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  • 1
    Electronic Resource
    Electronic Resource
    Factors affecting ammonium uptake in streams – an inter-biome perspective (2003)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 48 (2003), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. The Lotic Intersite Nitrogen eXperiment (LINX) was a coordinated study of the relationships between North American biomes and factors governing ammonium uptake in streams. Our objective was to relate inter-biome variability of ammonium uptake to physical, chemical and biological processes.2. Data were collected from 11 streams ranging from arctic to tropical and from desert to rainforest. Measurements at each site included physical, hydraulic and chemical characteristics, biological parameters, whole-stream metabolism and ammonium uptake. Ammonium uptake was measured by injection of 15N-ammonium and downstream measurements of 15N-ammonium concentration.3. We found no general, statistically significant relationships that explained the variability in ammonium uptake among sites. However, this approach does not account for the multiple mechanisms of ammonium uptake in streams. When we estimated biological demand for inorganic nitrogen based on our measurements of in-stream metabolism, we found good correspondence between calculated nitrogen demand and measured assimilative nitrogen uptake.4. Nitrogen uptake varied little among sites, reflecting metabolic compensation in streams in a variety of distinctly different biomes (autotrophic production is high where allochthonous inputs are relatively low and vice versa).5. Both autotrophic and heterotrophic metabolism require nitrogen and these biotic processes dominate inorganic nitrogen retention in streams. Factors that affect the relative balance of autotrophic and heterotrophic metabolism indirectly control inorganic nitrogen uptake.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.2003.01094.x
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  • 2
    Electronic Resource
    Electronic Resource
    Newly recognized anticarcinogenic fatty acids: identification and quantification in natural and processed cheeses (1989)
    s.l. : American Chemical Society
    Journal of agricultural and food chemistry 37 (1989), S. 75-81 
    Details
    ISSN: 1520-5118
    Source: ACS Legacy Archives
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jf00085a018
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  • 3
    Electronic Resource
    Electronic Resource
    Nutrient dynamics at the interface between surface waters and groundwaters (1998)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 40 (1998), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. The surface water/groundwater (SW/GW) interface is a crucial control point for lateral nutrient fluxes between uplands and aquatic ecosystems and for upstream/downstream (longitudinal) processes in lotic ecosystems.2. Hydrological and biogeochemical dynamics of the SW/GW ecotone are linked to the degree of channel constraint and the sediment characteristics of the floodplain and stream bed.3. The availability of specific chemical forms of electron donors and electron acceptors affects the spatial distribution of biogeochemical processes at the SW/GW interface. Temporal change in discharge is also a major factor affecting the rate and extent of these processes.4. The magnitude of SW/GW interactions in lotic ecosystems is predicted to be a major determinant of solute retention. Channel morphology, stream bed composition and discharge are predicted to be important controls on SW/GW interactions.5. Interdisciplinary research involving hydrologists, geomorphologists, aquatic ecologists, microbial ecologists and landscape ecologists is needed to further our present understanding of this critical interface linking terrestrial and aquatic ecosystems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.1998.00367.x
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  • 4
    Electronic Resource
    Electronic Resource
    The impact of flash floods on microbial distribution and biogeochemistry in the parafluvial zone of a desert stream (1998)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 40 (1998), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. The impact of flash flooding on microbial distribution and biogeochemistry was investigated in the parafluvial zone (the part of the active channel lateral to the surface stream) of Sycamore Creek, a Sonoran Desert stream in central Arizona.2. It was hypothesized that subsurface bacteria were dependent on the import of algal-derived organic matter from the surface stream, and it was therefore predicted that microbial numbers and rates of microbially mediated processes would be highest at locations of surface to subsurface hydrologic exchange and at times when algal biomass was high.3. Prior to a flash flood on 19 July 1994, chlorophyll a was high (≈ 400 mg m–2) in the surface stream and microbial numbers were highest at the stream–parafluvial interface and declined along parafluvial flowpaths, supporting the hypothesized algal–bacterial linkage. Immediately following the flash flood, chlorophyll a was low (≈ 7 mg m–2), and microbial numbers were reduced at the stream–parafluvial interface.4. Counter to expectations, parafluvial functioning (in terms of nitrate production and dissolved oxygen decline along flowpaths) re-established immediately after the flood receded. Therefore, material other than algal exudates supported parafluvial metabolism immediately postflood, and terrestrially derived dissolved organic matter is the likely source.5. Algae in the surface stream recovered quickly following flooding, but recovery of parafluvial bacteria lagged somewhat behind. These results highlight the importance of surface–subsurface interaction to stream ecosystem functioning and show that the nature of these interactions changes substantially in successional time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.1998.00362.x
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  • 5
    Electronic Resource
