Sedimentary diatom concentrations and accumulation rates as predictors of lake trophic state

Diatom concentrations in surface sediments are positively correlated with limnetic chlorophyll a concentrations in Florida (USA) lakes. Using this relationship, I examine models that provide quantitative inferences for trophic state in historical applications.The best model predicts chlorophyll a trophic state index (TSI) values from log-transformed diatom concentrations and explains approximately half the variance in the dependent variable. Diatom accumulation rates are not better than sedimentary diatom concentrations as predictors of TSI. The entire diatom assemblage is as sensitive an indicator of TSI as are the planktonic diatoms alone. A model that considers the ecological preferences of specific taxa was found to be a better predictor than the model based on total diatom concentration.The sedimentary diatom concentration model provides a useful method for assessing historical changes in primary productivity, except in lakes where factors (e.g., silica limitation, blue-green bacterial inhibition) limited diatom production, or post-depositional changes removed sedimentary diatoms. TSI inferences are presented for sediment cores from two Florida lakes, one of which demonstrates a problematic application, and the other of which does not.     

Sedimentary records of accelerated nutrient loading in Florida lakes

Transfer functions relating trophic state (Carlson's TSI_{chlorophyll-a}) to present day accumulation rate of (1) nutrients, (2) cations, and (3) organic sediment, are computed using Binford's ²¹⁰Pb-dilution method. As computed from surficial sediments of 27 lakes, former trophic states are reconstructed for recent (²¹⁰Pb-dated) sedimentary histories of 14 lakes. Of the three kinds of models potentially available, model (3) (TSI vs. organic accumulation) is the weakest statistically, and may be unduly influenced by exceptional deposition and/or preservation of allochthonous organic matter. At present, however, it is the only model applicable to all 14 of the histories tested. Results are encouraging in that model accurately predicts observed TSI's in several mesotrophic and eutrophic lakes. Clearly significant increases (accelerations) are inferred only for a of the most eutrophic lakes of the set, while the model consistently overpredicts TSI's of the 7 most oligotrophic lakes. As Whitmore's diatom-assemblage index is a better predictor of TSI than is model (3) in the one eutrophic lake in which it has been tested, we expect more persuasive results when models (1) and (2) can be tested within a more complete set of analytical data. We were surprised to find 3 severely disturbed lakes among the 12 that show little or no acceleration in rate of eutrophication in recent decades, but we defer attempts at explanation until former nutrient loading can be tested by model (1).     

Ecological correlates of net accumulation rates of Cladocera remains in lake sediments

Paleolimnological study of plant and animal microfossils is based on either relative abundances or net accumulation rates of various taxa. Interpretation of the latter is difficult because ecological factors that influence accumulation rates have been unknown. I use a novel method of ²¹⁰Pb assay to estimate net accumulation rates of bosminids and chydorids at the sediment-water interface of 15 Florida (U.S.A.) lakes which represent a wide range of trophic state, water chemistry, and morphometry. Thirty-two species of Chydoridae, and two genera of Bosminidae were recovered from the lake sediments. Accumulation rates of 6 of the 11 more abundant chydorid species and both bosminid taxa were positively correlated with trophic state as measured by chlorophyll a concentration. Lake size was positively correlated with accumulation rates of 4 chydorid species and both bosminids. Weedbed area was positively correlated with accumulation rates of 2 chydorids, but neither bosminid. Lakewater pH was positively correlated with only one chydorid species accumulation rate. Multiple regression models explain statistically nearly all of the variance in each of the limnological variables, and can be used as transfer functions for paleolimnological inference.     

Deepwater sediments and trophic conditions in Florida lakes

Sediment cores were taken from near maximum depth in 15 Florida lakes representing a wide range of trophic conditions. Chemical analyses of surface sediments showed Al, Fe, and Ca to be the most abundant elements in all samples, and the ratio of Al to Ca to be smaller for eutrophic lakes. Sediment organic matter increased with trophic state, as did the degree to which it was enriched in nitrogen. Corresponding sediment C/N ratios decreased with increasing lake trophic state and showed significant negative correlation with chlorophylla, total N, and total P in the water column. Concentrations of sedimentary chlorophyll derivatives showed some relation to trophic state but differences in basin morphometry hinder its use as an inter-lake index of chlorophyll production.     

