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1.
Simultaneous Monitoring of Phosphine and of Phosphorus Species in Taihu Lake Sediments and Phosphine Emission from Lake Sediments 总被引:4,自引:0,他引:4
Phosphine (PH3) was monitored in the Taihu Lake in China by a GC/NPD method, coupled with cryo-trapping enrichment technology. Results showed
that PH3 was universally detected in sediments, lake water and atmosphere of the Taihu Lake area. Total phosphorus (TPs) and fractions of different phosphorus species in lake sediments were separately measured as dissolved phosphate (DP), phosphorus
bound to aluminum (Al-P), iron (Fe-P) and calcium (Ca-P), occluded phosphorus (OP), and organic phosphorus (Org-P) by sequential
chemical extraction. High PH3 levels were correlated with high TPs values in sediments and with eutrophication at different sites. In addition, a positive linear correlation equation was obtained
between the concentrations of PH3 in lake sediments and of the phosphorus fractions. The resulting multiple linear regression equation is PH3 = −165 + 63.3 DP + 0.736 Al-P + 2.33 Ca-P + 2.29 Org-P. The flux of PH3 across the sediment–water interface was estimated from sediment core incubation in May and October 2002. The annual average
sediment–water flux of PH3 was estimated at ca. 0.0138±0.005 pg dm−2 h−1, the average yearly emission value of PH3 from Taihu Lake sediments to water was calculated to be 28.3±10.2 g year−1, which causes a water PH3 concentration of up to 0.178±0.064 pmol dm−3. The real importance of PH3 could be higher, because PH3 could be consumed in the oxic sediment–water boundary layer and in the water column. Spatial and temporal distributions of
total phosphorus (TPw) and chlorophyll a (Chl-a) in the water column of Taihu Lake were measured over the study period. Higher water PH3 has also been found where the TPw content was high. Similarly, high Chl-a was consistent with higher water PH3. Positive relationships between PH3 and TPw (average R2 = 0.47±0.26) and Chl-a (average R2 = 0.23±0.31) were observed in Taihu Lake water. 相似文献
2.
Long-term monitoring data (1968–2008) were used to investigate internal phosphorus (P) loading following external P loading
reduction in shallow Loch Leven, Scotland. A whole-lake sediment P inventory (upper 3 cm of sediment; 2005) suggested a release-potential
of 29.7 tonnes (t) from the release sensitive sediment P pools. 18.5 t was contained within shallow water sediments (<4.5 m
water depth) with 7.6 t in deeper water sediments below the photic zone (>5 m water depth). The “observed” release (<5.1 t),
estimated using a water column P mass balance approach (1989–2008), was <5.1 t, indicating the presence of regulating mechanisms.
Observed P release declined between 1989 and 2008, with the exception of 2003–2006. Observed P release estimates were positively
correlated with annual average water column P concentration after 1989, highlighting the role of internal loading in maintaining
poor water quality conditions after management intervention. Multiple regression analysis suggested that internal loading
was driven by the wave mixed depth in spring (positive driver), summer water temperature (positive driver) and spring water
clarity transparency (negative driver). The potential importance of biological and physico-chemical feedback mechanisms in
the regulation of benthic–pelagic coupling and water quality in Loch Leven are discussed. 相似文献
3.
Arsenic transport between water and sediments 总被引:1,自引:1,他引:0
Arsenic discharged into the Moira River has accumulated in the sediments of Moira Lake during the past century. The chronology of arsenic concentrations in the sediments, established using Pb-210 dating, has a subsurface concentration maximum (> 1000 g g–1) that reflects higher inputs to the lake 15 to 45 years ago. The distribution coefficient (Kd) of arsenic in the surficial sediments was low (4000–6000 L kg–1) and decreased below the sediment water interface. Higher concentrations of exchangeable As also were extracted deeper in the sediments. As a result, arsenic is mobile in the sediment column and the flux of arsenic via diffusion and particle resuspension from the sediments into the water is greater than current external loading from the Moira River. Less than 20% of the external input of arsenic is buried in the lake sediments. Using these flux measurements and a one dimensional model of arsenic transport in the sediment column, we constructed the history of arsenic exchange between water and sediments throughout the past century. The simulations predict that arsenic input into the water from the sediments has been > 20 % of external loading for the past 25 years and will continue to be important in the future as diffusion and resuspension regenerate arsenic from the mixed layer of the sediments into the overlying water. 相似文献
4.
