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1.
Studies of photosynthesis and respiration in the sheet-like green macroalgaUlva lactuca L. have typically made use of cut discs or individual thalli. Because this species accumulates in layered mats in the field, its structure has the potential to significantly alter metabolic rates compared to those measured for a single layer. The effect of biomass layering on photosynthesis and respiration inU. lactuca was assessed by incubating stacks of 1, 2, 4, and 8 thalli across a range of surface irradiance and in the dark. The photosynthesis-irradiance curve for a single thallus was hyperbolic in shape with maximum photosynthetic rates of 16–24.5 mg O2 g?1 dry weight h?1, a photosynthetic efficiency of 0.18 mg O2 g?1 dry weight h?1 (μE m?2 s?1)?1, and dark respiration rates of 0.95–1.2 mg O2 g?1 dry weight h?1. Weight-specific photosynthesis and respiration rates decreased as the amount of layering increased, with rates approximately twice as high in a single layer as for 8 layers. A simple model revealed that the reduced photosynthetic rates were due to attenuation of light through the stack. Each layer ofUlva reduced the light available to the next layer by approximately 55%, and variability in this absorption was directly related to thallus chlorophyll content. Model runs suggested that acclimation of the thalli by changes in chlorophyll content has the potential to reduce some, but not all of the effect of layering. Reduced respiration rates were atributed to the depletion of oxygen from the interstices between the layers. Results were incorporated into a model of anUlva mat, which predicted decreasing rates of weight-specific total mat production with increasing mat thickness as additional layers are added to the bottom of the mat that neither produce nor consume significant amounts of oxygen. The model predicted area-weighted mat production to increase up to a thickness of 10 layers, after which the rate was constant with increasing mat thickness for the same reason. SinceUlva has a tendency to accumulate in layers under natural conditions, these results improve upon metabolic measurements made with single thalli and will be useful for calculations of macroalgal production as well as in ecosystem models in whichUlva is an important primary producer.  相似文献   

2.
Seasonal responses in estuarine metabolism (primary production, respiration, and net metabolism) were examined using two complementary approaches. Total ecosystem metabolism rates were calculated from dissolved oxygen time series using Odum’s open water method. Water column rates were calculated from oxygen-based bottle experiments. The study was conducted over a spring-summer season in the Pensacola Bay estuary at a shallow seagrass-dominated site and a deeper bare-bottomed site. Water column integrated gross production rates more than doubled (58.7 to 130.9 mmol O2 m?2 day?1) from spring to summer, coinciding with a sharp increase in water column chlorophyll-a, and a decrease in surface salinity. As expected, ecosystem gross production rates were consistently higher than water column rates but showed a different spring-summer pattern, decreasing at the shoal site from 197 to 168 mmol O2 m?2 day?1 and sharply increasing at the channel site from 93.4 to 197.4 mmol O2 m?2 day?1. The consistency among approaches was evaluated by calculating residual metabolism rates (ecosystem ? water column). At the shoal site, residual gross production rates decreased from spring to summer from 176.8 to 99.1 mmol O2 m?2 day?1 but were generally consistent with expectations for seagrass environments, indicating that the open water method captured both water column and benthic processes. However, at the channel site, where benthic production was strongly light-limited, residual gross production varied from 15.7 mmol O2 m?2 day?1 in spring to 86.7 mmol O2 m?2 day?1 in summer. The summer rates were much higher than could be realistically attributed to benthic processes and likely reflected a violation of the open water method due to water column stratification. While the use of sensors for estimating complex ecosystem processes holds promise for coastal monitoring programs, careful attention to the sampling design, and to the underlying assumptions of the methods, is critical for correctly interpreting the results. This study demonstrated how using a combination of approaches yielded a fuller understanding of the ecosystem response to hydrologic and seasonal variability.  相似文献   

3.
Assessing nitrogen dynamics in the estuarine landscape is challenging given the unique effects of individual habitats on nitrogen dynamics. We measured net N2 fluxes, sediment oxygen demand, and fluxes of ammonium and nitrate seasonally from five major estuarine habitats: salt marshes, seagrass beds (SAV), oyster reefs, and intertidal and subtidal flats. Net N2 fluxes ranged from 332?±?116 μmol?N-N2?m?2?h?1 from oyster reef sediments in the summer to ?67?±?4 μmol?N-N2?m?2?h?1 from SAV in the winter. Oyster reef sediments had the highest rate of N2 production of all habitats. Dissimilatory nitrate reduction to ammonium (DNRA) was measured during the summer and winter. DNRA was low during the winter and ranged from 4.5?±?3.0 in subtidal flats to 104?±?34 μmol?15NH 4 + ?m?2?h?1 in oyster reefs during the summer. Annual denitrification, accounting for seasonal differences in inundation and light, ranged from 161.1?±?19.2 mmol?N-N2?m?2?year?1 for marsh sediments to 509.9?±?122.7 mmol?N-N2?m?2?year?1 for SAV sediments. Given the current habitat distribution in our study system, an estimated 28.3?×?106?mol of N are removed per year or 76 % of estimated watershed nitrogen load. These results indicate that changes in the area and distribution of habitats in the estuarine landscape will impact ecosystem function and services.  相似文献   