Nitrogen mass balances and denitrification rates in central Ontario Lakes

Nitrogen mass balances for seven unproductive lakes and 20 forested catchments in central Ontario were measured between 1977 and 1989. Average annual lake denitrification rates calculated with the N/P ratio method were strongly correlated with summer anoxic factor (extent of surficial sediment anoxia) whereas denitrification rates calculated with a²¹⁰Pb sediment N accumulation method were poorly correlated with the anoxic factor suggesting that the N/P method is superior. Substantial denitrification occurred in all lakes — an average of 36% of TN inputs or 75% of the net gain. On a regional area-weighted basis, 67% of bulk atmospheric TN deposition was stored or denitrified terrestrially, 12% was denitrified in lakes, 4% was stored in lake sediments, and 17% was exported from lakes. N/P ratios were generally less in streams than in precipitation suggesting preferential N retention in catchments, whereas the N/P ratios in lake outputs were slightly higher than lake input ratios, suggesting preferential P retention in lakes. This is consistent with the notion that P-limited lakes can exist adjacent to N-limited forests.     

Phosphorus Fractions and Fluxes in the Water Column and Sediments of a Tropical Reservoir (Lobo‐Broa – SP)

Sedimentation rates of organic and inorganic matter, chlorophyll a, P fractions, Ca, Mn, Fe and Al, were determined by sediment traps in a tropical oligo‐mesotrophic reservoir of São Paulo (Brazil). Vertical profiles of the sediments were analyzed for organic content, metals, P and surface P fraction composition. Estimated mean sedimentation rates, corrected for resuspension were: total solids, 1068 g m^—2 y^—1 (OM = 44.7%); chlorophyll a, 2.1 g m^—2 y^—1 and total phosphorus, 2.9 g m^—2 y^—1. The predominant P fraction in the settling flux was associated with aluminum minerals while surface sediments were dominated by organic P. The reservoir exhibited low sediment retention of P (13.0%), Al (9.9%), Fe (9.9%), Mn (1.4%) and Ca (traces), compared to trap sedimentation. This feature was related with a high vertical dynamics (resuspension and bottom release) and with the low retention time of the system.     

The effect of water depth on bacterial numbers,thymidine incorporation rates and C:N ratios in northeast Atlantic surficial sediments

The effect of water depth on bacterial biomass and their ability to synthesise DNA, by measuring their rate of [³H]-thymidine incorporation, was investigated in the northeast Atlantic at three sites of varying water depth (1100–3580 m) and sediment characteristics. Thymidine incorporation rates (y) in surficial sediments varied between 0.028 and 1.44 pmol h^–1 g^–1 and showed an exponential relationship with depth (x) according to the equation y= 2.05e^–0.0011x (r=0.9830 for n=7, P<0.001). However, this relationship failed when a layer of phytodetritus was found overlying the surface sediment and [³H]-thymidine incorporation rates increased by 80–339%. In contrast, bacterial numbers varied between 1.09 and 11.96 × 10⁸ cells g^–1 (dry weight) and showed no significant relationships with water depth or sediment POC/TN content. Significant exponential relationships were also found between water depth (x) and the POC (y ₁) and total nitrogen (TN, y ₂) content of surficial sediments according to the following equations: where y ₁ = 719e^–0.0003x (r=0.8700 for n=9, P<0.01) and y ₂ = 76e^–0.0002x(r=0.7582 for n=9 P<0.02). These relationships were irrespective of the presence or absence of an overlying layer of phytodetritus. This suggests that the POC and TN content of these surficial deep sea sediments is directly related to the flux of material through the water column, which significantly impacts bacterial production.     

