Macrophyte Cover Research Articles

Longitudinal and temporal variation in fish assemblage structure along lowland prairie Neotropical streams and relationships with environmental variables

The structure of fish assemblages in lotic systems usually varies from headwaters to the mouth, related to geomorphological and physicochemical changes. We evaluated the main processes that structure the fish assemblages on spatial, seasonal, and decadal (2009-2010; 2019-2020) scales and relationships with environmental variables in two low-impacted Neotropical Pampean streams tributaries to the Río de la Plata estuary (RdlP). Environmental variables related to the longitudinal variation in the fish assemblage were depth, macrophyte cover, and altitude, showing higher values in the headwater streams compared to downstreams. Species richness increased towards lower stream sectors due to the migration of riverine species from the RdlP. Beta diversity partitioning analysis showed that the greatest proportion of variability was explained by the turnover component in both the longitudinal and seasonal analyses. The headwater streams showed a more stable composition, consisting of species of the order Characiformes associated with aquatic macrophytes, while the downstream streams recorded greater variability due to the entry of migrant Siluriformes from the RdlP, highlighting the essential ecological function of Pampean streams for RldP fish assemblages. The decadal comparison showed that the longitudinal structure is persistent in the long term regardless of the study period. Therefore, the consistent pattern of longitudinal variation in fish assemblages and its explanatory variables have applicability in the conservation and biomonitoring of lowland streams, serving as reference for recovery efforts.

Wetlands function as carbon sink: Evaluation of few floodplains of middle Assam, northeast India in the perspective of climate change.

Floodplain wetlands are biologically rich and productive ecosystems that can capture carbon (C) from the atmosphere through macrophytes and phytoplanktons and hold it in soil for a long time thus playing a critical role in mitigating climate change. The Assam state of India has about 1392 floodplain wetlands engulfing around 100,000ha area in the Brahmaputra and Barak River basin. In the present study, five different wetlands in the middle Assam viz., 47-Morakolong, Jaliguti, Charan, Chatla, and Urmal were chosen for the estimation of C capture and its storage in soil. The net primary planktonic productivity (NPP) of Chatla was much higher (300mgC/m3/hr) than other wetlands where it ranged around 100-150 mgC/m3/hr. Macrophyte coverage was highest (80%) in Chatla followed by Urmal (50%) and 30% in others. Total organic carbon (TOC) content in water was also significantly higher in Chatla than in others. The C content at different depths of the soil (upper 15 and 15-30cm) of the wetlands varied widely from 1.3 to 7% and in absolute terms, the total C accumulated in top 30cm varied from 12.65 to 76.95 MgC/ha. The amount of C in upper 30cm of corresponding upland sites was estimated to be 8.8-33.62 MgC/ha. Thus, wetlands are superior in terms of C accumulation and storage in their soil compared to the corresponding upland sites. If properly managed, the wetlands can be very effective in capturing and storing C and offset GHG emission and global warming to a great extent.

Rotifers as indicators of trophic state in small water bodies with different catchments (field vs. forest)

AbstractCurrent methods for assessing lake trophic status using zooplankton are well-established, but there is a lack of approaches for small, shallow water bodies. This study addresses the gap by analyzing rotifer communities across 100 ponds in different catchment areas (field and forest). We hypothesized that the Rotifer Trophic State Index (TSIROT) is an effective tool for assessing trophic state, yielding comparable results to the Carlson TSI index. We also proposed that variations in physical and chemical parameters would significantly affect rotifer composition, impacting the trophic state assessment. Field ponds, exposed to agricultural runoff, exhibited higher trophic states and a predominance of detritivorous species. In contrast, forest ponds, with extensive macrophyte coverage, maintained lower trophic states and supported diverse algivorous species, particularly of littoral and mesotrophic origin. This confirmed our hypothesis that catchment type strongly influences trophic state and rotifer communities. We demonstrated that rotifer traits—abundance, species diversity, habitat type preferences and proportions of eutrophic versus mesotrophic species—along with TSIROT, are effective in assessing water quality in ponds. Overall, the results validate TSIROT as a reliable tool for small water bodies, comparable to Carlson’s TSI index, and highlight the importance of catchment type in influencing water quality.

Chalk stream restoration: Physical and ecological responses to gravel augmentation.

