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1.
L.A. Cifuentes R.B. Coffin L. Solorzano W. Cardenas J. Espinoza R.R. Twilley 《Estuarine, Coastal and Shelf Science》1996,43(6):781-800
Variations in elemental and isotopic ratios of suspended particulate matter (SPM) were investigated in the Guayas River Estuary Ecosystem (GREE) that empties into the Gulf of Guayaquil, Ecuador. Detritus in the system was identified on the basis of extremely high carbon:chlorophyll aratios (>1000). This material had mean δ13C of −26·4±0·3, δ15N of +4·8±0·2, and (C:N)atomicof 14·1±0·9. The isotopic data were comparable to measurements reported for fresh and degrading mangrove leaves, whereas the elemental ratio was comparatively enriched in nitrogen. Isotope measurements of SPM throughout the GREE were more similar to values for riverine material and detritus compared with that for the coastal end-member. Values indicative ofin situproduced algae, sewage and shrimp pond effluent were only found at selected sites. Bacterial bioassays, which were used to document potential sources of dissolved organic matter in the GREE, were isotopically similar to SPM. This correspondence coupled with the relatively low (C:N)aof SPM could be explained by bacterial immobolization of nitrogen onto detritus. Finally, tidal variations of (C:N)aand δ13C at a brackish mangrove site were similar in magnitude to spatial variations encountered throughout the GREE. Based on these results, the authors caution that care must be taken when samples are taken for food-web studies in these systems. 相似文献
2.
David D. Bosch Alisa W. Coffin Joseph Sheridan Oliva Pisani Dinku M. Endale Tim C. Strickland 《水文研究》2021,35(8):e14334
The US Department of Agriculture-Agricultural Research Service Southeast Watershed Research Laboratory (SEWRL) initiated a hydrologic research program on the Little River Experimental Watershed (LREW) in 1967. Long-term (52 years) streamflow data are available for nine sites, including rainfall-runoff relationships and hydrograph characteristics regularly used in research on interactive effects of climate, vegetation, soils, and land-use in low-gradient streams of the US EPA Level III Southeastern Plains ecoregion. A summary of prior research on the LREW illustrates the impact of the watershed on building a regional understanding of hydrology and water quality. Climatic and streamflow data were used to make comparisons of scale across the nine nested LREW watersheds (LRB, LRF, LRI, LRJ, LRK, LRO, LRN, LRM, and LRO3) and two regional watersheds (Alapaha and Little River at Adel). Annual rainfall for the largest LREW, LRB, was 1200 mm while average annual streamflow was 320 mm. Annual rainfall, streamflow, and the ratio between annual streamflow and rainfall (Sratio) were similar (α = 0.05) across LREWs LRB, LRF, LRI, LRJ, LRK, and LRO. While annual rainfall within the 275 ha LRO3 was found to be similar to LRO and LRM (α = 0.05), annual streamflow and Sratio were significantly different (α = 0.05). Comparisons of annual rainfall, streamflow, and Sratio between LRB and the regional watersheds indicated no differences (α = 0.05). Based upon this analysis, most regional watersheds shared similar hydrologic characteristics. LRO3 was an exception, where increases in row crops and decreases in forest coverage resulted in increased streamflow. LREW data have been instrumental in building considerable scientific understanding of flow and transport processes for these stream systems. Continued operation of the LREW hydrologic network will support hydrologic research as well as environmental quality and riparian research programs that address emerging and high priority natural resource and environmental issues. 相似文献
3.
David Drolet Michael R. S. Coffin Myriam A. Barbeau Diana J. Hamilton 《Estuaries and Coasts》2013,36(5):940-950
Movement of animals on intertidal mudflats can have profound consequences for population and community dynamics. Such movement is often influenced by biotic interactions, but the abiotic environment can also be important, affecting the strength of species’ interactions and even changing their outcome. Here, we focused on two biotic interactions and examined their effect on movement of the burrow-dwelling amphipod Corophium volutator: intraspecific interactions (specifically, the effect of conspecific density) and interspecific interactions with a competitor–predator, the mud snail Ilyanassa obsoleta (=Nassarius obsoletus). We assessed the magnitude of the temporal variation and examined the influence of pertinent abiotic variables (lunar cycle, presence of tide pools). Despite substantial temporal variation in movement levels, density of conspecifics did not influence emigration or immigration rates of C. volutator. Mud snails negatively affected immigration of C. volutator, and this was consistent across all lunar phases. However, mud snails influenced mortality and emigration of C. volutator in a contrasting way relative to lunar phases; sometimes amphipods evaded snails and survived, but at other times did not emigrate and were killed. The presence of tide pools did not change the nature or strength of the snail–amphipod interaction. Our results further clarify the complex interactions between C. volutator and I. obsoleta and suggest that resources on the mudflat are sufficient to sustain high densities of amphipods in a density-independent manner. Further, they highlight the importance of considering multiple environmental variables when examining interspecific interactions. 相似文献
4.
