When phenology matters: age–size truncation alters population response to trophic mismatch

Climate-induced shifts in the timing of life-history events are a worldwide phenomenon, and these shifts can de-synchronize species interactions such as predator–prey relationships. In order to understand the ecological implications of altered seasonality, we need to consider how shifts in phenology interact with other agents of environmental change such as exploitation and disease spread, which commonly act to erode the demographic structure of wild populations. Using long-term observational data on the phenology and dynamics of a model predator–prey system (fish and zooplankton in Windermere, UK), we show that age–size truncation of the predator population alters the consequences of phenological mismatch for offspring survival and population abundance. Specifically, age–size truncation reduces intraspecific density regulation due to competition and cannibalism, and thereby amplifies the population sensitivity to climate-induced predator–prey asynchrony, which increases variability in predator abundance. High population variability poses major ecological and economic challenges as it can diminish sustainable harvest rates and increase the risk of population collapse. Our results stress the importance of maintaining within-population age–size diversity in order to buffer populations against phenological asynchrony, and highlight the need to consider interactive effects of environmental impacts if we are to understand and project complex ecological outcomes

Quantitative analysis of the importance of wind-induced circulation for the spatial structuring of planktonic populations

1. Several studies have shown that wind-induced water movements have an important effect on the spatial distribution of crustacean zooplankton. However, few attempts have been made to quantify the effect of physical processes on these broad-scale patterns. Much of our understanding of this spatial structure has been based on the results of isolated surveys, which do not capture the dynamic nature of the pelagic environment. 2. In this study, we have used a combination of high-speed sampling (at a spatial resolution of 240 m) and spatial data analysis to quantify the factors influencing the horizontal spatial structure of the Daphnia galeata population in Windermere. 3. The results show that lake-wide circulation patterns, as indicated by water temperature, account for 29–47% of the basin-scale spatial variance in D. galeata abundance. However, these patterns are highly dynamic and change in response to the prevailing weather. This lack of temporal persistence means that the results of single-survey sampling campaigns must be interpreted with caution

Sunbiggin Tarn & Moors & Little Asby Common SSSI water quality monitoring survey

Report to Friends of the Lake District and Natural England. 1. Sunbiggin Tarn is a small marl lake on the Orton fells in North West England, where there is concern about nutrient levels and consequent algal growth that places the lake in an ecologically unfavourable state. This work was designed to investigate the causes of this nutrient enrichment based on monthly samples from seven inflow streams and the lake between April 2019 and February 2020 and a depth profile measured in mid-summer. 2. There are several lines of evidence for calcite precipitation in the tarn during summer. Alkalinity in summer is lower than in the winter; the tarn alkalinity in the winter is similar to the inflowing streams but lower than the streams in the summer; calculations show that the calcite was highly oversaturated in summer; finally, data from the Environment Agency from 2004 to 2006 show summer concentrations of dissolved calcium are about half that of winter concentrations. 3. There is some evidence for internal loading of total phosphorus during the summer since surface concentrations in May, June and July are higher than at other times of years. More frequent depth profiles would be needed to determine if this resulted from internal loading. The current data and calculations suggest that anoxia-triggered release of phosphorus from the sediment is likely to be more important than release of phosphorus from apatite dissolution at depth in producing the high concentrations of soluble reactive phosphorus measured at the bottom of the tarn. 4. The concentration of total phosphorus in the tarn seems to be consistent with the stream concentrations, although the effects of any groundwater inputs are unknown. In contrast, there is a large loss of total nitrogen within the tarn since the concentrations are much lower in the tarn than the inflowing streams. 5. The concentrations of total phosphorus in 2019-2020 was lower than in 2003 and 2004-2006 and the mean and median concentrations of phytoplankton chlorophyll a were lower in 2019-2020 than in 2004-2006 but slightly higher than in 2003. There is therefore some suggestion that the ecological conditions in the tarn are improving. 6. The concentrations of nitrate in the tarn are unlikely to inhibit charophyte growth directly but could have an indirect effect by stimulating phytoplankton and epiphytic algae growth that could shade the charophyte beds. The generally low concentrations of nitrogen in the tarn suggest that this is unlikely. Rather primary production could be limited by nitrogen rather than phosphorus, at least in some seasons. 7. More detailed, targeted future investigations are suggested to address some of the uncertainties noted in order to produce more evidence-based knowledge for the conservation and management of Sunbiggin Tarn

