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1.
Phosphorus sedimentation in four natural and four artificial Iowa lakes was measured by using sediment traps to determine if sedimentary phosphorus losses were greater in artificial lakes than in natural lakes and the limnological factors influencing phosphorus loss rates. Mean phosphorus sedimentation rates ranged from 13.3 to 218 mg · m–2 day–1. Although phosphorus sedimentation rates for the natural lakes as a group did not differ significantly from the rates for artificial lakes, there were significant differences among individual lakes. Phosphorus sedimentation rates also varied significantly during different seasons at different locations within a lake and at different depths within a location. Despite the variance, phosphorus sedimentation rates were strongly correlated with inorganic sediment concentrations and inorganic matter sedimentation rates, thus suggesting that inorganic sediments influence phosphorus sedimentation rates. When Iowa data were combined with data from published studies, mean sedimentation rates were directly correlated with mean chlorophyll a concentrations of the lakes. These data strongly suggest that sedimentation rates as measured by sediment traps are strongly influenced by the trophic status of a lake. Though sedimentation rates were higher in the more productive lakes, it is suggested that these rates represent only gross sedimentation rates rather than net sedimentation rates because of resuspension and resedimentation of bottom sediments. 相似文献
2.
The neutralization of acidic coal mine lakes by additions of natural organic matter: a mesocosm test
Cylindrical polyethylene enclosures 3 m in length and 1 m in diameter reaching from the surface to the bottom were constructed in an acid (pH=3.1) lake on a coal surface mine in southern Illinois. Wheat straw was added to the enclosures to test the effects of dissimilatory sulfate reduction on water chemistry. Added straw increased sulfide concentrations, raised pH to 6.5, reduced O2 and increased acid neutralizing capacity of the enclosed water columns when compared with a control enclosure and with the open lake. Generation of acid neutralizing capacity exceeded the standing stock of sulfide indicating that sulfide was removed either by precipitation of FeS or outgassing of H2S. The pH and acid neutralizing capacity within the enclosures eventually returned to the level of the surrounding lake because of water exchange around the enclosure walls. Our results show that additions of organic matter to acid surface mine lakes result in the generation of acid neutralizing capacity. 相似文献
3.
The movement of sediment between the lake bottom and water column of shallow lakes can be sizeable due to the large potential
for resuspension in these systems. Resuspended sediments have been shown to alter phytoplankton community composition and
elevate water column production and nutrient concentrations. We measured the summer sedimentation rates of two lakes in 2003
and six lakes in 2004. All lakes were shallow and located in the Alaskan Arctic. In 2004, turbidity, light attenuation, total
sediment:chlorophyll a mass in the sediment traps, and thermal stratification were also measured in each of the lakes. The sediment:chlorophyll
a mass was much greater than if the sediment was derived from phytoplankton production in all of the lakes, indicating that
the source of the sedimenting material was resuspension and allochthonous inputs. Consistent with these findings, the temporal
variation in sedimentation rate was synchronous between most lakes, and sedimentation rate was positively related to wind
speed and rainfall suggesting that sedimentation rate was strongly influenced by landscape-scale factors (e.g., wind and rain
events). Two of the lakes are located on deposits of loess that accumulated during past glacial periods. These two lakes had
sedimentation rates that were significantly greater and more variable than any of the other lakes in the study, as well as
high turbidity and light attenuation. Our results indicate that sedimentation in these shallow arctic lakes is supported primarily
by allochthonous inputs and resuspension and that landscape-scale factors (e.g., weather and geology) impact on the transport
of materials between the lake bottom and water column.
Handling editor: J. Saros 相似文献
4.
A model to predict gross sedimentation in small glacial lakes 总被引:2,自引:2,他引:0
Lars Håkanson 《Hydrobiologia》1994,284(1):19-42
This study is an attempt to quantify and rank variables of significance to predict gross sedimentation (i.e., net sedimentation plus resuspension) in small glacial lakes. Sediment traps were placed in 25 Swedish lakes and exposed for about 110 days during the summer for four years. Average values of rates of gross sedimentation in bottom traps were compared to catchment and morphometric parameters determined from different types of maps. Various hypotheses concerning the factors regulating gross sedimentation in lakes were formulated and tested. Different statistical tests were used to separate random influences from causal influences. The most important 'map parameters' were: the relative depth, linked to resuspension and the form and size of lakes, the forest and open land percent of the so-called near area (= the proximate area of the lake as determined by the drainage area zonation method), the distribution of mires and lakes in the catchment, the relief of the drainage area and the theoretical lake water retention time. Each of these variables only provides a limited degree of (statistical) explanation of the variability in gross sedimentation among the lakes. The predictability of models for gross sedimentation can be markedly improved by accounting for the zonation problem, i.e., the distribution of the characteristics in the drainage area. The stability of the final model, which gives a r
2-value of 0.78, has been tested with positive results. The model allows mean values of gross sedimentation to be estimated from readily available data of geological characteristics of the lake and its drainage area. The variability in gross sedimentation from other factors/variables, such as temperature, precipitation, wind, and load of nutrients, may then be quantitatively differentiated from the impact of these geological factors/constants. 相似文献
5.
