Impacts of stormwater discharges on the nearshore benthic environment of Santa Monica Bay     

Schiff K  Bay S 《Marine environmental research》2003,56(1-2):225-243

Although large loads of potentially toxic constituents are discharged from coastal urban watersheds, very little is known about the fates and eventual impacts of these stormwater inputs once they enter the ocean. The goal of this study was to examine the effects of stormwater discharges on the benthic marine environment of Santa Monica Bay. Sediment samples were collected across a gradient of stormwater impact following significantly sized storm events offshore Ballona Creek (a predominantly developed watershed) and Malibu Creek (a predominantly undeveloped watershed). Sediments offshore Malibu Creek had a greater proportion of fine-grained sediments, organic carbon, and naturally occurring metals (i.e., aluminum and iron), whereas sediments offshore Ballona Creek had higher concentrations of anthropogenic metals (i.e., lead) and organic pollutants (i.e., total DDT, total PCB, total PAH). The accumulation of anthropogenic sediment contaminants offshore Ballona Creek was evident up to 2 km downcoast and 4 km upcoast from the creek mouth and sediment concentrations covaried with distance from the discharge. Although changes in sediment texture, organic content, and an increase in sediment contamination were observed, there was little or no alteration to the benthic communities offshore either Ballona or Malibu Creek. Both sites were characterized as having an abundance, species richness, biodiversity and benthic response index similar to shallow water areas distant from creek mouths throughout the Southern California Bight. There was not a preponderance of pollution tolerant, nor a lack or pollution sensitive, species offshore either creek mouth.  相似文献   

Lake Sediment Core Records of Sulphur Accumulation and Sulphur Isotopic Composition in Central Ontario, Canada Lakes     

M. Catherine Eimers  Andrew M. Paterson  Peter J. Dillon  Sherry L. Schiff  Brian F. Cumming  Roland I. Hall 《Journal of Paleolimnology》2006,35(1):99-109

Stable isotopic compositions and concentrations of total sedimentary sulphur (S) were determined in cores from 6 lakes in the acid-sensitive Muskoka-Haliburton region of south-central Ontario. The isotopic composition of S in deep sediment (> ~ 20 cm) was approximately constant in all lakes, and indicated a pre-industrial δ ³⁴S value between +4.0 and +5.3‰, which is similar to current bulk deposition. Similarly, total S concentrations in deep sediment were relatively low (1.9–5 mg S g⁻¹ dwt) and approximately constant with depth within cores. All lakes exhibited up-core increases in total S and decreases in δ ³⁴S at a depth corresponding to the beginning of industrialization in the Great Lakes region ( ~ 1900), resulting in a generally reciprocal depth pattern between total S concentration and δ ³⁴S ratios. While initial shifts in total S and δ ³⁴S were likely due to enhanced SO₄ reduction of newly available anthropogenic SO₄, both the magnitude and pattern of up-core S enrichment and shifts in δ ³⁴S varied greatly among lakes, and did not match changes in S deposition post 1900. Differences between lakes in total S and δ ³⁴S were not related to any single hydrologic (e.g., residence time) or physical (e.g., catchment-area-to-lake area ratio) lake characteristic. This work indicates that sediment cores do not provide consistent records of changes in post-industrial S deposition in this region, likely due to redox-related mobility of S in upper sediment.  相似文献   

Nutrient limitation of the macroalgaEnteromorpha intestinalis collected along a resource gradient in a highly eutrophic estuary     

Kamer  Krista  Fong  Peggy  Kennison  Rachel  Schiff  Kenneth 《Estuaries and Coasts》2004,27(2):201-208

We conducted a laboratory experiment to quantify nutrient (nitrogen and phosphorus) limitation of macroalgae collected along a gradient in water column nutrient availability in Upper Newport Bay estuary, a relatively nutrient-rich system in southern California, United States. We collectedEnteromorpha intestinalis and water for use in the experiment from five sites ranging from the lower end of the estuary to the head. Initial algal tissue N and P concentrations and molar N∶P ratios—as well as water column NO₃ and total Kjeldahl nitrogen (TKN)—increased along a spatial gradient from the lower end toward the head. Water column soluble reactive phosphorus (SRP) varied among sites as well but did not follow a pattem of increasing from the seaward end toward the head. Algae from each site were assigned to one of four experimental treatments: control (C), nitrogen enrichment (+N), phosphorus enrichment (+P), and nitrogen and phosphorus enrichment (+N+P). Each week for 3 wk we replaced the water in each unit with the appropriate treatment water to mimic a poorly flushed estuary. After 3 wk, the degree of nutrient limitation ofE. intestinalis varied spatially with distance from the head of the estuary. Growth ofE. intestinalis collected from several sites increased with N enrichment alone and increased further when P was added in combination with N This indicated that N was limiting and that when N was sufficient, P became limiting. Sites from whichE. intestinalis exhibited nutrient limitation spanned the range of background water column NO₃ (12.9±0.4 to 55.2±2.1 μM) and SRP (0.8±0.0 to 2.9±0.2 μM) concentrations. Algae that were N limited had initial tissue N levels ranging from 1.18±0.03 to 2.81±0.08% dry weight and molar N∶P ratios ranging from 16.75±0.39 to 26.40±1.98.  相似文献   

