Bacteria and phytoplankton are integral in the mobilization and transfer of organic matter to higher trophic levels. Hence,
we examined their role in zooplankton diets and assessed trends in their nitrogen isotopic variability. We performed feeding
experiments with natural particulate organic matter (POM) and four zooplankton groups (Daphnia, Holopedium, large calanoids and small calanoids) to (1) examine whether there are differences in consumption (presented as clearance
and ingestion rates) of phytoplankton and bacteria, and (2) determine whether differences in zooplankton clearance and ingestion
rates are correlated with their δ15N isotopic signatures. In general, phytoplankton and bacteria clearance rates and biomass ingested per animal varied significantly
among different zooplankton groups within lakes and between lakes for a given zooplankton group. Within a given lake, Daphnia and Holopedium had the highest phytoplankton and bacteria clearance and ingestion rates, followed by large calanoids, and then small calanoids.
For a given zooplankton group, bacteria and phytoplankton clearance rates varied among lakes. In contrast, phytoplankton ingestion
rates were consistently highest in Dickie Lake for all taxa, whereas bacteria ingestion rates were more variable among lakes
for the different zooplankton taxa. The percentage contribution of different phytoplankton taxa to the biomass of phytoplankton
ingested also varied significantly among lakes for a given taxa, but there were few differences within a given lake among
zooplankton. Zooplankton δ15NDOMC values were correlated with their size adjusted phytoplankton and bacteria clearance and ingestion rates. The correlations
were stronger with (1) phytoplankton compared to bacteria, and (2) clearance rates compared to ingestion rates of biomass.
Together our results suggest that zooplankton taxa with low phytoplankton and bacteria clearance and ingestion rates and higher
δ15NDOMC are likely exploiting food sources from higher trophic levels. 相似文献
Nutrient fluxes across terrestrial-aquatic boundaries and their subsequent integration into lake nutrient cycles are currently
a major topic of aquatic research. Although pollen represents a good substrate for microorganisms, it has been neglected as
a terrestrial source of organic matter in lakes. In laboratory experiments, we incubated pollen grains of Pinus sylvestris in water of lakes with different trophy and pH to estimate effects of pollen input and its subsequent microbial degradation
on nutrient dynamics. In this ex situ experiment, we measured concentrations of organic carbon, phosphorus and nitrogen in the surrounding water as well as microbial
dynamics (bacteria and fungal sporangia) at well-controlled conditions. Besides leaching, chemical and microbial decomposition
of pollen was strongest within the first week of incubation. This led to a marked increase of soluble reactive phosphorus
and total dissolved nitrogen (up to 0.04 and 1.5 mg L−1, respectively, after 5 days of incubation) in the ambient water. In parallel, pollen grains were rapidly colonized by heterotrophic
bacteria and aquatic fungi. Leaching and microbial degradation of pollen accounted for ≥80, ≥40, ≥50% for organic C, N and
P, respectively, and did not significantly differ among water samples from the studied lakes. Thus, pollen introduces high
amounts of bio-available terrestrial organic matter and nutrients into surface waters within a short time. A rough calculation
on P input into oligotrophic Lake Stechlin indicates that pollen plays an important ecological role in nutrient cycling of
temperate lakes. This requires further attention in aquatic ecology. 相似文献
In inland waters, transparent exopolymer particles (TEP) can affect carbon export and sequestration in sediments with consequences
for lake C budgets. We measured TEP concentration in 32 lakes from two contrasting lake districts covering wide ranges in
biological and chemical characteristics. North temperate lakes, located in a wet region, have low to moderate ionic strength
and low to high dissolved organic carbon with corresponding variation in color (light absorbance). Mediterranean lakes located
in a semiarid region were characterized by high ionic strength and high concentrations of dissolved organic carbon but low
color. TEP concentrations were large relative to the living portion of the particulate organic carbon pool in both Mediterranean
(36%) and north temperate (33%) lakes. TEP concentrations ranged from 36 to 1,462 μg [as Gum Xanthan equivalents (GX eq)] L−1 in north temperate lakes. In the Mediterranean lakes, concentrations were higher that previously reported for other systems
and ranged from 66 to 9,038 μg GX eq L−1. TEP concentration was positive and significantly related to chlorophyll a (chl a) in north temperate lakes and in the entire data set. Although a significant and positive relationship between TEP and chl
