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1.
Chemical composition of interstitial water and diffusive fluxes within the diatomaceous sediment in Lake Myvatn, Iceland 总被引:2,自引:0,他引:2
Sigurdur Reynir Gíslason Eydís Salome Eiríksdóttir Jón Sigurdur Ólafsson 《Aquatic Ecology》2004,38(2):163-175
The sub-arctic Lake Myvatn is one of the most productive lakes in the Northern Hemisphere, despite an ice-cover of 190 days per year. This is due to relatively high solar radiation, nutrient rich inflow waters, N2 fixation and internal nutrient loading. In order to define direction and magnitude of diffusive fluxes, soil water samplers were used to collect interstitial water from 25–150 cm depth, from within the diatomaceous sediment at the bottom of Lake Myvatn. Water depth at the sampling site was 225 cm. The pH of the interstitial water ranged from 7.16 to 7.30, while the pH of the lake water was 9.80–10.00. The concentrations of most solutes were similar 16 cm above the bottom of the lake at the sampling site and at the lake outlet. The concentrations of NO3, S, F, O2, Al, Cr, Mo, V, U, Sn and Sb were higher in the lake water than in the interstitial water. They will therefore diffuse from the lake water into the interstitial water. The concentrations of orthophosphates, PO4, and total dissolved P were highest at 25 cm depth, but Co and NH4 concentrations were highest at 50 to 100 cm depth. Thus they diffuse both up towards the lake bottom and down deeper into the sediments. The concentrations of Na, K, Ca, Mg, Sr, Mn, Li and alkalinity were greater within the sediments than in the lake water and increased continuously with depth. The Si concentration of the interstitial water was higher than in the lake water, it was highest at 25 cm depth and decreased slightly down into the sediments. The concentration gradient was greatest for bicarbonate, HCO3
–, 1.5×10–7 mol cm–3 cm–1, and then in declining order for the solutes with the highest gradient; NH4, Si, Na, Ca, Mg, -S (diffusion into the sediments), K, PO4, Cl, Fe and Mn. The estimated annual diffusive flux of PO4 for Lake Myvatn was 0.1 g P m–2 yr–1, about 10% of the total PO4 input to Lake Myvatn. The H4SiO4° flux was 1.3 g Si m–2 yr–1, <1% of both the input and the annual net Si fixation by diatoms within the lake and the diffusive flux of dissolved inorganic carbon was 1% of the annual net C fixation by diatoms. Annual diffusive flux of NH4
+ was 1.9 g N m–2 yr–1 similar to the input of fixed N to the lake and 24% of the net N fixation within Lake Myvatn. Thus it is important for the nitrogen budget of Lake Myvatn and the primary production in the lake since fixed nitrogen is the rate determining nutrient for primary production. 相似文献
2.
Co-occurrence of denitrification and nitrogen fixation in a meromictic lake, Lake Cadagno (Switzerland) 总被引:1,自引:0,他引:1
Hannah Halm Niculina Musat Phyllis Lam Rebecca Langlois Florin Musat Sandro Peduzzi Gaute Lavik Carsten J. Schubert Bärbel Sinha Julie LaRoche Marcel M. M. Kuypers 《Environmental microbiology》2009,11(8):2190-2190
The nitrogen cycling of Lake Cadagno was investigated by using a combination of biogeochemical and molecular ecological techniques. In the upper oxic freshwater zone inorganic nitrogen concentrations were low (up to ~3.4 μM nitrate at the base of the oxic zone), while in the lower anoxic zone there were high concentrations of ammonium (up to 40 μM). Between these zones, a narrow zone was characterized by no measurable inorganic nitrogen, but high microbial biomass (up to 4 × 107 cells ml?1). Incubation experiments with 15N‐nitrite revealed nitrogen loss occurring in the chemocline through denitrification (~3 nM N h?1). At the same depth, incubations experiments with 15N2‐ and 13CDIC‐labelled bicarbonate, indicated substantial N2 fixation (31.7–42.1 pM h?1) and inorganic carbon assimilation (40–85 nM h?1). Catalysed reporter deposition fluorescence in situ hybridization (CARD‐FISH) and sequencing of 16S rRNA genes showed that the microbial community at the chemocline was dominated by the phototrophic green sulfur bacterium Chlorobium clathratiforme. Phylogenetic analyses of the nifH genes expressed as mRNA revealed a high diversity of N2 fixers, with the highest expression levels right at the chemocline. The majority of N2 fixers were related to Chlorobium tepidum/C. phaeobacteroides. By using Halogen In Situ Hybridization‐Secondary Ion Mass Spectroscopy (HISH‐SIMS), we could for the first time directly link Chlorobium to N2 fixation in the environment. Moreover, our results show that N2 fixation could partly compensate for the N loss and that both processes occur at the same locale at the same time as suggested for the ancient Ocean. 相似文献
3.
