The effect of human disturbance on the community composition and diversity of aquatic plants in the tropical wetlands of Lake Tana, Ethiopia

doi:10.21203/rs.3.rs-1949250/v1

Download PDF

Research Article

The effect of human disturbance on the community composition and diversity of aquatic plants in the tropical wetlands of Lake Tana, Ethiopia

https://doi.org/10.21203/rs.3.rs-1949250/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

The aquatic plants in wetlands have been threatened by increasing human disturbances in recent decades. The present study investigates to what extent human disturbance affects the community composition and richness of aquatic plants in 3 different wetland types in Lake Tana, Ethiopia. We selected twelve wetlands representing 3 different wetland types (four lacustrine, four river mouth, and four riverine papyrus wetlands) and collected data on aquatic plant species richness and community composition, major local environmental variables, and the degree of human disturbance at multiple plots along three transects in each wetland during the dry and wet season of 2018. The unique and shared contributions of human disturbance, local environmental variables, and wetland type on variations in community compositions of aquatic plants in wetlands were investigated using variation partitioning analyses. The Overlap and Decreasing Fill (NODF) metric was used to estimate the nestedness in aquatic plant communities. A total of 113 aquatic plant species, belonging to 38 families, were identified across all wetlands during the dry and wet season. Wetland types explained the greatest proportion of variation in community composition, followed by human disturbance and local environmental variables. The species richness was negatively correlated with the overall degree of human disturbance, while NODF was positively correlated. Irrespective of the degree of human disturbance, papyrus swamps had systematically the highest species richness and supported clearly different plant communities, therefore conservation efforts should focus on these habitats. In addition, measures should be taken to restore the highly disturbed and species-poor river mouth wetlands.

species richness

community composition

aquatic plants

wetlands

Lake Tana

human disturbances

Wetlands are important ecosystems that provide multiple ecosystem services (Hu et al. 2017) and strongly contribute to global biodiversity (Keddy 2010). Aquatic plants are key components of wetland biodiversity and influence many structural and functional aspects of wetlands. They are diverse communities that actively regulate carbon and nutrient cycles (Marzocchi et al. 2019), enhance sedimentation of suspended particles and nutrients (Mereta et al. 2020; Sileshi et al. 2020), and control flood and shoreline erosion (Peel et al. 2019). Aquatic plants influence wetland biota across multiple trophic levels by providing habitat and food (Mendonça et al. 2013). Aquatic plants are also useful to humans as building and craft materials, biofuel, fodder, and medicinal plants (Dida 2017). Aquatic plants are regarded as foundation species in wetlands (Dayton 1972) and their progressive disappearance can result in a drastic change in community characteristics of associated biota and ecosystem functioning (Hilt et al. 2017). As a result, wetland management plans largely target the conservation and protection of plant diversity and coverage (Rodrigo 2021).

Wetlands virtually occur in all geographical regions on earth (Hu et al., 2017). In Ethiopia, wetlands can be found in all climatic regions, with the wetlands of Lake Tana (Fig. 1) being the second largest in the country after the Gambella wetlands (Menbere and Menbere 2018). In the Lake Tana region, wetlands cover approximately 248 km² and are found mostly along lakeshores, rivers, and stream banks (Mengistu 2018). Lake Tana and its associated wetlands have been designated as Ethiopia's fourth UNESCO Biosphere Reserve due to their high biodiversity (Kalmbach 2017), and the region is a major development corridor (Worqlul et al. 2015). Lake Tana is also the source of the Blue Nile River (Vijverberg et al. 2009). In addition, Lake Tana and its associated wetlands support multiple endemic Labeobarbus species, and other commercially important fish species (Mengistu et al., 2017; Nagelkerke & Sibbing, 2000; Sibbing et al., 1998). Importantly, the fisheries employ over 3,000 people and provide a significant source of food for the surrounding communities (Yalew and Spliethoe 2012). Lake Tana and the associated wetlands are also internationally known as an important bird areas (Zelelew and Archibald 2021) and are one of the country's main tourist destinations (Genet and Kebede 2021),. Apart from this, the wetlands of Lake Tana provide vital ecosystem services, such as sediment retention, nutrient trapping, and lakeshore stabilization, and they have cultural, recreational, and educational purposes (Mucheye et al. 2018; Wondie 2018). The wetlands are also an essential habitat for multiple taxonomic groups, including fish, benthic invertebrates, and birds (Getahun and Dejen 2012; Gezie et al. 2017; Zelelew and Archibald 2021).

Despite their high ecological and economic importance, the wetlands of Lake Tana have been increasingly threatened by rapidly growing human demands for food and raw materials (Mingist and Gebremedhin 2016; Wondie 2018). Water withdrawals, overgrazing, agriculture, human settlement expansion industrial waste discharges, and mining in and around these wetlands have been identified as threats to wetland biodiversity and ecosystem functioning (Wondie 2018; Zelelew et al. 2021). Water withdrawals and drainage for irrigation and hydropower activities significantly alter the hydrology of wetlands in the Lake Tana sub-basin (Worqlul et al. 2015; Taye et al. 2021). Reduced water levels and flows result in a loss of connectivity between the river, lake, and associated wetlands (Ekka et al. 2020), as well as habitat loss for wetland plants (Zhao et al. 2021). Overgrazing by livestock appears to remove above- and below-ground aquatic plant biomass, reduce litter accumulation, compact and disturb the soil, and promote erosion through mechanical disturbance of the soil surface (Pettit et al. 2012). Furthermore, overgrazing by livestock in wetlands has been shown to cause shifts in aquatic plant functional types, including a decrease in the abundance of tall and rhizomatous species and an increase in species with an annual lifecycle and short canopy height (Kutschker et al. 2014). Additional disturbances result from overexploitation and infestation by water hyacinth (Pontederia crassipes) (Abebe and Minale 2017). The latter is one of the world's worst aquatic weed and is rapidly spreading along the shorelines of Lake Tana. The area covered by water hyacinth increased from 112 ha in 2013 to 1512 ha in 2015 (Asmare et al. 2020).

Human disturbance altered the community compositions and reduced species richness of water birds and benthic invertebrates in the wetlands of Lake Tana (Gezie et al. 2017), Alamgano, Kofe, and Kito wetlands of southwestern Ethiopian (Chawaka et al. 2018), and Lake Ziway in Ethiopia (Wondmagegn and Mengistou 2020). Human disturbance can affect the aquatic plant community composition and species richness in multiple ways. For example, Sass et al.(2010) observed changes in aquatic plants community composition and reduced species richness in response to human disturbance in wetlands in northern and southern Wisconsin, USA, whereas others (Elo et al. 2018; Lindholm et al. 2020) did not find a relation between aquatic plants community composition and human disturbance in boreal lakes in Eastern Finland. The differential effect of human activities on aquatic plant community characteristics results from differences in the frequency, intensity, and scale of human disturbance, as well as the ecological characteristics of the species under study (Dubois et al. 2018). However, a profound understanding of the effects of human disturbance on aquatic plant species richness and community composition is critical for the development of an effective management plan that aims to conserve and restore wetlands in the Lake Tana region. Despite this, the aquatic plants are the least studied and understood component of wetland biodiversity in the Lake Tana region, except for a few studies dealing with macrophyte species richness and abundance in relation to physicochemical characteristics in the southwestern littoral zone of the lake (Getnet et al., 2021 and Kassa et al., 2021).

