The effects of changes in soil moisture on nitrogen cycling in acid wetland types of the New Jersey Pinelands (USA)

• Published in: Soil biology & biochemistry Vol. 41; no. 12; pp. 2394 - 2405
• Main Authors: Yu, Shen, Ehrenfeld, Joan G.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 01.12.2009; Elsevier
• Subjects: acid soils; Agronomy. Soil science and plant productions; aquifers; Biochemistry and biology; biogeochemical cycles; Biological and medical sciences; botanical composition; Cedar swamp; Chemical, physicochemical, biochemical and biological properties; climatic factors; drainage; forest trees; Forested wetlands; Fundamental and applied biological sciences. Psychology; groundwater; Histosol; Hydric soils; hydrology; lowland forests; Maple swamp; mineralization; New Jersey; New Jersey Pinelands; nitrate nitrogen; nitrates; Nitrification; nitrogen; Nitrogen mineralization; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Pine swamp; plant communities; seasonal variation; Soil moisture; Soil science; soil structure; soil water content; topography; water holding capacity; water management; Water resources; wetland plants; wetlands; New Jersey; United States; North America; America; ANW, USA, New Jersey; Nitrogen mineralization; Pine swamp; Histosol; Soil moisture; Nitrification; Forested wetlands; New Jersey Pinelands; Cedar swamp; Maple swamp; Hydric soils; Water resources; Forests; Organic soil; Nitrogen cycle; Acids; Soil science; Histosols; Wetland
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/j.soilbio.2009.06.012

Wetlands are subject to changes in soil moisture as a result of both short-term seasonal climate variations and long-term changes in regional water resource management, both of which can modify the dynamics of ground and surface water inputs. In the New Jersey Pinelands, forested wetlands that differ in both plant communities and soil structure occur along a topographic and hydrological gradient associated with an unconfined aquifer. Proposed groundwater withdrawals may affect water content of soils along this gradient. We hypothesized that prolonged changes in soil moisture would alter net nitrogen mineralization and nitrification rates in proportion to the amount of moisture change, and that these changes would be similar for the different soils along the drainage catena. Soils from two catenary sequences of wetlands, including pine-dominated (driest landscape position), hardwood-dominated, and Atlantic white-cedar-dominated (wettest landscape position) communities were used in long-term laboratory incubations (36 weeks). Production of NH 4 +–N, NO 3 −–N, and dissolved organic N were measured under two sets of conditions: constant moisture levels of 100%, 60% and 30% water-holding capacity (WHC), and fluctuating moisture levels (alternating 2 week periods at 100% and 30% WHC). In soils from most of the wetlands, we observed increases in net mineralization and nitrification when constant low-moisture conditions were established, but not under fluctuating conditions. Contrary to expectations, responses to the drying treatments varied between wetland types and between replicate wetlands of each type. Under constant-moisture conditions, nitrification increased more in cedar swamps than in either type of pine wetland. Under all conditions, soils from all the wetlands within one of the catenas produced more inorganic and organic soluble N than did the wetlands from the other catena, suggesting that area-wide effects are as important as wetland type in regulating production of soluble N. Within both catenas, pine-hardwood wetlands generated more soluble N under all moisture conditions than did either pine-dominated or cedar wetlands. Our results suggest that changes in soil moisture due to management of water resources will affect N cycling in wetland soils, but that the magnitude of the effects, and the potential for large releases of nitrate, will depend on the specific soil properties of affected wetlands.