Using Freshwater Cladophora glomerata to Develop Sustainable Farming

Abstract

Cladophora glomerata is a species of green algae from the Cladophoraceae family belonging to the class Ulvophyceae. This filamentous macroalga is generally associated with freshwater habitats, especially in nutrient-rich ecosystems. It produces high biomass and occupies large areas of freshwater. The robust filaments of Cladophora glomerata form dense mats that are easy to harvest. It is also rich in proteins, macro- and micronutrients, and other bioactive compounds. Therefore, its biomass could be used in various fields of sustainable agriculture, for example, promoting plant growth and yield, purifying soil, improving crop properties against biotic and abiotic stress, or it could be used in husbandry as a feed supplement. It is also becoming increasingly attractive for use in sustainable farming. This review provides an update with the latest information on the use of freshwater Cladophora glomerata in sustainable farming and suggests the most promising fields of research.

1. Introduction

The use of algae in various sustainable areas has attracted steady interest from scientists and the market in recent decades. It is thought that algae could be used to produce highly valuable food and hence benefit human health. Since ancient times, the greatest interest has always been in the use of marine algae [1,2], based on the fact that marine algae (seaweeds) produce biomass rapidly in huge quantities and are highly adaptive to changing environments, especially salts. Seaweeds have been used as a source of organic matter in agriculture since the Roman Empire [3]. However, extensive research into using these algae to increase plant productivity did not begin until the introduction of the first commercial seaweed extract for plant fertilization in 1940 [4]. Marine algal biofertilizer effects have been widely tested on different cultivated plants, e.g., canola (Brassica napus), bean (Vicia faba) [5], soybean (Glycine max) [6], and lettuce [7]. Marine algae and their extracts also display antimicrobial, nematocidal, herbicidal, and insecticidal/acaricidal properties against crop pathogens and can be used as biopesticides [8]. They have good adsorption capacity for heavy metals and could remove pollutants such as nitrogen and phosphorus from polluted water and soil [9]. Marine algae are used in a variety of forms, e.g., raw material, solutions, and extracts. Some preparations of marine algae are registered and used in the market as products for so-called clean farming [1].

The literature on freshwater macroalgae use in farms is much lower, but in the last decade, the number of these studies has been gradually increasing. One of the most promising sustainable resources used for sustainable farming is freshwater filamentous green algae from the Cladophora genus. The genus includes 218 valid taxa [10,11]. These macroalgae provide a habitat for epiphytes and invertebrates in marine and freshwater environments [12]. Some Cladophora species are known to form blooms or green tides, and to have had negative effects on ecosystems [13]. Among Cladophora genus, C. glomerata is the most widely distributed and abundant species in marine, brackish, and freshwater environments [14,15]. Otherwise, freshwater C. glomerata has provided food for humans in Southeast Asia for a long time [16]. The most recent general review of the biology, ecology, and potential commercial use of freshwater macroalgae C. glomerata argues that the species contains up to 60% carbohydrates, 30% proteins, and a certain amount (about 5%) of lipids [15]. It is also rich in bioactive compounds [15]. Chlorophyll a and b and carotenoids vary depending on the season and habitat [17]. Minerals, vitamins, and secondary metabolites, i.e., phenolic acids (gallic acid, p-coumaric acid, p-hydroxybenzoic acid), fatty acids, sterols, terpenes, phenolic compounds, and volatiles, are also found in C. glomerata [18]. Secondary metabolites exhibit various biological activities, e.g., antioxidant, antibacterial, and antifungal, and could be used in agriculture or in the food supplement market [19]. In recent years, a high total content of phenolic compounds has been detected in C. glomerata from Lithuanian rivers. Three phenolic acids were identified, namely, gallic acid, p-hydroxybenzoic acid, and p-coumaric acid. The content of the pigments’ chlorophyll a, b and carotenoids was also measured [19]. Phenolic compounds improve a plant’s ability to adapt to environmental stress; carotenoids act as antioxidants by managing oxidative stress in cells. All chemical compounds of C. glomerata have special physiological properties, and when biomass decomposes, it releases all compounds into the soil and thus benefits the growth and development of cultivated plants. All these properties could make C. glomerata an attractive material for sustainable farms. Considering that the algae products market is projected to reach USD 7.3 billion by 2028, at a CAGR of 6.4% from 2023 to 2028 [20], it may be assumed that research on freshwater algae will receive more attention in future.

