1. Introduction
Aquatic plants and phytoplankton are important indicators of the health of urban aquatic ecosystems and play an important role in assessing water quality and the impact of human activities on the environment. Changes in the structure of these communities can indicate the effects of environmental changes such as pollution and eutrophication [1]. Macrophytes also filter pollutants, stabilize sediments, and provide habitats for various aquatic organisms, among other functions. Recent studies have also investigated the impact of urbanization on aquatic ecosystems and how macrophytes can be used in ecosystem restoration projects [2,3,4]. The state of ecosystems in urban water bodies is significantly affected by human activities, especially due to rapid urbanization. This degradation caused by human activities has led to a decrease in the quality of aquatic ecosystems.
In the city of Bucharest, the changes made to the courses and river banks of the Dâmbovița and Colentina rivers carried out in various periods of urban systematization had a significant impact on these ecosystems. The course of the Colentina River was anthropogenically fragmented and modified, resulting in 15 lakes along the Bucharest. These lakes are part of a water control system created to control the flow of the river and prevent flooding, as well as to create recreational areas [5,6]. Other impacts of changes in river morphology include reduced flow velocity, changes in water quality, eutrophication, and the introduction of opportunistic species. In addition, population growth due to urban development has increased pressure on ecosystems [7] and reduced their resilience.
The presence of macrophytes in the littoral zone of a water body is determined by factors such as shore type, land use, water depth, water flow, sediment type, and nutrient enrichment.
This study hypothesizes that the species composition and distribution of the macrophyte community in riverine waters are significantly influenced by geomorphological features, land use practices, and local environmental conditions. These factors differ between urban, peri-urban, and rural environments, as well as the intensity of anthropogenic pressures shaping macrophyte development and interactions with phytoplankton. This study aims to assess how the different environments of the Colentina River influence the composition and distribution of the macrophyte community, taking into account the geomorphological characteristics of the ecosystem (natural and artificial banks, lakes versus riverine areas) and the type of land use (urban, peri-urban, and rural). Interactions with phytoplankton, another important primary producer in aquatic ecosystems, were also assessed. Phytoplankton is known to be a valuable tool in investigating the extent to which anthropogenic activities affect water quality and how they affect biodiversity.
2. Materials and Methods
2.1. Study Area
The study took place in 2019 along the Colentina River, involving monthly in situ activities from March to November, which corresponds with the macrophytes’ growing season. Hydrotechnical works carried out between 1933 and 1936 modified the river’s course, leading to the formation of 15 lakes, mainly within Bucharest’s urban area. Today, the river exhibits geomorphologically distinct areas, including natural river zones and lakes linked by locks. It is also influenced by various anthropogenic factors, including rural/agricultural, peri-urban, and urban impacts. Ten stations were set up along the river (Figure 1), from upstream to downstream, considering different anthropogenic influences (Table 1).
2.2. Field Survey
2.2.1. Physicochemical Parameters
The physicochemical parameters of the water were measured in situ using various field instruments. A Hanna Instruments HI 9828 multi-parameter (Hanna Instruments, Woonsocket, RI, USA) device was employed to assess the dissolved oxygen (DO) in mg O2 L−1, DO saturation percentage, conductivity, temperature, oxidation-reduction potential (ORP), pH, total dissolved solids (TDS), and turbidity (FTU) in the water column. Light intensity was measured with a Lutron LX-1102 Lightmeter (Lutron Electronics Co., Inc., Coopersburg, PA, USA). Depth and transparency were determined using a Secchi disk, while water flow was measured with a Geopacks flowmeter (Geopacks Instrumentation; India). For nutrient analysis, samples were collected from the water column in plastic bottles, transported in cold boxes, and processed immediately. A 200 mL water sample was filtered through GF/F Whatman filters (65 μm diameter) (Cytiva, Whatman, MA USA) and stored at 4 °C for laboratory analysis. Nutrients NH4, NO3, and PO4 were determined spectrophotometrically following a modified Berthelot method for N-NH4 [8] and the method described by Tartari and Mosello [9] for N-NO3 and P-PO4.
2.2.2. Aquatic Vegetation
Macrophytes were collected using rakes and grapnel hooks. If identification could not be carried out on-site, plant samples were placed in polyethylene bags for laboratory identification based on the key species determinations [10,11]. Observations and sampling allowed for creating a taxonomic composition using floristic inventories, represented by a species list from the lake. Macrophytes were examined in four sampling units (1 m2 each) at each site, perpendicular to the lake shoreline. The distance between sampling units was determined by the presence of macrophytes at the stations and ranged from 3 to 10 m. The macrophytes were categorized as floating, emergent, floating and submerged, and submerged. Additionally, due to their prevalence in many stations, a separate category for macroscopic algae, such as filamentous algae, was included.
The DAFOR scale was used for the relative abundance assessment into five distinct classes [12]: Rare (1)—1% to 10% cover, Occasional (2)—11% to 25% cover, Frequent (3)—26% to 50% cover, Abundant (4)—51% to 75% cover, Dominant (5)—more than 75% cover.
