Connecticut Lakes Research Articles

Estimating historical in-lake alkalinity generation from sulfate reduction and its relationship to lake chemistry as inferred from algal microfossils

Sediment cores were used to estimate in-lake alkalinity generation resulting from sulfate reduction relative to inferred changes in lakewater pH and trophic status over the last century in three Connecticut lakes. Despite being situated in geological settings with crystalline bedrock and thin, poorly buffered soils, and being impacted with high rates of acidic precipitation, none of the study lakes have declined in inferred pH based on scaled chrysophyte and diatom remains. In fact, the pH of one of the lakes, Coventry Lake, has significantly increased over the last century. Over the last 44 to 69 years the amount of sulfur stored in the sediments from each lake increased from ~two to three times resulting in mean rates of alkalinity generation ranging from 78 to 145 meq m−2 yr−1, significantly higher than the 45 to 48 meq m−2 yr−1 of hydrogen ions falling directly on the lake surfaces. In-lake alkalinity generation resulting from sulfate reduction has been sufficient to neutralize all of the acid falling directly onto the lake surfaces, as well as between 9% and 25% of the acid deposited onto the surrounding watersheds. Despite the increased importance of in-lake alkalinity generation, our findings support the hypothesis that significant amounts of alkalinity are also being generated in the catchments of the study lakes. The bulk of the increases in stored sulfur in all three lakes were as Fe sulfides and not in the form of organic sulfur, suggesting that the increases were the result of dissimilatory bacterial reduction of sulfate. As a result of the large increases in storage of Fe sulfides the ratio of total iron to chromium reducible sulfur (Fe:CRS) has declined in all cores over time. Despite the overall decline in Fe:CRS in recent sediments, values are still largely above 3 in more recent sediments of two of the lakes. However, values of Fe:CRS have dropped below 1 in surface sediments of Uncas Lake, suggesting that in-lake loading of phosphorus may be responsible for a recent shift in the algal flora towards a slightly more eutrophic condition.

Factors Influencing Growth and Body Condition of Alewives in Connecticut Lakes

ABSTRACT Alewives were collected by nighttime gill netting during summer 1999 from 12 Connecticut lakes that support landlocked populations to determine relationships between population characteristics and physicochemical lake variables. Mean catch-per-unit-effort (CPUE) ranged from 0.2 to 16.4 age-1 and older alewives per net hour. Maximum ages of alewives among lakes ranged from two to five years, and mean back-calculated length-at-age-1, used to index growth rate, ranged from 78 to 146 mm. Mean back-calculated length-at-age-1 was positively correlated with mean relative condition factor (Kn), watershed area:lake surface area ratio, watershed area:lake volume ratio, lake surface area:lake volume ratio, conductivity, total nitrogen, alkalinity, calcium, magnesium, and chlorophyll a, and negatively correlated with retention time, maximum lake depth, mean lake depth, and transparency. Mean Kn ranged from 0.93 to 1.23 and was positively correlated with mean back-calculated length-at-age-1, watershed area:lake volume ratio, lake surface area:lake volume ratio, total nitrogen, chlorophyll a, and potassium, and negatively correlated with maximum lake depth and transparency. Growth and Kn of alewives were highest in shallow, productive lakes with low transparencies. CPUE was not related to growth rate or to any physicochemical lake variable.

Morphological studies in selected fragilarioid diatoms (Bacillariophyceae) from Connecticut waters (U.S.A.)

Several fragilarioid diatoms were found in surface sediment samples from Connecticut (U.S.A.) as part of a paleolimnological study on a set of 60 freshwater lakes. Observation of acid-digested material under scanning electron microscopy (SEM) revealed morphological variants of Staurosira and Stauroforma absent or seldom illustrated in the literature. Morphological variants of Staurosira reported here could be misidentified during routine ecological analyses due to limitations at the light microscopy (LM) level and because identification keys do not incorporate descriptions of such morphs. SEM observations also revealed the existence of two new fragilarioid taxa in 3 of the 60 Connecticut lakes. One of the new taxa is described here as Pseudostaurosira trainorii sp. nov. and appears to be distributed in fresh and brackish waters. For the second taxon, Pseudostaurosiropsis, nov. gen., is described based mainly on areolar and closing plate structure, features that are visible only at higher SEM magnifications. Pseudostaurosiropsis connecticutensis, sp. nov., with three freshwater populations in Connecticut, is the type species. Morphological aspects and ecology of the newly described taxa, as well as their relationship with other fragilarioid diatoms are discussed.Genus et species novae: Pseudostaurosiropsis, gen. nov.; P. connecticutensis, sp. nov.; Pseudostaurosira trainorii, sp. nov.

