Siombak lake (28 ha area) was a salty lake located in Medan coastal, Indonesia. Water fluctuation influenced by the sea tide. Therefore, it needed to do morphometry dynamical study as the first impression of lake physical characteristic. The purpose of this study was to understand the dynamical of Siombak lake morphometry. The research was done in September 2016. Lake mapping was done by making 100 line zig zag and draw with ArcMap. Bathymetry showed that the bottom of the lake was sloping at the center part of west and southeast of the lake, and steeping at north, south and east. Siombak Lake has shoreline length 2,535.78 m, with SDI value 2.70. Maximum length 756 m, with maximum width 246.15 m. Lake maximum depth was 17.7 m at MSL, 18.98 m at highest tide and 16.71 m at lowest tide, with average depth 5.33 m at MSL, 6.30 m at highest tide and 4.30 m at lowest tide. Lake volume was 783,607.16 m3 at MSL, 829,395.52 m3 at highest tide and 355,544.14 m3 at lowest tide, with water debit around 32.50 – 50.17 m3s-1. Water retention time was ± 4.33 – 6.75 hours

Tidal lakes are unique lakes because of the fluctuations of the water in the lake are influenced by the sea tides. Therefore, Tidal lakes are also called brackish lakes or salty lakes. Thus, the organisms that live in the lake must be able to adapt to the dynamics of brackish water changes. Therefore, the study of the biodiversity of flora and fauna is interesting to study related to organisms that are able to live and adapt to dynamic environments. This research was carried out in Siombak Lake, Medan City, North Sumatra Province from June to July 2018. The data collected were organisms in the form of flora (mangroves and aquatic plants) and fauna (ictiofauna or nekton which were fish, shrimp, crab, and mollusca). The results of research in the Siombak Lake ecosystem found 7 species of mangroves, 5 species of coastal plants, and 2 species of aquatic plant. Fauna found were 14 species of fish, 7 species of gastropods, and 1 species of bivalve, 1 species of shrimp and 1 species of crab.

Siombak Lake is a brackish or coastal lake in Medan, Indonesia. Water fluctuation in the lake was affected by sea tide, so it was more appropriately called tidal lake. Thus the influence of tides could affect the quality of water in the lake, especially temperature, salinity, dissolved oxygen, and pH. The purposed of this study was to describe the profile of temperature, salinity, dissolved oxygen, and pH in the waters of Siombak. Lake. This study was conducted in June to July 2018. The data measured and were analyzed in the waters spatially (horizontally) and vertically. The results showed no significant difference of temperature distribution in surface between high tide and low tide. However, it was more influenced by daily time differences. While salinity was quite different between high tide and low tide. In the dry season (April to June) salinity values were higher during high tide compared to low tide. Conversely, during the rainy season (June to August) the salinity values in low tide were higher than when they were in high tide. The vertically distribution of temperature, oxygen, and pH decreases with respect to increasing depth. But the salinity value increases with depth increased.

<strong>Limnological Status of Lake Siombak, Medan, North Sumatra.</strong> Lake Siombak is located in the coastal area of Medan city, making its waters influenced by the tides. The lake serves as a water catchment, flood control, fishing area, and tourist destination. Various activities in the lake have led to changes in the environmental quality of the lake. To maintain the sustainability of the lake, efforts are needed for proper management. Lake management should begin with a good understanding of the nature and characteristics of the waters. This study aimed to determine the limnological status of Lake Siombak through morphometric analysis, aspects of physics, chemistry, and biology, as well as trophic status of the waters. Morphometry included dimensions of water surface and subsurface. Physics parameters included temperature, Total Suspended Solid (TSS), water clarity, electrical conductivity (EC), and salinity. Chemical parameters included pH, dissolved oxygen (DO), Biological Oxygen Demand (BOD5), Chemical Oxygen Demand (COD), nitrates, and phosphates. Biological parameters included community structure of nekton and benthos. Measurement of lake morphometry was performed in April 2014 at high and low tides. Measurements of water quality and biological sample collection were conducted in May-July 2014 at high and low tides. The results showed that Lake Siombak has an area of 41.44 ha with a maximum depth of 5 m at high tide and 4 m at low tide. Based on the aspects of physics, chemistry, and biology of the waters, Lake Siombak was categorized as an open waters influenced by the tides and was saline with high level of oxygen. The lake water retention time (Rt) was 15.65 hours and discharged (Q) 3.7 x 107 m3/h of water at high tide and 3.0 x 107 m3/h at low tide. High phosphate concentration indicated these waters have already been polluted. However, the water quality of Lake Siombak was still suitable for fishing activities. Benthos and nekton communities were relatively unstable. Benthic community was dominated by Blue Mussel (Mytilus edulis) at high tide (57%) and Red-rimmed Melania (Melanoides tuberculata) at low tide (41.34%). Nekton community was dominated by Blue Panchax (Aplocheilus panchax) at high tide (74.07%) and low tide (64.79%). In general, Lake Siombak was classified as eutrophic. <br /><br />