Expression of intracellular ammonium assimilation enzymes were used to assess the response of nitrogen (N) metabolism in bacterioplankton to N-loading of sub-tropical coastal waters of Key West, Florida. Specific activities of glutamine synthetase (GS) and total glutamate dehydrogenase (GDHT) were measured on the bacterial size fraction (<0.8 μm) to assess N-deplete versus N-replete metabolic states, respectively. Enzyme results were compared to concentrations of dissolved organic matter and nutrients and to the biomass and production of phytoplankton and bacteria. Concentrations of dissolved inorganic N (DIN), dissolved organic N (DON), and dissolved organic carbon (DOC) positively correlated with specific activities of GDHT and negatively correlated with that of GS. Total dissolved N (TDN) concentration explained 81% of variance in bacterioplankton GDHT:GS activity ratio. The GDHT:GS ratio, TDN, DOC, and bacterial parameters decreased in magnitude along a tidally dynamic trophic gradient from north of Key West to south at the reef tract, which is consistent with the combined effects of localized coastal eutrophication and tidal exchange of seawater from the Southwest Florida Shelf and Florida Strait. The N-replete bacterioplankton north of Key West can regenerate ammonium which sustains primary production transported south to the reef. The range in GDHT:GS ratios was 5–30 times greater than that for commonly used indicators of planktonic eutrophication, which emphasizes the sensitivity of bacterioplankton N-metabolism to changes in N-bioavailability caused by nutrient pollution in sub-tropical coastal waters and utility of GDHT:GS ratio as an bioindicator of N-replete conditions. 相似文献
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6.
Jonathan H. Sharp Luis A. Cifuentes Richard B. Coffin Jonathan R. Pennock Kuo-Chuin Wong 《Estuaries and Coasts》1986,9(4):261-269
Gravitational circulation of the Delaware Estuary is dominated by a single river, the Delaware River. The seasonal variation in river discharge is large. Consequently, the water column varies between vertically homogenous conditions found during most of the year and strongly stratified conditions found during the high flow of the spring freshet. Both the variation in river discharge and the extent of stratification affect chemical distributions and biological processes in the estuary. With a simple advection-diffusion model, we show that the apparent nonconservative behavior of nitrate in the Delaware Estuary can result from varying endmember concentration and varying river discharge. In addition, we illustrate the relationship between water column stratification, phytoplankton production, and concurrent bacterial activity. Finally, as an indirect chemical response to phytoplankton growth during high river discharge, we show strongly nonconservative patterns for ammonium, phosphate, and silicate in the estuary. 相似文献
7.
Michael T. Montgomery Barry J. Spargo James G. Mueller Richard B. Coffin David C. Smith Thomas J. Boyd 《Ground Water Monitoring & Remediation》2002,22(3):144-150
Benzene, toluene, ethylbenzene, and xylene (BTEX) hydrocarbons are typically the most abundant carbon source for bacteria in gasoline-contaminated ground water. In situ bioremediation strategies often involve stimulating bacterial heterotrophic production in an attempt to increase carbon demand of the assemblage. This may, in turn, stimulate biodegradation of contaminant hydrocarbons. In this study, ground water circulation wells (GCWs) were used as an in situ treatment for a fuel-contaminated aquifer to stimulate bacterial production, purportedly by increasing oxygen transfer to the subsurface, circulating limiting nutrients, enhancing bioavailability of hydrocarbons, or by removing metabolically inhibitory volatile organics. Bacterial production, as measured by rates of bacterial protein synthesis, was stimulated across the zone of influence (ZOI) of a series of GCWs. Productivity increased from ∼102 to >105 ng C/L hour across the ZOI, suggesting that treatment stimulated overall biodegradation of carbon sources present in the ground water. However, even if BTEX carbon met all bacterial carbon demand, biodegradation would account for <4.3% of the total estimated BTEX removed from the ground water. Although bacterial productivity measurements alone cannot prove the effectiveness of in situ bioremediation, they can estimate the maximum amount of contaminant that may be biodegraded by a treatment system. 相似文献
8.
