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

Effects of brownification and warming on algal blooms, metabolism and higher trophic levels in productive shallow lake mesocosms

An increase of dissolved organic carbon (DOC) in inland waters has been reported across the northern temperate region but the effects of this on whole lake ecosystems, often combined with other anthropogenic stressors like nutrient inputs and warming, are poorly known. The effects of these changes on different component of the ecosystem were assessed in an experiment using twenty-four large (3000L) outdoor mesocosms simulating shallow lakes. Two different temperature regimes (ambient and ambient +4 °C) combined with three levels of organic matter (OM, added as filtered peaty water), simulating the DOC increase that is predicted to take place over the next 4 to 21 years were used. Neither temperature nor OM had significant effects on net ecosystem production, respiration or gross primary production. Phytoplankton chlorophyll a concentration was not significantly affected by warming, however in summer, autumn and winter it was significantly higher in mesocosms receiving intermediate OM levels (July–Feb DOC concentrations 2–6 mg L−1). Summer cyanobacterial blooms were highest in intermediate, and lowest in the highest OM treatments. OM concentration also influenced total macroinvertebrate abundance which was greater in spring and summer in mesocosms with intermediate and high OM. Fish abundance was not significantly affected by OM concentration, but abundance was greater in ambient (55 fish subsample−1) compared to heated mesocosms (17 fish subsample−1) and maximum abundance occurred two weeks later compared to heated mesocosms. The results suggest that changes in OM may have a greater effect on shallow lakes than temperature and that phytoplankton, especially cyanobacteria, benefit from intermediate OM concentrations, therefore, nuisance algal blooms might increase in relatively clear shallow eutrophic lakes where DOC concentrations increase

A meta-analysis of water quality and aquatic macrophyte responses in 18 lakes treated with lanthanum modified bentonite (PHOSLOCK®)

Lanthanum (La) modified bentonite is being increasingly used as a geo-engineering tool for the control of phosphorus (P) release from lake bed sediments to overlying waters. However, little is known about its effectiveness in controlling P across a wide range of lake conditions or of its potential to promote rapid ecological recovery. We combined data from 18 treated lakes to examine the lake population responses in the 24 months following La-bentonite application (range of La-bentonite loads: 1.4 to 6.7 tonnes ha-1) in concentrations of surface water total phosphorus (TP; data available from 15 lakes), soluble reactive phosphorus (SRP; 14 lakes), and chlorophyll a (15 lakes), and in Secchi disk depths (15 lakes), aquatic macrophyte species numbers (6 lakes) and aquatic macrophyte maximum colonisation depths (4 lakes) across the treated lakes. Data availability varied across the lakes and variables, and in general monitoring was more frequent closer to the application dates. Median annual TP concentrations decreased significantly across the lakes, following the La-bentonite applications (from 0.08 mg L-1 in the 24 months pre-application to 0.03 mg L-1 in the 24 months post-application), particularly in autumn (0.08 mg L-1 to 0.03 mg L-1) and winter (0.08 mg L-1 to 0.02 mg L-1). Significant decreases in SRP concentrations over annual (0.019 mg L-1 to 0.005 mg L-1), summer (0.018 mg L-1 to 0.004 mg L-1), autumn (0.019 mg L-1 to 0.005 mg L-1) and winter (0.033 mg L-1 to 0.005 mg L-1) periods were also reported. P concentrations following La-bentonite application varied across the lakes and were correlated positively with dissolved organic carbon concentrations. Relatively weak, but significant responses were reported for summer chlorophyll a concentrations and Secchi disk depths following La-bentonite applications, the 75th percentile values decreasing from 119 μg L-1 to 74 μg L-1 and increasing from 398 cm to 506 cm, respectively. Aquatic macrophyte species numbers and maximum colonisation depths increased following La-bentonite application from a median of 5.5 species to 7.0 species and a median of 1.8 m to 2.5 m, respectively. The aquatic macrophyte responses varied significantly between lakes. La-bentonite application resulted in a general improvement in water quality leading to an improvement in the aquatic macrophyte community within 24 months. However, because, the responses were highly site-specific, we stress the need for comprehensive pre- and post-application assessments of processes driving ecological structure and function in candidate lakes to inform future use of this and similar products

Nitrogen stable isotope ratios of lake macrophytes in relation to growth form and nutrient-limitation

