The sediment record from a 5.3-m core from Sargent Mountain Pond, Maine USA indicates strong co-evolutionary relationships among climate, vegetation, soil development, runoff chemistry, lake processes, diatom community, and water and sediment chemistry. Early post-glacial time (16,600–12,500 Cal Yr BP) was dominated by deposition of mineral-rich sediment, low in organic matter and secondary hydroxides of Al and Fe; pollen indicate tundra conditions; diatom taxa indicate pH between 7.5 and 8, and total P concentrations of about 25 μg L−1, favoring higher productivity. Chemical weathering was rapid, with high alkalinity, pH, Ca, and P in runoff. As climate ameliorated, about 12,500 Cal Yr BP, forest vegetation became established; soils would have developed vertical zonation, including organic matter accumulation, and incipient podzolic horizons, with accumulating secondary hydroxides of Al and Fe that sequestered P in the soils. Labile minerals (primarily apatite, Ca5(PO4)3(OH,F,Cl)) became depleted in the soil, further reducing the supply of P to the lake. Dissolved organic carbon (DOC) from soil organic matter mobilized Al and Fe to the lake where Al(OH)3 (primarily) and Fe(OH)3 (minor) were precipitated. The sedimenting hydroxides adsorbed P from the water column, further reducing bioavailable P. These long-term trends of moderating climate, and changing terrestrial biology, soils, and aquatic chemistry and phytoplankton were interrupted by the 1,000-year long Younger Dryas cooling, which led to a temporary reversal of these processes, a period that ended with the major onset of Holocene warming. The sequestration of P by soils would have strengthened because of long-term soil acidification and pedogenesis. The lake was transformed from a more productive, high P, high pH, low DOC system into an oligotrophic, relatively low P, acidic, humic lake over a period of 16,600 years, a natural trend that continues. In contrast to many human-affected lakes that become increasingly eutrophic, many lakes become more oligotrophic during their history. The precursors for that are: (1) absence of human land-use in watersheds, (2) bedrock lithology and soil with a paucity of soluble Ca-rich minerals, and (3) vegetation that promotes the accumulation of soil organic matter, podzolization, and increased export of metal-DOC complexes, particularly Al.

Historical phosphorus (P) dynamics were studied using sediment cores from three oligotrophic, acidic lakes in Maine, USA. Long-term oligotrophy of these lakes is consistent with high sediment aluminum (as Al(OH) 3 ) concentrations, as Al inhibits internal P loading, even under reducing conditions. The role of microbially-mediated reactions in controlling redox conditions was evaluated by estimating microbial biomass and relative abundance of specific functional groups. Sediments were fractionated using a sequential chemical extraction technique and all lakes met criteria for P retention based on threshold sediment concentrations of Al, Fe, and P fractions as determined by (Kopáček et al. ( 2005 ) Limnol Oceanogr 52: 1147–1155). Sediment NaOH-extractable molybdate-reactive P (rP) and non-reactive P (nrP) represent P associated with non-reducible phases, and organic matter-related P, respectively. Total P (TP) does not decrease with sediment depth, as is typical of eutrophic lake sediments; however, nrP/TP decreases and rP/TP increases for all three lakes, indicating nrP mineralization without any significant upward diffusion and release into the hypolimnion; i.e. diagenesis of P is conservative within the sediment. Two diagenetic models were developed based on nrP and rP concentrations as a function of sediment age. The first model assumes a first-order decay of nrP, the rate coefficient being a function of time, and represents irreversible nrP mineralization, where the produced PO 4 is permanently sequestered by the sediment. The second model assumes a first-order reversible transformation between nrP and rP, representing biotic mineralization of organic P followed by incorporation of inorganic P into microbial biomass. Both models reflect preservation of TP with no loss to overlying water. The rate coefficients give us insight into qualities of the sediment that have affected mineralization and sequestration of phosphorus throughout the 210 Pb-dateable history of each lake. Similar models could be constructed for other lakes to help reconstruct their trophic histories. Paleolimnological reconstruction of the sediment P record in oligotrophic lakes shows mineralization of nrP to rP, but unlike the case in eutrophic lake sediments, sediment TP is preserved in these sediments.

