Macrophyte Cover Research Articles

Water quality parameters affect dynamics of phytoplankton functional groups in Lake Hawassa, Ethiopia

The water quality of Lake Hawassa has been deteriorating due to high influent loads from various sources, including influents of a hospital, industries, hotels, and agricultural runoff, which can induce changes in Reynolds functional groups of phytoplankton (RFGs). The functional associations of algae can also be affected by the dominant zooplankton and macrophytes coverage. RFGs (species with similar ecological requirements) are indicative of water quality but have not been studied in Lake Hawassa. The functional approach detects stressor-induced changes in phytoplankton assemblages more effectively than taxonomy-based methods due to its higher discriminatory power. The main objective of this study was, therefore, to investigate the factors affecting the dynamics of RFGs in Lake Hawassa through monthly sampling (April–August in 2019) from four sites. A total of 130 species of phytoplankton were identified and classified into 17 RFGs. The dominant ten RFGs (D, J, K, LO, M, N, P, SN, TD,and W2) contributed 96.1% of the total fresh weight biomass. Redundancy analysis indicated that the RFGs were correlated significantly with electrical conductivity, dissolved oxygen, pH, turbidity, Secchi depth, and total phosphorus revealing the overriding importance of these parameters in influencing the dynamics of the algal functional assemblage in Lake Hawassa. The results supported our hypothesis that the biotic and the human-induced abiotic factors have significant impact on RFGs. Our findings could serve as baseline information for efforts directed toward water quality improvements.

Dense macrophyte cover has significant structural and functional influence on planktonic microbial communities leading to bacterial success

We intend to assess how macrophyte cover affects planktonic microbial communities by changing the physical and chemical environment, and how macrophyte-derived DOC affects the balance between autotrophy and heterotrophy/chemoorganotrophy in a shallow lake. The structure and production of phytoplankton and bacterioplankton in the open water of a large shallow lake and in the littoral zone were compared at two sampling stations with different macrophyte cover. According to the obtained results, uncoupling between bacterioplankton and phytoplankton was observed due to the high content of organic carbon of emergent macrophyte origin. While phytoplankton were regulated by TSS, bacterioplankton (in both heterotrophic and photoheterotrophic forms) were determined by dissolved organic carbon. As a result of these processes, the littoral and pelagic zones in the lake are completely separated from each other. In open water the autotrophic processes dominated, but at the sampling stations inside the reed belt, the metabolic processes shifted in the direction of chemoorganotrophy. Our results suggest that increase of macrophyte cover in shallow water bodies will increase the significance of microbe-based carbon pathways and weakens the efficiency of carbon transport from primary producers to higher trophic levels through the planktonic food chain.

Evaluation of Macrophyte Community Dynamics (2015–2020) in Southern Lake Garda (Italy) from Sentinel-2 Data

Macrophytes are of fundamental importance to the functioning of lake ecosystems. They provide structure, habitat, and a food source and are a required component in monitoring programs of lake ecological quality. The key aim of this study is to document the variation in spatial extent and density of macrophytes seasonally between 2015 and 2020 of the Sirmione Peninsula (Lake Garda, Italy), using Sentinel-2 imagery. In addition to this, our results were compared to previous data from imaging spectrometry; individual parameters affecting macrophyte communities were tested, and the possible effect of the COVID-19 lockdown on macrophyte colonization was evaluated. Satellite images allowed the mapping of the spatiotemporal dynamics of submerged rooted macrophytes in order to support monitoring of the shallow water ecosystem under study. Substantial changes were found in both spatial extent and density over the period from 2015 to 2020, particularly in 2019 when there was almost a complete absence of dense macrophytes. Variables found to influence the amount of macrophytes included transparency, chlorophyll–a, water level, winter wave height, and grazing by herbivores. A separate analysis focusing on areas associated with boat transit found a recovery in macrophyte coverage during the period of COVID-19 lockdown. The outcome of the study highlights a decline in the density of the macrophytes and a shift towards deeper areas compared to the situation in 1997. The area examined is part of an internationally important site containing the highest abundance and diversity of overwintering water birds in Italy. Exploiting satellite data at high frequency provided an insight to understand the dynamic changes and interactions with herbivorous birds, environmental factors, and anthropogenic pressures, revealing a delicately balanced and threatened ecosystem.

