Phosphate Removal Capacity of Palustrine Forested Wetlands and Adjacent Uplands in Virginia
1999
Axt, J. R. | Walbridge, M. R.
We examined the ability of soils in six nontidal palustrine forested wetlands (PFOs) in Virginia's Piedmont (PD) and Coastal Plain (CP) (n = 3 per physiographic province) to remove dissolved inorganic P from solution, and we compared the P sorption capacities of wetlands with those of streambanks (within wetlands) and adjacent uplands. We hypothesized that wetland soils would have higher P sorption capacities than streambank and upland soils due to the higher concentration of noncrystalline (oxalate-extractable) Al and Fe (Alₒ and Feₒ) favored by periodic flooding. We found that P sorption capacities varied both as a function of landscape position and soil depth. Wetlands had higher P sorption capacities than uplands in surface soils (0–15 cm), while below 50 cm the relationship was reversed. Streambank areas within wetlands generally had the lowest P sorption capacities. As hypothesized, Alₒ was correlated with P sorption capacity in wetland soils (r2 = 0.80), but so was soil organic matter (as estimated by mass loss on ignition [LOI]) (r2 = 0.78); in fact, Alₒ and organic matter were positively correlated in wetland soils (r2 = 0.84) In contrast, clay and silt content were the two soil parameters most highly positively correlated with P sorption capacity in upland soils (r2 = 0.87) Overall, these results suggest that differences in soil chemistry exist among landscape positions (wetland, streambank, upland) that have important implications with regard to P sorption capacity. Since wetlands and uplands may remove P from different hydrologic sources (i.e., surface runoff in wetlands and groundwater in uplands), hydrology may be a key factor in determining water quality functioning.
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