The present study aims to fill this important knowledge gap by investigating to what extent human disturbance affects aquatic plant species richness and community composition in three different wetland types of Lake Tana, namely (R) riverine papyrus swamps which are connected to a river, (RM) river mouth wetlands which are connected both to the tributary rivers and the lake; and (L) lacustrine wetlands which are primarily connected to the lake. We hypothesize that (i) human disturbance reduces aquatic plant species richness and (ii) alters the community composition of aquatic plants and (ii) increases nestedness patterns in aquatic plant communities across wetlands and plots

2.1. Study area

This study was conducted in 12 natural wetlands in the Lake Tana sub-basin, located in Northwest Ethiopia (Fig. 1). The sub-basin covers an area of 150,100 km², including the lake itself. The majority of annual rainfall is received during the main rainy season in June–September and the amount of rainfall varies from 800 to 1200 mm per year (Kebede et al. 2006). The mean annual air temperature is about 21°C. Over the last 40 years, there has been a decline in annual rainfall and an increase in annual average temperature (Addisu et al. 2015). The Lake Tana sub-basin is characterized by highly heterogeneous landscapes with a variety of ecosystems and is subjected to various types of land use. Dominant land cover in the region is cropland (7608.7 km²), waterbodies (2152.7 km²), settlement (2064.3 km²), bushland (1438.9 km²), grazing land (1242.1km²), and forest (546.9km²) (Tewabe and Fentahun 2020).

The selected wetlands represent three different wetland types: riverine papyrus swamps (n = 4), river mouth wetlands (n = 4), and lacustrine wetlands (n = 4). These are the three most common wetland types in the region. Lacustrine wetlands are associated with the shallow area of the lake and are partially covered by open water. They are mostly located on the lake's southern shore. River mouth wetlands are distributed along Lake Tana's main tributary rivers of Megech, Dirma, Gilgel-Abay, Ribb, and Gumara. River mouth wetlands are highly turbid, shallow, and warmer (Kahsay et al. 2022). Riverine papyrus swamps are distributed along the Gilgel Abay river and are recognized as a core zone of the Lake Tana biosphere reserve. These wetlands remain flooded well into the dry season.

2.2. Data collection: human disturbance, environmental variables, and aquatic plants

We collected information on environmental conditions and determined the plant community composition at multiple plots along three transects within each wetland during the dry (March to May) and wet (July to October) seasons of 2018. Data on the degree of human disturbance were collected at the same locations and almost simultaneously as the sampling for the environmental and aquatic plant data, but only during the dry season of the study period. Human activity in the Lake Tana wetlands is more intense and widespread during the dry season when the wetlands become more accessible as water levels decrease than during the wet season. However, given that human disturbance during the dry season can also affect plant community characteristics in the wet season, we also link patterns of community richness and composition as obtained during the wet season to human disturbance data collected during the dry season.

Three transect lines were established in each wetland using Google Earth. Transects covered the entire width of the wetland and started at the edge of the open water for lacustrine and river mouth wetlands and ended at the most outward part of the emergent plants that are associated with the wetland. In the riverine papyrus swamps, transects perpendicular to the flow direction were established. Six plots of 5m x 5m were established along each transect in each wetland and marked using a hand-held GPS. The plots were evenly distributed along the transect with distances between individual plots depending on the length of the transect.

The degree of different types of human disturbance was visually assessed in a 20-meter perimeter around each sampling plot during the dry season by categorizing human disturbance into ten categories (crop cultivation, livestock grazing, biomass harvesting, effluent discharge, waste dumping, water withdrawal, sand mining, tree plantation, open defecation, burning) (Table 1). The magnitude of each disturbance type was quantified on an ordinal scale (0 = not present, 1 = minimal, 2 = moderate, 3 = high; Hruby, 2004). The overall degree of human disturbance at the plot level was calculated by summing the scores of individual disturbance types.

Table 1

The different types of human activity considered in this study and their scoring on an ordinal scale
Disturbance activities	Score 0	Score 1	Score 2	Score 3
Crop cultivation	No cultivation	Minimal cultivation	Moderate cultivation	Highly cultivated
Livestock grazing	No grazing	Minimal grazing	Moderate grazing	Highly grazed
Biomass harvesting	No biomass harvesting	< 10% vegetation removal	10–50% of vegetation removal	> 50% vegetation removal
Effluent discharging	No effluents	Minimal effluents	Moderate effluents	High level of effluents discharge
Waste dumping	No waste dumping	Minimal waste dumping	Moderate waste dumping	High levels of waste disposal
Water withdrawals/pumping and diverting	No dewatering	Minimal dewatering/ pimping and diverting	Moderate dewatering/ Moderate pumping and diverting	Excessive water abstraction/ Excessive pumping and diverting
Sand mining	No sand mining	Minimal sand mining	Moderate sand mining activities	Excessive sand mining
Tree plantation	No tree plantation	Minimal tree plantation	Moderate tree plantation	Intensive tree plantation
Open defecations	No defecation	Minimal defecation	Moderate open defecation	Excessive open defecation
Burning/firing	No burning/firing	Minimal burning/firing	Moderate burning/firing	Excessive burning/firing

Water temperature, pH, specific conductance, and dissolved oxygen concentration (DO) were measured directly at each plot along the three transects in each wetland in the field using a multi-probe field meter (YSI 556 MPS). The concentration of Chlorophyll-a was used as a proxy of phytoplankton biomass and was measured in vivo in the field using a handheld fluorometer (AquaFluor™, Turner Designs). Similarly, water turbidity was measured directly in the field using aqualytic Turbidimeter (ALT250-IR). The water depth and sediment depth were measured with a wooden stick and a metal measuring tape.

The aquatic plant community composition was assessed in each plot in all wetlands during the wet and dry seasons by scoring the abundance of individual species using the Braun-Blanquet cover-abundance scale (with 5 = > 75 percent cover; 4 = 50–75 percent cover; 3 = 25–50 percent coverage; 2 = 5–25 percent coverage; 1 = numerous, but less than 5 percent coverage, or scattered, with cover up to 5 percent; + = few, with small cover; and r = rare, solitary, with low cover) (Van der Maarel 1979). The percent cover was estimated as the percentage of the sampling area covered by the vertical projection of individuals of each species present (Ellenberg and Mueller-Dombois 1974). Species identification was done in the field using Ethiopian flora books (Edwards et al. 1995, 2000). Specimens that were difficult to identify were collected, pressed, and transported to the National Herbarium at Addis Ababa University for more detailed inspection.

2.3. Data analysis

The association between wetland type and different types of human disturbance was first visually explored using an ordination plot of Principal Component Analyses (PCA) based on human disturbance data from individual plots within each wetland. The relation between wetland type and the overall degree of human disturbance was formally investigated using a linear mixed-effect model (LMM, lme4 R package, version 1.1–27.1) (Kuznetsova et al. 2017). Wetland type was treated as a fixed factor in the model, while wetland identity was included as a random factor The assumptions of normality and heterogeneity of variances were formally checked using a Shapiro-Wilk test and a Levene’s test respectively. The significance of the fixed effect (wetland type) in the LMM was tested using ANOVA, and differences between individual wetland types were further explored using Tukey-Kramer posthoc tests (multcomp package, version 1.4-1 ) (Kuznetsova et al. 2017). The P-values were adjusted following the Holm’s method to control for family-wise error rates associated with multiple comparisons.

Distance-based redundancy analyses (db-RDA) on Sørensen community distances were used to separately examine the effect of human disturbance and environmental variables on variation in aquatic plant community composition during the wet and dry seasons. The initial full model testing for the effect of environment on compositional variation included temperature, dissolved oxygen, specific conductance, water depth, sediment depth, pH, turbidity, and chlorophyll-a. The initial model testing for the effect of human disturbance included the different individual types of human disturbance. Significant explanatory variables were selected using the forward selection procedure using the function ordiR2step function in the vegan package (version 2.5-6) (Oksanen et al. 2019). db-RDA was conducted using the dbrda function from the vegan package. The significance of the models was assessed with 999 permutations using the anova function in vegan (version 2.5-6)(Oksanen et al. 2019). The db-RDA was based on the pooled data from aquatic plant community composition, human disturbance activities, and environmental variables at the wetland level (means across plots within the wetland). Additional db-RDA on Sørensen community distances were used to examine the effect of wetland types and wetland identity on variation in aquatic plant community composition during the wet and dry seasons.

