Phytoplankton production and phosphorus supply in Cayuga Lake (1968–1973)

The average annual rate of carbon production in Cayuga Lake, New York, was determined by ¹⁴C uptake and by a phosphorus supply method. The rate of phosphorus supply was converted to units of carbon production using observed sestonic C : P ratios. The two methods gave good agreement and annual carbon production was estimated to be 130 gC m⁻² yr⁻¹. Research supported by Federal Hatch Funds and by U.S. Department of Interior, Office of Water Resources Research.     

Phytoplankton community composition in Lake Xolotlán (Managua)

Results of two years of research on phytoplankton species composition in Lake Xolotlán (Managua) are presented. A summary of the planktonic algae from other Nicaraguan lakes is also included. One hundred and twenty phytoplankton taxa were identified. A list of species and comments about relevant properties of the most frequent taxa are given. The qualitative composition of Lake Xolotlán phytoplankton is compared with that of other tropical waterbodies.     

Phytoplankton community response to reservoir aging, 1968–92

The effects of reservoir aging on the phytoplankton community of amidwestern U.S. reservoir constructed in 1965 (Pawnee Reservoir) werestudied by comparing algal biovolume and species composition from April 1992through November 1992 to surveys conducted in 1968–73 and 1990. Meansummer total phosphorus, nitrate-nitrogen, Secchi disk depth, totalsuspended solids, chlorophyll a, and phytoplankton species composition datacharacterized Pawnee Reservoir during 1968–69 as a high nutrient,relatively clear water environment. Phytoplankton biomass was relativelylow, consisting mainly of cyanophytes and non-flagellated chlorophytes.During 1970–73, water clarity was poor, total suspended solids werehigh, and total phosphorus was lower, but was still greater than 100 µgl^–1. The 1970–73 phytoplankton biomass was high and wasdominated by cyanophytes. Mean summer total phosphorus remained >100µg l^–1, water clarity remained poor, but phytoplanktonbiomass decreased significantly during 1990–92. The dramatic drop inchlorophyll a and low mean volatile suspended solids indicated thatinorganic suspended sediments, rather than phytoplankton, accounted for themajority of the turbidity in 1990-92. In addition to lower phytoplanktonbiomass, community composition shifted away from buoyancy-regulatingcyanophytes toward flagellated chlorophytes. These data suggest that asreservoirs located in agricultural watersheds age, (1) inorganic suspendedsediments have a significant effect on the light environment as well asphytoplankton biomass and species composition, (2) the control ofphytoplankton biomass and species composition shifts away from nutrients tolight and suspended sediments, and (3) there is a 1–2 year lag in theresponse of phytoplankton biomass to maximum nutrient loading during thetrophic upsurge period. Thus, sedimentation has been shown to be a primarydeterminant of plankton and benthic macroinvertebrate community compositionas Pawnee Reservoir aged.     

Phytoplankton/zooplankton relationships during spring in the brackish Lake Grevelingen 1976–1978 (III)

Summary Rotifer species of the genusSynchaeta represent the dominating zooplankton organisms during early spring (BAKKERet al., 1977).Reproductive capacity of the rotifers (sensu EDMONDSON, 1965) was always significantly correlated with algal densities, cryptomonad flagellates being the main food. The slope of the curve representing the feeding relationSynchaeta-Cryptomonas was significantly steeper than forSynchaeta and the diatomSceletonema. Positive influences of increasing temperature forSynchaeta cf.vorax were only found within the range of 2–7°C. When temperature rose above 10°CS. vorax was succeeded byS.triophthalma. Negative temperatures, occurring in brackish lakes during periods of strong frost, caused a decrease of the egg ratio (numbers of eggs per animal) and of the population density.Development times ofS. vorax eggs were determined (VAN DAMet al., 1978) in order to calculate birth rates and production. Egg development time amounted to 3 days at 5°C and to 2 days at 10°C. Birth rates declined strongly when maximum population densities were reached. Mortality was approached by subtracting the actual rate of increase of population density from the birth rate. Sometimes negative mortalities were found, presumably caused by the development of resting eggs.Population dynamics of the rotifers were related to phytoplankton biomass and to primary productivity. Grazing effects of the rotifers on the algal population became evident during the final stage of the spring bloom (April). In the beginning (February–March) the mortality of the algal population could not be explained by grazing, other factors (cf. JASSBY and GOLDMAN, 1974) being responsible.     