The Species richness was evaluated as the number of species detected for each site [13].
2.2.3. Phytoplankton
Chlorophyll-a measurements were conducted in situ on the water column using the BBE-Moldaenke FluoroProbe (BBE Moldaenke GmbH, Kiel, Germany) at the phytoplankton component level. This field equipment is designed for in situ chlorophyll-a measurements, providing accurate data on the chlorophyll content of four distinct phytoplankton spectral groups, Chlorophyceae, Cyanobacteria, Bacillariophyceae, and Cryptophyta, based on fluorescence principles [14]. The equipment delivers detailed chlorophyll-a concentrations (µg L−1) for these phytoplankton groups, along with a total chlorophyll-a measurement. Chlorophyll-a concentration served as an estimator of phytoplankton biomass.
Based on the total chlorophyll-a concentration of the phytoplankton, the water trophic classification respected the Order MEWM no 161/2006—national legislation [15], as part of the European Water Framework Directive. The quality classes were determined by the total chlorophyll-a concentration (µg L−1) according to the following limits: oligotrophic 1–2.5; mesotrophic 2.5–8; eutrophic 8–25; hypereutrophic > 25.
Additionally, the abundances (cells L−1) of the main taxonomic groups—Chrysophyceae, Cyanobacteria, Euglenophyceae, Bacillariophyceae, Chlorophyceae, and Xanthophyceae—were assessed. Phytoplankton samples were collected from the water column using a Patalas-Schindler (4L) device, with 500 mL of unfiltered water taken for analysis. Samples were fixed with 4% formalin and analyzed in the laboratory. The sample procedure followed Utermöhl’s method [16] using a Zeiss-Observer D1 inverted microscope (Carl Zeiss AG, Oberkochen, Germany). Taxonomic identification was performed using the following keys, Cyanobacteria [17,18], Chlorophyceae [19,20], Bacillariophyceae [21,22,23,24], Euglenophyceae [25], Dinophyceae [26], and Chrysophyceae [27], and was revised on
2.3. Statistical Analysis
A non-parametric Chi-squared test (χ2) was applied to assess, as qualitative variables, the relationship between macrophytes’ DAFOR classes and phytoplankton parameters versus local influences, shore, and ecosystem types (as detailed in Table 1).
To analyze the response of macrophyte development to the trophic state of the ecosystems (oligotrophic, mesotrophic, eutrophic, hypereutrophic) and the chlorophyll-a concentration of the phytoplankton, the ANCOVA statistical technique was utilized. ANCOVA, or analysis of covariance, is a statistical method that combines analysis of variance (ANOVA) with regression [29].
Rényi diversity profiles were carried out to compare the diversities of the following ecosystems: Colentina natural river sector, Crevedia branch, Mogoșoaia, Plumbuita, Fundeni, Cernica lakes, and Cernica river sector. Rényi diversity curves highlight the complexity and richness of the communities, providing valuable insights into biodiversity through their comparative analysis across various diversity indices. Species richness (α = 0), Shannon–Wiener diversity index (α → 1), Simpson index (α = 2), and Berger–Parker (α→∞) in the analysis. Higher diversity is indicated by an elevated profile curve, which suggests a greater diversity of species and a homogenous distribution among them. Conversely, lower diversity is represented by a flatter curve, indicating dominance by fewer species [30].
Multivariate Analysis
Canonical Correspondence Analysis (CCA) is a statistical method used to explore the complex interactions between macrophyte communities and environmental factors. CCA identifies and quantifies the linear relationships between multidimensional variables, such as ecological parameters (e.g., water pH, temperature, and nutrients) and the structures of aquatic plant communities. The axes F1 and F2 represent the main gradients of variation in species composition explained by environmental variables. The eigenvalues measure the amount of variance explained by these axes [31].
Canonical Correlation Analysis (CCorA) was utilized to identify interactions between the main phytoplankton groups and macrophytes. The analysis included macrophyte coverage, densities of Cyanobacteria, Chlorophyceae, Bacillariophyceae, Euglenophyceae, Dinophyceae, and Chrysophyceae, as well as phytoplankton biomass estimated through chlorophyll-a concentrations for Chlorophyceae, Cyanobacteria, Bacillariophyceae, and Cryptophyta. In Canonical Correlation Analysis (CCorA), the results include eigenvalues, percentages of variance explained by the F1 and F2 axes, and the Wilks’ lambda test results, providing an overview of the relationships between independent and dependent variables [32].
Statistical analyses was performed using Past 3.0 soft [33] and XLSTAT pro 2013 [34].
3. Results
3.1. Physicochemical Parameters
During the study, physicochemical parameters varied from rural to urban areas along the course of the Colentina River. The river stations in rural areas with natural features differed from those in peri-urban and urban sections. In rural areas, depth, water flow, and turbidity were higher (Table 2). In contrast, the water temperature was moderate (18.59 °C), and both the pH (8.42) and transparency (0.44 m) were lower compared to other areas. Peri-urban ecosystems exhibited higher nutrient values, indicating potential long-distance influences from agricultural practices (Table 2). The water depth and transparency were similar to river sections, with a slightly higher water temperature of 19.58 °C and a pH comparable to urban areas. Oxygen and ORP indicated lower oxygenation conditions. Urban ecosystems had the lowest depth but the highest transparency and temperatures. Conductivity was highest compared to other areas, the pH was also high (8.68), and water flow was similar to that in peri-urban areas. Nutrient concentrations were generally low.
