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1.
Matthew Robert Palmer 《Ocean Dynamics》2010,60(2):219-226
Understanding the fate of freshwater runoff and corresponding nutrient and pollution loads is of critical importance for the
development of accurate predictive models and coastal management tools. A key element of such studies is the identification
and understanding of the interaction between stratification and current structure. This paper presents a new series of measurements
made in the Liverpool Bay region of freshwater influence (ROFI) during spring 2004 where freshwater-maintained horizontal
density gradients and strong tidal currents interact to produce strain-induced periodic stratification (SIPS). During stratification,
tidal current profiles are significantly modified such that the tidal flow deviates from the otherwise rectilinear E–W axis
generating counter rotating upper and lower mixed layers. This feature has often been reported for the Rhine ROFI but not
previously identified in Liverpool Bay despite previous investigation at this site. Investigation of an ongoing long-term
dataset collected nearby reveals this process to be a common feature throughout the year. Liverpool Bay is shown to maintain
three different regimes, long term mixed, long term stratified, and a transitional state when SIPS occurs. The phase of SIPS
relative to the tide results in a residual flow away from the Welsh coastline in the upper water column of 2.3–3.6 cm s−1 with a counterflow in the lower layer of 2.8–3.1 cm s−1 towards the coast. 相似文献
2.
Liverpool Bay is a region of freshwater influence which receives significant freshwater loading from a number of major English
and Welsh rivers. Strong tidal current flow interacts with a persistent freshwater-induced horizontal density gradient to
produce strain-induced periodic stratification (SIPS). Recent work (Palmer in Ocean Dyn 60:219–226, 2010; Verspecht et al. in Geophys Res Lett 37:L18602, 2010) has identified significant modification to tidal ellipses in Liverpool Bay during stratification due to an associated reduction
in pycnocline eddy viscosity. Palmer (Ocean Dyn 60:219–226, 2010) identified that this modification results in asymmetry in flow in the upper and lower layers capable of permanently transporting
freshwater away from the Welsh coastline via a SIPS pumping mechanism. Observational data from a new set of observations from
the Irish Sea Observatory site B confirm these results; the measured residual flow is 4.0 cm s−1 to the north in the surface mixed layer and 2.4 cm s−1 to the south in the bottom mixed layer. A realistically forced 3D hydrodynamic ocean model POLCOMS succeeds in reproducing
many of the characteristics of flow and vertical density structure at site B and is used to estimate the transport of water
through a transect WT that runs parallel with the Welsh coast. Model results show that SIPS is the dominant steady state,
occurring for 78.2% of the time whilst enduring stratification exists only 21.0% of the year and enduring mixed periods, <1%.
SIPS produces a persistent offshore flow of freshened surface water throughout the year. The estimated net flux of water in
the surface mixed layer is 327 km3 year
−1, of which 281 km3 year−1 is attributable to SIPS periods. Whilst the freshwater component of this flux is small, the net flux of freshwater through
WT during SIPS is significant, the model estimates 1.69 km3 year−1 of freshwater to be transported away from the coast attributable to SIPS periods equivalent to 23% of annual average river
flow from the four catchment areas feeding Liverpool Bay. The results show SIPS pumping to be an important process in determining
the fate of freshwater and associated loads entering Liverpool Bay. 相似文献
3.
4.
A critical factor controlling changes in the acidity of coastal waters is the alkalinity of the water. Concentrations of alkalinity
are determined by supply from rivers and by in situ processes such as biological production and denitrification. A 2-year
study based on 15 cruises in Liverpool Bay followed the seasonal cycles of changing concentrations of total alkalinity (TA)
and total dissolved inorganic carbon (DIC) in relation to changes caused by the annual cycle of biological production during
the mixing of river water into the Bay. Consistent annual cycles in concentrations of nutrients, TA and DIC were observed
in both years. At a salinity of 31.5, the locus of primary production during the spring bloom, concentrations of NO
x
decreased by 25 ± 4 μmol kg−1 and DIC by 106 ± 16 μmol kg−1. Observed changes in TA were consistent with the uptake of protons during primary biological production. Concentrations of
TA increased by 33 ± 8 μmol kg−1 (2009) and 33 ± 15 μmol kg−1 (2010). The impact of changes in organic matter on the measured TA appears likely to be small in this area. Thomas et al.
