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1.
增强的UV-B对湖泊生态系统的影响研究   总被引：2，自引：1，他引：2  
近20多年来，由于平流层臭氧层减薄引起紫外辐射（UV-B）增强而导致严重的生态学后果，已受到各国广泛的重视，并对此进行了深入研究，尤其集中在海洋浮游植物初级生产者及淡水食物网上。综述了国外在UV-B对湖泊生态系统影响的研究现状与动态，增强的UV-B在湖泊中呈指数衰减，不同湖泊衰减系数变化很大；光衰减系数与溶解性有机碳（DOC）、有色可溶性有机物（CDOM）一般呈显著性正相关；增强的UV-B对浮游植物、浮游细菌、浮游动物及鱼类均有不同程度的影响；由于不同生物具有不同适应UV-B伤害的机制，湖泊生态系统的结构和功能也势必会发生变化。最后提出了未来在太湖等富营养化湖泊UV-B的研究设想。  相似文献   

2.
To elucidate relationships between land cover and water quality along the central California coast, we collected monthly samples from 14 coastal waterway outlets representing various degrees of human development. Sites were distributed between three salinity categories, freshwater, estuarine, and marine, to better understand land cover-water quality relationships across a range of coastal aquatic ecosystems. Samples were analyzed for fecal indicator bacteria (FIB), dissolved nutrients, stable nitrogen isotopes in particulate organic matter, and chlorophylla (chla). Sediment samples from 11 sites were analyzed for the concentration of the anthropogenic organic contaminant perfluorooctane sulfonate and its precursors (ΣPFOS). While the data indicated impairment by nutrient, microbial, and organic contaminants at both agricultural and urban sites, the percentage of agricultural land cover was the most robust indicator of impairment, showing significant correlations (p<0.05) to FIB, nutrient, chla, and ΣPFOS levels. FIB densities were strongly influenced by salinity and were highest at sites dominated by agriculture and urbanization. Nutrient levels and chla correlated to both agricultural and urban land use metrics as well. Positive correlations among FIB, nutrients, chla, and ΣPFOS suggest a synergy between microbial, nutrient, and organic pollution. The results emphasize the importance of land management in protecting coastal water bodies and human health, and identify nutrient, microbial, and organic pollution as prevalent problems in coastal California water bodies.  相似文献   

3.
During June 2003, a period of mid level discharge (17,400 m−3 s−1), a parcel of water in the lower Mississippi River was sampled every 2 h during its 4-d transit from river km 362 near Baton Rouge to km 0 at Head of Passes, Louisiana, United States. Properties measured at the surface during each of the 48 stations were temperature, salinity, dissolved organic carbon (DOC), total dissolved nitrogen, dissolved macronutrients (NO3+NO2, PO4, Si(OH)4), chlorophylla (chla; three size fractions: < 5 μm, 5–20 μm, and > 20 μm) pigment composition by HPLC, total suspended matter (TSM), particulate organic carbon (POC), and particulate nitrogen (PN). Air-water CO2 flux was calculated from surface water dissolved inorganic carbon and pH. During the 4 d transit, large particles appeared to be settling out of the surface water. Concentrations of chla containing particles > 20 μm declined 37%, TSM declined 43%, POC declined 42% and PN declined 57%. Concentrations of the smaller chla containing particles did not change suggesting only large particulate materials were settling. There was no measurable loss of dissolved NO3, PO4, or Si(OH)4, consistent with the observation that chla did not increase during the 4-d transit. DOC declined slightly (3%). These data indicate there was little autotrophic or heterotrophic activity in the lower Mississippi River at this time, but the system was slightly net heterotrophic.  相似文献   

