Characteristics of Rainfall-Discharge and Water Quality at Limboto Lake, Gorontalo, Indonesia

Abstract

Abstract. Problems of high turbidity, sedimentation, water pollution and siltation occur at Limboto Lake, Gorontalo, Indonesia. The objective of this study was to analyze the rainfall-discharge relationship and its implications for water quality conditions. Secchi disk (water transparency), chlorophyll-a (chl-a), and total organic matter (TOM) were measured in May 2012, September 2012 and March 2013 at three sites of the lake (L-1, L-2 and L-3) to observe the impacts on the surrounding catchment. Based on representative stations for rainfall data from 2004 to 2013, monthly averages of rainfall in March-May (166.7 mm) and September (76.4 mm) were used to represent the wet and dry period, respectively. Moreover, sediment traps at these three sites were installed in September 2012. Based on the analysis it is suggested that rainfall magnitude and land use change at the Alopohu River catchment influenced the amount of materials flowing into the lake, degrading the water quality. Specifically, the higher average rainfall in May (184.5 mm) gave a higher average total sediment load (4.41 g/L/day). In addition, water transparency decreased with increasing chl-a. This indicates that the concentrations of sediment and nutrients, reflected by the high amount of chl-a, influenced the water quality conditions.

Mechanism of the Rapid Shrinkage of Limboto Lake in Gorontalo, Indonesia

“…In the previous studies, yearly lake water extent was extracted from global water surface data demonstrating a reduction of 12.8 km 2 , which is equivalent to 51.9%, from 2001 to 2014 [40]. Similarly, 51% lake coverage by water hyacinth was reported during the dry season of 2012 [17]. Hence, the long-term trend of lake shrinkage and the distribution of water hyacinth can be observed from satellite imagery even with a 30-60 m ground resolution.…”

“…Regression analysis was performed to interpolate the missing values of lake extent in 2003 and 2017 needed for further analysis. Average lake depths in 2003 and 2017 were calculated using regression based on the combination of field survey data conducted during 1993-2012 [7,17,20]. Accordingly, the total volume of lake sedimentation accumulated during 2003-2017 was calculated based on changes in lake extent and depth, the results of which were utilized for the discussion presented in Section 4.2.…”

“…A variety of research studies and projects have recently been conducted at diverse scales ranging from local to watershed levels to mitigate severe lake degradation due to increased sedimentation. These include environmental management strategies, such as sedimentation and sludge management [10,14], aquatic environment management [36], watershed management [37,38], environmental assessments [7,17,32,39], and lake extent monitoring [30,40]. Technical assistance for flood mitigation has been provided in collaboration with international development agencies from, for example, Canada and Japan [7].…”

Erosion Hazard Analysis in the Limboto Lake Catchement Area, Gorontalo Province, Indonesia

“…Stretched approximately 3.000 hectares wide, it is the estuary of 5 main rivers, namely Bone Bolango, Alo, Daenaa, Bionga, and Molamahu River. As an icon of both Gorontalo regency and province, Limboto Lake possesses a significant role, either as an ecological and hydrological function, or socio-economical support to the locals [4]. Research on Lake Limboto has been carried out mainly on microfacies and uplift rate of limestone.…”

“…The shrinkage occurred as a result of illegal logging and agricultural land conversions to maize fields. [4,10] also blamed the existence of water hyacinth, causing lake sedimentation and also damaging ecosystems of the lake. With that in mind, there is a bigger probability that flood might happen in high rainfall.…”