Lake and catchment-scale determinants of aquatic vegetation across almost 1,000 lakes and the contrasts between lake types

Aim The factors controlling macrophyte (aquatic plant) composition are complex, recent research having shown that the well-studied effects of lake environmental factors (the so-called “environmental filter”) can be constrained by hydrological and landscape factors. We investigated the factors determining macrophyte composition in lakes over water body and catchment- scales and the transferability of this pattern across lake types. Location Almost 1000 lakes distributed across Britain. Taxon Lake macrophytes Methods Lakes were partitioned into five types based on subdivision of alkalinity and elevation gradients. Data from botanical surveys were used to compare the spatial turnover and nestedness components of beta diversity between lake types. The relative importance of lake environment (based on local physicochemical data), hydrology (e.g. lake and stream density), landscape (e.g. fragmentation indices, land cover) and spatial autocorrelation in explaining variation in macrophyte composition were derived from variance partitioning. Results Species composition showed strong spatial structuring, suggestive of overland dispersal, enhanced by spatially-correlated abiotic factors such as alkalinity and elevation. Catchment-scale factors (e.g. land use, connectivity) promoted the establishment of different communities (more or less diverse, or differing in composition) but were of secondary importance. Turnover in composition between upland lakes was lower than in other lake types, reflecting a more specialist flora and increased potential for propagule exchange due to spatial aggregation and higher hydrological connectivity. Main conclusions Vegetation composition in lakes is more spatially-structured than previously appreciated, consistent with the importance of dispersal limitation, but this does not apply evenly to all lakes, being most acute in lowland high alkalinity lakes. Thus, spatially-structured abiotic factors, such as alkalinity, influence macrophyte composition most (suggestive of niche filtering) in high alkalinity lakes where human impacts tend to be greatest, although nestedness was also lowest in such lakes. By contrast, hydrological connectivity has a proportionally stronger structuring role in upland lakes

Rewilding wetlands: beaver as agents of within-habitat heterogeneity and the responses of contrasting biota

Ecosystem engineers can increase biodiversity by creating novel habitat supporting species that would otherwise be absent. Their more routine activities further influence the biota occupying engineered habitats. Beavers are well-known for transforming ecosystems through dam building and are therefore increasingly being utilised for habitat restoration, adaptation to climate extremes, and in long term rewilding. Abandoned beaver ponds develop into meadows or forested wetlands that differ fundamentally from other terrestrial habitats and thus increase landscape diversity. Active beaver ponds, by contrast, are superficially similar to other non-engineered shallow wetlands, but ongoing use and maintenance might affect how beaver ponds contribute to aquatic biodiversity. We explored the 'within-habitat' effect of an ecosystem engineer by comparing active beaver ponds (BP) in southern Sweden with coexisting other wetlands (OW), using sedentary (plants) and mobile (water beetles) organisms as indicators. BP differed predictably from OW in environmental characteristics and were more heterogeneous. BP supported more plant species at plot (+15%) and site (+33%) scales, and plant beta diversity, based on turnover between plots, was 17% higher than in other wetlands (OW), contributing to a significantly larger species pool in BP (+17%). Beetles were not differentiated between BP and OW based on diversity measures but were 26% more abundant in BP. Independent of habitat creation beaver are thus significant agents of within-habitat heterogeneity that differentiates beaver ponds from other standing water habitat; as an integral component of the rewilding of wetlands re-establishing beaver should benefit aquatic biodiversity across multiple scales

Using ecosystem engineers as tools in habitat restoration and rewilding: beaver and wetlands

Potential for habitat restoration is increasingly used as an argument for reintroducing ecosystem engineers. Beaver have well known effects on hydromorphology through dam construction, but their scope to restore wetland biodiversity in areas degraded by agriculture is largely inferred. Our study presents the first formal monitoring of a planned beaver-assisted restoration, focussing on changes in vegetation over 12 years within an agriculturally-degraded fen following beaver release, based on repeated sampling of fixed plots. Effects are compared to ungrazed exclosures which allowed the wider influence of waterlogging to be separated from disturbance through tree felling and herbivory. After 12 years of beaver presence mean plant species richness had increased on average by 46% per plot, while the cumulative number of species recorded increased on average by 148%. Heterogeneity, measured by dissimilarity of plot composition, increased on average by 71%. Plants associated with high moisture and light conditions increased significantly in coverage, whereas species indicative of high nitrogen decreased. Areas exposed to both grazing and waterlogging generally showed the most pronounced change in composition, with effects of grazing seemingly additive, but secondary, to those of waterlogging.  Our study illustrates that a well-known ecosystem engineer, the beaver, can with time transform agricultural land into a comparatively species-rich and heterogeneous wetland environment, thus meeting common restoration objectives. This offers a passive but innovative solution to the problems of wetland habitat loss that complements the role of beavers in water or sediment storage and flow attenuation. The role of larger herbivores has been significantly overlooked in our understanding of freshwater ecosystem function; the use of such species may yet emerge as the missing ingredient in successful restoration

