Give beavers permanent residence - we'd be dam stupid not to

First paragraph: Beavers have recently made a tentative return to Britain. Scotland has led the way, with an official trial population in Knapdale, a remote area of lochs and forest in the west of the country; and another in Tayside to the east, suspected to come from private-collection escapees and unlicensed releases. Further south, a small feral population in Devon in south-west England is currently being tolerated by officialdom and admired locally, while there are also plans for a trial in mid-Wales.https://theconversation.com/give-beavers-permanent-residence-wed-be-dam-stupid-not-to-5525

Invasion legacy effects versus sediment deposition as drivers of riparian vegetation

Riparian zones are formed by interactions between fluvio-geomorphological processes, such as sediment deposition, and biota, such as vegetation. Establishment of invasive alien plant (IAP) species along rivers may influence vegetation dynamics, evidenced as higher seasonal or inter-annual fluctuations in native plant diversity when IAP cover is high. This could impact the overall functioning of riparian ecosystems. Conversely, fine sediment deposited in riparian zones after floods may replenish propagule banks, thus supporting recruitment of native species. The interactive effects of invasion and fine sediment deposition have hitherto, however, been ignored. Vegetation surveys across rivers varying in flow regime were carried out over 2 years to assess changes in community composition and diversity. Artificial turf mats were used to quantify over-winter sediment deposition. The viable propagule bank in soil and freshly deposited sediment was then quantified by germination trials. Structural Equation Models were used to assess causal pathways between environmental variables, IAPs and native vegetation. Greater variation in flow increased the cover of IAPs along riverbanks. An increased in high flow events and sediment deposition were positively associated with the diversity of propagules deposited. However, greater diversity of propagules did not result in a more diverse plant community at invaded sites, as greater cover of IAPs in summer reduced native plant diversity. Seasonal turnover in the above-ground vegetation was also accentuated at previously invaded sites, suggesting that a legacy of increased competition in previous years, not recent sediment deposition, drives above-ground vegetation structure at invaded sites. The interaction between fluvial disturbance via sediment deposition and invasion pressure is of growing importance in the management of riparian habitats. Our results suggest that invasion can uncouple the processes that contribute to resilience in dynamic habitats making already invaded habitats vulnerable to further invasions

Submerged macrophyte decline in shallow lakes: What have we learnt in the last forty years?

Over the last 40 years there has been substantial evidence that high biomasses of submerged aquaticplants and phytoplankton rarely occur together in shallow lakes, but it is clear that when present, plantshave a competitive advantage over algae. Aquatic plants provide habitat structure, which influences the fish community such that zooplanktonand other macroinvertebrates maintain a top-down control on algal growth, and this control is largelyindependent of the nutrient supply to the lake. Nonetheless it is clear that many, but not all, lakes losetheir vegetation as nutrient loading increases. However, in eutrophic lakes, the subsequent dominanceby phytoplankton is more likely to be a result of the loss of vegetation rather than the cause. At higher nutrient levels, grazing or mechanical damage can reduce plant cover allowing rapid devel-opment of algae. Changes to fish community structure or the influence of toxic chemicals can reduceinvertebrate algal grazers, overcoming the positive feedback loops that stabilise the plant dominance. The longer-term stability of macrophyte dominance is also reduced if there are few surviving plantspecies. Such loss of species richness is associated with increased nitrogen loading. Submerged plantsalso depend on a spring clear-water phase to become established, and local weather conditions duringwinter and spring may determine the relative success of phytoplankton and plant growth, leading to aprogressively longer period of algal dominance and fewer surviving plant species. The loss of submerged vegetation from lakes, although often perceived as a rapid change, is more likelyto be the final conclusion of a process in which the competitive advantage of a diverse plant communityis eroded by many pressures that are collectively interpreted as eutrophication. In attempts to manage our environment we hope to find simple, closed stable systems that will respondto measures designed to meet our perceptions of improved ecological quality. What we increasingly findare more complex open systems, which do not necessarily respond as expected. We look for simple andwidely applicable explanations where none are likely to exist

Riverbanks as battlegrounds: why does the abundance of native and invasive plants vary?