To mitigate the morphological and ecological impacts of direct (e.g. dredging) and indirect (e.g. damaged river function) sediment loss, gravel augmentation is commonly practiced in river systems globally. Despite this, the effectiveness of this practice remains poorly understood, especially in less often considered systems such as chalk streams which present uncommon conditions (e.g. low stream power, stable flow) and may respond to interventions in ways that differ from systems more commonly studied. This study quantified immediate (0-1 years) and short-term (1-2 years) physical and ecological responses to gravel augmentation at two English chalk stream restoration sites: Home Stream (HS; River Test) and East Lodge (EL; River Itchen). We quantified habitat (depth, velocity, substrate composition), cover of different macrophytes, and macroinvertebrate (before-after-control-impact) abundance and community structure. Restoration reduced depth and increased gravel cover in both sites and decreased the cover of filamentous green algae in HS. Macroinvertebrate communities became more dominated by silt-intolerant taxa, while abundance [HS only] and taxon richness increased 1-2 years post-restoration. Whilst the responses found were generally positive in light of the restoration goals, the effects varied across sites, post-restoration time periods and ecological groups, emphasising the need for the more holistic monitoring of restoration projects considering community-level responses at different sites and systems over ecologically relevant timescales. This will help inform on the generality and longevity of responses and provide the evidence needed to develop sound restoration practice.

Monitoring the Dynamics of Aquatic Vegetation in a Typical Shallow Lake Using the Water Bloom Index Algorithm-A Case Study in Bao' an Lake in the Middle Reaches of the Yangtze River.

Understanding changes in the distribution and coverage of aquatic vegetation (AV) is of great significance for the restoration of lake ecosystems. In this study, the vegetation and bloom indices (VBI) algorithm were used to interpret submerged aquatic vegetation (SAV), floating/emergent aquatic vegetation (FEAV), and algal bloom (AB). The dynamics of AV and their influencing factors in Bao' an Lake, in the middle reaches of the Yangtze River in China, were studied from 2000 to 2023. The results showed that (1) the VBI algorithm can accurately distinguish AV and AB of different life forms with an overall accuracy of 93% and a kappa coefficient of 0.86. (2) Macrophyte coverage decreases. AV grew vigorously in spring, and SAV was the dominant type within it, whereas AV coverage was low in summer, and SAV had no summer species for a long time. In 2000, the coverage of AV was the highest, reaching 64.5%, but a gradual decrease that followed in the coming years finally led to a coverage percentage of less than 5% by 2023. (3) The correlation between SAV coverage and total phosphorus (p < 0.01), total nitrogen (p < 0.05), and water depth/transparency (p < 0.05) in Bao' an Lake were 0.23, 0.28, and 0.32, respectively. (4) The SAV species experienced three stages: richness (before 2003), monotonicity (2004-2020), and final disappearance (2021-present). This study shows that the coverage of AV in Bao' an Lake is too low and the number of SAV species is one (2010-now). Therefore, it is necessary to implement measures to improve vegetation coverage and diversity.

Drying out fish ponds, for an entire growth season, as an agroecological practice: maintaining primary producers for fish production and biodiversity conservation.

Agroecology largely focusses on terrestrial agroecosystems, but it can also be applied to fish farming. Indeed, ponds are typically used for fish production in Europe, but are also important reservoirs of biodiversity. Numerous studies demonstrate that both fish production and biodiversity are strongly determined by human management. One key practice in extensive fish farming, although more rare in Europe, is to dry out ponds. They are left dry for a complete year after several years of fish production. However, the extent to which this practice affects the functioning of the ecosystem, its biodiversity and fish production remain unclear. We investigated data from 85 fish ponds in the Dombes region, France, sampled between 2007 and 2014. We related variation in key abiotic characteristics to the time since last dry out. The dataset included organic matter content in pond sediments and concentrations of inorganic nitrogen and phosphorus in the water column, and biotic components such as macrophytes cover and richness, phytoplankton concentration and richness, macroinvertebrates density, and fish yield. Our results show that drying out facilitates the mineralization of organic matter in sediments and results in higher concentrations of inorganic nitrogen in the water column. Macrophytes cover is highest during the first year after drying out, and gradually declines after at the expense of increasing phytoplankton concentration. The diversity of both is highest in the first year after drying out and declines rapidly, especially for macrophytes. Fish yield is at its maximum in the second year. Drying out fish ponds appears to be an important agroecological practice in extensive fish farming with an application every three to four years. By nutrient recycling, this practice has a positive impact on the balance between primary producers and indirectly on the whole food web during two years. It optimizes fish production and allows biodiversity conservation.

