Dennis S. Anderson

137Cs and 210Pb dating of sediments from soft-water lakes in New England (U.S.A.) and Scandinavia, a failure of 137Cs dating☆

Abstract Deep-water sediment cores from 32 Scandinavian and 19 northern New England, U.S.A., lakes were analyzed for 137Cs; 210Pb was analyzed in cores from 16 and 14 of these lakes, respectively. Additional dating of the New England cores was based on chronostratigraphic pollen markers. The profiles in sediment of 137Cs deviate greatly from expectations based on fallout history. The profiles have their maxima at the surface, and 137Cs occurs at depths dated by 210Pb and pollen as many decades older than the beginning of 137Cs fallout. Non-exponential 210Pb profiles in certain lakes (most in New England) and pollen dates suggest that bioturbation, physical mixing, changes in sedimentation rate, or acidification may be occurring, but this is insufficient to account for the deviant 137Cs profiles. In most of the lakes there is no evidence of mixing. We argue that the occurrence of 137Cs at prefallout sediment depths is due mostly to net downward molecular diffusion and adsorption, and that surface concentration is due to net upward diffusion and adsorption (and possibly also biological uptake), recycling of sedimentary 137Cs in the water column, and delayed input from the watershed. It is probable that much of the 137Cs entering these lakes is carried by organic detritus. Mobility of 137Cs in this sediment may be a function of release by organic decomposition and scarcity of clay minerals for adsorption. Correlation analyses of the sedimentary radionuclide activities vs. physical and chemical characteristics of the lake water, sediment and watersheds suggest that considerable trapping of 137Cs and 210Pb by terrestrial vegetation and organic soils is occurring. The resultant delayed export to these lakes is contributing to the failure of 137Cs as a dating tool, but 210Pb dating can be valid under these circumstances.

Methods of pH calibration of sedimentary diatom remains for reconstructing history of pH in lakes

The pH history of lakes can be inferred from diatom remains in dated sediment cores. To derive transfer functions for pH inference in acidic lakes, we counted diatoms in surface-sediment from 31 soft-water lakes in n. New England (NE) and 36 in Norway (N), covering pH 4.4–7.1. Cluster analysis of each data set indicates that pH 6 is an upper limit for a group of similar diatom assemblages. For each set, we developed multiple linear regressions to relate three versions of the diatom data to pH of surface-waters: (1) relative frequencies of selected diatom taxa, (2) the first principal component (1 PC) of these frequencies, and (3) the frequencies of Hustedt pH groups. Also, simple linear regressions were developed for two versions: (1) Index B and (2) Index Alpha, both based on pH groups. Regressions were run separately for lakes with pH ≤ 6; these are most relevant for pH inference in acidic lakes. The best regressions (N: taxa & 1 PC taxa) have r2 0.69–0.91 and Se 0.24–0.31 pH units, the worst (NE: log alpha) have r2 0.27–0.57 and Se 0.51. In all cases, errors for NE are greater than N, partly due to greater diversity of NE lakes. Regressions based on pH groups (directly & by indices) have smaller r2 and larger Se than those based on taxa and 1 taxa. The Index Alpha is least useful because its requirement for alkaline diatom units is unsatisfied at many acidic lakes. Regressions based on taxa may give erratic pH inferences due to sensitivity to unusual frequencies of individual taxa; this effect is reduced by using 1 PC taxa. Four regressions based on pH ≤ 6 lakes were used for inferring pH in a 210Pb dated core from Nedre Målmesvatn, N (now pH 4.6). There is good agreement among three of the four (not for the regression based directly on taxa) that there has been a decrease of ca. 0.6 pH units starting in the late 1800s.

Relationships of bryophytes and lichens to environmental gradients in Maine peatlands

The most important environmental gradients of Maine peatlands are geologic substrate and alkalinity. Other gradients are coastal-inland climate, moisture content of the peat, P and K concentrations, and shade. Abundance weighted means of pH, Ca, and moisture content of peat are given for the 48 most frequently occurring bryophyte and lichen species. A TWINSPAN differentiated twenty associations. Environments of the first four TWINSPAN dichotomies differed largely by pH and related variables, though Fe, %H2O, shade, microtopography, and degree of humification were also significant. A CCA with forward selection entered pH, P, Fe, Na, %H2O, shade, and a climate factor as the minimum number of variables which best account for the species variation. Bryophyte and lichen distributions are determined primarily by edaphic and hydrologic factors, which determine the kinds and amounts of mineral solutes in peat interstitial water. Two independent chemical gradients were identified: (1) the acidity-alkalinity gradient related to base cation concentrations, and (2) a gradient of Fe, Al, Mn, and Si related to shallowness of peat and inputs from granitic lithologies.

