Diatom evidence of environmental changes in wetlands: Cape Cod National Seashore : Part I Prehistoric and historic trends in acidity of the Outer Cape ponds : Part II Comparison of two estuaries: Herring River in Wellfleet and Pamet River in Truro

Winkler, Marjorie

Outer Cape kettle ponds are acid-sensitive ecosystems set in non-weathering crystalline outwash sands. They range in pH from 4.3 to 7.5. The acid ponds characteristically have negative alkalinities, low specific conductance, high nitrate values, and contain more than 70% acid and periphytic diatoms, while the alkaline ponds are subject to tidal influence. Pondwater pH has been relatively stable for the past two years although Cape precipitation pH has varied from pH 3.5 to pH 6.2 during the same time. Diatoms in modern sediments from 15 ponds were divided into pH-related groups. Correlation analysis suggests that each pH-related group of diatoms reflects different characteristics of the ponds. Acidobiontic diatoms are inversely correlated with alkalinity while acidophilic and alkaliphilic diatoms are highly correlated with pH changes (but in different directions). Circumneutral diatoms are inversely correlated with % acid and % periphytic diatoms, while alkalibiontic diatoms are correlated with conductance and all the seawater-associated ions and reflect the coastal environment of the Cape. Changes in pH over the past 12,000 years in Duck Pond were reconstructed through a transfer function. The reconstructed pH suggests that the pond has been acid for its entire history with a mean pH of 5.2 + 0.3. High pH of 6 was caused briefly during the late-glacial by increased windiness and erosion. Although the diatom evidence indicates that Duck Pond did become more acid recently, the pH has varied both up and down throughout the Holocene, and Duck Pond has had acidity as low as the present at other times in the past 12,000 years. Significant correlation between charcoal influx and alkaline Fragilaria diatoms in the pre-European-settlement core and between % charcoal and total acid diatoms in the post-European-settlement core, highlight the effect of local alkaline inputs from forest fires in the drainage basin, in contrast to acidic inputs from windborne ash and gases from fossil fuel combustion. Inverse correlation between diploxylon Pinus species and reconstructed pH and linear correlation between haploxylon Pinus and alkaliphilic diatoms, suggest that vegetation changes reflecting climate and fire history, also affected the pH of the pond. Diatom analysis of sediments taken from the Herring and Pamet River basins in the Cape Cod National Seashore in Massachusetts contrast the recent land-use history of these estuarine environments. Herring River in Wellfleet has been extensively ditched, drained, and diked both for mosquito control and for development. The sediments were sampled from this river in 1982 after an episode where low pH of about 3 was measured at many sites in the river basin. The dominant diatom in these sediments, Eunotia exigua , reflects this low pH episode, which was probably caused by sudden flushing of the decomposed salt-marsh peat from the spoil piles along the ditches. The sample taken from the portion of the Herring River which drains from the Gull-Higgins-Williams- Herring Pond complex, had diatoms more representative of the pond diatom flora, than of the impacted stretch of river below. Sediments taken from the main channel of the river where tidal influence is still present, had more of a balance between freshwater and brackish diatom assemblages. Diatom scrapings from a dead alewife found upriver, showed that the fish had been in the ponds at the head of the river and was on its journey back to the sea when it died. The Pamet River basin in Truro has had less recent manipulation and the sediments contain a very diverse diatom flora. There is indication of some acid drainage coming from the Cranberry Bog near the head of the river, but most of the diatoms in the sediments of the Pamet drainage basin are from a wide range of both freshwater and brackish species.

Diatom evidence of environmental changes in wetlands: Cape Cod National Seashore : Part I Prehistoric and historic trends in acidity of the Outer Cape ponds : Part II Comparison of two estuaries: Herring River in Wellfleet and Pamet River in Truro

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