2. Methods

We investigated the relevant information on the use of the freshwater alga C. glomerata in sustainable agriculture. The Sustainable Development Goals set by the United Nations, ranging from poverty reduction to clean water and soil, were considered. For the typology of farms, the Eurostat Glossary of Farm Typology was used [21]. The databases Scopus, Google Scholar, ScienceDirect, PubMed, AGRIS, and SpringerLink were checked using the following keywords: Cladophora glomerata, freshwater, agriculture, farms, husbandry, pathogens, biochar, biostimulants, biofertilizers. Studies in the period 2020–2025—and in some cases outside of this period, especially when justification was needed—were included. All collected material was divided according to research topics that best reflect the latest research on C. glomerata in farming. Then, the most prominent fields were identified.

Cladophora glomerata

C. glomerata is a filamentous green alga that forms large mats in nutrient-rich water bodies, particularly in slow-flowing rivers [22,23]. It grows attached to the bottom or various substrates, lies as loose masses over sediments, or floats freely on the water surface [13,14,15]. An image of this is provided in Figure 1.

The thalli are characterized by a bright to dark green color and composed of densely to sparsely pseudodichotomous branched (sometimes unbranched uniseriate) filaments [15,24]. Due to the high morphological plasticity, C. glomerata growth forms depend on environmental conditions, with thalli reaching about 20 cm in length in stagnant water ecosystems and up to one or even several meters in flowing waters [15]. Light, temperature, and nutrients are the key factors affecting the species’ growth [15,22,25,26]. C. glomerata has a wide temperature tolerance range from 13 °C to 30 °C and occurs in water bodies from spring to autumn, with optimal growth under photosynthetically active radiation of 300 to 600 μmol photons/m²/s [22,25,26]. Anthropogenic eutrophication, especially elevated phosphorus concentration, accelerates the formation of filamentous green algal assemblages of C. glomerata growth and induces “blooms” [15,23,27]. Under favorable conditions, C. glomerata can significantly increase its daily biomass (up to threefold) and the mats can cover over 85% of a lake surface area, reaching a biomass level of approximately 4 kg of wet weight/m² [14]. Such heavy blooms caused by this alga reduce biodiversity, as often, the assemblages are formed by a single species, reduce habitat heterogeny and the recreational value of the water bodies, and have negative ecological and economic impacts [22]. C. glomerata is the most morphologically variable and widespread species of the genus Cladophora in freshwater ecosystems [28,29]. It can be found in Europe, North America, the Atlantic and Caribbean islands, Asia, Africa, Australia and New Zealand, the Pacific Islands, and other regions [25,30]. It usually develops and forms large aggregations in water bodies under high nitrate and phosphate conditions, and its huge biomass could potentially be used in experimentation in different areas of human lives.

3. Content and Composition of Raw Material

Using the biomass of freshwater Cladophora algae as a raw material for agriculture has already been successfully demonstrated. Messyasz et al. [18] pointed out the order of the richness of metals as Ca > K > Mg > Na > Fe > Cu > Zn > Pb > As > Ni > Cd > Mn > Cr > Co, and noted that the amount of proteins in the dry matter (DM) could increase from 14.45% in C. glomerata from a lake to 26.55% in C. glomerata cultivated in the laboratory, and the fatty acid content in DM could vary and reach 62.5% if obtained with the supercritical fluid extraction method. The amount of nitrogen increased by 1.46 to 4.15 mg/kg (DM), phosphorus by 0.16 to 0.49 mg/kg (DM), and potassium by 3.25 to 6.00 mg/kg in the DM of C. glomerata from Lithuanian rivers, depending on the season [31]. According to content and composition data, C. glomerata could be used to improve the nutritional value of agricultural crops. In the last five years, various preparations of C. glomerata have been tested on crops such as soybean, tomato, and radish to improve the morphological and qualitative characteristics of the cultivated plants. The other studies concern the improvement of the plants’ physiological characteristics using biologically active compounds (i.e., phenolic compounds, carotenoids) obtained from C. glomerata. In recent years, new data on the secondary metabolites of C. glomerata have been updated, i.e., phenolic compounds have been identified in the biomass and extracts of C. glomerata [19,32]. Phenolic compounds are known as substances that regulate plant defense mechanisms against abiotic stress, i.e., cold, drought, heavy metals, etc., and their use could improve the adaptability of crops to the environment. Further studies in this area would be very useful because C. glomerata could be a promising material for the use of algae in organic farming to improve the adaptability of plants. A summary of the composition of C. glomerata and a comparison with other Cladophora species are shown in

