Are multispecies models an improvement on single-species models for measuring fishing impacts on marine ecosystems?   总被引：13，自引：6，他引：7  

Hollowed  Anne B.; Bax  Nicholas; Beamish  Richard; Collie  Jeremy; Fogarty  Michael; Livingston  Patricia; Pope  John; Rice  Jake C. 《ICES Journal of Marine Science》2000,57(3):707-719

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A Reliability-Based Evaluation of the Effects of Geometry on Levee Underseepage Potential     

Lourdes Polanco  John Rice 《Geotechnical and Geological Engineering》2014,32(4):807-820

Levee foundations along meandering rivers are often modeled in seepage analyses with simplified models consisting of two layers having uniform thickness and soil properties. While this may simplify the analysis and allow for use of simplified reliability methods, it is important to realize the limitations of these simplifying assumptions. Due to the complex geomorphic regime that is often encountered in the fluvial environment, levee foundation geometry can range from simple to very complex. Variations in layer thickness and continuity affect the pore pressure and seepage regime and, consequently, affect the potential for internal erosion of the foundation soils. A study has been performed to assess the effects of complex subsurface geometry on the susceptibility of levees to underseepage related internal erosion. Reliability-based internal erosion analyses have been performed on eight hypothetical levee profiles using two analytical methods. The first-order second-moment-blanket theory (FOSM-BT) method applies a simplified reliability assessment technique to the US Army Corps of Engineers “Blanket Theory” equations. This method requires that the analysis profile be simplified to meet the requirements of the equations and places limitations on how the uncertainty of the various input parameters is modeled. The more complex response surface-Monte Carlo simulation method is capable of modeling more complex geometries and multiple failure modes and is flexible in how uncertainty of the various input parameters are modeled. The results of the two methods are compared to evaluate the effectiveness of the FOSM-BT in evaluating internal erosion potential in increasingly complex levee foundation conditions.  相似文献   

Comparison of Mineral Weathering and Biomass Macronutrient Uptake in Two Small Forested Watersheds Underlain by Quartzite Bedrock,Catoctin Mountain,Maryland, USA     

Karen C. Rice  Jason R. Price 《Aquatic Geochemistry》2014,20(2-3):225-242

To quantify chemical weathering and biological uptake, mass-balance calculations were performed on two small forested watersheds located in the Blue Ridge Physiographic Province in north-central Maryland, USA. Both watersheds, Bear Branch (BB) and Fishing Creek Tributary (FCT), are underlain by relatively unreactive quartzite bedrock. Such unreactive bedrock and associated low chemical-weathering rates offer the opportunity to quantify biological processes operating within the watershed. Hydrologic and stream-water chemistry data were collected from the two watersheds for the 9-year period from June 1, 1990 to May 31, 1999. Of the two watersheds, FCT exhibited both higher chemical-weathering rates and biomass nutrient uptake rates, suggesting that forest biomass aggradation was limited by the rate of chemical weathering of the bedrock. Although the chemical-weathering rate in the FCT watershed was low relative to the global average, it masked the influence of biomass base-cation uptake on stream-water chemistry. Any differences in bedrock mineralogy between the two watersheds did not exert a significant influence on the overall weathering stoichiometry. The difference in chemical-weathering rates between the two watersheds is best explained by a larger proportion of reactive phyllitic layers within the bedrock of the FCT watershed. Although the stream gradient of BB is about two-times greater than that of FCT, its influence on chemical weathering appears to be negligible. The findings of this study support the biomass nutrient uptake stoichiometry of K_1.0Mg_1.1Ca_0.97 previously determined for the study site. Investigations of the chemical weathering of relatively unreactive quartzite bedrock may provide insight into critical zone processes.  相似文献   

Response to L. Land Comment on Bricker,Rice, Bricker (2014) From Headwaters to Coast: Influence of Human Activities on Water Quality of the Potomac River Estuary. Aquatic Geochemistry 20: 291–324     

Suzanne B. Bricker  Karen C. Rice  Owen P. Bricker III 《Aquatic Geochemistry》2014,20(5):459-463

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Long-term spatial and temporal trends in frost indices in Kansas, USA   总被引：2，自引：0，他引：2  

Aavudai Anandhi  Sriram Perumal  Prasanna H. Gowda  Mary Knapp  Stacy Hutchinson  John Harrington Jr.  Leigh Murray  Mary B. Kirkham  Charles W. Rice 《Climatic change》2013,120(1-2):169-181