F. Andrieux-Loyer X. Philippon G. Bally R. Kérouel A. Youenou J. Le Grand 《Biogeochemistry》2008,88(3):213-231
The macrotidal estuary of Penzé (Brittany, Western part of the Channel, France) has been subjected to recurrent annual toxic
blooms of Alexandrium minutum since 1988. This study aims to specify the phosphorus dynamics and bioavailability in sediments in order to improve our understanding
of Alexandrium occurrences. Sediment-P pools and diffusive phosphate fluxes were studied under similar hydrodynamic conditions, in the intermediate
estuary in May, June and July 2003 and along the salinity gradient from August 2004 to June 2005. The results highlight a
decrease in bioavailable phosphorus (iron and organic bound) from the inner part of the estuary seaward. The ratio of iron-bound
phosphorus to iron-oxyhydroxides is lower in the inner and intermediate estuaries (5–8) than in the outer site (15), suggesting
a saturation of sorption sites and greater phosphorus bioavailability in this area. Pools of bioavailable phosphorus in surficial
sediments are about eight times higher than the annual net-export of P (7 ton year−1). Phosphate releases from sediments are always lower than 5 μmol m−2 d−1 in March. The highest supplies occur in June and August in the intermediate area (up to 400 μmol m−2 d−1) where they represent up to 50% of river loadings. These results further suggest that phosphate pulses coincide with occurrences
of Alexandrium reported in June. 相似文献
5.
Large blooms of opportunistic green macroalgae such as Enteromorpha intestinalis are of ecological concern in estuaries worldwide. Macroalgae derive their nutrients from the water column but estuarine sediments may also be an important nutrient source. We hypothesized that the importance of these nutrient sources to E. intestinalis varies along a nutrient-resource gradient within an estuary. We tested this in experimental units constructed with water and sediments collected from 3 sites in Upper Newport Bay estuary, California, US, that varied greatly in water column nutrient concentrations. For each site there were three treatments: sediments + water; sediments + water + Enteromorpha intestinalis (algae); inert sand + water + algae. Water in units was exchanged weekly simulating low turnover characteristic of poorly flushed estuaries. The importance of the water column versus sediments as a source of nutrients to E. intestinalis varied with the magnitude of the different sources. When initial water column levels of dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (SRP) were low, estuarine sediments increased E. intestinalis growth and tissue nutrient content. In experimental units from sites where initial water column DIN was high, there was no effect of estuarine sediments on E. intestinalis growth or tissue N content. Salinity, however, was low in these units and may have inhibited growth. E. intestinalis growth and tissue P content were highest in units from the site with highest initial sediment nutrient content. Water column DIN was depleted each week of the experiment. Thus, the water column was a primary source of nutrients to the algae when water column nutrient supply was high, and the sediments supplemented nutrient supply to the algae when water column nutrient sources were low. Depletion of water column DIN in sediment + water units indicated that the sediments may have acted as a nutrient sink in the absence of macroalgae. Our data provide direct experimental evidence that macroalgae utilize and ecologically benefit from nutrients stored in estuarine sediments. 相似文献
6.
《Chemical Speciation and Bioavailability》2013,25(3):171-181
AbstractPhosphorus (P) is a major nutrient for plant growth, and it is often the primary limiting nutrient in freshwater ecosystems controlling algal blooms. The Bronx River of New York City, New York, USA includes freshwater and coastal water systems. The water quality of both fresh and saline water is lower than the standard levels designated by New York State, and classified as Class B and Class I waters, respectively. Algal blooms and oxygen depletion within the river have degraded the water quality, endangered fishing, and limited recreational use. The internal loading of P, an important bioavailability indicator in the Bronx River, is determined by the sorption processes, i.e., cycling of P between solid and liquid phases. The objectives of this study were to understand how P sorption characteristics affect the internal loading of P and the conditions that might give rise to a flux of P from sediment to the water column, and to estimate the effects of physicochemical properties of the sediments on P sorption parameters. Bed sediments were collected from 15 sites along the Bronx River, from the origin in Westchester Davis Brook, Kensico Dam through the Bronx to the Sound View Park estuary. Phosphorus sorption maximum (Smax) were significantly correlated with oxalate–extractable iron (Ox–Fe) and aluminum (Ox–Al), acid-extractable calcium (HCl–Ca) and magnesium (HCl–Mg), and total organic matter (OM), suggesting that not only metal ions affected P sorption characteristics, but OM also influenced the P sorption processes. This study also showed that originally sorbed P (S0) was significantly correlated with Ox–Fe, Ox–Al, HCl–Mg, and OM. The extremely high values of the percentage of sorbed P retained in sediments (>98% for all sites except the two estuary sites: site 13 of 88% and site 14 of 92%) suggest that a large flux of P to the water column from the sediments could potentially occur under changing hydro-climatic conditions, such as the changes in pH, ionic strength and redox conditions, which may, in turn, exacerbate eutrophic conditions and subsequent algal blooms. 相似文献
7.
