This study explores the chemical composition of different macrophyte species and infers their potential in extracting nutrients and some heavy metals from water as well as the use of macrophytes’ biomass as natural fertilizers. It used a dataset obtained from a previous study composed of 445 samples of chemical concentrations in the dried biomass of 16 macrophyte species collected from the Santana Reservoir in Rio de Janeiro, Brazil. Correlation tests, analysis of variance, and factor analysis of mixed data were performed to infer correspondences between the macrophyte species. The results showed that the macrophyte species can be grouped into three different clusters with significantly different profiles of chemical element concentrations (N, P, K⁺, Ca²⁺, Mg²⁺, S, B, Cu²⁺, Fe²⁺, Mn²⁺, Zn²⁺, Cr³⁺, Cd²⁺, Ni²⁺, Pb²⁺) in their biomass (factorial map from PCA). Most marginal macrophytes have a lower concentration of chemical elements (ANOVA p-value < 0.05). Submerged and floating macrophyte species presented a higher concentration of metallic and non-metallic chemical elements in their biomass (ANOVA p-value < 0.05), revealing their potential in phytoremediation and the removal of toxic compounds (such as heavy metal molecules) from water. A cluster of macrophyte species also exhibited high concentrations of macronutrients and micronutrients (ANOVA p-value < 0.05), indicating their potential for use as soil fertilizers. These results reveal that the plant’s location in the reservoir (marginal, floating, or submerged) is a relevant feature associated with macrophytes’ ability to remove chemical components from the water. The obtained results can contribute to planning the management of macrophyte species in large water reservoirs.

The excessive proliferation of aquatic macrophytes in Brazilian reservoirs generates large amounts of biomass that must be removed to ensure water use and energy generation. This material is usually treated as waste, but its recycling as a biofertilizer could mitigate disposal problems while improving soil and crop productivity. To test this potential, we conducted a 4 × 3 factorial experiment using four macrophyte species (Salvinia auriculata Aubl., Myriophyllum aquaticum (Vell.) Verdc., Egeria densa Planch. and Pistia stratiotes L.) collected from the Santana Reservoir, applied at three incorporation doses (5, 10 and 20 t ha⁻¹ dry matter) plus a control in pots with Urochloa decumbens seedlings. Soil chemical properties and plant growth attributes were integrated into the relative Soil Quality Score (rSQS) and relative Plant Performance Score (rPPS). Both scores increased with macrophyte incorporation, though responses depended on species and dose. A significant positive relationship was found between rSQS and rPPS (R² = 0.73; $\rho$ = 0.85), indicating that improvements in integrated soil quality were generally associated with better plant performance. While most treatments improved score values, ELDDE at 20 t ha⁻¹ showed a further increase in rSQS but no proportional gain in rPPS, which was numerically lower than at 10 t ha⁻¹ but not statistically different. This pattern indicates that increases in integrated soil quality may not always translate linearly into plant performance. These results support the potential of selected macrophyte materials as organic amendments and highlight the need for biomass characterization, contaminant monitoring and field validation before practical recommendation.

Freshwater macrophytes harvested from eutrophic water bodies may be repurposed as soil amendments, but their species-specific effects on soil chemical and biological quality remain insufficiently understood. This study evaluated the effects of dried biomass from Egeria densa, Myriophyllum aquaticum, Pistia stratiotes, and Salvinia auriculata, incorporated at 20 g kg⁻¹ soil, on soil chemical attributes, organic carbon, and enzymatic activity after 30, 60, and 90 days of incubation. The experiment was conducted in a completely randomized 5 × 3 factorial design, comprising five amendment treatments (four macrophyte species and an unamended control), three incubation periods (30, 60, and 90 days), and five replications per treatment combination, under controlled conditions at 25 ± 1 °C and 60–70% of soil water-holding capacity. Macrophyte treatment, incubation period, and their interaction significantly affected most soil attributes, whereas the treatment × incubation-period interaction was not significant for soil organic carbon (SOC; p = 0.180). Myriophyllum aquaticum maintained the highest SOC values (55.0–56.4 g kg⁻¹), approximately 22–26% above the unamended control. Salvinia auriculata showed a delayed biological response, with β-glucosidase activity increasing from 17.7 to 114.4 μg PNP g⁻¹ soil h⁻¹ between 30 and 90 days. Pistia stratiotes maintained base saturation at approximately 82% throughout incubation and was more strongly associated with chemical fertility indicators. The first two RDA axes explained 77.2% of the total variation. Redundancy analysis confirmed that macrophyte identity and incubation time explained substantial variation in soil quality indicators. These findings indicate that freshwater macrophytes can be selected according to agronomic objectives, with M. aquaticum and S. auriculata showing greater potential to improve soil biological quality and P. stratiotes contributing more strongly to chemical fertility.

Aquatic macrophyte biomass removed from reservoirs represents a residue with potential for agricultural reuse, but its agronomic effectiveness and environmental safety require evaluation. This study assessed decomposed aquatic macrophyte biomass (DB) as a soil amendment for the initial growth of Joannesia princeps in soils from Piraí (RJ) and Jaboticabal (SP), Brazil. Plants were grown in 50 L pots under a completely randomized design with five replicates, using DB at 10, 20, and 40% of pot volume, applied alone or combined with mineral fertilization, plus a mineral-fertilized control. Soil chemical attributes, plant biometric traits, foliar nutrient concentrations, potentially toxic metals, and principal component analysis were evaluated. Increasing DB rates generally increased soil organic matter, sum of bases, cation exchange capacity, base saturation, and the availability of P, K, Ca, Mg, and micronutrients, while reducing potential acidity and aluminum saturation. Intermediate and high DB rates enhanced plant height, leaf number, leaf area, and dry biomass, although responses varied between locations and fertilization strategies. Ni and Pb remained low, with no consistent accumulation pattern. Overall, decomposed macrophyte biomass improved several soil chemical attributes associated with fertility and promoted the initial growth of J. princeps, supporting its potential use as an organic soil amendment under the evaluated conditions.