Just Add Water and Stir: An Artificial Suburban Lake Develops Into an Important Moulting Site for Large‐Bodied Herbivorous Wildfowl

ABSTRACTEgø Engsø is an artificial Danish suburban lake created in 2006, primarily for nutrient retention and flood control. Expanding submerged macrophyte cover (dominated by Stoneworts Chara spp. and Pondweeds Potamogeton spp.) attracted moulting concentrations of 600 mute swans Cygnus olor, 1100 greylag geese Anser anser and 280 Canada geese Branta canadensis. These unexpected additions to the avifauna benefit from reliable food supplies and effective protection from recreational disturbance on and near the water surface. Egø Engsø is a model of enabling intense human activity at a waterbird moulting site, and confirming appropriate planning can accommodate multiple functional objectives following wetland creation.

The dual role of benthic fish: Effects on water quality in the presence and absence of submerged macrophytes

Rebuilding a clear-water state dominated by submerged macrophytes is essential for addressing eutrophication, yet the impact of benthic fish on water quality is complex. We conducted two experiments to explore the interaction of submerged plants and benthic fish on the water quality. Experiment I investigated the water clearing effects of submerged macrophytes with varying coverage (from 0% to 40%) before and after the removal of benthic fish. Experiment II explored the impacts of benthic fish at different densities on aquatic ecosystems with and without submerged macrophytes. The results showed that an increase in submerged macrophytes coverage significantly enhanced the reduction of some major water quality parameters. We assert that the coverage of submerged macrophytes should not be lower than 40% to establish and sustain a clear-water state in shallow lakes. However, benthic fish significantly weaken the ability of submerged macrophytes to improve water quality. Surprisingly, the presence or absence of macrophytes may reverse the role of benthic fish in freshwater ecosystems. When macrophytes are present, benthic fish can cause water quality to deteriorate. Conversely, when macrophytes are absent, benthic fish with a density of ≤ 10 g/m3 can restrict the growth of phytoplankton by directly consuming algae or by disturbing sediments to increase turbidity, thereby potentially improving water quality. But the detrimental effects of benthic fish with higher densities may gradually outweigh their benefits to water clarity. Therefore, the percentage of submerged macrophyte cover in combination with the density of benthic fish play crucial roles in shaping the ecological effects of benthic fish and overall ecosystem dynamics. These findings underscore the importance of understanding ecosystem interactions and have practical implications for the management of shallow lakes.

Enhancing nitrate removal from small wetlands via regulating bacterial-algal symbiosis with macrophyte coverage

With increasing land resource constraints, wetlands, as ecological hotspots, are expected to enhance biogeochemical processes to mitigate nitrogen (N) pollution, particularly nitrate-nitrogen (NO3−-N). However, the interactions among bacteria, algae, and macrophytes in wetlands, which are crucial for N removal, remain largely unknown. This study explored how macrophyte coverage influences bacterial-algal interactions, shifting from mutualism to inhibition, thereby affecting N removal. Moderate coverage enhanced NO3−-N and total nitrogen (TN) removal (P < 0.05), which was correlated with increased microbial abundance (P < 0.05). This may have resulted from moderate algal photosynthesis, reduced physiological stress, and the expansion of ecological niches for microbes. Insufficient coverage promoted algal growth (chlorophyll-a > 31.8 μg·L−1), leading to increased competition for substrates and elevated pH, which further inhibited bacterial activity. Excessive coverage also inhibited bacterial activity by reducing illumination and oxidation-reduction potential. Consequently, insufficient and excessive coverage decreased N removal efficiencies by 2.7–15.7 % (NO3−-N) and 3.7–11.1 % (TN) while increasing methane emission potential by 1.4–6.9 times compared with moderate coverage. These findings offer insights into solving NO3−-N contamination using near-natural methods and balancing the ecological and practical considerations for small wetlands.

