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

Resistance and resilience of ecosystem descriptors and properties to dystrophic events: a study case in a Mediterranean lagoon

Mediterranean lagoons are naturally exposed, during the dry season, to dystrophic and hypoxic events determining dis-equilibrium conditions along temporal and spatial scales, which are linked to metabolism and life cycle of the biotic components. In summer 2008, Lesina lagoon (SE Italian coastline) was interested by a geographically localized dystrophic crisis which affected up to 8% of the total lagoon surface. Temporal dynamics of principal descriptors of abiotic (water, sediment) and biotic (phytoplankton, benthic macroinvertebrate) compartments have been followed during the 2008 by collecting data inside stressed and control lagoon areas before a dystrophic event and in the six months after the dystrophic event. The aim of the study was to analyse the pathways of ecosystem responses to dystrophic stress, searching for the characteristic scales of ecosystem compartment resistance and resilience. The characteristic time-scale of abiotic and biotic component time responses varied from days, for the selected markers of the water column, to year, for the benthic ones. Short-term biotic and abiotic responses in the water column were strongly coupled while biotic and abiotic responses at the sediment level were remarkably un-coupled. Dynamics and recovery time of water column and benthic components do not match in Lesina following the dystrophic crisis, highlighting an intrinsic individualistic behavior within the lagoon community driving ecosystem processes and ecosystem level responses. Taxonomic and non-taxonomic descriptors of both phytoplankton and benthic macroinvertebrates showed different response patterns as early warning signals and overall resilience. The emphasized differences in the stability components, i.e., resistance and resilience, of water column and sediment abiotic and biotic characteristics as well as of taxonomic and non-taxonomic descriptors has key implication in planning monitoring strategies and programs for transitional waters in the Mediterranean and Black Sea EcoRegions

What’s really damaging the Reef?: Tracing the origin and fate of the ecologically detrimental sediment and associated bioavailable nutrients

This report addresses six key systematic questions to help inform the debate on the influence of anthropogenic sediment and associated particulate nutrients delivered to the Great Barrier Reef (GBR) lagoon. They are: 1. What is the influence of the newly-delivered sediment (i.e. from flood plumes) on turbidity regimes at coral reef and seagrass locations of the inshore GBR? 2. What is the contribution of the anthropogenic component of this sediment on turbidity regimes? 3. What are the characteristics of the suspended particulate matter (and associated particulate nutrients) that influence light and turbidity regimes and how do these change over the estuarine mixing gradient of flood plumes? 4. How does the particulate organic component of the suspended particulate matter and associated microbial community composition change from the catchment to reef? 5. How bioavailable is the suspended particulate matter along the estuarine mixing gradient 6. Where does the sediment (and associated particulate nutrients) that influence light and turbidity regimes in the GBR come from in the Burdekin catchment so that management efforts can be prioritised? This final project report is divided into eight separate stand-alone research chapters which collectively address these six key questions

Chapter 06: Vulnerability of Great Barrier Reef plankton to climate change

Our approach here is to examine potential ways that climate change may alter plankton communities of the GBR in the future, focusing on the physical mechanisms that currently drive plankton productivity and composition. Many of the oceanographic and climatic features of the western Coral Sea and GBR region and the ways in which they may be influenced by climate change are detailed in Steinberg (see chapter 3). Smaller members of the plankton such as the viruses and bacteria are covered by Webster and Hill (see chapter 5). Key reef-associated organisms with planktonic life stages such as crown-of-thorns starfish, corals, fish and jellyfish, as well as the ecosystem-level responses such as their recruitment and patch connectivity, will be covered by Kingsford and Welch (see chapter 18). Since there are no long time series of plankton data for waters of the GBR for assessing climaterelated trends and their drivers, and few detailed studies in the laboratory or in the field, this review necessarily draws on relevant knowledge from other ecosystems, tropical where possible, and others when required.This is Chapter 6 of Climate change and the Great Barrier Reef: a vulnerability assessment. The entire book can be found at http://hdl.handle.net/11017/13

Evaluating \u3cem\u3eE. Coli\u3c/em\u3e Particle Attachment and the Impact on Transport During High Flows