Takeshi Tsuji Yasuyuki Nakamura Hidekazu Tokuyama Millard F. Coffin Keita Koda 《Island Arc》2007,16(3):361-373
Abstract To show the structure of oceanic crust and Moho around the eastern Ogasawara Plateau, we have analyzed industry-standard two-dimensional multichannel seismic reflection data. To obtain improved velocity models, phase information of seismic signals was used for velocity analysis and velocity models for oceanic crust above Moho were determined. We apply this velocity analysis technique to seismic reflection data around the eastern Ogasawara Plateau, with the result of clear images of structures within oceanic crust and Moho. South of the Ogasawara Plateau, Moho deepens proximal to the Plateau. Moho distal to the Plateau is ca 7 km below sea floor (bsf), whereas it is ca 10 km bsf near the Plateau. The characters of oceanic crust and Moho differ significantly north and south of the Plateau. To the north, the structure of oceanic crust is ambiguous, the sea floor is shallower and less smooth, and Moho is discontinuous. To the south, structures within oceanic crust and Moho are imaged clearly, and the sea floor is deeper. A strong Moho reflection south of the Plateau might represent a sharp boundary between layered gabbro and peridotite. However, discontinuous Moho reflections north of the Plateau might represent rough topography because of intensive magmatism or a gradual downward increase in velocity within a thick Moho transition zone. A fracture zone north of the Plateau also appears to separate oceanic crust and Moho of different characters, suggesting vigorous magmatism between the Plateau and the fracture zone, and that the Ogasawara Plateau and the fracture zone influenced the genesis of oceanic crust and upper mantle. Differences in acoustic characteristics to the north and south of the Plateau are apparent in profiles illuminated by seismic attributes. 相似文献
9.
Millard F. Coffin Philip D. Rabinowitz Robert E. Houtz 《Geophysical Journal International》1986,86(2):331-369
Summary. As part of integrated marine geophysical studies in the Western Somali Basin, we performed 118 sonobuoy experiments to define better the crustal structure of the margins and basin created by the separation of Madagascar and Africa. After using T 2 / X 2 , conventional slope-intercept methods, and slant-stacked t-p techniques to analyse the data, we combined our solutions with all previous velocity information for the area. Velocity functions were derived for the sediment coiumn, and we detected a high-velocity (4.58 ± 0.29 km s–1 ) sediment layer overlying acoustic basement. We confirmed that the crust is indeed seismically oceanic, and that it may be considered either in terms of a layered model – layers 2B (5.42 ± 0.19 km s–1 ), 2C (6.23 ± 0.22 km s–1 ), 3 (7.03 ± 0.25 km s–1 ), and mantle (7.85 ± 0.32 km s–1 ) were identified – or a more complex gradient model in which layer 2 is marked by a steeper velocity gradient than underlying layer 3. Integrated igneous crustal thicknesses (1.62 ± 0.22 s, 5.22 ± 0.64 km) are significantly less than what is considered normal. We present a revised seismic transect across the East African margin, as well as total sediment thickness, depth to basement and crustal thickness maps. 相似文献
10.
N. G. Direen B. E. Cohen R. Maas F. A. Frey J. M. Whittaker M. F. Coffin 《Australian Journal of Earth Sciences》2017,64(7):851-869
Volcanism associated with the Kerguelen Large Igneous Province is found scattered in southwestern Australia (the ca 136 to ca 130 Ma Bunbury Basalts, and ca 124 Ma Wallaby Plateau), India (ca 118 Ma Rajmahal Traps and Cona Basalts), and Tibet (the ca 132 Ma Comei Basalts), but apart from the ～70 000 km2 Wallaby Plateau, these examples are spatially and volumetrically minor. Here, we report dredge, geochronological and geochemical results from the ～90 000 km2 Naturaliste Plateau, located ～170 to ～500 km southwest of Australia. Dredged lavas and intrusive rocks range from mafic to felsic compositions, and prior geophysical analyses indicate these units comprise much of the plateau substrate. 40Ar/39Ar plagioclase ages from mafic units and U–Pb zircon ages from silicic rocks indicate magmatic emplacement from 130.6 ± 1.2 to 129.4 ± 1.3 Ma for mafic rocks and 131.8 ± 3.9 to 128.2 ± 2.3 Ma for silicic rocks (2σ). These Cretaceous Naturaliste magmas incorporated a significant component of continental crust, with relatively high 87Sr/86Sr (up to 0.78), high 207Pb/204 Pb ratios (15.5–15.6), low 143Nd/144Nd (0.511–0.512) and primitive-mantle normalised Th/Nb of 11.3 and La/Nb of 3.97. These geochemical results are consistent with the plateau being underlain by continental basement, as indicated by prior interpretations of seismic and gravity data, corroborated by dredging of Mesoproterozoic granites and gneisses on the southern plateau flank. The Cretaceous Naturaliste Plateau igneous rocks have signatures indicative of extraction from a depleted mantle, with trace-element and isotopic values that overlap with Kerguelen Plateau lavas reflect crustal contamination. Our chemical and geochronological results therefore show the Naturaliste Plateau contains evidence of an extensive igneous event representing some of the earliest voluminous Kerguelen hotspot magmas. Prior work reports that contemporaneous correlative volcanic sequences underlie the nearby Mentelle Basin, and the Enderby Basin and Princess Elizabeth Trough in the Antarctic. When combined, the igneous rocks in the Naturaliste, Mentelle, Wallaby, Enderby, Princess Elizabeth, Bunbury and Comei-Cona areas form a 136–124 Ma Large Igneous Province covering >244 000 km2. 相似文献