4.
Hypoxia is emerging as a major threat to marine coastal biota. Predicting its occurrence and elucidating the driving factors are essential to set successful management targets to avoid its occurrence. This study aims to elucidate the effects of warming on the likelihood of hypoxia. High-frequency dissolved oxygen measurements have been used to estimate gross primary production (GPP), net ecosystem production (NEP) and community respiration (CR) in a shallow macroalgae (Caulerpa prolifera) ecosystem in a highly human-influenced closed Mediterranean bay. Daily averaged GPP and CR ranged from 0 to 1,240.9 and 51.4 to 1,297.3?mmol?O2?m?2?day?1, respectively. The higher GPP and CR were calculated for the same day, when daily averaged water temperature was 28.3?°C, and resulted in a negative NEP of ?56.4?mmol?O2?m?2?day?1. The ecosystem was net heterotrophic during the studied period, probably subsidized by allochthonous organic inputs from ground waters and from the surrounding town and boating activity. Oxygen dynamics and metabolic rates strongly depend on water temperature, with lower oxygen content at higher temperatures. The probability of hypoxic conditions increased at a rate of 0.39?% °C?1 (±0.14?% °C?1). Global warming will increase the likelihood of hypoxia in the bay studied, as well as in other semi-enclosed bays.  相似文献   

5.
Sediment-water exchanges of ammonium (NH4 +), nitrate + nitrite (NOx ?), filterable reactive phosphorus (FRP, primarily ortho-phosphate), and oxygen (O2) under aphotic (heterotrophic) conditions were determined at 2–5 stations in the Neuse River Estuary, from 1987 to 1989. Shallow (1 m), sandy stations were sampled along the salinity gradient. Fluxes from deep (>2 m) sites were compared to the shallow sites in two salinity zones. Grain size became finer and organic content increased with depth in the oligohaline zone but not in the mesohaline zone. Net release of NH4 + and FRP occurred at all sites. Fluxes varied from slight uptake to releases of 200–500 μmol m?2 h?1 (NH4 +) and 150–900 μmol m?2 h?1 (FRP). Net NOx ? exchange was near zero, but were ±100 μmol m?2 h?1 over the year. Release of NH4 + and FRP from the shallow sandy stations decreased with distance down the estuary, but O2 uptake did not change. The deeper oligohaline site had twofold higher rates of NH4 + and FRP release and O2 uptake than the shallow site, but no differences occurred between depths in the mesohaline zone. Temperature and organic content were important controls for all fluxes, but water column NOx ? concentration was also important in regulating NOx ? exchanges. Ratios of oxygen consumption to NH4 + release were near the predicted ratio (Redfield model) at oligohaline sites but increased down estuary at mesohaline sites. This may be due to greater nitrification rates promoted by autotrophy in the sediments.  相似文献   

6.
Sediment oxygen uptake and net sediment-water fluxes of dissolved inorganic and organic nitrogen and phosphorus were measured at two sites in Fourleague Bay, Louisiana, from August 1981, through May 1982. This estuary is an extension of Atchafalaya Bay which receives high discharge and nutrient loading from the Atchafalaya River. Sediment O2 uptake averaged 49 mg m?2 h?1. On the average, ammonium (NH4 +) was released from the sediments (mean flux =+129 μmol m?2 h?1), and NO3 ? was taken up (mean flux =?19 μmol m?2h?1). However, very different NO3 ? fluxes were observed at the two sites, with sediment uptake at the upper, river-influenced, high NO3 ? site (mean flux =?112 μmol m?2 h?1) and release at the lower, marine-influenced low NO3 ? site (mean flux =+79 μmol m?2 h?1). PO4 3? fluxes were low and often negative (mean flux =?8 μmol m?2 h?1), while dissolved organic phosphorus fluxes were high and positive (mean flux =+124 μmol m?2 h?1). Dissolved organic nitrogen fluxes varied greatly, ranging from a mean of +305 μmol m?2 h?1 at the lower bay, to ?710 μmol m?2 h?1 at the upper bay. Total dissolved nitrogen and phosphorus fluxes indicated the sediments were a nitrogen (mean flux =+543 μmol m?2 h?1) and phosphorus source (mean flux =+30 μmol m?2 h?1) at the lower bay, and a nitrogen sink (mean flux =?553 μmol m?2 h?1) and phosphorus source (mean flux =+17 μmol m?2 h?1) in the upper bay. Mean annual O∶N ration of the positive inorganic sediment fluxes were 27∶1 at the upper bay and 18∶1 at the lower bay. Based on these data we hypothesize that nitrification and denitrification are important sediment processes in the upper bay. We further hypothesize that Atchafalaya River discharge affects sediment-water fluxes through seasonally high nutrient loading which leads to net nutrient uptake by sediments in the upper bay and release in the lower bay, where there is less river influnces.  相似文献   