We subsequently applied variation partitioning analyses on Sørensen community distances to assess the relative importance of unique and shared contributions of significant sets of explanatory variables (environment variables, individual types of human disturbance, identified with the above-mentioned forward selection procedure) and wetland type to variation in the aquatic plant community composition using varpart function in vegan (version 2.4-2) (Oksanen et al., 2017). The first analysis included environmental variables, human disturbance, and wetland type as separate sets of explanatory variables. A second variation partitioning analysis on Sørensen community distances also included wetland identity as an additional explanatory variable to consider unmeasured wetland-specific variables. The variation partitioning analyses were based on data from the pooled data from aquatic plant community composition, human disturbance activities, and environmental variables at the wetland level (means across plots within the wetland). Turbidity, water depth, and specific conductance were logarithmically transformed prior to the analyses to improve the normality of the data. Species data were Hellinger-transformed prior to the analyses (Legendre and Gallagher 2001).

In order to test whether variation in community composition reflects nestedness or turn-over patterns, we calculated the overall variation in aquatic plant community composition as Sørensen multiple sites dissimilarity coefficient for the entire study area for the dry and wet seasons separately using pooled data at the wetland level (means across plots within the wetland) following the approach proposed by Baselga et al., (2017) using the beta. sample in the beta part package version 1.5.6 (Baselga et al. 2018). Subsequently, the Sørensen dissimilarity was partitioned into its turnover (β_SIM) and nestedness (β_NES) components (Baselga 2010). It should be noted that the β_NES index is in fact a measure of the contribution of richness differences to overall community composition rather than of nestedness-resultant dissimilarity (Baselga 2010). The extent to which nestedness contributes to overall variation in community composition patterns can be calculated using the Nestedness metric based on the overlap and decreasing fill (NODF) (Almeida-Neto et al. 2008). The analyses based on Bray-Curtis (β_BC) dissimilarity yielded very similar results for variation in community composition (data not shown). The relationships of community composition to wetland types were inspected with Sørensen-based ordination (non-metric multidimensional scaling) from pooled data at the wetland level (means across plots within the wetland).

The degree to which plant communities in species poorer wetlands form nested subsets of communities in species richer wetlands was investigated using a Nestedness metric based on the overlap and decreasing fill (NODFwetlands; Almeida-Neto et al., 2008) based on presence/absence pooled data at the wetland level (means across plots within the wetland) using the ‘oecosimu’ function in vegan version 2.5-6 (Oksanen et al. 2019). The NODF value varies from 0 (no nestedness) to 100 (perfect nestedness). The rows and columns in the site by taxon matrix were ordered by the marginal totals and the significance of the nestedness patterns was tested by comparing the observed NODF value with those produced by null models (n = 1000) with proportional row and column totals using the Quasiswap algorithm (Gotelli and Entsminger 2001). This algorithm creates null matrices in which the rows and columns vary randomly, but in which the average row and column total in the generated matrices equals those of the original matrix (Matthews et al. 2015). The effect of human disturbance on nestedness patterns was investigated by correlating (spearman correlation) the nestedness wetland rank to the overall degree of human disturbance at the wetland level.

Differences in local aquatic plant species richness between wetland types and seasons were investigated using two-way ANOVA with Tukey’s HSD post hoc tests. Local richness was calculated as the mean local aquatic plant species richness at the wetland level by summing the number of recorded species at each plot and dividing it by the total plot number (means across plots within the wetland) for the dry and wet seasons separately. Normality and homogeneity of variances were examined by the Shapiro–Wilk test and Levene’s test, respectively. The effect overall degree of human disturbance and environmental variables on local aquatic plant species richness was investigated using multiple separate LMM’s for both the dry and wet seasons separately. In these analyses, aquatic plant local species richness was the response variable, while the mean overall human disturbance and mean values of environmental variables such as water depth, turbidity, chlorophyll a, pH, sediment depth, dissolved oxygen, specific conductance, and temperature were predictors variables. We used pooled data at the wetland level (means across plots within the wetland) for environmental variables, local species richness, and overall human disturbance score in this analysis. All environmental variables, except pH, were logarithmically transformed to improve the normality of the data.

Human disturbance and environmental variables were treated as fixed factors in the models, whereas wetland type was included as a random factor. We a priori checked for collinearly among multiple predictor variables. The residuals were checked for homogeneity of variance and normality. The results of LMMs on the relationship between mean overall human disturbance and local aquatic plant species richness were visualized using scatterplots prepared within the ggplot2 package (Wickham et al. 2016). All basic statistics were conducted in R version 3.6.3 (R CoreTeam, 2020), and ggpubr R package version 0.4.0 (Kassambara 2020).

3.1. Human disturbances in relation to wetland type

Livestock grazing was the most common human activity observed in the three wetland types, with livestock grazing being observed in 163 plots out of the 216 plots evaluated. Crop cultivation was the second most common human activity, with 94 of the plots showing clear signs of cultivation. Furthermore, water withdrawal was more common in river mouth wetlands, whereas biomass harvesting was more important in riverine papyrus swamps and lacustrine wetlands (Figs. 2 and Online Resource 2a). The overall human disturbance score was significantly higher in river mouth wetlands than in riverine papyrus swamps and lacustrine wetlands (Online Resource 2b). In addition, human disturbance in the river mouth and lacustrine wetlands was more profound along the shorelines compared to their open water sides. In papyrus swamps, the middle sections had less human disturbance than the shore areas. Despite this, multiple types of human disturbance were observed in the majority of plots in all investigated wetlands.

3.2. Relationships of aquatic plant community composition with human disturbances and environmental variables

A total of 113 aquatic plant species, belonging to 38 families, were found over the entire set of investigated plots during the dry and wet seasons (Online Resource 3). The aquatic plant family with the highest species diversity was Asteraceae with 21 species, followed by Cyperaceae (19 species), Poaceae, (17 species), and Fabaceae (4 species). Araceae, Nymphaeaceae, Onagraceae, Polygonaceae, and Potamogetonaceae are other families with three species each. The remaining twenty-eight families had two or one species (Online Resource 3). The most frequently recorded species were Cyperus papyrus (3.73% of the plots), Ludwigia adscendens (3.7% of the plots), Ludwigia leptocarpa (3.27% of the plots), Polygonum glabrum (3.13% of the plots), and Azolla pinnata (3.07% of the plots). Emergent, amphibious, free-floating, rooted floating, and submerged life forms were found in the area, and emergent life forms were the most representative aquatic plants, accounting for 73.45%, followed by amphibious life forms (9.73%). Free-floating (6.19%), rooted floating (5.31%), and submerged plants (5.31%) were also important (Online Resource 3).

db-RDA revealed that local environmental variables, human disturbances, wetland types, and wetland identity explained a significant proportion of the variation in community composition of aquatic plants during both the dry and wet seasons (Table 2). In addition, the NMDS plot revealed that different wetland types have different aquatic plant community compositions (Online Resource 4). Forward selection identified different sets of significant local environmental variables for the dry and wet season and human disturbance activities. Turbidity, pH, and specific conductance appeared to have a significant effect on the aquatic plant community composition in both seasons. Furthermore, temperature, DO, and water depth during the dry season, as well as sediment depth during the wet season, have a significant effect on the composition of the aquatic plant community. Livestock grazing, water withdrawals, sanding mining, effluent discharging, and biomass harvesting were identified as important variables determining variation in plant community composition during both the dry and wet seasons. Finally, crop cultivation was important during the wet season.