The abundance of invasive alien plants (IAPs) can vary dramatically over small spatial scales for reasons that are often unclear. Understanding these could offer key insights for containing invasions, accepting that eradication is often no longer feasible. This study investigated determinants of IAP cover on riverbanks, a well-known hotspot of invasion, using Impatiens glandulifera, a prolific invader across the Northern hemisphere, as a model species. Within this framework we included the potential for dominant native vegetation cover, mediated by favourable environmental conditions, to resist invasion by I. glandulifera through negative association. Our analyses, using structural equation modelling, showed that I. glandulifera is more sensitive to environmental conditions, than dominant native vegetation. High soil moisture was a key determinant of I. glandulifera cover, having negative effects across the riparian zone. Spatially, I. glandulifera and dominant native vegetation responded differently to environmental conditions. Sites with steeper banks had less dominant native vegetation at the water's edge, potentially favouring I. glandulifera cover through reduced competition. In general, greater abundance of dominant native vegetation presented a more invasion-resistan

The spatial dynamics of vertical migration by Microcystis aeruginosa in a eutrophic shallow lake: A case study using high spatial resolution time-series airborne remote sensing

Abstract: Time-series airborne remote sensing was used to monitor diurnal changes in the spatial distribution of a bloom of the potentially toxic cyanobacterium Microcystis aeruginosa in the shallow eutrophic waters of Barton Broad, United Kingdom. High spatial resolution images from the Compact Airborne Spectrographic Imager (CASI-2) were acquired over Barton Broad on 29 August 2005 at 09:30 h, 12:00 h, and 16:00 h Greenwich mean time. Semiempirical water-leaving radiance algorithms were derived for the quantification of chlorophyll a (R2 = 0.96) and C-phycocyanin (R2 = 0.95) and applied to the CASI-2 imagery to generate dynamic, spatially resolving maps of the M. aeruginosa bloom. The development of the bloom may have been fostered by a combination of the recent improvements in the ambient light environment of Barton Broad, allied to the acute depletion of bioavailable nutrient pools, and stable hydrodynamic conditions. The vertical distribution of M. aeruginosa was highly transient; buoyant colonies formed early morning and late afternoon near-surface aggregations across the lake during periods of nonturbulent mixing (wind speed <4 m s-1). However, the extent of these near-surface aggregations was highly spatially variable, and nearshore morphometry appeared to be crucial in creating localized regions of nonturbulent water in which pronounced and persistent near-surface aggregations were observed. The formation of these near-surface scums would have been vital in alleviating light starvation in the turbid waters of Barton Broad. The calm water refuges in which persistent near-surface accumulations occurred may have been an important factor in determining the persistence of the bloom

The influence of hydrological and land use indicators on macrophyte richness in lakes – A comparison of catchment and landscape buffers across multiple scales

In biogeography it is well established that environmental variables often have scale-dependent effects on abundance and distribution of organisms. Here we present results from a study on scale-dependency of macrophyte (aquatic plant) richness to hydrology and land use indicators. Hydrological connectivity and land use within the landscape surrounding 90 \{UK\} lakes, at nine buffer sizes varying from 0.25 km to 10 km from the shoreline, with (catchment buffer) and without (landscape buffer) adherence to the catchment boundary, were constructed using GIS. These variables were used to explain variation in macrophyte richness derived from field surveys. The results revealed strong scale-dependency. The effects of land use were most apparent at small buffer sizes and grossly outweighed the importance of hydrology at all spatial scales. The total richness of macrophytes was most strongly determined by land use and hydrology within 1 km of the lake for landscape buffers and 500 m for catchment buffers. The nature of the scale-dependent effect also varied with macrophyte growth habit. In terms of growth form composition, the effects of hydrological connectivity were stronger than those of land use, being greatest at an intermediate distance (∼5 km) from the lake. Our results indicate the value of maintaining some lake catchments with less intensive land use, at least within 1 km of the lake shore, while also minimising alterations to catchment hydrology (e.g. through drainage or impoundment) over distances extending at least 5 km from the lake shore

Twenty years of change in riverside vegetation: What role have invasive alien plants played?

