Image assessment of water hyacinth infestation in Lake Victoria,

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					Image assessment of water hyacinth infestation in Lake Victoria, East Africa
                                                              Joel Masselink, GISDE Graduate Student, Clark University,, December 2007
                                                              Project Purpose                  In the late 1990s, bays across Lake Victoria, the second largest lake in the world, were paralyzed by massive blooms of water
                                                                                               hyacinth, an invasive water-borne flower. This infestation was of massive scale, but was quickly alleviated by both biological and
                                                                                                                                                                                                                                                                                       Study Area
                                                              human factors. So what has happened since? The study period of 2000 to 2003 was chosen because of the scarcity of research following the alleviation of the
            Data Collected                                    horrible late 1990s infestation.
                                                                 Water hyacinth is an invasive species that first appeared in the lake in the late 1980s. It thrives in vulnerable ecosystems and cause a major nuisance. The
     Landsat Scenes - Path 170, Row 60                        aggressive growth pattern causes problems for transportation, fisheries, hydropower, and water intake systems. Hyacinth disturbs aquatic ecology by depleting
                                                              the oxygen content of the water and changing interaction between species. Thick mats of vegetation provide cover for smaller fish, and push larger fish further
     TM: 1986; ETM+: 2000, 2001, 2002, 2003                   from the shallows due to lack of oxygen. Infestations could structurally alter ecosystems if left unchecked. This study will assess post-outbreak persistence.