Table 2

Results of db-RDA’s separately testing for the effect of human disturbance, environmental variables, wetland type, and wetland identity on the community composition of aquatic plants.
Season	df		F	R 2 adj	p	Selected variables*
Dry	11	Human disturbances	3.41	0.18	0.001***	Livestock grazing, biomass harvesting, sand mining, water withdrawals, and effluent discharging
	7	Environmental variables	4.93	0.19	0.001***	Water depth, turbidity, pH, specific conductance, temperature, and DO
	2	Wetland type	24.68	0.29	0.001***
	11	Wetland ID	9.69	0.45	0.001***
Wet	11	Human disturbances	3.14	0.14	0.001***	Crop cultivation, livestock grazing, biomass harvesting, sand mining, water withdrawals, and effluent discharging
	7	Environmental variables	6.69	0.21	0.001***	Turbidity, pH, sediment depth, and specific conductance
	2	Wetland type	21.63	0.29	0.001***
	11	Wetland ID	10.59	0.43	0.001***
* Explanatory variables selected based on forward selection.

Variation partitioning analyses revealed that wetland type explained the largest amount of variation in community composition during both the wet and dry season (29% explained variation in both seasons), followed by local environmental variables (19% and 20% during dry and wet season respectively) and human disturbance (17% and 12% during dry and wet season respectively) (Fig. 3). Wetland type uniquely explained a rather large proportion of compositional variation (10%) in both seasons, but a considerable proportion of explained variation was shared with local environmental variables and/or human disturbance. Although human disturbance had a significant unique effect, the largest proportion of compositional variation explained by human disturbance was shared with wetland type and/or environment. The variation uniquely explained by the environment was rather small and a considerable proportion of variation explained by the environment was shared with wetland type and/or human disturbance. The overall patterns of variation explained by the three explanatory variable sets were very similar in both seasons. An additional variation partitioning also including wetland identity as an explanatory variable revealed that wetland id uniquely explained 13% and 10% of compositional variation in the dry and wet season respectively (Online Resource 5).

Sørensen dissimilarity for the entire dataset was 0.78 and 0.77 for the dry and wet seasons, respectively (Online Resource 6). The turnover component comprised the largest fraction of overall community dissimilarity during both seasons. The degree of nestedness obtained was 54 and 61 for the dry and wet seasons, respectively (Online Resource 6). The observed NODF was significantly lower than expected from the null models for both seasons (Online Resource 6; Fig. 4a and b). The wetland nestedness rank tended to be positively associated with the mean overall human wetland disturbance but the relation was not statistically significant (Fig. 4c and d).

3.3. The relation between local plant richness with wetland type, human disturbance, and environmental variables

Local plant species richness in the set of investigated wetlands ranged from 8 to 33 and differed significantly between wetland types (F = 9.3, df = 2, P = 0.001) and seasons (F = 4.89, df = 1, P = 0.04). The wetland type-season interaction was not significant (F = 0.37, df = 2, P = 0.69). Local richness was higher in riverine papyrus swamps and lacustrine wetlands than in river mouth wetlands. The local species richness was highest during the wet season (Fig. 5).

Local plant species richness was negatively correlated to mean overall human disturbance, but only during the dry season (Fig. 6a and b). Aquatic plant species richness is negatively related to turbidity and pH during both the dry and wet seasons (Online Resource 7), whereas water depth seemed to have a positive effect on species richness. Species richness was positively related to temperature and specific conductance during the dry season, and water depth, sediment depth, and chlorophyll-a during the wet season (Online Resource 7).

Wetlands are under threat primarily from a variety of human disturbances globally (Davidson et al., 2018; Xu et al., 2019), and this is particularly so in the tropical areas, mainly because of economic development and human population growth in low and middle-income regions. The present study investigated to what extent human disturbance affected aquatic plant species richness and community composition. Livestock grazing, cultivation, biomass harvesting, water withdrawals, and sand mining were the most common human disturbance activities in Lake Tana wetlands, especially during the dry season. However, the impact of these disturbances, especially water withdrawals and sand mining were greater in river mouth wetlands, resulting in turbid, shallower, and warmer local environmental conditions in these wetlands than in the other two wetland types. As a result, river mouth wetlands had a lower richness of local aquatic plant species and a very different community composition than the other two wetland types. Human disturbances altered the aquatic plant community composition in Lake Tana wetlands, supporting our primary hypothesis. Moreover, our second and third hypotheses were partially confirmed, as we discovered an increasing trend in nestedness patterns, and a decreasing trend as overall human disturbance increased.

Overall, wetland types explained the greatest proportion of variation in aquatic plant community composition, followed by human disturbance. Local environmental variables played a minor but significant role in explaining variation in aquatic plant community composition. The wetlands under consideration were highly variable in terms of overall human disturbance and environmental conditions (e.g., water depth, turbidity, specific conductance, and pH). Therefore, the high explained variation by wetland types may have been obtained because different aquatic plants required different habitat types and greater wetland heterogeneity may support a variety of aquatic plants (Grönroos et al. 2013; Bao et al. 2017; Soininen et al. 2018; Oikonomou and Stefanidis 2020). Much of this variation was co-explained by environmental and implies that some environmental conditions, such as water depth, turbidity, specific conductance, pH, and temperature, were specific to a particular wetland type. Riverine papyrus swamps, for example, were distinguished by high specific conductance and water depths, whereas river mouth wetlands were distinguished by high turbidity and temperature, and lacustrine wetlands by high pH. The variation in aquatic plant community composition in wetlands was also influenced by human disturbance. It explained slightly more variation during the dry season when water drawdowns made the wetlands more accessible to human activities than they did during the wet season. This finding is consistent with earlier studies highlighting the significant impact of human disturbance on aquatic plant community composition in wetlands. For example, Sievers et al.(2018) report that human disturbances were important in explaining compositional variation in aquatic plants in the wetlands of Yellow River in Henan Province of China. Much of this variation was co-explained by both environmental and wetland types. This is not surprising given that human disturbance frequently causes a change in local environmental conditions (Sievers et al. 2018). However, the shared explained variation between wetland type and human disturbance may imply that some human disturbance activities were wetland type specific. A significant portion (at least 60%) of the community variation in our dataset was unexplained by human disturbance, environmental factors, or wetland type. These unexplained components typically represent variables that were not quantified for the system, such as nutrients (e.g., TP, TN, carbon) Jones et al., 2012), aquatic weed infestation (e.,g Pontederia crassipes, Azolla spp.) (Stiers et al. 2011; Muthukrishnan and Larkin 2020), and other dispersal processes (Yuan et al. 2022).

