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

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

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

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. >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

Species effects on ecosystem processes are modified by faunal responses to habitat composition.

Heterogeneity is a well-recognized feature of natural environments, and the spatial distribution and movement of individual species is primarily driven by resource requirements. In laboratory experiments designed to explore how different species drive ecosystem processes, such as nutrient release, habitat heterogeneity is often seen as something which must be rigorously controlled for. Most small experimental systems are therefore spatially homogeneous, and the link between environmental heterogeneity and its effects on the redistribution of individuals and species, and on ecosystem processes, has not been fully explored. In this paper, we used a mesocosm system to investigate the relationship between habitat composition, species movement and sediment nutrient release for each of four functionally contrasting species of marine benthic invertebrate macrofauna. For each species, various habitat configurations were generated by selectively enriching patches of sediment with macroalgae, a natural source of spatial variability in intertidal mudflats. We found that the direction and extent of faunal movement between patches differs with species identity, density and habitat composition. Combinations of these factors lead to concomitant changes in nutrient release, such that habitat composition effects are modified by species identity (in the case of NH4-N) and by species density (in the case of PO4-P). It is clear that failure to accommodate natural patterns of spatial heterogeneity in such studies may result in an incomplete understanding of system behaviour. This will be particularly important for future experiments designed to explore the effects of species richness on ecosystem processes, where the complex interactions reported here for single species may be compounded when species are brought together in multi-species combinations

Release of aquatic carbon from two peatland catchments in E. Finland during the spring snowmelt period

Spring snowmelt in the arctic and boreal regions represents the most significant event in the hydrological year. We measured concentrations and fluxes of different carbon species in 2 small contrasting (control v drained) forested peatland catchments in E. Finland between April and June 2008 and compared these to long-term annual fluxes. Measurements were made using a combination of continuous sensors (CO2, temperature, pH, discharge) and routine spot sampling (DOC, POC, DIC, CO2, CH4, N2O). The highest concentrations of CO2 and CH4 in streamwater were observed under low flow conditions before the spring flood event,reflecting accumulation and downstream release of gaseous C at the end of the winter period. Over the length of the study mean CH4 concentrations were 10x higher in the drained site. The snowmelt event was associated with a dilution of DOC and CO2, with the drained catchment showing a much flashier hydrological response compared to the control site, and post-event, a slower recovery in DOC and CO2 concentrations. Fluxes of all carbon species during the snowmelt event were significant and represented 37–45% of the annual flux. This highlights the challenge of quantifying aquatic C fluxes in areas with large temporal variability and suggests that inability to ‘‘capture’’ the spring snowmelt event may lead to under-estimation of C fluxes in northern regions