On biogenic turbulence production and mixing from vertically migrating zooplankton in lakes

Vertical mixing in lakes is a key driver of transport of ecologically important dissolved constituents, such as oxygen and nutrients. In this study we focus our attention on biomixing, which refers to the contribution of living organisms towards the turbulence and mixing of oceans and lakes. While several studies of biomixing in the ocean have been conducted, no in situ studies exist that assess the turbulence induced by freshwater zooplanktonic organisms under real environmental conditions. Here, turbulence is sampled during three different sampling days during the sunset diel vertical migration of Daphnia spp. in a small man-made lake. This common genus may create hydrodynamic disturbances in the lake interior where the thermal stratification usually suppresses the vertical diffusion. Concurrent biological sampling assessed the zooplankton vertical concentration profile. An acoustic-Doppler current profiler was also used to track zooplankton concentration and migration via the backscatter strength. Our datasets do not show biologically-enhanced dissipation rates of temperature variance and turbulent kinetic energy in the lake interior, despite Daphnia concentrations as high as 60 org. L−1. No large and significant turbulent patches were created within the migrating layer to generate irreversible mixing. This suggests that Daphnia do not affect the mixing in the lake at the organism concentrations observed here

Effect of temperature on zooplankton vertical migration velocity

Zooplankton diel vertical migration (DVM) is an ecologically important process, affecting nutrient transport and trophic interactions. Available measurements of zooplankton displacement velocity during the DVM in the field are rare; therefore, it is not known which factors are key in driving this velocity. We measured the velocity of the migrating layer at sunset (upward bulk velocity) and sunrise (downwards velocity) in summer 2015 and 2016 in a lake using the backscatter strength (VBS) from an acoustic Doppler current profiler. We collected time series of temperature, relative change in light intensity chlorophyll-a concentration and zooplankton concentration. Our data show that upward velocities increased during the summer and were not enhanced by food, light intensity or by VBS, which is a proxy for zooplankton concentration and size. Upward velocities were strongly correlated with the water temperature in the migrating layer, suggesting that temperature could be a key factor controlling swimming activity. Downward velocities were constant, likely because Daphnia passively sink at sunrise, as suggested by our model of Daphnia sinking rate. Zooplankton migrations mediate trophic interactions and web food structure in pelagic ecosystems. An understanding of the potential environmental determinants of this behaviour is therefore essential to our knowledge of ecosystem functioning

Emerging opportunities and challenges in phenology: a review

Plant phenology research has gained increasing attention because of the sensitivity of phenology to climate change and its consequences for ecosystem function. Recent technological development has made it possible to gather invaluable data at a variety of spatial and ecological scales. Despite our ability to observe phenological change at multiple scales, the mechanistic basis of phenology is still not well understood. Integration of multiple disciplines, including ecology, evolutionary biology, climate science, and remote sensing, with long-term monitoring data across multiple spatial scales are needed to advance understanding of phenology. We review the mechanisms and major drivers of plant phenology, including temperature, photoperiod, and winter chilling, as well as other factors such as competition, resource limitation, and genetics. Shifts in plant phenology have significant consequences on ecosystem productivity, carbon cycling, competition, food webs, and other ecosystem functions and services. We summarize recent advances in observation techniques across multiple spatial scales, including digital repeat photography, other complementary optical measurements, and solar induced fluorescence, to assess our capability to address the importance of these scale-dependent drivers. Then we review phenology models as an important component of earth system modeling. We find that the lack of species-level knowledge and observation data lead to difficulties in the development of vegetation phenology models at ecosystem or community scales. Finally, we recommend further research to advance understanding of the mechanisms governing phenology and the standardization of phenology observation methods across networks. With the opportunity for “big data” collection for plant phenology, we envision a breakthrough in process-based phenology modeling

Evaluating the use of lake sedimentary DNA in palaeolimnology:A comparison with long‐term microscopy‐based monitoring of the phytoplankton community