(2009) suggested that denitrification may enhance the CO2 uptake of the North Sea by 25%, in contrast we find that although denitrification is a significant process in itself, it
does not increase concentrations of TA relative to those of DIC and so does not increase buffer capacity and potential uptake
of CO2 into shelf seawaters. For Liverpool Bay historical data suggest that higher concentrations of TA during periods of low flow
are likely to contribute in part to the observed change in TA between winter and summer but the appropriate pattern cannot
be identified in recent low-frequency river data. On a wider scale, data for the rivers Mersey, Rhine, Elbe and Weser show
that patterns of seasonal change in concentrations of TA in river inputs differ between river systems. 相似文献
5.
Naomi Greenwood Rodney M. Forster Veronique Créach Suzanne J. Painting Anna Dennis Stewart J. Cutchey Tiago Silva David B. Sivyer Tim Jickells 《Ocean Dynamics》2012,62(2):307-320
The seasonal and interannual variability in the phytoplankton community in Liverpool Bay between 2003 and 2009 has been examined
using results from high frequency, in situ measurements combined with discrete samples collected at one location in the bay.
The spring phytoplankton bloom (up to 29.4 mg chlorophyll m−3) is an annual feature at the study site and its timing may vary by up to 50 days between years. The variability in the underwater
light climate and turbulent mixing are identified as key factors controlling the timing of phytoplankton blooms. Modelled
average annual gross and net production are estimated to be 223 and 56 g C m−2 year−1, respectively. Light microscope counts showed that the phytoplankton community is dominated by diatoms, with dinoflagellates
appearing annually for short periods of time between July and October. The zooplankton community at the study site is dominated
by copepods and use of a fine mesh (80 μm) resulted in higher abundances of copepods determined (up to 2.5 × 106 ind. m−2) than has previously reported for this location. There is a strong seasonal cycle in copepod biomass and copepods greater
than 270 μm contribute less than 10% of the total biomass. Seasonal trends in copepod biomass lag those in the phytoplankton
community with a delay of 3 to 4 months between the maximum phytoplankton biomass and the maximum copepod biomass. Grazing
by copepods exceeds net primary production at the site and indicates that an additional advective supply of carbon is required
to support the copepod community. 相似文献
6.
Residual circulation and stratification in the Liverpool Bay region of freshwater influence 总被引:1,自引:1,他引:0
Florence Verspecht Tom P. Rippeth John H. Simpson Alejandro J. Souza Hans Burchard M. John Howarth 《Ocean Dynamics》2009,59(5):765-779
Wind and tidal straining are proposed as key mechanisms influencing the magnitude and timing of the horizontal flux of freshwater
across regions of freshwater influence (ROFIs). Evidence for this hypothesis is presented in estimates of the tidally averaged
residual current profile, obtained from 5 years of continuous acoustic doppler current profiler measurements in the Liverpool
Bay ROFI. The modified horizontal Richardson number (RxwtR_{x}^{wt}), which includes both the tidal and the wind forcing, was assessed as a measure of stratification. RxwtR_{x}^{wt} was found to be a good indicator of the timing of the evolution and destruction of stratification, but was not as successful
as an indicator of the magnitude of stratification, both enduring and periodic. The observed mean residual velocities are
compared to those predicted by a classical solution, and the eddy viscosity (N
z
) is shown to be a control on differences between the observed and predicted circulation. Principal component analysis is
used to show that the strongest residual currents occur when the water column periodically alternates between a well-mixed
and stratified state, a consequence of straining, rather than simply related to the density gradient. Evidence of wind straining
was found in the correspondence between the wind direction and the near surface and near bed residual current direction. 相似文献
7.