Benthic phosphorus regeneration in the Potomac River Estuary

The flux of dissolved reactive phosphate from Potomac riverine and estuarine sediments is controlled by processes occurring at the water-sediment interface and within surficial sediment.In situ benthic fluxes (0.1 to 2.0 mmoles m⁻² day⁻¹) are generally five to ten times higher than calculated diffusive fluxes (0.020 to 0.30 mmoles m⁻² day⁻¹). The discrepancy between the two flux estimates is greatest in the transition zone (river mile 50 to 70) and is attributd to macrofaunal irrigation. Bothin situ and diffusive fluxes of dissolved reactive phosphate from Potomac tidal river sediments are low while those from anoxic lower estuarine sediments are high. The net accumulation rate of phosphorus in benthic sediment exhibits an inverse pattern. Thus a large fraction of phosphorus is retained by Potomac tidal river sediments, which contain a surficial oxidized layer and oligochaete worms tolerant of low oxygen conditions, and a large fraction of phosphorus is released from anoxic lower estuary sediments. Tidal river sediment pore waters are in equilibrium with amorphous Fe (OH)₃ while lower estuary pore waters are significantly undersaturated with respect to this phase. Benthic regeneration of dissolved reactive phosphorus is sufficient to supply all the phosphorus requirements for net primary production in the lower tidal river and transition-zone waters of the Potomac River Estuary. Benthic regeneration supplies approximately 25% as much phosphorus as inputs from sewage treatment plants and 10% of all phosphorus inputs to the tidal Potomac River. When all available point source phosphorus data are put into a steady-state conservation of mass model and reasonable coefficients for uptake of dissolved phosphorus, remineralization of particulate phosphorus, and sedimentation of particulate phosphorus are used in the model, a reasonably accurate simulation of dissolved and particulate phosphorus in the water column is obtained for the summer of 1980.     

Paleolimnology of Slapton Ley,Devon, UK

Slapton Ley, a coastal lake in SW England, has been shown by a variety of paleolimnological studies, to have become increasingly eutrophic in the period since 1950 AD. Since that time, intensification of agriculture has resulted in increased erosion of topsoil from fields in the catchment of the Ley. Sediment accumulation rates, as estimated by ²¹⁰Pb-dating and multiple core correlation of peaks in whole core volume magnetic susceptibility, are equivalent to a catchment erosion rate of 13.4 t km^–2 a^–1, which figure agrees well with directly monitored data. Diatom and chlorophyll a analysis of the uppermost sediments shows that the Ley has recently experienced a major shift in its trophic status, changing from a clear water, macrophyte lake to one dominated by plankton in a hypertrophic system. This last point is further amplified in the paper by Heathwaite & O'Sullivan (1991).     

Chlorophylla and adenosine triphosphate levels in Antarctic and temperate lake sediments

Analysis of adenosine triphosphate (ATP) from surficial sediment layers in two antarctic lakes and two temperate lakes showed a high degree of similarity in spite of differences between trophic state, mictic state, or geographic location. Adenosine triphosphate was found at all levels sampled in temperate lake sediment cores but occasionally was present only in surficial layers of antarctic cores. Surficial sediment layers from antarctic lakes contained high chlorophylla (Chla) levels due to the extensive benthic algal mats which occur there. In some antarctic cores, Chla was detectable in deep, old mat layers, whereas Chla was not found in any of the temperate lake cores. Antarctic lake sediments appear to be unique environments where Chla molecules can remain intact for long periods of time due to low light, temperature, and microbial activity. As such, these lakes are important natural laboratories where a long history of microbial interactions can be studied without metazoan perturbation effects. Although there was much variability in concentration of Chla and ATP between samples, there appears to be no relationship between Chla or ATP levels to mictic or trophic states of the lakes. These data suggest that sediment microbial communities may be independent of environmental and biological properties of the overlying water masses.     

Interpretation of bryozoan microfossils in lacustrine sediment cores

Bryozoan statoblasts were isolated from the surficial sediments of 30 Florida lakes representing a gradient of trophic conditions. A prerequisite for lake selection was a good data base for water chemistry that was collected within the past 5–10 years. A novel technique of employing 210-Pb as a dilution tracer was used to estimate sedimentation rates for each lake. The net annual accumulation rate for bryozoan statoblasts was calculated for each lake and correlated with twelve physical, chemical, and biological variables. The results suggest that bryozoan distributions are strongly controlled by the extent of the littoral zone and phytoplankton biomass. It appears that bryozoan abundance in excessively weeded lakes may be limited by phytoplankton in spite of the richly developed habitat. Separation of the importance of food requirements from habitat requirements was not possible from this initial survey.     

Sedimentary losses of phosphorus in some natural and artificial Iowa lakes

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.     

