title: Constructed treatment wetlands: Tools to attenuate diffuse agricultural pollution and enhance the biodiversity of eutrophic peat lake ecosystems

authors: Eivers, Rebecca Sylvia

subjects: biodiversity

abstract: Agricultural land use is a major source of nitrogen (N), phosphorus (P) and suspended sediment (SS) to aquatic ecosystems.  Elevated inputs of N, P and SS associated with agricultural expansion and intensification have led to widespread degradation of surface waters throughout the world, causing eutrophication and excessive sedimentation of many rivers, lakes, wetlands, and estuaries.  In excess, these contaminants cause diverse negative impacts on lake ecosystems such as prolific growth of phytoplankton and aquatic plants, toxic algal blooms and collapse of macrophyte beds, high turbidity and in-filling, as well as reduced biodiversity, health and resilience.  Shallow peat lakes in the Waikato region of New Zealand have catchment soils that are highly erodible and readily leach nutrients, with low capacity to assimilate elevated loads of N, P and SS. These lakes have some of the poorest water quality amongst lakes in New Zealand.  
Constructed treatment wetlands (CTWs) are used internationally as technologies to improve the quality of stormwater and wastewater from municipal, industrial and agricultural point sources.  Further, CTWs are becoming increasingly prevalent as mitigation tools to manage diffuse pollution from agricultural runoff. However, discrepancies among studies of the performance of CTWs treating diffuse sources of N, P and SS have created uncertainty for end-users.  As such, more field-based research is required to establish the suitability of CTWs as management tools for diffuse agricultural runoff where flow rates are unregulated and pollutant concentrations can be highly variable.  Improving our knowledge of the efficacy of CTWs within intensive agricultural landscapes will increase confidence and encourage more widespread implementation of these mitigation tools by those involved with water quality management.
Actions are underway to restore several highly eutrophic Waikato peat lakes that have catchments used for intensive dairy production.  Local land-care groups, landowners and lake managers are working collaboratively to improve water quality and enhance biodiversity.  CTWs have been implemented as mitigation tools to manage diffuse sources of N, P and SS and reduce loads to the receiving lakes. Restoration group members additionally anticipate that CTWs will improve biodiversity through provision of supplementary habitat within the highly modified, homogeneous agricultural landscape.  The primary objective of my research was to evaluate the dual benefits of CTWs as tools for nutrient and sediment attenuation, and restoration of biodiversity within peat lake ecosystems.
The efficacy of CTWs treating diffuse agricultural pollution is influenced by three key elements: CTW morphology, internal contaminant cycling, and the composition of influent constituents.  I quantified the magnitude, composition and variability of constituent inputs in surface waters draining small subcatchments of five shallow peat lakes.  Up to 26 channelised streams were sampled seasonally over 18 months from 2010 to 2011.  Subcatchments had predominantly peat, peaty loam or clay loam soil types and ranged in area from c. 1 to 195 ha (mean 23 ha; median 6 ha).  Extensive spatial and temporal variation in nutrient and sediment loads was evident, driven by seasonality and differences between subcatchment soil types and farm-scale management practices. Total N concentrations were highly variable (0.24 - 13.55 mg L-1; median 2.13 mg L-1), attributable to varying concentrations of nitrate-N and particulate organic-N, which ranged from 0.01 to 10.28 mg L-1 and 0.01 to 4.63 mg L-1, respectively.  Total P concentrations ranged widely (0.01 - 3.02 mg L-1; median 0.13), with exceptionally high concentrations of dissolved P in watercourses draining subcatchments with deep (≥7 m) peat soils and very low surface-water pH (< 4) (mean 1.29 mg PO4-P L-1; n=15).  These results stress the importance of considering soil type when deriving appropriate environmental targets and controls for diffuse pollution from intensive agricultural peat lake catchments.  Lake-catchment nutrient loads calculated from subcatchment daily loads were greater than many of those reported elsewhere in New Zealand, indicating the significance of the nutrient problem faced by water quality managers of Waikato’s shallow peat lakes.  