Stream invertebrate diversity reduces with invasion of river banks by non-native plants

1. Invasion of riparian zones by non-native plants is a global issue and commonly perceived as a challenge for river and fishery managers, but the type and extent of ecological changes induced by such invasions remain poorly understood. Established effects on sediment delivery, allochthonous inputs and channel shading could potentially alter aquatic macroinvertebrate assemblages, with implications for in-stream ecological quality. 2. We assessed responses in the diversity, quality and heterogeneity of stream macroinvertebrate communities to riparian invasion by non-native plants. Macroinvertebrates were collected from 24 sites on low order streams in central and southern Scotland during spring and autumn. The effect of invasive non-native plants (INNP) on macroinvertebrates was assessed relative to that of local physical and chemical factors. 3. INNP cover was associated with stronger effects than other factors on local diversity of macroinvertebrates (33% reduction at the highest INNP cover) but also increased macroinvertebrate abundance across sites. Invaded sites were also associated with lower macroinvertebrate biomonitoring scores. Community composition differed between invaded and uninvaded sites in autumn, but not in spring. However, INNP influence on macroinvertebrate composition was generally secondary to that of physicochemical variables (e.g. channel shade, substrate diversity). 4. We demonstrate that the influence of INNP extends beyond well-known impacts on plant communities to reductions mainly in stream macroinvertebrate diversity. Combined with the negative impact on pollution-sensitive macroinvertebrate taxa this raises concerns over the ecological health of streams with heavily invaded riparian zones. Our findings suggest that efforts to improve low order streams by actively managing severe riparian invasions are merited, but the size and uncertainty of the likely ecological gains must also be evaluated against the effort involved

Deriving nutrient criteria to support 'good' ecological status in European lakes: An empirically based approach to linking ecology and management

European water policy has identified eutrophication as a priority issue for water management. Substantial progress has been made in combating eutrophication but open issues remain, including setting reliable and meaningful nutrient criteria supporting ʽgoodʼ ecological status of the Water Framework Directive. The paper introduces a novel methodological approach - a set of four different methods - that can be applied to different ecosystems and stressors to derive empirically-based management targets. The methods include Ranged Major Axis (RMA) regression, multivariate Ordinary Least Squares (OLS) regression, logistic regression, and minimising the mismatch of classifications. We apply these approaches to establish nutrient (nitrogen and phosphorus) criteria for the major productive shallow lake types of Europe: high alkalinity shallow (LCB1; mean depth 3–15 m) and very shallow (LCB2; mean depth

Re-evaluating expectations for river phytobenthos assessment and understanding the relationship with macrophytes

The reference model underlying the UK phytobenthos (diatom) tool for Water Framework Directive assessments is revisited and a new approach is proposed which uses quantile regression to predict the lowest values of the Trophic Diatom Index (equating to the best available condition) at any level of alkalinity . Whilst a reference model based on least disturbed or minimally impacted conditions would be preferable in theory, in practice the absence of lowland high alkalinity streams in a minimally impacted condition in the UK precludes the use of these approaches. Having proposed a revised reference model for phytobenthos, we then go on to examine the relationship between phytobenthos and macrophytes. These two groups respond to nutrients and other stressors in different ways with phytobenthos being more sensitive to nutrients whilst macrophytes better reflect the extent to which secondary effects are likely. We argue that averaging the two sub-elements of the “macrophytes and phytobenthos” biological quality element is a more realistic option than the current approach of taking the lower of the two assessments. It is, however, possible, to predict the value of the combined quality element from either sub-element, though we recognize that this also risks misclassifications

Slender naiad (Najas flexilis) habitat quality assessment – site prioritisation.