Table 1. Chemical composition of freshwater Cladophora species raw material.

Compounds	Cladophora sp.	Cladophora glomerata
Protein, % (DW)	up 10.7 to 17.69	up 14.49 to 26.59
Lipids, % (DW)	up 2.04 to 2.56	up 0.78 to 5.16
Ash, % (DW)	up 14.7 to 16.9	up 14.69 to 39.25
Moisture, % (DW)	up 9.9 to 11.3	1.60
Fiber, % (DW)	up 20.7 to 26.1	up 15.6 to 27.19
Carbohydrate, % (DW)	up 52.5 to 60.9	up 62.8 to 74.5
Phenols, mg GAE/g	up 1.32 to 29.62
Macroelements	N, P, K	N, P, K
Vitamins	E, C, B1 = B2, A	E, C, B1 = B2, A
Pigments	chlorophyll a,b, lutein, zeaxantin, β-carotene	chlorophyll a,b, carotenoids, lutein
Metals	Mg, Fe, Ca, K, Zn	Mg, Fe, Ca, K, Zn, Cu, Na
References	[15,33]	[15,17,18,19,31,32,34]

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4. Different Forms of Organic Fertilizers from C. glomerata

Algae have been used as an organic fertilizer for crops for many centuries. However, scientific studies on how algae influence the growth and development of crops, or which properties of the compounds obtained from algae improve the quality of crops were only carried out in the middle of the twentieth century. Much attention is being paid to the possibilities of using seaweed in agriculture [35]. High adaptability to the environment and rapid growth make seaweed more attractive than freshwater algae. It is only in recent years that research on the latter has increased. During the last five years, different forms of freshwater C. glomerata preparation have been tested on cultivated plants such as soybean, tomato, radish, and garden cress. The research generally aimed to improve the quality of plant nutrition or plant growth, and the development of the formation of the productivity elements. C. glomerata could be used in agriculture in different forms, as raw material, dried material, powder, different percentage of solutions, extracts, etc. There are various forms of biomass presentation, i.e., row, dried, or fallowed algae material are dug into the ground; leaves are spread with algae solutions or extracts; seeds are soaked in algae solutions; or irrigation systems are supplemented with solutions. The presentation of plant studies with C. glomerata are presented in

Table 2. Plant growth studies using freshwater Cladophora glomerata-based materials.

Plant Species	Form of C. glomerata	Measured Effects	References
Soybean Glycine max varieties	extract obtained with ultrasound-assisted extraction	morphometric biochemical parameters; seed germination	[36,37]
Common name Carrots	extract obtained with ultrasound-assisted extraction	morphometric biochemical parameters; seed germination	[38]
Lupin varieties (cv. Homer, Jowisz, and Tytan)	extract obtained with ultrasound-assisted extraction	seed germination; morphometric biochemical parameters	[39]
Red radish (Raphanus sativus)	extract	morphometric parameters	[40]
Vigna radiata	biomass	morphometric parameters	[41]
Sezamum indicum	biomass	morphometric parameters	[41]
Garden cress Lepidium sativum	extract	productivity; morphometric parameters	[42]
Maize	liquid fertilizer with NPK	morphometric parameters; productivity	[43]
Tomato (Solanum lycoperiscum)	aqueous extract with silver nanoparticles (Ag-NPs)	nematicidal effect	[44]