The efficacy of CTWs as management tools to attenuate diffuse sources of N, P, and SS from agricultural subcatchments of the five peat lakes was investigated concurrently.  Different potential predictors of CTW performance were evaluated for up to 26 CTWs and the effect of morphological and environmental variables on internal nutrient cycling and treatment performance were elucidated.  All CTWs were comprised of a sedimentation pond 'module', with around half including shallow wetland modules planted with native plant species, and three with additional sedimentation pond modules. Inflows were surface-flow watercourses diverted from modified or artificial drainage networks, and outflows were either surface-flow (through drainage channels or culverts) or filtration (through vegetated riparian margins). Morphological predictors of CTW performance included area (range 7 – 1950 m²), depth (0.2 – 2.1 m), volume (12 – 2030 m³), wetland to catchment area ratio (0.01 – 1.18), hydraulic retention time (0.2 – 37.2 h), and hydraulic loading rate (0.4 – 130 m d-1). The presence/absence of macrophytes, the outlet type and the number of CTW modules were included in analyses as categorical variables. Reductions in N, P and SS differed considerably among CTWs, driven by varying influent concentrations and dominant forms of N, P, and SS, as well as CTW morphologies and internal nutrient cycling. Generally, CTWs with larger areas and volumes had higher removal rates of nitrate, total N and coarse sediments, while deeper CTWs more effectively reduced particulate N and volatile SS. Macrophytes improved removal of nitrate and P, whereas filtration outlets frequently increased ammonium. Greater accumulated sediment depths were associated with reduced P removal efficiency, signifying the importance of CTW maintenance such as periodic removal of accumulated sediment. Increasing the number of CTW modules generally improved pollutant removal performance; thus, implementing individualised CTW treatment-train concepts is recommended.  
Zooplankton communities were studied to investigate the value of CTWs as tools to improve the biodiversity of peat lake ecosystems through provision of supplementary habitat.  Zooplankton are an essential component of healthy functioning lake and wetland ecosystems. Despite this, zooplankton communities within CTWs in agricultural landscapes remain unstudied.  Zooplankton taxa richness, total abundance and community composition were compared among three habitat types (lakes, CTWs and drainage ditches) within the five study catchments.  CTWs supported zooplankton species otherwise absent from lake and drain habitats, increasing the biodiversity of the highly-modified peat lake catchments. Taxa richness of CTWs was higher than that of drains, and a few CTWs had greater diversity than some of the lakes.  Zooplankton communities were significantly influenced by habitat area, depth and pH, as well as ammonium and phosphate concentrations, water temperature, dissolved oxygen, and macrophyte cover.  This thesis explored opportunities for refining CTW designs, to enhance habitat diversity and support zooplankton species that improve ecosystem function and may increase CTW performance in agricultural landscapes.
The results of my research present key design considerations for surface flow CTWs treating diffuse agricultural pollution from peat lake catchments used for intensive dairy production.  Collectively, the findings of this thesis provide a scientific basis for more comprehensive, holistic CTW designs to mitigate inputs of N, P and SS, and quantitative evidence of the value of agricultural CTWs as water quality and restoration management tools for peat lake ecosystems.  This thesis also provides recommendations for future research to improve our understanding of the complex hydrological and biogeochemical processes driving nutrient losses from peat lake catchments used for intensive dairy production, to inform restoration and rehabilitation of shallow peat lake ecosystems in New Zealand.