Assessment of the importance of internal nutrient loading is essential for managing and restoring eutrophic shallow lakes.
To date, studies of internal loads have tended to focus on one of two abiotic processes, either molecular diffusion or sediment/nutrient
entrainment (resuspension). This study presents a new approach to determining the non-biological fluxes of nitrogen (N) and
phosphorus (P) from the sediment to the water column of shallow lakes. Three mutually exclusive flux processes: (i) molecular
diffusion, (ii) turbulent diffusion (eddy diffusivity) and (iii) wind-induced resuspension of N and P, were related to a gradient
of benthic shear stress. A model presented here allowed the durations and magnitudes of different non-biological fluxes to
be calculated over time, based on benthic shear stress. Two site-specific critical shear stress thresholds determined which
of the three flux processes dominated for any benthic shear stress value. The model was calibrated for a shallow lake and
the continuous flux of nutrient from the sediment to the overlying water generated by each process during that period was
calculated, enabling the estimation of the relative importance of each of the three flux processes over a one-year period.
Wind-induced resuspension dominated the internal nutrient flux, operating for 38% of the time and contributing 0.9 T P year−1 and 10.2 T N year−1 to the internal nutrient load. In contrast, molecular diffusion only contributed 0.01–0.02 T P year−1 and 0.12–0.20 T N year−1 to the water column, while turbulent diffusion provided up to 0.6 T P year−1 and 6.2 T N year−1. Our model suggests that turbulent diffusion is a neglected and potentially important process contributing to internal nutrient
loading in shallow lakes, whereas molecular diffusion appears to be relatively unimportant in lakes that experience turbulence
at the sediment–water interface.
Handling editor: L. Naselli-Flores 相似文献
8.
Benthic phosphorus regeneration in the Potomac River Estuary 总被引:2,自引:2,他引:0
The flux of dissolved reactive phosphate from Potomac riverine and estuarine sediments is controlled by processes occurring
at the water-sediment interface and within surficial sediment.In situ benthic fluxes (0.1 to 2.0 mmoles m−2 day−1) are generally five to ten times higher than calculated diffusive fluxes (0.020 to 0.30 mmoles m−2 day−1). The discrepancy between the two flux estimates is greatest in the transition zone (river mile 50 to 70) and is attributd
to macrofaunal irrigation.
Bothin situ and diffusive fluxes of dissolved reactive phosphate from Potomac tidal river sediments are low while those from anoxic lower
estuarine sediments are high. The net accumulation rate of phosphorus in benthic sediment exhibits an inverse pattern. Thus
a large fraction of phosphorus is retained by Potomac tidal river sediments, which contain a surficial oxidized layer and
oligochaete worms tolerant of low oxygen conditions, and a large fraction of phosphorus is released from anoxic lower estuary
sediments. Tidal river sediment pore waters are in equilibrium with amorphous Fe (OH)3 while lower estuary pore waters are significantly undersaturated with respect to this phase. Benthic regeneration of dissolved
reactive phosphorus is sufficient to supply all the phosphorus requirements for net primary production in the lower tidal
river and transition-zone waters of the Potomac River Estuary. Benthic regeneration supplies approximately 25% as much phosphorus
as inputs from sewage treatment plants and 10% of all phosphorus inputs to the tidal Potomac River.
When all available point source phosphorus data are put into a steady-state conservation of mass model and reasonable coefficients
for uptake of dissolved phosphorus, remineralization of particulate phosphorus, and sedimentation of particulate phosphorus
are used in the model, a reasonably accurate simulation of dissolved and particulate phosphorus in the water column is obtained
for the summer of 1980. 相似文献
9.
