ESTIMATION OF NUTRIENT DISCHARGE FROM FISH FARMING IN THE SÃO CAMILO RIVER MICRO-WATERSHED, BRAZIL

Objective: Estimate the nutrient input from aquaculture in the São Camilo River micro-watershed using geotechnological tools. Theoretical Framework: The municipalities that share the São Camilo River micro-watershed stand out in fish production. Nitrogen and phosphorus are the principal waste products from fish farming that affect water quality in rivers. Open access geotechnologies make it possible to produce maps and documents that help in the sustainable planning of the use of natural resources in river micro-watersheds. Method: Qualitative exploratory methodology for fish production in the municipalities. Mapping of physical and natural resources and excavated ponds using geotechnologies to estimate the nutrient input from fish farming. Results and Discussion: The São Camilo River micro-watershed has morphology and morphometry favorable to aquaculture in excavated ponds. Aquaculture production in its municipalities accounted for 4.42% of all national production. The estimated daily input for the rearing phase was 976 kg of Nitrogen and 113 kg of Phosphorus. This estimate could reach 10,950 kg of Nitrogen and 2,190 kg of Phosphorus per day of harvesting, if there is no planning among the micro-watersheds. Research Implications: Knowledge of the need to plan the harvesting of excavated ponds among fish farmers in the micro-watershed, and the preparation of maps and characterization of the micro-watershed. Originality/Value: This paper contributes to the development of maps and important data, such as morphometric indices and estimates of nutrient inputs, which are important for the sustainable planning of fish farming in the São Camilo River micro-watershed.


INTRODUCTION
The São Camilo River is part of the Piquiri River sub-watershed, in its lower course, which is part of the larger Paraná River watershed (Parolin, 2010).This area is characterized by the Semideciduous Seasonal Forest, where in addition to the occasional occurrence of frost, the flora is influenced by a period of low rainfall, during which 20 to 50% of the trees in the forest canopy lose their leaves, significantly altering the physiognomy of the vegetation (Roderjan et al., 2002).The high quality of the soils in these seasonal forests, combined with the expansion of coffee-growing, was a determining factor in their almost total disappearance, making it the most drastically anthropized phytoecological unit in Paraná (Roderjan et al., 2002).Among the state's phytogeographic formations, the semideciduous seasonal forest was the most affected by the deforestation process to convert native vegetation into agricultural land (Fuentes Llanillo et al., 2006).
In the lower reaches of the river watershed, land use is predominantly for intensive agriculture, growing soybeans, corn and wheat.This region is home to one of the largest cultivated areas in the state, forming part of Paraná's Agricultural Belt.The presence of fertile soils and a favorable climate make this region one of the most productive in Paraná (Parolin, 2010).Within this area, amidst the extensive plantations, is the São Camilo Biological Reserve (385 hectares), which contains one of the last remnants of the Semideciduous Seasonal Forest in western Paraná (Parolin, 2010).
Studies can identify areas favorable for agricultural activities, specifying their physical, geological and biological characteristics (Nath et al., 2000).Maps of soil types and land use and occupation indicate the best locations for agricultural, livestock or aquaculture practices.
In the context of aquaculture, planning the use of water resources is essential for the success of the activity, making it possible to anticipate environmental implications and prepare measures to mitigate anthropogenic actions (Lira et al., 2022).
Geotechnologies are a vital tool in determining the potential for sustainable development of regional aquaculture.They make it possible to quantify and map excavated ponds, optimize logistics and explore areas with greater aquaculture potential, avoiding unnecessary expenses and minimizing environmental risks (Bernardi, 2014;Feiden et al., 2018).
With advances in geotechnologies in terms of user-friendliness and quality of information, they are becoming attractive for use in small municipalities and micro-watersheds.Moreover, morphometric analyses in micro-watersheds, as highlighted by Menezes et al. (2014), help to evaluate water resources and the use of different types of soil.Specifying the location of excavated ponds and the characteristics of the soil are fundamental for the sustainable development of new aquaculture projects (Macedo et al., 2024), both in areas where aquaculture activities are already underway and in those that are to be started.
Exploitation of the soil for agricultural activities, such as planting crops, livestock breeding and fish farming liberates nutrients into the environment, such as Nitrogen and Phosphorus, which are deposited in adjacent rivers and can cause eutrophication of water resources, compromising the environment and the expansion of agricultural activities.The preservation of a watershed's natural resources, therefore, is fundamental both for the economic growth of municipalities and for the quality of life of their residents.
Therefore, the main objective of this work was to estimate the environmental impact of nutrient inputs from aquaculture activities in the São Camilo River micro-watershed and to contribute to planning the sustainable expansion of agribusiness activities by producing maps of natural physical resources and the location of excavated ponds in the São Camilo River micro-watershed.