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5. Responses of Crops to Fertilizers of C. glomerata Origin

The response of Japanese and Polish soybean varieties to freshwater algal extract in farming was investigated by Lewandowska et al. [36]. They applied foliar spray consisting of a 20% C. glomerata extract obtained using ultrasound-assisted extraction to two varieties of soybean (Glycine max), Polish Erica and Japanese Enrei, in the beginning of flowering. The results show increased plant height, first pot height, number of first branches, 1000-seed weight, and yield. The authors concluded that the improved growth of the plant could be due to the presence of growth-promoting substances, without specifying which ones, in the algal extract [36]. They also investigated the synergistic effect of C. glomerata extracts obtained with ultrasound-assisted extraction and magnetic field on soybean (Glycine max) germination, seedling growth, chlorophyll, and carotenoid content in leaves [37]. It is known that the magnetic field is the simplest physical method that can be used to stimulate seed germination. It was found that separate 20% and 80% extracts of C. glomerata positively influenced plant growth and the development of quantitative and qualitative plant parameters. A recommendation was suggested of a simultaneous application of a 20% extract of C. glomerata and a 3 min magnetic induction of 250 mT to achieve the best result for soybean seed germination [37]. Similar experiments were conducted with carrots. The highest germination capacity of carrot seeds was observed with 20% and 80% C. glomerata extracts. The authors found that parallel stimulation with a magnetic field and an algal extract did not significantly increase the number of germinated seeds. However, it was found that carrot seeds treated with C. glomerata extract showed an increased content of Ca, K, Mg, S, Cu, Fe, Mn, and Zn. However, the authors did not confirm the stimulating effect of the alga extract and the magnetic field on the germination of carrot seeds [38].

In a study employing 10% and 20% extracts obtained with ultrasound-assisted extraction (UAE) from C. glomerata, the germination and early growth of three lupin varieties (cv. Homer, Jowisz, and Tytan) were examined [39]. The germination percentage, root, hypocotyl, epicotyl length, and chlorophyll content were also investigated. The 20% extract stimulated the growth of seedlings of all lupin cultivars better than the 10% application [39]. The authors of the study suggest the use of C. glomerata to increase the yield of lupins and thus enrich infertile soils with nitrogen compounds, as lupins can fix atmospheric nitrogen [39]. Algal extracts from the waste biomass of C. glomerata at five concentrations (20%, 40%, 60%, 80%, and 100%) and ZnO nanoparticles at three concentrations (10 mg/L, 50 mg/L, and 100 mg/L) were used to study their effects on the growth of red radish (Raphanus sativus) seedlings [40]. The algal extracts at all concentrations had a positive effect on the morphological parameters of the plants, i.e., root length, hypocotyl length, epicotyl length, total plant length, and fresh biomass weight. ZnO nanoparticles also increased the plant growth parameters, but not at a statistically significant level [40]. The results of the experiment with different proportions of biomass enriched with Cladophora spp. showed an increase in the total length, total dry weight, and leaf area of Vigna radiata and Sesamum indicum. These plants showed measurable differences in the morphological traits shoot and root length, leaf area, increased shoot and root dry weight, and number of grains [41]. The effects of the C. glomerata aqueous extract for three concentrations (2.5, 5, and 10 mg extract per mL of tap water) were tested on the growth and productivity of garden cress (GCR). Lepidium sativum algal extract at 2.5 mg/mL had the most positive effect on the productivity and biochemical characteristics of phenolic compounds, flavonoids, and chlorophyll content [42]. In this case, it was proposed to evaluate C. glomerata extract as a biostimulant that influences plant growth and the stress resistance system [42]. Experiments by Munir et al. [43] with maize crops using liquid fertilizer of C. glomerata and NPK (Phonska) show a positive effect for maize growth and yield. The authors suggested that C. glomerata and NPK (Phonska) interaction improves soil chemical properties. Although a number of laboratory studies have been conducted in recent years on the effects of C. glomerata on cultivated plants, these studies are not focused, for example, on plant growth or development physiology or yield investigations. Only the last few works adopted certain proposals regarding the effects of C. glomerata on crops.