Phytoplankton of Lake Bol’shie Shvakshty (Belarus) during the Shift of the Ecosystem from a Macrophyte–Weakly Eutrophic to a Phytoplankton–Hypereutrophic State

Changes in the quantitative characteristics and functioning of phytoplankton in Lake Bol’shie Shvakshty have been assessed. The changes are evoked by the introduction of herbivorous fishes into the lake and the resulting disturbance of ecological balance in the ecosystem and the shift of the lake into a hypertrophic state from a weakly eutrophic state. Human interference has caused the cyanobacteria density (abundance) and biomass values in the overall phytoplankton composition to strongly exceed (3.5 × 10⁹ cells/L and above 68 μg/L chlorophyll-а, respectively) the threshold value for safe recreational use of water bodies (20 million cells/L and 10 μg/L chlorophyll-а) established by the World Health Organization (WHO). The lake can be assigned to the third level of hazard to human health within the classification proposed by the WHO, as the cyanobacteria density is higher than 100 million cells/L and chlorophyll-а content is higher than 50 μg/L. MC-producing Microcystis species were identified among the cyanobacteria that has propagated in the lake in recent years, and five microcystin variants, including the highly toxic MC-LR, have been detected in the water.     

Stoichiometric homeostasis in response to variable water and nutrient supply in a Robinia pseudoacacia plant–soil system

刺槐植物-土壤系统生态化学计量内稳性对水分和养分变异的响应特征所有生物体都需要一定比例的元素来维持正常的生理代谢过程,它们的可塑性取决于它们利用外部资源的效率。阐明不同资源供应水平下植物、土壤和土壤微生物生物量生态化学计量特征之间的相互作用非常重要。本研究以一年生刺槐(Robinia pseudoacacia)幼苗为研究对象,测定不同水平水分、氮素和磷素处理下刺槐叶片、细根、土壤和微生物生物量C、N、P含量及其化学计量学指标。结果表明,刺槐叶片、细根、土壤和微生物生物量C、N、P含量及其化学计量特征会对其生存环境水分和养分条件的变化表现出一定程度的可塑性;方差分解分析结果表明,细根计量比解释了微生物生物量计量比方差的很大一部分;结构方程模型进一步揭示了细根计量比和叶片计量比是影响土壤微生物生物量C:N和C:P 的两个直接因素,而细根计量比具有较大的直接作用。此外,内稳性特征分析表明土壤微生物生物量C 和C:P对土壤养分变化较为敏感,其他指标均具有内稳性。这些结果明确了土壤微生物生物量化学计量的重要性,提高我们对不同生境水分和养分供应水平下植物-土壤系统养分循环机理的认识。     

Phytoplankton periodicity in Ogelube Lake,Anambra State,Nigeria during 1979–1980

Ogelube is a tropical oligotrophic lake having a desmid dominated phytoplankton with maximum density during the warmest season. During the rainy season, the lake cools, phytoplankton declines and dominance shifts to algae other than desmids. The lake cools further as harmattan advances, while phytoplankton reaches its minimum, suggesting water temperature to be more important than other environmental conditions. Decrease in phytoplankton density with falling water temperature was probably due to slower reproduction, rather than to increased death rate.     

Phytoplankton structure and dynamics in Lake Sanabria and Valparaíso reservoir (NW Spain)

The aim of this work is to compare the composition and seasonality of the phytoplankton population in a natural oligotrophic lake (Lake Sanabria) and a mesotrophic reservoir (Valparaíso). Both ecosystems are located on the Tera river course (NW Spain), which runs along an area of ancient metamorphic and plutonic rocks. Some physical and chemical parameters, chlorophyll a and phytoplankton biovolume were studied from monthly samples collected at different depths during the periods 1987–1989 (Lake Sanabria) and 1991–1992 (Valparaíso). Phytoplankton biovolume and chlorophyll a concentration were about five times higher in Valparaíso than in Lake Sanabria. Species composition (and main phytoplankton groups) were different. Valparaíso was highly dominated by diatoms and Lake Sanabria by cryptophytes and small chlorophytes. In spite of the fact that both sites were nitrogen limited, heterocystous cyanophytes (Anabaena sp.) were detected only in Valparaíso. The relationships between phytoplankton structure and trophic level, hydrological conditions and nitrate content are discussed.     