David P. Hamilton Katherine R. O’Brien Michele A. Burford Justin D. Brookes Chris G. McBride 《Aquatic Sciences - Research Across Boundaries》2010,72(3):295-307
The factors affecting vertical distributions of chlorophyll fluorescence were examined in four temperate, warm monomictic
lakes. Each of the lakes (maximum depth >80 m) was sampled over 2 years at intervals from monthly to seasonal. Profiles were
taken of chlorophyll fluorescence (as a proxy for algal biomass), temperature and irradiance, as well as integrated samples
from the surface mixed layer for chlorophyll a (chl a) and nutrient concentrations in each lake. Depth profiles of chlorophyll fluorescence were also made along transects of the
longest axis of each lake. Chlorophyll fluorescence maxima occurred at depths closely correlated with euphotic depth (r
2 = 0.67, P < 0.01), which varied with nutrient status of the lakes. While seasonal thermal density stratification is a prerequisite
for the existence of a deep chlorophyll maximum (DCM), our study provides evidence that the depth of light penetration largely
dictates the DCM depth during stratification. Reduction in water clarity through eutrophication can cause a shift in phytoplankton
distributions from a DCM in spring or summer to a surface chlorophyll maximum within the surface mixed layer when the depth
of the euphotic zone (z
eu) is consistently shallower than the depth of the surface mixed layer (z
SML). Trophic status has a key role in determining vertical distributions of chlorophyll in the four lakes, but does not appear
to disrupt the annual cycle of maximum chlorophyll in winter. 相似文献
8.
Naomi Greenwood David J. Hydes Claire Mahaffey Andrew Wither Jon Barry David B. Sivyer David J. Pearce Susan E. Hartman Olga Andres Helen E. Lees 《Ocean Dynamics》2011,61(12):2181-2199
This paper presents data for the temporal and spatial distribution of nutrients in Liverpool Bay between 2003 and 2009 and
an analysis of inputs of nutrients from the major rivers. The spatial distribution of winter nutrient concentrations are controlled
by the region of freshwater influence (ROFI) in Liverpool Bay through the mixing of riverine freshwater and Irish Sea water,
with strong linear relationships between nutrient concentration and salinity between December and February. The location of
highest spring and summer phytoplankton biomass reflects the nutrient distributions as controlled by the ROFI. Analysis of
7 years of data showed that the seasonal cycle of winter maximum nutrient concentrations in February and drawdown in April/May
is a recurrent feature of this location, with the timing of the drawdown varying by several weeks between years. A comparison
of observed nutrient concentrations in Liverpool Bay with those predicted from inputs from rivers has been presented. Nutrient
concentrations in the rivers flowing into Liverpool Bay were highly variable and there was reasonable agreement between predicted
freshwater nutrient concentrations using data from this study and riverine nutrient concentrations weighted on the basis of
river flow, although the exact nature of mixing between the rivers could not be determined. Predicted Irish Sea nutrient concentrations
in the winter were lower than those reported for the input waters of the North Atlantic, supporting findings from previous
work that nitrogen is lost through denitrification in the Irish Sea. 相似文献
9.
