Luki Subehi

Sustainable reservoir management requires seasonally targeted mitigation measures to control sediment and nutrient inputs. However, such efforts are often constrained by limited understanding of how seasonal runoff pulses interact with internal mixing processes to shape water quality dynamics. This study investigates the spatiotemporal variability of water quality in Cileunca Reservoir, a tropical agricultural reservoir in West Java, Indonesia, with a focus on the coupling between catchment runoff and in-reservoir processes. Field observations during the wet and dry seasons (2023–2024) included vertical profiling, spatial transect sampling, and laboratory analyses. Multivariate statistical techniques, including Principal Component Analysis and Cluster Analysis, combined with spatial interpolation, were applied to characterise variability in key parameters. The results revealed pronounced seasonal contrasts and marked spatial heterogeneity. During the wet season, Total Suspended Solids (TSS) increased by up to 21-fold relative to the dry season, while the relationship between TSS and turbidity depended on seasonal changes in particle size distribution and composition. Total Nitrogen (TN) and Total Phosphorus (TP) increased by 125% and 100%, respectively, particularly near inflow zones, indicating strong catchment-driven inputs. In the dry season, reduced surface turbidity but persistent bottom oxygen depletion indicated active internal nutrient recycling. The reservoir remained consistently eutrophic, with mean Trophic State Index values of 57.8 (wet) and 60.4 (dry). These findings demonstrate that interactions between external loading and internal processes sustain water quality variability. Improved understanding of these dynamics is essential for designing effective seasonal mitigation strategies to support sustainable reservoir management.

Global warming is modifying precipitation patterns, and hence increasing the hazards of severe and extended rainstorms. Addressing the gap in integrating economic and environmental assessments into urban stormwater management—a key challenge in urban water resource analysis—this study utilizes the analytical hierarchy process (AHP) and SUSTAIN model to identify and evaluate low-impact development (LID) stormwater management strategies, assessing their impacts on runoff volume, peak flow reduction, chemical oxygen demand (COD), and suspended solids (SS) across four planning scenarios under five rainfall recurrence intervals, culminating in a cost–benefit analysis to ascertain the optimal scenario. The reduction rates for COD and SS varied from 41.85% to 87.11% across different scenarios, with Scenario Three (RM03) demonstrating the highest efficacy in pollutant management. (The four labels RM01–RM04 are used throughout the text to represent the four scenarios) Implementing the best plan may result in a reduction of yearly carbon emissions of 189.70 metric tons, with emissions from the operational load of the drainage network and COD pollution treatment potentially decreasing by 2.44% and 2.06%, respectively, indicating an overall annual reduction of 85.46%. This approach not only mitigates urban rainwater and flooding issues but also prevents resource wastage, optimizes resource utilization and benefits, offers a scientific foundation for urban construction and planning, and serves as a reference for sponge city development in other regions.

This article aims to assess the ecosystem services related to water purification by analyzing the water quality conditions of three lakes in Jakarta, each with distinct characteristics. The analysis utilizes both national quality standards and the Water Quality Index (WQI). Water samples collected during the rainy and dry seasons were evaluated using the WQI, which combines various physical, chemical, and biological parameters into a single standardized score, comprehensively representing overall water quality. The study found that several water quality data points did not meet national standards for recreational use due to high levels of water pollutants. The fluctuating WQI values across the seasons indicated that seasonal variability significantly impacts water quality. The WQI scores for the lakes were categorized as medium to poor, with scores of 51.40 for Situ Babakan Lake, 45.20 for Srengseng Urban Forest Lake, and 46.20 for South Sunter Lake. Additionally, the results highlighted that water purification ecosystem services are influenced by the surrounding landscape conditions, human activities, and the presence of wastewater treatment plant (WWTP) facilities. This information is expected to provide valuable insights for local government agencies to enhance lake water quality within environmental policy frameworks.