Gesa A. Weyhenmeyer Pirkko Kortelainen Sebastian Sobek Roger Müller Miitta Rantakari 《Ecosystems》2012,15(8):1295-1307
The quantity of carbon dioxide (CO2) emissions from inland waters into the atmosphere varies, depending on spatial and temporal variations in the partial pressure of CO2 (pCO2) in waters. Using 22,664 water samples from 851 boreal lakes and 64 boreal streams, taken from different water depths and during different months we found large spatial and temporal variations in pCO2, ranging from below atmospheric equilibrium to values greater than 20,000???atm with a median value of 1048???atm for lakes (n?=?11,538 samples) and 1176???atm for streams (n?=?11,126). During the spring water mixing period in April/May, distributions of pCO2 were not significantly different between stream and lake ecosystems (P?>?0.05), suggesting that pCO2 in spring is determined by processes that are common to lakes and streams. During other seasons of the year, however, pCO2 differed significantly between lake and stream ecosystems (P?<?0.0001). The variable that best explained the differences in seasonal pCO2 variations between lakes and streams was the temperature difference between bottom and surface waters. Even small temperature differences resulted in a decline of pCO2 in lake surface waters. Minimum pCO2 values in lake surface waters were reached in July. Towards autumn pCO2 strongly increased again in lake surface waters reaching values close to the ones found in stream surface waters. Although pCO2 strongly increased in the upper water column towards autumn, pCO2 in lake bottom waters still exceeded the pCO2 in surface waters of lakes and streams. We conclude that throughout the year CO2 is concentrated in bottom waters of boreal lakes, although these lakes are typically shallow with short water retention times. Highly varying amounts of this CO2 reaches surface waters and evades to the atmosphere. Our findings have important implications for up-scaling CO2 fluxes from single lake and stream measurements to regional and global annual fluxes. 相似文献
6.
Morphometry and sedimentation as regulating factors for nutrient recycling and trophic state in coastal waters 总被引:1,自引:1,他引:0
The aim of this work is to quantify the importance of morphometry and sedimentation/resuspension on nutrient recycling and trophic characteristics in coastal waters. Extensive field work has been carried out in 23 coastal areas in the Swedish and Finnish part of the Baltic Proper. Sediment traps were deployed for two one-week periods in all areas. On average, 56% of the total sedimentation in sediment traps 3 m below the water surface (SedS) and 62% of the total sedimentation on sediment traps 1 m above the bottom (SedB) was resuspended material. Coastal morphometric parameters, surface water retention time and bottom dynamic conditions were determined for all areas. There is a marked relationship between SedS and inorganic-N concentration in the surface water. The relationship was improved significantly by using sedimentation of the resuspended fraction at 3 m water depth (SedR) instead of SedS.This led to the hypothesis that increased concentration of inorganic nitrogen in the surface water results from increased mineralisation of resuspended organic particles. A model describing SedS is presented where inorganic nitrogen concentration, the water surface area and the surface water retention time can explain 82% of the variation in SedS. In another model inorganic nitrogen and water surface area can explain as much as 93% of the variation in SedR.These results emphasise the importance of resuspension for nutrient recycling and trophic state in coastal waters. The importance of coastal morphometry and surface water retention time on total sedimentation and nutrient recycling makes it possible to classify coastal areas in terms of potential nutrient recycling capacity/trophic state from these simple sensitivity parameters. 相似文献
7.
