Can small zooplankton mix lakes?

The idea that living organisms may contribute to turbulence and mixing in lakes and oceans (biomixing) dates to the 1960s, but has attracted increasing attention in recent years. Recent modeling and experimental studies suggest that marine organisms can enhance turbulence as much as winds and tides in oceans, with an impact on mixing. However, other studies show opposite and contradictory results, precluding definitive conclusions regarding the potential importance of biomixing. For lakes, only models and lab studies are available. These generally indicate that small zooplankton or passive bodies generate turbulence but different levels of mixing depending on their abundance. Nevertheless, biogenic mixing is a complex problem, which needs to be explored in the field, to overcome limitations arising from numerical models and lab studies, and without altering the behavior of the animals under study

Dissolved organic nutrient uptake by riverine phytoplankton varies along a gradient of nutrient enrichment

The concentration of dissolved organic matter (DOM) in freshwaters is increasing in large areas of the world. In addition to carbon, DOM contains nitrogen and phosphorus and there is growing concern that these organic nutrients may be bioavailable and contribute to eutrophication. However, relatively few studies have assessed the potential for dissolved organic nitrogen (DON) or dissolved organic phosphorus (DOP) compounds to be bioavailable to natural river phytoplankton communities at different locations or times. Temporal and spatial variations in uptake, relative to environmental characteristics were examined at six riverine sites in two contrasting catchments in the UK. This study also examined how the uptake by riverine phytoplankton of four DON and four DOP compounds commonly found in rivers, varied with concentration. Total nitrogen (TN) and phosphorus (TP) concentrations, the proportion of inorganic nutrient species, and nutrient limitation varied temporally and spatially, as did the potential for DON and DOP uptake. All eight of the DOM compounds tested were bioavailable, but to different extents. Organic nutrient use depended on the concentration of the organic compound supplied, with simple compounds (urea and glucose-6-phosphate) supporting algal growth even at very low concentrations. DON use was negatively correlated with the TN and ammonia concentration and DOP use was negatively correlated with soluble reactive phosphorus (SRP) and dissolved organic carbon (DOC) concentration. The evidence indicates that DOM in rivers has been overlooked as a potential source of nutrients to phytoplankton and therefore as an agent of eutrophication

Water quality digital twin survey

Stakeholders’ views on the creation of a Water Quality Digital Twin, for assessing the impacts of multiple stressors on standing and flowing freshwaters, were sought through an anonymous survey composed of closed and open questions. The work was funded as part of the UKSCAPE integration fund (https://ukscape. ceh.ac.uk/about ) and sought to co-develop a blueprint for a UKCEH water quality digital twin. Fifty-nine participants responded and provided a wealth of viewpoints, from academia, industry, regulators, and policy makers’ perspectives. In general, the catchment scale was considered the most feasible, useful, realistic, and deliverable scale for a Water Quality Digital Twin. Respondents considered the desired temporal scale to be dependent on the use envisaged for the digital twin. However, sub-daily or daily scales emerged as providing the most actionable knowledge if data were available and it was computationally feasible. Overall, there was consensus that nutrient concentrations were the most important determinands to include in a water quality digital twin (100% of respondents scoring these as one of their three most important determinand categories). However, several additional abiotic and biotic determinands were also scored highly, partly depending on the required use of the resultant digital twin

Strength and uncertainty of phytoplankton metrics for assessing eutrophication impacts in lakes

Phytoplankton constitutes a diverse array of short-lived organisms which derive their nutrients from the water column of lakes. These features make this community the most direct and earliest indicator of the impacts of changing nutrient conditions on lake ecosystems. It also makes them particularly suitable for measuring the success of restoration measures following reductions in nutrient loads. This paper integrates a large volume of work on a number of measures, or metrics, developed for using phytoplankton to assess the ecological status of European lakes, as required for the Water Framework Directive. It assesses the indicator strength of these metrics, specifically in relation to representing the impacts of eutrophication. It also examines how these measures vary naturally at different locations within a lake, as well as between lakes, and how much variability is associated with different replicate samples, different months within a year and between years. On the basis of this analysis, three of the strongest metrics (chlorophyll-a, phytoplankton trophic index (PTI), and cyanobacterial biovolume) are recommended for use as robust measures for assessing the ecological quality of lakes in relation to nutrient-enrichment pressures and a minimum recommended sampling frequency is provided for these three metrics