3.2. Spatial Distribution of Macrophytes in Relation to Ecosystem Types
Macrophyte communities were sparsely represented, encompassing fifteen plant taxa categorized as follows: six emergent, two floating, two floating and submerged, and four submerged taxa (Table 3). The majority of these species were located in areas outside urban influences, specifically in stations 0, 1, 8, and 9 (Table 3—see species richness).
In station 0 of the Colentina River (Supplementary Materials), the canopy structure was complex, comprising all types of macrophytes. Among these, Phragmites australis was dominant in the autumn months and present throughout the study period. Reeds were associated with T. angustifolia, which was also dominant in five out of the eight months of the study. Species like C. demersum and P. natans shared the habitat with P. australis and T. angustifolia.
In station 1 (Crevedia branch), similar rural influences with natural banks were observed, but submerged plants were absent, and the canopy structure consisted mainly of emergent species such as P. australis and T. angustifolia, with occasional B. umbellatus and P. hydropiper.
From Mogoșoaia (stations 2 and 3) onwards, the river’s course and bank features were modified. P. australis was well-developed in these conditions, while T. angustifolia lost its cover. T. natans dominated Mogoșoaia Lake during the summer months of June, July, and August. Submerged macrophytes were poorly developed, with occasional P. crispus.
Both Plumbuita and Fundeni lakes, influenced by urban activities, showed low macrophyte diversity, with occasional emergent species like P. australis and T. angustifolia. Other species found included floating Lemna sp., floating P. natans, submerged C. demersum, N. marina, P. crispus, and filamentous algae. In Plumbuita Lake, anthropogenic influences resulted in a poor macrophyte canopy structure, with occasional species such as filamentous algae, Lemna, and reeds (abundant in station 4 in October). Among submerged species, C. demersum was frequent in August at station 4 and abundant in early summer at station 5, along with occasional N. marina and P. natans.
Lake Fundeni, characterized by urban influences and proximity to residential areas and parks, showed a scarcity of submerged plants, with occasional N. marina in July. Throughout the study, P. australis was well-developed, with an increase in T. angustifolia towards the fall, and Lemna sp. was present with reduced abundance.
In Lake Cernica, station 8, a peri-urban transition zone, emergent, floating, and submerged macrophytes were found, with abundant reeds associated with P. hydropiper during the warm period. In station 9, on the natural river side of the Colentina River after the lakes chain, macrophyte species richness increased, with well-represented reeds, T. angustifolia, S. lacustris, and P. hydropiper. Submerged plants like C. demersum, N. marina, P. crispus, and S. pectinata were also present, although in reduced abundance.
The characteristics of the water body type (lakes or river areas), shore type (natural or anthropized), and the degree of local influences (rural, peri-urban, urban) influenced the structure of aquatic macrophyte assemblages (Table 4). Species such as P. australis, P. hydropiper, S. lacustris, S. erectum, T. angustifolia, and S. pectinata were significantly associated with all three categories of study points. B. umbellatus and Lemna sp. responded significantly to shore types, preferring the modified deep shores of the lakes.
The Renyi diversity curves (Figure 2) compare biodiversity across the river areas and the four studied lakes. Plumbuita Lake and the Colentina River sections (stations 0 and 9) are represented by the uppermost curves, indicating the highest diversity. The next set of curves, representing Crevedia, Mogoșoaia, Fundeni, and the Cernica River area, is positioned lower, indicating significantly reduced diversity. The curve with the lowest diversity, highlighted in red, corresponds to Cernica Lake.
3.3. Interactions at the Level of Physicochemical Parameters vs. Macrophytes
A Canonical Correspondence Analysis (CCA) was utilized to determine the ecological preferences of macrophyte species along the modified flow of the Colentina River. This analysis was employed to identify the relationships between macrophytes and environmental variables, providing valuable insights into how different species adapt and thrive under altered river conditions. The analysis reveals clusters of species with similar preferences (Figure 3). For instance, B. umbellatus, S. erectum, and N. marina are associated with environments characterized by high temperatures, light, and NH4 levels. On the other hand, Lemna sp. and S. erectum show a tendency towards turbidity, indicating a preference for turbid waters. Additionally, S. lacustris, S. pectinata, and S. natans displays a preference for conditions linked to conductivity, total dissolved solids (TDS), NO3, and higher water flow rates. Species like P. crispus and T. natans were correlated with parameters such as transparency, PO4, and total phosphorus (P total), suggesting a preference for clearer waters and phosphorus-rich environments.
