Judul: The Aquatic Dynamics of Tidal Lake in the Perspective of  Siombak Lake Management
Abstrak: Siombak Lake is one of the tidal lakes in Indonesia. This lake is located on the coast of Medan City, North Sumatra Province. This lake is unique and distinctive. The uniqueness and peculiarity of this lake is the lake water system which is estuarine. The river flow that enters the 7 km long lake from the Belawan River Estuary (Malacca Strait) is still affected by the ebb and flow of seawater. On the lake border, some mangroves grow on the edge of the lake. The aquatic biota in Siombak Lake consists of groups of freshwaters, brackish, and marine organisms. Siombak Lake functions as a water catchment, flood control, fishing ground, as well as a tourist spot. The area around the lake is also home to various community activities such as fishponds, residential areas, industry, and landfills of Medan City. The Siombak Lake Ecosystem is also one of the Green areas in Medan City. The existence of utilization activities in the waters of Siombak Lake and its surroundings will put ecological pressure on the lake ecosystem. Proper management needs to be done to maintain the sustainability of this tidal lake. Thus, lake management studies by integrating conservation, fisheries, and ecotourism need to be carried out as an integrated and sustainable management effort. The purpose of this study is to develop a tidal lake management concept based on tidal dynamics based on resource conservation. Data collection in the field was one year (September 2018 – August 2019). The data collected consists of data on the physical shape of the lake, water quality, aquatic and terrestrial organisms, and water levels (tides). Lake water level elevation is obtained from tidal data which is measured every hour for 15 days. Water quality data and aquatic organisms are taken every month during a full moon. Data analysis was carried out descriptively, statistically, and spatially. Tidal lake water quality index (TL WQI) as a novelty was developed to determine the level of pollution in lake waters. TL WQI was developed from the National Sanitation Foundation - Water Quality Index (NSF-WQI) which was adapted to the characteristics of tidal lakes. Marxan and Quantum GIS were used to design and locate locations for lake management zoning. Siombak Lake has an area of 29.72 ha with an average lake depth ranging from 1.63 – 4.53 m when it rains (MSL = 3.27 m) and 1.61 – 4.38 when dry (MSL = 3.25 m). In general, changes in water level in Siombak Lake occur every 6 hours (in 1 day there are 2 high tides and 2 low tides), except for neap tides. Throughout the year the water level of Siombak Lake fluctuates following the tidal cycle. The highest water level in Lake Siombak was in November 2018 to reach 227 cm. The lowest water level occurred in February 2019 with a height of -24 cm. The water quality characteristics of Siombak Lake are characterized by high concentrations of salinity and TDS. In the rainy season, the salinity concentration on the surface ranges from 2-7 ppt, at the bottom, it reaches 10 to
Keyword: Biodiversity, tidal lake, tidal lake water quality index, habitat protection, zoning