Gaston E. Small James B. Cotner Jacques C. Finlay Rebecca A. Stark Robert W. Sterner 《Hydrobiologia》2014,731(1):95-108
The capacity of a lake to remove reactive nitrogen (N) through denitrification has important implications both for the lake and for downstream ecosystems. In large oligotropic lakes such as Lake Superior, where nitrate (NO3 ?) concentrations have increased steadily over the past century, deep oxygen penetration into sediments may limit the denitrification rates. We tested the hypothesis that the position of the redox gradient in lake sediments affects denitrification by measuring net N-fluxes across the sediment–water interface for intact sediment cores collected across a range of sediment oxycline values from nearshore and offshore sites in Lake Superior, as well as sites in Lake Huron and Lake Erie. Across this redox gradient, as the thickness of the oxygenated sediment layer increased from Lake Erie to Lake Superior, fluxes of NH4 + and N2 out of the sediment decreased, and sediments shifted from a net sink to a net source of NO3 ?. Denitrification of NO3 ? from overlying water decreased with thickness of the oxygenated sediment layer. Our results indicate that, unlike sediments from Lake Erie and Lake Huron, Lake Superior sediments do not remove significant amounts of water column NO3 ? through denitrification, likely as a result of the thick oxygenated sediment layer. 相似文献
4.
Morgan Botrel Laura A. Bristow Mark A. Altabet Irene Gregory-Eaves Roxane Maranger 《Biogeochemistry》2017,135(3):221-237
Nitrate dual stable isotopes (δ15N and δ18O of NO3 ?) have proven to be a powerful technique to elucidate nitrogen (N) cycling pathways in aquatic systems. We applied this technique for the first time in the pelagic zone of a small temperate meso-eutrophic lake to identify the dominant N cycling pathways, and their spatial and temporal variability. We measured the lake NO3 ? δ15N and δ18O signatures over an annual cycle and compared them to that of the watershed. Both δ15N and δ18O of NO3 ? in the lake increased during summer relative to the inputs. Relationships between lake NO3 ? isotopic composition and concentrations were different across thermal strata with an apparent isotope effect in the epilimnion of 15εepi = 4.6‰ and 18εepi = 10.9‰. We found a strong deviation of the lake NO3 ? δ18O and δ15N from the expected 1:1 line for assimilation (slope = 1.73) suggesting that nitrification was co-occurring. We estimated that nitrification could support between 5 and 30% of nitrate-based production during the growing season, but was negligible in early spring and fall, and probably more dominant under ice. We showed that the technique is promising to study N processes at the ecosystem scale in shallow lakes, particularly during winter. Our results suggest that recycled NO3 ? could support primary productivity and influence phytoplankton composition in the surface waters of small lakes. 相似文献
5.
Primary production rates, chlorophyll and phytoplankton biovolume were measured monthly from April 2003 to November 2004 in
Lake Tana, a large tropical lake in the highlands of Ethiopia. The lake is characterised by low nutrient concentrations, and
a low water transparency due to high silt load of the inflowing rivers during the rainy seasons (May–November) and daily resuspension
of sediments in the inshore zone. The mean chlorophyll-a concentrations varied seasonally and ranged from 2.6 mg m−3 to 8.5 mg m−3 (mean: 4.5 mg m−3) in the offshore zone. Primary production was measured using the light–dark bottles technique. We incubated only at three
depths, i.e. 0.6, 1.2 and 1.8 m. Therefore, we may have missed a substantial part of the depth production profile and probably
also frequently missed P
max. Gross primary production in the openwater averaged 2.43 g O2 m−2 d−1 and ranged between 0.03 g O2 m−2 d−1 and 10.2 g O2 m−2 d−1; production was significantly higher in the inshore zone. The highest production rates were observed in the post-rainy season
(Oct–Nov), which coincided with a bloom of Microcystis and higher chlorophyll levels. This seasonal high production is probably caused by a relatively high nutrient availability
in combination with favourable light conditions. The gross primary production rates of L. Tana are among the lowest compared
with other tropical lakes. This will be partly the result of our underestimation of gross primary production by often missing
P
max. Another cause is the oligotrophic nature of the lake in combination with its relatively low water transparency. The gross
primary production per unit chlorophyll in the openwater zone was in the same range as in 30 other tropical lakes and reservoirs.