Calcium and magnesium in ryegrass some differences in accumulation by roots and in translocation to shoots

Summary Thirty-day old intact ryegrass plants (Lolium perenne) were exposed to solutions of Ca, Mg, or Ca+Mg. Each ion was present at 0.25 mM and each solution was labeled with an appropriate radioisotope (Ca⁴⁵ or Mg²⁸). Plants were harvested at various times over a 12-hour period and analyzed for incorporation of the radioisotopes and for the total quantities of Ca and Mg present. Uptake of the exogenous ions was calculated on the assumption that uptake of both carrier and isotopic species occurred in proportion to their concentrations in the ambient solution. Steady state rates of exogenous ion uptake by roots and translocation to shoots were observed for both ions during the 2–12 hour period. During this time the rate of exogenous Ca accumulation in the shoots substantially exceeded that in the roots, and the presence of ambient Mg had relatively little influence on either rate. However, ambient Mg did decrease the exogenous Ca taken up in the 0–2 hour period. The steady state rate of exogenous Mg accumulation in roots and shoots exceeded that of exogenous Ca, and the presence of ambient Ca suppressed both exogenous Mg rates about equally. Significant net accumulation of Ca occurred in the root tissue during the 2–12 hour period whereas with Mg there was little net accumulation. A constant rate of depletion of endogenous Mg, which was restricted by presence of ambient Ca, was observed. Evidence from the observed 2–12 hour y-intercept values for root accumulation of the two ions suggests the possibility of specific adsorption sites for Ca.Paper Number 4513 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, North Carolina. These investigations were supported in part by the U.S. Atomic Energy Commission, Grant No. AT-(40-1)-2410.Paper Number 4513 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, North Carolina. These investigations were supported in part by the U.S. Atomic Energy Commission, Grant No. AT-(40-1)-2410.     

Influence of <Emphasis Type="Italic">Potamogeton crispus</Emphasis> growth on nutrients in the sediment and water of Lake Tangxunhu

An incubation experiment was performed on Potamogeton crispus (P. crispus) using sediment collected from Lake Tangxunhu in the center of China, in order to determine the effects of plant growth on Fe, Si, Cu, Zn, Mn, Mg, P, and Ca concentrations in the sediments and overlying waters. After 3 months of incubation, Ca, Mg, and Si concentrations in the water column were significantly lower, and P and Cu concentrations were significantly higher than in unplanted controls. The effect of P. crispus growth on sediment pore waters and water-extractable elements varied. Concentrations of Ca, Mg, Si, Fe, Cu, and Zn were significantly higher, and P was significantly lower, than in pore waters of the control. Water-extracted concentrations of Fe, Mg, and Si in the sediments were lower, and P was higher, than in the control. Presence of P. crispus generally enhanced concentration gradients of elements between pore waters and overlying waters but not for P. The growth of P. crispus was associated with an increase in water pH and formation of root plaques, resulting in complex effects on the sediment nutritional status. Handling editor: S. M. Thomaz     

Reconstruction of human influence during the last two centuries on two small oxbow lakes near Warsaw (Poland)

Short sediment cores from two small oxbow lakes located in the Vistula valley near Warsaw (Poland) were analysed for chemical composition and zooplankton (Cladocera) remains. The results of these analyses were evaluated using ordination techniques and the results were used to reconstruct the history of human impact of the lakes. The cores were dated using the ²¹⁰Pb method. These analyses show that the collected sediments (60 cm- and 67 cm-long-cores) were deposited during the last 150–200 years. Cladocera assemblages were different in the two lakes; however, Bosmina longirostris was dominant among subfossil Cladocera species in both lakes. The presence of this species indicates the high trophic state of the lakes. Changes in Cladocera species composition suggest that a significant increase in the lakes’ trophic levels has occurred since the 1920s. The change could be related to the construction of flood dikes along the river Vistula, the isolation of the studied lakes from the river, changes in land use, or some combination of these factors. The chemical composition of sediments, particularly the increase in phosphorus and sulphur concentrations, confirms that the construction of dikes against flood was the major factor inducing eutrophication of the oxbow lakes. This study shows that the Warsaw small water bodies are especially sensitive to local disturbances caused by human activity, mainly water management, land use changes and agriculture. Guest editors: K. Buczkó, J. Korponai, J. Padisák & S. W. Starratt Palaeolimnological Proxies as Tools of Environmental Reconstruction in Fresh Water     

Trophic Classification of Non‐Perennial Reservoirs Utilized for the Development of Culture‐Based Fisheries,Sri Lanka