7.
Sediment-water oxygen and nutrient (NH4 +, NO3 ?+NO2 ?, DON, PO4 3?, and DSi) fluxes were measured in three distinct regions of Chesapeake Bay at monthly intervals during 1 yr and for portions of several additional years. Examination of these data revealed strong spatial and temporal patterns. Most fluxes were greatest in the central bay (station MB), moderate in the high salinity lower bay (station SB) and reduced in the oligohaline upper bay (station NB). Sediment oxygen consumption (SOC) rates generally increased with increasing temperature until bottom water concentrations of dissolved oxygen (DO) fell below 2.5 mg l?1, apparently limiting SOC rates. Fluxes of NH4 + were elevated at temperatures >15°C and, when coupled with low bottom water DO concentrations (<5 mg l?1), very large releases (>500 μmol N m?2 h?1) were observed. Nitrate + nitrite (NO3 ?+NO2 ?) exchanges were directed into sediments in areas where bottom water NO3 ?+NO2 ? concentrations were high (>18 μM N); sediment efflux of NO3 ?+NO2 ? occurred only in areas where bottom water NO3 ?+NO2 ? concentrations were relatively low (<11 μM N) and bottom waters well oxygenated. Phosphate fluxes were small except in areas of hypoxic and anoxic bottom waters; in those cases releases were high (50–150 μmol P m?2 h?1) but of short duration (2 mo). Dissolved silicate (DSi) fluxes were directed out of the sediments at all stations and appeared to be proportional to primary production in overlying waters. Dissolved organic nitrogen (DON) was released from the sediments at stations NB and SB and taken up by the sediments at station MB in summer months; DON fluxes were either small or noninterpretable during cooler months of the year. It appears that the amount and quality of organic matter reaching the sediments is of primary importance in determining the spatial variability and interannual differences in sediment nutrient fluxes along the axis of the bay. Surficial sediment chlorophyll-a, used as an indicator of labile sediment organic matter, was highly correlated with NH4 ?, PO4 3?, and DSi fluxes but only after a temporal lag of about 1 mo was added between deposition events and sediment nutrient releases. Sediment O:N flux ratios indicated that substantial sediment nitrification-denitrification probably occurred at all sites during winter-spring but not summer-fall; N:P flux ratios were high in spring but much less than expected during summer, particularly at hypoxic and anoxic sites. Finally, a comparison of seasonal N and P demand by phytoplankton with sediment nutrient releases indicated that the sediments provide a substantial fraction of nutrients required by phytoplankton in summer, but not winter, especially in the mid bay region.  相似文献   

8.
Sediment denitrification was monthly evaluated in two tropical coastal lagoons with different trophic states using the 15N isotope pairing technique. Denitrification rates were very low in both environments, always <5.0 μmol N2 m?2 h?1 and were not significantly different between them. Oxygen consumption varied from 426 to 4248 μmol O2 m?2 h?1 and was generally three times higher in the meso-eutrophic than the oligotrophic lagoon. The low denitrification activity was ascribed to both low water NO3 ? concentrations (<2.0 μM) and little nitrate supply from nitrification. There was no correlation of denitrification with nitrate or ammonium fluxes. Sediments in temperate environments with similar oxygen consumption rates usually presented a higher proportion of nitrification–denitrification rates. Sediment oxygen consumption was a good predictor of sediment denitrification in both studied lagoons.  相似文献   