No abstract

Abstract. Muhtadi A, Pulungan A, Nurmaiyah, Fadlhin A, Melati P, Sinaga RZ, Uliya R, Rizki M, Rohim N, Ifanda D, Leidonald R, Wahyuningsih H, Hasani Q. 2020. The dynamics of the plankton community on Lake Siombak, a tropical tidal lake in North Sumatra, Indonesia. Biodiversitas 21: 3707-3719. The tidal lake is a very dynamic estuary ecosystem and very vulnerable to environmental stresses and disturbances. Plankton is an aquatic organism that is very easily affected by environmental pressures and disturbances. This study aimed to reveal the phenomenon of plankton dynamics in tropical tidal lakes in Indonesia. The study was conducted at Siombak Lake from September 2018 to August 2019. Data were collected at high and low tides every month during the full month. The data analysis included plankton abundance, diversity index, and the relationship between water quality and plankton with PCA and succession analysis. The results showed that in Siombak Lake was found 66 genera which consisted of 54 phytoplankton genera and 12 zooplankton genera. Plankton abundance is higher in parts of the lake (stations 1-8) than in the river (stations 9-11) at both high and low tide. Temporally it shows that plankton abundance is higher in the rainy season (Feb-Aug, outside May) than in the rainy season (Sep-Jan, and May). Spatially, plankton in Siombak Lake at high tide is more influenced by TSS, phosphate, and salinity, while at low tide, it is influenced by TSS, Water transparency, BOD, silicate, salinity, and dissolved oxygen. Temporally, plankton in Siombak Lake at high tide is more influenced by salinity, conductivity, Debit, TSS, and salinity, while at low tide, it is influenced by salinity, conductivity, turbidity, TSS, TDS, DO, BOD, and COD. Based on the plankton Frontier succession graph, it shows that Siombak Lake is included in stage 1 and stage 2. Stage 1 occurs before the rainy season (August-September) and the peak of the dry season (March-April).

Abstract. Desrita, Muhtadi A, Leidonald R, Sibagaring RD, Nurfadillah 2020. Biodiversity of nekton in Batangtoru River and its tributaries in North Sumatra, Indonesia. Biodiversitas 21: 2344-2352. Batangtoru River which flows from the Tapanuli highlands (i.e., Sipirok, Tarutung, Siborong-borong, and Silangit) to the southwestern Indian Ocean is an important habitat for aquatic organisms in the western region of North Sumatra. This research was done to provide basic data on biodiversity of aquatic organisms in Indonesia, especially North Sumatra. The study was conducted in July-August 2019. Nekton was captured using backpack electrofishing units (12 volts and 9 Amperes), traps, nets, and bamboo trap. This study found 68 nekton species, consisting of fish (57 species), crab (3), shrimp (6), lobster (1), and 1 freshwater turtle (1). In general, nekton found in the Batangtoru River and its tributaries are native and economically valuable fish (Tor and eel), including the newly discovered species, which was, Hemibagrus caveatus. Invasive fish found consisted of 6 species, i.e., Cyprinus carpio, Oreochromis mossambicus, Oreochromis niloticus, Xiphophorus helleri, Hypostomus plecostomus, and Trichogaster pectoralis. The only invasive crustacean found was freshwater crayfish (Cherax quadricarinatus).

HighlightsMangrove sampling was conducted to use the "spot check" methodMangrove ecosystem of Bagan Serdang Village was categorized damaged Diversity of mangroves in the Bagan Serdang Village mangrove ecosystem was categorized moderate, but diversity of aquatic organisms was higher than the mangrove.Pertamina's CSR activities had an impact on environmental sustainability such as a habitat for various fauna and improving the community's economyAbstractInformation about mangrove and fauna biodiversity in Bagan Serdang Village is essential to be studied as a basis for assessing the management and utilization potential of mangrove. This information could be used as a reference in sustainable mangrove management. This study aims to determine the biodiversity of flora and fauna in the mangrove ecosystem of Bagan Serdang Village. The research location is divided into three areas, with three observation points. The study was conducted in August-September 2019. The sampling of mangroves was carried out using the Spot Check Method. The results showed that the types of mangroves found were 18 species from 12 families consisting of 14 species of true mangrove and four types of associated mangroves while the fauna found in the mangrove ecosystem of Bagan Serdang Village was 16 species of fish, nine species of crustaceans, 13 species of mollusks, four species of birds, one species of reptile, one species of mammal and one species of horse shoe crab. The results of the mangroves analysis in the Bagan Serdang Village’s mangrove ecosystem, including in moderate heading to damage condition. This could be seen from the death of several trees and the flourishing of A. ilicifolius species as a marker of mangrove, which tends to be damaged. The diversity of mangroves in the Bagan Serdang Village is lower (1.63) compared to aquatic organisms that reach 2.09 - 2.44. Corporate responsibility or CSR that PT Pertamina (Persero) TBBM Medan Group carried out in the village of Bagan Serdang with mangrove planting activities and ecotourism, as well as the development of processed mangrove products, could increase the value of diversity and increase the economy of the surrounding community.