4.
SeaWiFS ocean color measurements were used to investigate interannual, monthly, and weekly variations in chlorophylla (chla) on the Louisiana shelf and to assess relationships with river discharge, nitrate load, and hypoxia. During the study period (2000–2003), interannual changes in shelf-wide chla concentrations averaged over January–July ranged from +57% to −33% of the 4-yr average, in accord with freshwater discharge changes of +20% to −29% and nitrate load changes of +20% to −35% from the Mississippi and Atchafalaya Rivers. Chla variations were largest on the shelf between the Mississippi and Atchafalaya Deltas. Within this region, which corresponds spatially to the area of most frequent hypoxia, lowest January–July mean chla concentrations (5.5 mg m−3 over 7,000 km2) occurred during 2000, the year of lowest freshwater discharge (16,136 m3 s−1) and nitrate load (55,738 MT N d−1) onto the shelf. Highest January–July mean chla concentrations (13 mg m−3 over 7,000 km2) were measured in 2002, when freshwater discharge (27,440 m3s−1) and nitrate load (101,761 MT N d−1) were highest and second highest, respectively. Positive correlations (R2=0.4–0.5) were found between chla and both fresh water and nitrate loads with 0 to 1 month lags, with the strongest relationships just west of the Mississippi Delta. In 2001, unusually clear skies allowed the identification of distinct spring and summer chla blooms west of the Mississippi Delta 4–5 wk after peaks in river discharge. East of the delta, the chla concentrations peaked in June and July, following the seasonal reversal in the coastal current. A clear linkage was not detected between satellite-measured chla and hypoxia during the 4-yr period, based on a time series of bottom oxygen concentrations at one station within the area of most frequent hypoxia. Clear relationships are confounded by the interaction of physical processes (wind stress effects) with the seasonal cycle of nutrient-enhanced productivity and are influenced by the prior year's nitrate load and carbon accumulation at the seabed.  相似文献   

5.
A sampling program was initiated in 1986 in the Skidaway River estuary, a tidally dominated subtropical estuary in the southeastern USA. Hydrography, nutrients, particulate organic matter (POM), and microbial and plankton abundance and composition were measured at weekly intervals at high and low tide on the same day at a single site. Hydrographic and nutrient data during 1986–1996 were given in Verity (2002); particulate organic carbon (POC), nitrogen (PON) and chlorophylla (chla) are presented here; plankton data will be presented elsewhere. Chla was fractionated into <8 μm and >8 μm size classes. All classes of POM exhibited distinct seasonal patterns superimposed upon significant long-term increases during the study period. Total chla, <8 μm chla, and >8 μm chla increased 36%, 61%, and 18%, respectively, however the fraction of total biomass attributable to small phytoplankton (<8 μm) increased 25%. The annual amplitude between minimum and maximum stock sizes increased significantly, meaning that bloom events became larger. POC and PON also increased 16% over the decade and, as observed with patterns in chla, exhibited increases in annual amplitude. The C:N ratio was typically 6.4–6.6 (wt:wt) and did not change significantly, while the annual mean C:Chla ratio decreased 19% from 165 to 140. These characteristics indicated highly labile POM composed of significant amounts of detritus, but which became increasingly autotrophic with time. Averaged over the decade, temperature explained 45–50% of the variance in POM. Nutrients were even better predictors of POM, as 60–75% of the variance in chla, POC, and PON were explained by ambient concentrations of DIN, or PO4. Combined with significant increases in NO3, NH4, PO4, Si(OH)4, and DON during 1986–1996, these data strongly suggest that anthropogenic activities contributed to increased loading of dissolved nutrients, which became incorporated into living and nonliving particulate organic matter.  相似文献   

6.
Using both the photosynthetically active chlorophylla (chla) content of the organic carbon fraction of suspended particulate matter (chla/POC) and the percentage of photosynthetically, active chla in fluorometrically measured chla plus pheophytina (% chla), we determined that under specified hydrodynamic conditions, neap-spring tidal differentiation in particle dynamics could be observed in the Columbia River estuary. During summer time neap tides, when river discharge was moderate, bottom chla/POC remained relatively unchanged from riverine chla/POC over the full 0–30 psu salinity range, suggesting a benign trapping environment. During summertime spring tides, bottom chla/POC decreased at mid range salinities indicating resuspension of chla-poor POC during flood-ebb transitions. Bottom % chla during neap tides tended to average higher than that during spring tides, suggesting that neap particles were more recently hydrodynamically trapped than those on the spring tides. Such differentiation supported the possibility of operation of a particle conveyor belt process, a process in which low-amplitude neap tides favor selective particle trapping in estuarine turbidity maxima (ETM)., while high-amplitude spring tides favor particle resuspension from the ETM. Untrapped river-derived particles at the surface would continue through the estuary to the coastal ocean on the neap tide; during spring tide some particles eroded from the ETM would combine with unsettled riverine particles in transit toward the ocean. Because in tensified biogeochemical activity is associated with ETM, these neap-spring differences may be critical to maintenance and renewal of populations and processes in the estuary. Very high river discharge (15, 000 m3 s−1) tended to overwhelm neap-spring differences, and significant oceanic input during very low river discharge (5,000 m3 s−1) tended to do the same in the estuarine channel most exposed to ocean input. During heavy springtime phytoplankton blooms, development of a thick bottom fluff layer rich in chla also appeared to negate neapspring differentiation because spring tides apparently acted to resuspend the same rich bottom material that was laid down during neap tides. When photosynthetic assimilation numbers [μgC (μgchl,a)−1h−1] were measured across, the full salinity range, no neap-spring differences and no river discharge effects occurred, indicating that within our suite of measurements the compositional distinction of suspended particulate material was mainly a function of chla/POC, and to a lesser extent % chla. Even though these measurements suggest the existence of a conveyor belt process, proof of actual operation of this phenomenon requires scalar flux measurements of chla properties in and out of the ETM on both neap and spring tides.  相似文献   