The aim of this study was to check the suitability of some trophic models developed for temperate regions to classify the non‐perennial reservoirs of Sri Lanka in order to manage culture‐based fisheries of those reservoirs. A limnological study was carried out in 45 non‐perennial reservoirs, which have been randomly selected for stocking of fish fingerlings for the development of culture‐based fisheries. High total phosphorous (TP) content in relation to algal biomass indicates high non‐algal turbidity in all reservoirs. Carlson's trophic state indices (TSI) measured on the basis of Secchi disc depth [TSI (SDD)], TP [TSI (TP)] and chlorophyll a [TSI (Chl‐a)] show that the 45 reservoirs studied are characterized by TSI (TP) = TSI (SDD) > TSI (Chl‐a), indicating that non‐algal particulate matter or colour dominates underwater light attenuation. As TSI (Chl‐a) is positively correlated to culture‐based fisheries yield, it is useful for planning culture‐based fisheries development strategies in non‐perennial reservoirs of Sri Lanka, and has the potential to be used elsewhere in the tropics for comparable developments. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The inventories of anthropogenic Ph,Zn, As,Cd, and the radionuclides 137Cs and excess 210Pb in lake sediments of the Adirondack region,USA

We determined the inventories of four anthropogenic trace elements, Pb, Zn, As, and Cd, and two radionuclides, ¹³⁷Cs and excess ²¹⁰Pb, in sediment cores collected from eight remote lakes in the Adirondack region of the northeastern United States. The inventories of all six substances vary considerably among the sediment cores, although the lakes and their associated catchments must have received similar cumulative per unit area atmospheric inputs of these substances. These variations are highly correlated, indicating that the trace elements and radionuclides are affected in a coherent way by the processes controlling their deposition to the sediments of these lakes. Assuming that the anthropogenic trace element inventories in each sediment core are enhanced or depleted relative to cumulative atmospheric deposition to the extent indicated by the sediment core inventories of either ¹³⁷Cs or excess ²¹⁰Pb, we produced estimates of the cumulative atmospheric inputs of the four anthropogenic trace elements to this region. Comparison of the excess ²¹⁰Pb normalized anthropogenic Pb, Zn, Cd inventories of the Adirondack sediment cores with excess ²¹⁰Pb normalized inventories of the same substances in a group of South Central Ontario lakes suggests that the Adirondack region has received greater cumulative anthropogenic inputs of Pb, Zn and Cd by a factor of 1.6, 4.5, and 2.9, respectively.     

Sediment supply and accumulation in a small Moroccan lake: an historical perspective

Dayat-er-Roumi is a small lake (73 ha) located in the sub-humid region of NE Morocco. Lake sediment and catchment soils are examined to identify areas of sediment supply to the lake. Magnetic measurements and clay mineralogy are used to show that recent lake sediment is derived predominantly from eroded topsoil. ²¹⁰Pb dating of one sediment core provided a chronology for the calculation of sediment accumulation rates. The rate of sediment accumulation increased slowly throughout the earlier part of the 20th century and then rapidly in the mid-1970's. These increases are attributed to human disturbances in the catchment, initially by olive planting and then by drainage of a wetland area.     

Assessing microbial diversity using recent lake sediments and estimations of spatio‐temporal diversity

Aim Recent papers have used large palaeolimnological datasets to reveal the biodiversity patterns of aquatic microorganisms. However, scant attention has been paid to the influence of time on these patterns. Where lake surficial sediment samples are used as integrals of diversity, the time interval of each sample varies according to differences in sediment accumulation rates. This paper aims to test the reliability of using lake surface sediments to measure and to compare microbial diversity when the potential influences of the species–time relationships are taken into account. Location Alpine lakes in Europe. Methods We analysed microorganism (siliceous microalgae) assemblages in three European Alpine lakes using short sediment cores (²¹⁰Pb‐dated) and annual sediment trap samples from 12 UK lakes. The same number of individuals was pooled for each sample 500 times to avoid sampling effort effects and to standardize species diversity estimation. The influence of time on the diversity score was assessed by simulating an increase of time span for surface sediment samples by cumulatively adding in successive sediment core samples (from the most recent to the oldest). We used species richness (S) and the exponential of the bias‐corrected Shannon entropy index (exp(H_b‐c)) to estimate diversity. Results Increasing the time interval represented by a surficial sediment sample did not affect the diversity results. The estimation of diversity was similar for cumulative and non‐cumulative samples. Diversity estimation was only altered in lakes experiencing high community turnover due to strong environmental forcing during the time period spanned by the cumulative sample. Main conclusions The use of surface lake sediments is suitable for estimating the average site diversity of free‐living microorganisms. Diversity is integrated in a single sample and species assemblage composition is derived from microbial communities living in distinct lake microhabitats. Species remains, accumulated in a single sample over several years of environmental variability, represent a diversity integral that captures a spatio‐temporal component equivalent to the γ‐diversity measure.