Recovering P from a eutrophic lake via hypolimnetic withdrawal and purification

<p>Hypolimnetic withdrawal (HW) is a restoration method for eutrophied lakes that aims to remove phosphorus (P) and other nutrients from the system. It is conventionally carried out by pumping or siphoning nutrient-rich bottom water to the discharge of the lake during periods of thermal stratification. However, there is growing interest in developing closed circuit modifications of HW in which nutrients could be captured and the purified water returned to the same lake. This would tackle some problematic aspects of conventional HW, and additionally enable the capture and recycling of P stored in lakes. <br>A pilot closed circuit HW system has been constructed at a eutrophic dimictic lake located in Southern Finland. This hypolimnetic withdrawal and purification circuit (HWPC) consists of a withdrawal pipe installed at the lake deep, a treatment and filtering unit on shore, and a wetland. In the treatment unit, P is first precipitated and then captured by sand filters, while the purified water flows subsequently through a wetland and finally back into the lake. <br>In the current study, we investigated the pool of potentially removable P in the study lake, the optimal timing of HW within the annual cycle, and the functioning of the HWPC. The P retention capacity of the purification unit and the composition of the precipitate trapped in the filters were both examined. The results showed that P accumulation in the near-bottom water of the study lake during thermal stratification is substantial, allowing significant amounts of P to be removed from the lake via HW. The concentration of total P of the water entering the HWPC was over 300 µg/L, of which the system captured more than 80%. The P content of the precipitate trapped in the filters varied between 6-12 g P/kg, and consisted of both iron and calcium-bound P phases. These results imply that it is possible to recover P accumulated in eutrophied lakes for potential recycling purposes.</p>

A simple, robust, and automatic approach to extract water body from Landsat images (case study: Lake Urmia, Iran)

Lake Urmia is one of the largest saline lakes in the world, and has a great effect on its surrounding ecosystems as well as the economic, social, and even cultural condition of its basin inhabitants. Hence, continuous monitoring of lake area changes is necessary and unavoidable for better land management and prevention of its degradation. In this study, by using Landsat 8 images and by preforming some essential pre-processing tasks, the area of the lake was estimated using the number of traditional spectral indices and a new one and the automatic Otsu's thresholding method for 5 years (2013–2017). The results showed that this index shows more accurate results than other indices when estimating the area of the lake and can separate water class from land one with an average overall accuracy of 96%.