The effect of phytodetritus derived from Phaeocystis sp. bloom on benthic mineralization processes has been determined at four intertidal stations along the French coast of the
eastern English Channel. Sites were chosen to offer a diversity of sediment types, from permeable sandy beach to estuarine
mudflats. Sediment Oxygen Demand (SOD) as well as total fluxes of Dissolved Inorganic Nitrogen (DIN) at the sediment–water
interface were determined by using whole core incubation technique and diffusive fluxes were predicted from interstitial water
concentrations. In the absence of phytodetritus deposits, a marked gradient of granulometric characteristics and organic matter
contents were observed, and resulted in more intensive mineralization processes in muddy sediments. Highly significant correlations
(P < 0.05) were evidenced between SOD and porosity, bacterial biomass, Organic Carbon and Organic Nitrogen, evidencing the direct
link between sediment texture, organic matter accumulation and microbial activity. The spring bloom led to a massive input
of organic matter in surficial sediments and mineralization rates significantly increased while higher DIN release towards
the water column was observed. A modification of the mineralization pathways was evidenced but clearly depended on the sediment
type. With a global view, benthic mineralization processes in the intertidal zone provided significant a part of DIN inputs
in the coastal zone while water column was depleted in nutrients. 相似文献
10.
Over a period of three years, the flux of particulate phosphorus to the sediment–water interface of Lake Kinneret was monitored by using seston traps deployed near the bottom of both accumulation and resuspension zones. The trap material was subjected to sequential phosphorus extraction. The obtained data set was compared to the phosphorus distribution in the surface layer of bottom sediments. Due to the sequence of drought years less allochtoneous phosphorous is reaching the lake resulting in a continuous decline of total particulate phosphorus (TPP) in the upper sediment layer. The observed decline in sedimentary TPP in spite of increased TPP sedimentation can be seen as a dilution effect due to the sedimentation of material with a relatively lower P content. The change in sedimentation can be seen as the result of increased resuspension at low lake levels. With sedimentary P in the littoral zone being unaffected by the drop in the external P load, the changes observed in the profundal zone appear to be driven by internal wave activity. 相似文献
11.
Diffusive exchange of linear alkylbenze suifonates (LAS) between overlying water and bottom sediment
Linear alkylbenzenesulfonate (LAS) was detected in a 0–30 cm deep sediment column collected in Lake Teganuma (one of the most polluted lakes in Japan). The range of the LAS concentration in sediments was between 0.1 and 500 µg g–1 (C11-C14 homologs per dry solid) and its vertical profile showed a seasonal variation. A mathematical model, which includes a diffusion term and a biodegradation term, was used to simulate the temporal variation of LAS in the sediment column and to calculate the diffusive flux rate of LAS across the sediment/water interface. An averaged diffusion coefficient of 2.4 × 10–5 cm2 s–1 for the sediment interstitial water was obtained from sediment core samples located in Lake Teganuma. The biodegradation rate constant (0.002 d–1) of LAS in the sediment obtained from the model analysis was considerably less than that reported for LAS in anaerobic waters. These results confirm that a model describing diffusive transport and biodegradation of LAS in the sediments can simulate the temporal variation of LAS in near surface sediments. The diffusive flux rate from overlying water to bottom sediment was calculated to be between –0.20 and 0.52 (C11-C14 LAS) mg m–2 h–1 and the annual net flux rate was 0.7 g m–2 y–1. 相似文献
12.
Geochemical processes of iron and manganese in a seasonally stratified lake affected by coal-mining drainage in China 总被引:1,自引:0,他引:1
Lake water, pore water, and sediments were sampled in a seasonally stratified lake affected by coal-mining drainage. Contrasting
geochemical processes of iron and manganese in summer were investigated by studying the seasonal distributions of iron and
manganese species in the water column, pore water, and sediments. The results show that iron buildup in the water during summer
was mainly from the gradual dissolution of particulate matter due to the pH decrease, whereas manganese oxide reduction and
manganese-bound carbonate dissolution near the sediment–water interface were mainly responsible for manganese accumulation
in the stratified hypolimnion. The geochemical processes of iron and manganese in the sediments during early diagenesis were
also discussed in terms of the possible influence on the overlying water.
