Biodiversity and ecosystem processes in heterogeneous environments

The decline in biodiversity over the last decade has motivated researchers to investigate the relationship between species richness (biodiversity) and ecosystem function. Empirical approaches are becoming more realistic as more factors have been included. Spatial heterogeneity is an example. Heterogeneity is an inherent part of the environment and apparent in all habitat types creating a patchy, mosaic of natural landscape. Researchers have reported the extent of heterogeneity in the landscape, but surprisingly not yet included heterogeneity into biodiversity and ecosystem function (BEF) studies. In recent years, empirical studies of marine systems have enhanced the BEF debate. Depauperate estuarine systems are ideal candidates for establishing model systems. In this study, estuarine microphytobenthos (MPB) were used as a response variable since the relationship between MPB and primary productivity is well-known. This relationship was exploited to employ MPB biomass as a proxy for primary productivity. Benthic chambers were used to assess the effect of macrofauna in single species and multi-species treatments on both ecosystem function and net macrofaunal movement. Heterogeneity was created through enriching sediment ‘patches’ with Enteromorpha intestinalis, providing areas of high and low nutrient. Heterogeneity, macrofaunal biomass, species richness, species diversity and flow were all varied in order to assess combined effects on the functioning of the system. Heterogeneity was found to have a significant influence on ecosystem functioning and on macrofaunal movement, however, patch arrangement did not. MPB biomass was highest in patches containing organic enrichment suggesting that nutrients were obtained locally from the sediment/water interface rather than the water column. There was variation in MPB biomass with macrofaunal species, probably resulting from differences in behavioural traits. It was also evident that flow altered species behaviour, as there was a significant difference between static and flow treatments. This work shows the importance of heterogeneity for BEF relationships

Temporal variability in aquatic carbon and GHG concentrations and fluxes in a peatland catchment

Here we present a complete 5-year dataset of all aquatic carbon and GHG species (POC, DOC, DIC, CO2, CH4, N2O) from Auchencorth Moss, an ombrotrophic Scottish peatland. The study aims to analyse and explain temporal variability in concentrations and fluxes (both downstream export and evasion) at weekly, seasonal and annual time scales. The aquatic pathway is increasingly being recognised as an important component of catchment carbon and greenhouse gas (GHG) budgets, particularly in peatland systems due to their large carbon store and strong hydrological connectivity. However, due to a lack of long-term measurements few studies have been able to adequately consider temporal variability in total concentrations and fluxes. We show that short-term within year variability in concentrations exists across all species and this is strongly linked to changes in discharge. Seasonal cyclicity was only evident for DOC, CH4 and N2O concentrations; however temperature correlated with monthly means in all species except DIC. Whilst the temperature dependence in monthly DOC and POC concentrations appeared to be related to biological productivity in the terrestrial system, we suggest the temperature correlation with CO2 and CH4 was primarily due to in-stream temperature-dependent solubility of the two gases. Interannual variability in total aquatic carbon concentration was strongly correlated with catchment gross primary production (GPP) indicating a strong linkage between the terrestrial and aquatic systems. DOC represented the largest aquatic carbon flux term (19.3 ± 4.59 g C m-2 yr-1), followed by CO2 evasion (10.0 g C m-2 yr -1). Despite an estimated contribution to the total aquatic carbon flux of between 8 - 48%, evasion estimates contained the greatest uncertainty and therefore represent an area which requires a significant future research effort. Interannual variability in total carbon export was low in comparison with variability in terrestrial fluxes, and could be explained primarily by temperature and precipitation. Hence changes in catchment carbon cycling resulting from climatic or land-use influences may be easier to identify in terms of aquatic C fluxes compared to land-atmosphere exchange flux terms such as GPP and net ecosystem exchange (NEE)