Phytoplankton biomass in Lake Xolotlán (Managua): Its seasonal and horizontal distribution

Some well-documented studies on restoring eutrophic lake systems in The Netherlands by fish stock management have been evaluated with the emphasis on the role of macrophytes. Furthermore, the factors determining the light climate for submerged macrophytes in a large shallow eutrophic lake (Lake Veluwe) have been assessed and the potential success of biomanipulation in large scale projects is discussed. Today relatively little attention has been paid to macrophyte management although the importance of macrophytes in lake restoration has been recognized regularly. The biomanipulation strategy was successful in small scale projects. In a large scale project, however, wind-induced resuspension may largely determine the underwater light climate through attenuation by the water column and periphytic layer. Therefore, restoration of relatively large waterbodies by fish stock management only is expected not to lead to any noteworthy improvement of the light climate for submerged macrophytes. Additional measures aimed at reducing wind-induced resuspension of sediment particles and reestablishing of the macrophyte stands are required for successful biomanipulation strategies. Water quality managers should pay more attention to macrophyte stands in biomanipulation projects because macrophytes enhance a more stable and diverse ecosystem. Restoration objectives and the methods of their achievement must be carefully planned since an abundant submerged macrophyte vegetation may have undesirable effects as well.     

General index to volumes 161–170 (1987–1992)

General index to volumes 161–170 (1987–1992)     

Primary production of aquatic macrophytes and their epiphytes in two shallow lakes (Peipsi and Võrtsjärv) in Estonia

In shallow lakes with large littoral zones, epiphytes and submerged macrophytes can make an important contribution to the total annual primary production. We investigated the primary production (PP) of phytoplankton, submerged macrophytes, and their epiphytes, from June to August 2005, in two large shallow lakes. The production of pelagic and littoral phytoplankton and of the dominant submerged macrophytes in the littoral zone (Potamogeton perfoliatus in Lake Peipsi and P. perfoliatus and Myriopyllum spicatum in Lake Võrtsjärv) and of their epiphytes was measured using a modified ¹⁴C method. The total PP of the submerged macrophyte area was similar in both lakes: 12.4 g C m^?2 day^?1 in Peipsi and 12.0 g C m^?2 day^?1 in Võrtsjärv. In Peipsi, 84.2% of this production was accounted for by macrophytes, while the shares of phytoplankton and epiphytes were low (15.6 and 0.16%, respectively). In Võrtsjärv, macrophytes contributed 58%, phytoplankton 41.9% and epiphytes 0.1% of the PP in the submerged macrophyte area. Epiphyte production in both lakes was very low in comparison with that of phytoplankton and macrophytes: 0.01, 5.04, and 6.97 g C m^?2 day^?1, respectively, in Võrtsjärv, and 0.02, 1.93, and 10.5 g C m^?2 day^?1, respectively, in Peipsi. The PP of the littoral area contributed 10% of the total summer PP of Lake Peipsi sensu stricto and 35.5% of the total summer PP of Lake Võrtsjärv.     

On polynuclear aromatic hydrocarbons contamination levels in the ecosystem of Lake Peipsi in the 1970s–1980s

The data on benzo(a)pyrene (BaP) and other polynuclear aromatic hydrocarbons (PAH) pollution of Lake Peipsi and its tributaries in the 1970s–1980s have been summarized. Systematic data on the pollution of Lake Peipsi by BaP are available. The BaP content in lake water varied from <0.1 to 237 ng 1^–1. The content and qualitative composition of PAH varied in different observations. PAH were accumulated mainly in the bottom sediments; in their surface layer BaP concentrations were 10³–10⁶ times higher than in water. The concentration of the PAH in bottom sediments varied from 16 to 580 µg kg^–1 in the lake and from 40 to 2800 µg kg^–1 in its tributaries. The content of BaP in fish and biota was not high. Among the pollution sources the atmospheric pollution played quite a significant role. The lake was also polluted by oil spillage and fuel exhausts from boats and ships. The PAH concentration in the water of the tributaries was somewhat higher than in the area of Lake Peipsi.     

The budgets of nitrogen and phosphorus in shallow eutrophic Lake Võrtsjärv (Estonia)

Hydrobiologia - The nutrient budget, phytoplankton primary productionand sedimentation rate were studied weekly in the large(270 km2) and shallow (mean depth 2.8 m)eutrophic Lake...     

Modelling beef cows’ individual response to short nutrient restriction in different lactation stages

