Third Prize: Caitlin Neary - GIS Analysis of Land Use Change and its Impact on Lesina Lagoon, Italy

GIS Analysis of Land Use Change

 and its Impact on Lesina Lagoon, Italy

 

Caitlin Neary

 

 

Abstract

            Land use, watershed processes, and coastal water resources are intricately linked. Changes in land use due to human development, therefore, present a potential threat to the health of coastal ecosystems through increased flux of contaminants to the coast. A Geographical Information Systems (GIS) analysis was performed to assess land use changes from 1975 to 2011 within the Lesina Lagoon, Italy drainage basin. Land use was assessed by applying maximum likelihood supervised classification techniques to 5m resolution thematic data derived from Landsat satellite images from 1975 and 2011. The majority of the observed changes can be attributed to an increase in continuous urban fabric in the traditionally rural, agriculturally dependent region.  Urban development has been identified as a primary cause of habitat alteration and biochemical stress in coastal water bodies.

             Periodic eutrophication events, initiated by increased concentrations of nutrients, have been observed in the Lesina Lagoon during the last decade. To quantify how land cover change may be influencing biochemical stress within the lagoon, nitrate concentrations monitored in summer, 2012 were compared to nitrate data collected in 1975. An overall increase of >1000% was observed.

In the midst of regional development, an assessment of land cover is necessary to identify factors currently impacting the lagoon. Continued urbanization of the watershed may have serious implications for the ecological welfare of Lesina Lagoon.

 

 

 

           

 

 

 

 

            Land use and coastal water resources are inexorably linked. Coastal environments exemplify the concept of “open systems” because of the vital exchanges of materials, energy, and organisms between terrestrial and water ecosystems (Stoms et al., 2005). Coastal water bodies, such as lagoons, are valuable in providing habitat for countless flora and fauna populations. In addition, they perform essential ecosystem services such as ground-water recharge, nutrient cycling, heavy metal retention, and flood control (Torbick et al., 2006; Hilbert, 2006). Coastal ecosystems are vital in offering social, economic, and aesthetic values to human populations (Stolt et al., 2011).  Yet, many coastal ecosystems are also extremely susceptible to stress due to anthropogenic alterations, physical and/or chemical.  In fact, shallow, near-shore marine ecosystems are some of the most environmentally sensitive coastal habitats in the world (Stolt et al, 2011); nearly half of which have been altered by human activity worldwide (Torbick et al., 2006). Human induced changes in land use, including agricultural and urban development, within the drainage basin of coastal water bodies can result in direct ecosystem loss or fragmentation, decreased water quality, and increased ecological stress.

            The Holocene era Lesina Lagoon lies along the southern Adriatic coast of Italy, situated on a large karst massif, jutting into the sea (Boenzi et al., 2006). The lagoon lies within the Gargano Promontory, and is now protected as part of the Gargano National Park (Boenzi et al., 2006).  In addition to providing ecosystem services, the lagoon is valuable as an overwintering habitat to migratory bird species (Ballarini et al., 2013).  Indeed, it is internationally known as a breeding area for many avian species.  The sandy barrier island separating the lagoon from the open Adriatic Sea also provides a habitat for the critically endangered plant Cistus clusi, a species included in the national Red List (Ballarini et al., 2013).

            Historically, the plains lining the Gargano Promontory were used for animal husbandry, although with the development of drainage systems during the 19th century, the Gargano Plains have become some of the most agriculturally productive in Italy (Ballarini et al., 2013).  In comparison to the national average, Apulia’s economy historically depends largely on agriculture and less on industry than other regions of Italy. In addition to agriculture, fishing within the lagoon, especially for eel (Anguilla anguilla), supports much of the local economy in the small city of Lesina, situated on the lagoons western shore (D’Adamo et al., 2008).  This employment sector, needless to say, relies heavily on the health of the lagoons waters.  Animal husbandry for cheese production also represents an important employment sector in the lagoon area, with livestock farms housing approximately 6500 head of cattle. This is number of cattle is notable, as there appears to be a general trend between quantity of livestock waste and nitrogen-enriched systems in rural, agricultural regions (Nixon et al., 2007).  Agriculture, human population growth, and urban development have also been correlated with increased nitrogen loading to lagoon systems (Kinney et al., 2011; Nixon et al., 2007). Nitrate (NO3) has been identified as a driving factor of increased biochemical stress and harmful eutrophication events (Kinney et al., 2011). The Lesina Lagoon has been marked by periodic eutrophication events over the last decade.