The state of Esthwaite Water in 2010

1. Esthwaite Water is one of the most nutrient-enriched lakes in the English Lake District, but the enrichment has mainly occurred in the last 50 years and in particular since the establishment of the wastewater treatment works (WwTW) at Hawkshead in 1973 and a fish farm on the lake in 1981. The fish cages were removed from the lake in November 2009 and recent upgrades have been made to the WwTW. This report describes the conditions and water quality at Esthwaite Water in 2010, places them into the context of recent conditions and assesses evidence for any change. 2. The seasonal temperature and stratification cycle was typical with surface water reaching nearly 20 °C and the bottom temperature only 10 °C. Stratification lasted for about 180 days from the beginning of April to mid-October. 3. The average alkalinity was 0.43 equiv m-3 placing Esthwaite Water in the medium alkalinity category of the Water Framework Directive. 4. Nutrients showed typical seasonal patterns. Total phosphorus was relatively conservative with peaks during time of high phytoplankton biomass and an average concentration of 21.4 mg m-3. Soluble reactive phosphorus had peak concentrations of about 12 mg m-3 at the start of the year but fell rapidly in March to the limit of detection, 0.6 mg m-3, and the concentration remained low for most of the summer and only increased on the breakdown of stratification in autumn. Silica concentrations also fell rapidly in spring as is was removed by the growing spring diatoms. Nitrate was the dominant form of nitrogen and fell more slowly than phosphorus and silica and reached minima of 30 mg m-3 that could indicate a short-period of nitrogen limitation in an otherwise phosphorus-limited lake. 5. The phytoplankton produced a spring bloom of about 16 mg m-3 comprising mainly diatom and an extensive summer bloom of cyanobacteria that reached 35 mg m-3 that did not decline until the beginning of November. The annual average concentration was 15.6 mg m-3. 6. The phytoplankton had a major effect on the light climate with Secchi depth minim of 1.5 m in August. The annual average light attenuation coefficient of about 0.87 m-1 would allow macrophyte colonisation down to between 2 and 4.3 m depending on species. 7. Nine species of crustacean zooplankton were recorded with an early summer peak population in May dominated by Daphnia hyalina/galeata. Later in the year, smaller bodied Bosmina longirostris and Ceriodaphnia quadrangula produced a population peak in mid September. 8. Statistical comparisons of the monthly-average and annual-average values of various water quality parameters in 2010 and the previous ten years showed encouraging changes. Statistically significant reduction in concentration in 2010 compared to the previous ten years were found for: (i) total phosphorus in ten months and as an annual average; (ii) soluble reactive phosphorus in 4 months and as an annual average; (iii) nitrate in eight months and as an annual average. This led to statistically significant reductions in the concentration of chlorophyll a in eight months and as annnual average and increases in Secchi depth in five months and as an annual average. The minimum concentrations of oxygen at depth were essentially unchanged and the density of zooplankton was lower in some months. 9. The current ecological status of Esthwaite Water under the Water Framework Directive is ‘Moderate’ for both total phosphorus and chlorophyll a. In previous years, the ecological status was close to the Moderate: Poor boundary for both measures. This underlines the necessity of the programme of measures that are currently underway on the lake. 10. While these results are extremely encouraging, weather patterns can lead to periods of improvement and worsening in water quality so continued monitoring is essential. Furthermore, some of these improvements started to be evident in 2009 (concentrations of total phosphorus, soluble reactive phosphorus and nitrate) and so in order to be able, confidently, to link these to management changes, it is very to obtain more information on waste-water handling at the Hawkshead WwTW and the stocking densities and feeding regime of the fish farm on the lake

Spatial structure in the zooplankton of a newly formed and heavily disturbed urban lake