text: Constructed treatment wetlands: Tools to attenuate diffuse agricultural pollution and enhance the biodiversity of eutrophic peat lake ecosystems Agricultural land use is a major source of nitrogen (N), phosphorus (P) and suspended sediment (SS) to aquatic ecosystems.  Elevated inputs of N, P and SS associated with agricultural expansion and intensification have led to widespread degradation of surface waters throughout the world, causing eutrophication and excessive sedimentation of many rivers, lakes, wetlands, and estuaries.  In excess, these contaminants cause diverse negative impacts on lake ecosystems such as prolific growth of phytoplankton and aquatic plants, toxic algal blooms and collapse of macrophyte beds, high turbidity and in-filling, as well as reduced biodiversity, health and resilience.  Shallow peat lakes in the Waikato region of New Zealand have catchment soils that are highly erodible and readily leach nutrients, with low capacity to assimilate elevated loads of N, P and SS. These lakes have some of the poorest water quality amongst lakes in New Zealand.  
Constructed treatment wetlands (CTWs) are used internationally as technologies to improve the quality of stormwater and wastewater from municipal, industrial and agricultural point sources.  Further, CTWs are becoming increasingly prevalent as mitigation tools to manage diffuse pollution from agricultural runoff. However, discrepancies among studies of the performance of CTWs treating diffuse sources of N, P and SS have created uncertainty for end-users.  As such, more field-based research is required to establish the suitability of CTWs as management tools for diffuse agricultural runoff where flow rates are unregulated and pollutant concentrations can be highly variable.  Improving our knowledge of the efficacy of CTWs within intensive agricultural landscapes will increase confidence and encourage more widespread implementation of these mitigation tools by those involved with water quality management.
Actions are underway to restore several highly eutrophic Waikato peat lakes that have catchments used for intensive dairy production.  Local land-care groups, landowners and lake managers are working collaboratively to improve water quality and enhance biodiversity.  CTWs have been implemented as mitigation tools to manage diffuse sources of N, P and SS and reduce loads to the receiving lakes. Restoration group members additionally anticipate that CTWs will improve biodiversity through provision of supplementary habitat within the highly modified, homogeneous agricultural landscape.  The primary objective of my research was to evaluate the dual benefits of CTWs as tools for nutrient and sediment attenuation, and restoration of biodiversity within peat lake ecosystems.
The efficacy of CTWs treating diffuse agricultural pollution is influenced by three key elements: CTW morphology, internal contaminant cycling, and the composition of influent constituents.  I quantified the magnitude, composition and variability of constituent inputs in surface waters draining small subcatchments of five shallow peat lakes.  Up to 26 channelised streams were sampled seasonally over 18 months from 2010 to 2011.  Subcatchments had predominantly peat, peaty loam or clay loam soil types and ranged in area from c. 1 to 195 ha (mean 23 ha; median 6 ha).  Extensive spatial and temporal variation in nutrient and sediment loads was evident, driven by seasonality and differences between subcatchment soil types and farm-scale management practices. Total N concentrations were highly variable (0.24 - 13.55 mg L-1; median 2.13 mg L-1), attributable to varying concentrations of nitrate-N and particulate organic-N, which ranged from 0.01 to 10.28 mg L-1 and 0.01 to 4.63 mg L-1, respectively.  Total P concentrations ranged widely (0.01 - 3.02 mg L-1; median 0.13), with exceptionally high concentrations of dissolved P in watercourses draining subcatchments with deep (≥7 m) peat soils and very low surface-water pH (< 4) (mean 1.29 mg PO4-P L-1; n=15).  These results stress the importance of considering soil type when deriving appropriate environmental targets and controls for diffuse pollution from intensive agricultural peat lake catchments.  Lake-catchment nutrient loads calculated from subcatchment daily loads were greater than many of those reported elsewhere in New Zealand, indicating the significance of the nutrient problem faced by water quality managers of Waikato’s shallow peat lakes.  
