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Bioturbation by invasive crayfish can significantly alter sediment properties and its transport in invaded water bodies; however, the indirect impacts of this on ecosystem functioning are poorly understood. In this thesis I present data from mesocosm and field manipulation experiments used to assess the effect of bioturbation by three widely distributed invasive crayfish species (Procambarus clarkii, Pacifastacus leniusculus and Astacus leptodactylus) on a variety of ecosystem properties across seasons. In the mesocosm experiments, P. clarkii caused significantly more bioturbation than the other species, although increased bioturbation by all species in the spring and/or summer was associated with: reduced dissolved oxygen concentrations in near-surface water, indicating a large increase in oxygen demand by the water column; increased methane oxidation potential within the water (MOPwat), indicating the re-suspension of methane oxidising bacteria (MOB) along with the sediment; and a shift in zooplankton community structure towards dominance by large cladoceran species. Stable isotope analysis of the zooplankton showed a strong relationship between δ13C and MOPwat, suggesting that bioturbation increases MOB consumption. Given the importance of zooplankton as a trophic link to the higher food web, crayfish bioturbation may increase the importance of methane derived (chemosynthetic) carbon in invaded ecosystems. Temperature was identified as the key driver of seasonal variations in crayfish bioturbation intensity through laboratory mesocosm experiments, enabling estimation of the full annual pattern of bioturbation intensity for each species. The optimal temperature for P. clarkii was much higher than for the other species meaning that its bioturbation impacts exhibited large seasonal fluctuations whilst P. leniusculus and A. leptodactylus maintained a lower but more consistent level. Field manipulation experiments of enclosed sections of Chalgrove Brook, Oxfordshire, found significant bioturbation activity by P. leniusculus in early autumn; however, the increase in turbidity was too small to detect other effects observed in the mesocosm experiments.

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Agroforestry offers a land-use management methodology that may provide solutions to environmental degradation in the tropics. However, practitioners of agroforestry are faced with the dilemma of clearing more forest cover in order to increase crop size and sustain their income. The aim of this study is to understand the agroforester’s dilemma and to measure the value of the agroforestry ecosystem stewardship in yerba maté (Ilex paraguariensis A. St. Hil.) agroforestry parcels of the South American Atlantic forest eco-region. Biodiversity, carbon sequestration and vegetation cover were measured to be considerably higher in yerba maté (Ilex paraguariensis A. St. Hil.) agroforestry plantations than in neighboring monoculture crops. Agroforestry vegetation cover values were measured to have between 65-89% cover while monocultures had roughly 25% cover. Agroforestry stored carbon values ranged between 154.7-172.7 Mg C ha-1, compared to monoculture plantation values of 81.3 Mg C ha-1. Finally, as measured using the Shannon index, values of species richness ranged from 2.7-3.5 in agroforestry parcels and between 0.9-1.3 in monocultures, and values of evenness ranged between 0.6 and 0.8 in agroforestry parcels, and 0.2 in monocultures. These findings illustrate that yerba maté agroforestry can potentially contribute as a regional climate change mitigation strategy. Valuating and monetizing ecosystem services and engaging smaller farmers with worldwide ecosystem marketplaces offer the potential to expand the dialogue around payments for the valuable ecosystem services that agroforesters are providing. An analysis of market prices available within the ecosystem marketplace for total ecosystem services being conserved on agroforestry parcels amounted to a range in value between $16 – $160 ha-1 yr-1. To address environmental degradation in the Atlantic Forest region, in South America, governments should motivate environmental conservation to support a shift towards sustainable yerba maté production which supports livelihoods of small-scale farmers, economic justice and environmental sustainability. / Graduate

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