9.
In order to better understand the spatiotemporal variations and interrelationships of greenhouse gases (GHG), monthly surface fluxes and profile concentrations of GHG (CO2, N2O and CH4) in karst areas in the Guizhou Province, southwest China, were measured from June 2006 to May 2007. GHG fluxes showed high variability, with a range of 460.9?C1,281.2?mg?m?2?h?1 for CO2, ?25.4 to 81.5???g?m?2?h?1 for N2O and ?28.7 to ?274.9???g?m?2?h?1 for CH4, but no obvious seasonal change trends of the fluxes existed. Profile concentrations of CO2, N2O and CH4 varied between 0.5 and 31.5?mL?L?1, 0.273 and 0.734, and 0.1 and 3.5???L?L?1, respectively. In general, concentrations of CO2 and N2O increased with depth, while CH4 had an inverse trend. However, in October, November and January, the reversal of depth patterns of GHG concentrations took place below 15?cm, close to the soil?Crock interface. The spatiotemporal distribution of CO2 in soil profile was significantly positively correlated with that of N2O (p?<?0.05?C0.01) and negatively correlated with that of CH4 (p?<?0.01). The correlation analysis showed that soil temperature and moisture may be responsible for GHG dynamics in the soils, rather than the exchange of GHG between land and atmosphere.  相似文献   

10.
Benthic macroinvertebrate biomass and ammonium excretion rates were measured at four stations in the Gulf of Mexico near the Mississippi River mouth. Calculated areal excretion rates were then compared to sediment-water nitrogen fluxes measured in benthic bottom lander chambers at similar stations to estimate the potential importance of macroinvertebrate excretion to sediment nitrogen mineralization. Excretion rates for individual crustaceans (amphipods and decapods) was 2–21 nmoles NH4 + (mg dry weight)?1 h?1. The mean excretion rates for the polychaetes, Paraprionaspio pinnata [6–12 nmoles NH4 + (mg dry weight)?1h?1] and Magelona sp. [27–53 nmoles NH4 + (mg dry weight)?1h?1], were comparable or higher than previous measurements for similar size benthic or pelagic invertebrates incubated at the same temperature (22±1°C). Although the relatively high rates of excretion by these selective feeders may have been partially caused by experimental handling effects (e.g., removal from sediment substrates), they probably reflected the availability of nitrogen-rich food supplies in the Mississippi River plume. When the measured weight-specific rates were extrapolated to total areal biomass, areal macroinvertebrate excretion estimates ranged from 7 μmole NH4 + m?2h?1 at a 40-m deep station near the river mouth to 18 μmole NH4 + m?2h?1 at a shallower (28-m deep) station further from the river mouth. The net flux of ammonium and nitrate from the sediments to the water measured in bottom lander chambers in the same region were 15–53 μmole NH4 + m?2h?1 and ?25–21 μmole NO3 ? m?2h?1. These results suggest that excretion of NH4 + by macroinvertebrates could be a potentially important component of benthic nitrogen regeneration in the Mississippi River plume-Gulf shelf region.  相似文献   

11.
Measurements of primary production in surf-zone habitats are relatively rare and often utilize simulation approaches, owing to the physical challenges of working in surf. The study reported here examined primary production in situ at two open ocean sandy beaches in southeastern North Carolina during relatively calm summer conditions. In situ bottle incubations using 14C uptake methods were complemented by simultaneous measures of phytoplankton photo-physiology assessed by Fast Repetition Rate Fluorometry (FRRF) in flow-through mode at the two sites across a spring-neap tidal cycle in July, 2010. The surf-zone phytoplankton was dominated by small centric and pennate diatoms as well as cyanobacteria and chlorophytes with biomass concentrations of 3.63?C9.23?mg chl a m?3. Primary productivity was relatively high, ranging from 31.5?C88.0?mg?C?m?3?h?1 by 14C. Biomass-specific productivity averaged ??9.4?mg C (mg chl a)?1?h?1 by 14C, indicating healthy phytoplankton populations. Measurements of the functional absorption cross section of photosystem II, ??PSII, via FRRF were 327?C380, comparable to values reported by other investigators of open ocean phytoplankton. Averaged values of the maximum effective quantum yield, F v/F m, corresponded to proportions of photochemically competent PSII reaction centers of 62.6?% to 72?%, indicating that the phytoplankton were nutrient-replete. These data suggest that the surf zone, although a spatially confined habitat, is a productive one that plays a significant role in coastal ocean ecology. Further investigation is needed to better understand primary productivity of phytoplankton in the surf zone and the effect of the dynamic environment on their physiological responses.  相似文献   