3.4. Interactions at the Level of Primary Producers, Macrophytes vs. Phytoplankton
The taxonomic structure and abundance of macrophyte communities are closely related to their competition with phytoplankton, which are the second primary producers in aquatic ecosystems. The high development of algae and the increased concentration of chlorophyll-a exert direct pressure on macrophytes, affecting the trophic state. Phytoplankton has been significantly influenced by anthropogenic activities, as evidenced by prolonged eutrophication periods and total chlorophyll-a concentrations exceeding typical levels (Table 5). The abundance and biomass characteristics of phytoplankton components highlight the complexity of their dynamics in relation to local influences. Rural areas tend to exhibit low biomass and abundance, except for Euglenophyceae and Bacillariophyceae, which show higher biomass values compared to peri-urban and urban areas (Table 5). Peri-urban areas exhibited the highest total chlorophyll-a concentration (71.32 µg L−1), followed by urban areas (65.63 µg L−1) and rural areas (47.96 µg L−1). Peaks in abundance were also observed for Cyanobacteria (3.99 × 107 cells L−1), Xanthophyceae (3.91 × 105 cells L−1), and Bacillariophyceae (5.73 × 106 cells L−1). Urban areas were characterized by a mixed pattern, with a high abundance of Chlorophyceae and Cyanobacteria, and occasionally Bacillariophyceae, compared to other groups. Under these conditions, Cyanobacteria reached the highest chlorophyll-a concentration (12.56 µg L−1). Less-representative groups included Euglenophyceae, which preferred river areas, Dinophyceae and Chrysophyceae, which were present in urban ecosystems, and Xanthophyceae, which were favored by peri-urban and rural areas (Table 5).
Due to the massive proliferation of algae, it was noted that, out of 88 in situ measurements of total chlorophyll-a concentration (µg L−1), the most frequently observed trophic state was hypereutrophic (77 measurements), followed by eutrophic (5), mesotrophic (5), and 1 oligotrophic state. Although hypertrophic periods were dominant, significant differences were observed based on local ecological conditions (Figure 4).
The trophic status, assessed by the total chlorophyll-a, also demonstrated significant responses to ecosystem characteristics. A significant association (χ2(6, N=88) = 18.38; p = 0.005) was found between trophic status and local influences, with hypertrophic periods being more frequent in peri-urban (96%) and urban areas (97%) (Figure 4, first line). Additionally, the type of riverbank significantly influenced (χ2(6, N=88) = 62.43; p = 0.0001) phytoplankton development, which, unlike macrophytes, was promoted by anthropized banks showing higher hypertrophic stages (Figure 4, second line of pies). Examining the relationships between excessive phytoplankton biomass and ecosystem types, the results (χ2(3, N=88) = 17.81; p = 0.0004) demonstrated the advantage phytoplankton has in prevailing under unfavorable conditions compared to macrophytes (Figure 4, third line of pies).
Under conditions of abundant phytoplankton, certain macrophyte species responded significantly to deteriorating water quality, particularly during the transition to eutrophic or hypereutrophic states (Table 6). The ANCOVA analysis between plant species and phytoplankton chlorophyll-a (as indicator of trophic status) revealed significant impacts on macrophyte species development. The analysis identified indicator species of poor water quality. Specifically, P. australis (p = 0.0313), T. angustifolia (p = 0.002), S. natans (p < 0.0001), P. natans (p < 0.0001), and C. demersum (p = 0.002) exhibited a decline in abundance under hypereutrophic conditions.
The relationships between primary producers (phytoplankton and macrophytes) depend on environmental conditions, with resource and habitat preferences determining their associations. The CCorA analysis highlighted a competitive tendency between phytoplankton and macrophytes (Figure 5). The eigenvalues of F1 (0.66) and F2 (0.55) suggest that both axes significantly contributed to the analysis model. Additionally, the cumulative percentage of variance (46.27%) explained by the F1 and F2 axes indicates a strong relationship between macrophyte development and phytoplankton communities. The Λ values of the Wilks’ Lambda Test varied between 0.028 and 0.996, but only F1 (p < 0.0001) and F2 (p = 0.0101) showed significant correlations between the variable sets. In ecosystems where phytoplankton showed strong positive correlations among algae groups (Figure 5, left side of the biplot), most macrophyte species were disadvantaged. Positive correlations among macrophyte species were also established under phytoplankton pressures, suggesting that they develop adaptive response mechanisms to existing conditions. Conversely, the analysis shows that species such as T. angustifolia, P. natans, C. demersum, and P. australis, which are negatively correlated with the phytoplankton groups on the left side of the biplot, have developed different strategies to cope with phytoplankton pressures, tolerating the presence of Bacillariophyceae (µg L−1) and Euglenophyceae (cells L−1) (Figure 5, right side of the biplot).
4. Discussion
4.1. The Response of Macrophytes to Environmental Drivers
4.1.1. Ecosystem Types
The modified geomorphology of the Colentina River, featuring both river areas and constructed lakes with natural and artificial banks, provided varied ecological conditions for macrophyte species. Our study investigated how these species respond to different anthropogenic pressures based on the type of ecosystem and area. The overall findings highlight those human interventions, such as altering riverbanks and creating lakes and locks, lead to structural changes and a significant reduction in macrophyte populations. Under these conditions, macrophytes lost the competition with phytoplankton, which developed excessively, dominated by Cyanobacteria and Chlorophyceae. These cumulative anthropogenic pressures reduce macrophytes’ adaptive capacities, leading to ecosystem service deterioration and economic losses.