a was also detected in the Mediterranean lakes, bacterial abundance was most strongly related to TEP. In contrast with the
positive influence of phytoplankton and bacteria on TEP, there were weaker relationships between TEP and the chemical variables
tested. We observed a significant and positive relationship between pH and TEP (for all lakes) but this relationship was indirectly
driven by a co-variation of pH with phytoplankton biomass based on multiple regression analysis. For the Mediterranean lakes,
the negative (but not significant) trends between TEP and both conductivity and divalent cations suggest thresholds above
which TEP will likely be destabilized. Under these conditions, TEP may flocculate or disperse in the water column. 相似文献
We used a comparative data set for 25 lakes in Denmark sampled during summer to explore the influence of lake morphometry,
catchment conditions, light availability and nutrient input on lake metabolism. We found that (1) gross primary production
(GPP) and community respiration (R) decline with lake area, water depth and drainage ratio, and increase with algal biomass
(Chl), dissolved organic carbon (DOC) and total phosphorus (TP); (2) all lakes, especially small with less incident light,
and forest lakes with high DOC, have negative net ecosystem production (NEP < 0); (3) daily variability of GPP decreases with
lake area and water depth as a consequence of lower input of nutrients and organic matter per unit water volume; (4) the influence
of benthic processes on free water metabolic measures declines with increasing lake size; and (5) with increasing lake size,
lake metabolism decreases significantly per unit water volume, while depth integrated areal rates remain more constant due
to a combination of increased light and nutrient limitation. Overall, these meta-parameters have as many significant but usually
weaker relationships to whole-lake and benthic metabolism as have TP, Chl and DOC that are directly linked to photosynthesis
and respiration. Combining water depth and Chl to predict GPP, and water depth and DOC to predict R, lead to stronger multiple
regression models accounting for 57–63% of the variability of metabolism among the 25 lakes. It is therefore important to
consider differences in lake morphometry and catchment conditions when comparing metabolic responses of lakes to human impacts. 相似文献
The internal source, especially resuspension process of the sediments in lakes and its environ- mental effect has been paid shining attention in the West as well as in China[1—6] although the influence of external source is important to water environment[7]. S鴑dergaard et al. compared the releases of soluble reactive phosphorus (SRP) in the surface sediments of Lake Arres before and after disturbance and they found that disturbing can increase the release by 20—30 times[3]. Robarts and ot… 相似文献
Rotifera density, biomass, and secondary production on two marginal lakes of Paranapanema River were compared after the recovery of hydrologic connectivity with the river (São Paulo State, Brazil). Daily samplings were performed in limnetic zone of both lakes during the rainy season immediately after lateral inflow of water and, in the dry period, six months after hydrologic connectivity recovery. In order to identify the factors that affect rotifer population dynamics, lake water level, volume, depth, temperature, transparency, dissolved oxygen, pH, alkalinity, conductivity, suspended solids, nutrients, and chlorophyll-a were determined. Variations of water physical and chemical factors that affect rotifer population were related to the lake-river degree of connection and to water level rising after drought. The water lateral inflow from the river resulted in an increase in lake water volume, depth, and transparency and a decrease in water pH, alkalinity, and suspended solids. The lake with the wider river connection, more frequent biota exchange, and larger amount of particulate and dissolved materials was richer and more diverse, while rotifer density, biomass, and productivity were lower in both periods studied. Density, biomass, and secondary production were higher in the lake with the smaller river connection and the higher physical and chemical stability. Our results show that the connectivity affects the limnological stability, associated to seasonality. Stable conditions, caused by low connectivity in dry periods, were related with high density, biomass and secondary production. Conversely, instability conditions in rainy periods were associated to elevated richness and diversity values, caused by exchange biota due to higher connectivity. 相似文献