Among human disturbances, crop cultivation, biomass harvesting, water withdrawals, and effluent discharge, livestock grazing, tree plantation (eucalyptus spp. and Cupressocyparis x leylandii), and sand mining (mining of any aggregate regardless of particle size) were significant in affecting the compositional variation of aquatic plant communities among studied wetlands. Livestock overgrazing in wetlands has been shown to result in the total loss of palatable grass and sedge species due to trampling (Davidson et al., 2017; Reiss et al., 2010). As a result, the less desirable herbaceous aquatic plants become the dominant species in heavily grazed wetlands (Teuber et al. 2013). Livestock overgrazing in wetlands also promotes the establishment of annual or short-lived perennial aquatic plant species (Grime 2006). However, if managed properly, livestock grazing in wetlands can lead to greater aquatic plant diversity (Van den Broeck et al. 2019). Also, crop cultivation had a significant impact on the community composition of aquatic plants in our study area. In river mouth wetlands, irrigation agriculture had been practiced to grow vegetables, fruits, khat, and other crops by extracting water from wetlands and diverting rivers that flow to lakes and wetlands (Abera et al. 2020). Water withdrawals have a significant impact on the hydrology of wetlands, which in turn affects the aquatic plant community composition (Taye et al. 2021). Water withdrawals have been found to cause a loss of connectivity between wetlands and rivers and lakes (Döll et al. 2009), and led to a decline in the water level of wetlands (Li et al., 2021), which affects the success of aquatic plants. Similarly, sand mining was common in river mouth wetlands, and it is known to directly remove aquatic plants while also altering soil profiles, changing the hydrology and topography of the wetlands, and changing nutrient concentrations in the wetlands (Koehnken et al. 2020).

In the present study, aside from different human disturbances, different sets of individual environmental variables influenced the community composition of aquatic plants. However, hydrology-related factors such as water depth, turbidity, and sediment depth, overall seemed to be the most important variables determining variation in community composition in aquatic plants among different wetland types. It is widely accepted that the community composition of aquatic plants is primarily influenced by water depth and related variables such as turbidity, and sediment depth (Maltchik et al. 2007; Chen et al. 2015). Variations in water depth, in particular, can have an impact on the establishment, growth, and survival of aquatic plants in wetlands (Casanova and Brock 2000). Generally, in our study area, spatial and seasonal variation in water levels caused variation in aquatic plant species richness and variations in community composition. For example, the wider range of water depths (5-350 cm) in papyrus swamps and increased water depth during the wet season in most of the studied wetlands supported a higher number of microhabitats which allowed the coexistence of emergent, floating, and submerged species with different water depth requirements (Temmink et al. 2021), that ultimately increased species richness (Rutherford et al. 2022). Water depth is also likely to influence aquatic plant community composition by altering other physicochemical variables in wetlands (such as turbidity, temperature, and specific conductance) in wetlands (Boeckman 2007).

Our results revealed that the pattern in variation in aquatic plant community composition was structured more by species replacement (turnover; where one species replaces another with no change in richness), while the contribution of nestedness (species richness differences) was small. Previous studies have also shown that the contribution of turnover components to community composition variation is greater in heterogenous habitats than that of the nestedness components in aquatic plant communities, including water bodies in southern China, and coastal ponds in southern Brazil (Bertuzzi et al. 2019; Sun et al. 2022). A meta-analysis of 21 lakes from different countries also found turnover pattern dominance in lake macrophytes community composition (Alahuhta et al. 2017). The importance of turnover in heterogeneous environments has also been reported for fish communities in the Upper Paraná River floodplain (Peláez et al. 2017), as well as benthic invertebrate communities in both protected and unprotected wetlands of southern Ethiopia (Chawaka et al., 2018). However, as overall human disturbance increased, the contribution of nestedness to aquatic plant community composition variation increased. This implies that if the current level of human disturbance persists, some species will become locally extinct in the future (Mligo 2017; Osawa et al. 2020). Previous studies have found that the nestedness was more evident in habitats disturbed by human activities (Leprieur et al. 2011; Gutiérrez-Cánovas et al. 2013; Si et al. 2015). Baselga. (2010) and Legendre. (2014) have also pointed out that the proportion of the nestedness becomes more discernible in community composition variation as human disturbance increases. Human disturbance can increase the contribution of nestedness in aquatic plant community composition, resulting in the replacement of exotic species and the loss of native species in aquatic plant communities in wetlands (Ehrenfeld 2008; Loiselle et al. 2020). In our study, for example, several native Cyperaceae species that were dominant in less disturbed riverine papyrus swamps and lacustrine wetlands were absent from river mouth wetlands, whereas exotic Pontederia crassipes was dominant in these wetlands. A previous study found that Pontederia crassipes infestation and expansion in river mouth wetlands is caused by high nutrient inputs from agricultural activities (Derseh et al. 2019). The dominance of Pontederia crassipes in highly stressed river mouth wetlands is expected because due to its ecophysiological adaptations that aid in the colonization of disturbed areas (Meneguelli-Souza et al. 2016).

Our analysis showed that aquatic plant species richness decreased as overall human disturbance increased. In addition, in comparison to less and moderately disturbed wetlands (i.e., riverine papyrus swamps and lacustrine wetlands), highly disturbed wetlands, particularly river mouth wetlands, had a relatively low species richness. Increased human disturbance has been shown to prevent some aquatic plant species from colonizing a site (Yang et al. 2017), change environmental conditions to make them unsuitable for some species (Luísa et al. 2020), and facilitate the spread of invasive species, which may increase competitive exclusion (Wang et al. 2021), resulting in low species richness. Similar to our findings, Zhang et al. (2018) reported a decrease in functional diversity in floodplain aquatic plants as a result of increased human impacts. Similarly, Sievers et al.(2018) reported that human disturbance was a significant factor influencing plant species diversity in Yellow River wetlands in Henan Province, China.

In conclusion, this study found that wetland types, human disturbance, and local environmental variables had a significant effect on aquatic plant species richness and community composition in studied wetlands. In addition, as overall human disturbance increased, the nestedness pattern showed an increasing trend. The turnover component suggests that all three-wetland types have potential conservation value. However, if some wetland types must be prioritized, we then recommend selecting the riverine papyrus swamps with high aquatic plant species richness and unique communities. Human disturbances such as livestock overgrazing, crop cultivation, biomass harvesting, and water withdrawals all had a significant effect on the variation in aquatic plant community composition. It should also be noted that these disturbances are likely to intensify and spread into currently less or moderately disturbed riverine papyrus swamps and lacustrine wetlands. Also, if not carefully planned and managed, ongoing, and planned hydropower and irrigation projects in the Lake Tana region have the potential to cause hydrological irregularities in the lake, its rivers, and associated wetlands. This suggests that if current trends of increasing human disturbance and changes in local environmental conditions continue unabated, their effects on aquatic plant species richness and community composition in wetlands will be greatly amplified. Therefore, these human disturbances should be controlled and kept to a minimum in these wetlands. In addition, we propose that wetland management strategies prioritize the conservation of riverine papyrus swamps and the restoration of highly degraded and currently species-poor river mouth wetlands.

Acknowledgments

The authors are grateful to Vlaamse Interuniversitaire Raad – Universitaire Ontwikkelingssamenwerking (VLIR-UOS) for financing this study. The first author was a recipient of an IUC (Institutional University Cooperation) Ph.D. scholarship from VLIR (ET2017IUC036A103) to carry out this work. Vrije Universiteit Brussel (VUB-BAS42) and Bahir Dar University are thanked for their financial and logistic support.

Author Contributions

All authors contributed to the study's conception and design. Material preparation, data collection, and analysis were performed by Abrehet Kahsay, Pieter Lemmens, and Iris Stiers. The first draft of the manuscript was written by Abrehet Kahsay, and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Funding

This study was financially supported by Vlaamse Interuniversitaire Raad – Universitaire Ontwikkelingssamenwerking (VLIR-UOS) (ET2017IUC036A103).

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation, to any qualified researcher. Some of the datasets generated for this study are included in the article/Supplementary Information.

Code availability

Not Applicable.

Ethics approval

Not applicable.

Conflict of interest

The authors declare that they have no conflict of interest to disclose.

Consent to participate

Not applicable.

Consent for publication

Not applicable.