12.
The Yangla copper deposit, with Cu reserves of 1.2 Mt, is located between a series of thrust faults in the Jinshajiang–Lancangjiang–Nujiang region, Yunnan, China, and has been mined since 2007. Fluid inclusion trapping conditions ranged from 1.32 to 2.10 kbar at 373–409 °C. Laser Raman spectroscopy confirms that the vapour phase in these inclusions consists of CO2, CH4, N2 and H2O. The gas phases in the inclusions are H2O and CO2, with minor amounts of N2, O2, CO, CH4, C2H2, C2H4, and C2H6. Within the liquid phase, the main cations are Ca2+ and Na+ while the main anions are SO4 2? and Cl?. The oxygen and hydrogen isotope compositions of the ore-forming fluids (?3.05‰?≤?δ18OH2O?≤?2.5‰; ?100‰?≤?δD?≤??120‰) indicate that they were derived from magma and evolved by mixing with local meteoric water. The δ34S values of sulfides range from ?4.20‰ to 1.85‰(average on ?0.85‰), supporting a magmatic origin. Five molybdenite samples taken from the copper deposit yield a well-constrained 187Re–187Os isochron age of 232.8?±?2.4 Ma. Given that the Yangla granodiorite formed between 235.6?±?1.2 Ma and 234.1?±?1.2 Ma, the Cu metallogenesis is slightly younger than the crystallization age of the parent magma. A tectonic model that combines hydrothermal fluid flow and isotope compositions is proposed to explain the formation of the Yangla copper deposit. At first, westward subduction of the Jinshajiang Oceanic Plate in the Early Permian resulted in the development of a series of thrust faults. This was accompanied by fractional melting beneath the overriding plate, triggering magma ascent and extensive volcanism. The thrust faults, which were then placed under tension during a change in tectonic mode from compression to extension in the Late Triassic, formed favorable pathways for the magmatic ore-forming fluids. These fluids precipitated copper-sulfides to form the Yangla deposit.  相似文献   

13.
Concentration profiles of O2, NH4 +, NO3 −, and PO4 3− were measured at high spatial resolution in a 12-cm thick benthic mat of the filamentous macroalga Chaetomorpha linum. Oxygen and nutrient concentration profiles varied depending on algal activity and water turbulence. High surface irradiance stimulated O2 production in the surface layers and introduced O2 to deeper parts of the mat while the bottom layers of the mat and the underlying sediment were anoxic. Nutrient concentrations were highest in the bottom layers of the mat directly above the sediment nutrient source and decreased towards the surface layers due to algal assimilation and enhanced mixing with the overlying water column. Increased turbulence during windy periods resulted in more homogeneous oxygen and nutrient concentration profiles and shifted the oxic-anoxic interface downward. Denitrification within the mat, as measured by the isotope pairing technique on addition of 15NO3 −, was found to take place directly below the oxic-anoxic interface. Denitrification activity was always due to coupled nitrification-denitrification, whereby nitrifiers in the mat utilize NH4 + diffusing from below and O2 diffusing from above. The denitrification rate in the mat ranged from 22 μmol m−2 h−1 to 28 μmol m−2 h−1, approximately equivalent to that measured in the surrounding nonvegetated sediment. Although sediment denitrification is suppressed when the sediment surface is covered by a dense macroalgal mat, the denitrification zone may migrate up into the mat. In eutrophic estuaries with a large area of macroalgal cover, the physical structure and growth stage of algal mats may thus play an important role in the regulation of nitrogen removal by denitrification.  相似文献   

14.
In an attempt to more fully understand the dissolved inorganic nitrogen dynamics of the Neuse River estuary, 15NH4 + and 15NO3 ? uptake rates were measured and daily depth-integrated rates calculated for seven stations distributed along the salinity gradient. Measurements were made at 2–3-wk intervals from March 1985 to February 1989. Significant dark NH4 + uptake occurred and varied both spatially and seasonally, accounting for as much as 95% of light uptake with the median being 33%. Apparent NH4 + uptake ranged from 0.001 μmol N 1?1 h?1 to 4.2 μmol N 1?1 h?1, with highest rates occurring during late summer-fall in the oligohaline estuary. Apparent NH4 + uptake was significantly related to NH4 + concentration (p<0.01); however, the regression explained <3% of the variation. Daily-integrated NH4 + uptake ranged from 0.1 mmol N m?2 d?1 to 133 mmol N m?2 d?1 and followed the trend of apparent uptake. Annual NH4 + uptake of the estuary was significantly lower in 1988 than for any other year. Dark uptake of NO3 ? was only 14% of maximum light uptake. Apparent NO3 ? uptake rates ranged from 0.001 μmol N 1?1 h?1 to 1.84 μmol N 1?1 h?1 with highest rates occurring in the oligohaline estuary. Apparent NO3 ? uptake was significantly related to NO3 ? concentration (p<0.01); however, the regression explained <5% of the variation. In general, NO3 ? uptake was only 20% of total dissolved inorganic nitrogen (DIN) uptake. Daily-integrated NO3 ? uptake ranged from 0.1 mmol N m?2 d?1 to 53 mmol N m?2 d?1 and followed similar patterns of apparent uptake. Annual NH4 + uptake was 11.39 mol N m?2 yr?1, 10.28 mol N m?2 Yr?1, 10.93 mol N m?2 yr?1, and 7.38 mol N m?2 yr?1, and 1.84 mol N m?2 yr?1, with the 4-yr mean being 10.0. Annual NO3 ? uptake was 3.12 mol N m?2 yr?1, 3.40 mol N m?2 yr?1, 1.96 mol N m?2 yr?1, and 1.84 mol N m?2 yr?1, with the 4-yr mean being 2.6. The total annual DIN uptake was more than twice published estimates of phytoplankton DIN demand, indicating that there is an important heterotrophic component of DIN uptake occurring in the water column. The extrapolation of nitrogen demand from primary productivity results in serious underestimates of estuarine nitrogen demand for the Neuse River estuary and may be true for other estuaries as well.  相似文献   