Abundance and nutritional status of freshwater turtles to guide delivery of environmental flows in the Murray‐Darling Basin, south‐eastern Australia

Abstract Almost half of Australian freshwater turtle species are formally listed as threatened, but little is known about the effects of water management and other factors on the abundance and health of freshwater turtles in arid and semi‐arid regions. This study investigated how river flows (including the controlled release of water from an upstream storage facility, or ‘environmental flow’) and water quality might affect the abundance and nutritional status of three freshwater turtle species in three dryland rivers of the Murray–Darling basin in south‐eastern Australia. No response in abundance or nutritional status of the broad‐shelled turtle, Chelodina expansa, the eastern long‐necked turtle, Chelodina longicollis, and the Macquarie turtle, Emydura macquarii, was detected in relation to river flows, possibly because of the small magnitude of the environmental flow. However, for C. expansa, the catch per unit effort (CPUE) was negatively related to increasing macrophyte cover, electrical conductivity (EC, an indicator of salinity), and turbidity. CPUE for C. longicollis was positively related to macrophyte cover and EC, and for E. macquarii it was positively related to macrophyte cover. Haematological measurements suggested that the turtles had healthy nutritional status. Body condition and blood glucose and protein were related significantly to EC, whereas haematological measurements varied significantly among species and between spring and summer. The main conclusion is that water management measures to help the conservation of these turtles should include sufficient environmental flow to produce overbank flooding, thereby creating and maintaining a wide range of habitat suitable for the differing needs of the individual species.

Lake-wide mapping of littoral habitat using underwater videography

Littoral zones − referring to benthic areas above the light compensation depth − provide numerous ecosystem functions, including mediating light, temperature, and nutrient dynamics, and supporting important foraging and refuge areas for macroinvertebrates, fishes and water birds. Habitat assessments of littoral zones remain fundamental to lake and fisheries management, however traditional field surveys are time-intensive and limited in their spatial extent, whereas desktop evaluations using remote sensing and aerial imagery are cost prohibitive and require considerable data processing expertise. In light of these challenges, this study demonstrated the ability to use simple, cost-effective underwater videography to conduct lake-wide spatially-continuous assessments of littoral habitat. For lakes across a gradient of shoreline and riparian development in northwestern United States, we map the areal coverage of macrophytes, coarse woody habitat, bottom substrates, and artificial structures in littoral zones. Underwater videography represents a relevant tool for environmental monitoring because it allows for the estimation of littoral habitats at fine spatial grains across broad spatial extents. Data can also be obtained rapidly and at relatively low cost, providing a permanent record of habitat conditions that can used to monitor trends over time.

Variação espaço-temporal da cobertura de macrófitas aquáticas em reservatório usando imagens Landsat e Google Earth Engine

ABSTRACT The presence of large amounts of aquatic macrophytes in reservoirs can trigger several impacts on the local ecosystem and conventional methodologies used for their monitoring only returns information from the present moment. With that in mind, this study aimed to map spatio-temporal variation of macrophyte cover using Landsat 5, 7 and 8 images between 1984-2021 at Jupiá reservoir, in south east of Brazil, besides determining curves and maps of macrophyte cover permanence. The identification of these organisms in the images, and their distinction from other vegetations, was made through spectral indices (NDVI, GNDVI and GSAVI) and the determination of the characteristic range of each of these classes, which was given by probability distributions. Interannual variations were observed in the spatial arrangement of macrophytes and the area's growth trend, possibly being caused by the implantation of an upstream reservoir. Although the number of images without interference was a limitation, the construction of a historical series of macrophytes occupation and the determination of permanence curves and maps proved to be satisfactory and could help on the decision-making processes for the management of these organisms.

