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1.
Physical and biological processes controlling spatial and temporal variations in material concentration and exchange between the Southern Everglades wetlands and Florida Bay were studied for 2.5 years in three of the five major creek systems draining the watershed. Daily total nitrogen (TN), and total phosphorus (TP) fluxes were measured for 2 years in Taylor River, and ten 10-day intensive studies were conducted in this creek to estimate the seasonal flux of dissolved inorganic nitrogen (N), phosphorus (P), total organic carbon (TOC), and suspended matter. Four 10-day studies were conducted simultaneously in Taylor, McCormick, and Trout Creeks to study the spatial variation in concentration and flux. The annual fluxes of TOC, TN, and TP from the Southern Everglades were estimated from regression equations. The Southern Everglades watershed, a 460-km2 area that includes Taylor Slough and the area south of the C-111 canal, exported 7.1 g C m−2, 0.46 g N m−2, and 0.007 g P m−2, annually. Everglades P flux is three to four orders of magnitude lower than published flux estimates from wetlands influenced by terrigenous sedimentary inputs. These low P flux values reflect both the inherently low P content of Everglades surface water and the efficiency of Everglades carbonate sediments and biota in conserving and recycling this limiting nutrient. The seasonal variation of freshwater input to the watershed was responsible for major temporal variations in N, P, and C export to Florida Bay; approximately 99% of the export occurred during the rainy season. Wind-driven forcing was most important during the later stages of the dry season when low freshwater head coincided with southerly winds, resulting in a net import of water and materials into the wetlands. We also observed an east to west decrease in TN:TP ratio from 212:1 to 127:1. Major spatial gradients in N:P ratios and nutrient concentration and flux among the creek were consistent with the westward decrease in surface water runoff from the P-limited Everglades and increased advection of relatively P-rich Gulf of Mexico (GOM) waters into Florida Bay. Comparison of measured nutrient flux from Everglades surface water inputs from this study with published estimates of other sources of nutrients to Florida Bay (i.e. atmospheric deposition, anthropogenic inputs from the Florida Keys, advection from the GOM) show that Everglades runoff represents only 2% of N inputs and 0.5% of P input to Florida Bay.  相似文献   

2.
Seasonal meteorological events of high wind energy are important in the export of organic carbon from Biscayne Bay, Florida, by altering circulation and tidal flushing patterns coincident with increased resuspension. The accumulation of detrital organic carbon in the bay during productive summer months with light south-east breezes is reversed by the onset of the winter season and associated weekly cold fronts with sustained 15 knot northerly winds. The reversal of Biscayne Bay circulation patterns and increased discharge at Caesar's Creek result in an outwelling of dissolved organic carbon and particulate organic carbon. Southward advection at the seaward extremes of exchange channels prevents reintroduction of exported organic carbon by tidal currents.  相似文献   

3.
Spatial regression models were used to predict yields (kg?ha?1?yr?1) of nitrogen (N) and phosphorus (P) discharged from catchments throughout New Zealand under natural and current conditions. The models were derived using loads (kg?yr?1) of TN, NO3-N, TP and DRP calculated for 592 river water quality monitoring sites. Anthropogenic increases in yields above natural levels were associated with the proportions of catchments occupied by the intensive agricultural land cover and were unevenly distributed across regions. Anthropogenic increases in national loads of TN, NO3-N, TP and DRP exported to the ocean were 74%, 159%, 48% and 18%, respectively. Increases in loads exported to the ocean varied considerably at smaller scales, with catchments having significant load increases between 4- and 26-fold for N and 6- to 9-fold for P. Predictions of yields and loads reported here have utility in the development of strategies to manage nutrients.  相似文献   