            Previous land use studies (Kinney et al., 2007; Nixon et al., 2007; Rochette, 2009; Wolter et al., 2006) have found strong correlations between population density, urbanization, and industrialization and the deterioration of coastal systems, particularly due to land cover changes and wastewater runoff that lead to nutrient loading, while weaker correlations exist between agricultural practices and coastal deterioration.  Human population density alone (in the absence of land cover alteration) has been shown to account for significant variation in nitrogen (Nixon et al., 2007).  Lagoons with lower population densities in the watershed have relatively low dissolved inorganic nitrogen concentrations (Nixon et al., 2007).

            While assessments of land use and land cover change and its implications within the Lesina Lagoon drainage basin have been observed, such observations have only occurred at a very local level.  Small-scale lagoon assessments can result in drainage basin-scale conditions going largely unnoticed.  This may result in a deficiency of data as, when assessing coastal ecosystems, it is important to look at the big picture.  Watershed-scale analysis is vital in that these interactions affect the overall health of the lagoon, and these analyses are useful in investigating the causes of quality changes in coastal water bodies associated with land use change over time (Torbick et al., 2006).  While human population density in the watershed surrounding the Lesina Lagoon has remained low, estimates of land use change including agricultural, urban, and industrial development and the maintenance or loss of natural vegetation or wetlands have yet to be examined.

            Examination of land cover change is imperative in assessing and understanding the multiple human-induced pressures impacting ecologically fragile coastal water bodies (Hilbert, 2006). Like all coastal water bodies, Lesina Lagoon is extremely vulnerable to environmental pressures. Yet, the current land use status of the lagoons watershed is not well understood.  This study is part of a larger effort by the European Commission’s ARCH (Architecture and Roadmap to Manage Multiple Pressures on Lagoons) initiative, the goal of which is to develop methodologies and management strategies to address the multiple environmental and human pressures on lagoons in Europe.  As part of the ARCH assessment of the Lesina Lagoon, this study examined land use change over a 35-year period (1975-2011) within the lagoon drainage basin using Geographic Information System (GIS) analysis.

 

Methods

Study Area

            The Lesina lagoon (41.88°N and 15.45°E) is situated on the southern Adriatic coast in Apulia, Italy, lying along the northern fringe of the Gargano Peninsula. The characteristically shallow water body has a maximum depth of 1.5m (0.7m average depth), a total area of 51km2 and a NW to SE length of 22km.  A long, dune lined, sandy barrier (1-2km wide) separates the lagoon from the open Adriatic, and limits the lagoons exchanges with the sea.  Two manmade tidal channels control salt-water exchanges (Boenzi et al., 2006).  The lagoon also receives freshwater inputs from several small rivers and creeks, as well as two drainage pumps, originally built for land reclamation, which discharge water to low lying areas. Additionally, smaller canals drain runoff from agricultural and livestock fields into the lagoon.  Two wastewater treatment plants dispose of treated wastewater from the areas surrounding and within the cities of Lesina and nearby San Nicandro indirectly into the lagoon.  The quality of the treated water has been determined to be suitable for agricultural use.  The watershed is also home to several relatively large illegal settlements, which do not utilize the wastewater treatment plants.

            The entire drainage basin of the Lesina Lagoon is 869km2 in area, with a range of natural and artificial land covers including wetlands, natural Mediterranean vegetation, agriculture, quarries, and impervious surface. The main potential sources of lagoon pollutants and stressors are agricultural and urban development, including those introduced by synthetic fertilizers, and human and animal wastewater discharge.

 

Figure 1: A map illustrating the location of the Lesina Lagoon. Stars represent the collection of ARCH study sites.  The insert describes the location of the lagoon relative to the region (modified from Ballarini et al., 2012).