A 15-year Study of the Spatial Distribution of Rutilus rutilus and Perca fluviatilis in Late Summer in Two Shallow Lakes With Contrasting Trophic State

Roach (Rutilus rutilus) and perch (Perca fluviatilis) are dominant species in northern-temperate lakes of Europe, their relative importance depending on trophic state and habitat complexity. We studied the habitat distribution of roach and perch over a 15-year period in two Danish lakes, Lake Væng, undergoing major changes in water clarity and macrophyte coverage, and the permanent turbid Lake Søbygård. We used multi-mesh sized gill nets in 5-6 different sections of the lakes following the same program in all years. Both species were evenly distributed in the sections and among habitats, in Lake Væng during the turbid period and in Lake Søbygård during the whole study period. During the clear-water period in Lake Væng, however, the distribution of roach and perch was uneven and the density negatively correlated with macrophyte coverage and density, but the strength of the relationship differed between the two species and between small (≤ 8 cm for roach and <10 cm for perch) and larger fish. Our results suggest that water clarity and macrophyte density were of key importance in determining roach and perch distribution in these two shallow lakes.

High summer macrophyte cover increases abundance, growth, and feeding of juvenile Atlantic salmon.

Aquatic habitats are severely threatened by human activities. For anadromous species, managing freshwater habitats to maximize production of more, larger juveniles could improve resilience to threats in marine habitats and enhance population viability. In some juvenile salmonid habitats, complexity created by large substrates provides resources and reduces competitive interactions, thereby promoting juvenile production. In lowland rivers, which lack large substrates, aquatic plants might provide similar complexity and enhance fish productivity. To test the influence of aquatic plants on juvenile Atlantic salmon and sympatric brown trout in a lowland river, we directly manipulated the cover of the dominant macrophyte, Ranunculus, in nine sites during summer and autumn for two years. We quantified the abundance, site retention and growth of salmon and trout under high, medium or low Ranunculus cover. To investigate the effects of Ranunculus cover on feeding opportunities and interspecific competition, we quantified available prey biomass and body size, fish diet composition and compared dietary niche overlap. Experimentally increased Ranunculus cover supported higher salmon abundance in summer and autumn, and higher site retention and growth of salmon in summer. Trout abundance and growth were not influenced by Ranunculus cover, but trout site retention doubled in high, relative to low, cover sites. Despite the weak effects of Ranunculus cover on prey availability, salmon and trout inhabiting high cover sites consumed larger prey and a higher biomass of prey. Furthermore, dietary niche overlap was lower in high, relative to low, cover sites, suggesting that abundant Ranunculus reduced interspecific competition. This field experiment shows that high Ranunculus cover can support more and better growing juvenile salmon, and facilitate foraging and co-existence of sympatric salmonid species. Maintaining or enhancing natural macrophyte cover can be achieved through sympathetic in-river and riparian vegetation management and mitigating pressures on them, such as sediment inputs and low flows, or through planting. Further research should test whether macrophyte cover benefits propagate to subsequent life stages, particularly juvenile overwintering associated with high mortality. This knowledge, in combination with our findings, would further clarify whether beneficial juvenile habitat can improve the viability of at-risk salmonid populations. Overall, our findings suggest that the aims of river restoration might be achieved through promotion of in-stream aquatic vegetation.

Characterizing the impacts of macrophyte-dominated ponds on nitrogen sources and sinks by coupling multiscale models

