Combined uses of supervised classification and Normalized Difference Vegetation Index techniques to monitor land degradation in the Saloum saline estuary system

peer reviewedSaltwater contamination constitutes a serious problem in Saloumestuary, due to the intermittent and reverse tide flows of the Saloum River. This phenomenon is caused by the runoff deficit, which forces the advance of saltwater 60 km upstream, contaminating surface water and thus causing the degradation of biodiversity and large areas of agricultural soils in this region. The present study aims to evaluate the consequences of saltwater contamination in the last three decades in this estuary by assessing the land-cover dynamics. Thus, latter consists of tracking the landscape-changing process over time to identify land-cover transitions. These transitions are closely related to the ecosystem-setting condition and can be used to assess the combined impacts of both natural and human-induced phenomena over a given period of time. In this study, special attention was given to mangrove degradation and to temporal progression of the salty barren soils locally called ‘‘tan’’. The loss of mangrove areas to tan and the general increase in salty barren soil areas can reflect the increase in the level of salinization in the study area over the time period under consideration. To fulfill this objective, four Landsat satellite images from the same season in the years 1984, 1992, 1999, and 2010 were used to infer time series land-use and land-cover maps of the Saloumestuary area. In addition to satellite imagery, rainfall records were used to evaluate climatic variation in terms of high-to-low precipitation during the time span considered. Spectral analysis indicated that from 1984 to 2010, mangroves and savanna/ rain-fed agriculture are converted to ‘‘tan’’ (denuded and salty soils). In addition, these results showed that significant changes in land use/land cover occur within the whole estuary system and reflecting therefore environmental degradation, such as land desertification and salinization, and vegetation degradation which reflect the advanced of salinit

Elemental composition and productivity of cyanobacterial mats in an arid zone estuary in north Western Australia

Extensive cyanobacterial mats are a feature of the high intertidal zone in the Exmouth Gulf, Western Australia. This study provides a description of the position of the mats within the intertidal zone and of the mats elemental composition and productivity. We found that the mats occupied 40 cm elevational range within the intertidal zone. They have a mean organic matter content of 1,600 g m(-2). Mean concentrations of nitrogen (N) were 1.82 g kg(-1) and phosphorus (P) 205 mg kg(-1). N:P ratio was 19.7 indicating P limitation, but N:P was variable. Rates of photosynthesis and biomass production were similar to those reported for mats in hypersaline conditions at other sites. When photosynthetic production was scaled-up for the region our data suggest that cyanobacterial mats are an important contributor to the carbon budget in the Exmouth Gulf, contributing between 5 and 15% of the total carbon fixed by primary producers. Additionally mats were observed to be a source of soluble carbohydrates in tidal waters indicating that fixed carbon from high intertidal cyanobacterial mats may enter near shore food webs through this pathway