Received: November 29, 1999 / Accepted: June 30, 2000 相似文献
13.
A study was conducted in Mona Lake, a small eutrophic lake located in western Michigan (USA) to address the temporal and spatial
variability of external and internal phosphorus loading. External P load varied among subbasins, which was mostly related
to discharge, but also to land use. Black Creek, which drains lands with natural cover and agriculture, accounted for the
majority of flow, and total phosphorus (TP) and soluble reactive phosphorus (SRP) load, to Mona Lake. However, the relative
contribution of SRP load was greater in Little Black Creek, which flows through a mostly urbanized subbasin, than in Black
Creek. The relative importance of internal loading was strongly related to season, as internal TP loads contributed only ∼9%
of the overall P load in April 2005, but ∼68–82% of the overall P load in the summer and early fall seasons. Internal TP and
SRP loading was greater under anaerobic than aerobic conditions. Mean anaerobic TP release rates ranged from 0.80 to 15.56 mg P m−2 d−1, varying with site and season. Spatial variability in both internal phosphorus loading and sediment P concentration was also
evident. By taking into account the spatial and temporal variability of different loading sources, management practices can
be targeted to optimize nutrient source control strategies. 相似文献
14.
Andreas Kleeberg 《Hydrobiologia》2002,472(1-3):53-65
The seasonal course of phosphorus (P) fractions of sinking particulate matter has been studied at the deepest location of dimictic eutrophic Lake Scharmützel (29.5 m) by paired sediment traps at 9 and 27 m water depth from May 1996 to December 1997. Relatively large depositional fluxes and considerably variable P fluxes, mainly carried by allochthonous particles, diatoms in spring, and iron during overturns transport almost 60% of the average water column P pool to the sediment surface. The contribution of resuspension and sediment focusing (24–34%) is relatively small. A sequential chemical P extraction of the matter entrapped revealed that ,loosely adsorbed` P contributed to 5–14%, organic bound P to 55–68%, and Ca-associated P to 3–6% of the annual P flux, depending on season and depth. The redox-sensitive (iron bound) P ranged from only 12% of the annual P flux during anoxic sulfidic conditions to 28% during oxic conditions. On an annual basis, 16–18% of sedimenting P was recycled within the water column, and 71–75% of total primary P flux was recycled at the sediment surface. Ultimately, 10–23% of P became incorporated into recent sediments indicating the long residence time for P and a high internal resupply of P for primary production. 相似文献
15.
Spatial variation of phosphorus fractions in bottom sediments and the potential contributions to eutrophication in shallow lakes 总被引:1,自引:0,他引:1
Yuichi Ishii Satoshi Harigae Shiho Tanimoto Tohru Yabe Tomohiko Yoshida Kazuo Taki Nobuyuki Komatsu Keiji Watanabe Masami Negishi Hideki Tatsumoto 《Limnology》2010,11(1):5-16
Spatial variation of phosphorus fractions in bottom sediment, pore water and overlying water in three shallow eutrophic lakes,
Nishiura, Kitaura and Sotonasakaura, Japan, and the contributions of the fractional P to mobilization of phosphorus from sediment
were examined in this study. The vertical distributions of dissolved inorganic phosphorus (DIP) concentrations in overlying
and pore water differed with lake and sampling site. In particular, DIP was high in pore water in the surface layer of the
sediment for the middle to downlake areas of Lake Kitaura. DIP release flux calculated from a gradient of the concentrations
at the sediment–water interface was high compared with other sites. The distribution of fractional P content in sediments
was highly variable. The citrate–dithionite–bicarbonate–non-reactive phosphorus (CDB–NRP) fraction, in particular, differed
greatly among the three lakes. According to correlation in the ratios between CDB–NRP and loss on ignition, sediments of these
lakes were classified in three clusters. The CDB–NRP fraction was suggested to play a role in DIP release from sediment. The
possibility of nitrate concentration playing a role in the control of DIP release was considered. 相似文献
16.