Acidity of twelve northern New England (U.S.A.) lakes in recent centuries

Studies of sediment cores from 12 acidic lakes in granitic, forested and uninhabited catchments in northern New England, U.S.A. produced diatom-inferred pH (IpH) 5.2 to 5.8 and alkalinity (Ialk) −12 to 31 µeq l−1, with slowly declining values at some lakes, for one to four centuries prior to logging. Increases of IpH (Δ0.05 to 0.60) and Ialk (Δ5 to 40 µeq l−1) correlate with logging in the catchments in the early-1800s to early-1900s. Recovery to pre-logging IpH and Ialk correlates with forest succession toward conifers, and is completed in the late-1800s to mid-1900s. Beginning at 1915–1920 (4 lakes), 1930–1950 (4 lakes) and 1965–1970 (4 lakes), IpH and Ialk start decreasing below pre-logging values due to atmospheric acidic deposition, leading to respective total decreases of 0.10 to 0.45 (X=0.25) and 5 to 25 µeq l−1 (X=15). Inputs of anthropogenic Pb, Zn, V, polycyclic aromatic hydrocarbons, and soot from the atmosphere are first detectable in early- to late-1800s sediment, and Cu in late-1800s sediment, increase rapidly in the late-1800s to mid-1900s, and level off or decrease since the 1960s — partly due to emission controls. Decreasing Ca, Mn, and possibly Zn relative to other metals and normalized to organic content, and increasing flux of Fe to the lakes, indicate soil and water acidification after 1900.

CLASSIFICATION AND DISTRIBUTION OF FRESHWATER PEATLANDS IN MAINE

Abstract This classification Maines freshwater organic wetlands (peatlands) uses nutrient source, geomorphic-hydrologic setting, gross topography of the peat mass, microtopographic pattern, and presence of pools for distinguishing peatland types. We apply these primarily hydro-geomorphological criteria to landscape units called peatland complexes. Vegetation, while important at lower levels of classification and for the description of individual peatlands, is not used in this classification because, typically, all but the smallest peatland complexes in Maine have major areas of differing vegetational physiognomies and types. This classification resembles the peatland division of Canadas current wetland classification more than the classification in most common use in the United States because a large percentage of Maine peatlands are northern in character. Our classification contains eight peatland types. Two of these are divided into two subtypes. Only one of the types has unique floristic and vegetational elements: plateau (coastal) bog. Large Maine peatlands typically contain multiple complexes, commonly of more than one type. We use the term multiple-unit peatland for these multiple complexes. Our classification and survey of the distribution of peatland types in Maine is based on a large representative sample of peatlands. We conducted an air photo survey of ∼1100 peatlands throughout the state, observed a representative subset of 171 of these from aircraft at low altitude, and studied a representative subset of 100 of the 171 on the ground. However, to classify a peatland using our system, only air photo study or aerial observation is needed. The distribution of peatland types in Maine is controlled by gradients of topography, geological substrate, climate, and hydrology. Peatlands are least abundant in the well-drained western uplands. Unpatterned fens occur throughout Maine; hundreds of the smaller ones (∼<10 ha) occur in ice-block depressions (kettles). Five types, all of which also occur in Canada, reach their eastern North American southern limits in Maine: ribbed (string) fens at 45°∼30′N, eccentric bogs at 45°∼10′N, domed bogs with concentric pattern at 44°∼45′N, plateau bogs at 44°∼15′N, and gently convex bogs at 43°∼20′N. These latitudinal limits exclude individual southern outliers). Distributions of peatland types in adjacent areas of New Hampshire and Canada are consistent with those in Maine. We propose that the geographic position of Maine along a steep south (coastal) to north (inland) climatic gradient and a less-steep west-southwest to east-northeast climatic gradient paralleling the coast are the major factors accounting for the diverse representation of peatland types in so limited an area.

Utility of scaled chrysophytes for inferring lakewater pH in northern New England lakes

Scaled chrysophytes in the surface sediments of 58 soft-water northern New England lakes were analyzed to assess their usefulness for inferring pH. The distributions of many taxa are correlated with lakewater pH and associated variables. Canonical correspondence analysis (CCA) and clustering grouped chrysophyte taxa according to their distributions along the pH gradient. For example, Chrysodidymus synuroideus, Mallomonas hindonii, and M. hamata commonly occur in acidic waters (pH<5.5), whereas M. caudata and M. pseudocoronata are common in circumneutral to alkaline waters. Of the five predictive models developed to infer pH, CCA based calibration had the lowest standard error (0.35 pH units). A CCA based predictive model was also developed to infer total alkalinity. The study provides strong evidence that, in the absence of past measured pH data, stratigraphic studies of sedimentary chrysophyte scales will provide accurate reconstructions of pH in northern New England lakes.

Relationships of sedimented diatom species (Bacillariophyceae) to environmental gradients in dilute northern New England lakes

Limnological gradients of small, oligotrophic, and low conductance lakes in northern New England were defined by principal components analysis; relationships of sedimented diatom species to the gradients were investigated by correlation analysis. Diatom distributions were most strongly related to the gradient of pH and alkalinity and the covarying variables, conductance, Mg, Ca, total Al, and exchangeable Al. Weaker relationships to lake morphology, dissolved organic carbon and water color, altitude and marine aerosol inputs, and the distinctive water chemistry of some New Hampshire lakes were also present. Results for 16 taxa of importance in our studies of lake acidity are given in detail and are compared to results from other regions of eastern North America. Planktonic taxa were absent below pH 5.5, with the exception of the long form of Asterionella ralfsii var. americana Korn. The two forms of this taxon differed ecologically: the long form (>45μm) had an abundance weighted mean (AWM) pH 4.90 and occurred mostly in lakes that were deep relative to transparency; the short form (<45μm)had an AWM pH and occurred on lakes that were shallow relative to transparency. The ecological advantage of a “splitter” approach to diatom taxonomy was demonstrated by examination of other taxa as well, including Tabellaria flocculosa (Roth) Kütz. These results have important implications for paleolimnological interpretations.