Frost indices such as number of frost days (nFDs), number of frost-free days (nFFDs), last spring freeze (LSF), first fall freeze (FFF), and growing-season length (GSL) were calculated using daily minimum air temperature (T_min) from 23 centennial weather stations across Kansas during four time periods (through 1919, 1920–1949, 1950–1979, and 1980–2009). A frost day is defined as a day with T_min?<?0 °C. The long- and short-term trends in frost indices were analyzed at monthly, seasonal, and annual timescales. Probability of occurrence of the indices was analyzed at 5 %, 25 %, 50 %, 75 %, and 95 %. Results indicated a general increase in T_min from 1900 through 2009 causing a decrease in nFDs. LSF and FFF occurred earlier and later than normal in the year, respectively, thereby resulting in an increase in GSL. In general, northwest Kansas recorded the greatest nFD and lowest T_min, whereas southeast Kansas had the lowest nFD and highest T_min; however, the magnitude of the trends in these indices varied with location, time period, and time scales. Based on the long-term records in most stations, LSF occurred earlier by 0.1–1.9 days/decade, FFF occurred later by 0.2–0.9 day/decade, and GSL was longer by 0.1–2.5 day/decade. At the 50 % probability level, Independence in the south-eastern part of Kansas had the earliest LSF (6 April), latest FFF (29 October) and longest GSL (207 days). Oberlin (north-western Kansas) recorded the shortest GSL (156 days) and earliest FFF (7 October) had the latest LSF (2 May) at the 50 % probability level. A positive correlation was observed for combinations of indices (LSF and GSL) and elevation, whereas a negative correlation was found between FFF and elevation.  相似文献   

Chronic and episodic acidification of streams along the Appalachian Trail corridor,eastern United States     

Douglas A. Burns  Todd C. McDonnell  Karen C. Rice  Gregory B. Lawrence  Timothy J. Sullivan 《水文研究》2020,34(7):1498-1513

Acidic atmospheric deposition has adversely affected aquatic ecosystems globally. As emissions and deposition of sulfur (S) and nitrogen (N) have declined in recent decades across North America and Europe, ecosystem recovery is evident in many surface waters. However, persistent chronic and episodic acidification remain important concerns in vulnerable regions. We evaluated acidification in 269 headwater streams during 2010–2012 along the Appalachian Trail (AT) that transits several ecoregions and is located downwind of high levels of S and N emission sources. Discharge was estimated by matching sampled streams to those of a nearby gaged stream and assuming equivalent daily mean flow percentiles. Charge balance acid-neutralizing capacity (ANC) values were adjusted to the 15th (Q15) and 85th flow percentiles (Q85) by applying the ANC/discharge slope among sample pairs collected at each stream. A site-based approach was applied to streams sampled twice or more and a second regression-based approach to streams sampled once to estimate episodic acidification magnitudes as the ANC difference from Q15 to Q85. Streams with ANC <0 μeq/L doubled from 16% to 32% as discharge increased from Q15 to Q85 according to the site-based approach. The proportion of streams with ANC <0 μeq/L at low flow and high flow decreased from north to south. Base cation dilution explained the greatest amount of episodic acidification among streams and variation in sulfate (SO₄²⁻) concentrations was a secondary explanatory variable. Episodic SO₄²⁻ patterns varied geographically with dilution dominant in northern streams underlain by soils developed in glacial sediment and increased concentrations dominant in southern streams with older, highly weathered soils. Episodic acidification increased as low-flow ANC increased, exceeding 90 μeq/L in 25% of streams. Episodic increases in ANC were the dominant pattern in streams with low-flow ANC values <30 μeq/L. Chronic and episodic acidification remain an ecological concern among AT streams. The approach developed here could be applied to estimate the magnitude and extent of chronic and episodic acidification in other regions recovering from decreasing levels of atmospheric S and N deposition.  相似文献   

Time-dependent models of the structure and stability of self-gravitating protoplanetary discs     

W. K. M. Rice  Philip J. Armitage 《Monthly notices of the Royal Astronomical Society》2009,396(4):2228-2236

Angular momentum transport within young massive protoplanetary discs may be dominated by self-gravity at radii where the disc is too weakly ionized to allow the development of the magneto-rotational instability. We use time-dependent one-dimensional disc models, based on a local cooling time calculation of the efficiency of transport, to study the radial structure and stability (against fragmentation) of protoplanetary discs in which self-gravity is the sole transport mechanism. We find that self-gravitating discs rapidly attain a quasi-steady state in which the surface density in the inner disc is high and the strength of turbulence very low (  α∼ 10⁻³  or less inside 5 au). Temperatures high enough to form crystalline silicates may extend out to several astronomical units at early times within these discs. None of our discs spontaneously develop regions that would be unambiguously unstable to fragmentation into substellar objects, though the outer regions (beyond 20 au) of the most massive discs are close enough to the threshold that fragmentation cannot be ruled out. We discuss how the mass accretion rates through such discs may vary with disc mass and with mass of the central star, and note that a determination of the     relation for very young systems may allow a test of the model.  相似文献   