The efficacy of CTWs as management tools to attenuate diffuse sources of N, P, and SS from agricultural subcatchments of the five peat lakes was investigated concurrently.  Different potential predictors of CTW performance were evaluated for up to 26 CTWs and the effect of morphological and environmental variables on internal nutrient cycling and treatment performance were elucidated.  All CTWs were comprised of a sedimentation pond 'module', with around half including shallow wetland modules planted with native plant species, and three with additional sedimentation pond modules. Inflows were surface-flow watercourses diverted from modified or artificial drainage networks, and outflows were either surface-flow (through drainage channels or culverts) or filtration (through vegetated riparian margins). Morphological predictors of CTW performance included area (range 7 – 1950 m²), depth (0.2 – 2.1 m), volume (12 – 2030 m³), wetland to catchment area ratio (0.01 – 1.18), hydraulic retention time (0.2 – 37.2 h), and hydraulic loading rate (0.4 – 130 m d-1). The presence/absence of macrophytes, the outlet type and the number of CTW modules were included in analyses as categorical variables. Reductions in N, P and SS differed considerably among CTWs, driven by varying influent concentrations and dominant forms of N, P, and SS, as well as CTW morphologies and internal nutrient cycling. Generally, CTWs with larger areas and volumes had higher removal rates of nitrate, total N and coarse sediments, while deeper CTWs more effectively reduced particulate N and volatile SS. Macrophytes improved removal of nitrate and P, whereas filtration outlets frequently increased ammonium. Greater accumulated sediment depths were associated with reduced P removal efficiency, signifying the importance of CTW maintenance such as periodic removal of accumulated sediment. Increasing the number of CTW modules generally improved pollutant removal performance; thus, implementing individualised CTW treatment-train concepts is recommended.  
Zooplankton communities were studied to investigate the value of CTWs as tools to improve the biodiversity of peat lake ecosystems through provision of supplementary habitat.  Zooplankton are an essential component of healthy functioning lake and wetland ecosystems. Despite this, zooplankton communities within CTWs in agricultural landscapes remain unstudied.  Zooplankton taxa richness, total abundance and community composition were compared among three habitat types (lakes, CTWs and drainage ditches) within the five study catchments.  CTWs supported zooplankton species otherwise absent from lake and drain habitats, increasing the biodiversity of the highly-modified peat lake catchments. Taxa richness of CTWs was higher than that of drains, and a few CTWs had greater diversity than some of the lakes.  Zooplankton communities were significantly influenced by habitat area, depth and pH, as well as ammonium and phosphate concentrations, water temperature, dissolved oxygen, and macrophyte cover.  This thesis explored opportunities for refining CTW designs, to enhance habitat diversity and support zooplankton species that improve ecosystem function and may increase CTW performance in agricultural landscapes.
The results of my research present key design considerations for surface flow CTWs treating diffuse agricultural pollution from peat lake catchments used for intensive dairy production.  Collectively, the findings of this thesis provide a scientific basis for more comprehensive, holistic CTW designs to mitigate inputs of N, P and SS, and quantitative evidence of the value of agricultural CTWs as water quality and restoration management tools for peat lake ecosystems.  This thesis also provides recommendations for future research to improve our understanding of the complex hydrological and biogeochemical processes driving nutrient losses from peat lake catchments used for intensive dairy production, to inform restoration and rehabilitation of shallow peat lake ecosystems in New Zealand.

