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  • 1
    Digitale Medien
    Digitale Medien
    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
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2427.2003.01094.x
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  • 2
    Digitale Medien
    Digitale Medien
    Characterizing nitrogen dynamics, retention and transport in a tropical rainforest stream using an in situ15N addition (2002)
    Oxford UK : Blackwell Science Ltd
    Freshwater biology 47 (2002), S. 0 
    Details
    ISSN: 1365-2427
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: 1. This study was part of the Lotic Intersite Nitrogen eXperiment (LINX); a series of identical 15NH4 tracer additions to streams throughout North America. 15NH4Cl was added at tracer levels to a Puerto Rican stream for 42 days. Throughout the addition, and for several weeks afterwards, samples were collected to determine the uptake, retention and transformation pathways of nitrogen in the stream.2. Ammonium uptake was very rapid. Nitrification was immediate, and was a very significant transformation pathway, accounting for over 50% of total NH4 uptake. The large fraction of NH4 uptake accounted for by nitrification (a process that provides energy to the microbes involved) suggests that energy limitation of net primary production, rather than N limitation, drives N dynamics in this stream.3. There was a slightly increased 15N label in dissolved organic nitrogen (DON) the day after the 15NH4 addition was stopped. This DO15N was 〈 0.02% of DON concentration in the stream water at the time, suggesting that nearly all of the DON found in-stream is allochthonous, or that in-stream DON production is very slow.4. Leptophlebiidae and Atya appear to be selectively feeding or selectively assimilating a very highly labelled fraction of the epilithon, as the label found in the consumers became much higher than the label found in the food source.5. A large spate (〉20-fold increase in discharge) surprisingly removed only 37% of in-stream fine benthic organic matter (FBOM), leaves and epilithon. The fraction that was washed out travelled downstream a long distance (〉220 m) or was washed onto the stream banks.6. While uptake of 15NH4 was very rapid, retention was low. Quebrada Bisley retained only 17.9% of the added 15N after 42 days of 15N addition. Most of this was in FBOM and epilithon. Turnover rates for these pools were about 3 weeks. The short turnover times of the primary retention pools suggest that long-term retention (〉1 month) is minimal, and is probably the result of N incorporation into shrimp biomass, which accounted for 〈 1% of the added 15N.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2427.2002.00785.x
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  • 3
    Digitale Medien
    Digitale Medien
    New perspectives in ecotoxicology (1984)
    Springer
    Environmental management 8 (1984), S. 375-442 
    Details
    ISSN: 1432-1009
    Schlagwort(e): Ecotoxicology ; Environmental regulation ; Fate and transport of anthropogenic chemicals ; Keystone and critical species
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract The task of regulating potentially harmful chemicals in the environment is presently hindered by the lack of appropriate concepts and methods for evaluating the effects of anthropogenic chemicals on ecosystems. Toxicity tests at the molecular and physiological levels have been used successfully as indicators of adverse effects on test organisms and have been extrapolated to humans to establish a basis for risk assessment. However, laboratory measurements of effects upon individuals do not translate readily into potential effects upon natural populations, in part because natural populations interact with other populations and with the physical environment. Even more difficult to assess are the deleterious impacts of anthropogenic chemicals on ecosystems, because of effects on species interactions, diversity, nutrient cycling, productivity, climatic changes, and other processes. Effects on ecosystems resulting from chemical stresses are outside the realm of classical toxicology, and an ecosystem-level perspective is essential for the consideration of such effects; but the science that deals with ecosystem-level effects,ecotoxicology, is still developing. This article synthesizes the topics discussed at a workshop on ecotoxicology held by the Ecosystems Research Center at Cornell University. Topics covered include: the regulatory framework in which ecotoxicological research must be applied; ecosystem modification of toxicant fate and transport; how ecosystem composition, structure, and function are influenced by chemicals; methods currently available for predicting the effects of chemicals at the ecosystem level; and recommendations on research needs to enhance the state of the science of ecotoxicology.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01871807