Biodiversity and ecosystem processes in heterogeneous environments

The decline in biodiversity over the last decade has motivated researchers to investigate the relationship between species richness (biodiversity) and ecosystem function. Empirical approaches are becoming more realistic as more factors have been included. Spatial heterogeneity is an example. Heterogeneity is an inherent part of the environment and apparent in all habitat types creating a patchy, mosaic of natural landscape. Researchers have reported the extent of heterogeneity in the landscape, but surprisingly not yet included heterogeneity into biodiversity and ecosystem function (BEF) studies. In recent years, empirical studies of marine systems have enhanced the BEF debate. Depauperate estuarine systems are ideal candidates for establishing model systems. In this study, estuarine microphytobenthos (MPB) were used as a response variable since the relationship between MPB and primary productivity is well-known. This relationship was exploited to employ MPB biomass as a proxy for primary productivity. Benthic chambers were used to assess the effect of macrofauna in single species and multi-species treatments on both ecosystem function and net macrofaunal movement. Heterogeneity was created through enriching sediment ‘patches’ with Enteromorpha intestinalis, providing areas of high and low nutrient. Heterogeneity, macrofaunal biomass, species richness, species diversity and flow were all varied in order to assess combined effects on the functioning of the system. Heterogeneity was found to have a significant influence on ecosystem functioning and on macrofaunal movement, however, patch arrangement did not. MPB biomass was highest in patches containing organic enrichment suggesting that nutrients were obtained locally from the sediment/water interface rather than the water column. There was variation in MPB biomass with macrofaunal species, probably resulting from differences in behavioural traits. It was also evident that flow altered species behaviour, as there was a significant difference between static and flow treatments. This work shows the importance of heterogeneity for BEF relationships.EThOS - Electronic Theses Online ServiceNatural Environment Research CouncilGBUnited Kingdo

Five year record of aquatic carbon and greenhouse gas concentrations from Auchencorth Moss

Dataset contains concentrations of particulate and dissolved organic carbon, inorganic carbon, CO2, CH4 and N2O in the Black Burn stream which drains Auchencorth Moss peatland in South East Scotland. Auchencorth Moss is part of the Centre for Ecology & Hydrology's UK Carbon Catchment project. Concentrations have been measured approximately weekly from January 2007 to December 2011 and are published in Global Change Biology doi: 10.1111/gcb.1220

Direct and continuous measurement of dissolved carbon dioxide in freshwater aquatic systems — method and applications

Understanding of the processes that control CO2 concentrations in the aquatic environment has been hampered by the absence of a direct method to make continuous measurements over both short- and long-term time intervals. We describe an in situ method in which a non-dispersive infrared (NDIR) sensor is enclosed in a water impermeable, gas permeable polytetrafluoroethylene (PTFE) membrane and deployed in a freshwater environment. This allows measurements of CO2 concentration to be made directly at a specific depth in the water column without the need for pumps or reagents. We demonstrate the potential of the method using examples from different aquatic environments characterized by a range of CO2 concentrations (0.5–8.0 mg CO2-C L-1, equivalent to ca 40–650 μmol CO2 L-1). These comprise streams and ponds from tropical, temperate and boreal regions. Data derived from the sensor was compared with direct measurements of CO2 concentrations using headspace analysis. Sensor performance following long-term (>6 months) field deployment conformed to manufacturers’ specifications, with no drift detected. We conclude that the sensor-based method is a robust, accurate and responsive method, with a wide range of potential applications, particularly when combined with other in situ sensor-based measurements of related variables

Stream water hydrochemistry as an indicator of carbon flow paths in Finnish peatland catchments during a spring snowmelt event

Extreme hydrological events are known to contribute significantly to total annual carbon export, the largest of which in arctic and boreal catchments is spring snowmelt. Whilst previous work has quantified the export of carbon during snowmelt, the source of the carbon remains unclear. Here we use cation hydrochemistry to trace the primary flowpaths which govern the export of carbon during the snowmelt period; specifically we aim to examine the importance of snowpack meltwater to catchment carbon export. The study was carried out in two forested peatland (drained and undrained) catchments in Eastern Finland. Both catchments were characterised by base-poor stream water chemistry, with cation concentrations generally decreasing in response to increasing discharge. Streamflow during the snowmelt period was best described as a mixture of three sources: pre-event water, snowpack meltwater and a third dilute component we attribute to the upper snow layer which was chemically similar to recent precipitation. Over the study period, pre-event water contributed 32% and 43% of the total stream runoff in Välipuro (undrained) and Suopuro (drained), respectively. The results also suggest a greater near-surface throughflow component in Suopuro, the drained catchment, prior to snowmelt. CO2 and DOC concentrations correlated positively with cation concentrations in both catchments indicating a common, peat/groundwater flowpath. CH4 concentrations were significantly higher in the drained catchment and appeared to be transported in near-surface throughflow. Meltwater from the snowpack represented an important source of stream water CO2 in both catchments, contributing up to 49% of total downstream CO2 export during the study period. We conclude that the snowpack represents a potentially important, and often overlooked, transient carbon store in boreal snow-covered catchments

Influence of macrofaunal assemblages and environmental heterogeneity on microphytobenthic production in experimental systems