 

Data Collection

            Landsat satellite imagery was obtained for July, 1975 and July, 2011 from the United States Geological Survey (USGS). Additionally, an on-site ground truthing campaign was performed throughout the drainage basin to better ensure the accuracy of interactive supervised land use classifications.

Data Processing

            Satellite imagery was processed using GIS software. A shape file was created to delineate the boundaries of the Lesina Lagoon drainage basin based on visible hydrological and geological features.  An interactive supervised classification was performed on both images within the defined boundary.  This required defining training samples for the different classes of land use: water, continuous urban fabric (CUF), Macchia Mediterranea (natural vegetation), active fields, fallow fields, olive orchards, agriculture (other), and quarries.  These are the dominant land use types in the region.

            Training samples were defined by visually identifying features unique to each class, which could not be mistaken for a different class. Once the reclassification was complete via training samples, ground truth points were cross-referenced with the newly generated map to ensure accurate classifications. Finally, the total area of each land use type was calculated using a zonal statistic software tool, making it possible to calculate the land use change over the study period. In an effort to quantify the possible effects of any observed land use change, nitrate data from 1975 was compared to nitrate data collected as part of the ARCH lagoon assessment in summer, 2012.

 

Results

            The land use classes of the Lesina Lagoon drainage basin for 1975 and 2011 are shown in Figures 2 and 3, respectively.  Figure 4 depicts the areas of each land use type relative to each other and the total area of the drainage basin for each year.  The extent of land use change by class from 1975 to 2011 is summarized in Table 1. All land cover classes (agriculture, Macchia Mediterranea, water, and quarry) besides CUF (continuous urban fabric) experienced net losses, with lands used for agriculture and quarries showing the greatest loss (both 17%). It is important to note, however, that the change in the extent of the quarries is likely an artifact of the classification, as it is unlikely that quarry land could recover in such a short period of time. However, total quarry extent represents such a small portion of total land use, it is unlikely to be significant in total land use change in the drainage basin.

            Notable expansions in impervious surface (CUF) were observed (325%), indicating marked increases in urban development. Agricultural land appears to have been lost to urbanization (Fig. 3), and consequently moved south into areas previously dominated by natural vegetation. As such, some natural shrub lands appear to have been cleared during agricultural expansion.   

 

Figure 2. Landsat image of the Lesina Lagoon drainage basin from summer 1975, showing the extensive agricultural land use, as well as urban landscapes and natural shrub land vegetation (Macchia Mediterranea).

 

Figure 3. Landsat image of Lesina Lagoon drainage basin from summer 2011, showing the continued use of the land for primarily agricultural purposes, but also a significant increase in urban development and thinning of natural vegetation.

 

Agricultural Land Use Changes

            In 1975, agricultural land cover made up 58% (515.8km2) of the entire watershed surrounding the Lesina Lagoon (894.1km2).  An 86km2 (17%) loss in agricultural area occurred between 1975 and 2011, representing the largest loss in area among the land cover types. Despite these losses, in 2011 agriculture continued to be the dominant class of land cover within the lagoon watershed, making up 50% (430.0km2) of the total watershed area, despite the visible loss of large portions of agricultural land to urban development.

Changes in Natural Vegetation

            Natural shrub land (Macchia Mediterranea) also experienced net losses between 1975 and 2011 (12%).  Macchia Mediterranea occupied the second largest land cover type in both 1975 and 2011, with 278km2 (31%) in 1975, and 245km2 (28%) in 2011. Visually, shrub land has clearly thinned between 1975 and 2011, apparently due to the expansion of agricultural land into the area south of the lagoon, previously dominated by natural vegetation.  Still, natural vegetation and agricultural classes together make up the majority of the land cover types within the basin, in both 1975 (89%) and 2011 (78%). However, both classes experienced area losses, presumably as a result of urbanization.

Urban Development

            Changes in continuous urban fabric (CUF) make up the largest land cover change during the 35-year period.  In 1975, only 3% of the total watershed was defined by impervious surface.  In 2011, that number spiked to 15%, representing a 325% (96.4 km2) increase in impervious surface over 3 decades. Most of the gains in urban land occurred in areas dominated by agriculture, though significant growth is also apparent in areas immediately bordering the lagoon.