4.
《Marine Geology》2005,214(4):411-430
The Atchafalaya River in Louisiana shares the third largest drainage basin in the world with the Mississippi River. Sediment cores and seismic profiles were used to examine the development and impact on land accretion of an early-stage subaqueous delta accumulating on the shallow (<25 m water depth) continental shelf seaward of the Atchafalaya River mouths in the period (∼100 years) since the Atchafalaya has captured a significant fraction of the overall Mississippi discharge. The subaqueous clinoform is muddy (70–100% finer than 63 μm) and extends approximately 21–26 km seaward of the shell reef (to 8 m water depth) across the mouth of the Atchafalaya Bay, with a discontinuous, and, in places, mobile modern mud layer <20 cm thick covering a relict deltaic shoal area further seaward. The sigmoidal clinoform has a topset surface that steepens from east to west (1:2500 to 1:1600), a foreset with maximum slopes of about 1:550, and a limited bottomset region (<0.5 km wide). 210Pb and 137Cs geochronology show maximum sediment accumulation rates (>3 cm/year) correspond to the foreset and bottomset region, with rates decreasing to as low as 0.9 cm/year on the shelf topset region and its extension inside Atchafalaya Bay. Seven sedimentary facies are observed in the subaqueous delta, with differences created by degree of biological destruction of physical stratification, which is inversely related to sediment accumulation rate, and by the proximity of an area to the riverine sand source. There is a marked alongshore sediment dispersal pattern observed by the progressive winnowing of sand and coarse silt to the west. There is also a significant increase in shell content in Atchafalaya Bay relative to shelf facies. The resulting sigmoidal clinoform deposit (<3 m thick) more closely resembles strata geometries of subaqueous mud deltas associated with energetic systems (e.g., Amazon, Ganges–Brahmaputra, Fly), than it does the mature Mississippi delta 180 km to the east, albeit on a smaller scale and in shallow water.  相似文献   

5.
Water quality of a lowland stream in a New Zealand dairy farming catchment   总被引：3，自引：2，他引：1  
A small stream in a predominantly dairying catchment in the Waikato region of New Zealand was monitored for 2 years at three sites. Total nitrogen (TN) concentrations were up to 7.09 g m‐3 in winter, with the bulk comprising nitrate nitrogen (NO‐ 3‐N). During summer NO‐ 3‐N was near zero and TN mostly comprised organic nitrogen. Maximum concentrations of total phosphorus (TP) and dissolved reactive phosphorus (DRP) were 1.64 and 0.555 g m‐3, respectively, and peaks coincided with spring and autumn applications of phosphorus fertiliser. Ammoniacal nitrogen concentrations exceeded 1 g m‐3 on several occasions and mean concentrations at the three sites were 0.165–0.272 g m‐3. Faecal coliform and enterococci bacteria concentrations were 64–26000 and 7–23000 cfu per 100 ml, respectively. Specific yields of TN and NO‐ 3‐N (35.3 and 30.7 kg ha yr‐1, respectively) were much greater than any previously reported for New Zealand pasture catchments, whereas TP and DRP yields (1.16 and 0.54 kg ha yr‐1, respectively) were more in accord with other studies. Greater use of land treatment of liquid wastes will reduce stream inputs of faecal organisms, NH4‐N and P.  相似文献   

6.
Nutrient and chlorophyll concentrations were measured in January 1997, 1998 and 1999 in the Gulf of the Farallones, CA at locations stretching north/south from Point Reyes to Half Moon Bay, and seaward from the Golden Gate to the Farallon Islands. The cruises were all carried out during periods of high river flow, but under different climatological conditions with 1997 conditions described as relatively typical or ‘neutral/normal’, compared to the El Niño warmer water temperatures in 1998, and the cooler La Niña conditions in 1999. Near-shore sea-surface temperatures ranged from cold (9.5–10.5°C) during La Niña 1999, to average (11–13°C) during 1997 to warm (13.5–15°C) during El Niño 1998. Nutrients are supplied to the Gulf of the Farallones both from San Francisco Bay (SFB) and from oceanic sources, e.g. coastal upwelling near Point Reyes. Nutrient supplies are strongly influenced by the seasonal cycle of fall calms, with storms (commencing in January), and the spring transition to high pressure and northerly upwelling favorable winds. The major effect of El Niño and La Niña climatic conditions was to modulate the relative contribution of SFB to nutrient concentrations in the coastal waters of the Gulf of the Farallones; this was intensified during the El Niño winter and reduced during La Niña. During January 1998 (El Niño) the oceanic water was warm and had low or undetectable nitrate, that did not reach the coast. Instead, SFB dominated the supply of nutrients to the coastal waters. Additionally, these data indicate that silicate may be a good tracker of SFB water. In January, delta outflow into SFB produces low salinity, high silicate, high nitrate water that exits the bay at the Golden Gate and is advected northward along the coast. This occurred in both 1997 and 1998. However during January 1999, a La Niña, this SFB feature was reduced and the near-shore water was more characteristic of high salinity oceanic water penetrated all the way to the coast and was cold (10°C) and nutrient rich (16 μM NO3, 30 μM Si(OH)4). January chlorophyll concentrations ranged from 1–1.5 μg l−1 in all years with the highest values measured in 1999 (2.5–3 μg l−1) as a result of elevated nutrients in the area. The impact of climatic conditions on chlorophyll concentrations was not as pronounced as might be expected from the high temperatures and low nutrient concentrations measured offshore during El Niño due to the sustained supply of nutrients from the Bay supporting continued primary production.  相似文献   