Our results show that species distribution was influenced by ecosystem type (geomorphology and local influences), physicochemical drivers, and competition with phytoplankton (Table 4 and Table 6; Figure 3 and Figure 5).
The characteristics of the Colentina River in peri-urban/rural areas, which resemble natural conditions, led to a preference for these areas by macrophytes. These areas exhibited greater species richness and higher plant abundances compared to urban areas (Table 3). Natural areas support the growth of wetland species due to sediment features and nutrient content. According to Andersson [35], the geomorphology of basins defines the formation of ecotonal habitats, and the shape of lake shores influences sediment dynamics and vegetation development.
A decline in diversity (Figure 2) was observed during the transition from rural/agricultural and peri-urban environments to more anthropogenic zones in Bucharest, reflecting the expected detrimental impacts of human influence. Anthropization disrupts the natural balance of ecosystems, leading to species loss [36].
The natural regime and lotic character of stations 0, 1, and 9 positively influenced macrophyte diversity. In these areas, species richness and abundance were higher compared to other sections of the Colentina River, with emergent, floating, and submerged macrophytes being present. Lukács et al. [37] highlighted that ecosystem function and shoreline typology are crucial for freshwater biodiversity conservation, supporting a high number of macrophyte species. As the river transitioned from a natural to an urban anthropized regime, species diversity decreased. In peri-urban stations 2, 3, and 8, representing the transition between river and lake ecosystems, biodiversity was maintained at a moderate level. In particular, in Mogoșoaia Lake, the high coverage of T. natans could negatively impact the development of submerged plants like P. crispus, according to Yuan et al.’s [38] observations that T. natans proliferation can harm aquatic plant growth and community health.
A common feature of urban areas (stations 4–7) was the rarity of submerged species, with canopy structures dominated by emergent species like P. australis and, to a lesser extent, T. angustifolia. Anthropogenic influence negatively affected submerged species’ biodiversity and favored pollution-tolerant species like filamentous algae and Lemna sp. Throughout all of the investigated areas, reed was the dominant species, being well-adapted to various ecological conditions and present in all stations, including those with strong anthropogenic influences. This suggests that P. australis is an opportunistic species that thrives in both natural and anthropogenic environments. Conversely, another key species, T. angustifolia, was found in both river areas and lakes, with a preference for natural shores.
The dominance of emergent species like P. australis and T. angustifolia while submerged species become increasingly rare aligns with Sayer et al.’s [39] findings, highlighting a progressive reduction in submerged macrophyte species richness under anthropogenic disturbances and emphasizing the detrimental effects of nutrient loading. Other studies indicate that anthropogenic factors, including pollution and habitat alteration, significantly impact macrophyte diversity. Halabowski and Lewin [40] highlighted that hydromorphological transformations adversely affect vegetation in river ecosystems, reducing species richness. Akasaka et al. [41] found that land use changes in urbanized areas negatively influence the diversity of aquatic macrophytes. Overall, anthropogenic conditions adversely affect the biodiversity of submerged macrophytes, favoring pollution-tolerant species.
4.1.2. Physicochemical Parameters
The significant species distribution results in Colentina (Figure 3) showed that macrophyte development depends on environmental conditions. Factors such as depth, transparency, temperature, nutrient load, and water residence time are crucial in shaping both phytoplankton and macrophytes. The analysis revealed relationships between macrophytes and environmental factors, offering insights into how different species adapt and thrive in altered river conditions. B. umbellatus, S. erectum, and N. marina form a cluster associated with high temperatures, light, and high ammonium (NH4) concentrations, indicating a preference for habitats with sun exposure, high temperatures, and ample resources for growth. This demonstrates that a combination of environmental factors determines the development of different macrophyte groups.
The significance of turbidity in supporting the growth of duckweed and S. erectum can be explained by the increased access to nutrients in turbid waters. Additionally, the distinct preferences of P. crispus and T. natans for clearer, phosphorus-enriched waters suggest a broader tolerance for this nutrient. P. crispus actively contributes to maintaining clear water conditions through its nutrient absorption capabilities, while T. natans shows adaptability across various nutrient conditions but may be less effective at mitigating eutrophication effects when nutrient levels become excessively high [42,43,44,45].
4.1.3. Relationship with Phytoplankton Communities
At the level of primary aquatic producers, the competition for resources between macrophytes and phytoplankton was intense and influenced by various factors defining the investigated areas. Phytoplankton communities were significantly impacted by anthropogenic factors, leading to increased biomass and abundance of Chlorophyceae and Cyanobacteria. These conditions, characterized by prolonged high temperatures and extended periods of algal blooms, further exacerbated the competition (Table 5, Figure 4).
