Do phytoplankton nutrient ratios reflect patterns of water column nutrient ratios? A numerical stoichiometric analysis of Lake Kinneret

AbstractThe N:P stoichiometry of a water body is one of the most commonly used indicators of its nutrient status. However, in a dynamic aquatic ecosystem the N:P stoichiometry of phytoplankton is highly variable depending on a range of factors that influence their growth. In this study, a 1D hydrodynamic-ecological model was used to examine how the internal nutrient ratios of phytoplankton relate to nutrient ratios within the water column in Lake Kinneret, Israel. We identified that seasonal patterns of the simulated dissolved inorganic N to total P (DIN:TP) ratios in the water column were a useful indicator of the N:P stoichiometry of the combined phytoplankton community. However, the internal N:P patterns of individual phytoplankton groups did not necessarily relate to DIN:TP patterns

Marked deleterious changes in the condition, growth and maturity schedules of Acanthopagrus butcheri (Sparidae) in an estuary reflect environmental degradation

As Acanthopagrus butcheri typically completes its life within its natal estuary and possesses plastic biological characteristics, it provides an excellent model for exploring the ways and extent to which a fish species can respond to environmental changes over time. The environment of the Swan River Estuary in south-western Australia has deteriorated markedly during the last two decades, reflecting the effects of increasing eutrophication and hypoxia in the upper regions, where A. butcheri spends most of the year and spawns. In this study, the biological characteristics of A. butcheri in 2007-11 were determined and compared with those in 1993-95. Between these two periods, the condition factor for females and males of A. butcheri across their length ranges declined by 6 and 5%, respectively, and the parameters k and L∞ in the von Bertalanffy growth curves of both sexes underwent marked reductions. The predicted lengths of females and males at all ages ≥1 year were less in 2007-11 than in 1993-95 and by over 30% less at ages 3 and 6. The ogives relating maturity to length and age typically differed between 1993-94 and 2007-10. The L50s of 156 mm for females and 155 mm for males in 2007-10 were less than the corresponding values of 174 and 172 mm in 1993-94, whereas the A50s of 2.5 years for both females and males in 2007-10 were greater than the corresponding values of 1.9 and 2.0 years in 1993-94. The above trends in condition, growth and maturity parameters between periods are consistent with hypotheses regarding the effects of increasing hypoxia on A. butcheri in offshore, deeper waters. However, as the density of A. butcheri declined in offshore, deeper waters and increased markedly in nearshore, shallow waters, density-dependent effects in the latter waters, although better oxygenated, also probably contributed to the overall reductions in growth and thus to the changes in the lengths and ages at maturity

Predicting the resilience and recovery of aquatic systems: A framework for model evolution within environmental observatories

Maintaining the health of aquatic systems is an essential component of sustainable catchment management, however, degradation of water quality and aquatic habitat continues to challenge scientists and policy-makers. To support management and restoration efforts aquatic system models are required that are able to capture the often complex trajectories that these systems display in response to multiple stressors. This paper explores the abilities and limitations of current model approaches in meeting this challenge, and outlines a strategy based on integration of flexible model libraries and data from observation networks, within a learning framework, as a means to improve the accuracy and scope of model predictions. The framework is comprised of a data assimilation component that utilizes diverse data streams from sensor networks, and a second component whereby model structural evolution can occur once the model is assessed against theoretically relevant metrics of system function. Given the scale and transdisciplinary nature of the prediction challenge, network science initiatives are identified as a means to develop and integrate diverse model libraries and workflows, and to obtain consensus on diagnostic approaches to model assessment that can guide model adaptation. We outline how such a framework can help us explore the theory of how aquatic systems respond to change by bridging bottom-up and top-down lines of enquiry, and, in doing so, also advance the role of prediction in aquatic ecosystem management

Climate change overtakes coastal engineering as the dominant driver of hydrological change in a large shallow lagoon

