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1.
《Limnologica》2020
The ecological functioning of floodplain lakes is largely influenced by the interaction with the river mainstem. In this study, seasonal variation in water chemistry and the relationship with the river conditions were compared between floodplain lakes that differ in the level of connection to the Usumacinta River, the largest river of Mesoamerica. Samples for suspended solids, nutrients, and chlorophyll a were collected through the year in lakes permanently connected to the river and in lakes that only received water from the Usumacinta for a short period during peak flow. Floodplain lakes showed higher total suspended solids than the river during the dry season while during the rainy season greater differences were observed between the river and the lakes, probably explained by higher concentrations in the river and greater sedimentation in the lakes. Greater organic matter content in the suspended solids was observed in the floodplain lakes, particularly in the more isolated lakes, likely related to high algal biomass. Nitrate concentrations were always higher in the river than in the lakes and lower nitrate concentrations occurred at the isolated lakes, suggesting that processes that remove nitrate occur through the year and are a common feature of floodplain lakes. Phosphorus in the connected lakes was higher than in the river only during the dry season, while in the isolated lakes concentrations were always greater than in the river. Chlorophyll a concentrations were higher in the connected lakes than in the river only during the dry season, while the more isolated lakes exhibited higher values through the year, showing signs of eutrophication. Suspended organic matter, nitrate, and chlorophyll showed larger differences between lake and river sites in the more isolated lakes, probably related to greater water residence time and its influence on primary production. Less connected lakes are more vulnerable to flow alteration because the brief period of connection to the river can be compromised and the effects of eutrophication exacerbated. 相似文献
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Phytoplankton dynamics and cyanobacterial dominance in Murchison Bay of Lake Victoria (Uganda) in relation to environmental conditions 总被引:2,自引:0,他引:2
Sigrid Haande Thomas RohrlackRonald P. Semyalo Pål BrettumBente Edvardsen Anne Lyche-SolheimKai Sørensen Petter Larsson 《Limnologica》2011,41(1):20-29
Murchison Bay is a shallow embayment in the north-western part of Lake Victoria, strongly influenced by urban pollution from the Ugandan capital Kampala. Two stations, representing the semi-enclosed innermost part of the bay and the wider outer part of the bay, were sampled in the period from April 2003 to March 2004, in order to assess the phytoplankton community and the nutrient status in the bay. Murchison Bay was highly eutrophic with average concentrations (n=25) of total phosphorous >90 μg L−1 and total nitrogen >1100 μg L−1 in the inner part of the bay. The phytoplankton community was dominated by a variety of cyanobacterial species and diatoms. Cyanobacteria were dominant in the whole bay, whereas diatoms were more abundant in the outer part of the bay. Moreover, the proportion of N-fixing species like Anabaena sp. was higher in the outer part of the bay, whereas species like Microcystis sp. were more abundant in the inner part of the bay. The phytoplankton community, especially in the outer part of the bay, may be influenced by light limitation. Low NO3-N concentrations in the bay may also indicate a possible N-limitation, thus favouring growth of N-fixing cyanobacteria. The open bay is, however, a complex system, and additional environmental factors and loss processes most likely affect the phytoplankton community. 相似文献
4.
Bla?enka Gašparovi? Tamara DjakovacNataša Tepi? Danilo Degobbis 《Continental Shelf Research》2011,31(10):1149-1160
Surface-active organic substances (SAS), nutrients, chlorophyll a (Chl a), dissolved oxygen (O2), salinity (S) and temperature (T) were measured approximately monthly in the northern Adriatic Sea (NA) during two years. Results were elaborated for two stations of different trophic status. Exhaustive statistical examinations of measured variables were performed to contribute to better understanding of the processes and interdependence of the measured parameters. The results of those analyses allowed the region to be described based on several groups of data relevant for particular processes. Chl a appear to be independent parameter; orthosilicate, nitrite and ammonium represent the parameter group most relevant for regeneration processes; the second group includes nutrients dominant in freshwater inputs (orthophosphate and nitrate), while in the third group are parameters related to primary production processes (T, O2, organic phosphorus and SAS). Probably due to time lags between nutrient uptake and phytoplankton growth as well as between cells growth/division and SAS release, both, the correlation between nutrients and Chl a and the correlation between Chl a and SAS were not statistically significant. Although significantly higher nutrient and Chl a concentrations were found in the mesotrophic western part of the region in comparison to the oligotrophic eastern part, the SAS concentration differences were less marked. It is assumed that more OM is produced, but also at the same time remineralized, at the mesotrophic western part, leading to higher concentrations of regenerated nutrients there. Presence of different phytoplankton taxa and/or fractions (micro and nano) at the two stations may have also contributed to minimize the difference in SAS contents. Higher SAS acidities were noticed in the mesotrophic than in the oligotrophic part. 相似文献
5.