7.
Benthic fluxes of dissolved inorganic nitrogen (NO3− and NH4+), dissolved organic nitrogen (DON), N2 (denitrification), O2 and TCO2 were measured in the tidal reaches of the Bremer River, south east Queensland, Australia. Measurements were made at three sites during summer and winter. Fluxes of NO3− were generally directed into the sediments at rates of up to −225 μmol N m−2 h−1. NH4+ was mostly taken up by the sediments at rates of up to −52 μmol N m−2 h−1, its ultimate fate probably being denitrification. DON fluxes were not significant during winter. During summer, fluxes of DON were observed both into (−105 μmol m−2 h−1) and out of (39 μmol m−2 h−1) the sediments. Average N2 fluxes at all sampling sites were similar during summer (162 μmol N m−2 h−1) and winter (153 μmol N m−2 h−1). Denitrification was fed both by nitrification within the sediment and NO3− from the water column. Sediment respiration rates played an important role in the dynamics of nitrification and denitrification. NO3− fluxes were significantly related to TCO2 fluxes (p<0.01), with a release of NO3− from the sediment only occurring at respiration rates below 1000 μmol C m−2 h−1. Rates of denitrification increased with respiration up to TCO2 fluxes of 1000 μmol C m−2 h−1. At sediment respiration rates above 1000 μmol C m−2 h−1, denitrification rates increased less rapidly with respiration in winter and declined during summer. On a monthly basis denitrification removed about 9% of the total nitrogen and 16% of NO3− entering the Bremer River system from known point sources. This is a similar magnitude to that estimated in other tidal river systems and estuaries receiving similar nitrogen loads. During flood events the amount of NO3− denitrified dropped to about 6% of the total river NO3− load.  相似文献   

8.
桑沟湾养殖海域营养盐和沉积物-水界面扩散通量研究   总被引：7，自引：0，他引：7  
利用2006年4,7,11月和2007年1月4个航次对桑沟湾养殖海域的观测资料,分析了该海域营养盐分布、结构特征、主要控制过程以及沉积物-水界面扩散通量,结果表明,该海域的营养盐分布具有明显的季节变化,海水中NO3-,NO2-,PO43-,DOP,TDP和SiO32-浓度皆是秋季最高,而NH4+,DON,TDN浓度则为夏季最高;各种营养盐的最低值除DON外都出现在春季。春季湾内外海水交换不畅,再加上大型藻类海带等生长旺盛期的消耗,使营养盐浓度处于较低水平,在夏秋两季丰水期沿岸河流注入对该海域营养盐的影响较大,冬季无机营养盐浓度分布主要受沿岸流的影响。磷的结构变化较大,其中DOP百分含量在夏季最高,达到81%。从春季到秋季海水中TDN的结构变化从以DON为主转变成以DIN为主。硅和氮的原子比值全年变化不大,硅和氮和氮和磷原子比值春夏两季的高于秋冬季的。分析营养盐化学计量限制标准和浮游植物生长的最低阈值结果表明,磷是春夏两季桑沟湾浮游植物生长的限制性因素;春季硅浓度低于浮游植物生长的最低阀值,也是一个潜在的限制因素。计算结果显示桑沟湾沉积物释放的NH4+,SiO32-和PO43-对初级生产力的贡献较小,与其他浅海环境相比,桑沟湾沉积物-水界面的营养盐通量处于较低或中等水平。  相似文献   