THEORETICAL FRAMEWORK
Section 1 was dedicated to presenting the importance of the São Camilo River basin and the use of geotechnological tools to expand production in the municipalities through the rational use of the basin's resources.It presents citations of works that have used geotechnology to 5 prepare documents and maps with the aim of estimating the input of nutrients from fish farming.
Finally, section 1 presents the aim of the research.This section presents the theoretical framework used in this article.Section 3 presents the methodology used to obtain the fish production of the municipalities that make up the São Camilo River micro-watershed and the methodology used to calculate the morphometric indices and the maps of natural and physical resources and excavated ponds.Section 4 presents the results and discussion of the morphometric indicators and maps of the São Camilo River microwatershed.The mapping and classification of excavated ponds were used to estimate the contribution of Total Nitrogen and Total Phosphorus from fish farming to the micro-watershed, using the methodology adapted from Coldebella et al. (2020).The conclusion of the research is described in section 5 and the references in the final section of the paper.

METHODOLOGIES
Initially, exploratory documentary research was carried out, using a quantitative and qualitative approach on the official website of the Brazilian Institute of Geography and Statistics

DELIMITATION OF THE SÃO CAMILO RIVER MICRO-WATERSHED
The São Camilo River micro-watershed was delimited using a Digital Elevation Model (MDE), acquired from the USGS -Earth Explorer website, with a spatial resolution of 30 meters.The DEM was processed using QGIS software, version 3.22.14BIATOWIEZA (QGIS Development Team, 2021).This process involved the application of advanced hydrological analysis methods, such as depression correction using (r.fill.dir),flow direction calculation (r.watershed), the identification of catchment areas and drainage channels (r.water.outlet),followed by vector conversion (r.to.vect).The use of these tools allowed for the precise delineation of the watershed, which is essential for water resource studies and environmental management.All data were then reprojected to the SIRGAS 2000 UTM 22S reference system.c

THE MUNICIPALITIES' FISH PRODUCTION
The aquaculture production of the municipalities of Palotina, Maripá and Nova Santo Rosa, which share the São Camilo River micro-watershed, was obtained through a qualitative and quantitative exploratory search in Table Sidra 3940, under aquaculture production, on the website of the Brazilian Institute of Geography and Statistics (IBGE, 2023).

MAPPING PHYSICAL AND NATURAL RESOURCES
The maps of declivityand hypsometry c of the São Camilo River micro-watershed were drawn up using the MDE, through the QGIS software, in version 3.22.14BIATOWIEZA (QGIS Development Team, 2021) in a similar way to the works by Macedo et al. (2023) and Werneck et al. (2023).Land use and occupation analyses were acquired from the MapBiomas project website, in raster format (GeoTiff) with a scale of 1:100,000 and a spatial resolution of 30 meters (Brazil, 2019).
The soil type map was created using the methodology of Francisco et al. 2019 andMorsoleto et al. (2023).The analysis of soil types was carried out using information from the Brazilian Agricultural Research Corporation -EMBRAPA (dos Santos et al., 2018), presented in vector format on a scale of 1:250,000 (IBGE, 2020).
The road map was created according to the methodology of Junior et al. (2024).The road vectors at a scale of 1:250,000 were obtained from the website of the Brazilian Institute of The list and description of the formulas and morphometric indices that were calculated for the São Camilo River micro-watershed can be seen in Table 1.These calculations were carried out using the attributes table in the QGIS software, version 3.22.14BIATOWIEZA (QGIS Development Team, 2021).

Table 1
List of formulas for the morphometric indices calculated for the São Camilo River microwatershed, a right-side tributary of the Piquiri river, western Paraná state, Brazil.for the stages of creation and during harvest can be seen in Table 2.

Table 2
Reference values for the intake of Total Nitrogen and Phosphorus during the cultivation and harvest phases, considering an average stocking density of 5 fish per m² of water surface.