6. C. glomerata: Bioindicator of Heavy Metal Pollution and Water Purification

Green algae, especially C. glomerata, are generally considered as the best bioindicator of contamination of aquatic bodies by nutrients as well as by heavy metals. Many of the latter, e.g., mercury, lead, arsenic, nickel, chromium, zinc, and manganese, enter the animal and human body through the food chain [45]. In the 1970s, several studies postulated that C. glomerata was a very suitable alga for the uptake of heavy metals in water [46,47,48]. Some methods for using C. glomerata to monitor metal concentrations in rivers were developed in 1989. The characteristics of the use of macroalgae were compared with those of mosses [49]. A model was then proposed for the ability of macroalgae to absorb and concentrate organic and inorganic substances from solution. For example, C. glomerata has been found to be able to bioconcentrate an annual average of 54% of available atrazine, the most used agricultural herbicide in the Midwestern United States, from water [50].

Because C. glomerata occupies a large surface area of ecosystems and can absorb heavy metals from the environment, the field is still under development. The latest data show that C. glomerata has a high bioconcentration factor for Cd (98.42%) and Pb (92.57%) [51]. It removed 48.75% of Cd and 57.027% of Pb from industrial wastewater [51]. It was also found that this filamentous alga reduces nitrate (75%) and phosphate (86%) in organic wastewater from farms, and a simple system was proposed for nutrient reduction [52]. Another study shows that dry biomass of C. glomerata or even a residue after extraction and ZnO nanoparticles are both good sorbents for Cr(III) ions from aqueous solution [40]. The extract obtained with ultrasound-assisted extraction from C. glomerata was used to biosynthesize ZnO nanoparticles; it was found that the heavy metal concentration in algae can be used as a bioindicator for the pollution of an ecosystem. In 2023, high concentrations of the elements Fe, Pb, Cu, and Zn were detected in macroalgae from Cladophora, Spirogyra, and Zygnema, as species from all three genera accumulated high amounts of heavy metals from water reservoirs [53]. Recently, information on the ability of Cladophora spp. to remove microfiber pollutants from fresh and marine waters was published. The study reported on the natural accumulation of microplastics and microfibers by macroalgae or other submerged aquatic vegetation in the Great Lakes [54]. The authors claimed that freshwater Cladophora algae interacted with microplastics via adsorptive forces and physical entanglement. They speculated that passing the treated wastewater over algae may be a fairly simple way to collect most of the microplastics that remain in the final effluent [54]. A 2024 study demonstrated that the functionalization of C. glomerata biochar with metal–organic framework (MOF) nanoparticles enhanced the hydrophilicity of nanofiltration membranes, thereby augmenting their efficiency in the removal of heavy metals. The removal efficiency exhibited a greater than 95% increase, while the water permeability demonstrated a more than 60% increase [55].