9.
Flow-through flumes were used to quantify net areal fluxes of nutrients in the fringe mangrove zone of lower Taylor River in the southern Everglades National Park. We also quantified net areal fluxes along the open water portion of the channel to determine the relative importance of either zone (vegetated vs. unvegetated) in the regulation of nutrient exchange in this system. Taylor River's hydrology is driven mainly by precipitation and wind, as there is little influence of tide. Therefore, quarterly samplings of the vegetated and unvegetated flumes were slated to include typical wet season and dry season periods, as well as between seasons, over a duration of two years. Concentrations of dissolved and total organic carbon (DOC and TOC) were highest during the wet season and similar to one another throughout the study, reflecting the low particulate loads in this creek. Dissolved inorganic nitrogen (nitrate+nitrite+ammonium) was 10–15% of the total nitrogen (TN) content, with NO−x and NH+4 showing similar concentration ranges over the 2-year study. Soluble reactive phosphorus (SRP) was usually <0·05μM, while total phosphorus (TP) was typically an order of magnitude higher. Net areal fluxes were calculated from nutrient concentration change over the length of the flumes. Most flux occurred in the vegetated zone. Dissolved inorganic nitrogen and DOC were usually taken up from the water column; however, we saw no seasonal pattern for any constituent over the course of this study. Total nutrients (TOC, TN, and TP) showed little net exchange and, like SRP, had fluxes that shifted irregularly throughout the study. Despite the lack of a clear seasonal pattern, there was a great deal of consistency between vegetated flumes, especially for NO−x and NH+4, and fluxes in the vegetated flumes were generally in the same direction (import, export, or no net flux) during a given sampling. These findings suggest that the fringe mangrove zone is of considerable importance in regulating nutrient dynamics in lower Taylor River. Furthermore, the influence of this zone may at times extend into northeast Florida Bay, as the bay is the primary recipient of water and nutrients during the wet season.  相似文献   

10.
This work examines the tidal exchanges of heat, inorganic nitrogenous nutrients and various forms of organic matter at the mouth of San Quintin Bay, Baja California, Mexico. It also attempts to elucidate the main factors responsible for the short-term fluctuations of these seawater properties. To accomplish this, a time series sampling was carried out at the mouth of the bay from 25 June to 5 July, 1979. The bay systematically exported heat, with an average of 1·2×1010 kcal per half tidal cycle during the sampling period. Inputs of nitrite and nitrate during upwelling were of major importance to the productivity of the lagoon. During non-upwelling conditions the trend was toward a dynamic equilibrium in the oxidized inorganic nutrient fluxes. There were significant exports of ammonia. These ammonia exports were, on average, about 20% of the nitrate plus nitrite imports. Ammonia concentrations were related to metabolic and mixing processes. Ammonia might be an important export product throughout the year, as a result of the reduced state of the sediments. During the sampling, there were imports of particulate organic carbon and nitrogen. The C/N ratio suggests that the main origin of organic detritus was other than the breakdown of eelgrass in the bay. There were mostly imports of diatom carbon, but fluxes of dinoflagellate carbon were always near equilibrium. Zooplankton showed both exports and imports. Variability in the zooplankton carbon was mostly related to diel vertical migration. There were no significant exports of floating seagrass, not even during spring tides.  相似文献   

