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

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

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

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.&nbsp; This review focuses on marl lake ecology and chemistry, their known responses to eutrophication, and also highlights questions that remain unanswered.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; In good condition, marl lakes support a diversity of macrophytes, especially Characeae and Potamogetonaceae, which can grow to considerable depth.&nbsp; High water transparency and low phosphorus and phytoplankton concentrations are facilitated by the coprecipitation of marl and phosphorus.&nbsp; Although large amounts of phosphorus can be thus removed, buffering against eutrophication, macrophyte communities can undergo significant change under rather low nutrient concentrations.&nbsp; Maximum colonisation depth declines and tolerant species replace sensitive species, with losses particularly among charophytes.&nbsp; Marl lakes are therefore ecologically highly sensitive. &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; The effects of coprecipitation on long-term burial of phosphorus are contested.&nbsp; 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.&nbsp; 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.&nbsp; The phosphorus binding capacity of marl sediment has not to our knowledge been adequately researched. &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 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.&nbsp; Highly impacted marl lakes having low species diversity and lacking precipitation may be misidentified as eutrophic, high-alkalinity lakes.&nbsp; 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

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

Consequences of pond management for chironomid assemblages and diversity in English farmland ponds

Ponds represent a large potential resource for biodiversity in agricultural areas of lowland Europe though many are lost through natural succession towards damp woodland depressions (terrestrialisation). Managing ponds back towards their former open-water state may result in dramatic increases of biodiversity, even on heavily farmed land. Here, evidence is presented of the effects of terrestrialised farmland pond restoration on chironomid assemblages. Chironomid pupal exuviae were collected from three terrestrialised ponds on intensively-farmed land in North Norfolk, Eastern England. Two of the ponds had trees, scrub and sediment removed, while the third pond remained undisturbed as a control. Pupal exuviae collection resumed after the restoration period. In addition, nine unmanaged farm ponds and two formerly restored ponds were sampled. Nearby, another five restored ponds were also sampled for chironomid pupal exuviae. Water data revealed alkalinity, conductivity and phosphorus decreased while pH and dissolved oxygen increased after pond restoration. Chironomid species diversity, similarity and species compositional change were compared pre- and post-restoration. Assessments were made of chironomid species associated with colonisation of restored ponds as well as ponds without such management. After scrub and sediment removal the earliest colonisation of the ponds was by mud-eating species with rapid colonisation traits such as parthenogenesis, multiple generations in one year and tolerance of low oxygen conditions. Subsequent plant growth due to the opening up of the canopy led to consequent improved oxygenation and habitat structure. Other chironomid species dependent on these conditions were then able to compete with the early colonisers. Restoration also made a significant improvement in the number of chironomid species, as assessed by rarefaction curves

Revisiting hydro-ecological impacts of climate change on a restored floodplain wetland via hydrological/hydraulic modelling and the UK Climate Projections 2018 scenarios

The hydro-ecological impacts of 40 UK Climate Projections 2018 scenarios on a restored lowland England river floodplain are assessed using a MIKE SHE / MIKE 11 model. Annual precipitation declines for 60% of scenarios (range: -26%–21%, with small, <5%, declines for the central probability level). Potential evapotranspiration increases for all probability levels except the most extreme, very unlikely, 10% level (range: -4%–43%, central probability 9%–20%) Mean, peak and low river discharges are reduced for all but the extreme 90% probability level. Reduced frequency of bankfull discharge dominates (at least halved for the central probability level). Floodplain inundation declines for over 97% of 320 scenario-events. Winter water table levels still intercept the surface, while mean and summer low levels are reduced. Declines in mean summer floodplain water table levels for the central probability level (0.22 m and 0.28 m for the 2050s and 2080s, respectively) are twice as large as those in the more dynamic riparian area. Declines reach 0.39 m for some 10% probability level scenarios. Simulated hydrological changes differ subtly from a previous assessment using earlier UK climate projections. A soil aeration stress index demonstrates that, under baseline conditions, prolonged high winter floodplain water tables drive long periods of low root-zone oxygen, in turn favouring vegetation communities adapted to waterlogged conditions. Climate change reduces aeration stress and the extent of appropriate conditions for these plant communities in favour of communities less tolerant of wet conditions

Habitat heterogeneity enables spatial and temporal coexistence of native and invasive macrophytes in shallow lake landscapes

Macrophyte invasive alien species (IAS) fitness is often hypothesised to be associated with beneficial environmental conditions (environmental matching) or species-poor communities. However, positive correlations between macrophyte IAS abundance and native plant richness can also arise, due to habitat heterogeneity (defined here as variation in abiotic and native biotic conditions over space and time). We analysed survey and palaeoecological data for macrophytes in satellite lakes along the Upper Lough Erne (ULE) system (Northern Ireland, UK), covering a gradient of eutrophication and connectivity to partition how environmental conditions, macrophyte diversity and habitat heterogeneity explained the abundance of Elodea canadensis, a widely distributed non-native macrophyte in Europe. E. canadensis abundance positively correlated with macrophyte richness at both the within- and between-lake scales indicating coexistence of native and invasive species over time. E. canadensis was also more prolific in highly connected and macrophyte-rich lakes, but sparser in the more eutrophic-isolated ones. Partial boosted regression trees revealed that in eutrophic-isolated lakes, E. canadensis abundances correlated with water clarity (negatively), plant diversity (positively), and plant cover (negatively) whereas in diverse-connected lakes, beta diversity (both positively and negatively) related to most greatly E. canadensis abundance. Dense macrophyte cover and unfavourable environmental conditions thus appear to confer invasibility resistance and sufficient habitat heterogeneity to mask any single effect of native biodiversity or environmental matching in controlling E. canadensis abundance. Therefore, in shallow lake landscapes, habitat heterogeneity variously enables the coexistence of native macrophytes and E. canadensis, reducing the often-described homogenisation effects of invasive macrophytes.Output Status: Forthcoming/Available Onlin