Review of best management practices for aquatic vegetation control in stormwater ponds, wetlands, and lakes

Auckland Council (AC) is responsible for the development and operation of a stormwater network across the region to avert risks to citizens and the environment. Within this stormwater network, aquatic vegetation (including plants, unicellular and filamentous algae) can have both a positive and negative role in stormwater management and water quality treatment. The situations where management is needed to control aquatic vegetation are not always clear, and an inability to identify effective, feasible and economical control options may constrain management initiatives. AC (Infrastructure and Technical Services, Stormwater) commissioned this technical report to provide information for decision- making on aquatic vegetation management with in stormwater systems that are likely to experience vegetation-related issues. Information was collated from a comprehensive literature review, augmented by knowledge held by the authors. This review identified a wide range of management practices that could be potentially employed. It also demonstrated complexities and uncertainties relating to these options that makes the identification of a best management practice difficult. Hence, the focus of this report was to enable users to screen for potential options, and use reference material provided on each option to confirm the best practice to employ for each situation. The report identifies factors to define whether there is an aquatic vegetation problem (Section 3.0), and emphasises the need for agreed management goals for control (e.g. reduction, mitigation, containment, eradication). Resources to screen which management option(s) to employ are provided (Section 4.0), relating to the target aquatic vegetation, likely applicability of options to the system being managed, indicative cost, and ease of implementation. Initial screening allows users to shortlist potential control options for further reference (Section 5.0). Thirty-five control options are described (Section 5.0) in sufficient detail to consider applicability to individual sites and species. These options are grouped under categories of biological, chemical or physical control. Biological control options involve the use of organisms to predate, infect or control vegetation growth (e.g. classical biological control) or manipulate conditions to control algal growth (e.g. pest fish removal, microbial products). Chemical control options involve the use of pesticides and chemicals (e.g. glyphosate, diquat), or the use of flocculants and nutrient inactivation products that are used to reduce nutrient loading, thereby decreasing algal growth. Physical control options involve removing vegetation or algal biomass (e.g. mechanical or manual harvesting), or setting up barriers to their growth (e.g. shading, bottom lining, sediment capping). Preventative management options are usually the most cost effective, and these are also briefly described (Section 6.0). For example, the use of hygiene or quarantine protocols can reduce weed introductions or spread. Catchment- based practices to reduce sediment and nutrient sources to stormwater are likely to assist in the avoidance of algal and possibly aquatic plant problems. Nutrient removal may be a co-benefit where harvesting of submerged weed biomass is undertaken in stormwater systems. It should also be considered that removal of substantial amounts of submerged vegetation may result in a sudden and difficult-to-reverse s witch to a turbid, phytoplankton dominated state. Another possible solution is the conversion of systems that experience aquatic vegetation issues, to systems that are less likely to experience issues. The focus of this report is on systems that receive significant stormwater inputs, i.e. constructed bodies, including ponds, amenity lakes, wetlands, and highly-modified receiving bodies. However, some information will have application to other natural water bodies

Qualitative models to predict impacts of human interventions in a wetland ecosystem

The large shallow wetlands that dominate much of the South American continent are rich in biodiversity and complexity. Many of these undamaged ecosystems are presently being examined for their potential economic utility, putting pressure on local authorities and the conservation community to find ways of correctly utilising the available natural resources without compromising the ecosystem functioning and overall integrity. Contrary to many northern hemisphere ecosystems, there have been little long term ecological studies of these systems, leading to a lack of quantitative data on which to construct ecological or resource use models. As a result, decision makers, even well meaning ones, have difficulty in determining if particular economic activities can potentially cause significant damage to the ecosystem and how one should go about monitoring the impacts of such activities. While the direct impact of many activities is often known, the secondary indirect impacts are usually less clear and can depend on local ecological conditions. <br><br> The use of qualitative models is a helpful tool to highlight potential feedback mechanisms and secondary effects of management action on ecosystem integrity. The harvesting of a single, apparently abundant, species can have indirect secondary effects on key trophic and abiotic compartments. In this paper, loop model analysis is used to qualitatively examine secondary effects of potential economic activities in a large wetland area in northeast Argentina, the Esteros del Ibera. Based on interaction with local actors together with observed ecological information, loop models were constructed to reflect relationships between biotic and abiotic compartments. A series of analyses were made to study the effect of different economic scenarios on key ecosystem compartments. Important impacts on key biotic compartments (phytoplankton, zooplankton, ichthyofauna, aquatic macrophytes) and on the abiotic environment (nutrients and sediment resuspension) were observed through model analysis. These models results do not indicate a definite relationship between activity and a possible impact, but a potential impact that can be further studied and modelled. Likewise, the model is not intended to be an end in itself, but as a tool to help focus further ecological study, monitoring and modelling. In the real world of wetland management, it is not always possible to conduct extensive (and expensive) analysis of all the principal ecological compartments. In the same manner, the construction of larger and more complex models for resource management usually needs to be focused to those areas most likely to effect resource quality or ecosystem functioning. In this light, the development of qualitative models was considered as a first step to help researchers and decision makers focus their efforts (and economic resources) in an intensive ecological sampling programme and the construction of predictive models

