Carbon and nitrogen in aquatic systems: sources and cycling
Helen Murray (PhD student), James Harley (PhD student), Dr Kate Heal, Dr Susan Waldron (University of Glasgow), Dr Hugh Flowers (University of Glasgow), Dr Tom Nisbet (Forest Research), Dr Ute Skiba (Centre for Ecology and Hydrology), Dr Laurence Carvalho (Centre for Ecology and Hydrology), Dr Bob Rees (Scottish Agricultural College)
SAGES, University of Glasgow, NERC Centre for Ecology and Hydrology
There are two ongoing projects in this research area.
1) Helen Murray is researching the effects of soil disturbance associated with wind farm development on carbon and nutrient fluxes in runoff. The research is contInuing ongoing long-term monitoring of different forms of carbon, nitrogen and phosphorus in nine nested catchments draining the Whitelee wind farm, near Glasgow, which is currently the largest operational onshore wind farm in Europe. In the development of the wind farm the turbines were located mainly on deep peat soils and some surrounding forest plantations were felled. Measurements of streamwater chemistry and flows are being related to the amount of disturbance in each of the catchments.
2) James Harley is investigating carbon and nitrogen processing from source to sea. Fieldwork is focusing on quantifying seasonal and spatial variations in fluxes of different forms of carbon and nitrogen in water and sediment in the Tay River catchment, Scotland. Laboratory studies utilising aquatic sediment cores from the catchment are being conducted to improve understanding of the processes controlling carbon and nitrogen cycling.
Helen Murray's results to date show an apparent increase in soluble reactive phosphorus concentrations in the catchments most affected by disturbance after wind farm development started.
Waldron, S., Flowers, H., Arlaud, C., Bryant, C., and McFarlane, S. (2009). The significance of organic carbon and nutrient export from peatland-dominated landscapes subject to disturbance, a stoichiometric perspective. Biogeosciences, 6, 363-374.
Carbon and nitrogen cycling in forests
Dr Xiangqing Ma (Fujian Agriculture and Forestry University, China ), Dr Kate Heal, Dr Maurizio Mencuccini (School of GeoSciences), Prof. John Moncrieff (School of GeoSciences), Dr Robert Clement (School of GeoSciences), Prof. Paul Jarvis (School of GeoSciences)
NERC, Chinese Government Scholarship
With others, Maurizio Mencuccini's metadata analyses have controversially shown a strong influence of atmospheric nitrogen deposition on carbon sequestration by temperate forest ecosystems (Magnani, Mencuccini et al., 2007). We will be quantifying the relationship between nitrogen deposition and carbon balance of temperate forests in a paired catchment experiment in the field and also through modelling and examination of Forest Research plot data in the UK. The field experiment will be conducted at Griffin Forest, a Sitka spruce plantation in Perthshire, Scotland, which is a CarboEurope and NitroEurope site where we have been monitoring carbon and water fluxes since 1998. The experiment will be conducted over 5 years and involves monitoring of carbon and nitrogen aqueuos and gaseous fluxes in two sub-catchments before, during and after airborne application of nitrogen by helicopter to one of the sub-catchments.
Previous monitoring of aqueous carbon and nitrogen fluxes at Griffin Forest by Xiangqing Ma and Kate Heal showed that aquatic carbon loss from the forest was <1% of the annual carbon sequestration. The ratio measured between deposited nitrogen and carbon storage was c.170 kg C/kg N, very similar to the ratio calculated in Maurizio Mencuccini and others' metadata analyses.
Magnani, F., Mencuccini, M., et al. (2007) The human footprint in the carbon cycle of temperate and boreal forests. Nature, 447, 848-852.
Ma, X., Heal, K.V., Liu, A. and Jarvis, P.J. (2007) Nutrient cycling and distribution in different-aged plantations of Chinese fir in southern China. Forest Ecology and Management, 243, 61-74.
The impact of high-flow events on phosphorus delivery to lakes
Dr Lindsey Defew (completed PhD student), Dr Kate Heal, Dr Linda May (Centre for Ecology and Hydrology)
NERC, Scottish Environment Protection Agency (SEPA)
Loch Leven is the largest eutrophic loch in Scotland and it has, historically, suffered from eutrophication problems due to large inputs of phosphorus (P) from point and diffuse sources within the catchment. Significant reductions in point source P inputs through efficient management now means that in many rural catchments, diffuse P sources dominate P inputs. Large inputs of P from diffuse sources during high flow events can prevent the complete restoration and recovery of a eutrophic water body. The aims of this research were to quantify the contribution of high flow events in delivering different forms of P to Loch Leven. A P loading survey in the Loch Leven catchment conducted in 2005-2006 showed that particulate phosphorus (PP) now contributes a greater proportion (~57%) of the TP load to Loch Leven, compared with a decade ago (~38%). Per unit of catchment area, the sub-catchment of the Pow Burn contributed notably more P, compared to other sub-catchments, which reflected the intense agricultural land use in this area. High-frequency (2-hourly) P monitoring in the Pow Burn between October and December 2006 showed very large temporal variations in P concentrations and loads caused by high stream flow events. The high-frequency monitoring also highlighted the importance of selecting an appropriate sampling interval to enable P loads to be estimated accurately. Settled stream bed sediments were an important source of the P-laden sediment delivered to Loch Leven at the start of the high-flow winter season. These sediment sources are an important part of the aquatic system because they often play a vital role in the regulation of soluble reactive phosphorus (SRP) concentrations in the water column and in the delivery of P through fluvial systems to standing water bodies.