Measurement of the photodissociation coefficient of NO2 in the atmosphere: II,stratospheric measurements     

S. Madronich  D. R. Hastie  H. I. Schiff  B. A. Ridley 《Journal of Atmospheric Chemistry》1985,3(2):233-245

The photodissociation coefficient of NO₂, J _{NO 2}, has been measured from a balloon platform in the stratosphere. Results from two balloon flights are reported. High Sun values of J _{NO 2} measured were 10.5±0.3 and 10.3±0.3×10^-3 s^-1 at 24 and 32 km respectively. The decrease in J _{NO 2} at sunset was monitored in both flights. The measurements are found to be in good agreement with calculations of J _{NO 2} using a simplified isotropic multiple scattering computer routine.  相似文献   

Calculations of the temperature dependence of the NO2 photodissociation coefficient in the atmosphere     

S. Madronich  D. R. Hastie  B. A. Ridley  H. I. Schiff 《Journal of Atmospheric Chemistry》1984,1(2):151-157

The photodissociation coefficient, J _NO2 of NO₂ in the atmosphere was calculated at 235 and 298 K using the measured temperature dependences of the absorption cross-sections and quantum yields. These calculations gave a ratio J _NO2(298 K)/J _NO2(235 K)=1.155±0.010 which is only weakly dependent on altitude, surface albedo and solar zenith angle.  相似文献   

Measurement of the photodissociation coefficient of NO2 in the atmosphere: I. Method and surface measurements     

S. Madronich  D. R. Hastie  B. A. Ridley  H. I. Schiff 《Journal of Atmospheric Chemistry》1983,1(1):3-25

An instrument, specifically designed for measurements from a balloon platform in the stratosphere, has been used to obtain ground-level values of the atmospheric photodissociation coefficient of nitrogen dioxide, J _{NO 2}.A typical clear-sky value is 8.0×10^-3 s^-1 when the solar zenith angle is 40°. Measurements were made as a function of solar zenith angle and correlated with a calibrated Eppley UV radiometer. It is shown that J _{NO 2}may be expressed as a simple function of the radiometer output so that estimates of J _{NO 2}can be made using just an upward looking radiometer to an accuracy of about 20%. The measurements are also found to be in good agreement with calculations of J _{NO 2}using a simplified isotropic multiple scattering computer routine.  相似文献   

Berechnung der potentiellen Verdunstung und deren Vergleich mit aktuellen Verdunstungswerten von Lysimetern     

Dr. H. Schiff 《Theoretical and Applied Climatology》1975,23(4):331-342

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Capturing temporal variability for estimates of annual hydrochemical export from a first‐order agricultural catchment in southern Ontario,Canada     

M. L. Macrae  M. C. English  S. L. Schiff  M. Stone 《水文研究》2007,21(13):1651-1663

This 2‐year study (2000, 2001) reports annual nutrient (phosphorus, nitrate) export from a first‐order agricultural watershed in southern Ontario based on an intensive monitoring programme. The importance of storm and melt events in annual export estimates is demonstrated and the temporal variability in nutrient loading during events is related to processes occurring within the catchment. The feasibility of predicting event‐related nutrient export from hydrometric data is explored. The importance of sampling frequency throughout events is also shown. Export of total phosphorus (TP), soluble reactive phosphorus (SRP) and nitrate ( ) for 2000 and 2001 averaged 0·35 kg ha^?1 year^?1, 0·09 kg ha^?1 year^?1, and 35 kg ha^?1 year^?1 (as N) respectively. Approximately 75% of annual TP export, 80% of annual SRP export and 70% of annual export occurred during 28 events per year. A small number of large‐magnitude events (>34 mm) accounted for 18–42% of annual TP export, 0–61% of annual SRP export and 13–33% of annual NO export. Our results show that temporal variability in nutrient export is largely governed by discharge in this basin, and export can be predicted from discharge. SRP and TP export can also be predicted from discharge, but only for events that are not large in magnitude. The sampling interval throughout events is important in obtaining precise estimates of nutrient export, as infrequent sampling intervals may over‐ or under‐estimate nutrient export by ± 45% per event for P. This study improves our understanding of and P export patterns and our ability to predict or model them by relating temporal variability in event nutrient export to discharge and processes occurring within the basin, and also by exploring the significance of sampling interval in the context of the importance of individual events, season and temporal variability during events. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Measurement of nitric oxide in the stratosphere between 17·4 and 22·9 km     

