We measured the impact of riparian zone vegetation on ecosystem metabolism in paired forested and meadow reaches on 13 streams in southeastern Pennsylvania and Maryland, USA. Metabolism estimates ...were based on open-system measurements of dissolved oxygen changes, with reaeration determined from propane evasion. Daily gross primary productivity (GPP) in meadow and forested reaches averaged 2.85 and 0.86 g O₂ m⁻² d⁻¹, respectively, at water temperatures of 12°C or greater when the forest canopy was developed and 1.74 and 1.09 g O₂ m⁻² d⁻¹, respectively, at temperatures below 12°C when the canopy was bare. Community respiration (CR₂₄) also was greater in meadow reaches than in forested reaches, averaging 5.58 and 3.57 g O₂ m⁻² d⁻¹, respectively, in the warm season and 4.87 and 2.88 g O₂ m⁻² d⁻¹, respectively, during the cold season. Thus, both meadow and forested reaches were heterotrophic. Forested reaches were always wider and nearly always shallower than companion meadow reaches. When ecosystem function was assessed per unit of stream length, the difference in average GPP between meadow and forested reaches was reduced from three-fold to 1.9-fold in the warm season, and mean GPP was greater in the forested reaches during the cold season. Mean CR₂₄ per meter stream length was greater in forested reaches during both seasons. Even though riparian shading reduced primary productivity per unit area of streambed, the greater stream width of the forested reaches counteracted that reduction in part. Thus, when rates of ecosystem function were expressed per length of stream, differences between reaches were always smaller than when expressed per area, and activity per unit stream length was sometimes greater in forested reaches than in meadow reaches.
A study of 16 streams in eastern North America shows that riparian deforestation causes channel narrowing, which reduces the total amount of stream habitat and ecosystem per unit channel length and ...compromises in-stream processing of pollutants. Wide forest reaches had more macroinvertebrates, total ecosystem processing of organic matter, and nitrogen uptake per unit channel length than contiguous narrow deforested reaches. Stream narrowing nullified any potential advantages of deforestation regarding abundance of fish, quality of dissolved organic matter, and pesticide degradation. These findings show that forested stream channels have a wider and more natural configuration, which significantly affects the total in-stream amount and activity of the ecosystem, including the processing of pollutants. The results reinforce both current policy of the United States that endorses riparian forest buffers as best management practice and federal and state programs that subsidize riparian reforestation for stream restoration and water quality. Not only do forest buffers prevent nonpoint source pollutants from entering small streams, they also enhance the in-stream processing of both nonpoint and point source pollutants, thereby reducing their impact on downstream rivers and estuaries.
NeuLAND (New Large-Area Neutron Detector) is the next-generation neutron detector for the R3B (Reactions with Relativistic Radioactive Beams) experiment at FAIR (Facility for Antiproton and Ion ...Research). NeuLAND detects neutrons with energies from 100 to 1000 MeV, featuring a high detection efficiency, a high spatial and time resolution, and a large multi-neutron reconstruction efficiency. This is achieved by a highly granular design of organic scintillators: 3000 individual submodules with a size of 5 × 5 × 250 cm3 are arranged in 30 double planes with 100 submodules each, providing an active area of 250 × 250 cm2 and a total depth of 3 m. The spatial resolution due to the granularity together with a time resolution of σt≤ 150 ps ensures high-resolution capabilities. In conjunction with calorimetric properties, a multi-neutron reconstruction efficiency of 50% to 70% for four-neutron events will be achieved, depending on both the emission scenario and the boundary conditions allowed for the reconstruction method. We present in this paper the final design of the detector as well as results from test measurements and simulations on which this design is based.
The effects of abandoned mine drainage (AMD) on streams and responses to remediation efforts were studied using three streams (AMD-impacted, remediated, reference) in both the anthracite and the ...bituminous coal mining regions of Pennsylvania (USA). Response variables included ecosystem function as well as water chemistry and macroinvertebrate community composition. The bituminous AMD stream was extremely acidic with high dissolved metals concentrations, a prolific mid-summer growth of the filamentous alga,
Mougeotia
, and >10-fold more chlorophyll than the reference stream. The anthracite AMD stream had a higher pH, substrata coated with iron hydroxide(s), and negligible chlorophyll. Macroinvertebrate communities in the AMD streams were different from the reference streams, the remediated streams, and each other. Relative to the reference stream, the AMD stream(s) had (1) greater gross primary productivity (GPP) in the bituminous region and undetectable GPP in the anthracite region, (2) greater ecosystem respiration in both regions, (3) greatly reduced ammonium uptake and nitrification in both regions, (4) lower nitrate uptake in the bituminous (but not the anthracite) region, (5) more rapid phosphorus removal from the water column in both regions, (6) activities of phosphorus-acquiring, nitrogen-acquiring, and hydrolytic-carbon-acquiring enzymes that indicated extreme phosphorus limitation in both regions, and (7) slower oak and maple leaf decomposition in the bituminous region and slower oak decomposition in the anthracite region. Remediation brought chlorophyll concentrations and GPP nearer to values for respective reference streams, depressed ecosystem respiration, restored ammonium uptake, and partially restored nitrification in the bituminous (but not the anthracite) region, reduced nitrate uptake to an undetectable level, restored phosphorus uptake to near normal rates, and brought enzyme activities more in line with the reference stream in the bituminous (but not the anthracite) region. Denitrification was not detected in any stream. Water chemistry and macroinvertebrate community structure analyses capture the impact of AMD at the local reach scale, but functional measures revealed that AMD has ramifications that can cascade to downstream reaches and perhaps to receiving estuaries.