Inmaculada de Vicente Eva Ortega-Retuerta Ignacio P. Mazuecos Michael L. Pace Jonathan J. Cole Isabel Reche 《Aquatic Sciences - Research Across Boundaries》2010,72(4):443-453
In inland waters, transparent exopolymer particles (TEP) can affect carbon export and sequestration in sediments with consequences
for lake C budgets. We measured TEP concentration in 32 lakes from two contrasting lake districts covering wide ranges in
biological and chemical characteristics. North temperate lakes, located in a wet region, have low to moderate ionic strength
and low to high dissolved organic carbon with corresponding variation in color (light absorbance). Mediterranean lakes located
in a semiarid region were characterized by high ionic strength and high concentrations of dissolved organic carbon but low
color. TEP concentrations were large relative to the living portion of the particulate organic carbon pool in both Mediterranean
(36%) and north temperate (33%) lakes. TEP concentrations ranged from 36 to 1,462 μg [as Gum Xanthan equivalents (GX eq)] L−1 in north temperate lakes. In the Mediterranean lakes, concentrations were higher that previously reported for other systems
and ranged from 66 to 9,038 μg GX eq L−1. TEP concentration was positive and significantly related to chlorophyll a (chl a) in north temperate lakes and in the entire data set. Although a significant and positive relationship between TEP and chl
a was also detected in the Mediterranean lakes, bacterial abundance was most strongly related to TEP. In contrast with the
positive influence of phytoplankton and bacteria on TEP, there were weaker relationships between TEP and the chemical variables
tested. We observed a significant and positive relationship between pH and TEP (for all lakes) but this relationship was indirectly
driven by a co-variation of pH with phytoplankton biomass based on multiple regression analysis. For the Mediterranean lakes,
the negative (but not significant) trends between TEP and both conductivity and divalent cations suggest thresholds above
which TEP will likely be destabilized. Under these conditions, TEP may flocculate or disperse in the water column. 相似文献
10.
11.
The fate of inflows into lakes has been extensively studied during summer stratification but has seen relatively little focus
during the weak winter stratification, with or without ice-cover. Field observations are presented of groundwater inflow into
a shallow bay of a subarctic lake. Atmospheric forcing of the bay during the study period was extremely variable and coincided
with spring ice-cover break-up. Two dominant wind regimes were identified; (1) weak wind-forcing (wind speed <5 m s−1 or land-fast ice-cover), and (2) strong wind-forcing (wind speed >5 m s−1 and open water). At a relatively constant temperature of ~3.3°C, the groundwater inflow was closer to the temperature of
maximum density than the water in the main body of the lake, which during the observed winter stratification is ~1.2°C. During
weak wind-forcing, the stratification within Silfra Bay approximated two-layers as this denser groundwater formed a negatively
buoyant underflow. A calculated underflow entrainment rate of 2.8 × 10−3 agrees well with other underflow studies. During strong wind-forcing, the water column out to the mouth of the bay became
weakly stratified as the underflow was entrained vertically by wind-stirring. Observed periods of mixing can be predicted
to occur when turbulent kinetic energy (TKE) production by wind stirring integrated over the underflow hydraulic residence
time in the bay exceeds the potential energy associated with the stratification. A decrease of ice cover, as observed in the
studied subarctic lake over the last decade, will result in the underflow being more frequently exposed to the strong wind-forcing
regime during winter, thereby altering the winter distribution of groundwater inflow within the lake. 相似文献
12.
We examined the effects of freshwater flow and light availability on phytoplankton biomass and production along the Louisiana continental shelf in the region characterized by persistent spring–summer stratification and widespread summer hypoxia. Data were collected on 7 cruises from 2005 to 2007, and spatially-averaged estimates of phytoplankton and light variables were calculated for the study area using Voronoi polygon normalization. Shelf-wide phytoplankton production ranged from 0.47 to 1.75 mg C m−2 d−1 across the 7 cruises. Shelf-wide average light attenuation (kd) ranged from 0.19–1.01 m−1 and strongly covaried with freshwater discharge from the Mississippi and Atchafalaya Rivers (R2=0.67). Interestingly, we observed that the euphotic zone (as defined by the 1% light depth) extended well below the pycnocline and to the bottom across much of the shelf. Shelf-wide average chlorophyll a (chl a) concentrations ranged from 1.4 to 5.9 mg m−3 and, similar to kd, covaried with river discharge (R2=0.83). Also, chl a concentrations were significantly higher in plume versus non-plume regions of the shelf. When integrated through the water-column, shelf-wide average chl a ranged from 26.3 to 47.6 mg m−2, but did not covary with river discharge, nor were plume versus non-plume averages statistically different. The high integrated chl a in the non-plume waters resulted from frequent sub-pycnocline chl a maxima. Phytoplankton production rates were highest in the vicinity of the Mississippi River bird's foot delta, but as with integrated chl a were not statistically different in plume versus non-plume waters across the rest of the shelf. Based on the vertical distribution of light and chl a, a substantial fraction of phytoplankton production occurred below the pycnocline, averaging from 25% to 50% among cruises. These results suggest that freshwater and nutrient inputs regulate shelf-wide kd and, consequently, the vertical distribution of primary production. The substantial below-pycnocline primary production we observed has not been previously quantified for this region, but has important implications about the formation and persistence of hypoxia on the Louisiana continental shelf. 相似文献
13.