                                                                   Technical                    This project uses available image data to assess distribution of water hyacinth in the Winam Gulf of Kenya from 2000-2003.
                                                                                                Complementing this study period were freely available, high-quality Landsat images. A multispectral scene was collected for 1986
                                                                   Procedure                    and each year of the study period. Raw scenes were imported, assessed for quality, and windowed to matching extents.
                                                                 Characterization of water-borne vegetation required separation of land and water, to avoid misclassification of vegetation. The lake extent was calculated by
                                                              comparing image bands 5 from 1986 and 2001 and band 7 from 1986. Water is characterized by very low reflectance values in bands 5 and 7, which record                                                                     Winam Gulf, Kenya
                                                              reflectance in the mid-infrared range (1.55-1.74 µm and 2.08-2.35 µm respectively). The 1986 Landsat TM scene was used to calculate the lake’s surface because
                                                              it was taken before record of hyacinth in the lake. Band 5 from 2001 was carefully chosen for its absence of water-born vegetation. A Boolean mask was created to                                                           Lake Victoria
                                                              eliminate land from the assessment. This mask is valuable for image overlay calculations allowing for quantification and analysis of water-borne vegetation.                                                         The Winam Gulf is the main Kenyan portion of Lake Victoria. According to a
                                                                 NDVI was calculated for each time to characterize vegetation using the NDVI formula of (NIR-R) / (NIR+R). Positive NDVI was assumed to represent live                                                          comprehensive lake-wide study for 1989-2001, this gulf was covered with over
                                                              vegetation. NDVI values were reclassified to Boolean representing vegetation and none. These images were used for comparison calculations. Clouds induced                                                         17,000 hectares of hyacinth in November 1998 (Albright et al.), the very worst of
                                                              error by causing uncertain positive NDVI values in 2003, so parameters were changed to cause maximum elimination of unknown NDVI and minimal                                                                      the lake wide infestation.
                                                              misclassifications of water-borne vegetation.
                                                                                                                                                                                                                                                                                   This study focuses on the cities of Kisumu and Kusa. Kisumu is the third largest
                                                                 The Boolean NDVI images were aggregated into groups of contiguous vegetation and assigned area in hectares. Groups with area greater than 10 hectares
                                                                                                                                                                                                                                                                                city in Kenya, with a population of over 300,000. Most commerce is directly
                                                              were considered significant, because mats that size would be a nuisance. This threshold of 10 hectares eliminates unwanted noise and error associated with
                                                                                                                                                                                                                                                                                related to the advantageous lake front location. Kusa is located near the mouth of
                                                              misclassification of the lake and clouds. The three images depicting groups were compared in chronological order, producing three comparison images for:
  Image Processing Model                                      2000:2001, 2001:2002, and 2002:2003. These were compared in a three image crosstab to show persistence throughout the entire study period.
                                                                                                                                                                                                                                                                                the river Nyando. This confluence forms a sizeable wetland habitat characterized
                                                                                                                                                                                                                                                                                by papyrus stands. Papyrus is valuable for making mats, and the wetland habitat
                                                                                                                                                                                                                                                                                is favorable for rice cultivation, so the stands are disappearing.
 2000/03/06                                                                                                                                                                                                                                                                        Population and industry around the lake have grown rapidly in the last few
 2001/02/05                                                                                                                                                                                                                                                                     decades. Today, Lake Victoria supports a population of around 30 million people
  2002/03/28                                                                                                                                                                                                                                                                    whose livelihood is largely dependent on local resources. The vulnerability of this
  2003/05/18                                     Cluster                                                                                                                                                                                                                        ecosystem is cause for serious concern.
                                                1= Land
                                                2= Water
                       Band 5                                                                                                                                                                                                                                                                                                                                   Rank   Persistence
                                                                                                                                                                                                                                                                                                                        Crosstab & Reclass
                     2001/02/05                                                                                                                                                                                                                                                                                                                                  7     All 4 images
 Window                                       Overlay (*) &                                                                                                                                                                                                                                                              Rank & Compare
                       Band 5                                                                                                                                                                                                                                                                                                                                    6     3 in a row
                                               Reclass                                                                                                                                                                                                                                                                      Persistence
                     1986/03/08                                                                                                                                                                                                                                                                                                                                  5     3 of 4
                       Band 7                                                                                                                                                                                                                                                                                                                                    4     2 in a row
                                                                                                                                                                                                                                                                                                                                                                 3     2 of 4
                                              MASK1 =                                                                                                                                                                                                                                  Crosstab                             4 = Vegetation both
                                                                                                                                                                                                                                                                                                                                                                 2     1 of 4
Windowed Bands 3 & 4                          Land Mask                                                                                                                                                                                                                               Comparing                             3 = Veg later time
                                                                                                                                                                                                                                                                                                                                                                 1     0 of 4
  for all study years                                                                                                                                                                    Boolean NDVI                                                                                 Consecutive                           2 = Veg earlier time
                                  Overlay                                                        Overlay             NDVI                                                                                                                          Grouped NDVI                                                                                                  0     Land Mask
                                                                   Masked images of                                                                          Reclass                                                          Group & Area         Only hyacinth                        Years                               1 = No vegetation
                               Band * MASK1                                                                                                                                              Vegetation = 1
                                                                    all study years               NDVI            (4-3) / (4+3)                              NDVI > 0
                                                                                                                                                                                           None = 0                              >10 ha            mats > 10 ha

         Results                                              Map 1. Persistence 2000-2003                                            Figure 1. Area affected by Vegetation                                                        Interpretation of Results                                    What can prevent future infestations?
                                                                                                                                                                                                                                                                                                  Water level, climatic conditions, siltation, pollution and biodiversity
                                                                                                                                                                Hyacinth in Study Area                                                                                                          are factors in the prevention equation. Relief from the 1998 outbreak
    Kisumu and Kusa experienced most of the                                                                                                                                                                                          Any explanation for spatial trends requires analysis of    was largely credited to predatory weevils and El Nino induced winds,
 observed hyacinth persistence during the study                                                                                           800                                                                                     climate and environmental policy factors.                     but sustained hyacinth control requires adaptive management of
 period. As shown in Map 1, significant concentrations                                                                                    700                                                                                        Highest quantities were measured in 2002, while the        several factors.
 were found in Kusa for every time and in Kisumu all                                                                                      600                                                                                     most mats appeared in 2000 and 2003. Defining a cause
 but one of the times assessed. Kusa’s bay had an                                                                                         500                                                                                     for these macro-scale trends is beyond the scope of this
                                                                                                                                                                                                                                                                                                                 Lake Level compared to 10 yr Mean