Dual impacts of hydrology and damming on eutrophication: Comparison of two Ramsar wetlands in the middle Yangtze floodplain

Dam construction for social-economic benefits has raised substantial biological and ecological concerns. However, contrasting findings have been reported regarding the role of hydrological modification in floodplain lake ecosystems. Here, we evaluated the influence of hydrology and dam construction on the eutrophication of floodplain lakes over the last 200 years by studying Zn/Al (an indicator of industrial activities), nutrient influxes (total phosphorus, TP), cyanobacteria production (canthaxanthin) and aquatic invertebrate dynamics (chironomids) in 210Pb dated sediment cores from two Ramsar Wetlands of International Importance in the middle Yangtze floodplain, one dammed (Wanghu) and the other freely connected (Poyang) with the Yangtze River. The results show that Wanghu Lake transitioned to a macrophyte-dominated clear water state (as indicated by the increases in pigment derived ultraviolet radiation index and dominance of macrophyte-related chironomid taxa) after local dam construction when anthropogenic nutrient loadings were relatively low. With increases in nutrient loadings, phytoplankton increased in both lakes, but water clarity declined and macrophyte-related chironomids decreased only in the lake which was locally dammed. Our study reveals that local damming facilitates the response of floodplain lake ecosystems to eutrophication and decouples it from the effects of hydrological variability. This study highlights the potential influence of hydrology and damming on the eutrophication of floodplain lakes by influencing water clarity and macrophyte coverage, implying that evaluating the role of local dam construction on ecosystem states should be based on knowledge of nutrient conditions in floodplain lakes.

Resistance and resilience: Tidal freshwater marsh response and recovery to acute and chronic saltwater intrusion

The ability to both resist and recover from disturbances like storm surge and saltwater intrusion plays a key role in shaping the structure and function of tidal marshes. In this study, porewater chemistry, vegetation, and soil elevation change were measured in field plots of a tidal freshwater marsh exposed to four years of experimental press (chronic) and pulse (acute) brackish water additions followed by five years of recovery to assess their resistance and resilience to saltwater intrusion. Press additions produced significant, widespread changes in marsh structure and function including increased porewater N and P, reduced macrophyte cover and species richness, and loss of soil surface elevation whereas pulse additions had little effect. Once dosing ceased, porewater chemistry, vegetation and soils in press plots recovered at differing rates, with porewater N and P declining to background levels after one year, plant cover and species richness increasing within two to four years, and soil surface elevation increasing to similar levels found in control plots after five years. The plant community in the press treatment converged with the other treatments after 3–4 years, though macrophyte species exhibited varying rates of recovery. Ground cover (Ludwigia repens) and soft stem species (Persicaria) that declined first, recovered faster than Zizaniopsis miliacea that was more resistant but less resilient to brackish water intrusion. While tidal freshwater marshes are resistant and resilient to pulses such as those that stem from hurricanes and storm surges, continued long-term intrusion events like sea level rise (SLR) will likely lead to conversion into brackish marsh. Understanding long-term responses and tradeoffs in resistance and recovery as shown in this experiment offers insight into the future trajectory of tidal freshwater marshes as well as broader ecosystem responses to disturbance and recovery crucial to management and restoration.

Impacts of hydrologic management on the eutrophication of shallow lakes in an intensive agricultural landscape (Saskatchewan, Canada)

Abstract Hydrologic management of shallow lakes is often undertaken to prevent fluctuations in lake level, and to ensure sufficient water volume for economic, domestic, and recreational uses, but there is inconsistent evidence of whether lake‐level stabilisation through hydrological management promotes or hinders eutrophication. Here we used multi‐proxy paleolimnological assessments of water quality (sedimentary carbon, nitrogen, total phosphorus, fossil pigments), and zooplankton community ecology (fossil Cladocera assemblages), combined with Landsat‐derived estimates of lake surface area in two shallow eutrophic lakes, in the Prairies of southern Saskatchewan, Canada, to quantify how 8 decades of contrasting hydrological management strategies (continuous or intermittent) affect primary production and phytoplankton composition. Analysis revealed that irregular hydrological management of Pelican Lake led to sharp increases in primary production concomitant with lake‐level decline. In contrast, continuously managed Buffalo Pound Lake, a drinking water reservoir for regional cities, exhibited slow, persistent eutrophication over decades despite active regulation of water levels. In both lakes, strong correlations of δ 15N values with pigments from diazotrophic cyanobacteria (canthaxanthin) showed that N2‐fixation increased during eutrophication irrespective of the timing of change. Finally, variation in fossil cladoceran density and composition reflected changes in pelagic and littoral habitats (e.g., reduced macrophyte cover) due to changes in both lake level and water quality. Basin comparison shows that while hydrologic management can moderate water quality degradation due to lake‐level change, it does not prevent eutrophication when nutrient influx remains high. Given that regional water availability is forecast to decline in coming decades, we anticipate that continued hydrological management will be unavoidable and will be unable to improve water quality unless nutrient influx is also controlled.