Question  Which environmental factors influence the occurrence of invasive alien plants (IAPs) in riparian habitats, and how much can IAPs account for change in native vegetation compared with other environmental variables?  Location  Rivers distributed throughout mainland Britain.  Methods  We quantified change in river bank vegetation using survey data collected approximately 20yr apart and assessed the contribution of major IAPs (Impatiens glandulifera, Heracleum mantegazzianum and Fallopia japonica) to these changes. We also determined the importance of abiotic factors such as flow regime and land use in driving these changes.  Results  Comparing data from pre- and post-1990 surveys revealed that IAPs occurred mainly on lowland rivers (<200m a.s.l.), regardless of time period, and their probability of occurrence increased over time and with rising frequency of high flows. Native plant species diversity declined over time with increasing IAP cover, along lowland rivers and along all rivers that experienced extended low flows during the growing season. These conditions particularly favoured native dominant species, whereas native subordinate species responded both positively and negatively to increased flood frequency depending on survey period. Over time, Salix spp. and larger native hydrophilic species, such as Sparganium erectum, increased along lowland rivers, replacing smaller-statured ruderal species and driving a shift towards increased shade tolerance of subcanopy and groundcover species. Smaller compositional changes occurred in the uplands and these changes lacked a clear environmental signature.  Conclusions  National-scale changes in native riparian vegetation are likely driven primarily by environmental changes and land-use effects, rather than invasion by IAPs. However, IAPs, and indeed native species that benefit from abiotic changes, in turn, likely exert secondary effects on native riparian vegetation. The trend towards reduced diversity, increased shade tolerance and increased dominance of some native species and IAPs is likely linked to a set of interacting factors, including drier summers, wetter winters, increased riparian tree cover, reduced livestock access to river banks and increased fine sediment input. Determining combined effects of land use, IAPs and climate-related changes in flow regime over decadal time scales (i.e. ~20yr) is important for predicting ecological responses of vulnerable habitats under future disturbance scenarios

Feeding behaviour of Lumbriculus variegatus as an ecological indicator of in situ sediment contamination

Previous studies have demonstrated that the feeding behaviour of Lumbriculus variegatus may be significantly inhibited during exposure to toxic substances. The potential use of an in situ sediment bioassay, using L.variegatus post-exposure feeding inhibition as an endpoint, was investigated. The bioassay consisted of exposing animals in the field for a six-day exposure period and feeding rates were measured immediately afterwards over a twenty-four hour post-exposure period. The bioassay methodology developed in the laboratory produced a consistent baseline response that was reliable and repeatable. Endpoint sensitivity was demonstrated under laboratory conditions, where bioassay organisms exhibited delayed recovery from feeding inhibition after previous exposure to sediment-associated contaminants. The apparent insensitivity of the bioassay to sediment-associated metals means that the technique should only be used as part of a suite of bioassays that employ representative deposit feeders. The ecological relevance of the bioassay endpoint was also demonstrated by comparing short-term measures of post-exposure feeding inhibition with the longer-term effects of a toxicant on L.variegatus populations. The bioassay methodology was successfully adapted for in situ use. Post-exposure feeding inhibition was detected at contaminated field sites. However, the consistent baseline response produced in the laboratory could not be replicated during deployments of the bioassay at upstream (“clean”) field sites. Increased environmental “noise” may have been a result of a number of confounding factors that could limit the sensitivity of the bioassay endpoint if not adequately controlled. Despite the above concerns, the in situ bioassay is suggested to represent a useful tool, which uses a more realistic field exposure scenario to investigate the effects of sediment-associated toxicants with an important functional component of aquatic ecosystems.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

All change at the water's edge: invasion by non-native riparian plants negatively impacts terrestrial invertebrates

Riparian zones are complex, dynamic habitats that play a critical role in river ecosystem functioning. Terrestrial invertebrates comprise much of the diversity found in riparian habitats and facilitate the transfer of energy between aquatic and terrestrial systems. However, the consequences for terrestrial invertebrates of invasion of riparian zones by invasive non-native plants (INNP) remain poorly understood. Responses of terrestrial macroinvertebrate morphospecies to invasion by two common INNP, Fallopia japonica (Japanese knotweed) and Impatiens glandulifera (Himalayan balsam) were assessed, relative to local environmental factors. Terrestrial invertebrates were collected from 20 sites on low order streams in June and August alongside data on physical attributes and land use. Greater cover of F. japonica and I. glandulifera cover reduced total invertebrate abundance and morphospecies diversity at the individual sample scale, whilst increasing spatial heterogeneity of invertebrates at the site scale. Impatiens glandulifera reduced morphospecies diversity at the site scale with increasing cover, but this was not observed for F. japonica. INNP affected terrestrial invertebrate morphospecies abundance and diversity, to a greater extent than prevailing environmental conditions. Our findings therefore offer support for managing riparian plant invasions to improve habitat heterogeneity, restore terrestrial invertebrate diversity and repair aquatic-terrestrial linkages