Geographic variation in nutrient availability, stoichiometry, and metal concentrations of plants and pore-water in ombrotrophic bogs in New England, USA

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Geographic trends in surface water chemistry and leaf tissue nutrients may reflect gradients of nutrient limitation and broad-scale anthropogenic inputs. In 24 rain-fed (ombrotrophic) peatland bogs in Massachusetts and Vermont, we measured nutrient and metal concentrations in pore-water and in leaf tissues of three common bog plant genera - leather leaf (Chamaedaphne calyculata), northern pitcher plant (Sarracenia purpurea), and peat moss (Sphagnum spp.). The concentrations of N, P, and K were low in leaf tissues of all three plant genera, as were the concentrations of many trace heavy metals, including Cr, Cu, Co, Cd, Mo, and Pb. Stoichiometric ratios of macronutrients (N:P, P:K, and N:K) in plant leaves suggested that plant growth in the sampled bogs was limited by P, or was co-limited by all three macronutrients. N:P and N:K nutrient ratios of Sarracenia purpurea and Sphagnum spp. increased toward the northwest and with elevation, but stoichiometric ratios of Chamaedaphne calyculata did not show any clear geographic trends. A principal components analysis revealed additional distinct differences among the three plant genera in their nutrient and metal concentrations. Furthermore, dissolved organic carbon (DOC), dissolved organic nitrogen (DON), Cu, Mg ,N O 3, Al, and K in pore- water increased from the northwest (northwestern Vermont) to the southeast (Cape Cod and eastern Massachusetts near Boston), a gradient of increasing human population density and urbanization. In contrast, pore-water concentrations of SO4 and Al were highest in the western sites, and SO4 concentrations increased with elevations. These patterns may reflect atmospheric inputs from the Ohio River Valley leading to increased acidic deposition, causing Al to be leached from soils. Because bogs are naturally low in nutrients and do not receive substantial inputs from surrounding groundwater, the chemical signatures and nutrient stoichiometry of specific bog plant species or genera may provide useful indicators for assessing spatiotemporal changes in atmospheric deposition.