Fecal indicator bacteria, including E. coli, are the leading cause of water quality impairments within assessed waters in the United States. The source of E. coli includes WWTP, leaking sewers, animal manure, wildlife, livestock, and stream bed sediment. Storm events contribute to bacteria loading within waters through wash-in of land sources of bacteria and resuspension of bacteria within sediments. Bacteria introduced into the water column are either attached to particles or are unattached (or free-living). The goal of this study was to examine the attachment of E. coli to different particle sizes, including their impact on contributing to water quality impairments during storm events. A series of storm events and baseflow conditions were monitored within an impaired stream (Skunk Creek) located in eastern South Dakota. Samples were taken during storm events over a 5- hour duration via autosampler while baseflow samples were taken via grab sampling. In addition, flow and water quality parameters (i.e. turbidity and temperature) were monitored, and the bed shear stress was estimated. These variables were used in a correlation analysis to determine their relationship with E. coli, including the prediction of E. coli within the water column during storm events. Unattached E. coli dominated total E. coli concentration across both storm and baseflow events (i.e. at least 75% of total E. coli concentrations). The water quality standard during baseflow conditions was satisfactory while storm events consistently exceeded the standard. Total, settleable and free-living E. coli concentrations ranged from 7 × l02 to 22 × l03 CFU 100 mL-1 , 4 × l01 to 66 × l02 CFU 100 mL-1, and 5× l02 to 15 × l03 CFU 100 mL-1, respectively. The high levels and exceedance rate of free-living E. coli mean that sedimentation of the settleable fraction of E. coli would not be adequate to reduce bacteria to within the microbiological water quality standard. Many instream water quality models assume that the total bacteria concentration within the water column can be predicted by modeling bacteria as free-living; this assumption was tested by assessing the statistical difference between total and unattached bacteria. The findings revealed that free-living E. coli concentrations were equal to total E. coli concentrations 5 out of 8 times (63%), meaning that over one third of events would not be accurately modelled with only unattached bacteria. Thus, increased understanding of attachment and incorporation of bacteria partitioning between attached and unattached (free-living) into water quality models could improve model performance and predictive capabilities. The correlation analysis revealed a weak (p \u3e 0.05) relationship between flow, temperature, turbidity, shear stress and E. coli fractions. Regression models developed to predict total E. coli and those attached to different particle fractions during storm events performed poorly (R2 = 0.09-0.22). The results presented in this study will further the understanding of fate and transport of bacteria within water as well as provide information that can be incorporated into the development of microbial water quality models

From Land to Lake: Contrasting Microbial Processes Across a Great Lakes Gradient of Organic Carbon and Inorganic Nutrient Inventories

Freshwater ecosystems have strong linkages to the terrestrial landscapes that surround them, and contributions of carbon and inorganic nutrients from soil, vegetation and anthropogenic sources subsidize autochthonous water body productivity to varying degrees. Abundant freshwater phytoplankton and bacterioplankton are key to linking the planet\u27s geosphere and atmosphere to the food webs in the hydrosphere through their growth and respiration. Rich resources that move through land margin waterways make them active sites for cycling organic carbon and thus important, but understudied, contributors to global climate. During 2010-2011, we examined seasonal changes in carbon and nutrient inventories, plankton community composition and metabolism along a land-to-lake gradient in a major West Michigan watershed at four interconnected habitats ranging from a small creek to offshore Lake Michigan. In all seasons Lake Michigan had significantly lower concentrations of CDOM and DOC than any of the other sites. Lake levels of NO3 were not significantly lower than tributaries other than Cedar Creek, and SRP was not measurable in any of the sites other than Cedar Creek. Bacterial production as % of GPP revealed a distinct land-to-lake gradient from an average of 448% in Cedar creek to 5% in Lake Michigan. Microbial activity in Cedar Creek (bacterial production 3- 93 μg C/L/d, and plankton respiration 9-193 μg C/L/d) was generally higher than all other sites. Muskegon Lake dominated GPP among the sites reaching a peak of \u3e1000 μg carbon/L/d during a large fall Microcystis bloom. Offshore Lake Michigan had less variation in GPP and R than the other sites with GPP:R ratio close to 1 in all seasons but spring. Metabolism appears to be substantially subsidized by terrigenous inputs in the creek/river ecosystem with heterotrophy dominant over autotrophy. Autotrophy was maximized in the coastal/estuary, whereas both autotrophy and heterotrophy were minimal but in near-balance in offshore waters receiving little subsidy from the land. Along this land-to-lake gradient terrestrial subsidies combined with a host of other factors making conditions “just right” for a hot-spot to emerge, highlighting Muskegon Lake estuary a “Goldilocks Zone” of net biological productivity

Hidden sources and sinks of Fe(II) in the sedimentary biogeochemical iron cycle - The role of light

In dieser Dissertation werden bisher verborgene Quellen und Senken von Eisen(II) im sedimentären Eisenkreislauf untersucht und dabei insbesondere auf die Rolle des Lichts eingegangen. Durch die lichtinduzierte Reduktion von gelösten Eisen(III)-Organik-Komplexen im Sedimentporenwasser wird Eisen(II) gebildet, das von Eisen(II)-oxidierenden Bakterien als Substratquelle verwendet kann. Auch durch physikalische Umwäzungen des Sediments wird Eisen(II) freigesetzt. Im Hinblick auf die neu entdeckten Quellen und Senken von Eisen(II) im Sediment, muss die bisherige Vorstellung des sedimentären Eisenkreislaufs überdacht werden

Water quality control in coastal aquaculture system: a Tuscany fish farm as a case study.

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Coastal upwelling in the Rias Bajas, NW Spain: Contrasting the benthic regimes of the Rias de Arosa and de Muros

Nutrient-rich North Atlantic water upwells off the NW coast of Spain and intermittently intrudes into the rias, coastal embayments, by displacement during periods of offshore winds. High primary production associated with the upwelling supports an intensive raft culture of the edible mussel, Mytilus edulis. This culture is most intensive (ca. 2000 rafts) in the Ria de Arosa, and results in one of the highest protein yields per unit area on earth...