7.
We present a comparative analysis of 1400 data series of water chemistry (particularly nitrogen and phosphorus concentrations), phytoplankton biomass as chlorophylla (chla) concentrations, concentrations of suspended matter and Secchi depth transparency collected from the mid-1980s to the mid-1990s from 162 stations in 27 Danish fjords and coastal waters. The results demonstrate that Danish coastal waters were heavily eutrophied and had high particle concentrations and turbid waters. Median values were 5.1 μg chla 1−1, 10.0 mg DW 1−1 of suspended particles, and Secchi depth of 3.6 m. Chlorophyll concentration was strongly linked to the total-nitrogen concentration. The strength of this relationship increased from spring to summer as the concentration of total nitrogen declined. During summer, total nitrogen concentrations accounted for about 60% of the variability in chlorophyll concentrations among the different coastal systems. The relationship between chlorophyll and total phosphorus was more consistant over the year and correlations were much weaker than encountered for total nitrogen. Secchi depth could be predicted with good precision from measurements of chlorophyll and suspended matter. In a multiple stepwise regression model with In-transformed values the two variables accounted for most of the variability in water transparency for the different seasons and the period March–October as a whole (c. 80%). We were able to demonstrate a significant relationship between total nitrogen and Secchi depth, with important implications for management purposes.  相似文献   

8.
We investigated whether climate change results in long-term changes in phytoplankton biomass and phenology in a turbid eutrophic coastal plain estuary. Changes in annual mean chlorophyll a (chla) concentrations were studied for the period 1978–2006 in the eutrophic and turbid macro-tidal Western Scheldt estuary. Three stations were investigated: WS1, at the mouth of the estuary; station WS6, halfway up the estuary; and station WS11, near the Dutch–Belgian border near the upstream end of the estuary. No significant long-term changes in yearly averaged chla concentrations were observed in WS1 and WS6, but in WS11 the phytoplankton biomass decreased considerably. This is most likely due to an increase in grazing pressure as a result of an improvement in the dissolved oxygen concentrations. Spectral analyses revealed a possible periodicity of 7 years in the mean chla which was related to periodicity in river discharge. We also observed strong phenological responses in the timing of the spring/summer bloom which were related to a well-documented increase in the temperature in the estuary. The fulcrum, the center of gravity or the day at which 50% of the cumulative chla was reached during the year, advanced by 1–2 days/year. A similar trend was observed for the month in which the maximum bloom was observed, with the exception of station WS1. All stations showed an earlier initiation of the bloom, whereas the day at which the phytoplankton bloom was terminated also moved forward in time excepted for WS11. As a result, the bloom length decreased at station WS1, remained the same at station WS6, and increased at WS11. This complicated pattern in bloom phenology demonstrates the complex nature of ecosystem functioning in estuaries.  相似文献   

9.
The Pomeranian Bay is a coastal region fed by the Oder River, one of the seven largest Baltic rivers, whose waters flow through a large and complex estuarine system before entering the bay. Nutrients (NO3 −, NO2 −, NH4 +, Ntot, PO4 3−, Ptot, DSi), chlorophylla concentrations, oxygen content, salinity, and temperature were measured in the Pomeranian Bay in nine seasonally distributed cruises during 1993–1997. Strong spatial and temporal patterns were observed and they were governed by: the seasonally variable riverine water-nutrient discharges, the seasonally variable uptake of nutrients and their cycling in the river estuary and the Bay, the character of water exchange between the Pomeranian Bay and the Szczecin Lagoon, and the water flow patterns in the Bay that are dominated by wind-driven circulation. Easterly winds resulted in water and nutrient transport along the German coastline, while westerly winds confined the nutrient rich riverine waters to the Polish coast and transported them eastward beyond the study area. Two water masses, coastal and open, characterized by different chemical and physical parameters and chla content were found in the Bay independently of the season. The role of the Oder estuary in nutrient transformation, as well as the role of temperature in transformation processes is stressed in the paper. The DIN:DIP:DSi ratio indicated that phosphorus most probably played a limiting role in phytoplankton production in the Bay in spring, while nitrogen did the same in summer. During the spring bloom, predominated by diatoms, the DSi:DIN ratio dropped to 0.1 in the coastal waters and to 0.6 in the open bay waters, pointing to silicon limitation of diatom growth, similar to what is being observed in other Baltic regions.  相似文献   