Linking carbon storage with land use dynamics in a coastal Ramsar wetland

Coastal wetland ecosystems make an important contribution to the global carbon pool, yet their extent is declining due to aquaculture-related land use changes. We conducted an extensive investigation into the carbon stock and area coverage of macrophytes in a tropical coastal Ramsar wetland, Kolleru in Andhra Pradesh, India. A total of 72 quadrats of size 1 × 1 m2 were laid in the wetland, 19 species of macrophytes were collected and analyzed for carbon content using a CNHS analyzer. To assess changes in the wetland macrophytes, Normalized Difference Vegetation Index (NDVI) was estimated using Landsat time series data from 1975 to 2023. The importance value index (IVI) of macrophytes scored highest for the Ipomoea aquatica (41.4) and the lowest for Ottelia alismoides (1.9). Non-metric multidimensional scaling (NMDS) significantly (r = 0.1905, p = 0.0361) revealed a clear separation of macrophytes in ordination space. ANOVA indicated highly significant (p < 0.0001) variations in the carbon content of aboveground and belowground components of macrophytes. Among the different macrophytes, the highest carbon content was found in Phragmites karka (0.6 g. g−1) and the lowest was recorded in Utricularia stellaris (0.2 g. g−1). On an average, emergents in the Kolleru wetland sequester 1525 ± 181 g C m−2 yr−1, rooted floating species sequester 858 ± 101 g C m−2 yr−1, submerged macrophytes sequester 480 ± 60 g C m−2 yr−1, and free-floating macrophytes sequester 221 ± 90 g C m−2 yr−1. Land cover mapping revealed a decrease in spread of aquatic vegetation from 225.2 km2 in 1975 to 100.6 km2 in 2023. Although macrophytes are vital carbon sinks, the wetland conversion into fishponds has resulted in a loss of 55.3 % of carbon storage. Therefore, immediate restoration of macrophyte cover is vital for the proper functioning of carbon sequestration and mitigation of climate change impacts.

Diversity of Macrophytes and Macroinvertebrates in Different Types of Standing Waters in the Drava Field

The diversity of macrophytes and macroinvertebrates in small standing waters of different origins and characteristics was investigated. This survey covered 19 ponds in the Drava field in northeastern Slovenia. The influence of the macrophytes on the macroinvertebrates was investigated and the main environmental factors that had the most significant influence on the composition of the two communities were identified. Sixty-seven taxa of macrophytes and seventy-three families of macroinvertebrates were identified. We found that a diverse macrophyte community has a positive effect on the macroinvertebrate community. In contrast, the dominance of a single macrophyte species has a strong negative influence on the richness of the macroinvertebrate community. The taxonomic richness and abundance of the macroinvertebrate community in the natural ponds was statistically significantly higher than that in artificial ponds. The significant differences in the environmental characteristics between the natural and artificial ponds, such as the macrophyte cover, conductivity, and riparian zone width, may account for these differences. Our study suggests that a greater diversity of macrophyte and macroinvertebrate communities in natural ponds is enabled by abundant but diverse macrophyte cover, low phosphorus content, and wide riparian zones, which require appropriate management of ponds and their catchments.

Can artificially induced habitat complexity alter macroinvertebrates diversity? A case study from a freshwater wetland ecosystem