Physico-chemical gradients and local biotic interactions combine at different scales to cause spatial heterogeneity among lake zooplankton. However, current understanding is based overwhelmingly on natural systems and there have been few assessments of zooplankton spatial pattern in artificial lakes subjected to intensive management. Here, we investigate spatial structure among crustacean zooplankton at scales ranging from 1 m to 2700 m in the newly-formed Cardiff Bay (UK). We hypothesised that zooplankton spatial structuring in Cardiff Bay would be weakened by artificial aeration that was expected to create intense, continuous disturbance that homogenised physico-chemical conditions. Water quality across Cardiff Bay varied only moderately, and variations in zooplankton community composition were weakly related to temperature, oxygen, chlorophyll-a concentration and salinity at scales of around 2 km. However, spatial pattern explained over 60 % of variance in zooplankton composition at the smallest scales (0-5 m), implying that inter-specific interactions were involved. Additionally, the numerically dominant zooplankton (Daphnia hyalina (Leydig 1860), Eurytemora affinis (Poppe 1880) and Eucyclops agilis (Koch 1838)) had highly contagious distributions in warmer locations with increased chlorophyll-a reflecting aggregated response to abundant food. These data suggest that local biotic interactions among zooplankton and broader-scale links between dominant species and their algal food are sufficiently intense to persist despite the homogenising effects of artificial aeration and lake mixing. Such spatial pattern and scale-dependence has ramifications for zooplankton sampling while illustrating the self-organising capacity of predator-prey interactions even in novel, disturbed environments

A survey of the lakes of the English Lake District: the Lakes Tour 2010

1. This report presents information resulting from a survey of the limnology of the 20 major lakes and tarns in the English Lake District based on samples taken in January, April, July and October 2010. This ‘Lakes Tour’ supplements similar tours in 1984, 1991, 1995, 2000 and 2005. 2. On each sampling occasion depth-profiles were collected of water temperature and oxygen concentration and Secchi depth was measured. An integrated water sample was analysed for pH and alkalinity, major cations and anions, plant nutrients, phytoplankton chlorophyll a and species composition and zooplankton abundance and species composition. Some of the field work and chemical analyses were carried out collaboratively between staff from CEH and the Environment Agency. 3. The lakes had a range in tendency to stratify in summer with the weakest stratification in large, relatively shallow and exposed lakes such as Bassenthwaite Lake. During summer stratification oxygen-depletion at depth was only found in the more productive lakes. 4. Water clarity, assessed by Secchi disc, varied between about 13 m in clear unproductive lakes such as Wastwater to less than 2 m in the more productive lakes during summer such as Esthwaite Water. 5. Major ion composition varied with geology and altitude. Lakes on the Silurian slates (those in the Windermere and Coniston Water catchments) tended to have anions dominated by alkalinity (bicarbonate) and cations dominated by calcium whereas the other lakes tended to have anions dominated by chloride and cations dominated by sodium. 6. Availability of phosphorus is the main factor that affects lake productivity. Concentrations were lowest in Wastwater and Ennerdale Water and highest in Elterwater and Esthwaite Water. Nitrate was the dominant form of nitrogen. Nitrate concentrations tended to be lowest in July because of biological uptake and seasonal fluctuations were most marked in the productive lakes. Silica, an essential nutrient for diatoms, showed a similar seasonal pattern to nitrate but the depletion was more marked in April because the spring bloom is typically dominated by diatoms. In unproductive lakes such as Wastwater and Ennerdale Water concentrations of silica did not vary seasonally. 7. The concentration of chlorophyll a was used as a measure of phytoplankton abundance. Comparisons across lakes showed low concentrations all the year in the unproductive lakes and seasonally high concentrations in the more productive lakes. Loughrigg Tarn had the highest annual average concentration of chlorophyll a. 8. The species composition varied seasonally in all the lakes, even unproductive ones with limited seasonal changes in nutrient concentrations, underlying the sensitivity of phytoplankton to environmental conditions. Overall, diatoms dominated in January and particularly, April, but in .July and October a range of different groups dominated depending on the lake. 9. Zooplankton abundance was very variable and greatest in the productive lakes and seasonally, abundance tended to be greatest in July and October. Seventeen genera of zooplankton were recorded in total. The unproductive lakes tended to be dominated by Eudiaptomus gracilis and this species dominated most of the lakes in January. Daphnia spp. were often important in the summer in the more productive lakes. Another cladoceran, Bosmina spp. was in appreciable numbers in January in some lakes. Ceriodaphnia and Mesocyclops were an important part of the zooplankton community in some lakes. 10. The known status of fish populations, although not undertaken in the project, was summarised. Eighteen species have been recorded in these lakes, but of these six are probably introduced. Some lakes have very little fish-data and require more research. 11. Heavy metals were measured for the first time. Although many samples were below the limit of detection, copper concentrations were elevated in Coniston Water and Haweswater, lead was elevated in Haweswater and zinc was elevated in Bassenthwaite Lake, Brothers Water, Buttermere and Haweswater. 12. Micro-organic pollutants were measured for the first time and most samples were below current detection limits. Of the 128 compounds analysed, 16 gave values above the detection limit but only five exceeded the limit more than once. Of these, Diazinon, an organophosphorus insecticide, had concentrations that exceeded Environmental Quality Standards in Buttermere and was high in a number of other lakes; this merits further investigation. 13. The current state of each lake was summarised in terms of key limnological variables, trophic state and ecological status under the current definitions of the Water Framework Directive. 14. Only Buttermere and Wastwater were at High ecological status for both total phosphorus and chlorophyll a. Brothers Water, Coniston Water, Crummock Water, Derwent Water, Ennerdale Water and Haweswater were at Good ecological status. Bassenthwaite Lake, Blelham Tarn, Elterwater, Esthwaite Water, Grasmere, Loweswater, Rydal Water, Thirlmere, Ullswater and the North and South Basins of Windermere were at Moderate ecological status, although Ullswater was close to Good status. Loughrigg Tarn was at Poor status because of high phytoplankton chlorophyll a. Lakes at Moderate or Poor ecological status will require further work to bring them to Good ecological status by 2015 under the Water Framework Directive (WFD), although Rydal Water and Loughrigg Tarn are not on the UK –list of WFD lakes. 15. Long-term change from 1984 to 2010 (1991 to 2010 for some variables) were analysed. There have been changes in the concentration of major ions in many sites. This has largely been caused by reduction in sulphate deposition from acid rain, causing widespread increases in alkalinity and pH and reductions in concentration of calcium, magnesium, sodium and potassium because of reduced cation-exchange in the soil. Reducing concentrations of sodium and chloride are probably related to reductions in stormy weather since the mid 1990s and hence reduced input of sea-salt in rain. On average, in comparison to the 2005 Lakes Tour, there has been a reduction in concentration of TP and phytoplankton chlorophyll a and an increase in Secchi depth. While the magnitude of change is small, it is, encouragingly in the right direction. 16. The lakes in the English Lake District are extremely valuable scientifically as they are highly diverse. This was illustrated by showing the link between catchment altitude (as a proxy for land use and soil type) and a range of water chemistry variables and the relationship between phytoplankton chlorophyll a and total phosphorus which shows that the productivity of these lakes is controlled by phosphorus. The magnitude of the seasonal changes in silica and nitrate is positively linked to lake productivity. Secchi depth is negatively correlated with phytoplankton, but in January Secchi depth is less for a given chlorophyll a concentration, probably because of attenuation by dissolved organic carbon and particulate material brought in to the lakes by winter rains. Minimum oxygen concentration at depth is also negatively related to phytoplankton chlorophyll a. 17. It is suggested that more work is needed at lakes which have failed Good ecological status, and at Ennerdale Water in particular where there has been a dramtic decrease in Secchi depth that appears to be linked to increased productivity. The fish populations in many lakes need to be studied in more detail. 18. The joint-manning of the Lakes Tour by CEH and the EA worked well and could be a model for other work in the future