J. Christopher Rutherford Roger G. Young John M. Quinn Robert J. Wilcock 《新西兰海洋与淡水研究杂志》2020,54(3):410-430
ABSTRACT Instream processes alter the concentration and bioavailability of nutrients as they are transported downstream. By relating primary production and periphyton composition to changes in nutrient concentration in a gravel-bed river this study made inferences about recycling and attenuation. Where dissolved inorganic nitrogen (DIN) was abundant, concentrations decreased linearly with distance but by less than required to meet the nitrogen demand of primary production. Where DIN was barely measurable photosynthesis was reduced but only by 50%. We infer that recycling sustained primary production even when DIN concentrations were negligibly small. One implication is that DIN removal underestimates attenuation. Further experimental research on recycling and improved modelling is required to better quantify the length of streams adversely affected by nutrients. 相似文献
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Seasonal DOC accumulation in the Black Sea: a regional explanation for a general mechanism 总被引:2,自引:0,他引:2
Gustave Cauwet Gaëlle Dliat Anton Krastev Galina Shtereva Sylvie Becquevort Christiane Lancelot Andr Momzikoff Alain Saliot Adriana Cociasu Lucia Popa 《Marine Chemistry》2002,79(3-4)
During three cruises in the Black Sea, organised in July 1995 and April–May 1997, biological and chemical parameters that can influence the carbon budget were measured in the water column on the NW shelf, particularly in the mixing zone with Danube River waters. We observed in early spring (end of April–May) conditions an important input of freshwater organisms that enhanced the microbial activity in the low salinity range. High bacterial activity regenerates nitrogen in the form of nitrates, but is also responsible for an important consumption of ammonium and phosphate, leading to a high N/P ratio and a strong deficit in phosphorus. The consequence is a limitation of phytoplankton development but also a production of carbohydrates that accumulate all along the salinity gradient. These mechanisms are responsible for a seasonal accumulation of dissolved organic carbon (DOC) that increases from 210 μM in winter to about 280 μM in summer. All this excess DOC disappears during winter, probably degraded by bacterial activity. The degradation of carbon-rich organic matter increases the phosphorus demand by bacteria bringing limitation to phytoplankton primary production. 相似文献
8.
Observations of wintertime nutrient concentrations in surface waters are scarce in the temperate and subarctic North Atlantic Ocean. Three new methods of their estimation from spring or early summer observations are described and evaluated. The methods make use of a priori knowledge of the vertical distribution of oxygen saturation and empirical relationships between nutrient concentrations and oxygen saturation. A south–north increase in surface water winter nutrient concentration is observed. Winter nitrate concentrations range from very low levels of about 0.5 μmol dm−3 at 33°N to about 13.5 μmol dm−3 at 60°N. Previous estimates of winter nitrate concentrations have been overestimates by up to 50%. At the Biotrans Site (47°N, 20°W), a typical station in the temperate Northeast Atlantic, a mean winter nitrate concentration of 8 μmol dm−3 is estimated, compared to recently published values between 11 and 12.5 μmol dm−3. It is shown that most of the difference is due to a contribution of remineralised nitrate that had not been recognized in previous winter nutrient estimates. Mesoscale variation of wintertime nitrate concentrations at Biotrans are moderate (less than ±15% of the regional mean value of about 8 μmol dm−3). Interannual variation of the regional mean is small, too. In the available dataset, there was only 1 year with a significantly lower regional mean winter nitrate concentration (7 μmol dm−3), presumably due to restricted deep mixing during an atypically warm winter. The significance of winter nitrate estimates for the assessment of spring-bloom new production and the interpretation of bloom dynamics is evaluated. Applying estimates of wintertime nitrate concentrations of this study, it is found that pre-bloom new production (0.275 mol N m−2) at Biotrans almost equals spring-bloom new production (0.3 mol N m−2). Using previous estimates of wintertime nitrate yields unrealistically high estimates of pre-bloom new production (1.21–1.79 mol N m−2) which are inconsistent with observed levels of primary production and the seasonal development of biomass. 相似文献
9.
