A Bayesian Belief Network, validated using past observational data, is applied to conceptualize the ecological response of Lake Maninjau, a tropical lake ecosystem in Indonesia, to tilapia cage farms operating on the lake and to quantify its impacts to assist decision making. The model captures ecosystem services trade-offs between cage farming and native fish loss. It is used to appraise options for lake management related to the minimization of the impacts of the cage farms. The constructed model overcomes difficulties with limited data availability to illustrate the complex physical and biogeochemical interactions contributing to triggering mass fish kills due to upwelling and the loss in the production of native fish related to the operation of cage farming. The model highlights existing information gaps in the research related to the management of the farms in the study area, which is applicable to other tropical lakes in general. Model results suggest that internal phosphorous loading (IPL) should be recognized as one of the primary targets of the deep eutrophic tropical lake restoration efforts. Theoretical and practical contributions of the model and model expansions are discussed. Short- and longer-term actions to contribute to a more sustainable management are recommended and include epilimnion aeration and sediment capping.

Ranggeh River is one of the inlets of Lake Maninjau (West Sumatra, Indonesia), which has a vital role in supporting the life of native fish. Increasing anthropogenic activities (agriculture and human settlements) around the river can harm benthic macroinvertebrates as natural food for fish. Therefore, this study aimed to analyze and observe water quality changes and their impact on the benthic macroinvertebrate communities in the Ranggeh River. Sampling was conducted from February to August 2019 using the Hess Sampler tool. The results indicate that the anthropogenic impacts around the Ranggeh River on water quality has changed the macroinvertebrate benthic community structures (composition, abundance, and biological index). Furthermore, the Ephemeroptera Plecoptera and Trichoptera (EPT) number of taxa index were superior in reflecting disturbances in the Ranggeh River compared to the Family Biotic Index (FBI) and the Percent Model Affinity (PMA). In conclusion, the anthropogenic effect on the macroinvertebrate community in the Ranggeh River prominently was caused by habitat changes rather than enrichment by nutrients (TN and TP).

AbstrakKeberadaan logam berat di ekosistem akuatik telah sering dilaporkan menimbulkan masalah ke biota perairan. Salah satu biota perairan yang memiliki resiko untuk terpapar logam berat dari sedimen adalah organisme makrozoobentos. Penelitian ini bertujuan untuk mendeskripsikan pengaruh kontaminasi logam berat di sedimen pada struktur komunitas makrozoobentos yang berada di ekosistem lentik (situ dan waduk). Penelitian ini telah dilakukan pada bulan Juni 2009 -September 2011 di beberapa situ dan waduk yang berada di Provinsi Jawa Barat dan Jakarta. Sampel makrozoobentos dikumpulkan dengan menggunakan alat Ekman grab. Hasil penelitian menunjukkan bahwa terdapat korelasi antara indeks keanekaragaman makrozoobentos dengan kontaminasi logam arsen yang tinggi. Kontribusi logam Pb dan Cd dalam memberikan pengaruh pada indeks keanekaragaman relatif masih kecil. Keberadaan makrozoobentos Coleoptera (Simsonia sp.), lintah (Placobdella sp.), larva chironomid (Ablabesmyia sp.), dan (Tanytarsus sp.) relatif toleran dengan kontaminasi logam arsen di sedimen yang tinggi, pH dan suhu yang rendah. Penggunaan indeks keanekaragaman pada penelitian ini masih relatif sensitif dalam mencerminkan gangguan akibat kontaminasi logam berat di sedimen.Kata kunci: logam berat, makrozoobentos, sedimen, situ, waduk, polutan. Abstract Presence of heavy metals in aquatic ecosystems have been reported to cause problems in aquatic organisms. One of the aquatic organisms that have risk for exposure by heavy metals from sediments is macrozoobenthos. This paper aims to describe the influence of heavy metal contamination in sediments to the structure of macrozoobenthos communities in lentic ecosystem (small lakes and reservoirs). This study was conducted in

Concerns over the impacts of floating cage aquaculture (FCA) systems on ecosystem health have led to the exploration of alternative green technologies as a way of improving water quality and preventing eutrophication problems in Lake Maninjau, Indonesia. This lake has been suffering from frequent harmful algal blooms (HABs) and hypoxic conditions due to excess nutrient and organic inputs from FCA. These have caused mass fish kills and decreased the local fish population. The main goal of this study was to assess the effectiveness of using integrated floating treatment wetlands (FTWs) and a lake fountain aeration system (LFAS) to improve lake water quality and enhance ecological conservation. The FTWs, which resembled artificial islands (AFIs) and covered an area of 23.75 m2, were planted with Echinodorus palaefolius. An LFAS was installed at the front of the FTWs. The impacts of the FTWs were evaluated from July to December 2018, while those of the LFAS was evaluated from October to November 2018. Lower nutrient and chlorophyll-a concentrations were observed within and around the FTWs and LFAS. Also, the LFAS increased the dissolved oxygen concentrations in the water to more than 100% at night. The results suggested that FTWs and LFAS could be used to prevent eutrophication and lake hypoxia. The plants in the FTWs grew much faster in the parts that were facing the waves, with their higher plant biomass suggesting that more nutrients had been removed from the lake. Also, the FTWs and LFAS, which resembled floating gardens, help to make the lake landscape more attractive and increase its amenity value. The improved water quality and habitat provision provided by these systems has attracted more local fish and other wildlife to the FTWs. The overall improvement in lake water quality and ecosystem health has the potential to ensure better provision of essential lake ecosystem services.