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  • 4
    Digitale Medien
    Digitale Medien
    A nitrogen budget for late-successional hillslope tabonuco forest, Puerto Rico (1999)
    Springer
    Biogeochemistry 46 (1999), S. 85-108 
    Details
    ISSN: 1573-515X
    Schlagwort(e): nutrient cycling ; tropical forest ; ecosystem studies
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie
    Notizen: Abstract Nitrogen budgets of late successional forested stands and watersheds provide baseline data against which the effects of small- and large-scale disturbances may be measured. Using previously published data and supplemental new data on gaseous N loss, we construct a N budget for hillslope tabonuco forest (HTF) stands in Puerto Rico. HTF stands are subject to frequent hurricanes and landslides; here, we focus on N fluxes in the late phase of inter-disturbance forest development. N inputs from atmospheric deposition (4-6 kg N/ha/yr) are exceeded by N outputs from groundwater, gaseous N loss, and particulate N loss (6.3–15.7 kg N/ha/yr). Late-successional HTF stands also sequester N in their aggrading biomass (8 kg N/ha/yr), creating a total budget imbalance of 8.3–19.7 kg N/ha/yr. We surmise that this imbalance may be accounted for by unmeasured inputs from above- and belowground N-fixation and/or slow depletion of the large N pool in soil organic matter. Spatial and temporal variability, especially that associated with gaseous exchange and soil organic matter N-mineralization, constrain the reliability of this N budget.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01007575
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  • 5
    Digitale Medien
    Digitale Medien
    The globalization of N deposition: ecosystem consequences in tropical environments (1999)
    Springer
    Biogeochemistry 46 (1999), S. 67-83 
    Details
    ISSN: 1573-515X
    Schlagwort(e): acidification ; anthropogenic nitrogen ; cations ; nitrate leaching ; nitric oxide ; nitrous oxide ; nutrient limitation ; phosphorus ; productivity ; tropical ecosystems
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie
    Notizen: Abstract Human activities have more than doubled the inputs of nitrogen (N) into terrestrial systems globally. The sources and distribution of anthropogenic N, including N fertilization and N fixed during fossil fuel combustion, are rapidly shifting from the temperate zone to a more global distribution. The consequences of anthropogenic N deposition for ecosystem processes and N losses have been studied primarily in N-limited ecosystems in the temperate zone; there is reason to expect that tropical ecosystems, where plant growth is most often limited by some other resource, will respond differently to increasing deposition. In this paper, we assess the likely direct and indirect effects of increasing anthropogenic N inputs on tropical ecosytem processes. We conclude that anthropogenic inputs of N into tropical forests are unlikely to increase productivity and may even decrease it due to indirect effects on acidity and the availability of phosphorus and cations. We also suggest that the direct effects of anthropogenic N deposition on N cycling processes will lead to increased fluxes at the soilwater and soil-air interfaces, with little or no lag in response time. Finally, we discuss the uncertainties inherent in this analysis, and outline future research that is needed to address those uncertainties.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01007574
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  • 6
    Digitale Medien
    Digitale Medien
    Nitrogen yields from undisturbed watersheds in the Americas (1999)
    Springer
    Biogeochemistry 46 (1999), S. 149-162 
    Details
    ISSN: 1573-515X
    Schlagwort(e): dissolved organic nitrogen ; nitrogen concentrations ; nitrogen cycle ; nitrogen yields ; nitrate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie
    Notizen: Abstract Yields of total fixed nitrogen and nitrogen fractions are summarized for thirty-one watersheds in which anthropogenic disturbance of the nitrogen cycle, either through land use or atmospheric deposition, is negligible or slight. These yields are taken as representative of background conditions over a broad range of watershed areas, elevations, and vegetation types. The data set focuses on watersheds of the American tropics, but also includes information on the Gambia River (Africa) and some small watersheds in the Sierra Nevada of California. For the tropical watersheds, total nitrogen yield averages 5.1 kg ha−1 y−1. On average, 30% of the total is particulate and 70% is dissolved. Of the dissolved fraction, an average of 50% is organic and 50% is inorganic, of which 20% is ammonium and 80% is nitrate. Yields are substantially lower than previously estimated for background conditions. Yields