    Electronic Resource
    Mechanisms of benthic algal recovery following spates: comparison of simulated and natural events (1994)
    Springer
    Oecologia 98 (1994), S. 280-290 
    Details
    ISSN: 1432-1939
    Keywords: Benthic algae ; Spates ; Recovery ; Scour ; Enrichment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We conducted a manipulative field experiment to examine individual and interactive effects of scour and short-term nutrient enrichment (4 h exposure) on postspate recovery of benthic algae in a desert stream. We then compared recovery from these simulated-spate conditions to algal recovery patterns following a natural spate that increased water-column nutrient levels for 2 weeks. That event differentially scoured communities on artificial substrata in place for a long-term experiment, significantly reducing biomass in 49-day-old communities but causing no significant reduction of biomass in older, 133-day-old communities. Thus, we were able to examine recovery of scoured and non-scoured benthic algal communities under natural post-spate conditions. Both natural and simulated spates reduced actual and relative abundances of diatoms within communities. In the manipulative experiment, scoured communities accrued biomass more rapidly than those not subjected to scour, but short-term enrichment had not effect. Accrual of diatoms and green algae was stimulated by the scour manipulations, while cyanobacteria maintained equal rates of growth in all treatments. Following the natural spate, diatom and green-algal densities increased in scoured communities, but recovery of algal biomass was slow on both scoured and non-scoured substrata, primarily because cyanobacteria, the dominant algal group on all tiles, did not increase under exposure to highly nitrate-enriched waters. Rates of algal cell accrual were inversely correlated with the amount of algal biomass present at the start of a recovery sequence. Algal immigration rates measured immediately after the natural spate and during an interflood period in the same season did not differ, indicating that the algal drift pool was not augmented by disturbance. Benthic algal recovery following spates is strongly influenced by the degree of scour generated by the event, but recovery patterns are also affected by the length of post-spate enrichment and the taxonomic composition of the affected community.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00324216
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  • 6
    Electronic Resource
    Electronic Resource
    A long-term perspective of dissolved organic carbon transport in Sycamore Creek, Arizona, USA (1996)
    Springer
    Hydrobiologia 317 (1996), S. 183-188 
    Details
    ISSN: 1573-5117
    Keywords: dissolved organic carbon ; organic matter export ; desert streams
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Dissolved organic carbon (DOC) dynamics were examined over five years (1989–1993) in Sycamore Creek, a Sonoran Desert stream, specifically focusing on DOC concentration in surface and hyporheic waters, and rates of export. In 1989 and 1990, the years of lowest stream discharge (0.08 and 0.04 m3 s−1 annual mean of daily discharge, respectively), DOC was high, averaging 7.37 and 6.22 mgC l−1 (weighted annual means). In contrast, from 1991 through 1993, a period of increased flow (1.1, 1.2 and 4.3 m3 s−1), concentration was significantly lower (P〈0.001) with annual mean concentrations of 3.54, 3.49 and 3.39 mgC l−1. Concentration exhibited little spatial variation between two sampling stations located 6 km apart along the mainstem or between surface and hyporheic waters. Annual export of DOC from Sycamore Creek varied 100-fold over the five-year period from a mean rate of only 24 kgC d−1 in 1990 to 2100 kgC d−1 in 1993. Ninety percent of DOC was exported by flows greater than 2.8 m3 s−1, and 50% during flows greater than 27 m3 s−1; flows of 2.8 and 24 m3 s−1 occurred only 9 and 1% of the time. The export of organic matter in Sycamore Creek appears to be coupled to El Niño-Southern Oscillation phenomena. The years of highest export, 1991–1993, had El Niño conditions while 1989 and 1990 had medial conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00036468
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  • 7
    Electronic Resource
    Electronic Resource
    Material Spiraling in Stream Corridors: A Telescoping Ecosystem Model (1998)
    Springer
    Ecosystems 1 (1998), S. 19-34 
    Details
    ISSN: 1435-0629
    Keywords: Key words: stream; riparian; disturbance; nutrients; hyporheic; hydrology; telescoping ecosystem.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: ABSTRACT Stream ecosystems consist of several subsystems that are spatially distributed concentrically, analogous to the elements of a simple telescope. Subsystems include the central surface stream, vertically and laterally arrayed saturated sediments (hyporheic and parafluvial zones), and the most distal element, the riparian zone. These zones are hydrologically connected; thus water and its dissolved and suspended load move through all of these subsystems as it flows downstream. In any given subsystem, chemical transformations result in a change in the quantity of materials in transport. Processing length is the length of subsystem required to “process” an amount of substrate equal to advective input. Long processing lengths reflect low rates of material cycling. Processing length provides the length dimension of each cylindrical element of the telescope and is specific to subsystem (for example, the surface stream), substrate (for instance, nitrate), and process (denitrification, for example). Disturbance causes processing length to increase. Processing length decreases during succession following disturbance. The whole stream-corridor ecosystem consists of several nested cylindrical elements that extend and retract, much as would a telescope, in response to disturbance regime. This telescoping ecosystem model (TEM) can improve understanding of material retention in running water systems; that is, their “nutrient filtration” capacity. We hypothesize that disturbance by flooding alters this capacity in proportion to both intensity of disturbance and to the relative effect of disturbance on each subsystem. We would expect more distal subsystems (for example, the riparian zone) to show the highest resistance to floods. In contrast, we predict that postflood recovery of functions such as material processing (that is, resilience) will be highest in central elements and decrease laterally. Resistance and resilience of subsystems are thus both inversely correlated and spatially separated. We further hypothesize that cross-linkages between adjacent subsystems will enhance resilience of the system as a whole. Whole-ecosystem retention, transformation, and transport are thus viewed as a function of subsystem extent, lateral and vertical linkage, and disturbance regime.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100219900003