Aggregation of humic acid in solution: Contributions of different fractions     

Gabriela Chilom  Angela S. Bruns  James A. Rice 《Organic Geochemistry》2009,40(4):455-460

The role of lipid components in the aggregation of several humic acids isolated from different sources was investigated using surface tensiometry. A combination of aqueous alkaline and organic solvent extractions was used to isolate two humic-like fractions (HA₁ and HA₂) and one lipid-like fraction from each humic acid. Fraction HA₁ represents approximately two-thirds of the total organic carbon of the original humic acid and under alkaline conditions is a weak surfactant that lowers the surface tension of water by only a small amount. The HA₂ fraction represents up to one-third of the humic acid and significantly lowers the surface tension of water. It is also intimately associated with the lipid fraction. Unlike the original humic acid samples, HA₂ does not show micelle-like aggregation over the concentration range studied. Aggregate formation is discussed as an emergent characteristic that results from the interaction of the humic acid’s components with the lipid components serving a facilitative role.  相似文献   

Stabilization of fine gravels by net‐spinning caddisfly larvae     

Matthew F. Johnson  Ian Reid  Stephen P. Rice  Paul J. Wood 《地球表面变化过程与地形》2009,34(3):413-423

We examined the impact of Hydropsychidae caddisfly larvae on the incipient motion of two sizes of narrowly graded fine‐gravel (4–6 and 6–8 mm). This impact was assessed relative to the collective impact of other abiotic and biotic processes that are potentially important conditioning agents of fine‐gravels. Trays of gravel were placed in the River Soar, Leicestershire, UK, where they were colonized to natural densities by caddisfly larvae. Identical trays that were surrounded by a 250 µm mesh were also deployed, preventing colonization but allowing field conditioning of sediments, including minor reworking of grains and biofilm development. After 21 days in the river, trays were removed to a laboratory flume where grain entrainment stresses were established. In addition to the colonized and conditioned treatments, critical shear stresses were measured for identical sediments that were not placed in the river (laboratory gravels). Gravels that were colonized by Hydropsychidae required significantly greater shear stresses for entrainment than conditioned trays (p ≤ 0·002), however, there was no significant difference between conditioned and laboratory gravels. This implies that the presence of caddisfly can be a more important influence on fine‐gravel stability than some conditioning processes. Shields parameter was compared across treatments and across the two gravel size‐fractions using two‐way ANOVA. No significant differences or interactions were observed, indicating that 4–6 mm gravel was stabilized to a similar degree as 6–8 mm gravel by conditioning and colonization processes. Our results extend earlier studies in two important ways: (1) entrainment stresses were established for fine gravels that were colonized at natural densities, under natural stream conditions; and (2) the caddisfly effect was measured relative to both field‐conditioned and unconditioned laboratory controls. The temporal and spatial distribution of silk‐spinning caddisfly larvae suggests that they have the potential to influence fine‐sediment mobility in many rivers, worldwide. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Disturbance regimes at the interface of geomorphology and ecology     

Stephen Rice  Markus Stoffel  Jens M. Turowski  Annett Wolf 《地球表面变化过程与地形》2012,37(15):1678-1682

Geomorphological processes are an integral part of ecosystem functioning and ecosystem functioning affects geomorphological processes. Increasingly widespread acknowledgement of this simple idea is manifest in a vigorous research community engaged with questions that address the two‐way interaction between biota and geomorphology, at a range of scales and in a variety of terrestrial and aquatic environments. Geomorphological disturbances are a core element of biogeomorphological interest, and although the disciplines of geomorphology and ecology have each developed languages and theories that help to explore, model and understand disturbance events, little attempt has been made to draw together these approaches. Following a brief review of these issues, we introduce thirteen papers that investigate the interactions and feedbacks between geomorphological disturbance regimes and ecosystem functions. These papers reveal the singularity of wildfire impacts, the importance of landsliding for carbon budgeting and of vegetation accumulation for landsliding, the zoogeomorphic role of iconic and ‘Cinderella’ animals in fluvial geomorphology, biophysical interactions in aeolian, fluvial and torrential environments and the utility of living ecosystems as archives of geomorphic events. Most of these papers were first presented in a conference session at the European Geoscience Union General Assembly in 2010 and several others are from recent volumes of Earth Surface Processes and Landforms. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献