10.
Estimating biomass of microphytobenthos (MPB) on intertidal mud flats is extremely difficult due to their patchy occurrence, especially at the scale of an entire mud flat. We tested two optical approaches that can be applied in situ: spectral reflectance and chlorophyll fluorescence. These two approaches were applied in 4 European estuaries with different sediment characteristics. At each site, paired replicate measurements of hyperspectral reflectance, chlorophyll fluorescence (after 15 min dark adaptation, Fo 15), sediment water content, and chlorophylla concentrations were taken (including breakdown products: [chla+phaeo]). Sediments were further characterized by grain size and organic content analysis. The spectral signatures of tidal flats dominated by benthic microalgae, mainly diatoms, could be easily distinguished from sites dominated by macrophytes; we present a 3 waveband algorithm that can be used to detect the presence of macrophytes. The normalized difference vegetation index (NDVI) was found to be most strongly correlated to sediment [chla+phaeo], except for the predominantly sandy Sylt stations. Fo 15 was also significantly correlated to sediment [chla+phaeo] in all but one grid (Sylt grid A). Our results suggest that the functional relationships (i.e., the slopes) between NDVI or fluorescence and [chla+ phaeo] were not significantly different in the muddier grids, although the intercepts could differ significantly, especially for Fo 15. This suggests a mismatch of the optical depth seen by the reflectometer or fluorometer and the depth sampled for pigment analysis. NDVI appears to be a robust proxy for sediment [chla+phaeo] and can be used to quantify MPB biomass in muddy sediments of mid latitude estuaries.  相似文献   

11.
Three sequential hurricanes in the fall of 1999 provided the impetus for assessing multi-annual effects on water quality and phytoplankton dynamics in southwestern Pamlico Sound, North Carolina. Two and a half years of post-hurricane data were examined for short- and long-term impacts from the storms and >100 year flooding. Salinity decreased dramatically and did not recover until May 2000. Inorganic nitrogen and phosphorus concentrations were briefly elevated during the flooding, but later returned to background levels. Dissolved organic carbon concentrations declined through the whole study period, but did not appear to peak as was observed in the Neuse River estuary, a key tributary of the Sound. Light attenuation was highest in the fall to spring following the storms and was best correlated with chlorophylla concentrations. Phytoplankton biomass (chla) increased and remained elevated until late spring 2000 when concentrations returned to pre-storm levels and then cycled seasonally. Phytoplankton community composition varied throughout the study, reflecting the complex interaction between physiological optimal and combinations of salinity, residence time, nutrient availability, and possibly grazing activity. Floodwater advection or dilution from upstream maxima may have controlled the spatial heterogeneity in total and group-specific biomass. The storms produced areas of shortterm hypoxia, but hypoxic events continued during the following two summers, correlating strongly with water column stratification. Nitrogen loading to the southwestern sound was inferred from network analysis of previous nitrogen cycling studies in the Neuse River estuary. Based on these analyses, nutrient cycling and removal in the sub-estuaries would be decreased under high flow conditions, confirming observations from other estuaries. The inferred nitrogen load from the flood was 2–3 times the normal loading to the Sound; this estimate was supported by the substantial algal bloom. After 8-mos, the salinity and chla data indicated the Sound had returned to pre-hurricane conditions, yet phytoplankton community compositional changes continued through the multi-year study period. This is an example of long-term aspects of estuarine recovery that should be considered in the context of a predicted 10–40 yr period of elevated tropical storm activity in the western Atlantic Basin.  相似文献   