Abebe WB, Minale AS (2017) Land use and watershed management practices in Lake Tana Basin. In: Social and Ecological System Dynamics. Springer, pp 479–521
Abera A, Verhoest NEC, Tilahun S, et al (2020) Assessment of irrigation expansion and implications for water resources by using RS and GIS techniques in the Lake Tana Basin of Ethiopia. Environmental monitoring and assessment 193:13. https://doi.org/10.1007/s10661-020-08778-1
Addisu S, Selassie YG, Fissha G, Gedif B (2015) Time series trend analysis of temperature and rainfall in lake Tana Sub-basin, Ethiopia. Environmental Systems Research 4:0–12. https://doi.org/10.1186/s40068-015-0051-0
Alahuhta J, Kosten S, Akasaka M, et al (2017) Global variation in the beta diversity of lake macrophytes is driven by environmental heterogeneity rather than latitude. Journal of Biogeography 44:1758–1769. https://doi.org/10.1111/jbi.12978
Almeida-Neto M, Guimaraes P, Guimaraes Jr PR, et al (2008) A consistent metric for nestedness analysis in ecological systems: reconciling concept and measurement. Oikos 117:1227–1239
Asmare T, Demissie B, Nigusse AG, GebreKidan A (2020) Detecting Spatiotemporal Expansion of Water Hyacinth (Eichhornia crassipes) in Lake Tana, Northern Ethiopia. Journal of the Indian Society of Remote Sensing 48:751–764. https://doi.org/10.1007/s12524-020-01107-6
Bao F, Leandro TD, Rocha M da, et al (2017) Plant species diversity in a Neotropical wetland: patterns of similarity, effects of distance, and altitude. Anais da Academia Brasileira de Ciências 90:85–97
Baselga A (2010) Partitioning the turnover and nestedness components of beta diversity. Global ecology and biogeography 19:134–143
Baselga A, Orme D, Villeger S, et al (2018) Package ‘betapart.’ betapart: Partitioning Beta Diversity into Turnover and Nestedness Components. R package version 1.5.1 1
Baselga A, Orme D, Villeger S, et al (2017) Partitioning beta diversity into turnover and nestedness components. Package betapart, Version 1–4
Bertuzzi T, Marques Pires M, Maltchik L (2019) Drivers of the beta diversity of aquatic plant communities along a latitudinal gradient in southern Brazilian coastal ponds. Journal of Vegetation Science 30:281–290
Boeckman CJ (2007) Spatial and seasonal variability in the water quality characteristics of an ephemeral wetland. In: Proceedings of the Oklahoma Academy of Science. pp 45–54
Casanova MT, Brock MA (2000) How do depth, duration and frequency of flooding influence the establishment of wetland plant communities? Plant ecology 147:237–250
Chawaka SN, Boets P, Goethals PLM, Mereta ST (2018) Does the protection status of wetlands safeguard diversity of macroinvertebrates and birds in southwestern Ethiopia? Biological Conservation 226:63–71
Chen X, Li X, Xie Y, et al (2015) Combined influence of hydrological gradient and edaphic factors on the distribution of macrophyte communities in Dongting Lake wetlands, China. Wetlands Ecology and Management 23:481–490. https://doi.org/10.1007/s11273-014-9396-9
Davidson KE, Fowler MS, Skov MW, et al (2017) Livestock grazing alters multiple ecosystem properties and services in salt marshes: A meta-analysis. Journal of Applied Ecology 54:1395–1405
Davidson NC, Fluet-Chouinard E, Finlayson CM (2018) Global extent and distribution of wetlands: trends and issues. Marine and Freshwater Research 69:620–627
Dayton PK (1972) Toward an understanding of community resilience and the potential effects of enrichments to the benthos at McMurdo Sound, Antarctica. In: Proceedings of the colloquium on conservation problems in Antarctica. Blacksberg, VA, pp 81–96
Derseh MG, Tilahun S, Worqlul AW, Moges MA (2019) Potential of Water Hyacinth Infestation on Lake Tana, Ethiopia : A Prediction Potential of Water Hyacinth Infestation on Lake Tana, Ethiopia : A Prediction Using a GIS-Based Multi-Criteria Technique. Water 11:1–17. https://doi.org/10.3390/w11091921
Dida G (2017) Floristic Composition of Wetland Plants and Ethnomedicinal Plants of Wonchi District, South Western Shewa, Oromia Regional State, Ethiopia. M. Sc. Thesis, Addis Ababa University, Addis Ababa
Döll P, Fiedler K, Zhang J (2009) Global-scale analysis of river flow alterations due to water withdrawals and reservoirs. Hydrology and Earth System Sciences 13:2413–2432
Dubois N, Saulnier-Talbot É, Mills K, et al (2018) First human impacts and responses of aquatic systems: A review of palaeolimnological records from around the world. The Anthropocene Review 5:28–68
Edwards S, Tadese M, Hedberg I (1995) Flora of Ethiopia and Eritrea vol. 2, Part 2: canellaceae to euphorbiaceae. AAU
Edwards S, Tadesse M, Demissew S, Hedberg I (2000) Flora of Ethiopia and Eritrea. Magnoliaceae to Flacourtiaceae, Vol. 2, Part 1. Addis Ababa, Ethiopia, and Department of Systematic Botany, Uppsala, Sweden: The National Herbarium
Ehrenfeld JG (2008) Exotic invasive species in urban wetlands: environmental correlates and implications for wetland management. Journal of Applied Ecology 45:1160–1169
Ekka A, Pande S, Jiang Y, Zaag P van der (2020) Anthropogenic modifications and river ecosystem services: A landscape perspective. Water (Switzerland) 12:1–21. https://doi.org/10.3390/w12102706
Ellenberg D, Mueller-Dombois D (1974) Aims and methods of vegetation ecology. Wiley New York
Elo M, Alahuhta J, Kanninen A, et al (2018) Environmental characteristics and anthropogenic impact jointly modify aquatic macrophyte species diversity. Frontiers in Plant Science 9:1–15. https://doi.org/10.3389/fpls.2018.01001
Genet A, Kebede M (2021) Collections, local interactions, conservation and tourism aspects of monastic heritage sites in the Lake Tana region of Ethiopia: the case of Mandeba Medahinealem Monastery. Journal of Cultural Heritage Management and Sustainable Development
Getahun A, Dejen E (2012) Fishes of Lake Tana: a guide book. Addis Ababa University Press
Getnet H, Mengistou S, Warkineh B (2021) Diversity of macrophytes in relation to environmental conditions in wetlands along the lower part of the Gilgel Abay River catchment in Ethiopia. African Journal of Aquatic Science 46:1–12
Gezie A, Anteneh W, Dejen E, Mereta ST (2017) Effects of human-induced environmental changes on benthic macroinvertebrate assemblages of wetlands in Lake Tana Watershed, Northwest Ethiopia. Environmental monitoring and assessment 189:152
Gotelli NJ, Entsminger GL (2001) Swap and fill algorithms in null model analysis: rethinking the knight’s tour. Oecologia 129:281–291
Grime JP (2006) Plant strategies, vegetation processes, and ecosystem properties. John Wiley & Sons
Grönroos M, Heino J, Siqueira T, et al (2013) Metacommunity structuring in stream networks: roles of dispersal mode, distance type, and regional environmental context. Ecology and evolution 3:4473–4487
Gutiérrez-Cánovas C, Millán A, Velasco J, et al (2013) Contrasting effects of natural and anthropogenic stressors on beta diversity in river organisms. Global Ecology and Biogeography 22:796–805
Hilt S, Brothers S, Jeppesen E, et al (2017) Translating regime shifts in shallow lakes into changes in ecosystem functions and services. BioScience 67:928–936