Values are presented of natural abundance nitrogen stable isotope ratios (15N ‰) for macrophyte samples from 30 U.K. upland tarns. Values for individual macrophyte species at the different sites varied between –9.9‰ and 10.6‰, a range of 20.5‰. The average value of a particular macrophyte species was slightly less variable with a range of 14.5‰ and the average range per site was 10.4‰. To explore the possible causes of this very high variation, macrophytes were allocated into three categories according to their growth form and hence whether they probably obtained their nitrogen i) from both water and sediment (such as elodeids and isoetids), ii) mainly from the sediment (such as rooted emergent or floating-leaved plants) and iii) mainly from the water (such as filamentous algae, bryophytes and rootless vascular plants). An analysis of variance showed that δ15N differed according to presumed nitrogen source: average values were 0.3, 1.6 and 3.0‰ for macrophytes that obtain their nitrogen respectively from the water, from both sources and from the sediment. Hence part of the overall variation may be related to the lower mean site δ15N of the total nitrogen in water (1.6‰) compared to the sediment (3.0‰). However, much of the observed wide variation in macrophyte δ15N could be related to differences in nutrient limitation. Macrophytes restricted to the water for their nitrogen source showed statistically significant positive correlations between δ15N and nitrogen-limitation at the site and negative correlations with phosphorus-limitation at the site. The results suggest that the large variation in the δ15N value of freshwater macrophytes may be caused by a combination of differences in the δ15N value of the main nitrogen source used and differential isotopic discrimination caused by variable nitrogen-availability relative to demand. Thus analysis of the δ15N value of macrophytes that obtain their nitrogen from the water, such as bryophytes and filamentous algae, might offer a convenient and effective way of assessing nitrogen-limitation at a site

A survey of the status of the lakes of the English Lake District: the Lakes Tour 2015

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 2015. This ‘Lakes Tour’ supplements similar tours in 1984, 1991, 1995, 2000, 2005 and 2010. 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, alkalinity, major anions and cations, heavy metals, micro-organic pollutants, 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 12 m in clear unproductive lakes such as Wastwater in January, to 2 m in the more productive lakes during summer such as Esthwaite Water in October. 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 of total phosphorus were lowest in Wastwater and Crummock Water and highest in Blelham Tarn and Elterwater. 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, with low biological demand, 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. Blelham Tarn had the highest annual mean concentration of chlorophyll a at 23 mg m 3, but the highest concentration recorded was 40 mg m 3 at Elterwater in July. The lowest annual annual mean concentration was 0.8 mg m 3 at Wastwater. 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. Cyanobacteria were generally more common in productive lakes. 9. Zooplankton abundance was very variable and greatest in the productive lakes and seasonally, abundance tended to be greatest in July and October. Fifteen 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. At the genus level, diversity increased in the summer and autumn. Abundance of Ceriodaphnia, Diaphanosoma and Mesocyclops were an important part of the zooplankton community in some lakes in summer. 10. The known status of fish populations, although not undertaken in the project, was summarised. Nineteen species have been recorded in these lakes, but of these seven are probably introduced. Some lakes have very few fish-data and require more research. 11. Heavy metals were measured for the second time. Although many samples were below the limit of detection, copper concentrations were elevated in Coniston Water, lead was elevated in Bassenthwaite Lake, Haweswater and Thirlmere and zinc was elevated in Bassenthwaite Lake, Buttermere, Crummock Water and Haweswater. 12. Micro-organic pollutants were measured for the second time and most samples were below current detection limits. Of the sixty-nine compounds analysed, five gave values above the detection limit but only three exceeded the limit more than twice. Of these, Diazinon, an organophosphorus insecticide, was detected on all four sampling occasions in Blelham Tarn, Buttermere, Crummock Water, Ullswater and the North Basin of Windermere; 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 (WFD), although note that this does not conform completely to WFD guidelines and Rydal Water and Loughrigg Tarn do not fall within the WFD remit. 14. Compared to 2010 there was an increase in the number of lakes at high or good status of from 10 to 14 for total phosphorus and from 11 to 14 for chlorophyll a. Of these, only Wastwater, Buttermere, and Brothers Water were at high status for both variables. Based on chlorophyll a, Loweswater, Loughrigg Tarn, Blelham Tarn, Esthwaite Water, Elterwater and the South Basin of Windermere were only at Moderate ecological status. 15. Long-term change from 1984 to 2015 (1991 to 2015 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 also linked to reductions in stormy weather since the mid 1990s and hence reduced input of sea-salt in rain. On average, in comparison to the 2010 Lakes Tour, there has been a reduction in concentration of TP and phytoplankton chlorophyll a and Secchi depth has remained stable. 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 elevation (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 in order to obtain a better understanding of the reasons for this and possible remediation actions. 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 again and could be a model for future work