Ecologically significant properties of wild-type and genetically engineered bacteria capable of degrading 3-chlorobenzoate (3-CB) were compared in the laboratory, and isolates were introduced into ...streambed sediments in microcosms to observe their population dynamics. 3-CB metabolism, growth on algal extract, temperature optima, and ingestion by protozoa were ecological properties considered relevant to the persistence of these bacteria if introduced into nature. Cell-specific Vmaxfor 3-CB metabolism and cell-specific mineralization rates each spanned ∼2 orders of magnitude, but isolates did not rank consistently. The Ksfor 3-CB metabolism for Alcaligenes sp. BR60 was ∼40-fold lower than the mean value for the other isolates, which differed only ∼4-fold among themselves. All isolates grew on an algal extract nearly as well as on tryptone-yeast extract, implying potential for survival on natural metabolic substrates in situ. Most isolates had temperature optima that were 3-15°C higher than maximum stream water temperature (22°C). Ciliates preferentially ingested P. acidovorans M3GY, and either P. putida RC-4(pSI30) or its parent strain were least preferred, but microflagellates did not exhibit consistent preferences. Fluorescent antibodies were prepared against isolates to permit detection of target cells in natural communities. In three different microcosm experiments the cell densities of introduced isolates declined over a period of days. In one experiment, 3-CB additions (100 mg/L) led to increases of P. alcaligenes C-0 and P. acidovorans M3GY cell densities within 1 day, although P. putida RC-4(pSI30) took 4 days. In a second experiment, the persistence of P. putida RC-4(pSI30) and its parent strain P. putida RC-4 were compared and rates of initial population decline were not statistically different. 3-CB addition stimulated the growth of other organisms while densities of the P. putida strains further declined. In a third experiment exposure to 100 mg 3-CB/L slowed the rate of decline of P. acidovorans M3GY densities compared to a 10 mg/L concentration or unamended control. Competition with the native flora was a significant factor affecting the persistence of introduced 3-CB degraders.
Diel fluctuations in stream water temperature and chemistry, microbial biomass, and bacterial activity were measured in White Clay Creek, Pennsylvania, during vernal algal blooms in three different ...years. DOC concentrations increased 24-37% over early morning minima and temperature increased nearly $10^\circ C$ over a 7-10-h period. Total carbohydrates and monosaccharides exhibited irregular fluctuations with total carbohydrates showing concentration peaks in the morning and affternoon. Acetate concentrations were highest in midafternoon, while the concentration pattern for primary amines differed from the DOC pattern with highest values at midnight. No distinct diel patterns were found for streambed ATP, GTP : ATP, Chl a, and total or active bacteria, although significant year-to-year and between-habitat differences were observed. Bacterial activity, measured by phopholipid biosynthesis, total lipid biosynthesis, respiration, and incorporation of $^3H$thymidine into DNA increased 1.4-fold to 3.0-fold from morning to afternoon. Microcosm experiments indicated that the activity of bacterial attached to sediments was more sensitive to increases in water temperature than to changes in water chemistry, whereas bacteria attached to porcelains disks responded to the influences of both tempereature and water chemistry.
Feeding interactions between microorganisms and their grazers range from broad and general to very specific. Here we examined routes of transfer of 3Hbenzoapyrene (BaP) and ...2,2‘,5,5‘14Ctetrachlorobiphenyl (PCB-52) from microorganisms in freshwater sediments to oligochaetes (Lumbriculus variegatus) and chironomid larvae (either Stictochironomus sp. or a mix of smaller taxa) when exposed to the compounds added either directly to sediments or to bacteria or diatoms previously labeled and then added to sediments. The appearance of radiolabel in animals after a gut clearing step to differentiate between ingested and absorbed compound was followed in time course experiments. Relative to the added radiolabel, BaP concentrations were greater than PCB concentrations in L. variegatus and were greater in animals fed radiolabeled sediments or bacteria than those offered diatoms. In contrast, the chironomids accumulated more PCB than BaP. The mix of small chironomids bioaccumulated more PCB when fed prelabeled algae than when fed sediment or bacteria. However, Stictochironomus sp. bioaccumulated more from sediments and/or bacteria. Food selection influences pathways of contaminant transfer, even to small animals at the base of the food web. We also tested whether the bioaccumulation of BaP and PCB would be predicted by the K oc for the sediment (i.e., BCF/K oc = 1). The quotients, averaged over experiments, were 1.08 and 1.53 for PCB-52 and BaP, respectively, but error terms were large, with coefficients of variation being 83% and 135%, respectively.
Aquatic organisms were monitored for their ability to incorporate trifluoroacetate (TFA), an atmospheric breakdown product of HFC and HCFC refrigerants containing a trifluoromethyl moiety. Because of ...the structural similarity of TFA to acetate, a biochemical intermediate and microbial nutrient, we suspected that organisms might use the fluorinated compound to synthesize biomolecules such as lipids and acetylated proteins. We exposed aquatic organisms (microbial communities, oligochaetes, macroinvertebrates, Callitriche sp., Lemna sp., and Impatiens capensis) to radioactive TFA (14CF3COOH) and examined them for distribution of radiolabel in different classes of biomolecules. The most label was found in oligochaetes and I. capensis leaves at 3 and 6 μg/g (as TFA), respectively, with the greatest proportion found in the protein fraction for each sample type. Aerobic microorganisms incorporated only a small fraction of the label (a few nanograms per gram as TFA), and the greatest proportion of label occurred in cell wall material. We have demonstrated that selected aquatic organisms spanning a range of trophic levels incorporated the xenobiotic TFA into their biomolecule fractions so that it was no longer extracted as TFA and thus was metabolically transformed.
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![Transfer of Benzo[a]pyrene ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0013-936X/small "Transfer of Benzo[a]pyrene and 2,2‘,5,5‘-Tetrachlorobiphenyl from Bacteria and Algae to Sediment-Associated Freshwater Invertebrates")