Macrophyte-dominated ponds, widely distributed in lowland areas, play an important role in nitrogen (N) retention for nonpoint source pollution. However, their impacts on N sources and sinks are scarcely quantified at a watershed scale. This study aimed to investigate N dynamics (sources, sinks, transport, etc.) of macrophyte-dominated ponds and their driving factors in a typical lowland artificial watershed (the Zhong River Watershed) in East China. For this purpose, an hourly-scale pond model (nitrogen dynamic model for macrophyte-dominated ponds, NDP-Pond) was developed, and coupled with a daily scale watershed model (Nitrogen Dynamic Polder model, NDP) to simulate N dynamics, and estimate N retention in macrophyte-dominated ponds. A comparison with the measured water level and total nitrogen (TN) revealed an acceptable model performance (coefficient of determination (R2) > 0.53) for these two models. Based on the N source/sink simulations, we found that 1) macrophyte-dominated ponds showed a large TN removal capacity with a rate of 55%, and a TN loading removal rate of 67 kg·ha−1·yr−1. 2) Denitrification was the main pathway for N removal with a contribution of 57.7%, followed by the uptake of macrophytes (35.8%) and sedimentation (6.5%). 3) The optimal coverage of macrophytes (Alternanthera philoxeroides) to enhance N removal is 2–4 kg·m−2. 4) During the macrophyte-growth period, the TN removal capacity of the pond was higher with a retention time of 1–10 days. Increasing the pond retention time would decrease the N removal efficiency. This study revealed the high value of coupling multiscale models to gain in-depth insights into N retention in macrophyte-dominated pond ecosystems.

Microalgae colonization of different microplastic polymers in experimental mesocosms across an environmental gradient.

A variety of organisms can colonize microplastic surfaces through biofouling processes. Heterotrophic bacteria tend to be the focus of plastisphere research; however, the presence of epiplastic microalgae within the biofilm has been repeatedly documented. Despite the relevance of biofouling in determining the fate and effects of microplastics in aquatic systems, data about this process are still scarce, especially for freshwater ecosystems. Here, our goal was to evaluate the biomass development and species composition of biofilms on different plastic polymers and to investigate whether plastic substrates exert a strong enough selection to drive species sorting, overcoming other niche‐defining factors. We added microplastic pellets of high‐density polyethylene (HDPE), polyethylene terephthalate (PET), and a mix of the two polymers in 15 lentic mesocosms in five different locations of the Iberian Peninsula, and after one month, we evaluated species composition and biomass of microalgae developed on plastic surfaces. Our results, based on 45 samples, showed that colonization of plastic surfaces occurred in a range of lentic ecosystems covering a wide geographical gradient and different environmental conditions (e.g., nutrient concentration, conductivity, macrophyte coverage). We highlighted that total biomass differed based on the polymer considered, with higher biomass developed on PET substrate compared to HDPE. Microplastics supported the growth of a rich and diversified community of microalgae (242 species), with some cosmopolite species. However, we did not observe species‐specificity in the colonization of the different plastic polymers. Local species pool and nutrient concentration rather than polymeric composition seemed to be the determinant factor defying the community diversity. Regardless of specific environmental conditions, we showed that many species could coexist on the surface of relatively small plastic items, highlighting how microplastics may have considerable carrying capacity, with possible consequences on the wider ecological context.

Assessing the long-term efficacy of internal loading management to control eutrophication in Lake Rauwbraken

ABSTRACT Lake Rauwbraken was impacted by eutrophication caused by diffuse external phosphorus (P) loads (total 1.21 mg m−2 d−1, estimated in 2008). Over 40 years, this load built up a legacy pool in the sediments, resulting in 6.82 mg m−2 d−1 PO4-P internal load (estimated in 2008), causing cyanobacterial blooms and swimming bans. To address the internal load in this lake, a low dose treatment of flocculant (polyaluminium chloride) combined with a solid phase phosphate fixative (lanthanum-modified bentonite) was applied in 2008. We examined the chemical and ecological responses to this treatment to demonstrate the efficacy of controlling internal loading without reducing external loading. Based on 2 years pre- and 10 years post-treatment monitoring, the mean Secchi disk depth (3.5–4.0 m) and the hypolimnetic oxygen concentration (0.86–4.55 mg L−1) increased while decreases occurred in turbidity (5.4 to 2.2 NTU), chlorophyll a (16.5 to 5.5 µg L−1), contribution of cyanobacteria (64% to 17% of chlorophyll a), total phosphorus (134 to 14 µg L−1), and total nitrogen (0.96 to 0.50 mg L−1). The treatment reduced the PO4-P release from sediment under anoxic conditions from 15.1 to 1.7 mg m−2 d−1 post-treatment in 2008, 2.3 mg m−2 d−1 in 2011, and 4.7 mg m−2 d−1 in 2013. Post-treatment, submerged macrophytes reached high coverage in 2008 and 2009. Longer term, post-treatment macrophyte cover was reduced. The lake is returning to a eutrophic state as a result of ongoing external P loads 10 years following the control of internal loading.