Annual Variation of Benthic Nutrient Fluxes in Shallow Coastal Waters (Gulf of Trieste, Northern Adriatic Sea) 总被引:5,自引:0,他引:5
Abstract. Benthic fluxes of dissolved N. Si and P nutrients, alkalinity, dissolved inorganic C (DIC), and O2 from sediments in the Gulf of Trieste (northern Adriatic, Italy) were measured monthly for 16 months, using laboratory incubated flux chambers at in siru temperatures in the dark. The annual average fluxes were: 02 = -19.3 ± 8.2, DIC = 13.7 ± 9.6, NO3 = -0.04 ± 0.16, NH4 = 0.3 ± 0.4. PO4= 4.001 ± 0.01, Si = 0.9 ± 0.1 mmol m-2 d-1, with strong temporal fluctuations. The highest effluxes of all nutrients and DIC were observed in the summer. Small effluxes of DIC and NH4 and influxes of Si and PO4 were observed in late winter. Only NH4 (ca. 50%) and Si (ca. 70%) fluxes were significantly correlated with temperature. This correlation suggests that the rate of downward input and the quality of sedimented organic matter (autochthonous and allochthonous) were superimposed on the temperature fluctuations. High DIC, NH4 and Si effluxes observed in May 1993 during low temperature were due to the degradation of sedimentary organic matter produced by an early spring bloom of benthic microalgae which occurred about 6 weeks earlies while the autumn phytoplankton bloom was simultaneously reflected in enhanced benthic fluxes due to higher temperature. The role of benthic biological advection in this transport across the sediment-water interface, evaluated by comparison between measured benthic and calculated diffusive fluxes from nutrient pore water concentrations, was of minor importance. This is probably due to low infaunal activity throughout the year it was localized mostly in the narrow surficial layer. The annual average diffusive fluxes of NH4 and PO4 were higher than those measured, probably due to the presence of nitrificationdenitrifi-cation processes and redox-dependent chemical reactions at the oxic sediment-water interface, respectively. Only during bottom-water hypoxia in September 1993 did strong PO4 effluxes prevail. Calculations based on the Redfield stoichiometry of oxic decomposition of organic N to NH4 and NO3, and differences between diffusive and measured NH4 fluxes showed that denitrifkation averaged 0.8 mmol m-2 d-1. Significant correlations between NH4 and PO4 DIC and Si, and NH4 and Si fluxes suggested their parallel regeneration and utilization at the sediment-water interface. The nutrient fluxes observed were not significantly linked to O2 consumption, suggesting also that anaerobic oxidation processes were important at the sediment-water interface in the gulf. The N, P and Si nutriqnts released from sediment pore waters are probably utilized in benthic microalgal and bottorn-hater primary production. This indicates that pelagic and benthic communities in the central part of the Gulf of Trieste function relatively independently of each other. 相似文献
10.
Sevim Polat 《Marine Ecology》2002,23(2):115-126
Abstract. The monthly changes in chlorophyll a , phytoplankton abundance and nutrient concentrations at two stations, one at the inshore and the other at the deep waters of the northern part of İskenderun Bay, were investigated between 1994 – 1995. The vertical distribution of nutrients and phytoplankton biomass were also studied at the deep station. The concentrations of NO3 +NO2 -N, PO4 -P and SiO4 -Si of surface water at both stations were 0.31 – 1.63 µg-at · l-1 , 0.08 – 0.60 µg-at · l-1 and 0.50 – 2.7 µg-at · l-1 , respectively. The highest concentrations were measured at the inshore station and clear differences were found between the inshore and deep-water stations. Chlorophyll a concentrations ranged from 0.17 to 2.78 µg · l-1 and the highest value was measured in March. At the inshore station, which was affected by land run-off, phytoplankton abundance reached the highest value (21,308 cells · l-1 ) in October 1995, with a marked dominance of Pseudonitzschia pungens (20,200 cells · l-1 ). The nutrient and chlorophyll a concentrations at the inshore station were higher than those at the deep station. One reason for this is the land-based nutrient input into the coastal area here. In spite of these effects, the bay is not eutrophicated because of circulation events in the northeastern Mediterranean. 相似文献