David Ryves, John Anderson & Keely Mills

1. High resolution limnological process studies from automatic samplers at Lake ChallaUnderstanding the present as key to interpreting the past David Ryves, John Anderson & Keely Mills Department of Geography Loughborough University, UK Lake Nyinambuga, Uganda

2. Introduction • Expertise: limnology, palaeolimnology, diatom analysis (+ isotopes) • Automatic sediment traps (interval) • Case studies (Lake Baikal, West Greenland, Rostherne Mere) • Automatic water samplers • Potential applications to Lake Challa • Technical aspects & considerations

3. Cyclotella minuta 10 μm 10 μm Aulacoseira baicalensis Diatoms: An overview • Ecology • Single-celled microscopic algae • Important primary producers • Great species diversity • Freshwater, brackish, marine • Range of habitats • Environmental monitoring • Palaeoecology • Silica cell wall - often preserves well in sediments • Intricately ornamented and shaped - identification • Inferences of past environments (qualitative) • Quantitative estimates of key parameters (transfer functions) • Si and C dynamics, stable isotopes (O, Si, C)

4. Automatic sediment traps (two available now) • Technicap (France)

5. Technicap automatic sediment samplers • Height: 1.3 m, weight: 32 kg (air), area: 0.05 sq. m • Twelve 250 ml bottles per carousel (*500 ml option) • Each bottle can be individually set to collect between 1 hour and 60 days • Batteries should last typically 2-3 years • Depth up to 5000 m • Typically, each bottle set to ~2 weeks and collected every 24 - 26 weeks (twice/year)

6. Lake Baikal, Siberia • Area 31,432 km2 • Volume 23,015 km3 • Depth 889 m mean, 1636 m max • ~20% global surface freshwaters • ~75% of 2500 plant & animal species are endemic • 7.5 km sediment over 25-30 million years • Crucial PAGES PEP II transect site Funding source: NERC, GEOPASS • 1. Linking limnological and ecological processes to sedimentary archives • Preservation of environmental signals in sediments

7. Shallow trap (~550 m): mass flux • Deep trap (~1400 m): mass flux • Shallow trap (~550 m): dissolution index • Deep trap (~1400 m): dissolution index Ryves et al. (2003), Limnol. Oceanogr.

8. Baikal trap work shows seasonality of diatoms, sediment formation • Demonstrated that substantial losses to diatom crops occurred in water column (~10%) and in surface sediment (~90%!) • Implies potential problems using diatom record and biogenic silica accumulation rate to infer past aquatic diatom communities and productivity

9. West Greenland • Biomarker seasonality study using sequencing trap • July production allowed inference of summer temperature in lake sediment core D’Andrea et al. (2011), PNAS, 108, 9765-9769

10. Long-term alkenone temperature record • Linked to human occupation over Holocene • Norse settlement and disappearance

11. Carbon flux and biogenic silica isotopes: Rostherne Mere • Rostherne Mere, Cheshire, UK • Eutrophic freshwater lake • Carbon dynamics • Test of δ30Si as proxy for diatom productivity • Sediment traps • Automatic water sampler

12. Rostherne Mere, UK • Two sequencing traps at 10 m, 25 m • Samples collecting for 2 weeks from April 2010 and on-going • Carbon flux from traps • Biogenic silica (diatoms) analysed for δ30Si and δ18O • Dissolved silica δ30Si also being analysed

13. Rostherne Mere – preliminary data • Shallow trap (10 m): organic C flux and OM% • Prim prod dominated by blue-green (summer) • Diatoms in spring, autumn (peak OM%) • Deep trap (25 m): organic C flux and OM% • Trap installed in May 2011 2010 2011 2012

14. Rostherne Mere – preliminary δ30Si data • Shallow trap (10 m): OM% and BSi-δ30Si ? Diatom productivity ? OM% d30Si • Preliminary results are encouraging that diatom blooms quickly deplete d28Si with resulting heavier d30Si signal in sediment

15. Automatic water samplers – potential at Lake Challa • LU also has 2 ISCO water samplers • Can take 24 samples up to 1L every week – or at finer resolution (e.g. multiple samples over a week totalling 1L) • Used at Rostherne Mere for d18O and for d30Si of water (samples collected with paraffin for O, conc. HCl for Si) • Collected from shore at Rostherne some 10 m into lake at 0.5 m depth via a 50 micron sieve bag over inlet • Batteries (12V) may be an issue (longevity) but can run in parallel • Lake isotope studies, littoral conditions, sediment in-wash from catchment?

16. ISCO water sampler

17. Rostherne Mere – ISCO data

18. Automatic traps – potential at Lake Challa • Seasonality and event studies (diatoms, pollen, aeolian dust, charcoal, phytoliths, catchment minerals, biomarkers, fluxes of total/organic/carbonate matter, mixing events…) • Taphonomy: How do these environmental signals change with depth? Are there lags between upper and lower water column? Are some signals attenuated, distorted or lost? • Vertical profiling: production of specific compounds e.g. biomarkers at certain depths. What happens in the deeper waters (meromictic, anoxic hypolimnion)?

19. Automatic traps – potential at Lake Challa • Spatial study: Trap in littoral for catchment/pelagic zone differences (sediment routes from inflow/catchment etc)? Which shore? • Ideally, need to link this to monitoring work in the (upper) water column and surface sediment studies • Also: can attach thermistors, probe (CTD, water chem)

20. Automatic sampling – practicalities • Funding issues: Loughborough/UK unlikely to get funding for project entirely based on traps (NERC) – small grant route now gone • Traps need upgrading – USB adaptor on motherboard is ~€900 each. New bottles, etc. • Installation and operation issues – access. Raft best for deployment and resetting of traps • Resetting traps with heavy weight (25kg at Rostherne) on/in lake bed and 95 m of water column may need a winch – tie two boats together (raft). Ask Caxton! • Trap batteries needed every year to be safe (but ~minor cost) • ISCO water sampler needs safe shore location. Problems of storage conditions of water – regularity of collection? • Preservation of bottle contents (for both sediment and water samplers) in warm, (an)oxic conditions?

21. Questions?

23. Rostherne Mere – ISCO data