Global relationship between phytoplankton diversity and productivity in the ocean

The shape of the productivity–diversity relationship (PDR) for marine phytoplankton has been suggested to be unimodal, that is, diversity peaking at intermediate levels of productivity. However, there are few observations and there has been little attempt to understand the mechanisms that would lead to such a shape for planktonic organisms. Here we use a marine ecosystem model together with the community assembly theory to explain the shape of the unimodal PDR we obtain at the global scale. The positive slope from low to intermediate productivity is due to grazer control with selective feeding, which leads to the predator-mediated coexistence of prey. The negative slope at high productivity is due to seasonal blooms of opportunist species that occur before they are regulated by grazers. The negative side is only unveiled when the temporal scale of the observation captures the transient dynamics, which are especially relevant at highly seasonal latitudes. Thus selective predation explains the positive side while transient competitive exclusion explains the negative side of the unimodal PDR curve. The phytoplankton community composition of the positive and negative sides is mostly dominated by slow-growing nutrient specialists and fast-growing nutrient opportunist species, respectively.Marie Curie International Outgoing Fellowship (FP7)Gordon and Betty Moore FoundationSpain. Ministerio de Economía y Competitividad (Ramon y Cajal Contracts

Ecosystem exploitation, sustainability and biodiversity: Are they compatible?

This articles offers a basis for describing sustainability and then seeks to place this concept on an energetic basis by reference to recent advances in the understanding of patterns and processes in (mainly pelagic) fresh waters. Finally, by relating these to terrestrial ecosystems, it is shown how their sustainability may be attained through encouraging healthy fresh waters. Features of population succession are taken from observations on phytoplankton ecology

Mechanistic origins of variability in phytoplankton dynamics. Part II: analysis of mesocosm blooms under climate change scenarios

Driving factors of phytoplankton spring blooms have been discussed since long, but rarely analyzed quantitatively. Here, we use a mechanistic size-based ecosystem model to reconstruct observations made during the Kiel mesocosm experiments (2005–2006). The model accurately hindcasts highly variable bloom developments including community shifts in cell size. Under low light, phytoplankton dynamics was mostly controlled by selective mesozooplankton grazing. Selective grazing also explains initial dominance of large diatoms under high light conditions. All blooms were mainly terminated by aggregation and sedimentation. Allometries in nutrient uptake capabilities led to a delayed, post-bloom dominance of small species. In general, biomass and trait dynamics revealed many mutual dependencies, while growth factors decoupled from the respective selective forces. A size shift induced by one factor often changed the growth dependency on other factors. Within climate change scenarios, these indirect effects produced large sensitivities of ecosystem fluxes to the size distribution of winter phytoplankton. These sensitivities exceeded those found for changes in vertical mixing, whereas temperature changes only had minimal impacts

The vulnerability of ecosystem trophic dynamics to anthropogenically induced environmental change: A comparative approach

The chapter, "The vulnerability of ecosystem trophic dynamics to anthropogenically induced environmental change: A comparative approach" was written by the listed authors including Jessica L. Clasen (Douglas College Faculty). The Ecological Dissertations in the Aquatic Sciences (Eco-DAS) symposia bring together 35-40 recent PhD recipients for one week in alternate years. Eco-DAS VIII was held in 2008. Eco-DAS is sponsored by the Center for Microbial Oceanography: Research and Education (C-MORE), the University of Hawai`i School of Ocean and Earth Science and Technology (SOEST) and its Department of Oceanography, and the Association for the Sciences of Limnology and Oceanography (ASLO). The Proceedings of Eco-DAS VIII includes nine chapters published in open access. We employed a comparative approach to review the vulnerability of the trophic interactions within aquatic systems to global threats associated with anthropogenic activities. The goal of this chapter was to identify and characterize mechanisms by which human-mediated environmental threats may modulate trophic dynamics across aquatic ecosystems. Trophic dynamics include some of the most obvious and pervasive factors influencing ecosystems and were used as a metric because of their importance and commonality across all aquatic environments. Our use of trophic dynamics proved to be insightful, illustrating that the flow of energy through aquatic food webs will be (or already has been) altered by invasive species, land-use change, nutrient loading, exposure to ultraviolet radiation, overharvesting, acidification, and increasing global temperatures. The response of trophic dynamics to these threats was often similar across oceans, estuaries, lakes, and rivers. This similarity proved to be interesting given the differences in both the level of concern expressed by scientists and the predicted variability in environment-specific responses. As the trophic interactions of an ecosystem are at the root of its function and structure, examining trophic dynamics could be an informative method for evaluating the response of aquatic environments to global threats. If future analyses validate the use of trophic dynamics as a metric, it is our hope that trophic dynamics can be used by scientists and politicians to mitigate the effects of human actions.book chapterpublishe