The higher quantitative presence of Chlorophyceae and Cyanobacteria in lakes compared to rivers indicates that lentic environmental factors (such as slow or stagnant water flow, shallow depth, temperature, light intensity, and nutrient levels) provide these algae with a competitive advantage over other primary producers in accessing resources (Table 2). In contrast, the flowing water and rich macrophyte vegetation in the Colentina River sectors may limit the growth and proliferation of these algae. Previous studies [46] have also shown that Chlorophyceae and Cyanobacteria dominate during algal blooms and adapt well to anthropogenic environmental conditions in the Colentina River. These prolonged algal blooms significantly impact aquatic ecosystems, leading to the restructuring of biotic components.
Despite these challenging conditions, some macrophytes have found strategic ways to occupy niches in hypereutrophic waterbodies (Table 6). For example, mesotrophic conditions stimulate the development of species like P. australis and T. angustifolia. Although the transition to a hypereutrophic state causes a population decline, these species demonstrate resilience. S. natans is present in very low abundance across oligotrophic, mesotrophic, and hypertrophic conditions, appearing only briefly during eutrophic conditions. Submerged species like C. demersum and P. natans show a progressive decrease in abundance as conditions shift from mesotrophic to eutrophic, with a sudden decline under hypereutrophic conditions.
According to Dubey and Dutta [47], macrophyte tolerance to eutrophication varies, favoring floating and emergent macrophytes over submerged ones. Sensitive species disappear from heavily affected areas, benefiting opportunistic species. These structural changes depend on factors such as morphometric parameters, size, depth, and nutrient availability.
Aquatic plants can play a major role in reducing the risks of cyanobacterial blooms. Human activities make aquatic ecosystems vulnerable to eutrophication, favoring harmful algal blooms (HABs) and biotic disruptions. The lower proportion of submerged macrophyte species in urban lakes compared to floating/emergent species indicates that anthropogenic pressures have negatively influenced their development. Submerged macrophytes are directly involved in competition with phytoplankton and in restoring optimal ecological conditions [15]. Their occasional presence in lakes suggests that changes in shore types have altered ecotonal habitats and limited growth opportunities.
In urban ecosystems, the high abundance of phytoplankton negatively impacts macrophytes. However, CCorA analysis showed a slight coexistence of these two primary producers (Figure 5). The relationships between them are complex and heavily influenced by anthropogenic pressures, varying by ecosystem type. Under these difficult conditions, allelopathic interactions may help macrophytes gain priority access to resources. For example, Celewicz-Gołdyn [48] found that C. demersum secretes allelopathic substances that significantly reduce phytoplankton presence nearby. Grazing can also affect phytoplankton population dynamics. Contrary to our results, macrophyte species often inhibit the development of diatoms while stimulating green algae. The spatial distribution of T. angustifolia and P. australis with diatoms can be explained by the presence of epiphytic species. Phytoplankton dynamics in aquatic ecosystems are influenced by macrophytes, with T. latifolia and P. australis preferred by species in open-water conditions [49,50]. Both phytoplankton and macrophytes respond to anthropogenic pressures simultaneously.
5. Conclusions
The varying degrees of urbanization along the Colentina River, influenced by local factors, shore types, and ecosystem types, have impacted the existing biota. Our results confirm that urbanization along the Colentina River causes ecological degradation, promotes the dominance of pollution-resistant macrophyte species, and significantly reduces biodiversity. These differences were notably influenced by anthropogenic pressures. Consequently, urban ecosystems were the most affected in terms of macrophytes and phytoplankton. Macrophytes exhibited reduced species richness and abundance compared to other areas near Bucharest, while phytoplankton were characterized by algal blooms, particularly involving cyanobacteria and green algae. The effects of human pressures on primary producers were evident from the presence of pollution-resistant species with high resilience, such as P. australis, T. angustifolia, and submerged P. crispus. Habitat alterations in urban areas of the Colentina River, due to changes in shoreline types and the introduction of characteristic pollutants, intensified the pressures on macrophytes. Therefore, the practice of sustainable management of urban aquatic ecosystems is recommended to mitigate the negative impacts of human activities, preserve ecological integrity, and improve ecosystem services.
Conceptualization, L.I.F., R.D.C. and M.M.M.; methodology, L.I.F., R.D.C., A.C.D. and M.M.M.; investigation, L.I.F., R.D.C., A.C.D. and M.M.M.; writing—original draft preparation, L.I.F., R.D.C. and M.M.M.; writing—review and editing, R.A.M. All authors have read and agreed to the published version of the manuscript.
All data generated during this study are included in this published article.
We thank Sofa Stela for technical support. We also thank the referees for their valuable comments.
The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
Footnotes
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Enlarge this image.Figure 1. Location of sampling points along the Colentina River. Yellow line—the administrative boundary of Bucharest (Google Earth).
Enlarge this image.Figure 2. Renyi diversity profiles of the ecosystems studied along the Colentina River course (Colentina River—rural; Crevedia branch—rural; Mogoșoaia—periurban; Plumbuita—urban; Fundeni—urban; Cernica lake—periurban; Cernica river—rural).
