Eutrophos

Eutrophication of surface waters was identified about 2 centuries ago but was enhanced in 1950’s with agriculture automation, the increased use of Nitrogen (N) and Phosphorus (P) fertilizers, and population concentration in large urban areas. Particularly vulnerable to this process are lakes and artificial reservoirs, where sediments and organic matter are accumulated, causing oxygen depletion in the deeper layers, or even in the entire water column, leading to large periods of poor water quality, and to fish killings.
The severity of the problem increases when eutrophication is related to cyanobacteria blooms and subsequent development of toxicity events. Cyanobacteria bloom is influenced mainly by the presence of N and P. Cyanobacteria can fix atmospheric N and become the dominant species during periods of N depletion in water. Since atmospheric N is always available to cyanobacteria, their growth control is only achieved by controlling P levels. The Enxoé catchment and reservoir are included in a list of Portuguese reservoirs where strong cyanobacteria blooms have been identified and are suitable for studying this problem.
P is generated by agriculture and by domestic and industrial waste waters. In aerobic conditions, P is adsorbed to some aluminium and/or iron compounds existing in the particulate matter. Its fate will, consequently, be determined by the processes affecting particulate matter, namely soil erosion, and its accumulation on the bottom of artificial reservoirs where water velocity is lower.
Detergents dragged in the urban waters have been the major P source up to the late 1990’s. With the modification of their composition and P removal in Waste Water Treatment Plants, agriculture and livestock became the major P sources, which can only be controlled by limiting soil erosion.

This project aims:

i) to assess the contribution of soil P to surface waters as a function of crops and agricultural practices, with particular emphasis to irrigation;

ii) to extrapolate results to the whole catchment, using mathematical models;

iii) to improve the existing catchment and reservoir models and determine maximum daily loads, and iv) to quantify the economic impact of agriculture
practices changes and assess their social implications.

The project will build on the experience of the partners on erosion control, soil physics, soil chemistry, irrigation, and modelling. It will have 5 tasks: (1) Erosion assessment and control, according to the use of different irrigation methods; (2) Monitoring of nutrients in Enxoé reservoir; (3) Modelling of the catchment and of the reservoir; (4) Assessment of soil use, agriculture practices, and the environmental, economic and social impacts of changing the agricultural practices; and (5) Project management and results dissemination.
The project involves teams from two Universities and the National Institute of Biological Resources.