Ecosystems in shallow micro-tidal lagoons are particularly sensitive to hydrologic changes. Lagoons are complex transitional ecosystems between land and sea, and the signals of direct human disturbance can be confounded by variability of the climate system, but from an effective estuary management perspective, the effects of climate versus direct human engineering interventions need to be identified separately. This study developed a 3D finite-volume hydrodynamic model to assess changes in hydrodynamics of the Peel–Harvey Estuary, a large shallow lagoon with restricted connection with ocean; this was done by considering how attributes such as water retention time, salinity and stratification have responded to a range of factors, focusing on the drying climate trend and the opening of a large artificial channel over the period from 1970 to 2016, and how they will evolve under current climate projections. The results show that the introduction of the artificial channel has fundamentally modified the flushing and mixing within the lagoon, and the drying climate has changed the hydrology by comparable magnitudes to that of the opening of the artificial channel. The results also highlight the complexity of their interacting impacts. Firstly, the artificial channel successfully improved the estuary flushing by reducing average water ages by 20–110 d, while in contrast the reduced precipitation and catchment inflow had a gradual opposite effect on the water ages; during the wet season this has almost counteracted the reduction brought about by the channel. Secondly, the drying climate caused an increase in the salinity of the lagoon by 10–30 PSU (Practical Salinity Unit); whilst the artificial channel increased the salinity during the wet season, it has reduced the likelihood of hypersalinity (>40 PSU) during the dry season in some areas. The opening of the artificial channel was also shown to increase the seawater fluxes and salinity stratification, while the drying climate acted to reduce the salinity stratification in the main body of the estuary. The impacts also varied spatially in this large lagoon. The southern estuary, which has the least connection with the ocean through the natural channel, is the most sensitive to climate change and the opening of the artificial channel. The projected future drying climate is shown to slightly increase the retention time and salinity in the lagoon and increase the hypersalinity risk in the rivers. The significance of these changes for nutrient retention and estuary ecology are discussed, highlighting the importance of these factors when setting up monitoring programmes, environmental flow strategies and nutrient load reduction targets

Growth, condition, and maturity schedules of an estuarine fish species change in estuaries following increased hypoxia due to climate change

Understanding challenges posed by climate change to estuaries and their faunas remains a high priority for managing these systems and their communities. Freshwater discharge into a range of estuary types in south‐western Australia between 1990 and 2015 is shown to be related to rainfall. This largely accounts for decreases in discharge in this microtidal region being more pronounced on the west coast than south coast, where rainfall decline was less. Results of an oxygen‐balance model imply that, as demonstrated by empirical data for the Swan River Estuary, declines in discharge into a range of estuary types would be accompanied by increases in the extent of hypoxia. In 2013–15, growth and body condition of the teleost Acanthopagrus butcheri varied markedly among three permanently open, one intermittently‐open, one seasonally‐closed and one normally‐closed estuary, with average time taken by females to reach the minimum legal length (MLL) of 250 mm ranging from 3.6 to 17.7 years. It is proposed that, in a given restricted period, these inter‐estuary variations in biological characteristics are related more to differences in factors, such as food resources and density, than to temperature and salinity. The biological characteristics of A. butcheri in the four estuaries, for which there are historical data, changed markedly between 1993–96 and 2013–15. Growth of both sexes, and also body condition in all but the normally‐closed estuary, declined, with females taking between 1.7 and 2.9 times longer to attain the MLL. Irrespective of period, body condition, and growth are positively related. Age at maturity typically increased between periods, but length at maturity declined only in the estuary in which growth was greatest. The plasticity of the biological characteristics of A. butcheri, allied with confinement to its natal estuary and ability to tolerate a wide range of environmental conditions, makes this sparid and comparable species excellent subjects for assessing estuarine “health.

Serving many at once: How a database approach can create unity in dynamical ecosystem modelling

Simulation modelling in ecology is a field that is becoming increasingly compartmentalized. Here we propose a Database Approach To Modelling (DATM) to create unity in dynamical ecosystem modelling with differential equations. In this approach the storage of ecological knowledge is independent of the language and platform in which the model will be run. To create an instance of the model, the information in the database is translated and augmented with the language and platform specifics. This process is automated so that a new instance can be created each time the database is updated. We describe the approach using the simple Lotka–Volterra model and the complex ecosystem model for shallow lakes PCLake, which we automatically implement in the frameworks OSIRIS, GRIND for MATLAB, ACSL, R, DUFLOW and DELWAQ. A clear advantage of working in a database is the overview it provides. The simplicity of the approach only adds to its elegance.

"Panta Rhei – Everything Flows”::Change in hydrology and society – The IAHS Scientific Decade 2013-2022

The new Scientific Decade 2013-2022 of IAHS, entitled Panta RheiEverything Flows, is dedicated to research activities on change in hydrology and society. The purpose of Panta Rhei is to reach an improved interpretation of the processes governing the water cycle by focusing on their changing dynamics in connection with rapidly changing human systems. The practical aim is to improve our capability to make predictions of water resources dynamics to support sustainable societal development in a changing environment. The concept implies a focus on hydrological systems as a changing interface between environment and society, whose dynamics are essential to determine water security, human safety and development, and to set priorities for environmental management. The Scientific Decade 2013-2022 will devise innovative theoretical blueprints for the representation of processes including change and will focus on advanced monitoring and data analysis techniques. Interdisciplinarity will be sought by increased efforts to connect with the socio-economic sciences and geosciences in general. This paper presents a summary of the Science Plan of Panta Rhei, its targets, research questions and expected outcomes