Multi-element fingerprints of marsh soils converted for agricultural uses

Background/Question/Methods The long agricultural history of China was, to a certain extent, a history of drainage and reclamation of wetlands. This trend is particularly marked in the Sanjiang Plain given the nutrient-rich soils and flat topography. The conversions from wetlands to farmlands directly or indirectly influence the geochemical position of metals bound to the soil. However, little is known about the influence of this conversion on the element composition of soils. We took soil cores of five wetlands of different land use types (natural freshwater marsh, drained marsh, marsh converted to soybean field for one year, marsh converted to paddy for seven years, and grazed marsh), and measured the concentrations of 56 elements, organic matter content, pH, total organic carbon, and total nitrogen at depths of 0-20cm, 20-40cm and 40-60cm.

Results/Conclusions Organic matter content was the most important variable explaining variation in element concentrations (60.6%), as indicated by RDA analysis, followed by land use (4.2%), TN (3%) and pH (2.4%). Organic matter correlated positively with P, S, Ca, As, Mo, Cd, Sb and Hg, negatively with most metals. After normalization for OM, similarity tree analysis revealed that element concentrations in the top soils of all types were more easily affected by wetlands conversion. In addition, wetlands conversion to agricultural uses did change more element concentrations and distributions than drained and grazed wetlands. Multi-element fingerprinting did reflect the variance in the progress of wetland converted for agricultural uses. This information is of importance particularly to sustainable management of agriculture-induced natural wetland loss.