The seasonal pattern of size-fractionated phytoplankton biomass, primary production and respiration was investigated along the longitudinal axis of the Nervión–Ibaizabal estuary (Bay of Biscay) from April 2003 to September 2004. Environmental factors influencing phytoplankton dynamics were also studied. Chlorophyll a biomass showed a longitudinal pattern of increase from the outer Abra bay to the inner estuary. On a seasonal scale, in the intermediate and inner estuary phytoplankton biomass maxima were registered in summer, the warmest and driest season, whereas in the outer bay chlorophyll a peaks occurred in May 2004, but were delayed to August 2003, likely due to a very rainy spring. Data suggest that river flow exerts a marked influence on the timing of phytoplankton biomass maxima in this estuary, decreased river flows providing a lowering of turbidity and an increase in water residence time needed for chlorophyll a to build up. Nutrient concentrations were high enough not to limit phytoplankton growth throughout the annual cycle, except silicate and occasionally phosphate in the outer bay during summer. Silicate concentration correlated positively with river flow, whereas ammonium and phosphate maximum values were generally measured in the mid-estuary, suggesting the importance of allochthonous anthropogenic sources. In the intermediate and inner estuary phytoplankton biomass was generally dominated by >8 μm size-fraction (ca. 60%), but in August 2003 <8 μm size-fraction increased its contribution in the intermediate estuary. It is argued that the lower nutrient concentrations measured in August 2003 than in August 2004 could have played a role. This is the first study in which phytoplankton primary production rates have been measured along the longitudinal axis of the Nervión–Ibaizabal estuary. Throughout the annual cycle these rates ranged from 0.001 to 3.163 g C m?3 d?1 and were comparable to those measured in nearby small estuaries of the Basque coast and other larger estuaries on the Bay of Biscay. Surface plankton community respiration rate maxima were measured during the spring 2004 chlorophyll a peak in the Abra bay and in summer months at the mid and inner estuary, coinciding with chlorophyll a biomass and primary production maxima. In general, respiration rates showed a positive correlation with temperature. In order to compare results from the Nervión–Ibaizabal estuary with other nearshore coastal and estuarine ecosystems within the Bay of Biscay a review of existing information on phytoplankton biomass and primary production dynamics was performed. 相似文献
14.
Physical and dynamical oceanography of Liverpool Bay 总被引:1,自引:1,他引:0
The UK National Oceanography Centre has maintained an observatory in Liverpool Bay since August 2002. Over 8 years of observational
measurements are used in conjunction with regional ocean modelling data to describe the physical and dynamical oceanography
of Liverpool Bay and to validate the regional model, POLCOMS. Tidal dynamics and plume buoyancy govern the fate of the fresh
water as it enters the sea, as well as the fate of its sediment, contaminants and nutrient loads. In this context, an overview
and summary of Liverpool Bay tidal dynamics are presented. Freshwater forcing statistics are presented showing that on average
the bay receives 233 m3 s − 1. Though the region is salinity controlled, river input temperature is shown to significantly modulate the plume buoyancy
with a seasonal cycle. Stratification strongly influences the region’s dynamics. Data from long-term moored instrumentation
are used to analyse the stratification statistics that are representative of the region. It is shown that for 65% of tidal
cycles, the region alternates between being vertically mixed and stratified. Plume dynamics are diagnosed from the model and
are presented for the region. The spring–neap modulation of the plume’s westward extent, between 3.5 °W and 4°W, is highlighted. The rapid eastward erosion of the plume during spring tides is identified as a potentially important freshwater
mixing mechanism. Novel climatological maps of temperature, salinity and density from the CTD surveys are presented and used
to validate numerical simulations. The model is found to be sensitive to the freshwater forcing rates, temperature and salinities.
