Distinct age and landscape influence on two reservoirs under the same climate

Abstract

With the purpose of finding out whether different landscape occupation could affect water quality in two reservoirs of distinct age and subjected to the same climatic influence, several factors were investigated in a study lasting from January 2000 till December 2001. Total phosphorus, orthophosphate, chlorophyll a concentrations and water colour were determined monthly in winter and biweekly in summer, in two reservoirs located in the Portuguese part of River Douro catchment. Complementarily, variables such as nitrate, ammonium ion and ammonia gas, as well as water temperature, dissolved oxygen, conductivity, and transparency were measured. Trophic state of both reservoirs was assessed by computation of Carlson's Trophic State Index. The potential allochthonous sources of phosphorus and nitrogen to both reservoirs were identified and estimated. Differences between reservoirs were found for conductivity, water temperature, transparency and water colour. According to Carlson's Trophic State Index both reservoirs were classified as meso-eutrophic from winter to the beginning of summer, and as eutrophic from this period onwards. Intrinsic factors such as age of reservoir, organic matter inputs from decomposition of flooded terrestrial vegetation and exposure of littoral sediments to cycles of drying and wetting, as well as extrinsic factors such as grazing and frequent land fires, can explain the trophic state of S. Serrada Reservoir. Allochthonous sources of nutrients originated from agriculture and grazing in the catchment area, and recreational activities in the reservoir probably are the factors with greatest influence on Azibo Reservoir trophic state. Based upon the obtained data, management measures are suggested to prevent further eutrophication and water quality degradation in both reservoirs.

What factors affect the pelagic cladocerans of the meso-eutrophic Azibo Reservoir?

“…During the period of study thermal stratification occurred from June to October and the reservoir was classified as meso-eutrophic. Further information concerning this reservoir can be found in Geraldes & Boavida (2003).…”

Limnological variations of a deep reservoir in periods with distinct rainfall patterns

“…Activities that take place throughout the year in the drainage basin include farming and grazing (mainly sheep). The potential nutrient loads generated by these activities are 243,275 kg of nitrogen (N) and 116,956 kg of phosphorus (P) per year (Geraldes and Boavida, 2003). Thermal stratification of the reservoir always occurs between June-October.…”

“…(Portuguese Meteorology Institute, 2009). Further information concerning the reservoir and its surroundings can be found in Geraldes and Boavida (2003).…”

Evaluation of the ecological status of an impaired watershed by using a multi-index approach

“…In spite of significant progress made in controlling point sources of water pollution (domestic sewage or industrial effluents, for instance), nonpoint pollution (runoff from agriculture, urban, mining, and livestock areas) is still a recurrent problem in many watersheds (Mainstone and Parr 2002;Williams et al 1997). Within the watershed, human activities result in higher surface runoff, the rate of which is influenced by land use, vegetation cover, and landscape mosaic (Geraldes and Boavida 2003). Increased runoff often results in eutrophication ultimately threatening water quality (Allan et al 1997;Mokaya et al 2004).…”