11.
We examined the effect of light on water column and benthic fluxes in the Pensacola Bay estuary, a river-dominated system in the northeastern Gulf of Mexico. Measurements were made during the summers of 2003 and 2004 on 16 dates distributed along depth and salinity gradients. Dissolved oxygen fluxes were measured on replicate sediment and water column samples exposed to a gradient of photosynthetically active radiation. Sediment inorganic nutrient (NH4+, NO3−, PO43−) fluxes were measured. The response of dissolved oxygen fluxes to variation in light was fit to a photosynthesis–irradiance model and the parameter estimates were used to calculate daily integrated production in the water column and the benthos. The results suggest that shoal environments supported substantial benthic productivity, averaging 13.6 ± 4.7 mmol O2 m−2 d−1, whereas channel environments supported low benthic productivity, averaging 0.5 ± 0.3 mmol O2 m−2 d−1 (±SE). Estimates of baywide microphytobenthic productivity ranged from 8.1 to 16.5 mmol O2 m−2 d−1, comprising about 16–32% of total system productivity. Benthic and water column dark respiration averaged 15.2 ± 3.2 and 33.6 ± 3.7 mmol O2 m−2 d−1, respectively Inorganic nutrient fluxes were generally low compared to relevant estuarine literature values, and responded minimally to light exposure. Across all stations, nutrient fluxes from sediments to the water column averaged 1.11 ± 0.98 mmol m−2 d−1 for NH4+, 0.58 ± 1.08 mmol m−2 d−1 for NO3−, 0.01 ± 0.09 mmol m−2 d−1 for PO43−. The results of this study illustrate how light reaching the sediments is an important modulator of benthic nutrient and oxygen dynamics in shallow estuarine systems.  相似文献   

12.
A sampling and computational approach for estimating nutrient fluxes from a salt marsh ecosystem is presented. Extensive and intensive sampling of tidal velocities, water depths, and nutrient concentrations was made synoptically across three tidal creeks, connecting a 34 km2 South Carolina salt marsh with surrounding coastal waters. An estimate of nutrient exchange over each sampling period is based on measurements over four tidal cycles during a neap and spring tidal regime. The computation of instantaneous fluxes of NO3?NO2?, NH4+, and o-PO24? was based on the cross-multiplication of concentration, velocity, and integrated over the cross-sectional area of each tidal creek. The net flux of nutrients was estimated using a least-squares regression model which included periodic functions simulating tidal and diurnal cycles. This computational approach allows for a rigorous test of the statistical significance of the measured nutrient fluxes and a basis on which interpretations of the ecological significance of the exchange can be made.Tidal patterns in inorganic nutrient concentrations and the corresponding exchanges are presented for a spring time sampling. Nitrate-nitrite was exported consistently from the marsh to the coastal ocean with a mean value of 8.0 kg per tidal cycle for the neap sampling set and 15.6 kg per tidal cycle for the spring set. This corresponded to high concentrations of nitrate-nitrite (0.6 μM) on the ebb tide with low concentrations (0.1 μM) on the flood tide. Ammonia flux was variable and did not portray a consistent tidal concentration pattern. Concentrations ranged from 1 to 6 μM. Ammonia flux was exported to the coastal ocean only during the spring tidal set with a mean value of 114 kg per tidal cycle. Ortho-phosphate was also exported only on the spring tidal set with a mean flux of 40.0 kg per tidal cycle. A tidal concentration pattern of high concentrations (0.6 μM) on the ebb tide and low concentrations (0.05 μM) on the flood was consistent for ortho-phosphate during both neap and spring tidal sets.  相似文献   

13.
Surface waters of Alsea Bay, an unpolluted estuary on the Oregon coast, were analysed for nitrous oxide, nitrate and nitrite on a weekly or biweekly basis during the summer of 1979. The estuary was found to be a variable source of N2O to the atmosphere. Large and rapid increases in the concentrations of N2O, NO3?, and NO2? occurred at the beginning of the sampling period and are attributed to the influx of nutrient-rich upwelling water into the estuary with the tide. The subsequent decline in concentrations of nitrate, nitrite and nitrous oxide over the remainder of the summer is attributed to a decrease in upwelling intensity, a decline in nitrification rates and to assimilatory nitrate reduction. Measurements of nitrous oxide at six stations along the Alsea River were also made in September and October before and after the onset of the rainy season. Samples taken after flood conditions were established were systematically 50% higher than pre-flood samples. The data suggest that soil runoff results in elevated concentrations of N2O in rivers.  相似文献   

