The diatom ecology and palaeoecology of shallow lakes subject to eutrophication: three examples from the English midlands

Lowland England abounds with shallow lakes subject to different levels of eutrophication. In the absence of long-term water chemistry records, palaeolimnology provides an alternative means of assessing the onset and extent of the nutrient enrichment process at a site. The diatoms preserved in lake sediments are extremely sensitive indicators of both past nutrient levels and of eutrophication-related changes in macrophyte-phytoplankton interactions. However the success of diatom-based palaeoecology depends upon a sound knowledge of the taxonomy, environmental requirements, and taphonomy of contemporary diatom communities. This thesis has focused on aspects of the diatom ecology, taphonomy and palaeolecology of three, small (<22 ha.), shallow (<3 m), alkaline lakes of contrasting nutrient and macrophyte status in the English Midlands. These lakes, Tween and Clifton Ponds and Groby Pool, were monitored on a monthly basis (Jan-Oct) for key water chemistry parameters. At the same time samples were collected from the diatom plankton and periphyton and in turn compared with the diatom assemblages which accumulated in sediment traps and at the sediment surface. The small centric diatoms that were found in these lakes were initially difficult to identify using the light microscope (LM), and a scanning electron microscope (SEM) study of the 'problematic' forms revealed considerable ecophenotypic and life-cycle related morphological plasticity. However with careful LM analysis it was possible to confidently distinguish between the different species in the samples. The ecological studies revealed strong associations between the presence or absence of submerged macrophytes and the seasonality and relative competitiveness of planktonic and periphytic diatom species. The relationship between the present-day diatom communities and the diatoms found in the traps and surface sediments of the lakes was relatively good, although there were some problems related to the dissolution of delicate forms. The timing of surface sediment sampling was found to be a critical factor affecting the sedimentary representation of species associated with different periods of the year. The eutrophication histories of Tween Pond (approx. last 30 yrs) and Groby Pool (approx. last 250 yrs) were inferred by comparing the fossil diatom record with the available historical records of lake disturbance, changing catchment land-use and submerged plant communities. The available modern data were used to assist in this process and using a simple life-form based approach it was possible to reconstruct past changes in the relative competitiveness of phytoplankton and submerged plants in both lakes. In Tween Pond the diatom stratigraphy clearly traced the dramatic increase in nutrient loading and the loss of submerged plants from the lake following the diversion of the Erewash in 1972. Similarly, in Groby Pool it was possible to identify the much slower transition- from a mesotrophic, diverse plant dominated state to a eutrophic, tall plant dominated situation. The implications of this study are discussed in relation to modern numerical methods of reconstructing past nutrient loading

Ecoacoustics as a novel tool for assessing pond restoration success:Results of a pilot study

1. Ecoacoustics is increasingly being used to monitor species populations and to estimate biodiversity in marine ecosystems, but the underwater soundscapes of freshwater environments remain largely unexplored in this respect. Few studies exist concerning the acoustic diversity of ponds, but because aquatic plants and many arthropods such as Coleoptera and Hemiptera are known to produce sound, there is potential to use ecoacoustic techniques to monitor changes in biodiversity and conservation value. 2. This pilot study compares the underwater soundscapes of recently restored open-canopy ponds and unmanaged highly terrestrialized ponds situated in an arable agricultural landscape of North Norfolk, UK, in order to assess the benefits of farmland pond restoration. 3. Daytime sound recordings were made for 10 min in each pond and analysed primarily for arthropod stridulations. In addition, six commonly used acoustic indices were calculated to assess the soundscape biodiversity between the unmanaged and the restored ponds. The stridulations of three diving beetle species (Dytiscidae) were recorded in tank studies to assess the potential for individual species recognition from underwater sound capture. 4. Sound-type richness and abundance, as estimated by visually and aurally identifying arthropod stridulation from spectrograms, were significantly higher in the restored open-canopy ponds compared with the unmanaged terrestrialized ponds. In addition, the acoustic indices ‘acoustic complexity’ and ‘biodiversity index’ were significantly higher in restored open-canopy ponds than in unmanaged terrestrialized ponds. 5. The three dytiscid water beetle species recorded in a tank were found to produce distinctive and recognizable sounds, indicating potential to create an audio reference library that could be used for automatic acoustic monitoring of freshwater arthropods. 6. Pond soundscapes are rich in biological information and this study suggests that, with further development, automated passive ecoacoustic monitoring could be an effective non-invasive technique for assessing pond conservation value and pond restoration and management success