There is renewed interest in the use of nitrate to treat the profundal zone of lakes to inhibit anaerobic biogeochemical processes
that result in the degradation of bottom water quality (e.g., sediment phosphorus release, mercury methylation). In this study
we used experimental sediment–water interface chambers to quantify the rate of sediment nitrate uptake (SNU) in profundal
sediments from Lake Perris, a eutrophic raw water reservoir in Southern California. Deoxygenated chamber water was spiked
with nitrate, and nitrate concentration was monitored over time under quiescent conditions, followed by mixed conditions with
average water velocities of 1 cm/s. Key findings included: (1) SNU decreased with decreasing nitrate concentration, (2) SNU
was higher under mixed versus quiescent conditions by nearly 50%, and (3) nitrate uptake as a function of nitrate concentration
followed a conventional sediment oxygen demand model in which nitrate uptake was proportional to the square root of nitrate
concentration. The probable mechanism for elevated SNU under mixed conditions was an increased diffusional concentration gradient
combined with a decrease in the diffusional boundary layer at the sediment–water interface, both of which enhanced the flux
of nitrate from overlaying water into sediment. Managers planning to implement lake nitrate addition should account for induced
nitrate demand when determining dosing rates. For example, based on our modeling efforts from this data set, SNU in Lake Perris
could range by an order of magnitude, from around 12 mg N/m2/d under quiescent, low nitrate conditions (0.1 mg N/l) to around 120 mg N/m2/d under mixed, high nitrate conditions (5 mg N/l).
Handling editor: L. Naselli-Flores 相似文献
17.
Natalia V. Ignatieva 《Hydrobiologia》1996,322(1-3):129-136
Sedimentary phosphorus fractions and phosphorus release from the sediments were studied in Lake Ladoga at altogether 46 sampling sites, representing the full range of sediment types encountered in the lake. Determination of P fractions and physico-chemical analyses were made of surface sediment cores (10–20 cm long, each sampled at 3–4 levels) and in the overlying water. The range of total phosphorus per dry weight of sediment was 0.2–3.3 mg g–1, and that of inorganic P 0.1–2.5 mg g–1. The levels of interstitial soluble phosphorus, range 2–613 µg 1–1 for total P and 1–315 µg 1–1 for inorganic P, were higher than those of dissolved P concentrations in the overlying water. Diffusive fluxes of phosphate from sediment to the overlying water were estimated using three independent methods. The estimated range was 4–914 µg P m–2 d–1; the mean value for the whole bottom area, 0.1 mg P m–2 d–1, is lower than previously published estimates. The estimated annual contribution of sedimentary inorganic P flux to Lake Ladoga water is equal to 620 tons of P per year, which amounts to more than 10% of the estimated external P load into the lake. 68% of the total diffusive flux emanates from deep water sediments, which are not exposed to seasonal variation of conditions. In deep lakes, such as Lake Ladoga, phosphorus release from the sediments is controlled primarily by diffusive mechanisms. Wave action and currents as well as bioturbation are probably of importance mainly in shallow near-shore areas. Phosphorus release by gas ebullition and macrophytes is considered negligible. 相似文献
18.
Phosphorus (P) dynamics in the agriculturally-dominated Minnesota River (USA) were examined in the lower 40 mile reach in
relation to hydrology, loading sources, suspended sediment, and chlorophyll to identify potential biotic and abiotic controls
over concentrations of soluble P and the recycling potential of particulate P during transport to the Upper Mississippi River.
Within this reach, wastewater treatment plant (WWTP) contributions as soluble reactive P (SRP) were greatest during very low
discharge and declined with increasing discharge and nonpoint source P loading. Concentrations of SRP declined during low
discharge in conjunction with increases in chlorophyll, suggesting biotic transformation to particulate P via phytoplankton
uptake. During higher discharge periods, SRP was constant at ~0.115 mg l−1 and coincided with an independently measured equilibrium P concentration (EPC) for suspended sediment in the river, suggesting
abiotic control over SRP via phosphate buffering. Particulate P (PP) accounted for 66% of the annual total P load. Redox-sensitive
PP, estimated using extraction procedures, represented 43% of the PP. Recycling potential of this load via diffusive sediment
P flux under anoxic conditions was conservatively estimated as ~17 mg m−2 d−1 using published regression equations. The reactive nature and high P recycling potential of suspended sediment loads in the
Minnesota River has important consequences for eutrophication of the Upper Mississippi River. 相似文献
19.