Hemolytic-Uremic Syndrome and Escherichia coli O121 at a Lake in Connecticut, 1999.

Non-O157 Shiga toxin-producing Escherichia coli (STEC) have emerged as an important public health problem. Outbreaks attributed to non-O157 STEC rarely are reported. In 1999, follow-up of routine surveillance reports of children with hemolytic- uremic syndrome (HUS) identified a small cluster of 3 cases of HUS, all of whom had spent overlapping time in a Connecticut lake community in the week before onset of symptoms. We conducted an investigation to determine the magnitude and source of the outbreak and to determine risk factors associated with the transmission of illness. We conducted a cohort study and an environmental investigation. The study population included all people who were at the lake in a defined geographic area during July 16-25, 1999. This time and area were chosen on the basis of interviews with the 3 HUS case-patients. A case was defined as diarrhea (>/=3 loose stools/d for >/=3 days) in a person who was at the lake during July 16-25, 1999. Stool samples were requested from any lake resident with diarrheal illness. Stools were cultured for Salmonella, Shigella, Campylobacter, and E coli O157. Broth cultures of stools were tested for Shiga toxin. Case-patients were asked to submit a serum specimen for antibody testing to lipopolysaccharides of selected STEC. Environmental samples from sediment, drinking water, lake water, and ice were obtained and cultured for E coli and tested for Shiga toxin. An environmental evaluation of the lake was conducted to identify any septic, water supply system, or other environmental condition that could be related to the outbreak. Information was obtained for 436 people from 165 (78%) households. Eleven (2.5%) people had illnesses that met the case definition, including the 3 children with HUS. The attack rate was highest among those who were younger than 10 years and who swam in the lake on July 17 or 18 (12%; relative risk [RR]: 7.3). Illness was associated with swimming (RR = 8.3) and with swallowing water while swimming (RR = 7.0) on these days. No person who swam only after July 18 developed illness. Clinical characteristics of case-patients included fever (27%), bloody diarrhea (27%), and severe abdominal cramping (73%). Only the 3 children with HUS required hospitalization. No bacterial pathogen was isolated from the stool of any case-patient. Among lake residents outside the study area, E coli O121:H19 was obtained from a Shiga toxin-producing isolate from a toddler who swam in the lake. Serum was obtained from 7 of 11 case-patients. Six of 7 case-patients had E coli O121 antibody titers that ranged from 1:320 to >1:20 480. E coli indicative of fecal contamination was identified from sediment and water samples taken from a storm drain that emptied into the beach area and from a stream bed located between 2 houses, but no Shiga toxin-producing strain was identified. Our findings are consistent with a transient local beach contamination in mid-July, probably with E coli O121:H19, which seems to be able to cause severe illness. Without HUS surveillance, this outbreak may have gone undetected by public health officials. This outbreak might have been detected sooner if Shiga toxin screening had been conducted routinely in HUS cases. Laboratory testing that relies solely on the inability of an isolate to ferment sorbitol will miss non-O157 STEC, such as E coli O121. Serologic testing can be used as an adjunct in the diagnosis of STEC infections. Lake-specific recommendations included education, frequent water sampling, and alternative means for toddlers to use lake facilities.

Lead analysis of sediment cores from seven Connecticut lakes

Lead analyses were performed on sediment cores from seven Connecticut lakes by dilute acid leaching. The absolute concentrations of lead varied from core to core, but the lead profiles were similar in all of the cores, and each depicted a point where the concentration of lead sharply increased above background levels. The background lead concentrations observed in the bottom portions of the cores ranged from 12-54 μg Pb/g sediment with a mean of 30 μg Pb/g, and increased to a mean maximum of 310 μg Pb/g. In six of the lakes significant increases above background levels were not noted until between 1924 and 1952, suggesting that, at least for Connecticut lakes, the point in a lake sediment core where the concentration of lead began to increase was after ca. 1924, and on average about 1930. Lead concentrations declined in the surface sediments of only three of the lakes, mostly since the 1980's, and presumably in response to the phasing out of leaded gasoline. However, significant declines in lead concentrations were not observed in the remaining cores, possibly due to increased motor vehicle use within the airshed of the lakes and/or changes in the export of lead to the lakes from their watersheds.

