Centre for Coastal Research, University of Agder, Kristiansand, Norway.
Norwegian Institute for Water Research (NIVA), Oslo, Norway.
Sci Rep. 2020 Oct 28;10(1):18451. doi: 10.1038/s41598-020-75532-5.
Declining atmospheric nitrogen (N) deposition, through reduction in the direct input of inorganic N, may result in less inorganic N being leached from soils to freshwaters (dissolved inorganic N = DIN). Declining sulphur deposition, through reducing the ionic strength in soil water, increases the solubility and mobility of organic soil compounds and may result in increased leaching of organically bound N to freshwaters (total organic N = TON). It is unknown to which extent these two independents and opposing trends, i.e. DIN decline versus TON increase, may affect the nutrient balance (load, stoichiometry) of river water draining into coastal zones. By combining long-term atmospheric and riverine monitoring data of the five major Norwegian rivers draining to the Skagerrak coast, we show that over the past 27 years (1990-2017) river water nutrient composition, and specifically N stoichiometry has been steadily shifting from inorganic to organic fractions, with correlations to changes in human pressures (air pollution), but especially climate (precipitation, temperature, discharge). This shift in nutrient quality may have large consequences on the nutrient cycling in both freshwater and coastal ecosystems and illustrates the complex interactions of multiple stressors (here: N deposition, S deposition, and climate change) on aquatic ecosystems.
大气氮（N）沉降减少，通过减少无机 N 的直接输入，可能导致从土壤中淋洗到淡水中的无机 N 减少（溶解无机 N = DIN）。硫沉降减少，通过降低土壤水中的离子强度，增加了有机土壤化合物的溶解度和迁移性，可能导致有机结合的 N 更多地淋洗到淡水中（总有机 N = TON）。目前还不清楚这两个独立的、相反的趋势，即 DIN 减少与 TON 增加，在多大程度上会影响流入沿海地区的河流水中的养分平衡（负荷、化学计量）。通过结合挪威五大流入斯卡格拉克海岸的河流的长期大气和河流监测数据，我们表明，在过去的 27 年里（1990-2017 年），河水的养分组成，特别是 N 化学计量，已经从无机向有机部分稳定地转变，与人为压力（空气污染）的变化相关，但特别是与气候（降水、温度、流量）相关。养分质量的这种转变可能对淡水和沿海生态系统的养分循环产生重大影响，并说明了多种胁迫因素（这里是：N 沉降、S 沉降和气候变化）对水生生态系统的复杂相互作用。