Re-introduction of structurally complex wood jams promotes channel and habitat recovery from overwidening: Implications for river conservation

Copyright © 2017 John Wiley & Sons, Ltd. Large wood is a powerful geomorphic agent in rivers, providing important habitat functions for a range of aquatic organisms, but has been subject to a long history of removal. Internationally, approaches to river restoration are increasingly incorporating large wood features, but generally favour simple flow deflectors (e.g. single logs, stripped of branches and anchored in place) over more complex structures that more accurately mimic natural wood jams. This paper explores channel response to wood-based restoration of an overwidened lowland chalk stream that incorporated whole felled trees. Hydraulics, sediment, topography and vegetation data were assessed for a 3year period for two restored reaches: an upstream reach where pre-restoration baseline data were obtained, and a downstream reach restored before data collection. Where pre-restoration data were available, the introduction of wood jams generated sediment deposition within jams leading to the development of vegetated marginal ‘benches’ and bed scour in adjacent areas of flow convergence. Patterns were less clear in the downstream reach, where restoration design was less ambitious and outcomes may have been affected by subsequent restoration work upstream. The results indicate that reintroduction of large wood (whole trees), can promote channel and habitat recovery from overwidening in lowland rivers, creating important ecological benefits through the provision of structurally complex marginal habitat and associated food resources. Longer-term assessments are required to establish whether the trajectories of change are persistent. The work emphasizes the effectiveness of restoration approaches that aim to ‘work with nature’. The ambitious design, incorporating structurally complex wood jams, was also low-cost, using materials available from the river corridor (existing riparian trees). Furthermore, ecosystem engineering effects were amplified by the colonization of wood jams by aquatic vegetation. The approach should, therefore, be transferable to other lowland rivers, subject to wider catchment constraints

Buried alive: Aquatic plants survive in ‘ghost ponds’ under agricultural fields

The widespread loss of wetlands due to agricultural intensification has been highlighted as a major threat to aquatic biodiversity. However, all is not lost as we reveal that the propagules of some aquatic species could survive burial under agricultural fields in the sediments of ‘ghost ponds’ - ponds in-filled during agricultural land consolidation. Our experiments showed at least eight aquatic macrophyte species to germinate from seeds and oospores, following 50–150 years of dormancy in the sediments of ghost ponds. This represents a significant proportion of the expected macrophyte diversity for local farmland ponds, which typically support between 6 and 14 macrophyte species. The rapid (< 6 months) re-colonisation of resurrected ghost ponds by a diverse aquatic vegetation similarly suggests a strong seed-bank influence. Ghost ponds represent abundant, dormant time capsules for aquatic species in agricultural landscapes around the globe, affording opportunities for enhancing landscape-scale aquatic biodiversity and connectivity. While reports of biodiversity loss through agricultural intensification dominate conservation narratives, our study offers a rare positive message, demonstrating that aquatic organisms survive prolonged burial under intensively managed agricultural fields. We urge conservationists and policy makers to consider utilizing and restoring these valuable resources in biodiversity conservation schemes and in agri-environmental approaches and policies