ABSTRACT
We tested whether pelagic light and nutrient availability, metabolism, organic pools and CO2-supersaturation were related to lake size and surrounding forest cover in late summer–autumn measurements among 64 small
(0.02–20 ha), shallow seepage lakes located in nutrient-rich, calcareous moraine soils in North Zealand, Denmark. We found
a strong implicit scaling to lake size as light availability increased significantly with lake size while nutrient availability,
phytoplankton biomass and dissolved organic matter declined. Forest lakes had significantly stronger net heterotrophic traits
than open lakes as higher values were observed for light attenuation above and in the water, dissolved organic matter, pelagic
community respiration (R) relative to maximum gross primary production (R/GPP) and CO2-supersaturation. Total-phosphorus was the main predictor of phytoplankton biomass (Chl) despite a much weaker relationship
than observed in previous studies of larger lakes. Maximum gross primary production increased with algal biomass and decreased
with dissolved organic matter, whereas community respiration increased with dissolved organic matter and particularly with
gross primary production. These results suggest that exogenous organic matter supplements primary production as an energy
source to heterotrophs in these small lakes, and particularly so in forest lakes experiencing substantial shading from the
forest and dissolved humic material. This suggestion is supported by 20–30-fold CO2 supersaturation in the surface water of the smallest forest lakes and more than sixfold supersaturation in 75% of all measurements
making these lakes among the most supersaturated temperate lakes examined so far. 相似文献
8.
Andreas C. Bryhn 《Hydrobiologia》2009,636(1):413-419
Many general mass-balance models that simulate processes in one or two water layers have been successfully constructed, tested
and used to predict effects from remediating lake pollution and other environmental disturbances. However, these models are
poorly suited for meromictic lakes which consist of yet another water layer. In order to determine a cross-systems based algorithm
for the depth of the boundary between the two lowest layers (D
crit2; in m), data from 24 three-layer lakes were analysed, and this depth could be predicted from the maximum depth and the lake
surface area. The resulting model was tested with good results against independent data from 6 lakes which were not used for
model development. Furthermore, D
crit2 was predicted at a considerably lower depth than the theoretical wave base (a previously defined functional separator between
the two top layers) in 110 out of 113 meromictic lakes. This indicates that the equation for D
crit2 estimated in this study may be used for developing general mass-balance models for a large number of lakes which contain
three stable water layers. 相似文献
9.
Sedimentation in Boreal Lakes—The Role of Flocculation of Allochthonous Dissolved Organic Matter in the Water Column 总被引:1,自引:0,他引:1
We quantified sedimentation of organic carbon in 12 Swedish small boreal lakes (<0.48 km2), which ranged in dissolved organic carbon (DOC) from 4.4 to 21.4 mg C l−1. Stable isotope analysis suggests that most of the settling organic matter is of allochthonous origin. Annual sedimentation
of allochthonous matter per m2 lake area was correlated to DOC concentration in the water (R
2 = 0.41), and the relationship was improved when sedimentation data were normalized to water depth (R
2 = 0.58). The net efflux of C as CO2 from the water to the atmosphere was likewise correlated to DOC concentration (R
2 = 0.52). The losses of organic carbon from the water column via mineralization to CO2 and via sedimentation were approximately of equal importance throughout the year. Our results imply that DOC is a precursor
of the settling matter, resulting in an important pathway in the carbon cycle of boreal lakes. Thus, flocculation of DOC of
terrestrial origin and subsequent sedimentation could lead to carbon sequestration by burial in lake sediments. 相似文献
10.
A review of methods used to measure sediment resuspension 总被引:7,自引:6,他引:7
Jürg Bloesch 《Hydrobiologia》1994,284(1):13-18
Resuspension of bottom sediments is an important lake-internal process with regard to particle cycling and sedimentation. Current methods to measure sediment resuspension are reviewed, such as optical and acoustical instruments, instantaneous multiple point water samplers, sediment traps, sediment cores and grabs, radiotracers such as Pb210, Cs137 and Be7, mass balance calculations, various modelling approaches, statistical methods (correlation analysis), and laboratory experiments.For the quantification of resuspension, the combined use of sediment traps, sediment cores, near bottom current meters, and turbidity meters to measure suspended and settling particulate matter in the hypolimnion of lakes is recommended; in addition, wind stress, seiches, slumping and sliding, and riverine input may be monitored to elucidate the mechanisms behind the process. 相似文献
11.