Habitat complexity can enhance the resilience of wetlands against environmental stressors such as extreme weather events, pollution, and habitat loss. The introduction of artificial induced complexity (AIC) can play a significant role in reshaping the macroinvertebrate communities within wetland ecosystems by enhancing habitat quality in protected areas. Therefore, this study was designed to examine the variation of macroinvertebrates community structure in artificially induced complex sanctuary site (SS), partially protected (PP) and open sites (OS) from July 2019-April 2020. AIC in the sanctuary sites was established through the installation of cemented hexapods and ring pipes. Over the study period, a total of 665 macroinvertebrates were gathered, with 55.55% originating from SS, 31.14% from PP, and 18.21% from OS sites. The community consists mainly of Lymnaea acuminatatea and Tubifex tubifex, with the most abundant species being Limnodrillus hoffmeisteri and Branchiura sowerbyi. A notable positive impact of AIC was evident in the increased total abundance and diversity indices of macroinvertebrate communities. The Analysis of Similarity (ANOSIM) revealed significant distinctions in community structures among various intervention types, which was further corroborated by a non-metric multidimensional scaling (nMDS) plot. Similarity of Percentage Analysis (SIMPER) highlighted that Limnodrillus hoffmeisteri made the most significant contribution to the dissimilarity observed among the different intervention types. Canonical Correspondence Analysis (CCA) revealed a close association between the structure of the macroinvertebrate community and three key ecological factors: periphyton biomass, macrophyte cover, and sediment properties. These findings could offer a more effective approach for managers and policymakers engaged in the conservation of macroinvertebrates and the sustainable management of fisheries resources within wetland ecosystems.

Water quality in a shallow eutrophic lake is unaffected by extensive thinning of planktivorous and benthivorous fish species

Ambitious to fulfill the European Water Framework Directive obligations, the European governments support projects to rehabilitate lakes with poor water quality. However, most lake restorations having relied on biomanipulation by fish thinning have failed to improve or even maintain water quality. Previous attempts removed all target fish species simultaneously, thus making it impossible to assess the specific impact of each feeding group on water chemistry. Lake Bromme was selected for extensive, time-selective fish biomanipulation to improve water clarity and promote submerged macrophytes and piscivorous fish stocks over a three-year monitoring period. Thinning of adult benthivorous bream (Abramis brama) and tench (Tinca tinca) was conducted throughout year one while thinning in years two and three targeted planktivorous roach (Rutilus rutilus), juvenile bream, and small perch (Perca fluviatilis). Yearly fish surveys assessed changes in fish population structure and biomass. Water quality parameters were monitored continually, and the cover of submerged macrophytes was surveyed annually via sonar. We found no improvement in water clarity or reductions of nutrients, organic particles, chlorophyll concentrations, or watercolor, despite a 6-fold thinning of total estimated fish biomass, from 112 to 19 kg ha−1. Over the period, the macrophyte cover increased from 0.8 to 13.5 %, but no recruitment of large piscivorous fish (perch and pike (Esox lucius) > 10 cm) was detected. We found higher correlations of particle concentration and water clarity to water temperature than to wind speed, which indicates sediment particle resuspension by the remaining fish community (mostly carp Cyprinus carpio) that forage on benthos in shallow lakes. Further system-ecological research in Lake Bromme should evaluate whether thinning the stock of carp and increasing plant cover may improve water quality and test which optical properties sustain high water turbidity and prevent shallow, eutrophic lakes like Lake Bromme from responding to intense fish thinning.

Assessment of Ecosystem Services Provided by Macrophytes in Southern Baltic and Southern Mediterranean Coastal Lagoons

The ecological importance of macrophytes is well known and reflected in nature protection law, for example, as a key biological quality element. However, the socio-economic role, such as the impact of macrophyte presence on recreational activities, is often overlooked. The purpose of this study was to assess the human benefits (or ecosystem services) provided by macrophytes. We developed a list of 25 macrophyte ecosystem services and 79 assessment indicators based on expert knowledge and literature data. First, hypothetical scenarios of coastal lagoons were developed to assess the impact of different ecological states (i.e., macrophyte coverage) and management measures (i.e., fisheries) on the ecosystem service provision. Scenario assessments were carried out by stakeholder workshops and literature search. Second, the ecosystem service potential of submerged and emergent macrophyte habitats were assessed by macrophyte experts and literature data. Results showed that cultural services are most important in terms of the overall actual provision of ecosystem services (scenario assessment) but also showing highest potential of the hypothetical ecosystem service provision (habitat assessment). Highest overall potential is shown for reeds and tall forb communities (83 out of maximum 125), followed by seagrass beds (71) and seaweed communities (61). Our ecosystem service assessment approaches (i.e., scenario and habitat-based) using socio-cultural data (i.e., stakeholders and experts-based) and biophysical data (i.e., indicators-based) can serve as supportive tools for coastal management and policy implementation visualizing the benefits of macrophytes to humans.