7. The Use of Biochar from C. glomerata

In 2011, Bird and Wurster [56] evaluated the physicochemical properties and potential uses of macroalgal biochar derived from eight species of green algae from freshwater, brackish, and marine environments. Using trace element analysis, they demonstrated that macroalgal biochar produced from unpolluted water does not contain toxic trace elements above the levels mandated for unrestricted use as a biosolid amendment to soils [56]. In recent years, a few studies have been conducted looking at the use of biochar from C. glomerata as a fertilizer for crops or as a soil amendment. Beusch [57] reports how biochar in general affects the chemical, physical, hydrological, and biological properties of the soils reviewed and that macroalga-derived biochar has properties suitable for use as a soil amendment and as a tool for long-term carbon sequestration [56]. To produce freshwater C. glomerata biochar, pyrolysis, which is most feasible at 450–550 °C with a biochar yield of 32.21 (wt%), could be used as a fuel and for soil amendment [58,59]. According to the latest knowledge on the production of algal charcoal, it is produced by a pyrolysis process that involves the carbonization of biomass at limited oxygen content by conventional or microwave heating [55]. The application of biochar for environmental remediation is currently increasing due to its low cost, high absorption capacity, low energy consumption, good yield, and ease of application in wastewater and soil. It is estimated that the production of biochar from algae is now cheaper compared to commercial activated carbon [55]. Raw biomass and charred biomass in the form of biochar could be used to remove agrochemicals such as pesticides, insecticides, antibiotics, anti-inflammatory agents, metals, and metalloids from soil [55]. According to recent observations, macroalgae biochar significantly improves soil quality, adsorbs waste materials (especially heavy metals), and is therefore valuable and sustainable for farming [60]. Michalak et al. [59] have shown that biochar from C. glomerata has the potential to remove toxic metals from wastewater. They pointed out that as the pyrolysis temperature increases, the capacity of the algae charcoal towards Cr(III) ions also increases. According to the authors, the best temperature to produce C. glomerata biochar is 450 °C, at which 87.1 mg/g was obtained. C. glomerata biochar also showed a good ability to simultaneously remove metal ions from artificial effluents. The removal efficiency for Cr(III) ions was estimated at 89.9%; for Cu(II) ions, 97.1%; and for Zn(II) ions, 93.7% [59]. To the extent that it has been shown that C. glomerata biochar can absorb metals, it can also release various minerals into the soil. Moreover, biochar could provide a suitable habitat for soil microorganisms, and it is being discussed as a substrate for the soil biota [61]. Different properties and uses in the farming of biochar have been relatively little-studied and, in our opinion, still have perspectives to be developed.

8. C. glomerata for Feed Supplements

Already in the 1990s, experiments on the use of C. glomerata in fish feed supplements were being developed [62]. Today, the biomass of Cladophora spp. is used as a supplement for feeding livestock, chickens [63], rabbits [64], fish [65], and shrimp [66]. C. glomerata from the Lithuanian rivers Dubysa, Šventoji, Nevėžis, and Jūra was examined and found to contain acceptable levels of Ca, K, N, P, Mg, Zn, and Cu. The protein content of the algae was found to be between 16 and 21.5% DM. The content of essential amino acids, polyunsaturated fatty acids, saturated fatty acids, and omega-6/omega-3 fatty acids varied in the different rivers. It was concluded that C. glomerata could serve as a source of proteins as well as amino and fatty acids, suggesting that biomass could be an alternative and useful component for animal feed [31]. Further research in this area has focused on the use of C. glomerata biomass to improve rabbit meat. Californian rabbits were fed with standard compound diets (SCD) and varying amounts of C. glomerata. An analysis of the rabbit meat showed that treatment with SCD and 4% C. glomerata increased the levels of protein (22.17 g/kg), total protein (192.16 g/kg), and essential amino acids (threonine, valine, methionine, lysine, isoleucine) in rabbit muscle. In all cases, fat accumulation in the muscles was reduced. The authors concluded that supplementing the rabbit diet with C. glomerata is a beneficial and sustainable nutritional approach to improve rabbit meat [31]. An experiment conducted in 2023 demonstrated that the supplementation of rabbit diets with 4-8% C. glomerata biomass resulted in a substantial enhancement of meat quality, as evidenced by an increase in protein content, an improvement in the omega-3/omega-6 ratio, and a reduction in fat oxidation. Furthermore, no deleterious effects on the intestines or internal organs of the animals were observed [67]. In recent years, a comprehensive analysis of the biosorption of metal ions by macroalgae using ICP-OES (Inductively Coupled Plasma–Optical Emission Spectrometry), SEM-EDX (Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy), and FTIR (Fourier Transform Infrared Spectroscopy) techniques by Michalak et al. [68] has shown that the C. glomerata biosorption mechanism based on ion exchange could be valuable in preparing feed supplements. The separate enrichment of the biomass with Cr(III), Mn(II), and Mg(II) ions shows a significant reduction in the content of non-structural carbohydrates, e.g., simple sugars, starch, and fructan [68]. The authors suggest using this ability to produce advanced feed supplements with a low glycemic component. Some research treating animal diseases with C. glomerata was also conducted. Although these are only a few trials, they are noteworthy and should therefore be further developed in the future. The antioxidant effect of a methanolic extract (1% and 5%) from the biomass of C. glomerata on equine adipose-derived mesenchymal stem cells (EqASCs) was demonstrated. The authors concluded that it could be beneficial for the prevention of equine diseases associated with oxidative stress, including metabolic syndrome [69]. Another study by the authors suggests that the methanolic extract of C. glomerata promotes chondrogenic gene expression and cartilage phenotype differentiation in adipose-derived mesenchymal stromal stem cells from horses affected by metabolic syndrome. It could be useful for cartilage repair and regeneration [70].