Bacterial decomposition of allochthonous organic matter in shallow subtropical lakes

AbstractShallow lakes favour the development of aquatic macrophytes that can influence the limnological characteristics of these environments. In addition to macrophytes, allochthonous organic matter contributes to the metabolism of lakes through the bed of decomposing detritus. Among the decomposing microorganisms, bacteria can be important in the processing of organic matter when the abundance of fungi and invertebrates is low. The present study evaluated the effects of macrophyte coverage on bacterial‐mediated leaf decomposition of allochthonous debris in shallow subtropical lakes. Litter bags were incubated with senescent leaves of Erythrina crista‐galli in six shallow lakes, three with high (HML) and three with low (LML) macrophyte coverage. After 2, 7, 15 and 35 days of incubation, a set of litter bags was removed from each lake for bacterial, environmental and mass‐loss analyses. Decomposition rates were higher in the LML (49% of remaining mass), compared to the HML (63% of remaining mass). The bacterial density and biomass were higher in the LML. Limnological variables influenced bacterial morphotypes, especially branched filament. Thus, the high coverage of aquatic macrophytes can be a main factor influencing the bacterial colonization in the debris, delaying the decomposition process in these ecosystems.

Does the size structure of the littoral community reflect water level fluctuations in shallow waterbodies?

The littoral zone of shallow water bodies (SWB) is highly susceptible to water level fluctuations (WLF) caused by ongoing climate-related hydrologic regime changes. The present study assessed the macrozoobenthos structure in the littoral of three temperate SWB after pronounced WLF and accompanying reduction of macrophyte coverage caused by excessive precipitation. The three SWB differed in environmental conditions – S1 (transparent lake covered with submerged macrophytes dominated by Ceratophyllum demersum); S2 (turbid lake without macrophyte coverage) represented the two interconnected backwater basins of the Sutla River watershed; and SK (Škrčev kut oxbow; highly turbid lake sparsely covered by floating-leaved Nuphar lutea) located in the Krapina River watershed (Croatia). With the aim to disentangle the littoral food web structure, and interactions among environmental conditions as well as structural and functional traits of the littoral community within the three SWB, the macrozoobenthos functional traits, trophic guilds and body size were correlated with the littoral environmental conditions, and with the traits of the potential macrozoobenthos prey (zooplankton) and predators (fish). Our results suggest that the littoral macrozoobenthos assemblage responded to the water level increase mainly by the decline of macroinvertebrate diversity and abundance. Due to loss of habitat heterogeneity, in general, larger-sized macroinvertebrates dominated the littoral zone of turbid SWB, particularly with high WLF, while smaller-sized detritivores and grazers prevailed in the littoral zone of the transparent SWB covered by submerged macrophytes. The correlations between different macrozoobenthos, zooplankton and fish size classes indicated that the larger-sized predatory macroinvertebrates prey on smaller-sized zooplankters and avoid predation of mid-sized fish. On the other hand, the abundance of smaller-sized macroinvertebrate detritivores and grazers, which were significantly correlated with concentrations of suspended detritus and algae, prevailed in the SWB covered by submerged macrophytes. Within the macrophyte-covered littoral habitats, macroinvertebrates coexisted with small-sized fish and zooplankters as well as with large-sized pelagic zooplankters, likely seeking shelter from fish. We assume that the increased abundance of larger-sized specimens affected macroinvertebrates and fish within the littoral community upon water level increase. Such a pattern could be recognized as an indicative trait in the evaluation of ecosystem functioning. Furthermore, we conclude that the structural and functional traits of the SWBs’ littoral communities could help us predict the ecological consequences of the climate-induced WLF.