Macrophyte coverage drives microbial community structure and interactions in a shallow sub-tropical lake

Shallow lakes are typically dominated by macrophytes, which have important functional roles regulating trophic conditions and creating biological habitat. Macrophytes have been shown to strongly influence water chemistry and shape microbial communities in shallow lakes. In Florida, many large, shallow lakes are dominated by alien invasive, submersed macrophytes, such as hydrilla (Hydrilla verticillata [L.F.] Royle) and are intensively managed to reduce infestations and contain the spread of these alien invasive macrophytes. In this study, we investigated the effects of large (40 ha) herbicidal and mechanical control treatments on a large lake located in Central Florida that resulted in the reduction of Hydrilla and concomitant changes in water chemistry and microbial communities (both bacteria and protists [microbial eukaryotes]). We observed a considerable decrease in macrophyte coverage associated with plant control treatments as well as a temporal change in macrophyte coverage in Lake Tohopekaliga. We found that changes in macrophyte coverage, regardless of treatment type, significantly affected the water chemistry of the lake, resulting in a sharp increase of chlorophyll a concentration as well as an increase in turbidity with the decrease of macrophyte coverage. Moreover, the decline in macrophytes led to decreases in microbial community diversity with over-representation of phototrophic functional groups. Specifically, we observed an increase in cyanobacteria with the decrease in macrophyte coverage. Our study highlights the advantages and disadvantages of macrophyte control. Although there was an initial decrease in macrophyte coverage associated with the chemical and mechanical control of aquatic plants, after a few months, we found a considerable increase in coverage. In addition, the increase of cyanobacterial relative abundance demonstrates the possible consequences of aquatic plant control such as cyanobacterial blooms if there is a continued decline of macrophytes.

A shift in habitat use patterns of brown trout (Salmo trutta): A behavioural response to macrophyte removal

Mass development of macrophytes is an increasing problem worldwide and they are frequently removed where they are in conflict with local waterway users. Yet, macrophytes can provide important refuge and nursery habitats for fish. Little is known about the consequences of macrophyte removal for fish behavioural space use and habitat selection. We hypothesised that macrophyte removal would affect brown trout (Salmo trutta) movement during the partial removal of the aquatic plant Juncus bulbosus (L.) in an oligotrophic impounded Norwegian river.We tagged 94 brown trout and tracked them using passive acoustic telemetry for 10 months and mapped the cover of J. bulbosus. Trout behavioural patterns were quantified as space use (utilisation areas 50% and 95%) which was linked to habitat use and selection for J. bulbosus. Removal of J. bulbosus influenced space use of brown trout by reducing the core utilisation area by 22%. Habitat use and selection were likewise influenced by removal with increased use and selection of areas with low J. bulbosus cover (<25%) with corresponding reduction in high J. bulbosus cover (>25–75%). Finally, diurnal differences in space use and habitat use were found, with 19% larger utilisation areas at night and higher use of areas with low J. bulbosus during daytime. Yet, all effect sizes were relatively small compared to the size of the study area.This research provides a detailed case study on the effects of macrophyte removal on fish behavioural patterns in a section of a large Norwegian river with macrophyte mass development. We found no large effects of removal on trout behaviour but noted an increased use of areas with low macrophyte cover. This research is relevant for water managers and policy makers of freshwater conservation and provides a template for using acoustic telemetry to study the effects of macrophyte removal on fish.

Functional properties of planktic microalgae determine their habitat selection

In this study, we aim to investigate how the functional properties of microalgae help to delineate the major groups of aquatic habitats. Using functional trait-based and Reynolds’ functional group-based approaches similarities of the microalgal flora of all aquatic habitats occurring in Hungary were compared. The habitats covered the whole size spectrum of standing waters (10-2–108 m2) and water currents (watershed: 102–1011 m2), , limnological and chemical properties. Both functional trait-based and functional group-based habitat classifications overrode the hydromorphology-based typology, however, functional group-based clusters showed closer resemblance to limnological-hydromorphological types than clusters created by trait-based approaches both for qualitative and quantitative data. Most of the aquatic habitats that have similar limnological characteristics showed resemblance in the functional properties of their microflora. Rivers and river-related habitats were the most diverse functionally. These were followed by standing waters with extended macrophyte coverage. The small, unique habitats displayed the lowest functional richness. The occurrence of several functional groups in some extreme habitats implies two alternative explanations: first, the habitat template of the groups is wider than defined in the original description; second, detailed information on the autecology of species assigned to a functional group necessitates the creation of new groups specific for the unique habitats.