year: 2018

title: Changes in benthic ecosystem properties and functions across sedimentary gradients in estuaries

authors: Pratt, Daniel Robert

subjects: Ecosystem function

abstract: In estuaries, sediment properties dominate the inhabiting flora and fauna and their role in energy flows and nutrient cycling. Whilst sediment transport is a natural, key process, human intervention in estuaries and their catchments has altered the regime of terrigenous sediment loading and pose both short and long-term consequences to ecosystem functioning. Temporary increases in turbidity reduce light availability for primary production by microphytobenthos (MPB) that fuel benthic communities. Long-term alteration of grain size properties changes the distribution of key macrofaunal species and how they interact with their environment, carrying potentially serious implications for the ecological functioning of these systems. Our knowledge of how benthic ecosystems respond to changes in sedimentary regimes is crucial to our ability to project and manage the impacts of environmental change. In this thesis, I investigated the multifaceted effects of increased sediment loading on the benthic biota and their functioning using natural and experimental sedimentary gradients.

An in situ experiment was conducted on an intertidal sandflat to examine the effects of short-term increases in suspended sediment concentration (SSC) on benthic autotrophic (primary production) and heterotrophic processes. In sunlit conditions, increases in SSC led to dramatic declines in net primary production and concomitant increases in NH₄⁺ efflux from the sediment to the water column. Although sediment chlorophyll-⍺ concentration increased with higher levels of SSC, a result that was likely a photoadaptive response to reduced light intensity, SSC reduced O₂ production per unit of chlorophyll -⍺ . SSC had no significant effect on sediment properties or heterotrophic processes such as sediment oxygen consumption or nutrient efflux, suggesting that temporary increases in suspended sediments (within the range of SSC tested) primarily affected photosynthetic processes. 

Sediment properties, macrofaunal diversity and biogeochemical fluxes were measured across natural gradients of silt and clay (hereafter mud) to determine the effects of habitat change associated with chronic sediment loading on the structure and functioning of benthic communities. There were significant declines in measures of macrofaunal diversity and the maximum densities of key bioturbating bivalves (Austrovenus stutchburyi and Macomona liliana) with increased mud content. Concurrently, the maximum rates of sediment oxygen consumption (SOC), NH₄⁺ efflux (a proxy of nutrient regeneration)and biomass standardised gross primary production (GPPChl-⍺) also decreased with increasing mud content. A. stutchburyi contributed disproportionately to variation in SOC and NH₄⁺ efflux, suggesting that losses of strongly interacting key species concomitant with increased sediment mud content could have a significant impact on ecosystem function. The results from this study demonstrate the significant loss of ecosystem function in intertidal sandflats that is likely from increased sediment mud content associated with long-term increases in sedimentation stress. 

The spatial distributions of MPB biomass, macrofaunal grazer abundances and deposit feeding activity were measured across a gradient of sediment mud content to determine relationships between grazers and MPB biomass across transitional sedimentary environments. The density of feeding traces produced by M. Liliana was measured as a proxy of deposit feeding activity by this species. MPB biomass was generally lower in areas with higher deposit feeding activity but this relationship was scale dependent, emerging over larger areas (tens of centimetres) but absent at local (centimetre) scales relative to the animal’s feeding ambit. Despite higher MPB biomass in muddy sediments, feeding trace density was markedly lower, suggesting lower feeding activity and trophic exchange in muddy compared with sandy sediments. The suspension feeding bivalve A. stutchburyi was positively associated with MPB biomass and the interaction between A. stutchburyi density and mud was the strongest predictor of MPB biomass. Thus, non-trophic interactions that potentially facilitate production may override the deleterious effects of grazing on MPB biomass by large macrofaunal species. This thesis demonstrates the high capacity of sandflat systems for primary, secondary production and nutrient regeneration and the degradation of these ecological properties and functions in muddier and more turbid systems. The decline in this functional capacity reflects the alterations of multiple ecological components and their interactions corresponding to habitat change. Defining changes in these interaction networks can improve our ability to track changes in ecosystem functioning and elucidate underlying pathways and potential mechanisms. In particular, this thesis highlights the value of observing changes in these ecological properties and functions across natural and experimental gradients at the appropriate scales in time and space over which stressors operate.

text: Changes in benthic ecosystem properties and functions across sedimentary gradients in estuaries In estuaries, sediment properties dominate the inhabiting flora and fauna and their role in energy flows and nutrient cycling. Whilst sediment transport is a natural, key process, human intervention in estuaries and their catchments has altered the regime of terrigenous sediment loading and pose both short and long-term consequences to ecosystem functioning. Temporary increases in turbidity reduce light availability for primary production by microphytobenthos (MPB) that fuel benthic communities. Long-term alteration of grain size properties changes the distribution of key macrofaunal species and how they interact with their environment, carrying potentially serious implications for the ecological functioning of these systems. Our knowledge of how benthic ecosystems respond to changes in sedimentary regimes is crucial to our ability to project and manage the impacts of environmental change. In this thesis, I investigated the multifaceted effects of increased sediment loading on the benthic biota and their functioning using natural and experimental sedimentary gradients.

