**Monitoring Lake Ecosystems Using Integrated Remote Sensing / Gis Techniques: An Assessment in the Region of West Macedonia, Greece**

Stefouli Marianthi1, Charou Eleni2 and Katsimpra Eleni3 *1Institute of Geology and Mineral Exploration, Olympic Village, Acharnai, 2N.C.S.R. "Demokritos", Institute of Informatics & Telecommunications, 3Geographer, Independent Researcher, Greece* 

#### **1. Introduction**

184 Environmental Monitoring

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The environment and its land and water systems are put into constant stress through the various human activities, natural and climate processes. Water resource managers have long been incorporating information related to climate in their decisions. They also increasingly recognize that climate is an important source of uncertainty and potential vulnerability in long-term planning for the sustainability of water resources (Hartmann, 2005). These are leading to questions about the relative impacts of shifts in river hydraulics, land use, and climate conditions. Prospects for climate change due to global warming have moved from the realm of speculation to general acceptance. Climate change will have different effects on lakes. Lakes can be extremely sensitive to short- and long- term changes in the weather and so are intrinsically sensitive to climate change through a direct effect, or indirectly by affecting processes that take place in the catchment. Understanding the response of lakes to climate change is of great importance since year-to-year changes in the weather patterns can influence water quality and the ecological status of a lake in the terms of Water Framework Directive.

Characterizing the heterogeneity and temporal change of water quality across surface waters is difficult through conventional sampling methodologies (Tyler et al., 2006). In situ measurements and collection of water samples for subsequent laboratory analyses provide accurate measurements for a point in time and space, but do not give either the spatial or temporal view of water quality needed for accurate assessment or management of water bodies (Schmugge et al., 2002). Traditional monitoring of water quality as well as other environmental parameters involves specialized personnel and both on site and laboratory analysis. Field measurements for monitoring the environment are expensive and difficult to conduct. For example, the water quality monitoring of lakes often includes the monitoring of water clarity using a Secchi disk. Therefore the use of Sechi Disk Transparency (SDT) has been widely adopted in many lake monitoring programs worldwide (Bukata et al. 1988; Wallin and Hakanson 1992; Lee et al., 1995).

Substances in surface water can significantly change the backscattering characteristics of surface water. Remote sensing techniques for monitoring water quality depend on the ability

Monitoring Lake Ecosystems Using Integrated Remote

being observed in the central and eastern part of the Prespa basin.

could not explain the abrupt drop in water level, Figure 2.

evaluating their possible use for environmental monitoring.

commonplace (Cohen and Goward, 2004).

lake.

**3. Data** 

Sensing / Gis Techniques: An Assessment in the Region of West Macedonia, Greece 187

Macro Prespa lake is a transboundary lake that it is shared between FYR of Macedonia, Greece and Albania. The study area is extended to include the catchment of lake Macro & Micro Prespa, as well as that part of the region that is hydro-geologically related to Ohrid lake. The study area has a size of 4769 Km2 while the Prespa basin covers an area of 1380 Km2 and is bounded between latitude 40 38. 3 N to 41 19.3 N and longitude 20 33.2 E 21 18.6 E. Prespa lakes are selected for use as a case study because they have been used in a variety of settings, by multiple agencies, over a long period. Furthermore, Prespa and Ohrid lakes can explicitly accommodate a broad range of resource management concerns (e.g., transnational management, environmental protection / biodiversity concerns, recreation / tourism, water supply, water quality, and power plant support). The study area consists of mountainous ridges, surrounding valleys and the Macro / Micro Prespa and Ohrid lakes. The elevation of the study area lies within ~600 and ~2500 masl with the highest elevations

Vegoritis lake basin covers an area of 1894 sq kms and it is bounded between latitude 40 18. 4 N to 40 54.2 N and longitude 21 24.2 E 22 06.6 E. The lakes range in surface area from 1.8 to 59.7 sq kms with a mean of Secchi depth of 2 m. Emphasis is given on the environmental aspects of Vegoritis lake. Mean depth of the lake is 20 meters. The annual rainfall is about 600mm. There are two main aquifers in Vegoritis hydrologic basin. One of the acquifers is of phreatic type and it is developed in the loose sediments of the basin. Depth of groundwater table varies from about 0 m to more than 40 m. The other one is developed in the karstified limestones and is hydraulically connected directly with the

The criteria for lake monitoring involve complex considerations of meteorological, hydrological, geomorphic and socio-economic factors. The necessary secondary data sources are not always available, or they are out of date. The relevant lake features are either not on the maps or they are inaccurate. Hence the advantages of satellite RS imagery. Both lakes show an abrupt drop of water level during the last decades. Analysis of meteorologic data

Optical sensors are widely used for environmental impact monitoring. Satellite images with moderate to high spatial resolution have facilitated scientific research activities at landscape and regional scales. Different sensor properties are important to be considered, when