AQUACULTURE PRODUCTION IN THE MUNICIPALITIES
Brazilian aquaculture production reached 739,376.3 tons.Tilapia continues to be the main species produced in Brazil, with around 408,350 tons, or 55.23% of all aquaculture production in 2022 (IBGE, 2023).
In 2022, the combined aquaculture production of the municipalities of Palotina, Nova Santa Rosa and Maripá, which share the São Camilo River micro-watershed, reached 32,658.4tons, of which 32,500 tons (99.4%) were Oreochromis niloticus (tilapia).This represents 4.42% of all aquaculture production and 7.96% of tilapia production in Brazil.Among the other species produced (0.6%) are Piaractus mesopotamicus (pacu), Cyprinus carpio (carpa) and shrimp.
These data demonstrate the importance of the São Camilo River micro-watershed for fish farming and for the economy of its municipalities and the importance of proper planning for the use of its natural resources.The declivity of the area in the São Camilo River micro-watershed has two types of relief: flat slope and gently undulating slope, as illustrated in Figure 2.These types of relief are considered ideal for setting up excavated ponds (Francisco et al., 2019).The hypsometric ranges of the São Camilo River micro-watershed extend from 231 meters to 419 meters above sea level.The largest area of the watershed is in the hypsometric range from 300 to 400 meters of altitude (Figure 3).
The soil types found in the São Camilo River micro-watershed can be seen in Figure 4.
The Latosol type was predominant in the area, with an area of 14,489.63hectares corresponding to 66.31% of the total micro-watershed area.The Nitosol type accounted for 33.10% of the area, totaling 7,233.01 hectares.The Clay soil type was observed in an area of 129.01 hectares, which represents 0.59% of the total area.Latosol is often found in undulating and gently undulating terrain, such as the São Camilo River micro-watershed.This type of soil has good characteristics for the development of agriculture and the implementation of excavated ponds for fish farming, as it facilitates the movement of soil, machinery and equipment, reducing the risk of erosion (Francisco et al., 2019;Klein et al., 2023;Rios et al., 2024).12 Most of the soil in the São Camilo River micro-watershed is occupied by crops.The type of soil and relief favor agriculture and fish farming in excavated ponds.The land use and cover map can be seen in Figure 5.

Figure 5
Land use and occupation map of the São Camilo River micro-watershed, Brazil.Source: prepared by authors (2024).

MORPHOMETRICS
The morphometric indices of the São Camilo River micro-watershed can be seen in Table 3.The micro-watershed has an area of 218.84 km² and a perimeter of 85.04 km.The main channel of the São Camilo River is 33 km long.The hydrology of the watershed is 172 km, considering the entire course of the river and its tributaries, and has an amplitude of 179.13 m.
The watershed is long and elongated, with a low risk of flooding and the conservation of its waters indicates low surface water runoff and high infiltration of water into the soil (Vale et al., 2021).The sinuosity of the watershed falls into the straight class, indicating greater fluidity of the water in the main river channel, as indicated by Romero et al. (2017).The concentration time of 7 hours and 31 minutes obtained for the São Camilo River micro-watershed indicates the time required for a precipitation event to travel from one end of the watershed to the other (de Almeida et al., 2013).

ROADS AND EXCAVATED PONDS
The distribution of the roads and the mapping of the excavated ponds can be seen in Figure 6.Two state highways were found in the São Camilo River micro-watershed: PR -182 and PR -364 and other side roads.The roads totaled 43.31 km in length.The state highways PR-182 and PR-364 are paved with asphalt, in single lanes with two directions and permanent traffic.The side roads have a primary coating of loose pebbles, a single two-way track and constant traffic.These roads are important for transporting production from fish farms to fish warehouses and for supplying feed and other products (Feiden et al., 2018).
The excavated class I ponds, considered to be small, were the most abundant in the São Camilo River micro-watershed, while the class III ponds accounted for the largest amount of water surface, according to Table 4.A similar distribution was observed by Werneck et al. (2023).

Figure 6
Illustration of the roads that cross the São Camilo River micro-watershed, Brazil.

ESTIMATION OF NUTRIENT INPUT
The estimated input of Nitrogen and Phosphorus for the rearing stages (9 months) and during the day of harvest can be seen in Table 5.The results show that larger, class III ponds, inject higher levels of Total Nitrogen, both during the rearing stage and at harvest.During the creation stage, the ratio of nitrogen to phosphorus was 8/1 and during harvest the ratio was 5/1.Nitrogen and phosphorus ratios lower than 15:1 in aquatic environments is indicative of eutrophication with the potential to facilitate cyanobacterial blooms (Vidal & Capelo Neto, 2014).Similar results for the Nitrogen and Phosphorus ratio were also observed in the Açu river basin (Junior et al., 2024).

Table 5
Estimated input of total nitrogen and total phosphorus during the rearing and fishing phase for the excavated ponds in the São Camilo River micro-watershed, considering a stocking density of 5 fish per m² of water surface.

CONCLUSIONS
The São Camilo River watershed has morphology and morphometry that are favorable to aquaculture in excavated ponds.The municipalities that share its area were responsible for 4.42% of all Brazilian aquaculture in 2022.The use of geotechnology to characterize the microwatershed and its physical and natural aspects proved to be efficient for producing documents such as maps and indicators that promote sustainable planning of the productive activities of its municipalities.The daily nitrogen input during the cultivation phase of 946.8 kg can reach 10,950 kg during the harvest, while the phosphorus input can jump from 113 kg during one day of cultivation to 2,190 during the harvest.This data demonstrates the importance of planning harvesting within the micro-watershed's aquaculture enterprises, avoiding the simultaneous harvesting of ponds between fish farms.There is a need for studies and research to improve the filtering process in sedimentation ponds, which are obligatory and important for maintaining the water quality of water resources.