An in situ experiment was conducted on an intertidal sandflat to examine the effects of short-term increases in suspended sediment concentration (SSC) on benthic autotrophic (primary production) and heterotrophic processes. In sunlit conditions, increases in SSC led to dramatic declines in net primary production and concomitant increases in NH₄⁺ efflux from the sediment to the water column. Although sediment chlorophyll-⍺ concentration increased with higher levels of SSC, a result that was likely a photoadaptive response to reduced light intensity, SSC reduced O₂ production per unit of chlorophyll -⍺ . SSC had no significant effect on sediment properties or heterotrophic processes such as sediment oxygen consumption or nutrient efflux, suggesting that temporary increases in suspended sediments (within the range of SSC tested) primarily affected photosynthetic processes. 

Sediment properties, macrofaunal diversity and biogeochemical fluxes were measured across natural gradients of silt and clay (hereafter mud) to determine the effects of habitat change associated with chronic sediment loading on the structure and functioning of benthic communities. There were significant declines in measures of macrofaunal diversity and the maximum densities of key bioturbating bivalves (Austrovenus stutchburyi and Macomona liliana) with increased mud content. Concurrently, the maximum rates of sediment oxygen consumption (SOC), NH₄⁺ efflux (a proxy of nutrient regeneration)and biomass standardised gross primary production (GPPChl-⍺) also decreased with increasing mud content. A. stutchburyi contributed disproportionately to variation in SOC and NH₄⁺ efflux, suggesting that losses of strongly interacting key species concomitant with increased sediment mud content could have a significant impact on ecosystem function. The results from this study demonstrate the significant loss of ecosystem function in intertidal sandflats that is likely from increased sediment mud content associated with long-term increases in sedimentation stress. 

The spatial distributions of MPB biomass, macrofaunal grazer abundances and deposit feeding activity were measured across a gradient of sediment mud content to determine relationships between grazers and MPB biomass across transitional sedimentary environments. The density of feeding traces produced by M. Liliana was measured as a proxy of deposit feeding activity by this species. MPB biomass was generally lower in areas with higher deposit feeding activity but this relationship was scale dependent, emerging over larger areas (tens of centimetres) but absent at local (centimetre) scales relative to the animal’s feeding ambit. Despite higher MPB biomass in muddy sediments, feeding trace density was markedly lower, suggesting lower feeding activity and trophic exchange in muddy compared with sandy sediments. The suspension feeding bivalve A. stutchburyi was positively associated with MPB biomass and the interaction between A. stutchburyi density and mud was the strongest predictor of MPB biomass. Thus, non-trophic interactions that potentially facilitate production may override the deleterious effects of grazing on MPB biomass by large macrofaunal species. This thesis demonstrates the high capacity of sandflat systems for primary, secondary production and nutrient regeneration and the degradation of these ecological properties and functions in muddier and more turbid systems. The decline in this functional capacity reflects the alterations of multiple ecological components and their interactions corresponding to habitat change. Defining changes in these interaction networks can improve our ability to track changes in ecosystem functioning and elucidate underlying pathways and potential mechanisms. In particular, this thesis highlights the value of observing changes in these ecological properties and functions across natural and experimental gradients at the appropriate scales in time and space over which stressors operate.

year: 2014

title: Indigenous psychologies, fourth world peoples and the international literature: Finding ourselves in online abstracting and indexing databases

authors: Nikora, Linda Waimarie

subjects: indigenous psychologies

abstract: The presence and visibility of indigenous people and experience in the field of indigenous psychologies is vital to articulating existence, life, self-determination and future making. This article highlights examples of indigenous Psychology being both absent and present at the same time in OAD (online academic databases).

text: Indigenous psychologies, fourth world peoples and the international literature: Finding ourselves in online abstracting and indexing databases The presence and visibility of indigenous people and experience in the field of indigenous psychologies is vital to articulating existence, life, self-determination and future making. This article highlights examples of indigenous Psychology being both absent and present at the same time in OAD (online academic databases).

year: 2016