Indirect Estimate of Gill Net Mesh Size Selectivity for Landlocked Alewives

ABSTRACT During summer 1999, 5,004 landlocked alewives (Alosa pseudoharengus) were captured from 12 Connecticut lakes using horizontal gill nets with mesh sizes of 9.5, 12.7, 15.9, 19.1, 25.4, and 31.8 mm (bar measure). The most effective mesh size was 12.7-mm, capturing 3,035 alewives. The modal length of alewives caught in each mesh size increased as the mesh size increased from 9.5 to 25.4 mm. No alewives less than 70 mm total length or greater than 245 mm were captured. Modal lengths of selectivity curves estimated indirectly using the Holt model were 85, 114, 143, 172, and 228 mm for the 9.5-, 12.7–15.9-, 19. 1-, and 25.4-mm mesh sizes, respectively. Adding a 22.3-mm mesh and removing the 31.8-mm mesh is suggested to sample landlocked alewives between 100 and 245 mm in Connecticut lakes.

Century changes in Connecticut, U.S.A., lakes as inferred from siliceous algal remains and their relationships to land-use change

Scaled chrysophytes and planktonic diatoms are used to infer changes in lake water pH, specific conductivity, trophic score, and total nitrogen in 23 Connecticut waterbodies over the last 100 yr, and the changes are correlated with quantified changes in land use in the surrounding watersheds. In general, there was good agreement between the changes inferred from both organismal groups in this suite of lakes. Significant correlations were observed between chemical conditions inferred from organisms in surface sediments and present-day land uses, especially the percentages of the watersheds that are forest or residential land cover types. Approximately 20% of the water-bodies have significantly increased in pH since 1890, and none of the lakes have significantly declined in pH despite the fact that this region receives significant amounts of acidic deposition. These findings support previous work, indicating that the pH of Connecticut lakes has not declined over the recent past. One fourth of the lakes have significantly increased in specific conductivity, especially those situated in watersheds that have become highly residential in nature. Inferred specific conductivity has more than doubled in six of the lakes during the last century. Six of the lakes have become significantly more eutrophic, while only one lake has become more oligotrophic since 1890. The majority of the lakes situated in watersheds that have remained over ∼80% forested have not significantly changed, whereas those that have become over ∼25% residential have experienced the greatest amount of change. The potential influences of watershed-based alkalinity generation, winter road salt use, and implications of these findings in lake management are discussed.

Bioaccumulation and Biomagnification of Mercury in Two Warmwater Fish Communities

ABSTRACT Total mercury concentrations were determined in two Connecticut lakes for six fish species representing a range of trophic levels—largemouth bass (Micropterus salmoides), chain pickerel (Esox niger), black crappie (Pomoxis nigromaculatus), bluegill (Lepomis macrochirus), smallmouth bass (M. dolomieu), and yellow perch (Perca flavescens). Total mercury concentrations in all fishes increased with length and age. Slopes of log10 mercury concentration-age regressions, which were used to compare bioaccumulation rates, were different among species in both lakes. In both lakes, no difference in bioaccumulation rate was found between top-level predators. Top-level predators and intermediate trophic level species (black crappie and yellow perch) accumulated mercury at a faster rate than bluegills. Intermediate trophic level species had bioaccumulation rates comparable to top-level predators over the range of ages sampled. Differences in mercury concentrations between a top-level predator (largemouth bass) and intermediate trophic level species decreased with age, while differences between largemouth bass and bluegill increased with age.

Organochlorine Compounds in Fish Tissue from Connecticut Lakes

Due to a lack of information on residues of chlorinated com- pounds in fish from Connecticut lakes and ponds, we conducted a preliminary assessment of total chlordane, total DDT, and total PCBs in fish tissue. Preda- tors (largemouth bass and smallmouth bass) and bottom feeders (common carp, brown bullhead, yellow bullhead, and white sucker) were collected from 16 Connecticut lakes in 1998. Fish tissue samples consisted of a composite of one skin-on fillet from up to three individual fish representing one species. Fish were analyzed for chlorinated compounds by a gas chromatography/electron capture detector. Fish from seven lakes had detectable levels of chlordane. One lake had fish with chlordane residue levels exceeding the Food and Drug Administration action level of 300 micrograms per kilogram (gg/kg) wet weight. At all 16 sites, p,p'-DDE was detected in fish tissue. At seven sites, PCBs, primarily Aroclor-1254, were detected in fish tissue; the highest concen- tration reported was 2344 gg/kg wet weight.