 average total of 285 hectares each time. Seven                                                                                                                                                                                   project.
 hectares persisted through all four times. Vegetation
 clogged Kisumu’s bay in 2000, vanished in 2001 and                                                                                       300                                                                                       Measurable factors include rainfall and water level,                  0.5
 large mats persisted for 2002 and 2003.                                                                                                  200                                                                                     which is also a function of power demands. These have
    Table 1 shows the quantities found in key locations                                                                                   100                                                                                     caused hydro controllers to release the reservoir for power                      Time 1
 at each time. The quantities of vegetation                                                                                                 0                                                                                     generation, which accounts for changes in the lake level.                                                                                     Time 4
                                                                                                                                                                               2                         3                                                                                                0.2
                                                                                                                                                                                                                                                                                                                                                    Time 3
 persistence associated with Map 1 are shown in                                                                                                    1 tim e     2 times
                                                                                                                                                                          cons ecutive
                                                                                                                                                                                       3 of 4 times
                                                                                                                                                                                                    cons ecutive
                                                                                                                                                                                                                    4 times
                                                                                                                                                                                                                                     Land use should also be considered, as hyacinth has                  0.1
 Figure 1.                                                                                                                                                                                                                        been linked to low-water quality and siltation.

                                                                                                                                      Area (Ha)    718.84      155.55          96.98         43.21       109.82      6.82
    Two-thirds or 1130 of 1710 total observed hectares                                                                                                                           Persistence
 of hyacinth accounted for original incidence, while the
 remaining third or 580 hectares represented hyacinth
 persistence.                                                                                                                                                                                                                                                                                             -0.3

    Each study time had an average of 427.5 hectares
                                                                                                                                                  Table 2. Mat size per study time                                                                                                                        -0.4
                                                                                                                                                                                                                                                                                                                                       Time 2

 of hyacinth. Area of Mat size is located in Table 2.                                                                                        Mats (area ha)          2000         2001 2002 2003 Total                                                                                                    -0.5
                                                                                                                                                                                                                                                                                                                                                Study Pe riod
    Quantifying hyacinth concentrations found at these                                                                                                                   177           570     153       261
 locations may provide an idea as to the scale of                                                                                                                        157            72     108         50
 overgrowth and persistence that affected this                                                                                                                                                                                     Sources: USDA Foreign Agriculture Service PECAD, NASA Earth Observatory
                                                                                                                                                                          31                     21        21
 population.                                                          Table 1. Location of Vegetation                                                                     15                               18                    Acknowledgments: IDCE 371 classmates, Dr. Ogneva-Himmelberger, Benoit Parmentier, Dr. Les Kaufman, Clark Labs
                                                                                                                                                                          14                               17                    Citations: Albright, T. P., T. G. Moorhouse, and T.J. McNabb. 2004. The rise and fall of water hyacinth in Lake Victoria and the
                                                                     Location 2000      2001 2002 2003 Avg
How big is a hectare?                                                Kisumu    192         0 108    50 70
                                                                                                                                                                          13                               12                    Kagera River Basin, 1989-2001. Journal of Aquatic Plant Management 42:73-84
2.47 acres, 100 by 100 meters, or the size of Clark’s main quad.                                                                             COUNT                         6             2           3      6       17           Data providers: Clark Labs, Global Land Cover Facility –University of Maryland Institute for Advanced Computer Studies,
                                                                     Kusa      157       570 153 261 285                                     TOTAL AREA                  407           642     282       379 1710                Intergovernmental Authority on Development Livestock Policy Initiative:
How big was the largest mat?                                         Other        58      72     21    68 55                                 AVG SIZE (ha) 67.83 321.00 94.00 63.17                                137           GLCF – UMIACS:        
570 hectares, which is the size of an 18 hole golf course.           Total       407     642    282   379 246                                                                                                                    IGAD LPI Online Data Portal:
                                                                                                                                                                                                                                 Map Library: