title: Effects of macrofauna diversity on porewater nutrient concentrations following enrichment

authors: Hines, Laura Veronica

subjects: Macrofauna diversity

abstract: 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.

text: Effects of macrofauna diversity on porewater nutrient concentrations following enrichment 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.

year: 2015

title: Do productivity and disturbance interact to modulate macroinvertebrate diversity in streams?

authors: Tonkin, Jonathan D.

subjects: Dynamic equilibrium mode

abstract: Although disturbance and productivity are clearly strong influences on lotic diversity, rarely have their interactive effects been studied in running water systems. We hypothesised that the presence or absence of canopy cover in streams would alter productivity-disturbance-diversity relationships due to differential effects on the food base, and tested this hypothesis in 47 mountain streams in the central North Island of New Zealand. Canopy cover had no influence on algal biomass in these streams, but a link between disturbance and productivity was found in open canopy streams where taxonomic richness of invertebrates increased log-linearly with increasing algal biomass and peaked at intermediate levels of disturbance. Community evenness declined with disturbance, but only at closed canopy sites where both invertebrate taxonomic richness and Simpson's diversity index were higher. Although there was a peak in richness at intermediate rates of disturbance, our results do not directly match predictions of the dynamic equilibrium model which predicts that the level of disturbance maximising diversity interacts with habitat productivity. Rather, we suggest the combined effects of productivity and disturbance are additive rather than multiplicative such that productivity simply sets the upper limit to richness in streams.

text: Do productivity and disturbance interact to modulate macroinvertebrate diversity in streams? Although disturbance and productivity are clearly strong influences on lotic diversity, rarely have their interactive effects been studied in running water systems. We hypothesised that the presence or absence of canopy cover in streams would alter productivity-disturbance-diversity relationships due to differential effects on the food base, and tested this hypothesis in 47 mountain streams in the central North Island of New Zealand. Canopy cover had no influence on algal biomass in these streams, but a link between disturbance and productivity was found in open canopy streams where taxonomic richness of invertebrates increased log-linearly with increasing algal biomass and peaked at intermediate levels of disturbance. Community evenness declined with disturbance, but only at closed canopy sites where both invertebrate taxonomic richness and Simpson's diversity index were higher. Although there was a peak in richness at intermediate rates of disturbance, our results do not directly match predictions of the dynamic equilibrium model which predicts that the level of disturbance maximising diversity interacts with habitat productivity. Rather, we suggest the combined effects of productivity and disturbance are additive rather than multiplicative such that productivity simply sets the upper limit to richness in streams.

year: 2013

title: Understanding the potential exposure of coastal marae and urupā in Aotearoa New Zealand to sea level rise

authors: Bailey-Winiata, Akuhata Patrick Stephen

subjects: Marae

abstract: In Aotearoa New Zealand, Māori are Indigenous and have inhabited these islands for the past 700 years. They have an intricate physical and spiritual connection to places and the environment. This is reflected in the Māori creation story, where Ranginui (sky father) and Papatūānuku (Earth mother) are the ancestral parents of Māori. Between these two gods is the marae, the Māori meeting house. Marae are where the domestic life of Māori traditionally ran its course, with marae being an overarching term to illustrate multiple buildings which each have a specific role to play within the community. Often, marae have an associated urupā (burial ground). Historically, marae and their associated urupā are positioned along the low-lying coast, providing easy access to kaimoana (sea food), transport and trade. However, coastal marae and urupā are at an increasing threat of inundation and erosion from sea level rise, and will also be impacted by other effects of climate change such as drought and other changes to weather patterns such as storms.
Many coastal marae and urupā are already experiencing the impacts of coastal flooding and erosion, however, little is known about the exposure of coastal marae and urupā to sea level rise nationally. Therefore, the main aim of this thesis is to explore the potential exposure of coastal marae nationally, with a particular focus on the Bay of Plenty coastal marae including coastal urupā. This aim was achieved by addressing three objectives. The first of which was to investigate the potential national exposure of coastal marae to a 100 year annual recurrence interval extreme sea level event, with the addition of sea level rise. Second, I conducted a nationally-focused assessment of the local coastal geomorphology surrounding coastal marae to determine the potential response of the coast to sea level rise. I also undertook a case study on the BOP which included a more detailed assessment of the geomorphology around the coastal marae and urupā in this region. Third, findings from these two objectives are brought together to consider the next steps to determine how to move forward with planning to manage coastal marae and urupā with sea level rise.
A spatial mapping approach using Arc GIS and existing datasets was used to address these aims, combining the Coastlines and Islands polygon, marae and urupā locational data and the Aotearoa New Zealand coastal hydrosystem classification system proposed by Hume in 2016. This showed that 191 marae around Aotearoa New Zealand are within 1 km of the coast and in the Bay of Plenty 41 urupā are within 1 km. I then used the bathtub modelling approach to get a national first-pass assessment of the potential exposure of these marae and urupā to a 100 year extreme sea level event at current mean sea level, with 10 cm increments of sea level rise up to 3 m. Six coastal marae were potentially exposed to a 100 year extreme sea level event at current mean sea level, with 41 coastal marae are potentially exposed to a 100 year extreme sea level event with a 3 m rise in mean sea level. The most common type of coastal geomorphology nationally and in the Bay of Plenty was shallow drowned valleys, with 72 coastal marae in this category. The response of these systems to sea level rise manifests as changes in the tidal regime and sediment transport dynamics which will affect inundation and erosion of low-lying areas, where many coastal marae and urupā are positioned.
Thus, it is clear that marae and urupā are nationally at risk to sea level rise, and their responses will be highly variable with geomorphology. But what are the next steps? There are many legislative documents such as the coastal climate change and hazards report by the Ministry for the Environment which suggests that the Dynamic Adaptive Policy Pathways strategy to address the uncertainty surrounding climate change, recommended as a method for future planning. Another is the pending reform of the Resource Management Act which will introduce a climate change adaptation act where support for managed retreat will be made available. However, any management strategies for marae, hapū and iwi will need to be cognisant of the tapū and māna that these places hold, and there will be no one size fits all approach.

text: Understanding the potential exposure of coastal marae and urupā in Aotearoa New Zealand to sea level rise In Aotearoa New Zealand, Māori are Indigenous and have inhabited these islands for the past 700 years. They have an intricate physical and spiritual connection to places and the environment. This is reflected in the Māori creation story, where Ranginui (sky father) and Papatūānuku (Earth mother) are the ancestral parents of Māori. Between these two gods is the marae, the Māori meeting house. Marae are where the domestic life of Māori traditionally ran its course, with marae being an overarching term to illustrate multiple buildings which each have a specific role to play within the community. Often, marae have an associated urupā (burial ground). Historically, marae and their associated urupā are positioned along the low-lying coast, providing easy access to kaimoana (sea food), transport and trade. However, coastal marae and urupā are at an increasing threat of inundation and erosion from sea level rise, and will also be impacted by other effects of climate change such as drought and other changes to weather patterns such as storms.
Many coastal marae and urupā are already experiencing the impacts of coastal flooding and erosion, however, little is known about the exposure of coastal marae and urupā to sea level rise nationally. Therefore, the main aim of this thesis is to explore the potential exposure of coastal marae nationally, with a particular focus on the Bay of Plenty coastal marae including coastal urupā. This aim was achieved by addressing three objectives. The first of which was to investigate the potential national exposure of coastal marae to a 100 year annual recurrence interval extreme sea level event, with the addition of sea level rise. Second, I conducted a nationally-focused assessment of the local coastal geomorphology surrounding coastal marae to determine the potential response of the coast to sea level rise. I also undertook a case study on the BOP which included a more detailed assessment of the geomorphology around the coastal marae and urupā in this region. Third, findings from these two objectives are brought together to consider the next steps to determine how to move forward with planning to manage coastal marae and urupā with sea level rise.
A spatial mapping approach using Arc GIS and existing datasets was used to address these aims, combining the Coastlines and Islands polygon, marae and urupā locational data and the Aotearoa New Zealand coastal hydrosystem classification system proposed by Hume in 2016. This showed that 191 marae around Aotearoa New Zealand are within 1 km of the coast and in the Bay of Plenty 41 urupā are within 1 km. I then used the bathtub modelling approach to get a national first-pass assessment of the potential exposure of these marae and urupā to a 100 year extreme sea level event at current mean sea level, with 10 cm increments of sea level rise up to 3 m. Six coastal marae were potentially exposed to a 100 year extreme sea level event at current mean sea level, with 41 coastal marae are potentially exposed to a 100 year extreme sea level event with a 3 m rise in mean sea level. The most common type of coastal geomorphology nationally and in the Bay of Plenty was shallow drowned valleys, with 72 coastal marae in this category. The response of these systems to sea level rise manifests as changes in the tidal regime and sediment transport dynamics which will affect inundation and erosion of low-lying areas, where many coastal marae and urupā are positioned.
Thus, it is clear that marae and urupā are nationally at risk to sea level rise, and their responses will be highly variable with geomorphology. But what are the next steps? There are many legislative documents such as the coastal climate change and hazards report by the Ministry for the Environment which suggests that the Dynamic Adaptive Policy Pathways strategy to address the uncertainty surrounding climate change, recommended as a method for future planning. Another is the pending reform of the Resource Management Act which will introduce a climate change adaptation act where support for managed retreat will be made available. However, any management strategies for marae, hapū and iwi will need to be cognisant of the tapū and māna that these places hold, and there will be no one size fits all approach.

year: 2021