Self‐Organizing Maps for Evaluation of Biogeochemical Processes and Temporal Variations in Water Quality of Subtropical Reservoirs

Abstract

Water quality in reservoirs is often compromised in many regions worldwide by nutrients and trace metals. This demands continuous monitoring; however, analyses of large data sets collected during regular monitoring remain a difficult task. Multivariate techniques offer a fast and robust approach for interpreting complex results. The objective of this study was to check the efficacy of selforganizing maps (SOMs) as a tool to investigate biogeochemical processes. This tool can also help to illustrate influences of land use patterns on the water quality of reservoirs. Here we use the Itupararanga Reservoir in Brazil as a subtropical example. Vertical profiles were sampled from seven sites in the reservoir in a total of seven campaigns over 24 months. Next to physicochemical parameters in the water column (dissolved oxygen, Eh, pH, and temperature), levels of nutrients (NO 3 − , NH 4 + , and PO 4 3− ), transition and trace metals (Al, Ba, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, and Zn), and chlorophyll-a (Chla) were measured. These variables were correlated with land use using SOM. With this technique samples were classified into 17 distinct groups that showed distinct influences of spatial heterogeneity and seasonality. The analyses helped to reveal a seasonal stratification period, where Fe, Mn, and P were released from sediments. Nutrients and some metal inputs (Al and Fe) were related to agricultural, urban, and grass/pasture areas around the reservoir. Our approach also helped to explain physical and biogeochemical seasonality in the reservoir.

Análise de parâmetros da água por sensoriamento remoto para fins de aquicultura em reservatórios

“…Este gradiente de distribuição térmica do corpo d'água provavelmente se dá pela dinâmica de reservatórios. As áreas mais próximas a barragem constituem o ponto mais fundo do sistema e o fluxo de saída de água favorece as camadas médias, e não as camadas superficiais, ao contrário do que se observa em lagos (Melo et al, 2019). Esta camada superficial tende então ao isolamento e acúmulo de calor, principalmente nas épocas mais quentes, se estratificando termicamente do resto do reservatório.…”

Dominance of in situ produced particulate organic carbon in a subtropical reservoir inferred from carbon stable isotopes

“…Land use in the vicinity of sampling locations P1 and P2 is dominated by grass and pasture, however P1 also receives inputs from sewage discharge. Sampling locations P3 and P4 are in the vicinity to urban areas, whereas P5 to P7 are located in parts of the catchment that are dominated by forests, agriculture and silviculture 42 .…”

“…Temperature and pH profiles were measured at all sampling sites using a portable multiparameter probe (Horiba U-50) 42 . Samples for isotope measurements were filtered via nylon disk filters with a pore size of 0.45 μm into 40-mL amber glass vials according to standards of the U.S. Environmental Protection Agency (EPA vials).…”

“…These studies considered aspects of nutrients and cyanobacteria communities, sedimentary macroinvertebrates, metal toxicity and land-use in relation to water quality. This work has shown that the Itupararanga Reservoir receives substantial amounts of nutrients, mostly because of agricultural land use in the surrounding catchment 42 . Another important source of nutrients is sewage discharge from urban areas.…”

“…that the Itupararanga Reservoir receives substantial amounts of nutrients, mostly because of agricultural land use in the surrounding catchment 42 . Another important source of nutrients is sewage discharge from urban areas.…”