of all nitrogen fractions are strongly related to runoff, which also explains a large percentage of variance in yield of total nitrogen (r2=0.85). For total nitrogen and nitrogen fractions, yield increases at about two-thirds the rate of runoff; concentration decreases as runoff increases. There is a secondary but significant positive relationship between elevation and yield of DIN. Ratios DON/TDN and PN/TN both are related to watershed area rather than runoff; DON/TDN decreases and PN/TN increases toward higher stream orders. The analysis suggests for tropical watersheds the existence of mechanisms promoting strong homeostasis in the yield of N and its fractions for a given moisture regime, as well as predictable downstream change in proportionate representation N fractions. Yields and concentrations for small tropical watersheds are much larger than for the few temperate ones with which comparisons are possible.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01007577
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  • 7
    Digitale Medien
    Digitale Medien
    Nitrogen yields from undisturbed watersheds in the Americas (1999)
    Springer
    Biogeochemistry 46 (1999), S. 149-162 
    Details
    ISSN: 1573-515X
    Schlagwort(e): dissolved organic nitrogen ; nitrogen concentrations ; nitrogen cycle ; nitrogen yields ; nitrate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie
    Notizen: Abstract Yields of total fixed nitrogen and nitrogen fractions are summarized for thirty-one watersheds in which anthropogenic disturbance of the nitrogen cycle, either through land use or atmospheric deposition, is negligible or slight. These yields are taken as representative of background conditions over a broad range of watershed areas, elevations, and vegetation types. The data set focuses on watersheds of the American tropics, but also includes information on the Gambia River (Africa) and some small watersheds in the Sierra Nevada of California. For the tropical watersheds, total nitrogen yield averages 5.1 kg ha −1 y−1. On average, 30% of the total is particulate and 70% is dissolved. Of the dissolved fraction, an average of 50% is organic and 50% is inorganic, of which 20% is ammonium and 80% is nitrate. Yields are substantially lower than previously estimated for background conditions. Yields of all nitrogen fractions are strongly related to runoff, which also explains a large percentage of variance in yield of total nitrogen (r2 = 0.85). For total nitrogen and nitrogen fractions, yield increases at about two-thirds the rate of runoff; concentration decreases as runoff increases. There is a secondary but significant positive relationship between elevation and yield of DIN. Ratios DON/TDN and PN/TN both are related to watershed area rather than runoff; DON/TDN decreases and PN/TN increases toward higher stream orders. The analysis suggests for tropical watersheds the existence of mechanisms promoting strong homeostasis in the yield of N and its fractions for a given moisture regime, as well as predictable downstream change in proportionate representation N fractions. Yields and concentrations for small tropical watersheds are much larger than for the few temperate ones with which comparisons are possible.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006108315578
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  • 8
    Digitale Medien
    Digitale Medien
    The Long-term Effects of Disturbance on Organic and Inorganic Nitrogen Export in the White Mountains, New Hampshire (2000)
    Springer
    Ecosystems 3 (2000), S. 433-450 
    Details
    ISSN: 1435-0629
    Schlagwort(e): Key words: disturbance; dissolved organic carbon; dissolved organic nitrogen; fire; logging; nitrate leaching; nitrogen saturation; nitrogen retention; old growth; succession.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Traditional biogeochemical theories suggest that ecosystem nitrogen retention is controlled by biotic N limitation, that stream N losses should increase with successional age, and that increasing N deposition will accelerate this process. These theories ignore the role of dissolved organic nitrogen (DON) as a mechanism of N loss. We examined patterns of organic and inorganic N export from sets of old-growth and historically (80–110 years ago) logged and burned watersheds in the northeastern US, a region of moderate, elevated N deposition. Stream nitrate concentrations were strongly seasonal, and mean (± SD) nitrate export from old-growth watersheds (1.4 ± 0.6 kg N ha−1 y−1) was four times greater than from disturbed watersheds (0.3 ± 0.3 kg N ha−1 y−1), suggesting that biotic control over nitrate loss can persist for a century. DON loss averaged 0.7 (± 0.2) kg N ha−1 y−1 and accounted for 28–87% of total dissolved N (TDN) export. DON concentrations did not vary seasonally or with successional status, but correlated with dissolved organic carbon (DOC), which varied inversely with hardwood forest cover. The patterns of DON loss did not follow expected differences in biotic N demand but instead were consistent with expected differences in DOC production and sorption. Despite decades of moderate N deposition, TDN export was low, and even old-growth forests retained at least 65% of N inputs. The reasons for this high N retention are unclear: if due to a large capacity for N storage or biological removal, N saturation may require several decades to occur; if due to interannual climate variability, large losses of nitrate may occur much sooner.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s100210000039