The higher primary production in the inshore zone is probably the result of the daily water column mixing (Z
mix ≥ Z
t) in this area, enhancing nutrient recycling. A large proportion of the annual primary production is realised in one of the
four seasons only. This productive post-rainy season is relatively short (2 months) and therefore efficiency of transfer of
matter between the first and second trophic level of the Lake ecosystem will be poor. 相似文献
6.
This study reports the primary production of phytoplankton determined with a 13C tracer, and their related variables, in Lake Kasumigaura, a shallow, hyper-eutrophic lake, and the second largest lake in Japan. Measurements were conducted monthly from August 1981 to December 2013 at four stations within the lake. Monitoring was a component of the Lake Kasumigaura Long-term Environmental Monitoring program, conducted by the National Institute for Environmental Studies (NIES) since 1977. The program collects data on water quality, and plankton and benthic communities. Lake Kasumigaura is registered as a core site of the Japan Long-term Ecological Research Network (JaLTER), which is a member of the International Long-term Ecological Research Network (ILTER). This dataset includes daily primary production (Pzd gC m?2 d?1) and the six parameters required to calculate Pzd: maximum photosynthesis rate (P max gC gC?1 h?1); light irradiance at the junction of the initial slope (α (gC gC?1 h?1) (μmol photon m?2 s?1)?1) and P max of the photosynthesis vs. irradiance (P vs. E) curve (E k μmol photon m?2 s?1); attenuation coefficient of photosynthetically available radiation (PAR) (K PAR m?1); water depth at each sampling station (Z b , m); dissolved inorganic carbon (DIC mgC L?1) and particulate organic carbon concentrations (POC gC m?3); and chlorophyll a amounts (Chl.a μg L?1). Daily primary production was calculated by obtaining a P vs. E curve over a short-term incubation (approximately 1 h) in a water tank using in situ water temperature in the laboratory, based on the field conditions of the sampling date. The dataset has been used for ecological studies as well as for management studies on water quality and ecosystems. This dataset is unique among the available published papers concerning lakes or primary production in various ecosystems, collected over a long period of time and freely available. 相似文献
7.
Ryuji Kondo Misa Kodera Yumi Mori Takahiko Okamura Shinya Yoshikawa Kaori Ohki 《Limnology》2014,15(1):77-83
The spatiotemporal distribution of chlorophyll pigments (chloropigments) in the water column of a meromictic lake, Lake Suigetsu (Fukui, Japan), was investigated. Water samples were collected from the central basin of Lake Suigetsu bimonthly between May 2008 and March 2010 at appropriate depths, including the oxic surface, oxic–anoxic interface, and anoxic bottom layers. Chlorophyll a, related to cyanobacteria and eukaryotic phytoplankton, was detected throughout the water column during the years of the study, whereas bacteriochlorophyll e, related to brown-colored green sulfur bacteria, was detected in the anoxic layers below the chemocline at a maximum concentration of 825 μg L?1. The concentration of bacteriochlorophyll e was generally maximal at or just below the chemocline of the lake. The cellular content of bacteriochlorophyll e was estimated to be low in the upper part of the chemocline and tended to increase with increasing water depth. Bacteriochlorophyll a, which was presumably related to purple sulfur bacteria, was only detected at the chemocline during summer and autumn at concentrations of 5.4–16.3 μg L?1. Our analysis of the chloropigment distribution for the two years of the study suggested that brown-colored green sulfur bacteria are the predominant phototroph in the anoxic layers of Lake Suigetsu, and that these play a significant role in the carbon and sulfur cycling of the lake, especially from spring to summer. 相似文献
8.
Lake Muhazi, a small lake of Rwanda (East Africa) was studied from 1986 to 1990. A dramatic decrease of the catch of Oreochromis niloticus (350 T y−1 in the fifties vs 30 T y−1 in 1982) suggested a loss of productivity or overfishing. In the same period, other ecological changes occurred: the submerged
macrophytes regressed and there was a decrease in Secchi depth (0.65 m in 1987 vs 1.5 m in the fifties). Compared to other lakes of the same area, the plankton production seemed low. The results of the present
study characterize lake Muhazi as a shallow lake with a rather unstable diurnal stratification and with slight differences
in mixing regime between its eastern, deepest part and its western, shallowest part. Secchi disk depth does not vary seasonally
to a large extent. The water has a rather high mineral content (conductivity of about 500 μS cm−1 at 25 °C) and low concentrations of dissolved N and P, except in the hypolimnion, where NH
inf4
sup+
-N can be high.