C. A. Kelly J. A. Amaral M. A. Turner J. W. M. Rudd D. W. Schindler M. P. Stainton 《Biogeochemistry》1995,28(2):115-130
Experimental acidification of a softwater lake to below pH 5 fundamentally changed the sulfur cycle and lowered internal alkalinity generation (IAG). Prior to reaching pH 4.5, the balance of sulfur reduction and oxidation reactions within the lake was in favour of reduction, and the lake was a net sink for sulfate. In the four years at pH 4.5 the balance of reduction and oxidation reactions was in favour of oxidation, and there was a net production of sulfate (SO4
2–) within the lake. Evidence indicating a decrease in net SO4
2– reduction at pH 4.5 was also obtained in an anthropogenically acidified lake that had been acidified for many decades. In both lakes, the decrease in net SO4
2– reduction appeared to be linked not to a simple inhibition of SO4
2– reduction but rather to changes in benthic ecosystem structure, especially the development of metaphytic filamentous green algae, which altered the balance between SO4
2– reduction and sulfur oxidation.At pH's above 4.5, net SO4
2– reduction was the major contributor to IAG in the experimental lake, as it is in many previously studied lakes at pH 5 and above. At pH 4.5, the change in net annual SO4
2– reduction (a decrease of 110%) resulted in a 38% decrease in total IAG. Because of the important role of net SO4
2– reduction in acid neutralization in softwater lakes, models for predicting acidification and recovery of lakes may need to be modified for lakes acidified to pH <5. 相似文献
12.
We compared terrestrial net primary production (NPP) and terrestrial export of dissolved organic carbon (DOC) with lake water
heterotrophic bacterial activity in 12 headwater lake catchments along an altitude gradient in subarctic Sweden. Modelled
NPP declined strongly with altitude and annual air temperature decreases along the altitude gradient (6°C between the warmest
and the coldest catchment). Estimated terrestrial DOC export to the lakes was closely correlated to NPP. Heterotrophic bacterial
production (BP) and respiration (BR) were mainly based on terrestrial organic carbon and strongly correlated with the terrestrial
DOC export. Excess respiration over PP of the pelagic system was similar to net emission of CO2 in the lakes. BR and CO2 emission made up considerably higher shares of the terrestrial DOC input in warm lakes than in cold lakes, implying that
respiration and the degree of net heterotrophy in the lakes were dependant not only on terrestrial export of DOC, but also
on characteristics in the lakes which changed along the gradient and affected the bacterial metabolization of allochthonous
DOC. The study showed close links between terrestrial primary production, terrestrial DOC export and bacterial activity in
lakes and how these relationships were dependant on air temperature. Increases in air temperature in high latitude unproductive
systems might have considerable consequences for lake water productivity and release of CO2 to the atmosphere, which are ultimately determined by terrestrial primary production. 相似文献
13.
The small strongly stratified hard-water hypertrophic lake Verevi (max. depth 11.0 m, surface area 12.6 ha, mean depth 3.6 m) was investigated in 2000 and in 2001. The lake is sheltered from winds, and the role of waves in mixing the water column is minimal. Eutrophication favours the strengthening of stratification. Early warm springs cause a fast stagnation of the water column forming partly meromictic conditions. Seston content of water and in sediment traps in 3 layers was measured several times during the formation of stratification. Besides measuring particulate matter, in 2001, the nutrient content of the trapped sediment was analysed. During the first 7 days of the investigation, 30% of the total particle sedimentation took place. The sedimentation rate of particulate matter was 0.4–6.3 g m–2 d−1 dry weight in different layers of the water column. Daily average sedimentation loss rate was 27% of the total amount of seston of the epilimnion, whilst from the meta- and hypolimnion the settling was much slower (9.6 and 7.3%, respectively). In our experiments with twin sediment traps, to one of which formaldehyde was added, the PO43−-P concentration was 19% smaller in the trap without formaldehyde, probably due to planktonic uptake. The relationship between primary and export production is loop-like. The shape was irregular, indicating a high grazing rate of zooplankton. 相似文献
14.