12.
Data on hydrography, nutrients, suspended particles, and sedimented particles were collected at weekly intervals from November to May during 1995 to 1997 at a station in the coastal waters of Dona Paula Bay, India. Suspended and sedimented particles were analyzed for total suspended matter (SPM), total sedimented particulate matter (TPM), particulate organic carbon (POC), particulate organic nitrogen (PON), chlorophylla (chla), and diatom abundance. Variations in hydrography and nutrients influenced the quantity and composition of sedimented particles. The TPM, POC, PON, and chla fluxes showed small-scale seasonal variations and were higher in the summer (February to May) than in the winter (November to January). Resuspension of carbon accounted for approximately 25% of the gross POC and was highest in April 1997 (45%). The mean net POC flux was 197±90 mg C m−2 d−1 and accounts for 4.6% of the TPM. The average C∶N (w∶w) ratio of the sedimented material was 13.2±6.6. The POC:chla ratio was relatively higher in the sedimented material as compared to the suspended material. The particulate carbon reaching the bottom sediment was 39% of the primary production. The low organic carbon concentration (approximately 0.1% of dry sediment) in the sediments implies that about 98% of the sedimented carbon was either consumed at the sedimentwater interface or resuspended/advected before it was finally buried into the sediments.  相似文献   

13.
Epiphytic microbial biomass (as chlorophylla) was measured monthly in North Inlet Estuary, South Carolina, for 16 months on spatially distinct stem sections (bottom and middle) of dead and livingSpartina alterniflora growth forms (tall, medium, and short) exposed at low tide. The highest biomass was located on the bottom section of tall plants, presumably due to their relatively longer contact with creek water and associated phytoplankton, and their closer proximity to marsh sediments with associated benthic microalgae, both recruitment sources for epiphytes. Dead plants left standing from the previous year’s growth cycle had higher epiphytic biomass than living plants, which occurred mostly in late spring through fall. Epiphytic biomass was highest in the winter (mean of 1.77 mg chla (m2 marsh)−1) and lowest in the summer (mean of 0.34 mg chla (m2 marsh)−1). Because phytoplankton andSpartina production are lowest in the winter, the results emphasize the relative importance of epiphytes to growth of herbivores in this season.  相似文献   

14.
Freshwater inputs often play a more direct role in estuarine phytoplankton biomass (chlorophyll a) accumulation than nitrogen (N) inputs, since discharge simultaneously controls both phytoplankton residence time and N loading. Understanding this link is critical, given potential changes in climate and human activities that may affect discharge and watershed N supply. Chlorophyll a (chla) relationships with hydrologic variability were examined in 3-year time series from two neighboring, shallow (<5?m), microtidal estuaries (New and Neuse River estuaries, NC, USA) influenced by the same climatic conditions and events. Under conditions ranging from drought to floods, N concentration and salinity showed direct positive and negative responses, respectively, to discharge for both estuaries. The response of chla to discharge was more complex, but was elucidated through conversion of discharge to freshwater flushing time, an estimate of transport time scale. Non-linear fits of chla to flushing time revealed non-monotonic, unimodal relationships that reflected the changing balance between intrinsic growth and losses through time and along the axis of each estuary. Maximum biomass occurred at approximately 10-day flushing times for both systems. Residual analysis of the fitted data revealed positive relationships between chla and temperature, suggesting enhanced growth rates at higher temperatures. N loading and system-wide, volume-weighted chla were positively correlated, and biomass yields per N load were greater than other marine systems. When combined with information on loss processes, these results on the hydrologic control of phytoplankton biomass will help formulate mechanistic models necessary to predict ecosystem responses to future climate and anthropogenic changes.  相似文献   

15.
The objective of this study was to examine the interaction between the Atchafalaya River and the Atchafalaya Delta estuarine complex. Measurements of suspended sediments, inorganic nutrients (NO3 ?, NH4 +, PO4 3?), chlorophylla (chla), and-salinity were taken monthly from December 1996 to January 1998. These data were compiled by season, and the Atchafalaya River plume data were also analyzed using the Generalized Additive Model technique. There were significant decreases in NO3 ? concentrations during summer, fall, and winter as river water passed through the estuary, that were attributable to chemical and biological processes rather than dilution with ambient water. In some regions there were higher chla concentrations during summer and fall compared to winter and spring, when river discharge and the introduction of inorganic nutrients were highest, suggesting biological processes were active during this study. The presence of NH4 +, as a percentage of available dissolved inorganic nitrogen, increased with distance from the Atchafalaya River, indicative of remineralization processes and NO3 ? reduction. Mean PO4 3? concentrations were often higher in the estuarine regions compared to the Atchafalaya River. During summer total suspended solid (TSS) concentrations increased with distance from the river mouth, suggesting a turbidity maximum. Highest chla concentrations were found in the bayous and shallow water bodies of the Terrebonne marshes, as were the lowest TSS concentrations. The low chla concentrations found in other areas of this study, despite high inorganic nutrient concentrations, suggest light limitation as the major control of phytoplankton growth. Salinity reached near seawater concentrations at the outer edge of the Atchafalaya River plume, but much lower salinities (<10 psu) were observed at all other regions. The Atchafalaya Delta estuarine complex buffers the impact of the Atchafalaya River on the Louisiana coastal shelf zone, with a 41% of 47% decrease in Atchafalaya River NO3 ? concentrations before reaching Gulf waters.  相似文献   