Long term changes in aquatic plant communities in English lowland lakes

This thesis looks into the use of historical macrophyte records to assess long term changes in macrophyte communities in lakes and potential reasons for these changes. In particular it uses historical records to assess changes in macrophyte communities in the Norfolk Broads and West Midland Meres, two sets of lowland, eutrophic lakes in England. It provides a critical examination of the use of historical records, highlighting some of the constraints common to such data such as variations in recording effort, and bias in species recording and site selection. Having acknowledged these issues we then go on to develop a robust way to interpret such data, using a “change index” based on species persistence over the last 200 years within individual lakes. Species with high change index values, which represented species which had persisted or increased within the lake districts, were those known to be characteristic of eutrophic lakes. Conversely species with low index scores, which had declined in both the broads and meres over the last 200 years, included species associated with less fertile conditions but also a selection of typically eutrophic species. Averaging of change index scores in present day survey data served to identify the historically least changed lakes and to rank lakes in order of degree of botanical change over the last century. We then analysed the ecological basis of the change index in order to better understand the processes behind the decline of some species and survival of others in the Norfolk Broads and West Midland Meres. Functional groups determined from morphological and regenerative traits displayed significant differences in change index values in both groups of lakes, but declining taxa occurred across a wide range of plant growth forms. Non-hierarchical clustering of species based on their ecological preferences, obtained from published literature, resulted in groups with distinct change index values, indicating that changes in the status of species could be partly explained by these preferences. Of these, trophic preference was consistently the most important, with species of less fertile habitats consistently experiencing the greatest declines. However, some characteristically eutrophic species have also declined significantly, particularly in the broads. In these cases increasing loss of shallow water, low energy habitats in the broads, or loss of fluctuating water levels and less alkaline backwaters in the meres, appear to have been contributory factors. In addition to the change index approach, we also used historical records at a site level to complement palaeolimnological analysis and investigate the change in macrophyte community composition and structure at Barton Broad, Norfolk. Sediment samples were extracted from the bottom of the broad and analysed for sub-fossil remains and pollen of macrophytes. The historical records and palaeolimnological analysis combined showed that early communities did not consist entirely of low growing, oligotrophic and mesotrophic species as previously thought, but in fact comprised a mixture of these and other more characteristically high nutrient species associated with taller, or free-floating growth habit. As eutrophication progressed throughout the last century, the community was increasingly dominated by these latter growth forms. Diversity was maintained, however, since encroaching reedswamp generated a mosaic of low energy habitats which supported a range of species unable to withstand the hydraulic forces associated with more open water habitat. When the reedswamp disappeared in the 1950s, many of the dependent aquatic macrophytes also declined resulting in widespread macrophyte loss. The thesis demonstrates not just the complexities of using historical records, but also ways in which these can be overcome to make useful observations about macrophyte community change and lake ecological integrity to inform conservation and lake management, both on a site and lake district level.EThOS - Electronic Theses Online ServiceEnvironment AgencyStirling UniversityEnglish NatureBroads AuthorityGBUnited Kingdo

A novel ‘triple drawdown’ method highlights deficiencies in invasive alien crayfish survey and control techniques

Freshwater crayfish can be successful invaders that threaten native biota and aquatic ecosystems in numerous countries worldwide. Nonetheless, the inability of conventional crayfish survey techniques like trapping and handsearching to yield quantitative population data has limited the understanding of crayfish invasion biology and associated ecological impacts. Here, we employed a novel ‘triple drawdown’ (TDD) method to sample invasive populations of signal crayfish Pacifastacus leniusculus in a headwater stream in Northern England. The method was compared with conventional techniques of trapping and handsearching. The TDD method proved to be an effective technique with high capture efficiency, reporting signal crayfish densities from 20.5 to 110.4 animals/m2 at our study sites. These numbers exceed any previous estimates for similar streams. The TDD showed the vast majority of individuals across all sites were juvenile or sub‐adult (<26 mm CL), with only 2.3% of the population large enough (≥35 mm CL) to be caught in standard traps. Synthesis and applications. The triple drawdown (TDD) method demonstrates strong inefficiencies and biases in conventional crayfish survey and management techniques. Trapping is not recommended for representative sampling or control of juvenile dominated populations. TDDs, which can be adapted and modified to operate in multiple habitat types and freshwater systems, generate robust quantitative data on invasive crayfish population demographics in situ. This can advance our understanding of the biology of an important invader of freshwater systems around the world. Obtaining this data prior and post‐intervention is fundamental to evaluate invasive crayfish management, and we recommend the TDD method to assess the effectiveness of future control measures