These properties refer to spatial, spectral, radiometric temporal resolution, signal-to-ratio and finally launch date, length of the time series. Multi-temporal Landsat images are the main source of information. LANDSAT-1 was the world's first earth observation satellite, launched by the United States in 1972. Following LANDSAT-1, LANDSAT-2, 3, 4, 5, and 7 were launched. LANDSAT-7 is currently operated as a primary satellite, although an instrument malfunction occurred on May 31, 2003, with the result that all Landsat 7 scenes acquired since July 14, 2003 have been collected in 'SLC-off' mode. Of all remotely sensed data, those acquired by Landsat sensors have played the most pivotal role in spatial and temporal scaling: given the more than 30-year record of Landsat data, mapping land and vegetation cover change and derived surfaces in environmental modeling is becoming

to measure these changes in the spectral signature and relate these measured changes by empirical or analytical models to water quality parameters. The spectral resolution of most satellite imagery is insufficient to identify (concentrations of) individual components that affect water quality. In most cases, satellite remote sensing is used to investigate the dynamics of sediment loads in reservoirs and lakes (Vrieling, 2006). Many studies found significant linear or nonlinear relationships between in situ determined suspended sediment concentration near the surface of inland water bodies and atmospherically corrected spectral reflectance derived from satellite remote sensing data, such as Landsat (Nellis et al., 1998; Schiebe et al., 1992) and SPOT-HRV (Chacon-Torres et al., 1992). Because sediment characteristics, like texture and color, influence the water reflection, developed empirical relationships are not easily transferable to other regions where erosion entrains different sediment types. Therefore, until a universal equation does not exist, most models of suspended sediment are site-specific (Liu et al., 2003). Thermal infrared (TIR) satellite images can be also used to study transport processes in lakes, such as wind-driven upwelling and surface circulation, providing a measure of spatial variability and horizontal distribution of water temperature that conventional field-based measurements cannot provide, (Steissberg et al., 2006, Zhen-Gang Ji et al., 2006). There still remain many unanswered questions about the effective implementation of integrated remote sensing / GIS techniques into a lake / environmental monitoring program, and these are analyzed in this presentation.

The objective of our research is to better understand the use of integrated application of remote sensing / GIS techniques on monitoring various environmental factors of lake ecosystems.

#### **2. Pilot project area**

About 65% of the surface waters of Greece are in its north-western part, in the periphery of West Macedonia. Some of the most valuable lakes of Europe in terms of biodiversity are located in this area, (Figure 1). The analysis of the basins of Macro Prespa and Vegoritis lakes are included in the Chapter.

Fig. 1. Pilot project area

Macro Prespa lake is a transboundary lake that it is shared between FYR of Macedonia, Greece and Albania. The study area is extended to include the catchment of lake Macro & Micro Prespa, as well as that part of the region that is hydro-geologically related to Ohrid lake. The study area has a size of 4769 Km2 while the Prespa basin covers an area of 1380 Km2 and is bounded between latitude 40 38. 3 N to 41 19.3 N and longitude 20 33.2 E 21 18.6 E. Prespa lakes are selected for use as a case study because they have been used in a variety of settings, by multiple agencies, over a long period. Furthermore, Prespa and Ohrid lakes can explicitly accommodate a broad range of resource management concerns (e.g., transnational management, environmental protection / biodiversity concerns, recreation / tourism, water supply, water quality, and power plant support). The study area consists of mountainous ridges, surrounding valleys and the Macro / Micro Prespa and Ohrid lakes. The elevation of the study area lies within ~600 and ~2500 masl with the highest elevations being observed in the central and eastern part of the Prespa basin.

Vegoritis lake basin covers an area of 1894 sq kms and it is bounded between latitude 40 18. 4 N to 40 54.2 N and longitude 21 24.2 E 22 06.6 E. The lakes range in surface area from 1.8 to 59.7 sq kms with a mean of Secchi depth of 2 m. Emphasis is given on the environmental aspects of Vegoritis lake. Mean depth of the lake is 20 meters. The annual rainfall is about 600mm. There are two main aquifers in Vegoritis hydrologic basin. One of the acquifers is of phreatic type and it is developed in the loose sediments of the basin. Depth of groundwater table varies from about 0 m to more than 40 m. The other one is developed in the karstified limestones and is hydraulically connected directly with the lake.

The criteria for lake monitoring involve complex considerations of meteorological, hydrological, geomorphic and socio-economic factors. The necessary secondary data sources are not always available, or they are out of date. The relevant lake features are either not on the maps or they are inaccurate. Hence the advantages of satellite RS imagery. Both lakes show an abrupt drop of water level during the last decades. Analysis of meteorologic data could not explain the abrupt drop in water level, Figure 2.