Two species, Microcystis aeruginosa and Ceratium hirundinella, account for most of the phytoplankton biomass, which is about 50–80 mg chlorophyll a m−2 in the euphotic zone, usually with little seasonal variation. Daily gross production estimates amount to about 6 to 9.5 g
O2 m−2 d−1 with a significant difference between the two parts of the lake. Data on C:N and C:P ratio in the phytoplankton suggest that
some N deficiency might occur in the eastern part. Moreover, the Zm:Zc ratio could also lead to rather low net production
rates (0.21–0.25 d−1 for a mixed layer of 4 m)
In conclusion, the primary production of lake Muhazi is medium for African lakes and the hypothesis that decreased planktonic
production could account for a reduced fish production should be discarded. Whereas the present yield of the fishery is only
20 kg ha−1 y−1, the yield estimated from primary production ranges between 46 and 64 kg ha−1 y−1. This could be reached through proper management. Finally, some hypotheses are given to explain the ecological changes which
occurred in the lake. 相似文献
9.
Carbon dynamics in an ultra-oligotrophic epishelf lake (Beaver Lake, Antarctica) in summer 总被引:2,自引:0,他引:2
JOHANNA LAYBOURN-PARRY NANETTE J. MADAN WILLIAM A. MARSHALL HARVEY J. MARCHANT SIMON W. WRIGHT 《Freshwater Biology》2006,51(6):1116-1130
1. Microbial plankton dynamics in an ultra‐oligotrophic epishelf lake (Beaver Lake, Antarctica) were investigated over an austral summer (December 2002 to January 2003). The aim was to characterise carbon cycling in an environmentally extreme lake. 2. The lake had an unusual temperature profile with peak temperatures of 1.3–1.9 °C between 20 and 25 m. Photosynthetically active radiation penetrated to the lake bottom (110 m) on occasions. The ice cover underwent marked thinning and melting during the study period. 3. Chlorophyll a concentrations were consistently low, usually below 1 μg L?1, with highest concentrations close to the lake bottom, where the photosynthetic elements showed strong autofluorescence. Mean photosynthetic nanoflagellates ranged between 34.9 × 104 L?1 ± 33.5 (23rd December) and 130.9 × 104 L?1 ± 112.3 (4th December). Highest photosynthetic activity was usually recorded below 25 m. Rates of carbon fixation varied between 0.089 μg C L?1 h?1 ± 0.002 and 0.579 μg C L?1 h?1 ± 0.156. Primary production was limited by low temperature and orthophosphate availability. 4. Mean bacterial concentration throughout the water column ranged between 9.3 × 107 L?1 ± 1.2 (23rd December) and 14.0 × 107 L?1 ± 1.8 (28th January). Bacterial production was low, less than 10% of primary production and ranged between 2.1 ng C L?1 h?1 ± 0.8 and 12 ng C L?1 h?1 ± 0.9. Highest rates coincided with times of highest primary production. On occasion dissolved organic carbon (DOC) concentrations dropped to 20 μg L?1, probably below accurate limits of detection, suggesting that carbon substratum and phosphorus may have limited bacterial growth. 5. Heterotrophic nanoflagellates varied significantly over the summer from a mean of 26.6 × 104 L?1 ± 14.2 (23rd December) to 133.8 × 104 L?1 ± 33.5 (14th December). They imposed a significant grazing impact on the bacterioplankton, removing in excess of 100% of bacterial production in December. 6. The total organic carbon pool [DOC and particulate organic carbon (POC)] was below 600 μg L?1. The ratio of DOC : POC ranged between 0.44 : 1 and 2.8 : 1 in the upper 40 m of the water column, and 1.8 : 1 and 3.7 : 1 in the lower waters. The microbial plankton contributed 1–29% of POC, thus detrital POC made up the largest fraction of the POC pool. 7. Beaver Lake is an extreme lacustrine ecosystem where heterotrophic processes occasionally appear to be carbon limited. Significant summer ice‐melt, not seen in a previous opportunistic sampling, may be having an impact on the carbon cycle. 相似文献
10.
