Spatial and seasonal distribution of nitrogen in marsh soils of a typical floodplain wetland in Northeast China.

Horizontal and profile distributions of nitrogen in marsh soils in different seasons were studied in a typical site within the Erbaifangzi wetland in Northeast China. Results showed that there was higher spatial heterogeneity for nitrate nitrogen (NO[Formula: see text]N) and ammonium nitrogen (NH[Formula: see text]-N), as well as available nitrogen (AN), in surface soils in July compared to that in September. Relative to July, the mean nitrogen contents in surface soils were slightly higher in September; however, in November, soils contained significantly lower NO[Formula: see text]N and NH[Formula: see text]-N, higher AN, organic nitrogen (Org-N), and total nitrogen (TN). Except for mineral nitrogen, no significant differences were observed between Org-N and TN contents in September and November. Nitrogen contents generally declined exponentially with depth along soil profiles in three sampling dates (July, September, and November), except for a significant accumulation peak of NO[Formula: see text]N at the 20-30 cm depth in September. However, NH[Formula: see text]-N contents showed a vertical alternation of "increasing and decreasing" in both July and September, while nearly kept constant with depth in November. The depth ranking of nitrogen showed the shallowest distribution for AN, followed by Org-N and TN, while deeper distributions for NO[Formula: see text]N and NH[Formula: see text]-N. TN, Org-N, and AN were significantly correlated with soil organic matter and total phosphorus. Soil pH values were significantly correlated with TN and AN contents in surface soils. Clay contents showed significant correlations with nitrogen contents except for NO[Formula: see text]N in surface soils and NH[Formula: see text]-N in profile soils. However, soil moisture was not significantly correlated with nitrogen contents among all soil samples.