The effect of freshwater discharge on solute vertical mixing and horizontal transfer rates is evaluated in a variably stratified temperate fjord (Killary Harbour, Ireland) using the activity ratios of ²²⁴Ra and ²²³Ra in the water column. With high river discharge (>1.7 × 10⁶ m³ d⁻¹), surface ²²⁴Ra/²²³Ra activity ratios (ARs) decreased from 18.0 ± 7.1 to 8.6 ± 0.9 from the inner to the outer fjord and the system becomes stratified, resulting in clear differences of ²²⁴Ra/²²³Ra ARs between surface and bottom layers. When river discharge was low (<0.6 × 10⁶ m³ d⁻¹), ²²⁴Ra/²²³Ra ARs dipped from 19.6 ± 5.1 to 8.0 ± 1.8 in the inner system before increasing again towards the outlet to the sea up to 11.3 ± 3.6, and the water column was well mixed: the difference in ²²⁴Ra/²²³Ra ARs and salinity between surface and bottom layers was minimal. Longitudinal seaward decreases of surface water ²²⁴Ra/²²³Ra ARs within the inner fjord independently of river discharge suggested that the contribution of benthic-pelagic coupling to surface solute inventories is small in the inner section of the system. Conversely, the increase of ²²⁴Ra/²²³Ra ARs during low discharge conditions indicated that the slower flushing of the system, coupled with a well-mixed water column, facilitated solute transfers from deeper waters to the surface in the outer fjord. The effect of discharge on the residence time of water in the inner fjord was also determined using radium ages: longitudinal water flushing timescales are quickly reduced in the inner part of the bay with increasing discharge. We show that the degree of vertical mixing is an important driver of nutrient ratios in the system. Retention of soluble reactive phosphorus (SRP) and Ra in deep water and a higher molar N:P ratio in surface water were more likely under stratified conditions. Stratification may therefore amplify the effect of variable watershed inputs on the estuarine N:P ratio in Killary Harbour.

利用水柱中²²⁴ Ra和²²³ Ra的活度比，在一个分层的温带峡湾（爱尔兰凯拉尔港）中评估了淡水排放对溶质垂直混合和水平转移速率的影响。在高河流量（> 1.7×10 ⁶  m ³ d ^-1）下，从内峡湾到外峡湾的表面²²⁴ Ra / ²²³ Ra活度比（ARs）从18.0±7.1降低至8.6±0.9，系统分层。导致表层和底层之间存在²²⁴ Ra / ²²³ Ra ARs的明显差异。河流流量低时（<0.6×10 ⁶  m ³d ^-1），内部系统中的²²⁴ Ra / ²²³ Ra ARs从19.6±5.1降至8.0±1.8，然后再次向海出口增加至11.3±3.6，水柱混合得很好：²²⁴ Ra / ²²³ Ra ARs和表层与底层之间的盐度极小。与河流流量无关，内峡湾内地表水²²⁴ Ra / ²²³ Ra ARs的纵向向海减小表明，在系统内部，底栖-上层耦合对地表溶质清单的贡献很小。相反，增加²²⁴ Ra / ²²³在低排放条件下的Ra ARs表明，系统冲洗较慢，加上水柱充分混合，有助于溶质从较深的水转移到外峡湾的表面。排放对内峡湾中水停留时间的影响也通过使用镭龄来确定：随着排放量的增加，在海湾内部纵向冲洗水的时间尺度迅速减小。我们表明，垂直混合的程度是系统中营养比的重要驱动因素。在分层条件下，更可能在深水中保留可溶性反应性磷（SRP）和Ra，在地表水中保留较高的N：P摩尔比。因此，分层可能会扩大分水岭输入对基拉尔港河口N：P比率的影响。