14.
We used naturally occurring radium isotopes as tracers of water exchange in Apalachicola Bay, a shallow coastal-plain estuary in northwestern Florida. The bay receives fresh water and radium from the Apalachicola River, and mixes with Gulf of Mexico waters through four inlets. We deployed moored buoys with attached Mn-fibers at several stations throughout the estuary during two summer and two winter periods. After deployment for at least one tidal cycle we measured the ratio of the two short-lived radium isotopes 223Ra (half-life = 11 d) and 224Ra (3.6 d) to estimate “radium ages” of the water in the bay.During our four seasonal deployments the river discharge ranged from 338 to 1016 m3 s− 1. According to our calculations the water turnover time in the bay during these samplings ranged from 6 to 12 days. Age contours in the bay showed that winds and tides as well as river discharge influence the water movement and the residence time of freshwater in the bay. We also calculated the mean age of river water in the bay which was between 5 to 9 days during the studied periods. We suggest that this approach can be used to quantify transport processes of dissolved substances in the bay. For example, soluble nutrient or pollutant transport rates from a point source could be examined. We conclude that the radium age technique is well suited for flushing rate calculations in river dominated shallow estuaries.  相似文献   

15.
《Marine Chemistry》2001,73(3-4):215-231
In-situ benthic flux studies were conducted at three stations in Upper Galveston Bay twice during March 1996 to directly measure release rates of dissolved Mn, Fe, Ni and Zn from the sediments. Results showed reproducible increases with time in both replicate light and light–dark benthic chambers, resulting in average fluxes of −1200±780, −17±12, −1.6±0.6 and −2.4±0.79 μmol m−2 day−1 for Mn, Fe, Ni and Zn, respectively. Sediment cores collected during 1994–1996 showed that surficial pore water concentrations were elevated compared to overlying water column concentrations, suggesting diffusive release from the sediments. Diffusive flux estimates of Mn and Zn agreed in direction with chamber fluxes measured on the same date, but only accounted for 5–38% of the measured flux. Diffusive fluxes of Fe agreed with measured fluxes at the near Trinity River station but overestimated actual release in the mid and outer Trinity Bay regions, possibly due to inaccurate determination of the Fe pore water gradients or rapid oxidation processes in the overlying water at these stations.In general, measured fluxes of Mn and Ni were higher in the mid Trinity Bay region and suggested a mechanism for the elevated trace metal concentrations previously reported for this region of Galveston Bay. However, the fluxes of Fe were highest in close proximity to the Trinity River, supporting the elevated Fe concentrations measured in this region during this and other studies, and decreased towards middle and outer Trinity Bay. Trace metal turnover times were between 0.1 and 1.2 days for Mn, between 1.3 and 4.6 days for Fe, and between 27 and 100 days for Ni and 12–20 days Zn, and were considerably shorter than the average Trinity Bay water residence time (1.5 years) for this period. Comparing area averaged benthic inputs to Trinity River inputs shows the sediments to be a significant source of trace metals to Galveston Bay. However, while benthic inputs of trace metals were measured, water column concentrations remained low despite rapid turnover times for Mn and Fe, suggesting removal of these metals from the water column after release from the sediments.  相似文献   