Hruby T (2004) Washington State Wetland Rating System for Western Washington. Washington State Department of Ecology
Hu S, Niu Z, Chen Y, et al (2017) Global wetlands: Potential distribution, wetland loss, and status. Science of the Total Environment 586:319–327. https://doi.org/10.1016/j.scitotenv.2017.02.001
Jones JI, Collins AL, Naden PS, Sear DA (2012) The relationship between fine sediment and macrophytes in rivers. River Research and Applications 28:1006–1018
Kahsay A, Lemmens P, Triest L, et al (2022) Plankton Diversity in Tropical Wetlands Under Different Hydrological Conditions (Lake Tana, Ethiopia). Frontiers in Environmental Science 10:1–18
Kalmbach E (2017) Establishment of the Lake Tana biosphere reserve within the UNESCO world network of biosphere reserves. In: Social and ecological system dynamics. Springer, pp 523–544
Kassa Y, Mengistu S, Wondie A, Tibebe D (2021) Distribution of macrophytes in relation to physico-chemical characters in the south western littoral zone of Lake Tana, Ethiopia. Aquatic Botany 170:103351. https://doi.org/https://doi.org/10.1016/j.aquabot.2020.103351
Kassambara A (2020) ggpubr: “ggplot2” Based Publication Ready Plots.R package version 0.4.0.999.https://rpkgs.datanovia.com/ggpubr/
Kebede S, Travi Y, Alemayehu T, Marc V (2006) Water balance of Lake Tana and its sensitivity to fluctuations in rainfall, Blue Nile basin, Ethiopia. Journal of Hydrology 316:233–247. https://doi.org/10.1016/j.jhydrol.2005.05.011
Keddy PA (2010) Wetland ecology: principles and conservation. Cambridge University Press
Koehnken L, Rintoul M, Goichot M, et al (2020) Impacts of riverine sand mining on freshwater ecosystems: A review of the scientific evidence and guidance for future research. River Research and Applications 36:. https://doi.org/10.1002/rra.3586
Kutschker AM, Epele LB, Miserendino ML (2014) Aquatic plant composition and environmental relationships in grazed Northwest Patagonian wetlands, Argentina. Ecological Engineering 64:37–48. https://doi.org/https://doi.org/10.1016/j.ecoleng.2013.12.007
Kuznetsova A, Brockhoff PB, Christensen RHB (2017) lmerTest package: tests in linear mixed effects models. Journal of statistical software 82:1–26
Legendre P (2014) Interpreting the replacement and richness difference components of beta diversity. Global Ecology and Biogeography 23:1324–1334
Legendre P, Gallagher ED (2001) Ecologically meaningful transformations for ordination of species data. Oecologia 129:271–280
Leprieur F, Tedesco PA, Hugueny B, et al (2011) Partitioning global patterns of freshwater fish beta diversity reveals contrasting signatures of past climate changes. Ecology letters 14:325–334
Li Q, Lai G, Devlin AT (2021) A review on the driving forces of water decline and its impacts on the environment in Poyang Lake, China. Journal of Water and Climate Change 12:1370–1391
Lindholm M, Alahuhta J, Heino J, Toivonen H (2020) No biotic homogenisation across decades but consistent effects of landscape position and pH on macrophyte communities in boreal lakes. Ecography 43:294–305
Loiselle A, Pellerin S, Poulin M (2020) Impacts of urbanization and agricultural legacy on taxonomic and functional diversity in isolated wetlands. Wetlands Ecology and Management 28:19–34
Luísa A, Fares B, Batista L, et al (2020) Environmental factors a ff ect macrophyte diversity on Amazonian aquatic ecosystems inserted in an anthropogenic landscape. Ecological Indicators 113:106231. https://doi.org/10.1016/j.ecolind.2020.106231
Maltchik L, Rolon AS, Schott P (2007) Effects of hydrological variation on the aquatic plant community in a floodplain palustrine wetland of southern Brazil. Limnology 8:23–28. https://doi.org/10.1007/s10201-006-0192-y
Marzocchi U, Benelli S, Larsen M, et al (2019) Spatial heterogeneity and short-term oxygen dynamics in the rhizosphere of Vallisneria spiralis: Implications for nutrient cycling. Freshwater Biology 64:532–543
Matthews TJ, Sheard C, Cottee-Jones HEW, et al (2015) Ecological traits reveal functional nestedness of bird communities in habitat islands: a global survey. Oikos 124:817–826
Menbere IP, Menbere TP (2018) Wetland ecosystems in Ethiopia and their implications in ecotourism and biodiversity conservation. Journal of Ecology and the Natural Environment 10:80–96
Mendonça R, Kosten S, Lacerot G, et al (2013) Bimodality in stable isotope composition facilitates the tracing of carbon transfer from macrophytes to higher trophic levels. Hydrobiologia 710:205–218
Meneguelli-Souza AC, Vitória AP, Vieira TO, et al (2016) Ecophysiological responses of Eichhornia crassipes (Mart.) Solms to As5 + under different stress conditions. Photosynthetica 54:243–250
Mengistu AA, Aragaw C, Mengist M, Goshu G (2017) The fish and the fisheries of Lake Tana.Ethiopia. In: Stave K, Goshu G, Aynalem S (eds) Social and ecological system dynamics. Springer, pp 157–177
Mengistu W (2018) A First Directory of Ethiopian Wetlands:Descriptions, Ecosystem Services, Causes of Degradation & Recommendations for Restoration and Sustainability
Mereta ST, De Meester L, Lemmens P, et al (2020) Sediment and Nutrient Retention Capacity of Natural Riverine Wetlands in Southwest Ethiopia. Frontiers in Environmental Science 8:1–12. https://doi.org/10.3389/fenvs.2020.00122
Mingist M, Gebremedhin S (2016) Could sand mining be a major threat for the declining endemic Labeobarbus species of Lake Tana, Ethiopia? Singapore Journal of Tropical Geography 37:195–208. https://doi.org/10.1111/sjtg.12150
Mligo C (2017) Diversity and distribution pattern of riparian plant species in the Wami River system, Tanzania. Journal of Plant Ecology 10:259–270. https://doi.org/10.1093/jpe/rtw021
Mucheye T, Yitaferu B, Zenebe A (2018) Significance of wetlands for sediment and nutrient reduction in Lake Tana Sub-Basin, Upper Blue Nile Basin, Ethiopia. Sustainable Water Resources Management 4:567–572
Muthukrishnan R, Larkin DJ (2020) Invasive species and biotic homogenization in temperate aquatic plant communities. Global Ecology and Biogeography 29:656–667
Nagelkerke LAJ, Sibbing FA (2000) The large barbs (Barbus spp., Cyprinidae, Teleostei) of Lake Tana (Ethiopia), with a description of a new species, Barbus osseensis. Netherlands Journal of Zoology 50:179–214
Oikonomou A, Stefanidis K (2020) Α-and Β-Diversity Patterns of Macrophytes and Freshwater Fishes Are Driven By Different Factors and Processes in Lakes of the Unexplored Southern Balkan Biodiversity Hotspot. Water (Switzerland) 12:. https://doi.org/10.3390/w12071984
Oksanen J, Blanchet FG, Friendly M, et al (2017) vegan: Community Ecology Package, 2.4-2. Online [URL] http://CRAN. R-project. org/package = vegan
Oksanen J, Blanchet FG, Kindt R, et al (2019) Package ‘vegan.’ vegan: Community Ecology Package. R package version 2.5-6.
Osawa T, Nishida T, Oka T (2020) Paddy fields located in water storage zones could take over the wetland plant community. Scientific Reports 10:14806. https://doi.org/10.1038/s41598-020-71958-z
Peel RA, Hill JM, Taylor GC, Weyl OLF (2019) Food web structure and trophic dynamics of a fish community in an ephemeral floodplain lake. Frontiers in Environmental Science 7:192