15.
Rice cultivation in the Ebro Delta (Catalonia, Spain) has inverted the natural hydrological cycles of coastal lagoons and decreased water salinities for over 150 years. Adjustments in the water management practices—in terms of source and amount of freshwater inputs—have resulted in changes in the diversity, distribution and productivity of submerged angiosperms. Between the 1970s and late 1980s, a massive decline of the aquatic vegetation occurred in the Encanyissada–Clot and Tancada lagoons, but little information on the status is available after the recovery of macrophytes in the 1990s. Here, we evaluate the influence of salinity regimes resulting from current water management practices on the composition, distribution, seasonal abundance and flowering rates of submersed macrophytes, as well as on the occurrence of epiphyte and drift macroalgae blooms in three coastal lagoons. Our results show that Ruppia cirrhosa is the dominant species in the Encanyissada lagoon (185.97?±?29.74 g?DW?m?2?year?1; 12–27?‰ salinity) and the only plant species found in the Tancada lagoon (53.26?±?10.94 g?DW?m2?year?1; 16–28?‰ salinity). Flowering of R. cirrhosa (up to 1,011?±?121 flowers?m?2) was only observed within the Encanyissada and suggests that mesohaline summer conditions may favor these events. In contrast, low salinities in Clot lagoon (～3–12?‰) favor the development of Potamogeton pectinatus (130.53?±?13.79 g?DW?m2?year?1) with intersperse R. cirrhosa (8.58?±?1.71 g?DW?m?2) and mixed stands of P. pectinatus and Najas marina (up to ～57 g?DW?m?2?year?1) in some reduced areas. The peak biomasses observed during the study are 88 to 95 % lower than maximum values reported in the literature at similar salinities, and there is also little or no recovery in some areas compared to last reports more than 20 years ago. The main management actions to restore the natural diversity and productivity of submersed angiosperms, such as the recovering of the seagrass Zostera noltii, should be the increase of salinity during the period of rice cultivation, by reducing freshwater inputs and increasing flushing connections with the bays.  相似文献   

16.
Bojorquez Lagoon (BL), located on the Mexican Caribbean, has received sewage and dredging impacts as a result of tourism development. The lagoon supports a high diversity of primary producers compared to sheltered adjacent lagoons dominated byThalassia testudinum communities. The Diurnal Curve Method (Odum and Hoskin 1958) was used to measure community metabolism and assess eutrophication in BL by comparing it to the nonimpacted lagoons and to other systems studied with this method. Dissolved oxygen community input to the water column in BL ranged between 8.3 g O2 m?2 d?1 and 41.5 g O2 m?2 d?1 during 1985 and 1986, and averaged 17.1, whereas dissolved oxygen community consumption ranged from 6.4 g O2 m?2 d?1 during 1985 and 1986, and averaged 17.1, whereas dissolved oxygen community consumption ranged from 6.4 g O2 m?2 d?1 to 37.6 g O2 m?2 d?1 and averaged 15.2. These values are higher than those found for the adjacent lagoons and similar coastal lagoons, and are similar to results from other lagoons with sewage or seafood waste discharge. Net flux of oxygen from the community to the water column averaged 1.9 g O2 m?2 d?1 and ranged from ?9.8 g O2 m?2 d?1 to 8.1 g O2 m?2 d?1. These values are low compared to the adjacent lagoons, and close to zero, as in dystrophic environments. Primary productivity, as estimated by oxygen input, increased in BL during the period of study, indicating that eutrophication is proceeding, but the lagoon has not reached yet a level of “critical eutrophication” as defined by Mee (1988).  相似文献   

