, the Missouri River between the mouth of the Yellowstone River and Lake Sakakawea (the Yellowstone–Sakakawea segment (YSS)), a moderately altered segment and the Missouri River between Garrison Dam and Lake Oahe (the Garrison–Oahe segment (GOS)), a highly altered segment. The segments exhibited greatly different sucker communities. Bigmouth buffalo, Ictiobus cyprinellus, smallmouth buffalo, Ictiobus bubalus, and river carpsucker, Carpiodes carpio, represented 94% of the sucker catch in the YSS, whereas in the GOS, white sucker, Catostomus commersoni, and longnose sucker, Catostomus catostomus, constituted 98% of the sucker catch. In the YSS, high zooplankton densities led to greater sucker zooplanktivory and food niche overlap than in the GOS. Intense anthropogenic disturbances to the GOS are associated with the differences in sucker species composition, prey density and composition, and sucker feeding ecology between the two segments.     

Leaf breakdown in a regulated desert river: Colorado River, Arizona, U.S.A.

We compared processing rates (k _d) for leaves of the native willow (Salix exigua Nutt.) and cottonwood (Populus fremontii Wats.) to those of the non-native salt cedar (Tamarix chinensis Lour.) in the regulated Colorado River, U.S.A. Leaf packs of each species were incubated at Lees Ferry, approximately 26 km below Glen Canyon Dam, Arizona. Leaf packs were processed at 2, 21, 46, 84 and 142-d intervals. Water temperatures remained relatively constant (10 °C, SE ± 1 °C) during the study. There were significant differences in processing rates between species, with P. fremontii showing the fastest breakdown. After 142 d, only 20% of the P. fremontii leaf mass remained, whereas 30% and 52% of leaf masses remained for T. chinensis and S. exigua, respectively. The k _d value for P. fremontii was 0.0062 compared to 0.0049 and 0.0038 for T. chinensis and S. exigua, respectively. Invertebrate colonization was not significantly different between native and non-native plant species with oligochaetes the most abundant animal colonizing the leaf packs. Dual stable isotope analysis showed that leaf material was not the primary food for invertebrates associated with leaf packs. Processing rates for all leaf types were slow in the regulated Colorado River compared to rates reported in many other systems. This is likely due to the lack of caddisfly and stonefly shredders and perhaps slow metabolic rates by microbes.