An RShiny app for modelling environmental DNA data: accounting for false positive and false negative observation error

Environmental DNA (eDNA) surveys have become a popular tool for assessing the distribution of species. However, it is known that false positive and false negative observation error can occur at both stages of eDNA surveys, namely the field sampling stage and laboratory analysis stage. We present an RShiny app that implements the Griffin et al. (2020) statistical method, which accounts for false positive and false negative errors in both stages of eDNA surveys that target single species using quantitative PCR methods. Following Griffin et al. (2020), we employ a Bayesian approach and perform efficient Bayesian variable selection to identify important predictors for the probability of species presence as well as the probabilities of observation error at either stage. We demonstrate the RShiny app using a data set on great crested newts collected by Natural England in 2018, and we identify water quality, pond area, fish presence, macrophyte cover and frequency of drying as important predictors for species presence at a site. The state‐of‐the‐art statistical method that we have implemented is the only one that has specifically been developed for the purposes of modelling false negative and false positive observation error in eDNA data. Our RShiny app is user‐friendly, requires no prior knowledge of R and fits the models very efficiently. Therefore, it should be part of the tool‐kit of any researcher or practitioner who is collecting or analysing eDNA data.

Foodweb biodiversity and community structure in urban waterbodies vary with habitat complexity, macrophyte cover, and trophic status

Foodweb biodiversity and community structure in urban waterbodies vary with habitat complexity, macrophyte cover, and trophic status

Macrophyte functional traits in channelized streams

In lowland streams, channelization is a severe hydromorphological modification with negative impacts on ecosystem functioning and biological communities. We assessed the functional structure and spatial patterns of macrophyte assemblages in channelized streams, and we identified the most affected traits by this practice. We studied unchannelized (UCS) and channelized sites (CS) using a null model approach and functional diversity indices. The macrophyte coverage was higher in the UCS (mean: 86 ± 15 %) than in the CS (50 ± 35 %). Unchannelized sites revealed a random pattern, with predominating submerged and free-floating species, as well as reproduction by turions and tubers. Channelized sites showed a segregation pattern (C-score obs.: 23.08; C- core exp.: 22.20; SES: 3.20) of functionally similar species indicating interspecific competition, and lower functional richness, evenness, and Rao quadratic entropy compared to the UCS. The predominant traits found for macrophyte assemblages of these sites were emergent life form, and dispersion by stolons. Our results indicate that in CS, the abiotic environment and biotic interactions act as filters and only macrophyte species with key traits can colonize these streams. In this sense, the creation of backwater areas, the reestablishment of longitudinal and lateral connections of the streams, as well as macrophyte transplants could favor the dispersal and establishment of macrophyte species. These rehabilitation measures could positively improve the functionality of these ecosystems.

Seasonal Variation in Populations of Eurasian Coot Fulica atra: Relationships with Environmental Variables in Mediterranean Wetlands

Mediterranean wetlands represent a broad variety of natural resources with a huge role in the maintenance of biological diversity. Waterbirds are significant components of this diversity. Among them, the Eurasian Coot Fulica atra is a key species when studying the correlations and interactions between waterbirds and environmental variables, because of its abundance, ease of detection, and relation with some basic aspects of the functioning of wetlands. The present study aimed to analyse the annual and seasonal variation in populations of Eurasian Coot in 31 wetlands in Andalusia, southern Spain, from 2003 to 2008, paying particular attention to correlations with biotic and abiotic variables. The results showed a positive correlation between water depth and coot abundance, while a negative relationship was observed with salinity and no correlation was observed between wetland size and coot abundance. These environmental variables, together with submerged macrophyte coverage, stand out as playing important roles in the use of habitat by coots in Andalusian wetlands.