Development of paleolimnological inference models for pH, total nitrogen and specific conductivity based on planktonic diatoms

Canonical correspondence analysis (CCA was used to explore and identify statistically significant relationships between the distributions of planktonic diatoms and the physical and chemical properties of 50 Connecticut lakes. Six variables (pH, total nitrogen, calcium, sulfate, potassium and chlorophyll- a concentrations) were found to be significantly correlated with either or both of the first two extracted axes. The pH and calcium concentration, and to a lesser extent total nitrogen concentrations, were the most important variables controlling the distributions of planktonic diatoms in this suite of lakes. Paleolimnological inference models were developed for pH, total nitrogen (TN) and specific conductivity. Weighted averaging with (WAtol) and without (WA) tolerance downweighting, with and without bootstrap resampling techniques, and using either classical or inverse deshrinking methods were used to develop inference models for each variable. The pH and TN yielded sufficiently high λ1/λ2 ratios and a highly significant first (constrained) axis when entered as single variables in both constrained and partially constrained CCA analyses, supporting the idea that reliable inference models could be developed for these variables. The r2 and RMSE of prediction values ranged from 0.73 to 0.86 and 0.37 to 0.6, respectively for pH, and from 0.4 to 0.64 and 59 μg/l to 95 μg/l, respectively for TN. Inference models for specific conductivity also yielded significant goodness-of-fit statistics. However, because specific conductivity was removed from the CCA analysis due to its high variance inflation factor and did not yield a significant relationship when entered as the sole variable in a partial constrained CCA, inference models for this variable will probably not yield any additional environmental information. The use of only planktonic diatoms in construction of inference models is discussed.

Relationships between Concentrations of Mercury in Largemouth Bass and Physical and Chemical Characteristics of Connecticut Lakes

Abstract Concentrations of total mercury were determined for axial muscle tissue of 438 largemouth bass Micropterus salmoides from 46 lakes representing five regions in Connecticut to determine relationships between mercury concentrations and lake characteristics and to assess regional differences in mercury concentrations. Expected concentrations of mercury (EHg) predicted for a length of 356 mm for each population ranged from 0.103 to 0.795 μg/g wet weight. Principal components analysis revealed that, in general, two types of lakes were represented in the data set and were grouped based on hydrologic characteristics. Type-II lakes (artificial impoundments) had a significantly lower mean retention time than type-I lakes (natural drainage lakes) and a significantly larger mean watershed area, watershed area : surface area ratio, watershed area: lake volume ratio, and shoreline development index. Mean EHg was approximately 20% higher in type-II lakes (0.514 μ/g wet weight) than in type-I lakes (0.410 μg/g ...

Seasonal and Size-Related Food Habits of Largemouth Bass in Two Connecticut Lakes

Stomach contents of 425 largemouth bass were identified and quantified using the Relative Importance (RI) index over three seasons (spring, summer, and fall) from Lake Lillinonah and Pickerel Lake, Connecticut. In Lake Lillinonah during spring, aquatic insects had the highest RI, followed by crayfish and fish (primarily white perch). During summer and fall, the RI of aquatic insects decreased, the RI of crayfish remained consistent, and the RI of fish approximately doubled. Fish (primarily bluegill) was the most important diet item of largemouth bass from Pickerel Lake during all seasons. Aquatic insects were the second most important diet item during spring and summer. In Lake Lillinonah and Pickerel Lake, the RI of aquatic insects decreased and the RI of fish increased with increasing fish length; aquatic insects were most important in largemouth bass less than 300 mm. In contrast to Lake Lillinonah where the RI of crayfish and fish were of equal importance in largemouth bass ≥ 380 mm, largemouth bass ≥ 380 mm in Pickerel Lake fed almost exclusively on fish. Our results suggest that food habits of largemouth depend on the type of lake system and the dominant prey types. In Connecticut lakes that lack suitable littoral areas and associated panfish species, largemouth bass may rely on pelagic fishes and crayfish as food sources.

