Liz Morris

Multiple sources of nutrients add to the complexities of predicting marine benthic community responses to enrichment

Understanding biological responses to nutrient enrichment under different environmental conditions is integral for the effective management of eutrophication in coastal environments. However, current conceptual models of nutrient enrichment are limited as they are based on studies that only consider a single source of nutrients, when in reality it is more likely that enrichment is a result of multiple sources. Here, we test the hypothesis that biological responses to nutrient enrichment in intertidal mudflat assemblages depend on the source by comparing enrichment from a controlled release fertilizer with that from decomposing macroalgae. Sediment at two sites in Port Phillip Bay, Victoria, were dosed with the different nutrient sources and monitored through time. After six weeks, the macroalgae-enriched plots had significantly higher abundances and biomass of some taxa of deposit-feeding polychaetes. In the fertilizer-enriched plots, the porewater nutrients increased but there was no detectable change in abundances or biomass of infauna, suggesting that the nutrients did not assimilate into the foodweb. The rate of assimilation of anthropogenic nutrients potentially occurs over longer time scales compared with the rapid assimilation and biological responses to decomposing macroalgae. Responses to the different nutrient sources provide new insights into the complexity of nutrient enrichment models that are applied to the management of aquatic ecosystems worldwide.

Testing the effects of nutrient additions on mudflat macroinfaunal assemblages in the presence and absence of shorebird predators

An issue that is of increasing concern worldwide relates to the possibility that areas subject to conservation agreements, owing to the resident and migratory bird populations they support, will be adversely affected by attempts to reduce organic inputs into nearshore environments. In the present study, we investigated the effects of nutrient additions and shorebird exclusion on the infaunal assemblages of an intertidal mudflat. Where responses to nutrient additions were observed they only occurred in the high-dose treatments, indicating that a high nutrient loading is required before infaunal responses are initiated at this site. There was no evidence to support the idea that nutrient additions would only stimulate macroinfaunal assemblages where shorebird foraging was reduced. Instead, nutrient additions were detectable separately from any effects of shorebird predation and, contrary to expectations, appeared to be of more importance than shorebird predation in this environment. There was also no evidence to suggest that shorebird predation has a strong interaction with the infaunal prey assemblage and, although further studies will be needed to support this statement, it is possible that moderate changes in nutrient status will not impact on the shorebird populations at this site.

Effects of nutrient additions on intertidal seagrass (Zostera muelleri) habitat in Western Port, Victoria, Australia

Loss of seagrass habitat in many parts of the world has been attributed to increases in nutrient loading to nearshore areas. The role of excess epiphyte, macroalgal or phytoplankton growth in shading of seagrass leaves and negatively affecting seagrass health is generally agreed to be a prevalent mechanism in seagrass decline worldwide. In the present study nutrient addition experiments were undertaken at three sites in Western Port, Victoria. Nutrients were added to the water column using the controlled release fertiliser Osmocote™ in late summer 2005. The experiments ran for one month at two of the sites (Blind Bight and Hastings) and at the third site (Crib Point) the experiment ran for three months. Control and nutrient addition plots were monitored for concentrations of inorganic nutrients, number of seagrass leaves, seagrass, epiphyte and loose algal biomass and invertebrate faunal assemblages. Nutrient additions had increased ash free dry weight of seagrass leaves and loose algae at two of the three sites studied. There was also an increase in gammarid amphipod densities at the Crib Point site. We consider that Western Port seagrass habitat is sensitive to increased loads of nutrients within the water column with the Blind Bight region most at risk.

Municipal wastewater effluent licensing: A global perspective and recommendations for best practice

Advances in wastewater treatment have greatly improved the quality of municipal wastewater effluents in many parts of the world, but despite this, treated wastewaters can still pose a risk to the environment. Licensing plays a crucial role in the regulation of municipal wastewater effluents by setting standards or limits designed to protect the economic, environmental and societal values of waterbodies. Traditionally these standards have focused on physical and chemical water quality parameters within the discharge itself, however these approaches do not adequately account for emerging contaminants, potential effects of chemical mixtures, or variations in the sensitivity and resilience of receiving environments. In this review we focus on a number of industrialised countries and their approach to licensing. We consider how we can ensure licensing is effective, particularly when considering the rapid changes in our understanding of the impacts of discharges, the technical advances in our ability to detect chemicals at low concentrations and the progress in wastewater treatment technology. In order to meet the challenges required to protect the values of our waterways, licensing of effluents will need to ensure that there is no disconnect between the core values to be protected and the monitoring system designed to scrutinise performance of the WWTP. In many cases this may mean an expansion in the monitoring approaches used for both the effluent itself and the receiving waterbody.