Seasonal dynamics of picophytoplankton in Lake Kinneret, Israel 总被引:1,自引:0,他引:1
1. Picophytoplankton (picocyanobacteria and picoeukaryotes) communities in Lake Kinneret were studied from 1988 to 1992. No prochlorophytes were observed in the lake. 2. Picocyanobacteria were a prominent and ubiquitous component of the phytoplankton, being present at all depths throughout the year, with concentrations ranging from 2 ± 10–8 ± 105 cells ml?1. Low cell numbers in winter and spring were followed at the end of the annual dinoflagellate bloom by maximal abundances in summer-autumn in the epilimnion. High cell numbers (> 104 cells ml?1) were sometimes also found in the anaerobic hypolimnion. Net growth rates for picocyanobacteria ranged from 0.29 to 0.60 divisions day?1. 3. Picoeukaryotes were a very minor constituent of the picoplankton, mostly present in winter and spring, and sometimes at the end of autumn, with concentrations ranging from 44 to 5700 cells ml?1. Higher cell numbers tended to occur in the near surface water layers. In August-September, picoeukaryotes were found only in the hypolimnion. In December, the occurrence of picoeukaryotes in the deep water layers probably resulted from advection with cold water currents from the Jordan river. Net growth rates for picoeukaryotes ranged from 0.26 to 0.43 divisions day?1. 4. Overall, the contribution of picophytoplankton to the phytoplankton standing crop in Lake Kinneret was limited; picocyanobacteria and picoeukaryotes accounted for no more than 7.0 and 0.1% of total algal biomass (semiannual average), respectively. 5. Picophytoplankton cell numbers in pelagic waters were usually similar to those in shallower lake stations. 6. Picocyanobacteria appear to be an autochthonous population, whereas picoeukaryotes are probably brought annually by the Jordan River and do not maintain themselves in the lake. 相似文献
11.
SAIRAH Y. MALKIN SERGHEI A. BOCANIOV RALPH E. SMITH STEPHANIE J. GUILDFORD ROBERT E. HECKY 《Freshwater Biology》2010,55(12):2468-2483
1. Despite the recognition of its importance, benthic primary production is seldom reported, especially for large lakes. We measured in situ benthic net primary production by monitoring flux in dissolved inorganic carbon (DIC) concentration in benthic incubation chambers, based on continuous measurements of CO2(aq) flux, alkalinity, and the temperature‐dependent dissociation constants of carbonic acid (K1 and K2). This methodology has the advantages of monitoring net primary production directly as change in carbon, maintaining continuous water recirculation, and having sufficient precision to detect change in DIC over short (i.e. 15 min) incubations, even in alkaline waters. 2. Benthic primary production on Cladophora‐dominated rocky substrata in western Lake Ontario was measured biweekly. Maximum biomass‐specific net photosynthetic rates were highest in the spring (2.39 mgC g Dry Mass?1 h?1), decreased to negative rates by early summer (?0.76 mgC g DM?1 h?1), and exhibited a regrowth in late summer (1.98 mgC g DM?1 h?1). 3. A Cladophora growth model (CGM), previously validated to predict Cladophora biomass accrual in Lake Ontario, successfully simulated the seasonality and magnitude of biomass‐specific primary production during the first cohort of Cladophora growth. Averaged over this growing season (May–Aug), mean areal net benthic production at the estimated depth of peak biomass (2 m) was 405 mg C m?2 d?1. 4. We measured planktonic primary production in proximity to the benthic study and constructed a depth‐resolved model of planktonic production. Using the CGM, benthic primary production was compared with planktonic primary production for the period May–Aug. Net benthic production from the shoreline to the 12 m contour (1–2 km offshore) equalled planktonic production. Closer to shore, benthic primary production exceeded planktonic primary production. Failure to account for benthic primary production, at least during abundant Cladophora growth, will lead to large underestimates in carbon and nutrient flows in the nearshore zone of this Great Lake. 相似文献
12.
The importance of isoetids for the exchange of dissolved inorganic nitrogen (DIN) between sediment and water was studied in shallow Lake Kvie, Denmark. Vegetated sediments from the littoral zone (55% of lake area) were compared to unvegetated sediments from the littoral and profundal zone. Clear effects of the isoetids were found on DIN in the porewater. At the vegetated station, NH4
+ showed the highest concentrations just below the surface (< 40 µM) whereas NO3
- was dominating below 5 cm depth with concentrations up to 100 µM during the spring. The unvegetated littoral sediment showed a distinct change between winter where NH4
+ dominated and summer where NO3
- was most abundant. NH4
+ dominated in the profundal sediment and showed increasing concentration with depth. The Eh was high (> 400 mV) in the vegetated sediment, indicating isoetid release of O2 in the rhizosphere. A low DIN uptake was observed at the vegetated station while, based on porewater data, a diffusive release from the sediment was expected. This difference was due to plant assimilation. In general a release of NH4
+ and an uptake of NO3
- was seen in all sediments. The denitrification rate calculated from the mass balance for the entire lake was 0.4 mmol m - 2 d-1 and accounted for removal of 77% of the annual N-input to Lake Kvie. 相似文献
13.