End-to-end models of marine ecosystems: exploring the consequences of climate change and fishing using a minimal framework

Marine ecosystems are vital to human society: as a source of food, for economic growth and for their potential to mitigate climate change. With marine ecosystems threatened by climate change and overfishing, there is a need for sustainable fisheries management, which has been the basis for an ecosystem-based approach to management. This has led to considerable interest in end-to-end ecosystem models, where the physical effects of the environment and the population dynamics of all marine organisms are coupled together into one framework. In this thesis, I studied an end-to-end model which coupled together a box-component model representing phytoplankton and zooplankton, with a size-structured fish community model. I investigated the potential artefacts in model results, caused by numerical methods or by model architecture. I found that care needs to be taken with the choice of numerical method used to simulate size-structured models, as the choice of numerical resolution can yield numerically stable results but can also affect large-scale behaviours of the system, such as the slope and mathematical stability of the size-spectra solutions. With regards to model architecture, coupling together two submodels which differ in structure and resolution can lead to large-scale behaviours of the system which appear plausible and consistent with empirical data, but which impose serious discrepancies in the underlying life-histories of the fish. By distinguishing model artefacts from ecosystem-effects, the interactions and feedbacks between the higher and lower trophic level organisms can be investigated. I studied the potential impact of climate change upon the marine ecosystem, and in particular, upon the seasonal dynamics of phytoplankton. I found that under a warming climate, the spring phytoplankton bloom occurs earlier and for a longer duration, and the model predicts the loss of the autumn phytoplankton bloom. These changes were not solely due to the direct effect of temperature, but also due to the indirect effect of the interactions of the fish population with zooplankton. The effect of fishing upon the marine ecosystem was also explored with this end-to-end model, with two potential fishing strategies applied to the system. Regardless of the choice of fishing strategy, intensive exploitation of fish stocks can lead to a significant shift in the dynamics of phytoplankton. The phytoplankton's dynamics change from stable annual patterns to unpredictable periodic behaviours. This thesis has developed an end-to-end model which uses a minimal framework to study the interactions of organisms at different trophic levels, and highlights the importance of these interactions and the associated feedbacks under different scenarios. It combines important theoretical insights into the consequences of model architecture and model-derived artefacts upon ecosystem-scale behaviours, at the same time as highlighting the potential for end-to-end models as a practical and flexible management tool

Improving productivity in tropical lakes and reservoirs

Freshwater aquaculture, Inland fisheries

On the occurrence and ecological features of deep chlorophyll maxima (DCM) in Spanish stratified lakes

Deep chlorophyll maxima (DCM) are absolute maxima of Chlorophyll-a concentration among the vertical profile that can be found in deep layers of stratified lakes. In this manuscript I review the principal mechanisms that have been argued to explain the formation of DCM, which include, among others, in situ growth of metalimnetic phototrophs, differential impact of grazing between the different lake strata, and passive sedimentation to the layers where water density and cell density are equalized. The occurrence of DCM in Spanish lakes, as well as the main ecology characteristics of the oxygenic phototrophs that form DCM in these lakes is also reported. Cyanobacteria, either filamentous or unicellular, and cryptophytes, are the main components of most DCM found in the reported Spanish lakes, although diatoms, chrysophytes, dinoflagellates, and chlorophytes also contribute to these chlorophyll maxima. These organisms cope with strong physical and chemical gradients, among which those of water density, light and inorganic nutrient availability, and sulphide concentrations appear to be the most determinant factors influencing planktonic community structure.Los máximos profundos de clorofila (DCM) son máximos absolutos de concentración de clorofila-a que pueden encontrarse en capas profundas de los lagos estratificados. En este manuscrito se revisan los principales mecanismos que se han propuesto para explicar la formación de los DCM, entre los que se cuentan, al margen de otros secundarios, el crecimiento in situ de los microorganismos fotótrofos metalimnéticos, el impacto diferencial del herbivorismo en diferentes estratos del lago, y la sedimentación pasiva hasta las capas en las que se iguala la densidad del agua con la densidad celular. También se revisa la existencia de DCM descritos en lagos españoles, así como las principales características ecológicas de los microorganismos fotótrofos oxigénicos que los forman. Tanto las cianobacterias, sean filamentosas o unicelulares, como las criptófitas, son los principales componentes de los DCM encontrados en los lagos españoles, aunque también contribuyen a ellos otras algas como las diatomeas, crisófitas, dinoflagelados y clorófitas planctónicas. Estos microorganismos se enfrentan a acusados gradientes físico-químicos, entre los cuales la densidad del agua, la disponibilidad de luz y de nutrientes inorgánicos, y la concentración de sulfhídrico, aparecen como los factores más determinantes para la estructuración de la comunidad planctónica