Anadromous alewives in linked lake–stream ecosystems: do trophic interactions in lakes influence stream invertebrate communities?

Abstract.  Trophic interactions can influence the flux of energy and nutrients between donor and recipient ecosystems, thereby altering recipient food webs and communities. We investigated the potential for anadromous alewife to influence filter-feeding insects in lake outflow streams by altering seston and zooplankton export from lakes to streams through size-selective consumption of zooplankton in lakes. We compared spring and summer zooplankton biomass and body size and seston concentration in 6 lakes and their respective outflow streams (3 with alewife access, 3 without alewife access) in Maine, USA. The contribution of seston particles ≥500-µm and mean pelagic zooplankton size decreased from spring to summer in alewife lakes, but not in lakes without alewife. However, we found no seasonal change in zooplankton body size and seston ≥500-µm in the outflow streams of alewife lakes. Furthermore, zooplankton biomass and seston concentration differed between lakes and streams, a result indicating the influence of additional factors on seston movement from lakes to streams. Last, we found no relationship between filter-feeder biomass or community structure and seston quantity, a result indicating that stream communities probably were not strongly regulated by seston availability. Our results illustrate that strong trophic interactions may not be propagated from lakes to streams and suggest the importance of boundaries in modulating the extent to which trophic interactions in one ecosystem can influence the flow of energy to adjacent ecosystems.

Response of temperate lakes to drought: a paleolimnological perspective on the landscape position concept using diatom-based reconstructions

The hydrological position of a lake within the landscape can affect a number of lake chemical, physical, and biological features, as well as how lakes respond to environmental change. We present a paleolimnological test of the model for landscape position and lake response to climate change proposed by Webster et al. (2000). To investigate how diatom communities have responded to drought relative to landscape position, we examined sedimentary diatom profiles extending through the twentieth century from an upland site (Crystal Lake) and a lowland site (Allequash Lake) in the Northern Highlands region of north-central Wisconsin (USA). To explore changes in diatom communities at each site, we developed a calibration set and transfer functions from 48 lakes in Wisconsin’s Northern Highland Lake District. We further determined planktic:benthic ratios in the two target lakes, developed lake level models, and investigated the sensitivity of planktic:benthic diatom ratios to climatic variability over the past century. In the upland lake, diatom communities responded indirectly to climate via drought-induced changes in lake level, which resulted in shifts in planktic versus benthic habitat availability. This response of diatoms to changes in habitat availability provides an alternative approach for tracking climate change in upland lakes, though careful consideration must be given to the effect of the bathymetry and its relationship to lake level change and habitat zonation at individual sites. In the lowland lake, changes in diatom communities were related to temperature (and possibly lakewater chemistry) and physical changes secondarily. These results are consistent with the model by Webster et al. (2000), with chemical changes occurring in the lowland system and little chemical response in the upland system. However, the biological changes in sediment records presented here provide additional insight into how lake response to climatic change is shaped by landscape position, contributing to a clearer understanding of potential changes in ecosystem structure and function during drought conditions.

Trophic status may influence top–down effects of anadromous alewife Alosa pseudoharengus (Actinopterygii, Clupeidae) in lakes

We investigated the seasonal influence of an effective size-selective planktivore, the anadromous alewife (Alosa pseudoharengus Wilson), on summer zooplankton and phytoplankton communities in a series of lakes in Maine, USA (4 with and 4 without alewife) that ranged from oligotrophic to eutrophic to determine the role of lake trophic state in influencing the relative strength of top–down forces on phytoplankton biomass. Predation by young of the year alewife reduced the mean body length of cladoceran and copepod biomass from spring to summer in alewife lakes, while mean body length remained unchanged in nonalewife lakes. Cladoceran biomass decreased substantially from spring to summer in 3 of 4 alewife lakes, increasing only in the most eutrophic lake. Conversely, cladoceran biomass increased from spring to summer in 3 of 4 nonalewife lakes. Predation by alewife on zooplankton did not have consistent cascading effects on phytoplankton biomass. Analysis of planktonic biomass ratios (phytoplankton biomass: zooplankton biomass) suggests that cascading effects were stronger in oligotrophic systems and weakened with increasing trophic status, as ratios in alewife and nonalewife lakes converged at higher total phosphorous levels. Our results suggest that lake trophic status may influence the relative importance of top–down control of both zooplankton and phytoplankton biomass. The mechanisms that explain this pattern remain elusive and likely require additional efforts to estimate alewife densities, rates of zooplankton and phytoplankton production relative to consumption, and the influence of other physical lake features.