16.
This study investigates the biogeochemical processes that control the benthic fluxes of dissolved nitrogen (N) species in Boknis Eck – a 28 m deep site in the Eckernförde Bay (southwestern Baltic Sea). Bottom water oxygen concentrations (O2−BW) fluctuate greatly over the year at Boknis Eck, being well-oxygenated in winter and experiencing severe bottom water hypoxia and even anoxia in late summer. The present communication addresses the winter situation (February 2010). Fluxes of ammonium (NH4+), nitrate (NO3−) and nitrite (NO2−) were simulated using a benthic model that accounted for transport and biogeochemical reactions and constrained with ex situ flux measurements and sediment geochemical analysis. The sediments were a net sink for NO3− (−0.35 mmol m−2 d−1 of NO3−), of which 75% was ascribed to dissimilatory reduction of nitrate to ammonium (DNRA) by sulfide oxidizing bacteria, and 25% to NO3− reduction to NO2− by denitrifying microorganisms. NH4+ fluxes were high (1.74 mmol m−2 d−1 of NH4+), mainly due to the degradation of organic nitrogen, and directed out of the sediment. NO2− fluxes were negligible. The sediments in Boknis Eck are, therefore, a net source of dissolved inorganic nitrogen (DIN = NO3− + NO2− + NH4+) during winter. This is in large part due to bioirrigation, which accounts for 76% of the benthic efflux of NH4+, thus reducing the capacity for nitrification of NH4+. The combined rate of fixed N loss by denitrification and anammox was estimated at 0.08 mmol m−2 d−1 of N2, which is at the lower end of previously reported values. A systematic sensitivity analysis revealed that denitrification and anammox respond strongly and positively to the concentration of NO3− in the bottom water (NO3−BW). Higher O2−BW decreases DNRA and denitrification but stimulates both anammox and the contribution of anammox to total N2 production (%Ramx). A complete mechanistic explanation of these findings is provided. Our analysis indicates that nitrification is the geochemical driving force behind the observed correlation between %Ramx and water depth in the seminal study of Dalsgaard et al. (2005). Despite remaining uncertainties, the results provide a general mechanistic framework for interpreting the existing knowledge of N-turnover processes and fluxes in continental margin sediments, as well as predicting the types of environment where these reactions are expected to occur prominently.  相似文献   

17.
The distributions, sources and atmospheric fluxes of nitrous oxide (N2O) in the seawater of Jiaozhou Bay were investigated during four surveys in 2003 to evaluate this area as a source of N2O to the atmosphere. N2O concentrations in both the surface and bottom waters of Jiaozhou Bay showed obvious variability with both seasons and tidal cycles. Atmospheric fluxes of N2O in Jiaozhou Bay showed seasonal and spatial variations, with the highest values occurring in summer and the lowest in winter. The annual emission of N2O from the bay was estimated to be 1.09 × 106–2.23 × 106 mol yr−1. N2O in the water column of Jiaozhou Bay was found to come from several external sources including riverine water, sewage water and groundwater input, among which the riverine input was dominant while the groundwater input was rather limited. The spatial variation in distribution and atmospheric fluxes of N2O in Jiaozhou Bay was influenced by the input of polluted river waters and sewage effluent along the eastern coast, which highlights the effects of human impacts on N2O emission rates.  相似文献   

18.
The nitrogen isotopic composition of time-series sediment trap samples, dissolved NO-3, and surficial sediments was determined in three regions along the margin of the eastern North Pacific: Monterey Bay, San Pedro Basin, and the Gulf of California (Carmen and Guaymas Basins). Complex physical regimes are present in all three areas, and each is influenced seasonally by coastal upwelling. Nevertheless, sediment trap material evidently records the isotopic composition of new nitrogen sources, since average δ15N is generally indistinguishable from δ15N values for subsurface NO-3. Surficial sediments are also very similar to the average δ15N value of the sediment traps, being within 1‰. This difference in δ15N between trap material and sediment is much less than the previously observed 4‰ difference for the deep sea. Better organic matter preservation at our margin sites is a likely explanation, which may be due to either low bottom O2 concentrations or higher organic matter input to the sediments. All sites have δ15N for sub-euphotic zone NO-3 (8–10‰) substantially elevated from the oceanic average (4.5–5‰). This isotopic enrichment is a result of denitrification in suboxic subsurface waters (Gulf of California) or northward transport of denitrification influenced water (Monterey Bay and San Pedro Basin). Our results therefore suggest that downcore δ15N data, depending on site location, would record the intensity of denitrification and the transport of its isotopic signature along the California margin. Temporal variations in δ15N for the sediment traps do appear to respond to upwelling or convective injections of NO-3 to surface waters as a result of isotopic fractionation during phytoplankton uptake. Overall, though, the coupling between NO-3 injection, δ15N, and flux is looser than previously observed for the open-ocean, most likely the result of the smaller time/space scales of the events. In the Gulf of California, wintertime convective mixing/upwelling does produce distinct δ15N minima co-occurring with particle flux maxima. Interannual variations are apparent in this region when these winter-time δ15N minima fail to occur during El Niño conditions. There appears to be a positive relationship between the Southern Oscillation Index (SOI) anomaly and annual average δ15N. One explanation calls for hydrographic changes altering the δ15N of subeuphotic zone NO-3.  相似文献   