17.
Excessive growth of biomass and retention of solids associated with air bubbles lead to bed clogging, which affects the biofilters?? performance. Two experiments were carried out in a submerged biofilter at the flow velocity of 0.5?m?h?1, for an organic loading rate of 51?g C m?3?h?1 and a nitrogen loading rate of 13?g NH4-N?m?3?h?1, one with the biofilter not aerated, the other with the biofilter partially aerated. The results showed that the higher head losses occurred in the upper section of the biofilter, where there was a greater biomass development and a higher removal of organic carbon, ammonia and solids, with the maximum allowed head loss being reached in 16 and 8?days. In any case, the steady-state conditions were achieved after 2?days and were interrupted on the tenth day of experiment E1 and on the fifth day of experiment E2. This allowed defining different operating cycles that enabled an average organic removal rate of 12.7?g C m?3?h?1 (27?%) and an average ammonia removal rate of 1.1?g NH4-N?m?3?h?1 (9?%) without aeration, and of 35.8?g C m?3?h?1 (76?%) and 6.3?g NH4-N?m?3?h?1 (51?%) with aeration. Regardless of the aeration conditions, more than 90?% of TOC and NH4-N removal occurred in the upper section. After the backwashing cycle, the biofilter returned to steady-state conditions in 6?h (without aeration) and 7?h (with aeration).  相似文献   

18.
Accurate measures of intertidal benthic microalgal standing stock (biomass) and productivity are needed to quantify their potential contribution to food webs. Oxygen microelectrode techniques, used in this study, provide realistic measures of intertidal benthic microalgal production. By dividing a salt-marsh estuary into habitat types, based on sediment and sunlight characteristics, we have developed a simple way of describing benthic microalgal communities. The purpose of this study was to measure and compare benthic microalgal biomass and production in five different estuarine habitats over an 18-mo period to document the relative contributions of benthic microalgal productivity in the different habitat types. Samples were collected bimonthly from April 1990 to October 1991. Over the 18-mo period, tall Spartina zone habitats had the highest (101.5 mg chlorophyll a (Chl a) m?2±6.9 SE) and shallow subtidal habitats the lowest (60.4±8.9 SE) microalgal biomass. There was a unimodal peak in biomass during the late winter-early spring period. The concentrations of photopigments (Chl a and total pheopigments) in the 0–5 mm of sediments were highly correlated (r2=0.73 and 0.88, respectively) with photopigment concentrations in the 5–10 mm depth interval. Biomass specific production (μmol O2 mg Chl a ?1 h?1) was highest in intertidal mudflat habitats (206.3±11.2 SE) and lowest in shallow subtidal habitats (104.3±11.1 SE). Regressions of maximum production (production at saturating irradiances) vs. biomass (Chl a) in the upper 2 mm of sediment by habitat type gave some of the highest correlations ever reported for benthic microalgal communities (r2 values ranged from 0.43 to 0.73). The habitat approach and oxygen microelectrode techniques provide a useful, realistic ranged from 0.43 to 0.73). The habitat approach and oxygen microelectrode techniques provide a useful, realistic method for understanding the biomass and production dynamics of estuarine benthic microalgal communities.  相似文献   