Identifying sediment discontinuities and solving dating puzzles using monitoring and palaeolimnological records

Palaeolimnological studies should ideally be based upon continuous, undisturbed sediment sequences with reliable chronologies. However for some lake cores, these conditions are not met and palaeolimnologists are often faced with dating puzzles caused by sediment disturbances in the past. This study chooses Esthwaite Water from England to illustrate how to identify sedimentation discontinuities in lake cores and how chronologies can be established for imperfect cores by correlation of key sediment signatures in parallel core records and with long-term monitoring data (1945‒2003). Replicated short cores (ESTH1, ESTH7, and ESTH8) were collected and subjected to loss-on-ignition, radiometric dating (210Pb, 137Cs, and 14C), particle size, trace metal, and fossil diatom analysis. Both a slumping and a hiatus event were detected in ESTH7 based on comparisons made between the cores and the long-term diatom data. Ordination analysis suggested that the slumped material in ESTH7 originated from sediment deposited around 1805‒1880 AD. Further, it was inferred that the hiatus resulted in a loss of sediment deposited from 1870 to 1970 AD. Given the existence of three superior 14C dates in ESTH7, ESTH1 and ESTH7 were temporally correlated by multiple palaeolimnological proxies for age-depth model development. High variability in sedimentation rates was evident, but good agreement across the various palaeolimnological proxies indicated coherence in sediment processes within the coring area. Differences in sedimentation rates most likely resulted from the natural morphology of the lake basin. Our study suggests that caution is required in selecting suitable coring sites for palaeolimnological studies of small, relatively deep lakes and that proximity to steep slopes should be avoided wherever possible. Nevertheless, in some cases, comparisons between a range of contemporary and palaeolimnological records can be employed to diagnose sediment disturbances and establish a chronology

Comparing RADseq and microsatellites to infer complex phylogeographic patterns, an empirical perspective in the Crucian carp, Carassius carassius, L.

The conservation of threatened species must be underpinned by phylogeographic knowledge. This need is epitomized by the freshwater fish Carassius carassius, which is in decline across much of its European range. Restriction site-associated DNA sequencing (RADseq) is increasingly used for such applications; however, RADseq is expensive, and limitations on sample number must be weighed against the benefit of large numbers of markers. This trade-off has previously been examined using simulation studies; however, empirical comparisons between these markers, especially in a phylogeographic context, are lacking. Here, we compare the results from microsatellites and RADseq for the phylogeography of C. carassius to test whether it is more advantageous to genotype fewer markers (microsatellites) in many samples, or many markers (SNPs) in fewer samples. These data sets, along with data from the mitochondrial cytochrome b gene, agree on broad phylogeographic patterns, showing the existence of two previously unidentified C. carassius lineages in Europe: one found throughout northern and central-eastern European drainages and a second almost exclusively confined to the Danubian catchment. These lineages have been isolated for approximately 2.15 M years and should be considered separate conservation units. RADseq recovered finer population structure and stronger patterns of IBD than microsatellites, despite including only 17.6% of samples (38% of populations and 52% of samples per population). RADseq was also used along with approximate Bayesian computation to show that the postglacial colonization routes of C. carassius differ from the general patterns of freshwater fish in Europe, likely as a result of their distinctive ecology

Bimodality and alternative equilibria do not help explain long-term patterns in shallow lake chlorophyll-a