SUMMARY. Surveys of the physico-chemical status of the River Zambezi in Moçambique were conducted between April 1973 and May 1974, to characterize the river prior to the closure of the Cabora Bassa Dam and to provide baseline data from which future changes in the river ecosystem can be followed. The temperature of the river water increases by about 3°C from Lake Kariba to the sea, and with an average pH of 7.8 the water is slightly more alkaline than Kariba Dam water. The river is well oxygenated with no sign of hydrogen sulphide. Transparency is generally very low and changes are mainly determined by the floods of local tributaries. The overall average total alkalinity is 55 mg 1?1 CaCO3, with no regular seasonal variation, average concentrations of chloride and sulphate are respectively, 5.4 mg 1?1 Cl? and 5.3 mg 1?1 SO2-4. They increase under both the influence of the ionically rich Shire River and the sea; the latter due to vertical mixing. Total hardness and calcium hardness behave in a similar way, while conductivity and silica concentrations increase slightly until the Zambezi—Shire confluence, at which point, conductivity increases by 25% to an average peak value of 153 μS cm?1, and silica decreases by 15% to a minimum average value of 15.5 mg 1?1 SiO2. Ammonia and nitrate concentrations show a clear seasonal variation, with respectively, minimum dry season and maximum wet season average values of about 0.05 mg 1?1 and 0.3 mg 1?1. The overall average concentration of nitrite is 0.004 mg 1?1. Orthophosphate in the river is mostly affected by Lake Kariba, though other sources are also of some importance. Maximum average concentrations of about 0.4 mg 1?1 PO3-4 were recorded during the dry season after the overturn of Lake Kariba. The concentration of dissolved metals is mainly determined by the outflow of Kariba and by the Shire River, with only K and Mg apparently affected by the outflow from Lake Kafue. It is concluded that the water quality of the Middle Zambezi is mainly determined by the Kariba Dam, with the Kafue Dam playing a minor role. At the time of the pre-impoundment survey, the main impact on water quality of the Lower Zambezi came from the Shire River. With the addition of yet another large reservoir on the Zambezi, in the form of Cabora Bassa, together with the appreciable effect of tributary rivers on the lake, and the likely increased impact of the Shire River on the now more regulated river, the quality of the Lower Zambezi is expected to alter considerably, with concomitant ecological changes. 相似文献
14.
Trophic status of Tilitso,a high altitude Himalayan lake 总被引:1,自引:1,他引:0
Morihiro Aizaki Akira Terashima Hiroyuki Nakahara Takayuki Nishio Yuzaburo Ishida 《Hydrobiologia》1987,153(3):217-224
The trophic status and water quality of Lake Tilitso (4920 m above sea level) in a high altitude region in central Nepal were
surveyed in September, 1984. The lake is rather large with a maximum depth of 95 m and a surface area of 10.2 km2. The lake water was turbid due to glacier silt and the euphotic layer was only 5 m deep. The nutrient concentration was very
low with total phosphorus concentration 1–6 μg l−1, and DTN concentration 0.10–0.22 mg l−1. The phytoplankton biomass and chlorophyll-a concentration were also low. Primary production was estimated to be about 12
mg C m−2 d−1. The concentrations of particulate matter and most cations and bacterial number were higher in the epilimnion than in the
hypolimnion. The trophic status of this lake was estimated as ultraoligotrophic. 相似文献
15.
Nutrient cycling and productivity in a desert saline lake: observations from a dry,low-productivity year 总被引:2,自引:1,他引:1
Martin E. Lebo John E. Reuter Cathryn L. Rhodes Charles R. Goldman 《Hydrobiologia》1992,246(3):213-229
Seasonal variability of nutrients and productivity were examined in Pyramid Lake, a hyposaline, N-deficient, terminal desert lake, during a dry period. River inflow and N-fixation during 1990 were minimal allowing internal nutrient cycling to be more closely studied. Nutrient cycling was strongly affected by seasonal thermal stratification that was typical for a warm monomictic lake. Concentrations of nitrate, phosphate, and silicate in surface waters were highest during winter mixing and decreased rapidly in the spring due to a diatom bloom. Maximum average chlorophyll concentration in surface waters was 2.7 ± 1.2 µg 1–1 and occurred in April while surface nutrients were being depleted. In contrast to chlorophyll, maximum particulate carbon in surface waters occurred in July–August when areal productivity was highest (367–398 mg C m–2 day–1). Concurrent with spring nutrient depletion in surface waters was increasing N-deficiency in the plankton. After the spring bloom dissipated in May, particulate matter (POM) became increasingly N-deficient reaching maximum elemental C : N of > 18 during summer-fall. Profiles of the C : N ratio of POM were nearly constant with depth for individual sampling dates suggesting that the residence time of POM in the water column was short (< 1 month). While surface waters were nutrient depleted during summer stratification, nutrient concentrations of bottom waters progressively increased, presumably through the oxidation of POM sinking to the bottom (103 m). Converting the rate of oxygen depletion in bottom waters to carbon equivalents of POM suggests that 42 % of mean annual phytoplankton production in overlying waters during 1990 was mineralized in bottom waters. 相似文献
16.