Nitrogen Content

            To assess biochemical changes in the lagoon that may be attributed to land cover change, nitrate data monitored in the summer of 2012 was compared to data collected in the summer of 1975.  In the 1975 sampling, the approximate mean value of mg/l of nitrate in water samples collected throughout the lagoon was .08mg/l.  The 2012 sampling campaign also collected water samples throughout the lagoon, and observed nitrate at an approximate mean of 1.1mg/l.  This represents a >1000% increase in nitrate concentrations within lagoon waters over three decades. 

 

Table 1. Historical land use and changes in Lesina Lagoon watershed (1975-2011).

 

1975

2011

Net Change

Land Cover

(km2)

(%)

(km2)

(%)

(km2)

(%)

Agriculture

515.8

58

430.3

50

-85.5

17

Macchia Med.

278.1

31

244.8

28

-33.3

12

CUF

29.6

3

126.0

15

96.4

325

Water

66.0

7

63.3

7

-2.7

4

Quarry

4.7

1

3.9

.4

-0.8

17

Total

894.1

100

868.3

100

218.7

 

 

 

Figure 4. The areas of land use types relative to the total drainage basin and each other, indicating the historical and continued dominance of agricultural land use in the region.

 

Discussion

            Land use land cover change is a critical ecological concern as it indicates changes in human demographics, natural resource use, and economic priorities.  GIS was successfully applied to classify land use from Landsat thematic maps of Lesina Lagoon in 1975 and 2011.  Different land uses impose varying environmental stressors on different ecological communities, with implications for ecosystem services, climate, water quality, and even human welfare. Landscape changes such as increased urbanization and impervious surface area, increased agricultural runoff of nutrients, increased pesticide/herbicide applications, and increased sediment erosion have impeded efforts to improve water quality in countries worldwide (Wolter et al., 2006), and need to be addressed regarding the Lesina Lagoon.

            Agriculture continues to be important to the human community living within the Lesina Lagoon watershed. Land use for farming is historically and currently extensive, and likely represents the factor having the largest effect on the ecological status of the lagoon. Agricultural practices have been linked to eutrophication of coastal water systems. The formation of extensive of biological “dead zones” in coastal waters as a result of the nutrient outflow from agricultural processes can be dramatic, and nutrient outputs should be monitored (Hongyu et al., 2004; Stoms et al., 2005). While a transition to more natural agricultural production based on a demand for organic produce is occurring throughout Italy (Ballarini et al., 2013), synthetic fertilizers, rich in NH4 and NO3 were used in the lagoon region for over 20 years. Despite the dominance of agricultural land use in the lagoon region, there was a notable net loss in agriculturally based land cover (17%) between 1975 and 2011.  The reduction in agricultural area, though small, may indicate a transition away from traditional land uses, a change that could be beneficial or detrimental to the lagoon, depending on the land cover that replaces it.  This should be closely monitored in the coming years.

            A net loss of natural Mediterranean shrub land (Macchia Mediterranea) was also observed (12%); large areas, however, appear to remain unaltered. Natural vegetation is vital to the lagoon ecosystem and the human population as it naturally filters runoff, prevents erosion, and is a vital part the nutrient cycle, as well as providing habitat for countless species.  Notably, a decreasing of natural vegetation in and of itself leads to higher input of nitrogen into receiving waters (Kinney et al., 2011). This loss in concert with an increase in impervious service can have severely detrimental effects on lagoon water quality.