Palaeolimnological records provide valuable information about how phytoplankton respond to long-term drivers of environmental change. Traditional palaeolimnological tools such as microfossils and pigments are restricted to taxa that leave sub-fossil remains, and a method that can be applied to the wider community is required. Sedimentary DNA (sedDNA), extracted from lake sediment cores, shows promise in palaeolimnology, but validation against data from long-term monitoring of lake water is necessary to enable its development as a reliable record of past phytoplankton communities. To address this need, 18S rRNA gene amplicon sequencing was carried out on lake sediments from a core collected from Esthwaite Water (English Lake District) spanning ~105 years. This sedDNA record was compared with concurrent long-term microscopy-based monitoring of phytoplankton in the surface water. Broadly comparable trends were observed between the datasets, with respect to the diversity and relative abundance and occurrence of chlorophytes, dinoflagellates, ochrophytes and bacillariophytes. Up to 20% of genera were successfully captured using both methods, and sedDNA revealed a previously undetected community of phytoplankton. These results suggest that sedDNA can be used as an effective record of past phytoplankton communities, at least over timescales of <100 years. However, a substantial proportion of genera identified by microscopy were not detected using sedDNA, highlighting the current limitations of the technique that require further development such as reference database coverage. The taphonomic processes which may affect its reliability, such as the extent and rate of deposition and DNA degradation, also require further research

Effective management of ecological resilience – are we there yet?

1. Ecological resilience is developing into a credible paradigm for policy development and environmental management for preserving natural capital in a rapidly changing world. However, resilience emerges from complex interactions, limiting the translation of theory into practice. 2. Main limitations include the following: (i) difficulty in quantification and detection of changes in ecological resilience, (ii) a lack of empirical evidence to support preventative or proactive management and (iii) difficulties in managing processes operating across socio-ecological systems that vary in space and time. 3. We highlight recent research with the potential to address these limitations including new and/or improved indicators of resilience and tools to assess scale as a driver of resilience. 4. Synthesis and applications. Effective resilience-based management must be adaptive in nature. To support this, we propose an operational model using resilience-based iterative management actions operating across scales

Integrating environmental understanding into freshwater floatovoltaic deployment using an effects hierarchy and decision trees

In an era of looming land scarcity and environmental degradation, the development of low carbon energy systems without adverse impacts on land and land-based resources is a global challenge. 'Floatovoltaic' energy systems—comprising floating photovoltaic (PV) panels over water—are an appealing source of low carbon energy as they spare land for other uses and attain greater electricity outputs compared to land-based systems. However, to date little is understood of the impacts of floatovoltaics on the hosting water body. Anticipating changes to water body processes, properties and services owing to floatovoltaic deployment represents a critical knowledge gap that may result in poor societal choices and water body governance. Here, we developed a theoretically-derived hierarchical effects framework for the assessment of floatovoltaic impacts on freshwater water bodies, emphasising ecological interactions. We describe how the presence of floatovoltaic systems may dramatically alter the air-water interface, with subsequent implications for surface meteorology, air-water fluxes and physical, chemical and biological properties of the recipient water body. We apply knowledge from this framework to delineate three response typologies - 'magnitude', those for which the direction and magnitude of effect can be predicted; 'direction', those for which only the direction of effect can be predicted; and 'uncertain', those for which the response cannot be predicted - characterised by the relative importance of levels in the effects hierarchy. Illustrative decision trees are developed for an example water body response within each typology, specifically, evaporative water loss, cyanobacterial biomass, and phosphorus release from bed sediments, and implications for ecosystem services, including climate regulation, are discussed. Finally, the potential to use the new understanding of likely ecosystem perturbations to direct floatovoltaic design innovations and identify future research priorities is outlined, showcasing how inter-sectoral collaboration and environmental science can inform and optimize this low carbon, land-sparing renewable energy for ecosystem gains

Decarbonization potential of floating solar photovoltaics on lakes worldwide

As climate change progresses, there is increasing emphasis on net zero and energy system decarbonization. Several technologies are contributing to this agenda, but among these, the growth of solar photovoltaics has consistently exceeded all projections. With increasing land-use pressures, and the expense of building-mounted photovoltaics, water surfaces are increasingly being exploited to host these technologies. However, to date, we lack an understanding of the global potential of floating solar photovoltaics and, as such, we do not yet have sufficient insight to inform decisions on (in)appropriate areas for future deployment. Here we quantify the energy generation potential of floating solar photovoltaics on over 1 million water bodies worldwide (14,906 TWh). Our analysis suggests that with a conservative 10% surface area coverage, floating solar photovoltaics could produce sufficient energy to contribute a considerable fraction (16%, on average) of the electricity demand of some countries, thus playing an important role in decarbonizing national economies