In improve the accuracy of P load estimates required to effectively assess and manage diffuse P pollution in catchments in general, high-frequency sampling programmes are required which capture high-flow events and apply extrapolation load calculation methods. The bioavailable P concentrations measured in particulate inputs to Loch Leven are sufficiently high to cause poor water quality and prevent the its complete restoration. To reduce the P inputs to Loch Leven (and other similar lochs) very specific contributing P source areas (e.g. hot spots of disproportionate P loss from fields and farmyards) need to be identified and managed.
Manganese in surface and groundwaters
Dr Alasdair Hardie (PhD student now working for SEPA), Sally Goring (now Homoncik) (MScR student now working for Mountain Environments Ltd.), Dr Kate Heal, Dr Allan Lilly (The Macaulay Land Use Research Institute), Dr Alan MacDonald (British Geological Survey), Dr Bryne Ngwenya (School of GeoSciences)
Scottish Water, the University of Edinburgh, British Geological Survey
Elevated concentrations of the trace metal manganese (Mn) may cause water supplies from upland catchments and groundwaters to fail the EU standards for drinking water, resulting in discolouration of water and increased treatment costs and potentially a health risk. We have conducted research into the processes controlling the release of Mn from natural sources into surface and groundwater drinking water supplies in Scotland.
1) Alasdair Hardie's PhD studentship explored the role of soil hydrology, pedology and land use in mobilising Mn from upland soils into surface waters. Field monitoring in the catchment of Loch Bradan, a major water supply reservoir in south west Scotland, found no effect of land use (conifer plantation and moorland) on soil water Mn concentrations. However soil water simulations, calibrated from field and laboratory measurements of soil hydraulic properties, showed that elevated Mn concentrations in surface waters are associated with the re-wetting of soil horizons containing a mixture of organic and mineral material. Mineral material provides a source of Mn, but relatively high soil organic matter content is required to facilitate mobilisation.
2) Working with British Geological Survey, Sally Goring determined the extent and magnitude of high Mn concentrations in groundwater in Scotland and investigated the factors controlling Mn concentrations. From a database of 475 groundwater samples for Mn, it was found that 28% of samples exceeded the drinking water standard for manganese. Water chemistry conditions (iron, pH, Eh, dissolved oxygen) have a greater control on Mn concentrations than rock type.
Mn release into surface water supplies in the uplands is favoured from soil horizons containing a mixture of organic and mineral material. Hence soil information can be used to identify catchments at risk of elevated Mn concentrations in surface water supplies. Mn concentrations in groundwater supplies cannot be predicted from rock type. Instead, more widespread monitoring of Mn concentrations in groundwater supplies is recommended, particularly in private water supplies in Scotland which are often subject to less rigorous testing.
Hardie, A.M., Heal, K.V. and Lilly, A. (2007). The influence of pedology and changes in soil moisture status on manganese release from upland catchments: soil core laboratory experiments. Water, Air and Soil Pollution, 182, 369-382.
Heal, K.V., Kneale, P.E. and McDonald, A.T. (2002). Manganese in runoff from upland catchments: temporal patterns and controls on mobilisation. Hydrological Sciences Journal, 47, 769-780.
Heal, K.V. (2001). Manganese and land use in upland catchments in Scotland. The Science of the Total Environment, 265, 169-179.
Loch Bradan drinking water supply reservoir in the uplands of south west Scotland
Trichloroacetic acid cycling in the environment
Dr Ruth Stidson (PDRA now working for SEPA), Dr Catherine Dickey (completed PhD student), Dr Kate Heal, Dr Mathew Heal (School of Chemistry), Prof. Neil Cape (Centre for Ecology and Hydrology)
Natural Environment Research Council (NERC)
Trichloroacetic acid (TCA: CCl3COOH) is a phytotoxic chemical, which has been detected in many environmental media, and is suggested as one stressor contributing to forest decline in Europe and North America. There is considerable controversy surrounding the modern-day sources and cycling of TCA in rural ecosystems. The main potential anthropogenic sources of TCA are atmospheric photo-oxidation of chlorinated hydrocarbon solvents, whilst natural sources are thought to include in situ production in soil organic matter. Knowledge of the sources and cycling of TCA in the environment is required for environmental risk assessments of manufactured chemicals. Sources and fluxes of TCA were investigated in a mass balance study of a small upland catchment in south west Scotland. From comparing the total TCA store in the catchment (mainly in the soil) with the annual flux, the average residence time of TCA in the catchment is 1-2 years. TCA inputs were balanced by outputs from the catchment over the course of a year, but there was evidence of more rapid TCA cycling in the forest canopy and soils. During her PhD, Catherine Dickey investigated TCA cycling in soil and trees in more detail. Results from laboratory experiments indicated that microbial activity is involved in the production and degradation of TCA in soils. Field lysimeter experiments also found rapid degradation of TCA applied to soil. Controlled greenhouse experiments with Sitka spruce saplings showed that TCA is taken up by trees from both the soil and atmosphere. However uptake of TCA which was applied to the foliage caused greater tree stress than TCA applied to the soil in which trees grow.
