Caracterização ambiental e contribuição da piscicultura para o aporte de nutrientes e a qualidade da água da Microbacia Hidrográfica da Sanga Guabiroba

Fish farming is an economically significant activity in western Paraná, Brazil, but it may contribute to nutrient inputs and the eutrophication of water resources. This study evaluated the morphological, morphometric, and environmental characteristics of the Sanga Guabiroba watershed in Nova Santa Rosa, Paraná, as well as estimated the total nitrogen (TN) and total phosphorus (TP) loads associated with excavated fishponds. The watershed was delineated using a Digital Elevation Model and geoprocessing techniques, supplemented by soil, land-use and land-cover, and municipal aquaculture production data. A total of 31 fishponds were identified, covering 12.11 hectares, with numerical predominance of Class I ponds and the largest total area corresponding to Class III ponds. The watershed exhibited an elongated shape, low drainage density, and predominantly gently undulating terrain. Assuming an average stocking density of 5 kg/m², the estimated nutrient inputs amounted to 24.58 metric tons of TN and 2.99 metric tons of TP over a nine-month production cycle, in addition to 1.02 and 0.19 metric tons, respectively, released during fish harvesting. The N:P ratio of approximately 8:1, close to the Redfield proportion, indicates the absence of severe phosphorus limitation and conditions favorable to cyanobacterial blooms. The results indicate a potential risk of eutrophication, concentrated in large ponds, reinforcing the need for monitoring and improved feed management to reconcile fish farming with water-resource conservation.