Effects of agricultural intensification on the ecology of upland stream invertebrate communities

Pearson, Caitlin E. 2015. Effects of agricultural intensification on the ecology of upland stream invertebrate communities. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Agricultural land use is a leading cause of habitat degradation and biodiversity loss in streams. Understanding the mechanisms by which land use change affects stream ecosystems is essential for their effective management. Despite this, the consequences of agricultural intensification for community composition and ecosystem functioning in streams remain poorly resolved. Using national-scale monitoring data and new field data from upland streams in South Wales, this study investigated the effects of pastoral intensification on the community composition, functional diversity and feeding interactions of stream macroinvertebrates. A combination of analytical tools were used, including propensity modelling, ecological traits, stable isotopes and Next Generation DNA sequencing to quantify diet. Taxonomic and functional diversity had non-linear relationships with pastoral intensity, declining beyond a threshold of 4 mg L-1 nitrate and 8% fine sediment cover. This decline occurred as a non-random loss of species possessing specific traits, including large body size and lack of resistance forms. Although monitoring data showed that at a UK-wide scale pastoral agriculture (cf. other land uses) had a positive effect on richness and sensitive species representation, the threshold intensity at which effects become negative is exceeded in many locations within the U.K. and globally. Invertebrates that feed by grazing algae were particularly vulnerable to agricultural stressors. Combined with changes in the availability and quality of basal resources with pastoral intensification, this decline in grazer representation resulted in invertebrate communities becoming increasingly reliant on detrital resources. Further, there was indication that methane-derived carbon contributed to the food web in high intensity sites, which has not previously been observed in upland streams. Although only relatively minor changes were observed in predator-prey interactions across the intensity gradient, there was a suggestion of simplification of the food web in high intensity sites. Together these changes could radically alter ecosystem properties such as secondary production, nutrient processing and resilience. Overall, the results highlight the management priorities of reducing fine sediment and nutrient inputs to agricultural streams. The identification of a threshold at which agricultural effects become deleterious will assist in guiding mitigation efforts. Further work is required to determine the generality of this threshold across stream ecosystems.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Biosciences
Subjects:	Q Science > QH Natural history > QH301 Biology
Uncontrolled Keywords:	Agriculture, streams, invertebrates, functional diversity, stream food webs, farming.
Funders:	BBSRC
Date of First Compliant Deposit:	30 May 2016
Last Modified:	21 Dec 2023 14:25
URI:	https://orca.cardiff.ac.uk/id/eprint/91332

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