Remote Sensing of Suspended Particulate Matter in Himalayan Lakes

Jun 11th, 2012 | By | Category: Glaciers, Global Warming, Land, Lessons, News, Pollution, Publication, Research, Wetlands

Bio-One: This study presents satellite data and in situ measurements to estimate the concentration of suspended solids in high altitude and remote lakes of the Himalayas. Suspended particulate matter (SPM) concentrations measured in 13 lakes to the south of Mount Everest (Nepal) in October 2008 and reflectance values of the Advanced Visible and Near Infrared Radiometer type 2 (AVNIR- 2) onboard ALOS, acquired a few days after the fieldwork activities concluded, were combined to build a relationship (R2 5 0.921) for mapping SPM concentrations in lakes of the Mount Everest region. The satellite-derived SPM concentrations were compared with in situ data (R2 5 0.924) collected in the same period in 4 additional lakes, located to the north of Mount Everest (Tibet, China). The 13 water samples collected in lakes in Nepal were also used to investigate the absorption coefficients of particles ap(l) and colored, dissolved organic matter a CDOM(l), with the aim of parameterizing a bio-optical model.

An accurate model (R2 5 0.965) to estimate SPM concentrations from ap(l) was found and could be adopted in the future for retrieving suspended solids from satellite imagery independently of ground measurements. In such a remote area, remote sensing was demonstrated to be a suitable tool to characterize the state of lakes, whose loads of suspended solids might be assumed to be direct and quick-responding indicators of de-glaciation processes and glacier–lake interactions. As a macro descriptor of water quality, the assessment of SPM in glacial lakes of the Himalayas might also be of interest for resource use in the downstream region.

Global warming has resulted in a large-scale retreat of glaciers throughout the world (Oerlemans 2005). The evidence for this is particularly strong in high-altitude areas, such as the central Himalaya (Solomon et al 2007; Hambrey et al 2009; Quincey et al 2009; Ye et al 2009), where widespread recession is evident from the rapid growth in the number and size of glacial lakes (Chikita et al 2001; Quincey et al 2007; Bolch et al 2008; Tartari et al 2008; Wang et al 2008; Ye et al 2009). De-glaciation processes are also revealed by the amount of suspended solids transported by glacier waters melting into the lake (Østrem et al 2005),with consequences for light propagation in the water body. If glacier water influx into a lake increases,then the density will increase, and this affects light scattering.

For decreased melt water input, absorption because of water increases and the preferential red absorption because of water are enhanced. In lakes that have no glacial input, lake water is clear, and there is almost no scattering or absorption because of suspended matter (Kargel et al 2005). The recognition of lakes hydraulically connected to the glacier hydrological systems, hence full of silt (eg moraine-dammed supra glacial lakes),as opposed to those that are isolated (eg cirque lakes),would add value to studies (eg Tartari et al 2008) on processes of glacial-lake formation and expansion. Ultimately, these studies might contribute to an assessment of glacial lake hazard, because some moraine-dammed lakes may be unstable and potentially susceptible to sudden discharge of large volumes of water and debris, which could cause floods hazardous to communities and infrastructure downstream (Richardson and Reynolds 2000; Kattelmann 2003; Bajracharya et al 2007; Quincey et al 2007; Bolch et al 2008).

Besides indicating the dynamics of the interaction between glaciers and lakes, suspended solids play a fundamental role in the aquatic system itself. They regulate the transport routes of all types of materials and contaminants in aquatic ecosystems (Wetzel 1983) and ultimately determine the primary productivity of water (Zhang et al 2008). As an indicator of water clarity (eg Secchi disk depth and water transparency, see Ha¢ª kanson et al 2007),suspended solid concentration is also a macro-descriptor of water quality directly related to many variables of general use in lake management (Baban 1999). Water quality monitoring in the Himalayan region would contribute to proper management of some glacial lakes that could provide valuable water, energy, and tourism resources to local residents in the downstream regions (Komori 2008; Salerno et al 2008).

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Started in year 2010, ‘Climate Himalaya’ initiative has been working on the mountain and climate related issues in the Himalayan region of South Asia. In the last two years this knowledge sharing portal has become one of the important references for the governments, research institutions, civil society groups and international agencies, those have work and interest in Himalayas. The Climate Himalaya team innovates on knowledge sharing, capacity building and climatic adaptation aspects in its focus countries like Bhutan, India, Nepal and Pakistan. Climate Himalaya’s thematic areas of work are mountain ecosystem, water, forest and livelihood. Read>>

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