Willett V B, Reynolds B A, Stevens P A, Ormerod S J, Jones D L
School of Agricultural and Forest Sciences, Deniol Road, University of Wales, Bangor, Gwynedd, LL57 2UW, UK.
J Environ Qual. 2004 Jan-Feb;33(1):201-9. doi: 10.2134/jeq2004.2010.
Dissolved organic nitrogen (DON) has been hypothesized to play a major role in N cycling in a variety of ecosystems. Our aim was to assess the seasonal and concentration relationships between dissolved organic carbon (DOC), DON, and NO3- within 102 streams and 16 lakes within catchments of differing complexity situated in Wales. Further, we aimed to assess whether patterns of land use, soil type, and vegetation gave consistent trends in DON and dissolved inorganic nitrogen (DIN) relationships over a diverse range of catchments. Our results reinforce that DON constitutes a significant component of the total dissolved N pool typically representing 40 to 50% of the total N in streams and lakes but sometimes representing greater than 85% of the total dissolved N. Generally, the levels of DON were inversely correlated with the concentration of DIN. In contrast to DIN concentrations, which showed distinct seasonality, DON showed no consistent seasonal trend. We hypothesize that this reflects differences in the bioavailability of these two N types. The amount of DON, DOC, and DIN was significantly related to soil type with higher DON export from Histosol-dominated catchments in comparison with Spodosol-dominated watersheds. Vegetation cover also had a significant effect on DON concentrations independent of soil type with a nearly twofold decrease in DON export from forested catchments in comparison with nonforested watersheds. Due to the diversity in catchment DON behavior, we speculate that this will limit the adoption of DON as a broad-scale indicator of catchment condition for use in monitoring and assessment programs.
溶解有机氮（DON）被认为在多种生态系统的氮循环中起主要作用。我们的目标是评估威尔士不同复杂程度集水区内102条溪流和16个湖泊中溶解有机碳（DOC）、DON和NO3-之间的季节关系及浓度关系。此外，我们旨在评估土地利用模式、土壤类型和植被在不同集水区的DON和溶解无机氮（DIN）关系中是否呈现一致趋势。我们的结果进一步证明，DON是总溶解氮库的重要组成部分，通常占溪流和湖泊中总氮的40%至50%，但有时占总溶解氮的比例超过85%。一般来说，DON的水平与DIN的浓度呈负相关。与呈现明显季节性的DIN浓度不同，DON没有一致的季节性趋势。我们推测这反映了这两种氮类型生物可利用性的差异。DON、DOC和DIN的含量与土壤类型显著相关，与以灰化土为主的集水区相比，以有机土为主的集水区DON输出量更高。植被覆盖对DON浓度也有显著影响，且与土壤类型无关，与非森林集水区相比，森林集水区的DON输出量减少了近一半。由于集水区DON行为的多样性，我们推测这将限制把DON用作监测和评估计划中集水区状况的广泛指标。