Seasonal patterns of mercury species in water and plankton from softwater lakes in Northeastern Minnesota 总被引:2,自引:0,他引:2
Twelve softwater lakes in NE Minnesota were sampled in spring, summer, and fall of 1992 and 1993 for labile (unextracted) methyl-Hg, total (extracted) methyl-Hg, and total Hg in lake water and net plankton (300 µm). The lakes are small (5.6–56 ha), low productivity, headwater drainage or seepage lakes. They are acid-sensitive (ANC 200 µeq/L) but not low pH lakes (average pH 6.6). The lakes ranged in color from 8.5 to 70 PCU. Statistical analysis of the water chemistry variables and mercury species support the conclusion that these were a homogeneous set of lakes; therefore, seasonality of mercury forms was analyzed on combined (mean) data from the 12 lakes. Methyl-Hg in water declined throughout the growing season. HgT also declined sharply from spring to summer but increased again in the fall. In contrast to the methyl-Hg and Hg in water, concentrations in plankton were at the lowest levels in spring and rose to higher levels in summer. The mass of mercury in plankton increased from spring to fall, as did the methyl-Hg fraction, which increased from 20% of HgT in spring to 52% in autumn. Bioaccumulation factors (BAF) for methyl-Hg in net plankton increased over the growing season. Overall, log BAF for HgT in net plankton (wet wt.) was 4.45. Log BAF for methyl-Hg in plankton was 4.90 to 5.43 depending on the analytical form of methyl-Hg in water (labile or total). Seasonal patterns of methyl-Hg and HgT did not covary in water, but did covary in plankton. These results support the conclusion that measurement of Hg in water is not adequate in itself to determine the amount of bioavailable Hg (i.e., methyl-Hg) in a lake. Labile (unextracted) methyl-Hg could be a useful measurement of bioavailable Hg. Labile methyl-Hg exhibits the same seasonal patterns as total methyl-Hg, but does not require the extraction steps necessary for measuring total methyl-Hg. 相似文献
15.
Algesten G Sobek S Bergström AK Jonsson A Tranvik LJ Jansson M 《Microbial ecology》2005,50(4):529-535
We measured sediment production of carbon dioxide (CO2) and methane (CH4) and the net flux of CO2 across the surfaces of 15 boreal and subarctic lakes of different humic contents. Sediment respiration measurements were
made in situ under ambient light conditions. The flux of CO2 between sediment and water varied between an uptake of 53 and an efflux of 182 mg C m−2 day−1 from the sediments. The mean respiration rate for sediments in contact with the upper mixed layer (SedR) was positively correlated
to dissolved organic carbon (DOC) concentration in the water (r2 = 0.61). The net flux of CO2 across the lake surface [net ecosystem exchange (NEE)] was also closely correlated to DOC concentration in the upper mixed
layer (r2 = 0.73). The respiration in the water column was generally 10-fold higher per unit lake area compared to sediment respiration.
Lakes with DOC concentrations <5.6 mg L−1 had net consumption of CO2 in the sediments, which we ascribe to benthic primary production. Only lakes with very low DOC concentrations were net autotrophic
(<2.6 mg L−1) due to the dominance of dissolved allochthonous organic carbon in the water as an energy source for aquatic organisms. In
addition to previous findings of allochthonous organic matter as an important driver of heterotrophic metabolism in the water
column of lakes, this study suggests that sediment metabolism is also highly dependent on allochthonous carbon sources. 相似文献
16.
Importance of tubificid populations on nitrogen cycle in two categories of shallow eutrophic lakes in the Danube Delta was quantitatively assessed for the 1992-1993 period. The structure of the primary producers in the studied lakes was used to discriminate between the two categories:(i) lakes dominated by macrophytes (A1) and (ii) lakes dominated by phytoplankton (A2). In both categories tubificid worms represented important fraction of the entire benthic community (35 and 32%, respectively, as number of individuals). They influence the sediment-water exchange of nutrients. The main processes involved are excretion of nutrients and their continuous release from sediments by molecular diffusion or through channels created by bioturbation. Inorganic nitrogen released from bottom sediments may regulate nitrogen load in the water body and thus, phytoplankton production. In 1992-1993, nitrogen stocks in tubificid biomass accounted for 5.3% in A1 lakes and 15.6% in A2 lakes of the amount stocked in phytoplankton, and only for 1.2 and 2.9% respectively, of the nitrogen load in water body. Nitrogen excretion rates ranged between 60.52 and 153.74 mg N m–2 year–1, and release rates from sediments between 378.26 and 960.87 mg N m–2 year–1, the lowest values being recorded for A2 category. Differences are related to tubificid biomass, structure and abundance of primary producers and to nutrient load in different ecosystems. Ratios between release rate of inorganic nitrogen by tubificid worms and sedimentation rate of organic nitrogen in the two categories of lakes were 8.3 and 6.4% respectively. Contribution of nitrogen released daily from sediments to the dissolved inorganic nitrogen load in the water column was less than 0.5%. However, in A1 and A2 lakes, the released nitrogen had a potential to sustain 24.74 and 8.01%, respectively, of the annual phytoplankton production. These values suggest the significance of tubificids in keeping the eutrophication process at a high level, especially during the periods when nitrogen is the main limiting factor for phytoplankton production. 相似文献
17.