Enlarge this image.Figure 3. CCA with the relationship between environmental factors and macrophyte communities. * Species under European Council Directive 92/43/EEC 1992 protection.
Enlarge this image.Figure 4. The share of hypertrophic (H), eutrophic (E), mesotrophic (M), and oligotrophic (O) status to the characteristics of the studied ecosystems.
Enlarge this image.Figure 5. Canonical correlation analysis (CCorA) for the relationship between a phytoplanktonic component and the macrophytes community. In red—phytoplankton group densities (cells L−1) and chlorophyll-a (μg L−1), and in green—abbreviation of macrophytes.
Characterization of sampling points.
| Sampling Points | GPS Coordinates | River Sections | Geomorphological Traits | Local Influences |
|---|---|---|---|---|
| Station 0 | 44°36′22.6″ | Colentina river | River | Rural—with |
| Station 1 | 44°26′48.6″ | Crevedia branch | River | Rural—with |
| Station 2 | 44°31′23.9″ | Mogoșoaia | Lake | Peri-Urban |
| Station 3 | 44°31′25.4″ | Mogoșoaia | Lake | Peri-Urban |
| Station 4 | 44°28′30.4″ | Plumbuita | Lake | Urban |
| Station 5 | 44°28′8.5″ | Plumbuita | Lake | Urban |
| Station 6 | 44°26′55.6″ | Fundeni | Lake | Urban |
| Station 7 | 44°26′45.8″ | Fundeni | Lake | Urban |
| Station 8 | 44°26′04.8″ | Cernica | Lake | Peri-Urban |
| Station 9 | 44°24′48.5″ | Cernica | River | Rural—with mixed interference |
Average of physicochemical parameter values depending on the areas of the Colentina River evaluated during the study period.
| Parameter | Rural | Peri-Urban | Urban |
|---|---|---|---|
| Light (lux) | 51,990 ± 38,674.83 | 47,022.22 ± 37,759.86 | 54,905.28 ± 39,677.29 |
| Depth (m) | 0.97 ± 0.58 | 0.88 ± 0.45 | 0.75 ± 0.34 |
| Transparency (m) | 0.44 ± 0.18 | 0.47 ± 0.16 | 0.53 ± 0.22 |
| Turbidity | 26.12 ± 18.17 | 18.36 ± 5.57 | 18.88 ± 9.46 |
| Temperature (°C) (water) | 18.59 ± 6.43 | 19.58 ± 6.47 | 20.39 ± 6.35 |
| pH | 8.42 ± 0.81 | 8.67 ± 0.57 | 8.68 ± 0.48 |
| Water flow (m/s) | 0.10 ± 0.05 | 0.06 ± 0.00 | 0.06 ± 0.01 |
| Conductivity (μS/cm) | 495.56 ± 89.01 | 473.74 ± 83.66 | 497.47 ± 77.56 |
| DO (mg O2L−1) | 10.67 ± 15.99 | 8.18 ± 3.89 | 9.76 ± 8.54 |
| DO (%) | 77.30 ± 34.38 | 87.58 ± 39.84 | 92.93 ± 41.08 |
| ORP | 5.62 ± 55.13 | −7.97 ± 35.08 | −22.01 ± 27.14 |
| TDS | 251.68 ± 41.37 | 236.89 ± 41.82 | 248.64 ± 38.77 |
| NH4 (mg N-NH4 L−1) | 0.24 ± 0.27 | 0.29 ± 0.27 | 0.24 ± 0.25 |
| NO2 (mg N-NO2 L−1) | 0.04 ± 0.05 | 0.04 ± 0.05 | 0.03 ± 0.04 |
| NO3 (mg N-NO3 L−1) | 3.12 ± 1.88 | 2.63 ± 2.74 | 2.36 ± 1.52 |
| PO4 (mg P-PO4 L−1) | 0.10 ± 0.18 | 0.12 ± 0.17 | 0.10 ± 0.16 |
| P-total (mg P L−1) | 0.68 ± 0.45 | 0.72 ± 0.48 | 0.69 ± 0.45 |
The aquatic macrophyte composition of the Colentina River during the study.
| St0 | St1 | St2 | St3 | St4 | St5 | St6 | St7 | St8 | St9 | |
|---|---|---|---|---|---|---|---|---|---|---|
| Species Richness | 9 | 6 | 4 | 4 | 6 | 4 | 4 | 4 | 7 | 10 |
| Emergent | 4 | 5 | 2 | 2 | 2 | 0 | 3 | 2 | 2 | 4 |
| Butomus umbellatus L. | + | + | ||||||||
| Phragmites australis (Cav.) Trin. ex Steud | + | + | + | + | + | + | + | + | + | |
| Polygonum hydropiper L. | + | + | + | + | ||||||
| Scirpus lacustris L. | + | + | ||||||||
| Sparganium erectum L. | + | |||||||||
| Typha angustifolia L. | + | + | + | + | + | + | + | + | ||
| Floating | 1 | 1 | 1 | 1 | 1 | |||||
| Lemna sp. | + | + | + | |||||||
| Salvinia natans L. * | + | + | ||||||||
| Floating and submerged | 1 | 1 | 1 | 1 | ||||||
| Trapa natans L. * | + | + | ||||||||
| Potamogeton natans L. | + | + | ||||||||
| Submerged | 3 | 0 | 1 | 1 | 2 | 2 | 0 | 1 | 3 | 4 |
| Ceratophyllum demersum L. | + | + | + | + | + | |||||
| Najas marina L. * | + | + | + | + | ||||||
| Potamogeton crispus L. | + | + | + | + | + | + | ||||
| Stuckenia pectinata (L.) Böerner | + | + | ||||||||
| Filamentous algae | 1 | 1 | 1 | 1 | 1 | 1 |
* Species under European Council Directive 92/43/EEC 1992 protection; +—the presence of a species or genus.