19.
Mass fluxes of diatom opal, planktonic foraminifera carbonate and coccolithophorid carbonate were measured with time-series sediment traps at six sites in the Arabian Sea, Bay of Bengal and Equatorial Indian Ocean (EIOT). The above fluxes were related to regional variations in salinity, temperature and nutrient distribution. Annual fluxes of diatom opal range between 3 and 28 g m−2 yr−1, while planktonic foraminifera carbonate fluxes range between 6 and 23 g m−2 yr−1 and coccolithophorid carbonate fluxes range between 4 and 24 g m−2 yr−1. Annual planktonic foraminifera carbonate to coccolithophorid carbonate ratios range between 0.8 and 2.2 and coccolithophorid carbonate to diatom opal ratios range between 0.5 and 3.3.In the western Arabian Sea, coccolithophorids are the major contributors to biogenic flux during periods of low nutrient concentrations. Coccolithophorid carbonate fluxes decrease and planktonic foraminiferal carbonate and diatom opal fluxes increase when nutrient-rich upwelled waters are advected over the trap site. In the oligotropic eastern Arabian Sea, coccolithophorid carbonate fluxes are high throughout the year. Planktonic foraminiferal carbonate fluxes are the major contributors to biogenic flux in the EIOT. In the northern and central Bay of Bengal, when surface salinity values drop sharply during the SW monsoon, there is a drastic reduction in planktonic foraminiferal carbonate fluxes, but coccolithophorid carbonate and diatom opal fluxes remain steady or continue to increase. Distinctly higher annual molar Sibio/Cinorg (>1) and Corg/Cinorg (>1.5) ratios are observed in the northern and central Bay of Bengal mainly due to lower foraminiferal carbonate production as a result of sharp salinity variations. We can thus infer that the enhanced freshwater supply from rivers should increase oceanic CO2 uptake. Its silicate supply favours the production of diatoms while the salinity drop produces conditions unfavourable for most planktonic foraminifera species.  相似文献   

20.
The whole core squeezing method was used to simultaneously obtain profiles of nitrous oxide (N2O), nitrogenous nutrients, and dissolved oxygen in sediments of Koaziro Bay, Japan (coastal water), the East China Sea (marginal sea), and the central Pacific Ocean (open ocean). In the spring of Koaziro Bay, subsurface peaks of interstitial N2O (0.5–3.5 cm depth) were observed, at which concentrations were higher than in the overlying water. This was also true for nitrate (NO3−) and nitrite (NO2−) profiles, suggesting that the transport of oxic overlying water to the depth through faunal burrows induced in situ N2O production depending on nitrification. In the summer of Koaziro Bay, sediment concentrations of N2O, NO3− and NO2− were lower than in the overlying water. In most East China Sea sediments, both N2O and NO3− decreased sharply in the top 0.5–2 cm oxic layer (oxygen: 15–130 μM), which may have indicated N2O and NO3− consumption by denitrification at anoxic microsites. N2O peaks at subsurface depth (0.5–6.5 cm) implied in situ production of N2O and/or its supply from the overlying water through faunal burrows. However, the occurrence of the latter process was not confirmed by the profiles of other constituents. In the central Pacific Ocean, the accumulation of N2O and NO3− in the sediments likely resulted from nitrification. Nitrous oxide fluxes from the sediments, calculated using its gradient at the sediment–water interface and the molecular diffusion coefficient, were −45 to 6.9 nmolN m−2 h−1 in Koaziro Bay in the spring, −29 to −21 nmolN m−2 h−1 in the summer, −46 to 37 nmolN m−2 h−1 in the East China Sea, 0.17 to 0.23 nmolN m−2 h−1 in the equatorial Pacific, and <±0.2 nmolN m−2 h−1 in the subtropical North Pacific, respectively.  相似文献   

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