Habitat point records from 1988 OPRU HRE Taf, Tywi & Gwendraeth Estuaries survey

The estuaries of the Taf, Tywi and Gwendraeth are known locally as the `Three rivers` as they converge and enter into Camarthen Bay in South West Wales through a common mouth. The rivers drain agricultural catchments of 246, 1335 and 175 km2, respectively, and the underlying rocks are, for the most part slightly acidic. Of the three river estuaries, the Tywi is the larger at over 20 km in length. The Taf and Tywi are both typical coastal plain estuaries and the Gwendraeth is a bar-built estuary formed by the north westerly movement of sand from the Pembrey coast dune system. All three estuaries are presently undergoing substantial infilling by marine sediments originating from Camarthaen Bay and as a result are shallow and drain almost completely at low tide. Tidal flows within the system and in particular in the Taf and Tywi, are of considerable strength and the tidal wave symmetry is distorted producing a longer ebb than flood. This report describes the habitats and associated communities at twenty-one sites surveyed in the study area; eighteen intertidal sites and three dredge sites from the main channels. Species present have been identified and tabulated. Hard substrata communities are not well represented in the `Three Rivers` and those examples occuring are markedly sand scoured and support depauperate communities. Sedimentary habitats dominate the system, and there is a gradation of sand flats to mudflats from the mouth to the upper estuaries. The lower shore flats are generally unstable environments being subject to large tidal salinity fluctuations and strong tidal currents. More stable sand flats are found on the upper middle shore with considerably richer communities. Mussel scars occur at three sites in the system and are subject to scouring losses. Both mussels and cockles are collected commercially on a small scale and some netting also occurs. Mussel culture is presently being evaluated in the Gwendraeth Estuary. The Taf and Tywi have naturally low oxygen levels in their estuaries at times of continued fine weather, low river discharges and spring tides. These are compounded in the Tywi by effluent from a large sewage treatment works which significantly increases the biological oxygen demand (B.O.D.). The `Three Rivers` are flanked by Sites of Special Scientific Interest (SSSI) to the east, west and north. Notification of these was for the sand dune flora and fauna and maritime cliff communities. The south shore of the Gwendraeth, including Towyn Point, and Salmon Point Scar are the only marine habitats protected by the designations. The area is also of nature conservation interest for the populations of migrant and over-wintering waterfowl. Several species reach levels of National Importance, though they are not afforded any other specific site protection at the present time. rivers塔夫河（Taf）、泰威河（Tywi）与格温德雷思河（Gwendraeth）的河口在当地被称为‘三河’，因三者在威尔士西南部汇聚，并通过共同入海口注入卡马森湾（Camarthen Bay）。三条河流的农业集水区面积分别为246、1335与175平方千米，其下伏岩层整体呈弱酸性。三条河口之中，泰威河河口规模最大，长度超过20千米。塔夫河与泰威河均为典型的海岸平原河口，而格温德雷思河河口则是由彭布雷海岸沙丘系统的沙体向西北移动形成的沙坝型河口（bar-built estuary）。目前三条河口均正经历源自卡马森湾的海洋沉积物的大量充填，因此水体较浅，低潮时几乎完全干涸。该系统内的潮流，尤其是塔夫河与泰威河河段的潮流，强度可观，且潮汐波形态发生畸变，落潮时长大于涨潮时长。本报告描述了研究区域内21个调查点位的生境及其伴生群落：其中18个为潮间带点位，3个为主航道疏浚采样点位。已对调查发现的物种进行鉴定并制表统计。‘三河’区域内硬质底质群落占比极低，现存的硬质底质群落均遭受显著沙蚀，支撑的群落物种贫乏。沉积型生境是该系统的主导生境，从入海口到河口上游，存在从沙滩到泥滩的渐变序列。潮下带浅滩通常属于不稳定环境，易受大幅潮汐盐度波动与强潮流影响。较为稳定的沙滩分布于中上部潮间带，其伴生群落的物种丰富度显著更高。该系统内3个点位存在贻贝附着痕，且会因沙蚀出现群落损失。当地存在小规模商业性贻贝与鸟蛤捕捞活动，同时也有少量网捕作业。目前格温德雷思河口正在开展贻贝养殖的评估工作。塔夫河与泰威河的河口在持续晴好天气、河流径流量偏低以及大潮期间，天然存在低氧水平。泰威河的这一问题因一座大型污水处理厂排放的废水而加剧，该排放显著提升了区域的生化需氧量（B.O.D.）。‘三河’区域的东、西、北三面均被特殊科学价值地点（Sites of Special Scientific Interest, SSSI）环绕，这些地点的划定初衷是保护其沙丘动植物与海崖群落。仅格温德雷思河的南岸（包括托温角（Towyn Point）与鲑鱼角崖（Salmon Point Scar））被划入上述保护地的海洋生境范围。该区域对于迁徙与越冬水鸟种群同样具有自然保护价值，部分物种的种群数量达到了国家级重要水平，但目前尚未获得其他专项场地保护。