Vertical migration of infaunal invertebrates in response to dosing with secondary treated sewage effluent: a microcosm experiment

Short-term experiments testing behaviouralresponses to a toxicant are liable to besensitive indicators of the potential effectsof a pollutant and allow predictions abouthabitat preferences of organisms in the field.We have undertaken short-term microcosmexperiments with intact assemblages ofintertidal invertebrate infauna andinvestigated the responses of these assemblagesto dosing with a secondary treated sewageeffluent. Infaunal assemblages were taken fromsites that differed in their proximity toeffluent discharges and in recent exposure todisturbances. We observed a range of responsesto different dose treatments during theseexperiments with differential migration intothe water column by the corophiid amphipodCorophium insidiosum and changes in depthdistribution within the sediment by severalannelid taxa. We discuss these results withrespect to potential field responses followingexposure to treated sewage effluents andbiological monitoring programs.

Can moderate increases in nutrient loads cause ecological effects in rivers already impacted by nutrients

Predicting the ecological responses to moderate nutrient additions in systems that are already impacted to some degree by nutrient inputs is an important management task. In this study, we have investigated the responses of phytoplankton and periphyton and macroinvertebrate assemblages to experimental nutrient additions using both laboratory and field bioassays. We looked at six lower river reach/upper estuary sites in two flow seasons (high flow and low flow) in the Glenelg Hopkins Region of Victoria, Australia. Despite the considerable differences in the physical and chemical environments between sites in this study, the results suggest that within the lower river reaches of the Glenelg Hopkins region all systems are likely to have the potential for nutrient limitation. Also, addition of moderate and realistic loads of nutrients are likely to cause ecological changes, including a reduction in diversity H′, increases or decreases in algal growth and increases in densities of consumers. Incorporating this information into land use suitability options for the area will provide mangers an insight into potential outcomes relating to river health in the region.

Structural and functional measures of marine microbial communities: An experiment to assess implications for oil spill management

Microbial communities are ecologically important in aquatic environments and impacts on microbes have the potential to affect a number of functional processes. We have amended seawater with a crude oil and assessed changes in species composition as well as a measure of functional diversity (the ability of the community to utilise different carbon sources) and the community level metabolic signature. We found that there was a degree of functional redundancy in the community we tested. Oiled assemblages became less diverse and more dominated by specialist hydrocarbon degraders, carbon source utilisation increased initially but there was no change in metabolic signature in this small scale laboratory experiment. This study supports the decision framework around management of oil spills. This package of methods has the potential to be used in the testing and selection of new dispersants for use in oil spill response.

Monitoring for a specific management objective: protection of shorebird foraging habitat adjacent to a waste water treatment plant

Intertidal invertebrates are often used in environmental monitoring programs as they are good indicators of water quality and an important food source for many species of fish and birds. We present data from a monitoring program where the primary aim is to report on the condition of the potential invertebrate prey abundance, biomass and diversity for migrating shorebirds on mudflats adjacent to a waste water treatment plant in a Ramsar listed wetland in Victoria, Australia. A key threat to the foraging habitat at this site has been assessed as a reduction in potential prey items as a result of the changes to the waste water treatment processes. We use control charts, which summarise data from intertidal mudflats across the whole shoreline of the adjacent waste water treatment plant, to elicit a management response when trigger levels are reached. We then examine data from replicate discharge and control sites to determine the most appropriate management response. The monitoring program sits within an adaptive management framework where management decisions are reviewed and the data is examined at different scales to evaluate and modify our models of the likely outcomes of management actions. This study provides a demonstration of the process undertaken in a year when trigger levels were reached and a management decision was required. This highlights the importance of monitoring data from a range of scales in reducing uncertainty and improving decision making in complex systems.