Spatial and temporal distribution of freshwater sponges in Connecticut lakes based upon analysis of siliceous spicules in dated sediment cores

A survey of 28 Connecticut water bodies for spicular remainsoffreshwater sponges preserved in lacustrine sediments revealed14species representing 10 genera. Sediments were examined atfivelevels (ca 1991, ca 1970, ca 1934, ca 1890, ca ≤ 1875)todocument changes in species composition, distribution, andabundance. Five species were recorded statewide in all fivegeologic regions: Spongilla lacustris, Heteromeyeniatubisperma, Anheteromeyenia ryderi, Eunapius fragilis, andEphydatia muelleri. Spongilla lacustris was the mostcommonand widely distributed species. Factors that may havecontributedto the observed distribution of the spongillids in Connecticutareregional differences in lake water chemistries, individualspeciestolerances, and differences in extent of dispersal of variousspecies. Most of the more abundant species are widelydistributedwith respect to water quality parameters. Anheteromeyeniaargyrosperma, Duosclera mackayi and Trochospongillapennsylvanica appear to be restricted to waters exhibitingthelower ranges for conductivity, alkalinity and calcium content.Ingeneral, a greater number of spicules was found in bottomsedimentsof the surveyed lakes as compared with the surface sediments.Oftenthis was correlated with increased sediment accumulation ratesinmore recent periods. When this fact is taken into account, itappears that populations of a number of sponge species haveremained relatively constant in many of the lakes over thepastcentury. However, in some lakes exhibiting lower or onlyslightlyhigher sediment accumulation rates at the surface, fewerspiculeswere also found in more recent sediments, suggesting an actualdecline in sponge population sizes. Changes in abundance overthelast 100 years may be related to changes in land use practicesinsurrounding watersheds and the associated changes in waterchemistries.

Distribution and ecology of freshwater sponges in Connecticut

A survey of Connecticut lakes and rivers revealed the presence of 7 species of freshwater sponge: Spongilla lacustris, Ephydatia muelleri, Eunapius fragilis, Anheteromeyenia ryderi, A. argyrosperma, Corvomeyenia carolinensis, and Corvospongilla novaeterrae in order of decreasing frequency of occurrence. Corvomeyenia carolinensis has not been reported previously beyond its type locality in South Carolina. In addition, microscleres of Spongilla lacustris, Anheteromeyenia-like megascleres, Ephydatia muelleri-like megascleres, and smooth megascleres (amphioxeas), which could not be assigned to a particular species, were found in surface sediments from lake cores. Spongilla lacustris inhabiting small rivers produced brown, thick-capsuled gemmules during the summer and yellow, thin-capsuled gemmules during the fall. The thick-capsuled gemmules, but not the thin-capsuled gemmules, are tolerant of desiccation; and populations of Spongilla lacustris and Ephydatia muelleri survived severe drying of their habitats during the summer.

Historical Changes in Connecticut Lakes Over a 55‐Year Period

AbstractChanges in the chemical and physical conditions of 42 Connecticut lakes are compared between three time periods, the late 1930s, the mid‐ to late 1970s and the early 1990s. On average, lakes have decreased in Secchi disk depth by 1.2 m and doubled in total phosphorus concentration, many in a unidirectional manner. As a result, the suite of lakes can be characterized as having shifted from an oligo‐mesotrophic condition (1930s) to a late mesotrophic condition (1990s). Since the 1970s, lakes have increased in base cation concentrations an average of 70 μeq/L, many as the result of an increase in sodium. Increases in sodium were generally coupled with increases in chloride ions. Many of the lakes positioned in watersheds that have become more residential since the 1930s and/or 1970s have also increased in alkalinity. Despite the overall increase in base cations, chloride, and alkalinity, about 25% of the waterbodies that have remained situated in primarily forested watersheds in crystalline rock regions have decreased in total cation concentrations; about half of these lakes have also significantly decreased in alkalinity since the 1930s. The changes are discussed in relation to the degree of urbanization of the watersheds over the same time period.