The existing CTD survey grid is shown to not extend sufficiently near the coast to capture the near coastal and vertically
mixed component the plume. Instead the survey grid captures the westward spreading, shallow and transient, portion of the
plume. This transient plume feature is shown in both the long-term averaged model and observational data as a band of stratified
fluid stretching between the mouth of the Mersey towards the Isle of Man. Finally the residual circulation is discussed. Long-term
moored ADCP data are favourably compared with model data, showing the general northward flow of surface water and southward
trajectory of bottom water. 相似文献
15.
The distributions of dimethylsulfide (DMS) and its precursor, dimethylsulfoniopropionate (DMSP), were examined in the surface microlayer and corresponding subsurface water of the Yellow Sea, China, in April 2006. The average concentrations of DMS and DMSP of dissolved (DMSPd) and particulate (DMSPp) forms were 5.42 (1.78–12.75), 9.22 (2.85–19.73) and 17.50 (4.33–36.09) nmol L−1 in the subsurface water, and those in the surface microlayer were 4.92 (1.69–10.66), 17.08 (3.13–38.82) and 22.54 (4.85–47.24) nmol L−1, respectively. The enrichment factor (EF) of DMS in the microlayer ranged from 0.47 to 2.24 with a mean of 0.98. In contrast, DMSPd and DMSPp appeared to be enriched in the microlayer with average EFs of 1.98 and 1.39, respectively. A close correlation of integrated DMS, DMSPp and chlorophyll a concentrations for compiled data from all stations in the microlayer and the subsurface water indicated that phytoplankton biomass might play an important role in controlling the distributions of biogenic sulfurs in the study area. Moreover, a statistically significant relationship was found between the microlayer concentrations of DMS, DMSP and chlorophyll a and their subsurface water concentrations, suggesting a close linkage between these two water compartments. Interestingly, we observed higher biological production rates and consumption rates of DMS in the microlayer relative to the subsurface water. Furthermore, the DMS production rates were closely correlated both with DMSPd and chlorophyll a concentrations. Our study showed that the major sink of DMS in microlayer was escape into the atmosphere, which greatly exceeded its bacterial consumption. A preliminary estimate for average flux of DMS from the Yellow Sea to the atmosphere was 6.41 μmol m−2 d−1 during spring. 相似文献
16.
Harmful algal blooms (HABs) in Daya Bay, China: An in situ study of primary production and environmental impacts 总被引:1,自引:0,他引:1
Xingyu Song Liangmin Huang Jianlin Zhang Honghui Huang Tao Li Qiang Su 《Marine pollution bulletin》2009,58(9):1310-1318
A month-long investigation of phytoplankton biomass and primary production (PP) was carried out during a harmful algal bloom (HAB) in Daya Bay, China, in 2003. During the bloom, the phytoplankton community was dominated by Scrippsiella trochoidea and Chattonella marina. The phytoplankton biomass (Chl a) and PP reached peak levels of 519.21 mg m−3 and 734.0 mgC m−3 h−1, respectively. Micro-phytoplankton was the key contributor to Chl a and PP in a cage-culture area and in the adjacent HAB-affected waters, with percentages of up to 82.91% and 84.94%, respectively. The HAB had complicated relationships with hydrological and meteorological factors in Daya Bay. However, the water around the cage-culture area always showed statistically greater phytoplankton biomass and nutrient loadings than in adjacent waters, suggesting that this was the “trigger area” of the bloom. The spatial and temporal distribution of diverse HABs in Daya Bay, their ecological characteristics, and their environmental impacts are also discussed in this paper. 相似文献
17.