Phosphorus (P) may be liberated from lake sediments by reductive dissolution of Fe(OH)(3(S)) during periods of hypolimnetic anoxia. P, however, remains adsorbed to Al(OH)(3(S)) regardless of redox conditions. During chronic or episodic acidification of a catchment, ionic Al is mobilized from soils to receiving waters. A fraction of the mobilized Al may precipitate as a consequence of higher pH of the receiving waters. We hypothesized that phosphorus retention in lake sediments is directly related to the magnitude of Al loading in response to low pH in the watershed. We studied cores representing over 200 years of sediment accumulation in historically acidic Mud Pond and Little Long Pond in eastern Maine, USA. Sequential chemical extractions of sediment were used to assess the history of Al, Fe, and P interactions. Mud Pond is a first-order pond with a pH of similar to 4.7, having acidified slightly in response to anthropogenic acidification from similar to 1930. The inlet stream to Mud Pond has dissolved Al concentrations often exceeding 500 mu g/L, of which more than half is organically-bound. Mud Pond drains into Little Long Pond, a second-order pond with a historical pH of <6, and which has shown little pH or alkalinity response to increases or decreases in atmospheric SO42- input.Sequential extractions show that Al and P are predominantly in the 0.1 M NaOH-extractable fraction in the sediments from both ponds throughout the cores. The concentration of the likely biogenic and non-reactive P within the NaOH fraction increases up core from <30% to similar to 60%. Extractable Fe (<20% of extractable Al) is mainly in the 0.1 M NaOH-extractable fraction, except for the top few cm, which are predominantly in the bicarbonate-dithionite reducible fraction. Accumulation rates of sediment, Al, Fe, and P in both ponds have increased in the last 50-60 yr, but fractions remain in the same proportion. Throughout both sediment cores the molar ratio of specific ALP fractions greatly exceeds 25, and molar ratio of specific Al:Fe fractions greatly exceeds 3, the thresholds proposed by Kopacek et al. [Kopacek J, Borovec J, Hejzlar J, Ulrich K-U, Norton SA, Amirbahman A. Aluminum control of phosphorus sorption by lake sediments. Environ Sci Technol 2005; 39: 8784-89.] for P release during anoxia. The data illustrate a continuous association of P with Al in both ponds during the last two centuries, likely due to the persistent natural acidity of the catchments. (C) 2008 Elsevier B.V. All rights reserved.

To further evaluate the potential use of Mg/Ca and Sr/Ca ratios as a paleothermometer in the shell carbonate of the blue mussel Mytilus edulis, we grew juvenile mussels (∼15 mm shell height; <2 years old) collected from Maine, USA, in controlled environments for 4 months. The four-by-three factorial design consisted of four circulating temperature baths (7, 11, 15 and 19°C), and three salinity ranges (23, 28, and 32). During the experiment, water Mg/Ca and Sr/Ca molar ratios were monitored weekly, and showed little variation across all salinity and temperature ranges. Data from sampled shells including all salinity treatments yielded relatively poor relationships between shell elemental chemistry and water temperatures. However, if only the low salinity treatment data (23) are used, the relationships between shell elemental chemistry and water temperature improve moderately. Based on the data presented here, it may be possible to use Mg/Ca and Sr/Ca ratios from the shell carbonate of juvenile M. edulis to reconstruct paleotemperatures in estuarine settings (salinity below 24) with a corresponding RMSE (root mean squared error; 95% confidence interval) of ±2.4°C and ±2.8°C, respectively. In order for this methodology to be statistically meaningful, water temperature changes must be rather large, as the errors associated with using Mg/Ca and Sr/Ca ratios from the shell material of M. edulis are substantial. Further work is required to determine if the findings presented here can be duplicated, and if the potential salinity effect is pervasive.

Lake sediment cores, dated by 210Pb, were collected from Spectacle Pond (SP), Massachusetts, and Side Pistol Lake (SPL) and Sargent Mountain Pond (SMP), Maine, USA. SP is a kettle seepage lake in granitic sand and gravel. SMP is a drainage pond on granite with little soil in the small watershed. SPL is a drainage lake in granitic till. The three cores were analyzed for total Cd. For SP and SMP, maximum concentrations of 1.7 and 3.9mg/kg, four and eight times background concentrations, respectively, occur in the late 1960s. Accumulation rates reach maximum values concurrently with concentration and are 0.054 and 0.016μg/cm2/a, more than 10 times background. Concentration and accumulation rate age relationships in SMP and SP are similar for background values, timing and magnitude of increase to peak values, and the decrease nearly to background values since about 1975. The chemical response to decreased atmospheric deposition lags in SPL sediment. Kettle-like lakes more clearly indicate changes in atmospheric deposition than drainage lakes.