Peláez OE, Azevedo FM, Pavanelli CS (2017) Environmental heterogeneity explains species turnover but not nestedness in fish assemblages of a Neotropical basin. Acta Limnologica Brasiliensia 29:
Pettit NE, Jardine TD, Hamilton SK, et al (2012) Seasonal changes in water quality and macrophytes and the impact of cattle on tropical floodplain waterholes. Marine and Freshwater Research 63:788–800
R CoreTeam (2020) R: A Language and Environment for Statistical Computing.R Foundation for Statistical Computing, Vienna, Austria.URL https://www.R-project.org/
Reiss KC, Brown MT, Lane CR (2010) Characteristic community structure of Florida’s subtropical wetlands: the Florida wetland condition index for depressional marshes, depressional forested, and flowing water forested wetlands. Wetlands Ecology and Management 18:543–556
Rodrigo MA (2021) Wetland restoration with hydrophytes: A review. Plants 10:1035
Rutherford R, Hartsock JA, Danz NP (2022) Physical and plant community changes at a Lake Michigan coastal marsh related to a two-meter increase in lake level. Wetlands Ecology and Management 1–14
Sass LL, Bozek MA, Hauxwell JA, et al (2010) Response of aquatic macrophytes to human land use perturbations in the watersheds of Wisconsin lakes, USA. Aquatic Botany 93:1–8
Si X, Baselga A, Ding P (2015) Revealing beta-diversity patterns of breeding bird and lizard communities on inundated land-bridge islands by separating the turnover and nestedness components. PLoS One 10:e0127692
Sibbing FA, Nagelkerke LAJ, Stet RJM, Osse JWM (1998) Speciation of endemic Lake Tana barbs (Cyprinidae, Ethiopia) driven by trophic resource partitioning; a molecular and ecomorphological approach. Aquatic Ecology 32:217–227
Sievers M, Hale R, Parris KM, Swearer SE (2018) Impacts of human-induced environmental change in wetlands on aquatic animals. Biological Reviews 93:529–554
Sileshi A, Awoke A, Beyene A, et al (2020) Water purifying capacity of natural riverine wetlands in relation to their ecological quality. Frontiers in Environmental Science 8:39
Soininen J, Heino J, Wang J (2018) A meta-analysis of nestedness and turnover components of beta diversity across organisms and ecosystems. Global Ecology and Biogeography 27:96–109
Stiers I, Crohain N, Josens G, Triest L (2011) Impact of three aquatic invasive species on native plants and macroinvertebrates in temperate ponds. Biological Invasions 13:2715–2726
Sun J, Doeser A, Cao Y, et al (2022) Regional macrophyte diversity is shaped by accumulative effects across waterbody types in southern China. Aquatic Botany 176:103468. https://doi.org/https://doi.org/10.1016/j.aquabot.2021.103468
Taye MT, Haile AT, Fekadu AG, Nakawuka P (2021) Effect of irrigation water withdrawal on the hydrology of the Lake Tana sub-basin. Journal of Hydrology: Regional Studies 38:100961
Temmink RJM, Dorenbosch M, Lamers LPM, et al (2021) Growth forms and life-history strategies predict the occurrence of aquatic macrophytes in relation to environmental factors in a shallow peat lake complex. Hydrobiologia 848:3987–3999
Teuber LM, Hölzel N, Fraser LH (2013) Livestock grazing in intermountain depressional wetlands—Effects on plant strategies, soil characteristics and biomass. Agriculture, Ecosystems & Environment 175:21–28. https://doi.org/https://doi.org/10.1016/j.agee.2013.04.017
Tewabe D, Fentahun T (2020) Assessing land use and land cover change detection using remote sensing in the Lake Tana Basin, Northwest Ethiopia. Cogent Environmental Science 6:1778998
Van den Broeck M, Rhazi L, Waterkeyn A, et al (2019) Livestock disturbances in Mediterranean temporary ponds: A mesocosm experiment with sheep manure and simulated trampling. Freshwater biology 64:856–869
Van der Maarel E (1979) Transformation of cover-abundance values in phytosociology and its effects on community similarity. Vegetatio 39:97–114
Vijverberg J, Sibbing FA, Dejen E (2009) Lake Tana: Source of the Blue Nile BT - The Nile: Origin, Environments, Limnology and Human Use. In: Dumont HJ (ed). Springer Netherlands, Dordrecht, pp 163–192
Wang Y, Tan W, Li B, et al (2021) Habitat alteration facilitates the dominance of invasive species through disrupting niche partitioning in floodplain wetlands. Diversity and Distributions 27:1861–1871
Wickham H, Chang W, Wickham MH (2016) Package ‘ggplot2.’ Create Elegant Data Visualisations Using the Grammar of Graphics. 2:1–189
Wondie A (2018) Ecological conditions and ecosystem services of wetlands in the Lake Tana Area, Ethiopia. Ecohydrology & Hydrobiology 18:231–244. https://doi.org/https://doi.org/10.1016/j.ecohyd.2018.02.002
Wondmagegn T, Mengistou S (2020) Effects of anthropogenic activities on macroinvertebrate assemblages in the littoral zone of Lake Hawassa, a tropical Rift Valley Lake in Ethiopia. Lakes & Reservoirs: Research & Management 25:61–71
Worqlul AW, Collick AS, Rossiter DG, et al (2015) Assessment of surface water irrigation potential in the Ethiopian highlands: The Lake Tana Basin. Catena 129:76–85
Xu T, Weng B, Yan D, et al (2019) Wetlands of international importance: Status, threats, and future protection. International Journal of Environmental Research and Public Health 16:1818
Yalew A, Spliethoe P (2012) The Contribution of Small Scale Fisheries in Rural Food Security and Livelihood Improvements; The Experiences of Fish For All (Local NGO)-Ethiopia
Yang N, Zhang Y, Duan K (2017) Effect of Hydrologic Alteration on the Community Succession of Macrophytes at Xiangyang Site, Hanjiang River, China. Scientifica 2017: https://doi.org/10.1155/2017/4083696
Yuan Z, Xiao M, Su X, et al (2022) Effects of Environment and Human Activities on Plant Diversity in Wetlands along the Yellow River in Henan Province, China. Diversity 14:470
Zelelew SA, Abebe WB, Amsalu T (2021) Land-use cover change impact on Cranes nesting space in the Lake Tana Biosphere Reserve area, Blue Nile Basin. Wetlands Ecology and Management 1–11
Zelelew SA, Archibald G (2021) Nest characteristics and morphometry of Black Crowned Cranes Balearica pavonina ceciliae in Lake Tana area wetlands. African Zoology 1:58–64
Zhao F, Fang X, Zhao Z, Chai X (2021) Effects of water level fluctuations on the growth characteristics and community succession of submerged macrophytes: A case study of yilong lake, china. Water (Switzerland) 13:. https://doi.org/10.3390/w13202900

No competing interests reported.

SupplementaryInformation.docx

Download PDF

Version 1

posted

You are reading this latest preprint version

The effect of human disturbance on the community composition and diversity of aquatic plants in the tropical wetlands of Lake Tana, Ethiopia

Status:

Version 1

Abstract

Figures

1. Introduction

2. Material And Methods

2.1. Study area

2.2. Data collection: human disturbance, environmental variables, and aquatic plants

2.3. Data analysis

3. Results

3.1. Human disturbances in relation to wetland type

3.2. Relationships of aquatic plant community composition with human disturbances and environmental variables

3.3. The relation between local plant richness with wetland type, human disturbance, and environmental variables

4. Discussion

5. Conclusion

Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1