Time scales and mechanisms of estuarine variability,a synthesis from studies of San Francisco Bay 总被引:2,自引:2,他引:0
This review of the preceding papers suggests that temporal variability in San Francisco Bay can be characterized by four time scales (hours, days-weeks, months, years) and associated with at least four mechanisms (variations in freshwater inflow, tides, wind, and exchange with coastal waters). The best understood component of temporal variability is the annual cycle, which is most obviously influenced by seasonal variations in freshwater inflow. The winter season of high river discharge is characterized by: large-scale redistribution of the salinity field (e.g. the upper estuary becomes a riverine system); enhanced density stratification and gravitational circulation with shortened residence times in the bay; decreased tissue concentrations of some contaminants (e.g. copper) in resident bivalves; increased estuarine inputs of river-borne materials such as dissolved inorganic nutrients (N, P, Si), suspended sediments, and humic materials; radical redistributions of pelagic organisms such as copepods and fish; low phutoplankton biomass and primary productivity in the upper estuary; and elimination of freshwater-intolerant species of macroalgae and benthic infauna from the upper estuary. Other mechanisms modulate this river-driven annual cycle: (1) wind speed is highly seasonal (strongest in summer) and causes seasonal variations in atmosphere-water column exchange of dissolved gases, resuspension, and the texture of surficial sediments; (2) seasonal variations in the coastal ocean (e.g. the spring-summer upwelling season) influence species composition of plankton and nutrient concentrations that are advected into the bay; and (3) the annual temperature cycle influences a few selected features (e.g. production and hatching of copepod resting eggs). Much of the interannual variability in San Francisco Bay is also correlated with freshwater inflow: wet years with persistently high river discharge are characterized by persistent winter-type conditions.Mechanisms of short-term variability are not as well understood, although some responses to storm events (pulses in residual currents from wind forcing, erosion of surficial sediments by wind waves, redistribution of fish populations) and the neap-spring tidal cycle (enhanced salinity stratification, gravitational circulation, and phytoplankton biomass during neap tides) have been quantified. In addition to these somewhat predictable features of variability are (1) largely unexplained episodic events (e.g. anomalous blooms of drift macroalgae), and (2) long-term trends directly attributable to human activities (e.g. introduction of exotic species that become permanent members of the biota). 相似文献
20.
Pascal M. A. Boderie John J. G. Zwolsman Gijsbertus T. M. Van Eck Cornelis H. Van der Weijden 《Aquatic Ecology》1993,27(2-4):309-318
The Scheldt river drains a densely populated and industrialized area in northern France, western Belgium and the south-west Netherlands. Mineralization of the high organic load carried by the river leads to oxygen depletion in the water column and high concentrations of dissolved nitrogen and phosphorus compounds. Upon estuarine mixing, dissolved oxygen concentrations are gradually restored due to reaeration and dilution with sea water. The longitudinal redox gradient present in the Scheldt estuary strongly affects the geochemistry of nutrients. Dissolved nutrients in the water column and dissolved nitrogen species in sediment porewaters were determined for a typical summer and winter situation. Water column concentration-salinity plots showed conservative behaviour of dissolved Si during winter. During summer (and spring) dissolved Si may be completely removed from solution due to uptake by diatoms. The geochemistry of phosphorus was governed by inorganic and biological processes. The behaviour of nitrogen was controlled by denitrification in the anoxic fluvial estuary, followed by nitrification in the upper estuary (prior to oxygen regeneration). In addition, nitrogen was taken up during phytoplankton blooms in the lower estuary. Dissolved inorganic nitrogen species in porewaters from the upper 20 cm of sediments were obtained from a subtidal site in the middle of the lower estuary. Dissolved nutrient concentrations were low in the upper 10–15 cm of the sandy and organic poor (<1% POC) sediments mainly as a result of strong sediment mixing. The porewater profiles of ammonium and nitrate were evaluated quantitatively, using a one-dimensional steady-state diagenetic model. This coupled ammonium-nitrate model showed ammonification of organic matter to be restricted to the upper 4 to 7 cm of the sediments. Total nitrification ranged from 3.7–18.1 mmol m?2 d?1, converting all ammonium produced by ammonification. The net balance between nitrification and denitrification depended on the season. Nitrate was released from the sediments during winter but is taken up from the water column during summer. These results are in good agreement with data obtained from the independently calibrated water column model for the Scheldt Estuary (VAN GILSet al., 1993). 相似文献