Macroinvertebrate communities and ecosystem functioning in peatland streams

• Main Author: Aspray, Katie Louise
• Published: University of Leeds 2012
• Subjects: 577.687
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.590494

Headwater streams are important habitats, unique in their heterogeneity and biodiversity. they are considered significant for the functioning of whole river systems. Many headwater systems. such as those in the temperate and sub arctic northern hemisphere, drain peat dominated catchments, a habitat that is increasingly threatened by climate change, acidification and pressures from an array of land management practices. Together these impacts are resulting in the widespread degradation of peatlands and it is hypothesised that stressors could severely impact streams draining these systems, causing shifts in macro invertebrate community composition and alterations to functional process rates. However, there is a lack of information on the exact impacts of these stressors to peatland streams and, furthermore, limited knowledge of these ecosystems in their intact state. Thus, the overarching aim of this work is to improve understanding surrounding the impacts of stressors to peatland streams and to contextualise this research with an improved knowledge of the dynamics of intact peatland streams. This work focused on streams originating from blanket peats in the UK, which form important headwaters of many major UK rivers, and had four main objectives. 1) Develop a holistic understanding of an intact peatland stream through intensive assessment of physico chemistry, macroinvertebrate communities and three functional processes (algae accrual, plant litter decomposition and whole stream metabolism) using both a longitudinal survey and intense seasonal monitoring. 2) Assess the impacts of two catchment-scale drivers of change in peatland habitats (rotational heather burning and erosion) on stream ecosystems, examining physicochemistry, macroinvertebrates and ecosystem functioning across fifteen streams. 3) Examine gradients of sedimentation associated with environmental change and land management using streamside mesocosm and reach experiments. 4) Consider the mechanisms that elicit a change in physicochemisty, macroinvertebrates and ecosystem function by considering interrelationships and advancement of conceptual models. The interdisciplinary approach used in this thesis allowed a novel assessment of the spatiotemporal variability of peatland stream ecosystems and for the first time hig~lighted alterations in both macroinvertebrate communities and ecosystem functioning along the stream length and across seasons in an intact peatland stream. Increases in macroinvertebrate abundance, primary production and community vi j b respiration were observed with increasing distance downstream and with increasing catchment size. These parameters, along with algae accrual and leaf litter decomposition rates, also showed strong seasonal patterns, decreasing in winter and amplifying in summer. Variations in these parameters were driven predominantly by increases in temperature, photosynthetically active radiation (PAR), suspended sediment concentrations (SSC), discharge and dissolved organic carbon (DOC). Erosion, and to some degree rotational heather burning, were found to impact physicochemical variables, with total oxidised nitrogen (TON) and SSC displaying increased concentration.s in impacted catchments. Associated shifts were found in macroinvertebrate communities, with amplified abundance in eroded catchments driven by increases in ' more sediment tolerate taxa, such as Chironomidae and Oligo chaeta. Streams draining eroded and burnt catchments also displayed lower numbers of sensitive Ephemeroptera, Plecoptera and Trichoptera taxa. Functional parameters did not reflect these changes in chemistry and biota, but there were clear differences between the fifteen individual streams. Experiments undertaken in streamside mesocosms and stream reaches showed impacts of organic sedimentation across several levels of ecological organisation. Increased benthic sedimentation led to declines in macroinvertebrate abundance, shifts in - species composition and increased sediment respiration rates. Short term influx of organic sediment in reach based experiments caused significant increases in the downstream drift of macroinvertebrates during nocturnal periods, however, these streams were quick to recover to pre-experiment drift rates and benthic communities were not affected over the period of the experiment. These influx events produced a rapid and severe decline in GPP measured though whole stream metabolism rates, This body of research highlights peatland streams as unique and heterogenic systems but also as systems that are sensitive to anthropogenic stressors at both the catchment and reach scale, These habitats have intrinsic importance, supporting diverse macroinvertebrate communities, are significant for the modulation of carbon and are good indicators of the condition of the surrounding catchment. Thus, this work emphasises the need for restorative measures and sustainable management in peatland habitats that considers the streams they support. In addition, this work furthers knowledge of the baseline conditions in these systems and increases understanding of the use of functional processes as ecological indicators in peatland..streams.