Our study aims to determine the development of sediment-rich freshwater plumes in a non-tidal brackish water-dominated (salinity < 6) estuary in the Halikonlahti Bay, Northern Baltic Sea. We studied three seasons with different wind conditions and discharges: two open water periods, one with low (~0.2 m³/s) and one with high (31–40 m³/s) river discharges, and one ice-covered period with high (28–40 m³/s) river discharge. To conduct our analyses, we measured suspended sediment concentration (SSC), turbidity, salinity and temperature of bottom and surface waters together with current measurements along the estuary. Water samples were collected with LIMNOS water sampler and current measurements were done with acoustic Doppler current profiler. The results indicate that river plume develops under high river discharge, while during low river discharge the plume is very limited in extent. In open water conditions, SSC increased approximately ten-fold in the estuary head, with increased discharge from 0.2 m³/s to 31 m³/s. Buoyant plumes developed in both open channel and ice-cover conditions during high river discharge periods even in a weakly stratified environment, where the salinity difference was less than five over the entire water column. Unlike salinity, small temperature differences between river and seawater did not contribute the development of buoyant sediment plume. Weak stratification together with reduced wind-induced mixing was found to limit the sediment mixing between fresh surface and saline (~5) bottom layers in both ice-covered and open water conditions. For example, even 2–5 times higher SSCs were found at surface waters compared to bottom waters over a shallow (~4 m) water column. Wind and river discharge induced estuarine currents were found. Inverse estuary circulation developed under the conditions of low river discharge and inshore directed wind. High river discharge together with salinity stratification formed a positive estuarine circulation pattern, with surface outflow and bottom inflow.

我们的研究旨在确定北波罗的海哈利孔拉赫蒂湾非潮汐咸淡水（盐度<6）河口中富含沉积物的淡水羽流的发育。我们研究了三个不同风况和流量的季节：两个开放水期，一个低流量（〜0.2m³/ s），一个高流量（31–40m³/ s），一个冰期高（ 28–40m³/ s）的河流流量。为了进行分析，我们测量了底泥和地表水的悬浮沉积物浓度（SSC），浊度，盐度和温度，以及沿河口的当前测量值。用LIMNOS水取样器收集水样品，并用声学多普勒电流剖面仪进行电流测量。结果表明，在高流量下河流羽流发育，在河水流量低时，羽流的范围非常有限。在开阔水域条件下，河口顶部的SSC增加了大约十倍，排放量从0.2m³/ s增加到31m³/ s。即使在弱分层的环境中，在整个河流水柱中盐度差小于5的情况下，在高流量河流期间，在明渠条件和覆冰条件下，浮羽也会形成。与盐度不同，河流和海水之间的小温差不会促进浮力沉积物羽流的发展。薄弱的分层以及减少的风引起的混合被发现限制了在冰覆盖和开阔水域条件下新鲜表面和盐水（〜5）底层之间的沉积物混合。例如，与浅水（〜4 m）水柱的底部水相比，地表水的SSC甚至高出2至5倍。发现了由风和河水引起的河口流。在河流量低和近海定向风的条件下，河口逆流发展。较高的河流排放量与盐分分层共同形成了正河口环流模式，地表流出和底部流入。