Estimating the Effects of Changing Land Use Patterns on Connecticut Lakes

AbstractChanges in land use of 30 Connecticut lake watersheds between 1934, 1970, and 1990 were quantified using aerial photographs. Results were used with existing land use models to estimate changes in concentrations of total phosphorus (TP) and total nitrogen (TN) over the 56‐yr period. On average, the watersheds have increased in urban‐residential land cover from 2% in 1934 to 16% in 1990, and decreased in agricultural land from 20 to 7% during the same time period. The mean percentage of forested land has remained relatively constant. Based on the land use models of Norvell et al. (1979) and Frink (1991), the mean estimated total phosphorus concentration (eTP) increased from 15 μg L−1 in 1934 to 25 μg L−1 in 1990. The eTP concentrations increased in 26 of the 30 study lakes. In contrast, the mean estimated concentration of total nitrogen (eTN) increased only 20% from 374 to 450 μg L−1. Principal component analysis (PCA) was used to score each study lake according to its current trophic and ionic condition using chemical data from 1991 to 1993, and the results regressed against the 1990 land use types. Trophic scores were most highly correlated with forest cover, while ionic scores were most highly correlated with forest cover and the degree of urban‐residential land cover. The effect of water retention time is discussed. Land use models provide useful tools in the management of lakes.

Chemical and Physical Properties of Connecticut Lakes, With Emphasis on Regional Geology

ABSTRACT Chemical and physical characteristics of 60 drainage lakes in Connecticut are discussed in relation to the geology of the state. Significant differences in composition and quantities of dissolved ions were observed for lakes in different geologic zones. Waterbodies situated on the Eastern Uplands, Western Uplands, and Coastal Slope were more dilute than lakes in the Marble and Central Valleys. Although there were significant differences in Na+, Ca+2, Mg+2, Cl−, SO4 −2, and alkaline anions between different regions, none were found for K+. Unlike ionic chemistry, few differences in trophic variables were observed for lakes in the different geologic areas. On a statewide basis chlorophyll a levels were highly correlated with total phosphorus (TP), total nitrogen (TN), and Secchi disk depths. Summer TN:TP ratios suggested that chlorophyll levels in many lakes may be related to both TP and TN levels. Results are compared to previous studies in Connecticut and other areas of the northeast.

Inferring the specific conductivity of lake water with scaled chrysophytes

Siliceous scale‐bearing chrysophytes have been used successfully in reconstructing the historical pH of lake water. In addition to pH, the distributions of many taxa of scaled chrysophytes are also significantly correlated with the concentration of dissolved salt. A model (r2 of 0.87), based on scaled chrysophytes, was developed with weighted averaging regression to infer the specific conductivity of lake water. The model was applied downcore in a small soft‐water lake in Connecticut whose inferred pH had remained between 6.2 and 6.5 for the past 170 yr. Despite the relatively stable pH, the inferred specific conductivity had more than tripled since the turn of the century. The rise in the salt level of the lake water correlated with known changes in the watershed, including the building of lakeside cottages and establishment of a surface silica mine.

Morphological and ecological characteristics of Chrysosphaerella longispina and C. brevispina (Chrysophyceae)

Although Chrysosphaerella longispina and C. brevispina are common species reported from freshwater localities, only scattered ecological records exist. In addition. most identifications and descriptions are based on features of their siliceous components as viewed with transmission electron microscopy. In this study details of scales and spines are made with scanning electron microscopy. Ecological data for both taxa along seasonal, temperature, pH, specific conductance and total phosphorus gradients are discussed for Connecticut lakes and compared to records compiled from the literature. C. brevispina and C. longispina were found to be distributed primarily in winter and summer/autumn months, respectively. As a result, C. brevispina had a much lower weighted mean temperature of 6°C. Both taxa were found to have maximal distribution between pH 5 and 7, and to be more common in waters low in specific conductance; however, C. brevispina was also observed in localities with higher specific conductance. The distribution of both taxa along trophic gradients is also discussed.

A paleolimnological assessment of lake acidification in five Connecticut lakes

New England has received significant amounts of precipitation with a pH between 4.2 and 4.6. Paleolimnological studies based on siliceous microalgal remains support the hypothesis that some lakes in northern New England have acidified as a result of the acidic deposition. However, paleolimnological analyses from five software lakes in southern New England suggest that these lakes have not acidified in recent years. In all of the study lakes the inferred pH has remained relatively stable, and in two lakes the pH has actually increased slightly in recent years. Despite the relatively stable inferred pH reconstructions, significant shifts in species assemblages were observed in each lake, many of which are believed to correlate with land use changes. It is possible that effects of land use changes (e.g. increased urbanization) have masked potential effects of acid deposition.