B.A. Ridley  H.I. Schiff  A.W. Shaw  L.R. Megill  L. Bates  C. Howlett  H. Levaux  T.E. Ashenfelter 《Planetary and Space Science》1974,22(1):19-24

On 16 March 1973, the York U./U.S.U. chemiluminescent nitric oxide instrument was flown successfully from Hollomon Air Force Base, New Mexico, 32° 50·1′ N lat. The instrument was operated between 17:40 and 22:05UT. Most of the measurements were carried out during three ascent, float and descent cycles between 17·4 and 22·9 km. Within the uncertainty of the measurements no differences were seen among results obtained during ascent, float and descent mode, which indicated that there were no major sampling problems resulting from contamination of the atmosphere. The NO mixing ratio was found to be 0·1 ppb v/v with an accuracy of 60 per cent. No change was observed within this accuracy over the small altitude range investigated.  相似文献   

N/N and O/O stable isotope ratios of nitrous oxide produced during denitrification in temperate forest soils     

David M. Snider  Sherry L. Schiff 《Geochimica et cosmochimica acta》2009,73(4):877-4688

Anaerobic incubations of upland and wetland temperate forest soils from the same watershed were conducted under different moisture and temperature conditions. Rates of nitrous oxide (N₂O) production by denitrification of nitrate () and the stable isotopic composition of the N₂O (δ¹⁵N, δ¹⁸O) were measured. In all soils, N₂O production increased with elevated temperature and soil moisture. At each temperature and moisture level, the rate of N₂O production in the wetland soil was greater than in the upland soil. The ¹⁵N isotope effect (ε) _{(product − substrate)} ranged from −20‰ to −29‰. These results are consistent with other published estimates of ¹⁵N fractionation from both single species culture experiments and soil incubation studies from different ecosystems.A series of incubations were conducted with ¹⁸O-enriched water (H₂O) to determine if significant oxygen exchange (O-exchange) occurred between H₂O and N₂O precursors during denitrification. The exchange of H₂O-O with nitrite () and/or nitric oxide (NO) oxygen has been documented in single organism culture studies but has not been demonstrated in soils prior to this study. The fraction of N₂O-O derived from H₂O-O was confined to a strikingly narrow range that differed between soil types. H₂O-O incorporation into N₂O produced from upland and wetland soils was 86% to 94% and 64% to 70%, respectively. Neither the temperature, soil moisture, nor the rate of N₂O production influenced the magnitude of O-exchange. With the exception of one treatment, the net ¹⁸O isotope effect (ε_net) _{(product-substrate)} ranged from +37‰ to +43‰.Most previous studies that have reported ¹⁸O isotope effects for denitrification of to N₂O have failed to account for the effect of oxygen exchange with H₂O. When high amounts of O-exchange occur after fractionation during reductive O-loss, the ¹⁸O-enrichment is effectively lost or diminished and δ¹⁸O-N₂O values will be largely dictated by δ¹⁸O-H₂O values and subsequent fractionation. The process and extent of O-exchange, combined with the magnitude of oxygen isotope fractionation at each reduction step, appear to be the dominant controls on the observed oxygen isotope effect. In these experiments, significant oxygen isotope fractionation was observed to occur after the majority of water O-exchange. Due to the importance of O-exchange, the net oxygen isotope effect for N₂O production in soils can only be determined using δ¹⁸O-H₂O addition experiments with δ¹⁸O-H₂O close to natural abundance.The results of this study support the continued use of δ¹⁵N-N₂O analysis to fingerprint N₂O produced from the denitrification of . The utilization of ¹⁸O/¹⁶O ratios of N₂O to study N₂O production pathways in soil environments is complicated by oxygen exchange with water, which is not usually quantified in field studies. The oxygen isotope fractionation observed in this study was confined to a narrow range, and there was a clear difference in water O-exchange between soil types regardless of temperature, soil moisture, and N₂O production rate. This suggests that ¹⁸O/¹⁶O ratios of N₂O may be useful in characterizing the actively denitrifying microbial community.  相似文献