9. C. glomerata Against Pathogenic Organisms

The possible role of C. glomerata against the aquatic human parasite Schistosoma mansoni was described in 1968 [71]. At that time, the authors concluded that C. glomerata can produce a substance (probably acrylic acid) that causes the high mortality of the snail Biomphalaria boissyi, which is the host of Schistosoma mansoni [71]. Following these experiments and statements, the idea was developed that algae or their extracts could be used to protect ponds or crops from pathogenic organisms. In recent years, macroalgae have been increasingly recognized as organisms with physiological biopesticide properties. Bioactive compounds such as ulvan, laminarin, alginate, carrageenan, glucuronan, fucans, and tannins from macroalgae are recognized as biopesticides with positive effects against viruses, bacteria, fungi, nematodes, etc. [72]. A whole series of articles deals with the results of extracts from green and brown algae or microalgal effects against plant pathogens. A few articles also presented experiments with C. glomerata in this way. The aqueous extract and the silver nanoparticles (Ag-NPs) synthesized from C. glomerata were used against the root-knot nematode Meloidogyne javanica, which causes severe damage to vegetables. The results showed that green-synthesized silver nanoparticles from C. glomerata exhibited the highest environmental nematocidal activity in a laboratory bioassay on egg hatchability. A significant reduction was observed in the number of galls, egg masses, females per root system, and juvenile mortality. The authors concluded that the green nanoparticles synthesized with freshwater C. glomerata could stimulate the plant’s immune system to defend against nematode infection and could be used against M. javanica [44]. Another study showed that the crude ethanolic extracts of C. glomerata in general have significant insecticidal effects against the cotton leafworm Spodoptera littoralis using the algal/cyanobacterial extract/larval contact method [73]. These techniques encourage further testing of the efficacy of C. glomerata against various pests of crops.

10. Disadvantages and Limitations of C. glomerata Use in Sustainable Farms

Despite the potential benefits of using freshwater C. glomerata as a natural alternative to synthetic fertilizers and additives in sustainable farming, its use may be limited by several factors. The disadvantages of using the algal biomass in farms include its ability to accumulate heavy metals and hazardous chemicals, as well as the risk of contamination with pathogenic microorganisms when the alga grows in polluted waters, especially near industrial or urban areas. Heavy metal concentrations in the algal biomass vary depending on water quality. Higher accumulation has been observed in algae collected from polluted sites [74].

If C. glomerata is collected from unpolluted waters, the concentration of heavy metals should not exceed the permissible limits for humans and animals. Current knowledge reveals that C. glomerata biomass collected from freshwater ecosystems in Poland and Lithuania did not contain toxic metal ions, or their concentrations were below the limit of detection [31,37]. Therefore, C. glomerata biomass unpolluted by heavy metals and away from industrial or urban pollution sources may be considered safe for agricultural purposes, although regular monitoring of metal content remains advisable.

Despite the potential for metal bioaccumulation, which limits this alga’s use as a food additive or biofertilizer, C. glomerata can effectively be used as a natural absorbent to clean polluted water bodies. Nevertheless, another study investigating C. glomerata grown in freshwater as feed concluded that it has significant feed value but should be used under controlled conditions [75].