The spatial and diurnal tidal variability of dissolved organic carbon (DOC) concentrations and the composition of dissolved
organic matter (DOM), as evaluated by high-temperature catalytic oxidation and excitation–emission matrix combined with parallel
factor analysis (EEM–PARAFAC), respectively, were determined in Liverpool Bay. EEM–PARAFAC modeling resulted in six fluorescent
components characterized as terrestrial humic-like (two), microbial humic-like (two), and protein-like (two). The spatial
distributions of DOC and the four humic-like components were negatively correlated with salinity in the high-salinity waters
observed in this study (30.41–33.75), suggesting that terrestrial DOM was conservatively distributed. The spatial patterns
of protein-like components were largely different from those of DOC, humic-like components, and chlorophyll a, suggesting that these distributions were the combined result of production and degradation in the bay in addition to river
inputs. These findings suggest that the DOM dynamics in Liverpool Bay are strongly controlled by river-dominated allochthonous
DOM inputs with some less significant contributions of autochthonous DOM within the bay. In addition, the temporal variations
of DOM associated with the diurnal tidal cycles were determined at one inshore (31.34–32.24 salinity) and one offshore (33.64–33.75
salinity) station in the bay. Negative linear relationships between salinity and DOM characteristics, i.e., DOC, humic-like,
and protein-like components, were observed at the inshore station. In contrast, no relationship was observed at the offshore
station, suggesting that the export of DOM through rivers and possibly tidal flats have a noticeable influence on DOM concentration
and composition up to a relatively elevated salinity of around 33 in Liverpool Bay. 相似文献
18.
Net autotrophy in a fluvial lake: the relative role of phytoplankton and floating-leaved macrophytes
Monica Pinardi Marco Bartoli Daniele Longhi Pierluigi Viaroli 《Aquatic Sciences - Research Across Boundaries》2011,73(3):389-403
This study combined water- and sediment flux measurements with mass balances of dissolved gas and inorganic matter to determine
the importance of pelagic and benthic processes for whole-system metabolism in a eutrophic fluvial lake. Mass balances of
dissolved O2, inorganic carbon (DIC), nitrogen (DIN), phosphorous (SRP), particulate N (PN) and P (PP) and Chl a were calculated at a nearly monthly frequency by means of repeated sampling at the lake inlet and outlet. Simultaneously,
benthic fluxes of gas and nutrients, including denitrification rates, and the biomass of the dominant pleustophyte (Trapa natans) were measured, and fluxes of O2 and CO2 across the water–atmosphere interface were estimated from diel changes in outlet concentrations. On an annual scale, Middle
Lake exhibited CO2 supersaturation, averaging 313% (range 86–562%), but was autotrophic with a net O2 production (6.35 ± 2.05 mol m−2 y−1), DIC consumption (−31.18 ± 18.77 mol m−2 y−1) and net export of Chl a downstream (8.38 ± 0.95 mol C m−2 y−1). Phytoplankton was the main driver of Middle Lake metabolism, with a net primary production estimated at 33.24 mol O2 m−2 y−1, corresponding to a sequestration of 4.18 and 0.26 mol m−2 y−1 of N and P, respectively. At peak biomass, T. natans covered about 18% of Middle Lake’s surface and fixed 2.46, 0.17 and 0.02 mol m−2 of C, N and P, respectively. Surficial sediments were a sink for O2 (−14.47 ± 0.65 mol O2 m−2 y−1) and a source of DIC and NH4
+ (18.84 ± 2.80 mol DIC m−2 y−1 and 0.83 ± 0.16 mol NH4
+ m−2 y−1), and dissipated nitrate via denitrification (1.44 ± 0.11 mol NO3
− m−2 y−1). Overall, nutrient uptake by primary producers and regeneration from sediments were a minor fraction of external loads.
