Late-glacial and Holocene acidity changes in Adirondack (N.Y.) Lakes

Lake chemical data from the National Surface Water Survey (NSWS) were corrected for the effects of regional atmospheric deposition and then used to evaluate the role of weathering in supplying base cations, silica, sulfate, and alkalinity to surface waters in alpine vs. subalpine, and in glaciated vs. unglaciated granitic terrane of the western and southeastern United States. Thermodynamic models, idealized reaction stoichiometry, and multivariate regression involving solutes and geographic variables indicate that irreversible weathering can largely account for lake chemistry. By contrast, relatively minor roles are played by reversible ion exchange in soils and sediments, terrestrial bioaccumulation, and transformations in lakes. The regional patterns in lake acidity components (NO,, SO4, DOC, CO3, and statistical relationships between acidity and base cations demonstrate that rock weathering is limited by acid inputs in many alpine catchments prior to fall overturn. The empirical success of the Henriksen alkalinity model depends on a high Ca : Na weathering ratio. The latter increases with increasing physical disturbance of the catchment (iuvenility), hence under natural circumstances attains a maximum as a result of on-going or recent glaciation. The Henriksen model fails in geochemically "old" terrane, where cation losses accompanying silicate weathering attain steady state proportions.

Section: Discussionmentioning

confidence: 48%

Granite weathering and the sensitivity of alpine lakes to acid deposition

Staufer¹

1990

“…He concluded that soils were not acidic immediately after deglaciation but acidified during each interglacial as a result of natural soil weathering processes. Whitehead et al (1986) used sedimentary fossil diatoms to reconstruct the pH history of several lakes in the Adirondack Mountains of New York. They found that some were alkaline shortly after deglaciation but acidified markedly in the early Holocene.…”

mentioning

confidence: 99%

Geochemical and mineralogical indications of pH in lakes and soils in central New Hampshire in the early Holocene1

Ryan

Kahler

1987

In central New Hampshire, sediments of some early Holocene lakes were alkaline and contained carbonate minerals despite granitic bedrock and currently acid soils and surface water in their watersheds. Nearby calcareous bedrock contributed to the till of these watersheds while other lakes, more remote from calcareous bedrock, had early Holocene sediments of neutral pH and devoid of carbonate minerals. Calcite rock fragments in alkaline sediments were eroded from alkaline soils in the watershed. Chemical weathering later acidified these soils and surface waters before modem acid precipitation.

“…Such a decline suggests a continuously decreasing terrestrial export of secondary Fe phase (oxyhydroxides). Weathering rates are high (as is the pH of runoff) in freshly deglaciated terrain as indicated by spatially distributed studies of soil chronosequences (Jacobson and Birks 1980) and site-specific paleolimnological studies at individual lake ecosystems (Whitehead et al 1986). Oxidative weathering of Fe sulfides and the dissolution of readily weatherable trace minerals such as apatite and calcite would deplete the upper soils of these phases rapidly.…”

Section: Resultsmentioning

confidence: 99%

Natural inactivation of phosphorus by aluminum in preindustrial lake sediments

Kopáček

Marešová

Hejzlar

et al. 2007

Noncalcareous phosphorus (P)-rich lake sediments typically release P associated with iron hydroxide [Fe(OH) 3 ] during the development of hypolimnetic anoxia. High concentrations of aluminum hydroxide [Al(OH) 3 ] in such sediments (e.g., in aluminum [Al]-treated lakes) can prevent the P release. Here we show that sediment ability to bind P can naturally develop during lake history because of changes in the Al(OH) 3 concentration and the Al(OH) 3 to Fe(OH) 3 ratio in sediment. We reconstructed the development of sediment Psorption characteristics through the Late Glacial and Holocene periods on the basis of sequential fractionation analysis of P, Al, iron, calcium, and magnesium in a ,14,000-yr-long sediment record, fresh settling seston, and bedrock from Plešné Lake, Czech Republic. The most significant change occurred at the Late Glacial-Holocene transition (,10,000 yr before present), when the watershed became forested and soil erosion decreased. The Late Glacial sediment was rich in mineral detritus, derived from the watershed till and bedrock, had most of its P associated with Fe(OH) 3 (37%) and calcite and/or apatite (42%), and was probably able to release P during anoxia. In contrast, the Holocene sediment was highly organic, the P release during anoxia was likely negligible, and .90% of P was associated with Al(OH) 3 . This Al(OH) 3 originated from photochemical liberation of Al from dissolved organically-bound Al (Al o ) exported to the lake from soils. Because the photochemical mechanism was a more efficient source for Al(OH) 3 than for Fe(OH) 3 , the sediment became a P trap by the beginning of the Holocene. The ability of the sediment to immobilize P increased further during the anthropogenic acidification era because of elevated terrestrial export of ionic Al. Similar sediment fractionation results in cores from six lakes in Maine suggest that this P-immobilizing mechanism is a general process that can occur in lakes with high Al o inputs.