Short-term nutrient restrictions can occur naturally in extensive beef cattle production systems due to low feed quality or availability. The aims of the study were to (1) model the curves of milk yield, plasma non-esterified fatty acids (NEFAs) and β-hydroxybutyrate (BHB) contents of beef cows in response to short nutritional challenges throughout lactation; (2) identify clusters of cows with different response profiles; (3) quantify differences in cows’ response between the clusters and lactation stages. Data of BW, body condition score (BCS), milk yield, NEFA, and BHB plasma concentration from 31 adult beef cows (626 ± 48 kg at calving) were used to study the effect of 4-day feed restriction repeated over months 2, 3 and 4 of lactation. On each month, all cows received a single diet calculated to meet the requirements of the average cow: 100 % requirements for 4 days (d-4 to d-1, basal period), 55 % requirements on the next 4 days (d0 to d3, restriction period) and 100 % requirements for 4 days (d4 to d7, refeeding period). Natural cubic splines were used to model the response of milk yield, NEFA and BHB to restriction and refeeding in the 3 months. The new response variables [baseline value, peak value, days to peak and to regain baseline, and areas under the curve (AUC) during restriction and refeeding] were used to cluster cows according to their metabolic response (MR) into two groups: Low MR and High MR. The month of lactation affected all the traits, and basal values decreased as lactation advanced. Cows from both clusters had similar BW and BCS values, but those in the High MR cluster had higher basal milk yield, NEFA and BHB contents, and responded more intensely to restriction, with more marked peaks and AUCs. Reaction times were similar, and baseline values recovered during refeeding in both clusters. Our results suggest that the response was driven by cows’ milk potential rather than size or body reserves, and despite high-responding cattle’s higher milk yield, they were able to activate metabolic pathways to respond to and recover from the challenge.     

The response of a freshwater wetland to long-term ’low level‘ nutrient loads: nutrients and water budget

Boney Marsh is a small constructed freshwater wetland located along thefloodplain of the Kissimmee River in south Florida, USA. River water, withaverage Tot-P concentrations of 0.052 mg l⁻¹, Tot-N of 1.70 mgl⁻¹, and Cl⁻ of 15.95 mg l⁻¹, wasdiverted through the marsh to quantify mass retention and fate.Comprehensive mass balance budgets for Tot-P, Tot-N, and Cl⁻were developed based on input (inflow, precipitation) and output (outflow,evapotranspiration, seepage). Cl⁻, as well asNa⁺, budgets indicated that groundwater accounted forapproximately 7% of the total water budget. Annual mass loadings toBoney Marsh were 0.5, 15.7, and 147.9 g m⁻²year⁻¹ for Tot-P, Tot-N, and Cl⁻, respectively.Mean annual nutrient removal was estimated at 72% for Tot-P and34% for Tot-N, and P-assimilation capacity remained high andunchanged for the period of record. The subtropical marsh system accumulatedTot-P at a much higher rate than Tot-N, with averaged net sedimentationrates of 20.4 and 8.3 year⁻¹, respectively. Boney Marsh netsedimentation coefficients were higher than lakes with similar depths. TheN:P mass ratio in the wetland water column increased during the period ofrecord, and was primarily due to a high P-sedimentation rate and a decliningN-sedimentation rate. The authors use the editor‘s suggestion forabbreviations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Phytoplankton–bacterioplankton interactions in a neotropical floodplain lake (Laguna Bufeos,Bolivia)

Laguna Bufeos is a floodplain lake of the river Ichilo, a tributary of the Amazon basin situated in Bolivia. Nutrient addition assays involving whole water (<200 μm) as well as fractionated water (<0.8 μm) treatments were carried out in incubation tubes to test whether bacterial growth is limited by the availability of inorganic nutrients and to test whether bacteria are able to utilize inorganic nutrients directly or are stimulated by inorganic nutrients through increased production of phytoplankton. The assays were carried out during two extreme hydrological conditions, the high-water and the low-water period. During the high-water period experiment, neither N or P limited bacterial growth rates. During the low-water period, bacterial growth was P limited. Bacterial growth was stimulated in the fractionated as well as in the whole water treatments, indicating that bacterial growth was directly stimulated by P. Bacterial growth corrected for grazing losses (determined by means of dilution experiments) was significantly higher in the fractionated water containing only bacteria when compared to the whole water containing also grazers and phytoplankton. This suggests that bacterial growth was suppressed by competition with phytoplankton rather than stimulated through the production of dissolved organic matter by phytoplankton.     

Zooplankton community changes in Lake Kinneret (Israel) during 1969–1985

Long-term records (1969–1985) of zooplankton density in Lake Kinneret indicated significant reduction of biomass (Copepods, Cladocera, Rotifera) and production (Copepods, Cladocera). Nauplius and adult copepod densities decreased but those of copepodites did not change. Mesocyclops was suppressed more than the smaller Thermocyclops and males of both genera became more abundant relative to the larger females. Ratios of small/large Cladocera densities became higher. Numbers of total cladocerans were stable, and therefore reduction of Cladocera grazing capacity is assumed. The abundant Keratella spp. were reduced. It is likely that intensification of fish visual-attack-predation pressure shifted the size-class structure towards smaller adult copepods and cladocerans. Reduction of Keratella spp. and copepod nauplii was probably affected by increasing pressure of fish filter-feeders. Data on fish food consumption, feeding behaviour and fisheries management suggested their direct impact on long-term changes of zooplankton in Lake Kinneret.