Lake Maninjau, like many surface water bodies worldwide, faces significant water pollution challenges due to extensive aquaculture activities, making it an ideal site to study the impact of fish farming on water quality, which has contributed to eutrophication and declining water quality. This study investigates the physicochemical parameters and pollution levels in the lake, aiming to provide insights into its environmental health. In August 2022, a comprehensive sampling campaign was undertaken at nine stations within the upper layers of open water and littoral zones of Lake Maninjau. In situ measurements, including temperature, dissolved oxygen, and pH, were conducted, accompanied by water sample collection for laboratory analysis of trace elements and heavy metals. Our study revealed notable variability in water parameters across different sites, with surface water layers exhibiting the greatest differences. While certain parameters such as temperature and conductivity remain relatively stable, pH levels show a decreasing trend with increasing water depth. Dissolved oxygen levels vary widely, while oxidation–reduction potential indicates water pollution, particularly in littoral zones. Potassium dominance within cations likely suggests anthropogenic influences, notably from aquaculture activities, that may also contribute to nutrient enrichment and heavy metal pollution. Elevated levels of total nitrogen and ammonia underscore the lake’s moderate pollution levels, with heavy metals such as mercury exceeding permissible limits, posing risks to aquatic life and human health.

Rawapening Lake is located in Semarang Regency, Central Java Province, Indonesia, and is the center of various activities, including agriculture, fisheries, sources of electrical energy, raw water, tourism, and culture. A 100-cm-long sediment sample was extracted from Rawapening Lake to reconstruct the dynamics of environmental change by observing the preserved diatoms. Diatoms are sensitive to changes in water quality, so their pattern of existence can reflect changes in lake conditions. The sampling location is located at the mouth of the Tuntang River, the only outlet of Rawapening Lake, which has 20 inlets as water sources. Sediment cores were sliced at 1-cm intervals for diatom analysis. Diatom slide mounts were prepared from about 5 grams of dry sediment using 10% hydrochloric acid followed by 10% peroxide to remove organic matter and carbonates. A total of 300 valva diatoms were counted for all samples in order to obtain the lowest level of diatom taxonomy. Vertical distribution analysis is used to determine the condition of Rawapening Lake in the past through cluster analysis using the Bray-Curtis model, which is based on depth similarities. The reconstruction of Rawapening Lake, which was carried out based on variations in the abundance and diversity of diatoms vertically, showed that the pH of the waters tended to increase. Indicators that strengthen this statement are the dominance of A. ambigua, A. granulate, S. ulna, and S. acus. This can occur due to two things: the occurrence of decomposition of organic material by microorganisms at the bottom of the lake or the use of lime in the manufacture of organic fertilizer from water hyacinth. When it rains, the lime will wash off and enter the lake. Total Nitrogen of 1.773 μg/l in Rawapening Lake indicates that the nutrient enrichment of these waters has reached hypereutrophic levels. The dominance of benthic indicators with high nutrient status indicates that Rawapening Lake has a long history of eutrophication. The condition of Rawapening Lake can be categorized into 3 zones, namely: (a) Zone 3 (90-100 cm layer) is dominated by diatoms N. palea, N. closterium, and T. apiculate, which indicate eutrophic water conditions; (b) Zone 2 (30-40 cm layer) is dominated by A. distans, N. closterium, T. apiculata, S. ulna, and N. radiosa species, where A. distans is widely distributed in clear and oligotrophic waters; (c) Zone 1 (1-20 cm layer) is found S. pupula of the genus Sellapora, which is an indicator of lake or river waters with mesotrophic-eutrophic conditions.

Lonthor DW, Miftahudin, Kayat, Julzarika A, Subehi L, Iswandono E, Dima AOM, Dianto A, Setiawan F, Nugraha MFI. 2023. Diversity of aquatic plants in the Rote Dead Sea area, East Nusa Tenggara, Indonesia, based on rbcL marker. Biodiversitas 24: 810-818. The Rote Dead Sea area in Rote Islands has two freshwater and 24 saltwater lakes. The saltwater lakes have salinity levels varied between 0-100 ppt. Every lake has specific aquatic plant species. Species identification through morphological analysis only has its limitations; therefore, DNA barcoding is a preference due to an effective, accurate, and faster method for species identification. In this study, we used the rbcL marker to identify and analyze the diversity of the aquatic plant species in lakes Ledulu, Oenduy, Oemasapoka, Oesotimori, and Landu Leko. Plants samples' DNA was amplified using rbcL primers, and the amplicons were sequenced. Species identification was based on morphological study and the rbcL sequence database. Diversity analyses were performed based on pairwise genetic distances, analysis of molecular variance, and genetic relationships based on the Kimura 2 parameter. The results showed that all 20 aquatic plants were correctly identified, and high genetic diversity was discovered. AMOVA analysis showed that genetic variations within the population were higher than among the population. All plant species were grouped into four groups based on the phylogenetic tree and fractional component analyses. The species belonging to the certain family were grouped in the same clade and the closely related plant families. The rbcL marker can be used to discriminate aquatic plant species and analyze their genetic diversity and relationships.