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  • 8
    Electronic Resource
    Electronic Resource
    Exchange between interstitial and surface water: Implications for stream metabolism and nutrient cycling (1984)
    Springer
    Hydrobiologia 111 (1984), S. 219-228 
    Details
    ISSN: 1573-5117
    Keywords: stream metabolism ; autotrophic ; streams ; production ; hyporheic ; interstitial water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Metabolism of a Sonoran Desert stream was investigated by both enclosure and whole system oxygen techniques. We used recirculating chambers to estimate surface sediment metabolism and measured deep sediment respiration in isolated sediment cores. Metabolism of the stream ecosystem was determined for a 30-m reach as dark and light oxygen change with and without black plastic sheeting that darkened the stream and prevented diffusion. Average ecosystem respiration for two dates in August (440 mg O2 m-2 h-1) exceeded respiration of either the surface sediment community (155 Mg O2 m-2 h-1) or the hyporheic community (170 mg O2 m-2 h-1) alone. Deep sediments show substantial oxygen and nitrate uptake when isolated. In the stream, this low nitrate interstitial water is exchanged with surface water. Metabolism of the isolated surface community suggests a highly productive and autotrophic system, yet gross production is balanced or exceeded by community respiration when ecosystem boundaries include the hyporheic zone. Thus, despite high rates of gross primary production (600–1200 mg O2 m-2 h-1), desert streams may be heterotrophic (PG 〈 R) during summer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00007202
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  • 9
    Electronic Resource
    Electronic Resource
    Nitrogen and phosphorus dynamics in hot desert streams of Southwestern U.S.A. (1981)
    Springer
    Hydrobiologia 83 (1981), S. 303-312 
    Details
    ISSN: 1573-5117
    Keywords: nitrogen ; phosphorus ; streams ; deserts ; nutrient limitation ; production ; Arizona
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nitrogen to phosphorus ratios and concentrations of nitrate and soluble reactive phosphate are presented for an array of Southwestern streams as evidence that nitrogen is the limiting nutrient where such limitation occurs. Nitrate uptake in sections of intermittent streams was attributable to autotrophic activity. Uptake of soluble reactive phosphate was unrelated to any indicator of autotrophic activity, thus concentrations of this nutrient in desert and semi-desert stream waters may be controlled by other factors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00008281
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  • 10
    Electronic Resource
    Electronic Resource
    Methanogenesis in Arizona, USA dryland streams (1995)
    Springer
    Biogeochemistry 31 (1995), S. 155-173 
    Details
    ISSN: 1573-515X
    Keywords: methane ; methanogenesis ; arid-lands ; Sonoran Desert ; streams ; hydrologic exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Methanogenesis was studied in five streams of central and southern Arizona by examining the distribution of methane in interstitial water and evasion of methane in three subsystems (hyporheic, parafluvial and bank sediments). In Sycamore Creek, the primary study site (studied during summer and early autumn), methane content of interstitial water exhibited a distinct spatial pattern. In hyporheic (sediments beneath the wetted channel) and parfluvial zones (active channel sediments lateral to the wetted channel), which were well oxygenated due to high hydrologic exchange with the surface stream and had little particulate organic matter (POM), interstitial methane concentration averaged only 0.03 mgCH4-C/L. Bank sediments (interface between the active channel and riparian zone), in contrast, which were typically vegetated, had high POM, low hydrologic exchange and concomitantly low dissolved oxygen levels, had interstitial concentration averaging 1.5 mgCH4-C/L. Methane emission from Sycamore Creek, similar to methane concentration, averaged only 3.7 mgCH4-C·m−2·d−1 from hyporheic and parafluvial zones as opposed to 170 mgCH4-C·m−2·d−1 from anoxic bank sediments. Methane in four additional streams sampled (one sampling date during late winter) was low and exhibited little spatial variation most likely due to cooler stream temperatures. Interstitial methane in parafluvial and bank sediments of all four streams ranged from only 0.005 to 0.1 mgCH4-C/L. Similarly methane evasion was also low from these streams varying from 0 to 5.7 mgCH4-C·m−2·d−1. The effects of organic matter and temperature on methanogenesis were further examined by experimentally manipulating POM and temperature in stoppered flasks filled with hyporheic sediments and stream water. Methane production significantly increased with all independent variables. Methane production is greatest in bank sediments that are relatively isolated hydrologically and lowest in hyporheic and parafluvial sediments that are interactive with the surface stream.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00004047
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