Moniamb Furnas e Sete Cidades

Reducing the load of nutrients and sediments from agricultural activity in a watershed is undoubtedly the main strategy for the recovery of the water body, based on the adoption of good land use practices. In the case of the Furnas basin, this policy has been actively implemented through various management measures, such as the afforestation of new areas and the elimination of direct grazing and fertilization in more than 50% of the pasture area. construction of a channel that will allow the diversion of a significant part of the runoff water coming from the area still subject to agricultural exploitation.

However, it is important that the effect of land use changes on the evolution of trophic conditions in the lagoon is properly monitored by obtaining data on the transport of nutrients and sediments that allow for a consistent follow-up, for an extended period of time, of the evolution of the characteristics of the water body. The monitoring of a watershed therefore intends not only to assess the quality of the water but also to provide more comprehensive information, including the soil and its nutrient load, in order to help establish cause-effect relationships.< /p>

The transfer of nutrients and phosphorus in particular from agricultural areas to water bodies is subject to considerable variability during and between runoff events, also varying from location to location. Therefore, collecting data over long periods is particularly useful and necessary for the perception of this variability. A reliable estimate of the nutrient loads that are transferred from a watershed to the water body necessarily requires the knowledge of two essential parameters: flow rates and water samples for analysis, collected with criteria of representativeness of that same flow.

During the study recently carried out on the “characterization and environmental monitoring of the soils of the Furnas lagoon watershed” an automatic sampler was installed to collect water samples for the estimation of transport of nutrients which was based on a limited number of analytical data obtained from only 4 sampling phases of surface runoff waters from the Salto da Inglesa sub-basin. It was found that the average values ​​of each of the four samplings performed varied considerably, with soluble P presenting an average value of 87 kg during the study period (about 1 year). Thus, it was considered that it would be necessary to develop analytical monitoring for a longer period in time, in order to consolidate and strengthen the preliminary information that was produced.