16.
Plant pigments in particulate organic carbon were examined in the lower Mississippi and Pearl Rivers (U.S.), along with physical variables and nutrients to study seasonal changes in the abundance and composition of phytoplankton. Water samples were collected monthly from September 2001 to August 2003 in the lower Mississippi River (MR; no samples were taken in February 2002) and from August 2001 to July 2003 in the Pearl River (PR). High concentrations of total suspended solids (TSS), nutrients, and chlorophylla (chla; dominated by diatoms) were observed in the lower MR. The smaller blackwater PR was characterized by lower nutrients and chla, higher ultraviolet absorbance, and a phytoplankton biomass dominated by chlorophytes. Chla concentrations in the lower MR was high in summer low-flow periods and also during interims of winter and spring, and did not couple with physical variables and nutrients, likely due to a combination of in situ production and inputs from reservoirs, navigation locks and oxbow lakes in the upper MR and Missouri River. Chla concentrations in the PR was only high in summer low-flow periods and were controlled by temperature and concentrations of chromophoric dissolved organic matter 9CDOM). The high, diatom-dominated phytoplankton biomass in the lower MR was likely the result of decreasing TSS (increased damming in the watershed) and increasing nutrients (enhanced agricultural runoff) over the past few decades. Lower phytoplankton biomass (dominated by chlorophytes) in the PR was likely linked with intense shading by CDOM and lower availability of nutrient inputs. An increase in the relative importance of phytoplankton biomass in large turbid rivers, such as the MR, could have significant effects on the age and lability of riverine organic matter entering the ocean, the stoichiometric balance of nutrients delivered to coastal margins, and the sequestration of atmospheric CO2 in these dynamic regions.  相似文献   

17.
Monitoring of estuarine condition depends on water quality parameters that have significant and interpretable ecological effects and can be assessed either in situ or via rapid laboratory techniques. Two commonly measured parameters are water column turbidity (NTU) and total suspended solids (TSS). Under certain conditions, either of these measures could represent a proxy for runoff and provide rapid, in situ measures to improve protection of the public by decreasing the time required to detect and monitor associated effects (e.g., reduced water clarity and eutrophication). The Neuse River Estuary (NRE) has experienced a decline in water quality due to anthropogenic inputs, including stormwater containing nutrient and particle loads. Water samples were collected from the NRE during both dry weather and storm events over 16 mo across the entire estuarine gradient. Particle size distributions, ratio of particulate organic carbon to nitrogen, chlorophylla (chla), TSS, and NTU were measured in each of these samples, with the data separated into regions based on salinity and depth of sample collection. Particle analyses were directed at identifying suspensions dominated by phytoplankton, runoff particles, or resuspended sediments. Particle size distributions for suspensions in Region I (all samples with salinity less than 2) varied little during sampling, resulting in a robust NTU-TSS relationship. This relationship confirmed the usefulness of turbidity as a measure of runoff and resuspension of recently deposited runoff in the upper NRE. Phytoplankton cells represented a majority of the particles in Region II (surface samples with salinity greater than 2), based on the close relationship between chla and total particle volume in these samples. Suspensions of large, nearly uniform diameter particles, which are likely aggregates and resuspended sediment, were observed in Region III (bottom samples with salinity greater than 2). Using these techniques as part of routine monitoring, particle suspension measures in different hydrographic regions of an estuary provide evidence useful for identifying the source and water quality consequences of particle suspensions (e.g., microbial contamination and algal blooms).  相似文献   