Francisco
et al. (2020) and da Silva Morsoleto et al. (2022) presented methodologies that use geotechnology to map, quantify and classify more appropriate areas with aquaculture potential in the western region of Paraná, Brazil.These new approaches demonstrate the benefits and importance of initial planning, preventing unnecessary expenses and minimizing environmental impacts resulting from the implementation of new aquaculture enterprises.

(
IBGE, 2023)  to determine the aquaculture production of the municipalities of Palotina, Nova Santa Rosa and Maripá, which have a territorial area within the São Camilo River microwatershed.The purpose of this research was to analyze the importance of the São Camilo River micro-watershed for aquaculture in Brazil.It then used geotechnologies to characterize and map the morphology, morphometry and excavated ponds present in the São Camilo River micro-watershed.The classification and mapping of the excavated ponds was used to estimate the discharge of nutrients, such as nitrogen and total phosphorus from the fish farm.This estimate was based on the proposal byColdebella et al. (2020) who presented a table of Total Nitrogen and Total Phosphorus inputs, resulting from a field survey considering at the time an average density of 5 fish per m² of water surface.Considering the weight of the fish to be between 900 and 1000 grams.

3. 1
STUDY AREA The São Camilo River micro-watershed is in the western region of the state of Paraná and is part of the Paraná 3 watershed.The area is in the municipality of Palotina and borders the municipalities of Nova Santa Rosa and Maripá, as illustrated in Figure 1.The São Camilo River flows into the Piquiri River, which is also part of the Paraná River watershed.The region of the São Camilo River micro-watershed has a humid subtropical climate, type Cfa, with hot and humid summers, mild winters, and well-distributed precipitation throughout the year.In winter, the temperature in this region typically ranges between 10°C and 20°C.Minimums can occasionally drop below 10°C, especially during cold spells, but winters are generally mild in the region.(INMET,2024;Köppen, 1936).

Figure 1
Figure 1 Geographical location of the São Camilo River micro-watershed, a right-side tributary of the Piquiri river, in the western region of the state of Paraná.
Geography and Statistics, IBGE(IBGE, 2020).The delimitation of the micro-watershed was used to cut out the roads located within it.The vectorization, classification, and quantification of excavated fishponds located in the watershed of the São Camilo River were performed using high-resolution images from Google Earth through the algorithm available in the QuickMapServices plugin of QGIS.The classification followed the methodologies described byFrancisco et al. (2020) and da Silva Morsoleto et al. (2024).Estimation of Nutrient Discharge from Fish Farming in the São Camilo River Micro-Watershed, Brazil ___________________________________________________________________________ Rev. Gest.Soc.Ambient.| Miami | v.18.n.8 | p.1-18 | e08520 | 2024 from Werneck et al. (2023).Estimation of Nutrient Discharge from Fish Farming in the São Camilo River Micro-Watershed, Brazil ___________________________________________________________________________ Rev. Gest.Soc.Ambient.| Miami | v.18.n.8 | p.1-18 | e08520 | 2024.9 3.6 ESTIMATION OF TOTAL NITROGEN AND PHOSPHORUS INPUTThe estimated calculations for the discharge of total nitrogen (NT) and total phosphorus (PT) residual in the São Camilo River micro-watershed due to fish farming carried out by excavated ponds were determined based on the study byColdebella et al. (2020).To make this estimate, the cultivation area and biomass of 5 kg per m² of water surface were considered for the ponds mapped and classified in this work.The reference values fromColdebella et al. (2020) ___________________________________________________________________________ Rev. Gest.Soc.Ambient.| Miami | v.18.n.8 | p.1-18 | e08520 | 2024

Figure 1
Figure 1 Declivity map of the São Camilo River micro-watershed, a right-side tributary of the Piquiri river, western Paraná state, Brazil.

Figure 3
Figure 3Map of the hypsometric ranges found in the São Camilo River micro-watershed

Figure 4
Figure 4 Soil type map of the São Camilo River micro-watershed, a right-side tributary of the Piquiri river, western Paraná state, Brazil.

Table 3
Morphometric indices of the São Camilo River micro-watershed, a right-side tributary of the Piquiri River, western Paraná state, Brazil.

Table 4
Classification of excavated ponds in the São Camilo River micro-watershed, a right-side tributary of the Piquiri River, western Paraná, Brazil.