Non-parametric Chi-squared test significances of the relationship between the ecosystem and the shore types, and local influences and macrophytes distribution (bold values are statistically significant p < 0.005).
| Ecosystem Type | Shore Type | Local Influences | |
|---|---|---|---|
| Emergent | |||
| Butomus umbellatus | 0.13 | 0.03 | 0.27 |
| Phragmites australis | <0.0001 | 0.0008 | <0.0001 |
| Polygonum hydropiper | <0.0001 | 0.01 | 0.0003 |
| Scirpus lacustris | 0.0002 | 0.006 | 0.002 |
| Sparganium erectum | 0.005 | 0.026 | 0.02 |
| Typha angustifolia | <0.0001 | <0.0001 | 0.0001 |
| Floating | |||
| Lemna sp. | 0.11 | 0.04 | 0.079 |
| Salvinia natans | 0.02 | 0.08 | 0.98 |
| Floating and submerged | |||
| Trapa natans | 0.349 | 0.188 | 0.018 |
| Potamogeton natans | 0.025 | 0.101 | 0.101 |
| Submerged | |||
| Ceratophyllum demersum | 0.182 | 0.508 | 0.301 |
| Najas marina | 0.225 | 0.073 | 0.448 |
| Potamogeton crispus | 0.992 | 0.569 | 0.217 |
| Stuckenia pectinata | 0.005 | 0.026 | 0.02 |
| Filamentous algae | 0.05 | 0.15 | 0.12 |
Biomass (µg L−1) and abundance averages (cells L−1) of phytoplankton groups in rural, peri-urban, and urban areas along the Colentina River.
| Biomass | Rural | Peri Urban | Urban |
|---|---|---|---|
| Total conc. Chlorophyll-a (µg L−1) | 47.96 | 71.32 | 65.63 |
| Chlorophyceae (µg L−1) | 21.32 | 38.79 | 33.08 |
| Cyanobacteria (µg L−1) | 6.93 | 8.82 | 12.56 |
| Bacillariophyceae (µg L−1) | 10.04 | 9.39 | 6.67 |
| Cryptophyta (µg L−1) | 9.66 | 14.32 | 13.33 |
| Abundance | |||
| Cyanobacteria (cells L−1) | 1.51 × 107 | 3.99 × 107 | 3.64 × 107 |
| Chlorophyceae (cells L−1) | 6.62 × 106 | 9.67 × 106 | 1.01 × 107 |
| Bacillariophyceae (cells L−1) | 3.59 × 106 | 5.73 × 106 | 2.89 × 106 |
| Euglenophyceae (cells L−1) | 2.07 × 105 | 8.81 × 104 | 1.11 × 105 |
| Dinophyceae (cells L−1) | 2.51 × 104 | 3.52 × 104 | 3.61 × 104 |
| Chrysophyceae (cells L−1) | 1.94 × 104 | 1.20 × 105 | 1.59 × 105 |
| Xanthophyceae (cells L−1) | 1.37 × 105 | 3.91 × 105 | 0 |
The results of ANCOVA analysis of the relationships between macrophytes development and phytoplankton content (expressed as Total Chlorophyll-a µg L−1 and the trophic state) (bold values are statistically significant p < 0.005).
| Chlorophyll a (µg L−1) | ||
|---|---|---|
| F-Value | p | |
| Emergent | ||
| Phragmites australis | 2.7939 | 0.0313 |
| Typha angustifolia | 4.697 | 0.002 |
| Floating | ||
| Salvinia natans | 7.540 | <0.0001 |
| Floating and submerged | ||
| Potamogeton natans | 7.677 | <0.0001 |
| Submerged | ||
| Ceratophyllum demersum | 4.776 | 0.002 |
Supplementary Materials
The following supporting information can be downloaded at:
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Details
; Catana, Rodica D 1
; Mihai, Raluca A 2
; Dumitrache, Alina C 1
; Moldoveanu, Mirela M 1
1 Institute of Biology Bucharest of Romanian Academy, 296 Splaiul Independentei, 060031 Bucharest, Romania;
2 Army Scientific and Technological Research Center—CICTE, Department of Life Science and Agriculture, Universidad de Las Fuerzas Armadas—ESPE, Av. General Ruminahui s/n y, Sangolqui 171103, Ecuador;