Since its inception, the theory of alternative equilibria in shallow lakes has evolved and been applied to an ever wider range of ecological and socioecological systems. The theory posits the existence of two alternative stable states or equilibria, which in shallow lakes are characterised by either clear water with abundant plants or turbid water where phytoplankton dominate. Here, we used data simulations and real-world data sets from Denmark and north-eastern USA (902 lakes in total) to examine the relationship between shallow lake phytoplankton biomass (chlorophyll-a) and nutrient concentrations across a range of timescales. The data simulations demonstrated that three diagnostic tests could reliably identify the presence or absence of alternative equilibria. The real-world data accorded with data simulations where alternative equilibria were absent. Crucially, it was only as the temporal scale of observation increased (>3 years) that a predictable linear relationship between nutrient concentration and chlorophyll-a was evident. Thus, when a longer term perspective is taken, the notion of alternative equilibria is not required to explain the response of chlorophyll-a to nutrient enrichment which questions the utility of the theory for explaining shallow lake response to, and recovery from, eutrophication.C.D.S. and T.A.D. would like to thank June and Derek Sayer for extraordinary support over many years. The authors of this work have been supported by a number of projects over the elephantine gestation period of this manuscript. These include support from the Poul Due Jensen Fonden, Danmarks Frie Forskningsfond Natur og Univers project GREENLAKES (No. 9040-00195B) and the UFM-funded project LTER_DK for Long Term Ecosystem Research in Denmark. In addition, support was provided by The European Union’s Horizon 2020 research and innovation programmes under grant agreement No 869296—The PONDERFUL Project”, TREICLAKE under grant agreement No 951963, and the AQUACOSM project and by the European Commission EU H2020- INFRAIA-project (No. 731065) and AQUACOSMplus (No. 871081). E.J. was also supported by the TÜBITAK outstanding researcher programme2232 (project 118C250) and AnaEE, Denmark. The work of D.G. was funded by the Fourth Period of Programme-oriented Funding, Helmholtz Association of German ResearchCentres, Research Field Earth and Environment.C.D.S. and T.A.D. would like to thank June and Derek Sayer for extraordinary support over many years. The authors of this work have been supported by a number of projects over the elephantine gestation period of this manuscript. These include support from the Poul Due Jensen Fonden, Danmarks Frie Forskningsfond Natur og Univers project GREENLAKES (No. 9040-00195B) and the UFM-funded project LTER_DK for Long Term Ecosystem Research in Denmark. In addition, support was provided by The European Union’s Horizon 2020 research and innovation programmes under grant agreement No 869296—The PONDERFUL Project”, TREICLAKE under grant agreement No 951963, and the AQUACOSM project and by the European Commission EU H2020- INFRAIA-project (No. 731065) and AQUACOSMplus (No. 871081). E.J. was also supported by the TÜBITAK outstanding researcher programme2232 (project 118C250) and AnaEE, Denmark. The work of D.G. was funded by the Fourth Period of Programme-oriented Funding, Helmholtz Association of German ResearchCentres, Research Field Earth and Environment

Microplastic burden in invasive signal crayfish (Pacifastacus leniusculus) increases along a stream urbanization gradient

Microplastics are a globally pervasive pollutant with the potential to directly impact species and accumulate in ecosystems. However, there remains a relative paucity of research addressing their accumulation in freshwater ecosystems and a near absence of work in crayfish, despite their high ecological and economic importance. This study investigated the presence of microplastics in the invasive signal crayfish Pacifastacus leniusculus along a stream urbanization gradient. The results demonstrate a ubiquitous presence of microplastics in crayfish digestive tracts at all sites and provide the first evidence of microplastic accumulation in tail tissue. Evidence of a positive linear trend was demonstrated between microplastic concentration in crayfish and upstream urban area size in generalized linear models. Evidence for a positive effect of the upstream urban area and a negative effect of crayfish length on microplastic concentrations in crayfish was demonstrated in multiple generalized linear regression models. Our results extend the current understanding of microplastics presence in freshwater ecosystems and demonstrate their presence in crayfish in the wild for the first time