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  • 9
    Digitale Medien
    Digitale Medien
    Long-Term Nitrogen Additions and Nitrogen Saturation in Two Temperate Forests (2000)
    Springer
    Ecosystems 3 (2000), S. 238-253 
    Details
    ISSN: 1435-0629
    Schlagwort(e): Key words: ammonium nitrate; biomass production; foliar chemistry; net mineralization; net nitrification; nitrogen deposition; nitrogen saturation; soil solution chemistry.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: ABSTRACT This article reports responses of two different forest ecosystems to 9 years (1988–96) of chronic nitrogen (N) additions at the Harvard Forest, Petersham, Massachusetts. Ammonium nitrate (NH4NO3) was applied to a pine plantation and a native deciduous broad-leaved (hardwood) forest in six equal monthly doses (May–September) at four rates: control (no fertilizer addition), low N (5 g N m-2 y-1), high N (15 g N m-2 y-1), and low N + sulfur (5 g N m-2 y-1 plus 7.4 g S m-2 y-1). Measurements were made of net N mineralization, net nitrification, N retention, wood production, foliar N content and litter production, soil C and N content, and concentrations of dissolved organic carbon (DOC) and nitrogen (DON) in soil water. In the pine stand, nitrate losses were measured after the first year of additions (1989) in the high N plot and increased again in 1995 and 1996. The hardwood stand showed no significant increases in nitrate leaching until 1995 (high N only), with further increases in 1996. Overall N retention efficiency (percentage of added N retained) over the 9-year period was 97–100% in the control and low N plots of both stands, 96% in the hardwood high N plot, and 85% in the pine high N plot. Storage in aboveground biomass, fine roots, and soil extractable pools accounted for only 16–32% of the added N retained in the amended plots, suggesting that the one major unmeasured pool, soil organic matter, contains the remaining 68–84%. Short-term redistribution of 15N tracer at natural abundance levels showed similar division between plant and soil pools. Direct measurements of changes in total soil C and N pools were inconclusive due to high variation in both stands. Woody biomass production increased in the hardwood high N plot but was significantly reduced in the pine high N plot, relative to controls. A drought-induced increase in foliar litterfall in the pine stand in 1995 is one possible factor leading to a measured increase in N mineralization, nitrification, and nitrate loss in the pine high N plot in 1996.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s100210000023
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  • 10
    Digitale Medien
    Digitale Medien
    Nitrogen transformations in a small mountain stream (1985)
    Springer
    Hydrobiologia 124 (1985), S. 129-139 
    Details
    ISSN: 1573-5117
    Schlagwort(e): heterotrophic streams ; nitrogen enrichment ; nitrification ; ammonification ; detritus ; bryophytes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Ammonium, urea, and nitrate were added to Bear Brook, a second and third order stream in the Hubbard Brook Experimental Forest, New Hampshire. Removal of ammonium and urea during downstream transport coincided with the release of nitrate. Nitrate removal did not occur when it was added alone or with dissolved organic carbon. Laboratory experiments showed that coarse particulate organic material (detritus) and bryophytes taken from the streambed were active in the removal of ammonium from enriched stream water, and in the release of nitrate upon the addition of ammonium. The patterns of removal and release observed in these experiments suggest a biologically mediated, oxidation process. Budgetary calculations show that the in-stream transformation of nitrogen inputs during summer and autumn could represent 12 to 25 percent of the nitrogen exported as nitrate during winter and spring from heterotrophic streams like Bear Brook. This type of internal cycling affects the timing and form of nitrogen export from small streams draining forested watersheds in the northeastern United States.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00006795
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