Delimitation of permanent preservation areas of Paurá Lagoon (Middle Coast of Rio Grande do Sul, Brazil) using multitemporal satellite image analysis

Abstract

Permanent Preservation Areas (PPA) are determined by the Brazilian Forest Code (Federal Law nº 12.651/2012) to protect biodiversity, soil, water, and climatic integrity. Around lakes and lagoons in rural areas, the law establishes marginal strips of PPA with a minimum width of 100 m (or 50 m for lakes with less than 20 ha). Some of these water bodies may have their surface dimensions markedly changed due to seasonal variations. PPA demarcated during periods of maximum water level would present ecological advantages. However, such variations were not included as criteria for PPA around lakes and lagoons in the new 2012 Forest Code. Moreover, seasonal variations effects are not yet sufficiently known in water bodies of most regions. In this work, a methodology previously developed was used to delimitate and measure water surface area and PPA of Paurá Lagoon during maximum water overflow - due to rain water excess (WE), and water deficit - due to rain water scarcity (WS). This lagoon is situated in a coastal area ranked as conservation priority in Brazil (31°34’ S, 51°18’ W; 31°34’ S, 51°17’ W; 31°35’ S, 51°18’ W and 31°35’ S, 51°19’ W). Analyses of rainfall records covering the 1992-2012 time series, water balance and remote sensing with freely available GIS application (SPRING) were employed to select satellite images from WS and WE dates. Two Landsat-5 TM images, dated 29/04/2009 (WS) and 06/09/1998 (WE) were selected and geoprocessed to detect differences in areas under WS and WE, respectively. For lagoon surface area and PPA, 66.29 ha and 42.36 ha were calculated during WS, and 92.27 ha and 53.25 ha during WE, respectively. At maximum WE (local winter and spring), lagoon surface area was 25.98 ha larger, while PPA had an addition of 10.89 ha. Although Landsat images have spatial resolution limitations, the methodology allowed the identification of the most suitable annual period to delimitate a larger area around the water body. Following in situ demarcation, the resulting larger PPA may provide superior ecological benefits to priority conservation regions. The methodology tested may be a useful tool to integrated management of lakes and wetlands in coastal zones.