This work suggests that the creation of fluvial lakes can produce net autotrophic systems, with elevated rates of phytoplanktonic
primary production, largely sustained by allochtonous nutrient inputs. These hypereutrophic aquatic bodies are net C sinks,
although they simultaneously release CO2 to the atmosphere. 相似文献
19.
Paul A. Bukaveckas Amy MacDonald Anthony Aufdenkampe John H. Chick John E. Havel Richard Schultz Ted R. Angradi David W. Bolgrien Terri M. Jicha Debra Taylor 《Aquatic Sciences - Research Across Boundaries》2011,73(3):419-436
Main channel habitats of the Ohio, Missouri, and Upper Mississippi Rivers were surveyed during the summers of 2004, 2005 and
2006 using a probability-based sampling design to characterize inter-annual and inter-river variation in suspended chlorophyll
a (CHLa) and related variables. Large (fivefold) differences in CHLa were observed with highest concentrations in the Upper
Mississippi (32.3 ± 1.8 μg L−1), intermediate values in the Missouri (19.7 ± 1.1 μg L−1) and lowest concentrations in the Ohio (6.8 ± 0.5 μg L−1). Inter-annual variation was small in comparison to inter-river differences suggesting that basin-specific factors exert
greater control over river-wide CHLa than regional-scale processes influencing climate and discharge. The rivers were characterized
by variable but generally low light conditions as indicated by depth-averaged underwater irradiance <4 E m−2 day−1 and high ratios of channel depth to euphotic depth (>3). Despite poor light conditions, regression analyses revealed that
TP was the best single predictor of CHLa (R
2 = 0.40), though models incorporating both light and TP performed better (R
2 = 0.60). Light and nutrient conditions varied widely within rivers and were inversely related, suggesting that riverine phytoplankton
may experience shifts in resource limitation during transport. Inferred grazing and sedimentation losses were large yet CHLa
concentrations did not decline downriver indicating that growth and loss processes were closely coupled. The contribution
by algae to suspended particulate organic matter in these rivers (mean = 41%) was similar to that of lakes (39%) but lower
relative to reservoirs (61%). 相似文献
20.
FANG JingYun LIU GuoHua ZHU Biao WANG XiaoKe & LIU ShaoHui Department of Ecology College of Environmental Sciences and Key Laboratory for Earth Surface Processes of the Ministry of Education Peking University Beijing China Research Center for Eco-Environmental Sciences Chinese Academy of Sciences Beijing China 《中国科学D辑(英文版)》2007,50(1):92-101
There is a general agreement that forest ecosystems in the Northern Hemisphere function as signifi-cant sinks for atmospheric CO2; however, their magnitude and distribution remain large uncertainties. In this paper, we report the carbon (C) stock and its change of vegetation, forest floor detritus, and mineral soil, annual net biomass increment and litterfall production, and respiration of vegetation and soils between 1992 to 1994, for three temperate forest ecosystems, birch (Betula platyphylla) forest, oak (Quercus liaotungensis) forest and pine (Pinus tabulaeformis) plantation in Mt. Dongling, Beijing, China. We then evaluate the C budgets of these forest ecosystems. Our results indicated that total C density (organic C per hectare) of these forests ranged from 250 to 300 t C ha-1, of which 35―54 t C ha-1 from vegetation biomass C and 209―244 t C ha-1 from soil organic C (1 m depth, including forest floor detritus). Biomass C of all three forests showed a net increase, with 1.33―3.55 t C ha-1 a-1 during the study period. Litterfall production, vegetation autotrophic respiration, and soil heterotrophic respira-tion were estimated at 1.63―2.34, 2.19―6.93, and 1.81―3.49 t C ha-1 a-1, respectively. Ecosystem gross primary production fluctuated between 5.39 and 12.82 t C ha-1 a-1, about half of which (46%―59%, 3.20―5.89 t C ha-1 a-1) was converted to net primary production. Our results suggested that pine forest fixed C of 4.08 t ha-1 a-1, whereas secondary forests (birch and oak forest) were nearly in balance in CO2 exchange between the atmosphere and ecosystems. 相似文献