CSIRO, Land and Water, GPO Box 1666, Canberra, ACT, 2601, Australia,
Environ Monit Assess. 2013 Nov;185(11):9191-219. doi: 10.1007/s10661-013-3246-8. Epub 2013 Jun 11.
To explore the value of high-frequency monitoring to characterise and explain riverine nutrient concentration dynamics, total phosphorus (TP), reactive phosphorus (RP), ammonium (NH4-N) and nitrate (NO3-N) concentrations were measured hourly over a 2-year period in the Duck River, in north-western Tasmania, Australia, draining a 369-km(2) mixed land use catchment area. River discharge was observed at the same location and frequency, spanning a wide range of hydrological conditions. Nutrient concentrations changed rapidly and were higher than previously observed. Maximum nutrient concentrations were 2,577 μg L(-1) TP, 1,572 μg L(-1) RP, 972 μg L(-1) NH₄-N and 1,983 μg L(-1) NO₃-N, respectively. Different nutrient response patterns were evident at seasonal, individual event and diurnal time scales-patterns that had gone largely undetected in previous less frequent water quality sampling. Interpretation of these patterns in terms of nutrient source availability, mobilisation and delivery to the stream allowed the development of a conceptual model of catchment nutrient dynamics. Functional stages of nutrient release were identified for the Duck River catchment and were supported by a cluster analysis which confirmed the similarities and differences in nutrient responses caused by the sequence of hydrologic events: (1) a build-up of nutrients during periods with low hydrologic activity, (2) flushing of readily available nutrient sources at the onset of the high flow period, followed by (3) a switch from transport to supply limitation, (4) the accessibility of new nutrient sources with increasing catchment wetness and hydrologic connectivity and (5) high nutrient spikes occurring when new sources become available that are easily mobilised with quickly re-established hydrologic connectivity. Diurnal variations that could be influenced by riverine processes and/or localised point sources were also identified as part of stage (1) and during late recession of some of the winter high flow events. Illustrated by examples from the Duck River study, we demonstrate that the use of high-frequency monitoring to identify and characterise functional stages of catchment nutrient release is a constructive approach for informing and supporting catchment management and future nutrient monitoring strategies.
为了探索高频监测在描述和解释河流营养物浓度动态方面的价值，在澳大利亚塔斯马尼亚州西北部的 Duck 河进行了为期 2 年的研究，每小时测量一次总磷（TP）、活性磷（RP）、铵（NH4-N）和硝酸盐（NO3-N）的浓度。在同一地点和同一频率观测河流量，跨越了广泛的水文条件范围。营养物浓度变化迅速，且高于以往观测到的浓度。最大营养物浓度分别为 2577μg/L 的 TP、1572μg/L 的 RP、972μg/L 的 NH₄-N 和 1983μg/L 的 NO₃-N。在季节性、个别事件和昼夜时间尺度上，存在不同的养分响应模式，这些模式在以前较少的水质采样中基本上未被发现。根据营养物源的可利用性、迁移和向溪流输送来解释这些模式，从而可以开发流域营养物动态的概念模型。确定了 Duck 流域养分释放的功能阶段，并通过聚类分析得到了支持，该分析确认了由于水文事件序列引起的养分响应的相似性和差异性：（1）在低水文活动期间养分的积累；（2）在高流量期开始时迅速可用养分源的冲洗，随后（3）从运输到供应限制的转变；（4）随着流域湿润度和水力连通性的增加，新养分源的可及性；（5）当新的易于移动且快速重新建立水力连通性的来源可用时，会出现高营养物峰值。受河流过程和/或局部点源影响的昼夜变化也被确定为阶段（1）的一部分，以及某些冬季高流量事件后期的退水中。通过 Duck 河研究的实例来说明，我们证明了使用高频监测来识别和描述流域养分释放的功能阶段是一种有用的方法，可以为流域管理和未来的养分监测策略提供信息和支持。