Critics charge that agricultural managers routinely overdose their fields with chemical N and P to levels that exceed the soil's capacity to adsorb these materials, creating a situation that promotes hypoxia in Iowa lakes. Soil colloidal particles, capable of forming complexes with inorganic and organic N and P, control the equilibrium concentration of dissolved nutrients in lake waters. However, it should be realized that adsorbed nutrients also exhibit strong influences on the potential of sediments to undergo dispersion, a condition that may directly impact nutrient bioavailability. Thus, direct links may exist between adsorbed nutrient compositions and flocculation/dispersion properties of lake colloidal material. This paper presents work involving four Iowa lakes undertaken to determine relationships between ion composition and the dispersion potential of sediments. Surface waters and lake‐bottom grab samples were collected at three separate collection times from August to October. Samples were characterized for dissolved and adsorbed cations. Dispersion potential of each water sample was characterized by relating the total suspended solids concentration to the absorbance at 560 nm. It was found that sediment dispersion was easily predictable by a simple yet significant linear correlation with the concentration ratio of Na (CRNa = [Na]/[Ca]–1/2) in solution. This correlation was further improved by including Na concentration, CRK, electrical conductivity, temperature, and solution P concentrations into the model. Nonlinear inter‐dependences were found between TSS and cation exchange capacity (CEC), and adsorbed Na, K, P, and heavy metals. Our analysis suggests that solution/solid phase constituents influenced the dispersion behavior of sediments through subtle manipulations of the excess surface charge. 相似文献
Studies investigating the effects of human activities on the functional organization of macroinvertebrate communities in tropical streams and rivers are very limited, despite these areas witnessing the greatest loss of natural forests globally. We investigated changes in taxon richness, numerical abundance and biomass of macroinvertebrate functional feeding groups (FFGs) in streams draining different land-use types in the Sosiani-Kipkaren River in western Kenya. Twenty-one sites in river reaches categorized as forested, mixed, urban or agricultural were sampled during the dry and wet seasons. Collected macroinvertebrates were identified to the lowest taxon possible (mainly genus) and classified into five major FFGs; collector-gatherers, collector-filterers, scrapers, predators and shredders. There were significant (p < 0.05) spatial variation in habitat quality, organic matter standing stocks, total suspended solids, electrical conductivity, dissolved oxygen, temperature and nutrient concentrations across land-uses, with forested sites recording lowest values in mean water temperature, electrical conductivity and nutrients while recording highest levels in dissolved oxygen concentrations. Responses in macroinvertebrates to changes in land-use varied with richness, abundance and biomass showing differences within FFGs. Biomass-based metrics responded more strongly to change in land-use while taxon richness was the least predictive, indicating replacement of taxa within FFGs across land-use types. Higher shredder abundance, biomass and richness were recorded in forested streams which were cooler with protected riparian areas and high biomass of coarse particulate organic matter. Collector-gatherers dominated agricultural and urban streams owing to an abundance of particulate organic matter and nutrients, while scrapers responded positively to increased nutrient levels and open canopy in mixed and agricultural streams where primary production and algal biomass was likely increased. Overall, this study provides further evidence of the effects of agricultural and urban land-uses on tropical streams and rivers and contributes to the use of macroinvertebrate FFGs as indicators of ecological health. 相似文献
Total phosphorus and its main forms: dissolved mineral, dissolved organic, particulate organic and particulate mineral in the vertical water column of three subalpine lakes of various types in Italy, has been estimated during the winter-vernal season. The range of variation in the phosphorus content in these waters was as follows: total phosphorus 16 ± 2860 μg/1 PO4, dissolved mineral phosphorus 4 ± 1040 μg/l PO4, dissolved organic phosphorus 1 ± 160μg/l PO4, particulate organic phosphorus 0 ± 290 μg/l PO4 and particulate mineral phosphorus 1 ± 100 μg/l PO4, Generally the content of total phosphorus and dissolved mineral phosphorus (phosphates) increased with the degree of eutrophy with the depth and with the progress of the vernal season towards the summer stagnation time. The amount of phosphates increased in water with the depletion of oxygen, both in the verical water column and with the progress of stagnation time. The amounts of dissolved organic phosphorus decressed with the depth of the vertical water column whereas the dissolved mineral phosphorus increased. The development of the particulate organic phosphorus