            The greatest amount of change in the Lesina Lagoon watershed between 1975 and 2011 is the result of urban expansion.  This trend was somewhat unexpected, as the region surrounding the lagoon has been traditionally regarded as a rural, agriculturally dependent community, and population density is historically and currently low.  Urban development has been identified as a disproportionate contributor to the deterioration of coastal water bodies compared to other land cover types (Kinney et al. 2011; Nixon et al., 2007; Stoms et al., 2005).  In the Lesina Lagoon drainage basin, the pace of land use change seems to be far exceeding population growth, though the consequences of urbanization alone may be profound (Wolter et al., 2006).  For instance, water quality has been shown to degrade when the impervious surface area within a given watershed exceeds 10% (Wolter et al., 2006).  As of 2011, the area of urban fabric in relation to the total area of the Lesina Lagoon drainage basin was 15%. Additionally, lands under development have been cited as contributing five times the suspended solids per unit area as other land cover types (Wolter et al., 2006).  Storm water runoff has also been shown to increase dramatically with urban development, resulting in a greater possibility of flooding events (Wolter et al., 2006), which could have drastic ecological, agricultural, and human consequences.  Particularly concerning is the urban development that appears to be occurring in the near-shore areas of the lagoon (Fig.3), as coastal wetlands provide habitat for a wide variety of fauna, support plant communities adapted to estuarine conditions, and buffer land/lagoon exchanges of nutrients and other materials (Wolter et al., 2006).

            Commercial and residential urban development may entice precipitous population growth in the traditionally rural region.  Human population density directly affects coastal waters, most notably due to increased waste generation (Nosakhare et al., 2012), especially in regions in which waste management techniques are not well developed (Nixon et al., 2007).  In fact, previous studies have found coastal water quality deterioration to be more strongly correlated with population density and waste production (including livestock waste) than any other factor, including agriculture (Kinney et al., 2011; Nixon et al., 2007).  The Lesina Lagoon watershed utilizes two wastewater treatment plants that dispose of treated wastewater indirectly into the lagoon. The treated water is suitable for agricultural use.  Several relatively large illegal communities (that it, communities without state approved or funded infrastructure or municipalities) exist within the watershed, and do not utilize wastewater treatment plants.

            The consequences of land use change in the Lesina Lagoon can be directly observed in the stark increase in nitrate concentrations over the last 35-years.  Comparisons of 1975 nutrient data with 2012 nutrient data revealed a >1000% increase in average nitrate concentrations. Since 1995, maximum concentrations of nitrate in the lagoon have increased one order of magnitude (Ballarini et al., 2012). This is concerning, as nitrogen loading has been correlated with increased algal biomass, hypoxia, and has been recognized as a leading cause of the deterioration of coastal water bodies.  The Lesina Lagoon has experienced periodic eutrophication during the last decade. The 2013 ARCH assessment classified the lagoon as having a moderate-high eutrophication level, suggesting the importance of continued monitoring of the lagoon and its watershed.

            The findings of this study, while offering a valuable foundation in assessing land use change with the Lesina Lagoon watershed and its implications, is not without limitations.  For instance, a loss of total area in the 2011 classification resulted from a differing resolution between the two Landsat images, though this likely to be reflected equally in each land use category.  Additionally, misclassifications are possible on land cover surfaces that look very alike.  For instance, the sliver of beach that runs along the eastern shore of the lagoon is classified as impervious surface, though the effect of this misclassification on the overall data is trivial.   

             

Conclusion

            When assessing a coastal water system, it is important to consider the strong linkages between terrestrial land use, watershed processes, and the estuarine ecosystem. Often, the normal functioning of one ecosystem is impeded by human activity in another. Agricultural and urban development in particular increase nutrient loads to receiving waters and fragment the valuable ecosystems that support the proper functioning of the water body. These phenomena were observed in the Lesina Lagoon, Italy drainage basin. A marked increase in urbanization and decrease in natural vegetation is contributing to increasing flux of nitrogen to receiving waters. In concert with a 325% increase in continuous urban fabric and 17% decrease in natural vegetation from 1995-2011, a >1000% increase in nitrate concentrations within the lagoon waters has been observed. Urban development of lagoon’s shore is particularly concerning.

            The Lesina Lagoon can be considered an at-risk coastal system due to the extensive agriculture in the region, and the simultaneous increase in urban landscape and decrease in natural vegetation is an additional cause for concern. Confronting possible precipitous urban development in the Lesina Lagoon drainage basin, it may be beneficial to begin efforts to manage nutrient loading in anticipation of future stress, and perhaps prevent further deterioration.

 

 

 

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