This report is the result of the second phase of the slender naiad (Najas flexilis) habitat quality assessment project

Chemical and biological responses of marl lakes to eutrophication

Eutrophication remains one of the foremost environmental issues threatening the quality of surface waters yet comparatively little is known of the timing, magnitude and characteristics of nutrient-related changes in highly calcareous (marl) lakes.  This review focuses on marl lake ecology and chemistry, their known responses to eutrophication, and also highlights questions that remain unanswered.                                 In good condition, marl lakes support a diversity of macrophytes, especially Characeae and Potamogetonaceae, which can grow to considerable depth.  High water transparency and low phosphorus and phytoplankton concentrations are facilitated by the coprecipitation of marl and phosphorus.  Although large amounts of phosphorus can be thus removed, buffering against eutrophication, macrophyte communities can undergo significant change under rather low nutrient concentrations.  Maximum colonisation depth declines and tolerant species replace sensitive species, with losses particularly among charophytes.  Marl lakes are therefore ecologically highly sensitive.             The effects of coprecipitation on long-term burial of phosphorus are contested.  Several palaeolimnological studies have identified iron complexes as more important than calcite, as chemical conditions in the sediment may promote either calcite dissolution or calcite-bound phosphorus exchange, or possibly both.  Some marl lakes have been shown to have phosphorus concentrations which, compared with other lake types, are higher than expected in winter and lower in summer.  The phosphorus binding capacity of marl sediment has not to our knowledge been adequately researched.             Marl precipitation may be inhibited by high phosphate or organic matter concentrations in the water, or when biological communities effecting precipitation (picoplankton, charophytes, epiphytes) are disturbed.  Highly impacted marl lakes having low species diversity and lacking precipitation may be misidentified as eutrophic, high-alkalinity lakes.  More studies addressing the interaction between external loading, phosphorus cycling and marl precipitation in relation to biological communities are required to assess to what extent marl lakes can buffer eutrophication, and what factors contribute to disturbed marl precipitation.&nbsp

Synthesising 35 years of invasive non-native species research

The growing focus on the threat of invasive non-native species (INNS) in international biodiversity targets highlights a need for targeted research to support effective understanding, legislation, and management. However, the publishing landscape of invasion biology is complex and expanding rapidly, making consolidation of information increasingly challenging. To identify the major research themes in the INNS literature and to understand how these have changed over the last 35 years, we applied a topic modelling approach. We analysed approximately 10,000 peer-reviewed article abstracts to identify 50 key topics being discussed in the literature. We also quantified how publications on these topics changed over time and how commonly different topics interacted within articles as a measure of their connectedness. Topics covering Population genetics, Policy, First records and Insect biocontrol were the most frequent. Topics were grouped into broad themes, with the largest theme related to Ecosystems, followed by Monitoring, then Management and decision-making. Significant overrepresentation for particular geographical regions and taxa in the literature were apparent. Considering relative changes through time, the most prevalent topics in each decade reflected policy influences, and technological developments. When assessing the degree of connectedness- Policy, Population Genetics and Management Strategies showed low levels of co-occurrence with other topics. This is of particular concern for topics focussed on Policy and Management Strategy as it suggests a weakness at the science-policy interface around accessing and exchanging of evidence. If progress towards future global targets is to be made, we argue that more interdisciplinary research must be encouraged, in particular to better incorporate policy and management considerations into the wider research landscape

Pond ecology and conservation: research priorities and knowledge gaps

Ponds are among the most biodiverse and ecologically important freshwater habitats globally and may provide a significant opportunity to mitigate anthropogenic pressures and reverse the decline of aquatic biodiversity. Ponds also provide important contributions to society through the provision of ecosystem services. Despite the ecological and societal importance of ponds, freshwater research, policy, and conservation have historically focused on larger water bodies, with significant gaps remaining in our understanding and conservation of pond ecosystems. In May 2019, pond researchers and practitioners participated in a workshop to tackle several pond ecology, conservation, and management issues. Nine research themes and 30 research questions were identified during and following the workshop to address knowledge gaps around: (1) pond habitat definition; (2) global and long-term data availability; (3) anthropogenic stressors; (4) aquatic–terrestrial interactions; (5) succession and disturbance; (6) freshwater connectivity; (7) pond monitoring and technological advances; (8) socio-economic factors; and (9) conservation, management, and policy. Key areas for the future inclusion of ponds in environmental and conservation policy were also discussed. Addressing gaps in our fundamental understanding of pond ecosystems will facilitate more effective research-led conservation and management of pondscapes, their inclusion in environmental policy, support the sustainability of ecosystem services, and help address many of the global threats driving the decline in freshwater biodiversity