Role of lakes for organic carbon cycling in the boreal zone 总被引:6,自引:0,他引:6
Grete Algesten Sebastian Sobek† Ann-Kristin Bergström Anneli Ågren Lars J. Tranvik† Mats Jansson 《Global Change Biology》2004,10(1):141-147
We calculated the carbon loss (mineralization plus sedimentation) and net CO2 escape to the atmosphere for 79 536 lakes and total running water in 21 major Scandinavian catchments (size range 437–48 263 km2). Between 30% and 80% of the total organic carbon that entered the freshwater ecosystems was lost in lakes. Mineralization in lakes and subsequent CO2 emission to the atmosphere was by far the most important carbon loss process. The withdrawal capacity of lakes on the catchment scale was closely correlated to the mean residence time of surface water in the catchment, and to some extent to the annual mean temperature represented by latitude. This result implies that variation of the hydrology can be a more important determinant of CO2 emission from lakes than temperature fluctuations. Mineralization of terrestrially derived organic carbon in lakes is an important regulator of organic carbon export to the sea and may affect the net exchange of CO2 between the atmosphere and the boreal landscape. 相似文献
18.
Human activities have altered riverine silica cycling and diminished the supply of silica to the oceans, but few rivers have
been intensively monitored to evaluate the magnitude of these changes. In this study we measured dissolved silica (DSi) and
amorphous silica (ASi) fluxes into and out of two large, culturally-impacted natural impoundments of the upper Mississippi
River, Lakes St. Croix and Pepin, USA. ASi sedimentation rates and sediment–water fluxes of DSi were calculated for each lake,
and a mass-balance approach was used to determine in-lake ASi production. ASi from terrestrial phytoliths in the lake sediments
was determined to be only partially available to biotic recycling, and in-lake ASi dissolution was small relative to the total
silica budgets. The river reaches upstream of the two lakes were found to have abundant DSi, and riverine diatom production
was found to contribute significant amounts of ASi to each lake. The average total phosphorus concentration in Lake Pepin
is four times that in Lake St. Croix but ASi production in Lake Pepin is only 2.3 times higher than in Lake St. Croix, indicating
that diatom growth in Pepin is limited by factors such as turbidity. Lake St. Croix currently traps about 10% of the inflowing
total bioavailable silica (TSib = DSi + ASi) while Lake Pepin traps closer to 20% of its inflowing TSib, clearly demonstrating the importance of silica retention in lakes and reservoirs along the land–ocean continuum. 相似文献
19.
Classification of central amazon lakes on the basis of their microbiological and physico-chemical characteristics 总被引:1,自引:0,他引:1
Twenty-four Central Amazonian Várzea and Ria lakes, lateral to the Rio Negro and the Rio Solimões, were studied for a year and are classified here in terms of physical, chemical and microbiological characteristics. White water (W), mixed water (M) and black water (B) lakes are ranked according to bacterial densities, electrical conductivity, pH, DO, POC, Fe, Si02 and PO4 consumption in the following order W > M > B. The range of Vmax decreased as net primary production increased. Further differentiation among the three lake types is made on the basis of dominant algal species and species diversity. 相似文献
20.
A. Heini I. Puustinen M. Tikka A. Jokiniemi M. Leppäranta L. Arvola 《Hydrobiologia》2014,731(1):139-150
In lakes, spatial and temporal variability of water chemistry and phytoplankton are characteristic phenomena although often difficult to link together. This motivated us to study their interplay in Lake Vanajanselkä, a eutrophic lake in Finland. We hypothesized that in summer spatial and temporal differences in phytoplankton and water chemistry can be extended in comparison to spring and autumn. Therefore, chlorophyll a and water chemistry was examined by six sampling campaigns with 15 sampling sites over the lake in May–October 2009–2010. In summer, chlorophyll, pH, and oxygen were horizontally and vertically unevenly distributed in the lake, and in the epilimnion pH and oxygen showed a distinct diurnal variability suggesting high photosynthesis during the day. Daily >1 pH unit difference between the sites and 2.5 pH unit difference between the epi- and hypolimnion were found. In agreement with pH and oxygen, NO3-N and NH4-N could be unevenly distributed in the epilimnion. In autumn no spatial differences were found, however. The results emphasized that algae and cyanobacteria were responsible, at least partly, for the variability in water chemistry in the surface layer, and short- and long-term gradients in space and time need to be considered when productive lakes are studied. 相似文献