stratification in the vertical water column was clearly visible in the eutrophic lake. The quantities of total phosphorus and its main component, dissolved mineral phosphorus, decreased evidently from January to May in all three lakes, mostly in the eutrophic lake. The reason of this decrease is sorption by lake sediments and to a certain degree sedimentation of phosphorus sorbed by ferric hydroxide. The increase of dissolved mineral phosphorus and that of total phosphorus in the vertical water column and with the progress of summer stagnation had as a reason the liberation of phosphorus from sediments, and not so much decomposition of sedimentating plankton or dissolved organic phosphorus. The share of single (mean) values of phosphorus forms in the total phosphorus was as follows: In the oligotrophic lake the share of particulate mineral phosphorus was extremely high in March (21% of the total), probably because of the inflow of the melting waters from the drainage area. The development of vertical stratification in waters of three subalpine Italian lakes at the end of the vernal season (May) indicates the quantitative prevailing of dissolved mineral phosphorus with its increase with the depth and domination of dissolved organic phosphorus in the trophogenic zone. 相似文献
The benthic invertebrate assemblages and functional feeding groups in different mesohabitats of the Middle Paraná River–floodplain system were analyzed. Benthic invertebrates and bottom sediments were sampled in a secondary channel (center and bank mesohabitats), a temporal marginal fluvial wetland adjacent to the river, an isolated lake and a connected lake during low water level. Cluster analysis of average invertebrate densities based on the Bray Curtis dissimilarity index yielded a group composed by the mesohabitats with higher species richness, the floodplain lakes, banks mesohabitats and the wetland. The center mesohabitat of the main channel characterized by sandy sediments with low organic matter content and the lowest invertebrate densities and species richness was classified separately. Alpha diversity increased from the center mesohabitat (6 taxa) to the adjacent wetland (71 taxa), and were similar between the floodplain lakes (24 and 22 taxa) and the river bank mesohabitat (24 taxa). Gamma and beta diversities (Whittaker index) were 92 and 2.19, respectively. The highest turnover of taxa was between the river and the other mesohabitats and the lowest between floodplain lakes. Detrended correspondence analysis (DCA) showed a clear separation of wetland and banks from other mesohabitats (axis 1 and 2 explained 52.25% variance) explained by shredders and collector-filterers. The other mesohabitats were arranged in a gradient from the main channel mostly related to collector-gatherers to the connected lake and the isolated lake that were mostly characterized by predators and scrapers. The invertebrate assemblage complexity and functional feeding groups composition increased in the lateral dimension, from the center of the main channel to the temporal marginal fluvial wetland due to the influences of the spatial heterogeneity caused by different sources of organic matter inputs. 相似文献
This study combined water- and sediment flux measurements with mass balances of dissolved gas and inorganic matter to determine
the importance of pelagic and benthic processes for whole-system metabolism in a eutrophic fluvial lake. Mass balances of
dissolved O2, inorganic carbon (DIC), nitrogen (DIN), phosphorous (SRP), particulate N (PN) and P (PP) and Chl a were calculated at a nearly monthly frequency by means of repeated sampling at the lake inlet and outlet. Simultaneously,
benthic fluxes of gas and nutrients, including denitrification rates, and the biomass of the dominant pleustophyte (Trapa natans) were measured, and fluxes of O2 and CO2 across the water–atmosphere interface were estimated from diel changes in outlet concentrations. On an annual scale, Middle
Lake exhibited CO2 supersaturation, averaging 313% (range 86–562%), but was autotrophic with a net O2 production (6.35 ± 2.05 mol m−2 y−1), DIC consumption (−31.18 ± 18.77 mol m−2 y−1) and net export of Chl a downstream (8.38 ± 0.95 mol C m−2 y−1). Phytoplankton was the main driver of Middle Lake metabolism, with a net primary production estimated at 33.24 mol O2 m−2 y−1, corresponding to a sequestration of 4.18 and 0.26 mol m−2 y−1 of N and P, respectively. At peak biomass, T. natans covered about 18% of Middle Lake’s surface and fixed 2.46, 0.17 and 0.02 mol m−2 of C, N and P, respectively. Surficial sediments were a sink for O2 (−14.47 ± 0.65 mol O2 m−2 y−1) and a source of DIC and NH4+ (18.84 ± 2.80 mol DIC m−2 y−1 and 0.83 ± 0.16 mol NH4+ m−2 y−1), and dissipated nitrate via denitrification (1.44 ± 0.11 mol NO3− m−2 y−1). Overall, nutrient uptake by primary producers and regeneration from sediments were a minor fraction of external loads.