TCA in the environment was found to be derived from natural (in situ soil processing) and man-made sources (atmospheric deposition). At the study site there was evidence for net natural TCA production in soils and also that the majority of TCA stores in soils are not involved with external fluxes. TCA stored in foliage can have a significant effect on tree health; trees exposed to cloudwater may be more likely to be damaged by TCA uptake.
Dickey, C.A., Heal, K.V., Cape, J.N., Stidson, R.T., Reeves, N.R. and Heal, M.R. (2005). Addressing analytical uncertainties in the determination of trichloroacetic acid in soil. Journal of Environmental Monitoring, 7, 137-144.
Dickey, C.A., Heal, K.V., Stidson, R.T., Koren, R., Cape, J.N., Schröder, P. and Heal, M.R. (2004). Trichloroacetic acid cycling in Sitka spruce (Picea sitchensis) saplings and the effects on tree health following long term exposure. Environmental Pollution, 130, 165-176.
Heal, K.V., Stidson, R.T., Dickey, C.A., Cape, J.N. and Heal, M.R. (2004). New data for water losses from mature Sitka spruce plantations in temperate upland catchments. Hydrological Sciences Journal, 49, 477-493.
Stidson, R.T., Dickey, C.A., Cape, J.N., Heal, K.V. and Heal, M.R. (2004). Fluxes and reservoirs of trichloroacetic acid at a forest and moorland catchment. Environmental Science & Technology, 38, 1638-1647.
Stidson, R.T., Heal, K.V., Dickey, C.A., Cape, J.N. and Heal, M.R. (2004). Fluxes of trichloroacetic acid through a conifer forest canopy. Environmental Pollution, 132, 72-84.
Cape, J.N., Reeves, N.M., Schroder, P. and Heal, M.R. (2003). Long-term exposure of Sitka spruce seedlings to trichloroacetic acid. Environmental Science & Technology, 37, 2953-2957.
Heal, M.R., Reeves, N.M. and Cape, J.N. (2003). Atmospheric concentrations and deposition of trichloroacetic acid in Scotland: Results from a 2-year sampling campaign. Environmental Science & Technology, 37, 2627-2633.
Methyl halide emissions from ecosystems
Emanuel Blei (PhD student), Catherine Hardacre (PhD student), Dr Julia Drewer (PhD student, now at Centre for Ecology and Hydrology), Dr Kate Heal, Dr Mathew Heal (School of Chemistry), Prof. Keith Smith (School of GeoSciences)
University of Edinburgh, EaStCHEM, Carnegie Trust, The University of Edinburgh Development Trust, Weir Fund
Methyl bromide and methyl chloride are trace gases involved in stratospheric ozone depletion. Whilst the anthropogenic sources of methyl bromide are well-known and regulated under the Montreal Protocol, natural sources of these gases from marine and terrestrial ecosystems are poorly characterised and quantified. Current global estimates of atmospheric methly halide losses, such as soil and ocean sinks, exceed emissions. Hence additional natural terrestrial sources may be important components of the global budget. We are conducting detailed field measurements using static flux chambers of methyl halide emissions from a range of ecosystems in the UK and overseas, including saltmarshes, temperate and tropical forests and temperate and Arctic wetlands.will be made with flux chambers in a range of terrestrial ecosystems in the UK (such as salt marshes, temperate forests and agricultural systems). Additional controlled experiments are investigating the influence of factors such as plant species, temperature, light, salinity and watertable fluctuation on CH3Br production.
Methyl bromide emissions from salt marshes showed both strong seasonal and diurnal cycles, being highest during the growing season and in the middle of the day associated with sunlight. Emissions are strongly associated with the presence of vegetation but differed considerably between different salt marsh, wetland and tree species in all ecosystems studied. Global scale-ups from our detailed datasets suggest that the current emissions for methyl halides need revising; for example, our estimate for methyl bromide emission from salt marshes is ∼10% of the figure regularly quoted in the literature.
Hardacre, C.J., Blei, E. and Heal, M.R. (2009). Growing season methyl bromide and methyl chloride fluxes at a sub-arctic wetland in Sweden. Geophysical Research Letters, 36, L12401, doi:10.1029/2009GL038277.
Drewer, J., Heal, K.V., Smith, K.A. and Heal, M.R. (2008). Methyl bromide emissions to the atmosphere from temperate woodland ecosystems. Global Change Biology, 14, 2539-2547.
Drewer, J., Heal, M.R., Heal, K.V. and Smith, K.A. (2006) Temporal and spatial variation in methyl bromide flux from a salt marsh. Geophysical Research Letters, 33, L16808, doi:10.1029/2006GL026814.