19.
The Nuri Cu‐W‐Mo deposit is located in the southern subzone of the Cenozoic Gangdese Cu‐Mo metallogenic belt. The intrusive rocks exposed in the Nuri ore district consist of quartz diorite, granodiorite, monzogranite, granite porphyry, quartz diorite porphyrite and granodiorite porphyry, all of which intrude in the Cretaceous strata of the Bima Group. Owing to the intense metasomatism and hydrothermal alteration, carbonate rocks of the Bima Group form stratiform skarn and hornfels. The mineralization at the Nuri deposit is dominated by skarn, quartz vein and porphyry type. Ore minerals are chalcopyrite, pyrite, molybdenite, scheelite, bornite and tetrahedrite, etc. The oxidized orebodies contain malachite and covellite on the surface. The mineralization of the Nuri deposit is divided into skarn stage, retrograde stage, oxide stage, quartz‐polymetallic sulfide stage and quartz‐carbonate stage. Detailed petrographic observation on the fluid inclusions in garnet, scheelite and quartz from the different stages shows that there are four types of primary fluid inclusions: two‐phase aqueous inclusions, daughter mineral‐bearing multiphase inclusions, CO2‐rich inclusions and single‐phase inclusions. The homogenization temperature of the fluid inclusions are 280°C–386°C (skarn stage), 200°C–340°C (oxide stage), 140°C–375°C (quartz‐polymetallic sulfide stage) and 160°C–280°C (quartz‐carbonate stage), showing a temperature decreasing trend from the skarn stage to the quartz‐carbonate stage. The salinity of the corresponding stages are 2.9%–49.7 wt% (NaCl) equiv., 2.1%–7.2 wt% (NaCl) equiv., 2.6%–55.8 wt% (NaCl) equiv. and 1.2%–15.3 wt% (NaCl) equiv., respectively. The analyses of CO2‐rich inclusions suggest that the ore‐forming pressures are 22.1 M Pa–50.4 M Pa, corresponding to the depth of 0.9 km–2.2 km. The Laser Raman spectrum of the inclusions shows the fluid compositions are dominated in H2O, with some CO2 and very little CH4, N2, etc. δD values of garnet are between ?114.4‰ and ?108.7‰ and δ18OH2O between 5.9‰ and 6.7‰; δD of scheelite range from ?103.2‰ to ?101.29‰ and δ18OH2O values between 2.17‰ and 4.09‰; δD of quartz between ?110.2‰ and ?92.5‰ and δ18OH2O between ?3.5‰ and 4.3‰. The results indicate that the fluid came from a deep magmatic hydrothermal system, and the proportion of meteoric water increased during the migration of original fluid. The δ34S values of sulfides, concentrated in a rage between ?0.32‰ to 2.5‰, show that the sulfur has a homogeneous source with characteristics of magmatic sulfur. The characters of fluid inclusions, combined with hydrogen‐oxygen and sulfur isotopes data, show that the ore‐forming fluids of the Nuri deposit formed by a relatively high temperature, high salinity fluid originated from magma, which mixed with low temperature, low salinity meteoric water during the evolution. The fluid flow through wall carbonate rocks resulted in the formation of layered skarn and generated CO2 or other gases. During the reaction, the ore‐forming fluid boiled and produced fractures when the pressure exceeded the overburden pressure. Themeteoric water mixed with the ore‐forming fluid along the fractures. The boiling changed the pressure and temperature, oxygen fugacity, physical and chemical conditions of the whole mineralization system. The escape of CO2 from the fluid by boiling resulted in scheelite precipitation. The fluid mixing and boiling reduced the solubility of metal sulfides and led the precipitation of chalcopyrite, molybdenite, pyrite and other sulfide.  相似文献   

20.
To determine the removal of regenerated nitrogen by estuarine sediments, we compared sediment N2 fluxes to the stoichiometry of nutrient and O2 fluxes in cores collected in the Childs River, Cape Cod, Massachusetts. The difference between the annual PO4 3− (0.2 mol P m−2 yr−1) and NH4 + (1.6 mol N m−2 yr−1) flux and the Redfield N∶P ratio of 16 suggested an annual deficit of 1.5 mol N m−2 yr−1. Denitrification predicted from O2∶NH4 + flux ratios and measured as N2 flux suggested a nitrogen sink of roughly the same magnitude (1.4 mol N m−2 yr−1). Denitrification accounted for low N∶P ratios of benthic flux and removed 32–37% of nitrogen inputs entering the relatively highly nutrient loaded Childs River, despite a relatively brief residence time for freshwater in this system. Uptake of bottom water nitrate could only supply a fraction of the observed N2 flux. Removal of regenerated nitrogen by denitrification in this system appears to vary seasonally. Denitrification efficiency was inversely correlated with oxygen and ammonium flux and was lowest in summer. We investigated the effect of organic matter on denitrification by simulating phytoplankton deposition to cores incubated in the lab and by deploying chambers on bare and macroaglae covered sediments in the field. Organic matter addition to sediments increased N2 flux and did not alter denitrification efficiency. Increased N2 flux co-varied with O2 and NH4 + fluxes. N2 flux (261±60 μmol m−2 h−1) was lower in chambers deployed on macroalgal beds than deployed on bare sediments (458±70 μmol m−2 h−1), and O2 uptake rate was higher in chambers deployed on macroalgal beds (14.6±2.2 mmol m−2 h−1) than on bare sediments (9.6±1.5 mmol m−2 h−1). Macroalgal cover, which can retain nitrogen in the system, is a link between nutrient loading and denitrification. Decreased denitrification due to increasing macroalgal cover could create a positive feedback because decreasing denitrification would increase nitrogen availability and could increase macroalgae cover.  相似文献   

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