Effects of macrofauna diversity on porewater nutrient concentrations following enrichment
Hines, L. V. (2015). Effects of macrofauna diversity on porewater nutrient concentrations following enrichment (Thesis, Master of Science (Research) (MSc(Research))). University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/9610
Permanent Research Commons link: https://hdl.handle.net/10289/9610
Macrofauna play a key role in the functioning of soft sediment intertidal ecosystems via bioturbation and feeding habits which modify sediment biogeochemistry and influence nutrient cycling. Eutrophication is a naturally occurring phenomenon; however, enrichment due to anthropogenic inputs has increased in frequency with largely unknown consequences to benthic macrofaunal assemblages. A decline in infaunal biodiversity is thought to result in the loss of ecosystem function due to increased disturbance in the form of enhanced nutrient addition. This is increasingly important to estuarine habitats, as benthic macrofauna play an important role in controlling sediment porewater nutrient concentrations, nutrient flux to the overlying water column and ultimately ecosystem function. Sediment modification by macrofauna behaviours (e.g. bioturbation) stimulate nutrient regeneration and influence denitrification rate. Thus understanding the responses of macrofauna to enhanced nutrient levels is vital for the understanding and subsequent management of benthic assemblages to estuarine eutrophication. The aim of this thesis was to stress the intertidal sediment of the Kaipara Harbour by the addition of slow-release fertiliser in order to identify key macrofaunal diversity responses and the influence this has in the overall nutrient processing ability. I also examined whether fertiliser addition influenced primary producers, microphytobenthos biomass and the percent coverage of seagrass. To gain a better understanding of porewater nutrient elevation and subsequent impacts to macrofaunal diversity, 28 site locations were selected based on high and low functional macrofaunal diversity and abundance characteristics previously identified within Tapora Bank, Kaipara Harbour (Greenfield 2013). Known amounts (1400g m⁻² (high treatment) and 600g m⁻² (medium treatment)) of 70-day slow-release fertiliser (42 % N) was added to the intertidal sediment across a gradient in macrofaunal diversity. Porewater and sediment properties were measured 28 and 47 days after enrichment, with macrofaunal diversity determined on day 47. The fertiliser enriched plots significantly elevated porewater ammonium concentrations in both treatments in upper (0-2 cm) and lower (5-7 cm) sediment depths. Lower sampling depths had greater concentrations of porewater ammonium than the upper sediments. This elevation resulted a decline in the overall macrofaunal abundance in both addition treatments however, only the decline in key functional species Macomona liliana was significant. The number of functional individuals and number of M. liliana were identified as significant factors controlling the variation in porewater ammonium concentration in ambient sediments. A switch was observed after fertiliser elevation where mud become the sole driver of porewater ammonium concentration in plots of high fertiliser addition. Normalisation treatment porewater ammonium concentration by the control plot values identified both the number of species and number of functional species as important drivers of porewater ammonium processing. No effect of fertiliser enrichment to seagrass percent coverage was observed. These results demonstrate that the elevation of porewater ammonium within intertidal sediments may have implications to the diversity and the subsequent functioning of intertidal benthic communities. In particularly, our study highlights the potential loss of functioning related to the decline of key species such as M. liliana; given their role as ecosystem engineers, their loss could reinforce the effects of eutrophication stress on the system and lead to further degradation.
University of Waikato
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