Sedimentary Environment Influences Ecosystem Response to Nutrient Enrichment |
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| Authors: | Emily J Douglas Conrad A Pilditch Andrew M Lohrer Candida Savage Louis A Schipper Simon F Thrush |
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| Institution: | 1.School of Science,University of Waikato,Hamilton,New Zealand;2.National Institute of Water and Atmospheric Research,Hamilton,New Zealand;3.Department of Marine Science,University of Otago,Dunedin,New Zealand;4.Marine Research Institute and Department of Biological Sciences,University of Cape Town,Rondebosch,South Africa;5.Institute of Marine Science,University of Auckland,Auckland,New Zealand |
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| Abstract: | As coastal catchment land use intensifies, estuaries receive increased nutrient and sediment loads, resulting in habitats that are dominated by muddy organic-rich sediments. Increased mud (i.e. silt-clay (particles <?63 μm)) content has been associated with negative effects on soft sediment biodiversity and ecosystem functioning, but the simultaneous impact of nutrient enrichment on ecosystem response is unclear. Nutrient recycling and denitrification in estuarine soft sediments represent important ecosystem functions regenerating nutrients for primary producers and regulating the ability to remove excess terrestrially derived nitrogen. To test the effect of sedimentary environment on ecosystem resilience to nutrient perturbation, we experimentally enriched sediments with slow release fertiliser across an intertidal sedimentary gradient (0–24% mud content). The enrichment successfully elevated pore water ammonium concentrations (median 36?×?control) to levels representative of enriched estuaries. Findings show that the sedimentary environment can influence ecosystem function response to nutrient stress. In particular, denitrification enzyme activity was suppressed by nutrient enrichment, but the effect was greater as sediment mud content increased. Furthermore, compared with sandy sediments, sediments with high mud content may restrict nutrient processing (release, uptake or transformation of organic nutrients by the benthos) facilitating ecosystem shifts toward eutrophication. These results show the value of investigating the impacts of stressors in different environmental settings and demonstrate that land use practices that increase the proportion of muddy habitats in estuaries may reduce denitrification which in turn may reduce ecosystem resilience to eutrophication. |
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