《African Journal of Aquatic Science》2013,38(2):165-173
The phytoplankton community and cyanotoxins in Lake Chivero (formerly Lake McIlwaine) and the presence of cyanotoxins in treated drinking water were investigated between 2003 and 2004. A typical seasonal succession of Cyanobacteria species occurred from January to April, Bacillariophyta from May to July, and Cryptophyta and Chlorophyta from August to December. Microcystis aeruginosa and M. wesenbergii, known producers of the toxin microcystin, and the non-toxic cyanobacterium M. novacekii dominated during summer. The highest concentrations of microcystins and lipopolysaccharide endotoxins occurred when cyanobacterial biomass was highest. Lipopolysaccharide endotoxin concentrations in the lake ranged between 8 and 3 200 Endotoxin Units (EU) ml?1. Microcystin concentrations in treated water were below the recommended safe limit for drinking water. Lipopolysaccharide endotoxin concentrations in treated water ranged from 0.15 to 11 EU ml?1. The phytoplankton community comprised non-microcystin-producing species for the greater part of the study period. 相似文献
17.
Ji-Hyung Park Myron J. Mitchell Patrick J. McHale Sheila F. Christopher Tilden P. Meyers† 《Global Change Biology》2003,9(11):1602-1619
Biogeochemical responses to changing climate and atmospheric deposition were investigated using nitrogen (N) and sulfur (S) mass balances, including dry deposition and organic solutes in the Arbutus Lake watershed in the Adirondack Mountains, New York State. Long‐term monitoring of wet‐only precipitation (NADP/NTN, 1983–2001) and dry deposition (AIRMoN, 1990–2001) at sites adjacent to the watershed showed that concentrations of SO42? in precipitation, SO42? in particles,and SO2 vapor all declined substantially (P<0.005) in contrast to no marked temporal changes observed for most N constituents (NH4+ in precipitation, HNO3 vapor, and particulate NO3?), except for NO3? in precipitation, which showed a small decrease in the late 1990s. From 1983 to 2001, concentrations of SO42? in the lake outlet significantly decreased (?2.1 μeq L?1 yr?1, P<0.0001), whereas NO3? and dissolved organic N (DON) concentrations showed no consistent temporal trends. With the inclusion of dry deposition and DON fluxes into the mass balance, the retained portion of atmospheric N inputs within the main subcatchment increased from 37% to 60%. Sulfur outputs greatly exceeded inputs even with the inclusion of dry S deposition, while organic S flux represented another source of S output, implying substantial internal S sources. A significant relationship between the annual mean concentrations of SO42? in lake discharge and wet deposition over the last two decades (r=0.64, P<0.01) suggested a considerable influence of declining S deposition on surface water SO42? concentrations, despite substantial internal S sources. By contrast, interannual variations in both NO3? concentrations and fluxes in lake discharge were significantly related to year‐to‐year changes in air temperature and runoff. Snowmelt responses to winter temperature fluctuations were crucial in explaining large portions of interannual variations in watershed NO3? export during the months preceding spring snowmelt (especially, January–March). Distinctive response patterns of monthly mean concentrations of NO3? and DON in the major lake inlet to seasonal changes in air temperature also suggested climatic regulation of seasonal patterns in watershed release of both N forms. The sensitive response of N drainage losses to climatic variability might explain the synchronous patterns of decadal variations in watershed NO3? export across the northeastern USA. 相似文献
18.