This work suggests that the creation of fluvial lakes can produce net autotrophic systems, with elevated rates of phytoplanktonic
primary production, largely sustained by allochtonous nutrient inputs. These hypereutrophic aquatic bodies are net C sinks,
although they simultaneously release CO2 to the atmosphere. 相似文献
One of the goals for paleaoenvironmental research is to predict the tendency of future climate and environmental changes based on the understanding of the past. The key approach is to find similar pictures which happened in the past. By understanding the background and mechanism of the paleaoenvironmen- tal changes, reliable parameters and verifications can be provided for the numerical model to predict the tendency of future climate and environmental changes. The Mid-Holocene as the nearest … 相似文献
Phytoplankton and zooplankton were monitored during 2 years in four eutrophic shallow lakes (two turbid and two clear water) from two wetland reserves in Belgium. In each wetland, phytoplankton biomass was significantly higher in the turbid lake than in the clear water lake. Although total macrozooplankton biomass and the contribution of daphnids to total zooplankton biomass was comparable in the clear water and the turbid lakes, the grazing pressure of macrozooplankton on phytoplankton as estimated from zooplankton to phytoplankton biomass ratios was higher in the clear water lakes. Estimated grazing by daphnids in the clear water lakes was always high in spring. In summer, however, daphnid biomass was low or daphnids were even absent during prolonged periods. During those periods phytoplankton was probably controlled by smaller macrozooplankton or by submerged macrophytes through nutrient competition, allelopathic effects or increased sedimentation rates in the macrophyte vegetation. 相似文献
Most existing studies on the algal communities of acid lakes are based on environments that have been caused by anthropogenic disturbances. Such lakes have a different origin compared to the natural acidic lakes and could be expected to differ also in the mechanisms controlling phytoplankton and trophic status. Planktonic community in Lake Caviahue is somewhat diverse in spite of the low pH of the water. Algae have a distinctive vertical distribution: the values of phytoplankton biomass remain constant throughout the water column and at times were highest in the upper end of the hypolimnion, forming a maximum or a layer of chlorophyll a at depth. The goal of this work was to investigate the factors influencing the seasonal and vertical distribution of phytoplankton. The lake was sampled between the years 2004 and 2006. Physical, chemical and biological parameters at different depths throughout the water column were determined. The interrelationships between environmental variables at different sampling dates were analyzed using an integration of multivariate matrices, multiple factor analysis, to analyze any joint partnerships in the samples. We found that phytoplankton biomass is dominated by Keratococcus rhaphidioides. With regard to zooplankton, we found a single species of rotifers (Philodina sp.). The two arms of the lake and the depths have different behaviours showing differences in the arms' conductivity, dissolved oxygen and pH. The more superficial layers were characterized by high values of phytoplankton and zooplankton biomass, organic and inorganic carbon, dissolved oxygen and pH. The deeper layers showed high values of chlorophyll a, ammonium and phosphorus (dissolved and particulate). From the multivariate analysis the relationships of the each algal species with pH, as a possible indicator of the degree of “acidophilia”, could be extracted. 相似文献