18.
An 11-month observation of dissolved and particulate organic matter, chlorophyll a(Chl a), C18 Sep-Pak extractable hydrophobic dissolved organic matter (hDOM) fraction and associated dissolved trace metals (Cd, Cu, V, Co, Ni, Mo, U) was performed in the Lot–Garonne River system. This system includes the Riou Mort, the Lot River and the downstream reaches of the Garonne River and represents the fluvial transport path of trace metals between the major point source of polymetallic pollution, located in the Riou Mort watershed and the Gironde estuary. Spatial and temporal variations of dissolved and particulate organic carbon and Chl areflect the presence of different types of organic matter and their relation with the hDOM fraction. Maximum Chl a/POC ratios (up to 0.03), indicate intense phytoplankton production from March to May. In the Lot River (Temple), DOC and POC concentrations were clearly higher and mean Chl a concentration (2.8 mg g−1) was about three times higher than those of the other sites. High Chl a/POC ratios suggest high phytoplankton activity with maxima in spring and late summer. In the Riou Mort River, very high POC concentrations of up to 40 (mean: 20) occurred, whereas Chl a concentrations were relatively low indicating low phytoplankton activity. High, strongly variable DOC and POC concentrations suggest important natural (Carboniferous soils, forests) or anthropogenic (e.g., former coal mines, waste areas, agriculture, sewage) carbon sources within the small Riou Mort watershed. Despite high DOC concentrations in the Riou Mort River, hDOM metal fractions were generally lower than those at the other sites. The general order of decreasing binding strength between metals and the organic hydrophobic phase (Cu, U > Co, Ni > V, Mo > Cd) at all four sites was in good agreement with the Irving–William series of transition element affinity towards organic ligands. Accordingly, the role of the hydrophobic phase in dissolved Cd transport appeared to be negligible, whereas the hDOM–Cu fraction strongly contributed to dissolved Cu transport.  相似文献   

19.
An increase in the transmission of solar radiation in the UV-B region (specifically, 290–320 nm) is expected to occur as a result of anthropogenic degradation of stratospheric ozone. The potential impact of increased levels of UV-B radiation upon the biosphere is of ecological concern. In a previous study a community of estuarine organisms received a daily exposure to a simulated solar spectrum enhanced in UV-B radiation for a period of six weeks. A dominant species of diatom growing at the surface of these communities was isolated and identified to beMelosira nummuloides. Short chains of this diatom were irradiated for a four-hour period on each of three consecutive days. Fluorescent sunlamps filtered by a 290 nm cut-off filter (0.13–0.50 mm cellulose acetate) or a 315 nm cut-off filter (0.13mm Mylar ‘S’) provided a range of fluence which closely approximated natural fluence levels. A least squares regression analysis of the number of cell divisions on the biologically weighted fluence indicated a significant depression in the growth of this species by radiation in the 290–320 nm waveband.  相似文献   

20.
Picoplankton abundance and distribution in the Mississippi River plume and its adjacent waters were studied during two cruises in April (high discharge) and October (low discharge) 2000 using flow cytometry. Concentrations of photosynthetic picoplankton,Synechococcus and picoeukaryotes were low in the turbid plume water but high in the coastal waters—i.e., the green waters resulting from mixing of river and oceanic waters. In this region, three types ofSynechococcus, characterized by their phycoerythrin chromophore composition, were found:Synechococcus cells with a low phycourobilin to phycoerythrobilin ratio (PUB:PEB) occurred throughout the region and dominated the totalSymechococcus abundance during both seasons; high PUB:PEB cells, which are the dominant strains in the open or blue ocean, occurred only at the outer shelf stations; and PEB-onlySynechococcus were abundant in most of the surveyed area during april, but were not observed during October.Prochlorococcus cyanobacteria only occurred at the oceanic stations, but extended farther inshore in October compared to April. This was a consequence of the reduced discharge and plume size during October. Picophytoplankton were a less important component of total phytoplankton biomass in the turbid river water and more important in the oligotrophic Gulf water. Seasonally, the contribution of picophytoplankton to total phytoplankton biomass in the surveyed area was higher during low discharge in October than during high discharge in April, even though the spring 2000 river discharge was unusually low and might not present a typical high discharge scenario. The abundance of heterotrophic bacteria was weakly correlated to chlorophylla (chla) concentration, but better correlated to picophytoplankton biomass. A higher proportion of High DNA bacteria occurred in the river-impacted regions during both seasons, with the ratio of High DNA bacteria to Low DNA bacteria significantly higher in April.  相似文献   

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