Investigation was made of the primary productivity of Lake Yunoko. The concentrations of PO4-P and NH3-N were highest in summer. The total amount of chlorophylla in the entire water column varied from 45 mg/m2 to 405 mg/m2 during the year with the maximum values occurring in late spring and in December. These values are very high compared with
those reported for other lakes in the same district. The standing crop of phytoplankton as organic carbon was approximately
50∼70% of the total particulate organic carbon in the lake with values as high as 80∼90% being obtained in the spring and
autumn. The rate of phytosynthesis under saturated light conditions was 3.7 mg C/mg chla/hr in the case of phytoplankton of the sun type and 1.2∼1.6 mg C/mg chla/hr in those of the shade type. The daily gross primary production in the lake varied from a low of 134 mg C/m2 to a high of 1,003 mg C/m2 during the year, the mean value being 372 mg C/m2. The total amount of daily microbial respiration varied from 177 mg C/m2 in winter to 1,476 mg C/m2 in summer. Thus, the daily balance of production and consumption of organic matter in the lake itself was concluded to be
negative. The main factor contributing to the rectification of this imbalance of material budget seems to be the leaf litter
coming from the forest surrounding the lake. In conclusion, Lake Yunoko is a very productive and at the same time, fairly
heterotrophic lake.
Special Project Research supported by the Ministry of Education on Dynamic State of Biosphere. This study was carried out
as part of JIBP-PF. 相似文献
19.
Ronnie Nøhr Glud Michael Kühl Oliver Kohls Niels Birger Ramsing 《Journal of phycology》1999,35(2):270-279
By applying planar optodes and imaging techniques to a benthic photosynthetic mat, we demonstrated an extensive vertical and horizontal variation in O2 concentrations, O2 consumption, and O2 production. In light, the oxic zone could be divided into three horizons: 1) an upper zone dominated by diatoms that had a moderate net O2 production, 2) another zone dominated by Microcoleus-like cyanobacteria with a high net O2 production, and 3) a lower zone with disintegrating microalgae and cyanobacteria with a high O2 consumption rate. From the O2 images, the net O2 production/consumption was calculated at a spatial resolution of 130 μM. This allowed us to identify microsites with high rates of O2 turnover within the photic zone. Sites with high net O2 consumption (>1.5 nmol·cm?3·s?1) were typically situated next to sites with a relatively high net production (>2 nmol·cm?3·s?1), revealing a mosaic in which the highest O2 consumption sites were surrounded by the highest O2 production sites. This suggested a tight spatial coupling between production and consumption of O2 within the photic zone. Light stimulated the O2 consumption within the photic zone. At irradiances above 400 μmol photons·m?2·s?1, the stimulated O2 production was almost completely balanced by enhanced O2 consumption at microsites exhibiting net consumption of O2 even at maximum irradiance (578 μmol photons·m?2·s?1). Our observations strongly supported the idea that light-stimulated respiration was caused by stimulated heterotrophic activity fueled by organic carbon leakage from the phototrophs. Despite microsites with high net O2 consumption, anoxic microniches were not encountered in the investigated mat. Images of gross photosynthetic rates also revealed an extensive horizontal variation in gross rates, with microsites of low or no photosynthesis within the otherwise photic zone. Calculations based on the obtained images revealed that at maximum light (578 μmol photons·m?2·s?1), 90% of the O2 produced was consumed within the photic zone. The presented data demonstrate the great potential offered by planar optode for studies of benthic photosynthetic communities. 相似文献
20.
Winter limnology: a comparison of physical,chemical and biological characteristics in two temperate lakes during ice cover 总被引:3,自引:3,他引:0
The winter dynamics of several chemical, physical, and biological variables of a shallow, polymictic lake (Opinicon) are compared
to those of a deep, nearby dimictic lake (Upper Rock) during ice cover (January to early April) in 1990 and 1991. Both lakes
were weakly inversely thermally stratified. Dissolved oxygen concentration was at saturation (11–15 mg l−1) in the top 3 m layer, but declined to near anoxic levels near the sediments. Dissolved oxygen concentrations in the deep
lake were at saturation in most of the water column and approached anoxic levels near the sediments only. Nutrient concentrations
in both lakes were fairly high, and similar in both lakes during ice cover. Total phosphorus concentrations generally ranged
between 10–20 μg l−1, NH4-N between 16–100 μg l−1, and DSi between 0.9–1.9 mg l−1; these concentrations fell within summer ranges. NO3-N concentrations were between 51–135 μg l−1 during ice cover, but occurred at trace concentrations (<0.002 μg l−1) during the summer. The winter phytoplankton community of both lakes was dominated by flagellates (cryptophytes, chrysophytes)
and occasionally diatoms. Dinoflagellates, Cyanobacteria and green algae were poorly represented. Cryptophytes often occurred
in fairly high proportions (20–80%) throughout the water column, whereas chrysophytes were more abundant just beneath the
ice. Zooplankton population densities were extremely low during ice cover (compared to maximum densities measured in spring
or summer) in both lakes, and were comprised largely of copepods. 相似文献