From ecological informatics to the generation of ecological knowledge: long-term research in the English Lake District

Lakes are highly connected systems that are affected by a hierarchy of stressors operating at different scales, making them particularly sensitive to anthropogenic perturbation. Traditionally, lakes are studied as a whole system ‘from physics to fish’ and long-term monitoring programmes were initiated on this basis, some starting over a century ago. This chapter describes the long-term monitoring programme on the Cumbrian lakes, UK, how it is operated and how its scientific value is increased by combining it with additional activities. Case-studies are presented on the advances long-term research has made to testing ecological theory and understanding teleconnexions and phenology. Automatic high-frequency measurements are an important complementary approach that has been made possible by technological revolutions in computing, and telecommunications. They provide a window into the true dynamic nature of lakes that cannot be achieved by manual sampling. The large volume of data produced can now be quality controlled and analysed by bespoke software that has been developed in recent years by a global network of lake and data scientists. Finally, lake models constructed using the insights from monitoring, as well as experiments, are powerful ways to identify knowledge gaps and allow forecasts to be made of future responses to environmental change or management intervention. As other approaches become incorporated into lake research, such as Earth Observation and citizen science, the scale of knowledge about the system will increase, improving our ability to provide robust scientific advice for the sustainable management of these fragile, but important ecosystems