Anthropogenic activities, especially due to agricultural practices, tourism, and other land-use forms, have resulted in serious pollution of Bukit Merah reservoir (BMR), the oldest artificial reservoir in Malaysia since the 1980s. This study assessed the past ecological conditions of the reservoir using 210Pb, dating techniques, selected metals, and physicochemical analysis of the sediment core to better manage the reservoir. 210Pb results indicated 34 years of human impact on the reservoir, with arsenic recording the least concentrations in the 1980s and the highest concentrations in 2016 and 2018. The minimum and maximum concentrations of lead and cadmium were found in 1990 and 2009. Whereas Copper and Zinc, concentrations peaked in 2012. The mean EF values of metals in the sediment core were above 1 (EF>1), indicating anthropogenic sources. The Igeo values of Arsenic and Cadmium ranged from uncontaminated to strongly contaminated, uncontaminated to moderately contaminated for Lead, Zinc, and Copper. Overall, the dated sediment of BMR revealed that human population growth and increasing economic and agricultural activities coupled with poor land-use forms at the catchment area are the main source of pollution to the reservoir. Therefore, regular monitoring and the enforcement of relevant environmental laws are needed to manage the reservoir.

Chenderoh Reservoir is a hydroelectric dam commissioned in 1930. Changes at the margin and littoral zone of the reservoir due to shoreline sedimentation and the growth of macrophytes have not been studied well. Therefore, a study on the spatial distribution of macrophytes at Chenderoh Reservoir was carried out to determine the diversity and distribution of macrophyte species based on reservoir morphometry. Field samplings were conducted at 18 sampling points covering the embayments and main river channel using echo sounding, line transect and quadrat methods. The results showed that the macrophyte species were distributed according to the slope of the reservoir. Thirty-four macrophyte species from four different types, emergent, floating-leaved, submerged and free-floating, were recorded. The morphometric characteristic, particularly water depth, resulted in the zoning of macrophytes according to their types, determined by the availability of light and hydrological attributes. This study indicated that the macrophytes distribution at all sampling points in Chenderoh Reservoir was determined by morphometric characteristics influenced by seasonality and water level fluctuations of the dam operation. Hence, the bathymetric study is important to identify reservoirs morphometry and helps in mapping the vegetation for better management by the authority.

Lake Maninjau is a caldera lake with a volcano-tectonic type. The existing land management of Lake Maninjau catchment area influenced water quality, included River Kurambik as one of the rivers that flow into Lake Maninjau. It influenced degradation of water quality, nutrient enrichment and exceeded the carrying capacity. The source of pollutants, especially non-point sources pollution can be a point source in large numbers. For example, runoff from agricultural areas containing pesticides and fertilizers, runoff from residential areas (domestic). In order to gain insight into the effect of watershed conditions on water quality in Lake Maninjau, we statistically analyzed Total Suspended Solid (TSS), Nitrite, Nitrate, discharge, water temperature (Tw) and, air temperature (Ta) at River Kurambik, Lake Maninjau. Besides water level and water temperature (HOBO sensor), also Teledyne ISCO sampler equipment was used to take sample water for analysis. Some results showed the relation among parameters such as TSS, Nitrite, Nitrate, discharge, and water temperature as long as our observation in periods September – November 2018. Based on data, it could be explained that the seasonal variability of atmospheric conditions influenced fluctuations in air and water temperature nearly proportionally (R² = 0,883). The change of discharge influenced Total Suspended Solid (TSS) significantly (R2 = 0,917). It indicated the land use change contributed to the water quality during rainfall events through runoff sediment and materials into the lake. On the other hand, Nitrite, Nitrate parameters seemed to have various changes during rainfall events. The land use management and economic values of these lakes and ecosystem should be elucidated. In order to maintain the sustainability of the lake, land cover management at the catchment area is also necessary for the next study.