Despite the complexity of natural systems, heterogeneity caused by the fragmentation of habitats has seldom been considered when investigating ecosystem processes. Empirical approaches that have included the influence of heterogeneity tend to be biased towards terrestrial habitats; yet marine systems offer opportunities by virtue of their relative ease of manipulation, rapid response times and the well-understood effects of macrofauna on sediment processes. Here, the influence of heterogeneity on microphytobenthic production in synthetic estuarine assemblages is examined. Heterogeneity was created by enriching patches of sediment with detrital algae (Enteromorpha intestinalis) to provide a source of allochthonous organic matter. A gradient of species density for four numerically dominant intertidal macrofauna (Hediste diversicolor, Hydrobia ulvae, Corophium volutator, Macoma balthica) was constructed, and microphytobenthic biomass at the sediment surface was measured. Statistical analysis using generalized least squares regression indicated that heterogeneity within our system was a significant driving factor that interacted with macrofaunal density and species identity. Microphytobenthic biomass was highest in enriched patches, suggesting that nutrients were obtained locally from the sediment–water interface and not from the water column. Our findings demonstrate that organic enrichment can cause the development of heterogeneity which influences infaunal bioturbation and consequent nutrient generation, a driver of microphytobenthic production

Relationships between biodiversity and the stability of marine ecosystems: Comparisons at a European scale using meta-analysis

The relationship between biodiversity and stability of marine benthic assemblages was investigated through meta-analyses using existing data sets (n = 28) covering various spatial (m-km) and temporal (1973-2006; ranging from 5 to >250 months) scales in different benthic habitats (emergent rock, rock pools and sedimentary habitats) over different European marine systems (North Atlantic and western Mediterranean). Stability was measured by a lower variability in time, and variability was estimated as temporal variance of species richness, total abundance (density or % cover) and community structure (using Bray-Curtis dissimilarities on species composition and abundance). Stability generally decreased with species richness. Temporal variability in species richness increased with the number of species at both quadrat (<1 m(2)) and site (similar to 100 m(2)) scales, while no relationship was observed by multivariate analyses. Positive relationships were also observed at the scale of site between temporal variability in species richness and variability in community structure with evenness estimates. This implies that the relationship between species richness or evenness and species richness variability is slightly positive and depends on the scale of observation. Thus, species richness does not stabilize temporal fluctuations in species number, rather species rich assemblages are those most likely to undergo the largest fluctuations in species numbers and abundance from time to time. Changes within community assemblages in terms of structure are, however, generally independent of biodiversity. Except for sedimentary and rock pool habitats, no relationship was observed between temporal variation of total abundances and diversity at either scale. Overall, our results emphasize that the relation between species richness and species-level measures of temporal variability depends on scale of measurements, type of habitats and the marine system (North Atlantic and Mediterranean) considered

Age and source of different forms of carbon released from boreal peatland streams during spring snowmelt in E. Finland

Isotopic data are increasingly being used to quantify and understand the processes that control the release of carbon (C) from northern peatlands. We used δ13C and 14C measurements to investigate the source and age of different forms of aquatic C (DOC, POC and evasion CO2) released from 2 contrasting (undrained v drained) forested peatland catchments at the end of the winter snowmelt period in boreal E Finland. The δ13CVPDB values of DOC (range −28.3 to −28.8 ‰) were generally more 13C depleted than evasion CO2 (range −22.7 to −31.5 ‰) and showed no clear differences between the pre-flood, flood and post-flood periods. Both forms of C had evidence of bomb-14C (i.e. &gt;100%modern), indicating that they contained substantial quantities of C fixed since the mid AD 1950s. However, DOC was 14C enriched compared to evasion CO2, with 14C concentrations suggesting that, on average, DOC-C was ~5–6 years younger than evasion CO2–C, with the most recently fixed C being released when temperatures were highest. POC was significantly depleted in 14C with conventional (uncalibrated) radiocarbon ages of 805–1135 BP. In contrast to other studies, the isotopic compositions of DOC and evasion CO2 were very similar, suggesting a predominantly single and consistent C source (decomposition of soil organic matter; SOM) during the snowmelt period. Whilst we found no evidence to suggest that old (pre-bomb) C was being released at the end of the winter period, the drained site was associated with more 14C depleted and 13C enriched evasion CO2, suggesting a closer link to the atmospheric CO2 pool. Our isotopic data suggest that the various forms of C released to the aquatic system from these forested Finnish peatlands are closely related, largely unaffected by drainage and (at least in the case of evasion CO2 and DOC) indicate strong connectivity between C cycling in the soil–plant–water system