Effects of released farmed mallards on species richness of breeding waterbirds and amphibians in natural, restored and constructed wetlands

Common practices in current game management are wetland restoration and creation, as well as releases of quarry species. We studied the impact of releases of mallard ducklings on species richness of wild waterbirds and amphibians on three types of wetlands: natural, constructed and restored. Data on species richness, macrophyte cover and water characteristics (total phosphorous and pH) were collected at 32 sites in an agricultural landscape in southern Sweden. In total, 14 species of waterbirds were recorded, ranging from zero to seven per wetland and survey. Amphibians were present in 24 of the 32 wetlands; in total five species were found, ranging from zero to three per wetland. By using generalized linear modelling we found that wetland type best predicted waterbird species richness. Constructed wetlands had significantly more waterbird species, regardless of whether they were used for mallard releases or not. There were breeding amphibians in 62% of natural, 100% of restored and 77% of constructed wetlands. Breeding amphibians were present in 84% of wetlands without, and in 62% of wetlands with releases. However, included variables did not explain amphibian species richness in the wetlands. Releasing large numbers of mallards on a wetland and providing food ad libitum is likely to affect water quality, nutrient availability and predation pressure. Indeed, phosphorous levels were significantly higher in release wetlands, but no differences were found between wetland types.This means that mallard releases may increase nutrient loads in environments that are already eutrophied. However, in our study system releases did not influence species richness of waterbirds and amphibians locally. Constructing wetlands for mallard releases can thus have positive local effects on species richness.

The role of emergent physical and chemical properties of Florida spring complexes in predicting fish assemblage structure

Florida spring complexes (springs and their associated runs) represent patches of clear, cool freshwater habitat in a landscape of tannin-stained wetlands, streams, and rivers. These spring complexes differ in morphology, water quantity and quality, and biotic characteristics as well as in their connections to other water bodies. The purpose of this study was to determine whether watershed effects or emergent physical, chemical, and biologic properties of Florida spring complexes would predict fish assemblage structure. Spring complex morphology and water quality metrics were collected from water managers or from the literature, with the exception of dissolved oxygen, which was measured in situ. Fish data were collected by video surveys using GoPro® cameras on stationary tripods at 2 to 5 locations on the banks of each spring complex. Videos were analyzed for the total number of individuals of each species/video, species richness, and diversity. The environmental characteristics of spring complexes differed between watersheds, as the St Johns River spring complexes, which are near the east coast, differed from watersheds closer to the west coast of Florida. However, specific characteristics that discriminated between springs, like low dissolved oxygen concentration or abundant macrophytes, crossed watershed boundaries. Fish assemblages also differed between the St Johns River and western watersheds, but the differences were more subtle than the differences in environmental characteristics, and the characteristics of individual spring complexes also predicted fish assemblage structure. Conductivity, dissolved oxygen concentration, and macrophyte coverage best explained the variation in the fish assemblage structure among spring complexes. The overlap in spring complex fish assemblages across watersheds may be the result of the geologic youth of the freshwater fish assemblages, the high degree of hydrologic connectivity between water bodies, and possible impairment of spring complexes in Florida.

Unraveling the ecological processes modulating the population structure of Escherichia coli in a highly polluted urban stream network

Escherichia coli dynamics in urban watersheds are affected by a complex balance among external inputs, niche modulation and genetic variability. To explore the ecological processes influencing E. coli spatial patterns, we analyzed its abundance and phylogenetic structure in water samples from a stream network with heterogeneous urban infrastructure and environmental conditions. Our results showed that environmental and infrastructure variables, such as macrophyte coverage, DIN and sewerage density, mostly explained E. coli abundance. Moreover, main generalist phylogroups A and B1 were found in high proportion, which, together with an observed negative relationship between E. coli abundance and phylogroup diversity, suggests that their dominance might be due to competitive exclusion. Lower frequency phylogroups were associated with sites of higher ecological disturbance, mainly involving simplified habitats, higher drainage infrastructure and septic tank density. In addition to the strong negative relationship between phylogroup diversity and dominance, the occurrence of these phylogroups would be associated with increased facilitated dispersal. Nutrients also contributed to explaining phylogroup distribution. Our study proposes the differential contribution of distinct ecological processes to the patterns of E. coli in an urban watershed, which is useful for the monitoring and management of fecal pollution.