Wild-collected C. glomerata biomass may also be contaminated with human pathogenic bacteria, especially when decaying biomass is harvested [76]. However, long-term composting for 3 to 5 months can eliminate these bacteria and biomass, rendering the biomass safe for use. In addition, the biochemical composition and the amount of health-promoting substances in C. glomerata biomass fluctuate seasonally depending on environmental conditions, such as nutrient availability, light, and temperature, so its collection is not favorable at all times of the year and complicates standardization and consistent use of the material in agricultural applications. All these factors reduce the attractiveness of using C. glomerata in sustainable farms. To draw conclusions, much more research, especially that demonstrating crop yield improvement under field conditions, is needed to confirm the positive effects of using C. glomerata, establish its advantages, benefits, and possible limitations, and assess its economic feasibility.

11. Future Perspectives and Conclusions

Our analysis of the use of the freshwater macroalga C. glomerata in sustainable operations revealed that research in this area is moderately developed. In the last few years, approximately 70 related studies were found in the scientific literature. The low amount of research on freshwater algae could be explained by the fact that seaweeds were studied more often. Seaweeds are recognized as algae with more flexible physiological properties, higher protein complex or more rapid rates of growth, and the ability to form large amounts of biomass.

Nevertheless, we were able to identify some potential areas for the use of freshwater C. glomerata biomass. The use of freshwater C. glomerata can promote plant growth, development, and nutrient uptake as a potential alternative to chemical fertilizers in crop production and avoid detrimental effects on agricultural crop quality. C. glomerata raw biomass and biochar can be used to clean soils and water reservoirs and to improve soil properties for agricultural crop production. C. glomerata can be used as a feed additive in animal husbandry. It can also protect crops from pathogens. In our opinion, these are the potential research areas that need to be explored for the utilization of C. glomerata for the development of sustainable agriculture.

Its prospects of being used are also ensured by certain ecological features. For example, it is the most widespread filamentous green alga in the world and usually proliferates in shallow aquatic ecosystems; therefore, its biomass can easily be collected due to sedentary habits. Moreover, its mat-forming thallus structure facilitates easy biomass collection manually, mechanically, or using specialized harvesting machines [18,77]. The species is considered as non-toxic and stress-tolerant, reproduces rapidly, and is categorized as “R-strategic” [27]. In eutrophic water bodies, the growth rate of biomass is accelerated, particularly in the presence of elevated phosphorus levels. In such ecosystems, excessive macroalgal growth is often considered harmful, as it can lead to reduced biodiversity and habitat quality, and decreased light penetration into deeper water layers, whereas decomposing biomass can cause unpleasant odors and an increase in pathogenic microorganisms [12,15,23,37]. On the other hand, C. glomerata efficiently accumulates nutrients such as nitrogen and phosphorus; therefore, the removal of excessive biomass from water bodies can improve ecosystem health and contribute to nutrient load reduction. However, the timing, appropriate biomass harvesting methods, and locations of biomass harvesting are crucial to ensuring environmental benefits. Biomass should be collected selectively during the periods of mass algal growth and at the right time, before biomass decay, leaving some biomass to preserve habitat functions. Poorly timed or excessive removal of biomass can disturb benthic habitats and temporarily alter community structure. Therefore, harvesting C. glomerata can be considered environmentally beneficial when performed under controlled, ecologically sensitive conditions. Proper management of C. glomerata biomass harvesting can help mitigate eutrophication and improve water quality.

Moreover, biomass rich in micro- and macroelements, proteins, carbohydrates, and secondary metabolites could be easily utilized in sustainable farming practices. Additionally, raw material could be used in the simplest way on farms near rivers or lakes making biomass utilization more economically feasible.

Of the various attempts to utilize freshwater C. glomerata mentioned above, data on its biostimulant potential are still limited. As data on the secondary metabolites of C. glomerata are increasing, future research should focus on exploring the alga’s potential role in sustainable agriculture, particularly in crop cultivation. Furthermore, data are lacking on the utilization of complex products consisting of organic compounds or groups of organic compounds with relevant content derived from C. glomerata. As the knowledge of their composition grows, future studies could also be expanded to develop and optimize freshwater C. glomerata-based materials for agricultural use, such as biofertilizers, biostimulants, soil amendments, or other sustainable agricultural applications.