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

Protecting key pedagogical features in the pivot to online hydrology learning at UWA

The COVID-19 pandemic necessitated a rapid transition to online hydrology instruction at The University of Western Australia (UWA). Key requirements of this transition were to create supportive, inclusive online educational settings, and to maximize student engagement.  Here, we draw on experiences in four hydrology units to illustrate how we used a holistic approach spanning course structure, content delivery, active learning experiences and authentic assessment to protect these key pedagogical features during the transition to online learning.  Learning content that was streamlined, chunked and recorded facilitated effective student-paced learning. Structuring material to support a growth-mindset and providing varied active learning opportunities was also beneficial for establishing a constructive learning culture. Field and laboratory experiences were replaced with digital analogues and “virtual” site visits. While these have limitations for experiential learning, they are also able to span a broader range of conditions than can be physically visited or simulated in the lab. The outcomes in these units as measured by student engagement, enrolment and self-reported satisfaction were positive, with student evaluations remaining similar to those of pre-pandemic levels.  Previous interest in running flipped classrooms and familiarity with technology among instructors and students were helpful in enabling the transition.

A prototype framework for models of socio-hydrology: identification of key feedback loops and parameterisation approach

It is increasingly acknowledged that, in order to sustainably manage global freshwater resources, it is critical that we better understand the nature of human–hydrology interactions at the broader catchment system scale. Yet to date, a generic conceptual framework for building models of catchment systems that include adequate representation of socioeconomic systems – and the dynamic feedbacks between human and natural systems – has remained elusive. In an attempt to work towards such a model, this paper outlines a generic framework for models of socio-hydrology applicable to agricultural catchments, made up of six key components that combine to form the coupled system dynamics: namely, catchment hydrology, population, economics, environment, socioeconomic sensitivity and collective response. The conceptual framework posits two novel constructs: (i) a composite socioeconomic driving variable, termed the Community Sensitivity state variable, which seeks to capture the perceived level of threat to a community's quality of life, and acts as a key link tying together one of the fundamental feedback loops of the coupled system, and (ii) a Behavioural Response variable as the observable feedback mechanism, which reflects land and water management decisions relevant to the hydrological context. The framework makes a further contribution through the introduction of three macro-scale parameters that enable it to normalise for differences in climate, socioeconomic and political gradients across study sites. In this way, the framework provides for both macro-scale contextual parameters, which allow for comparative studies to be undertaken, and catchment-specific conditions, by way of tailored "closure relationships", in order to ensure that site-specific and application-specific contexts of socio-hydrologic problems can be accommodated. To demonstrate how such a framework would be applied, two socio-hydrological case studies, taken from the Australian experience, are presented and the parameterisation approach that would be taken in each case is discussed. Preliminary findings in the case studies lend support to the conceptual theories outlined in the framework. It is envisioned that the application of this framework across study sites and gradients will aid in developing our understanding of the fundamental interactions and feedbacks in such complex human–hydrology systems, and allow hydrologists to improve social–ecological systems modelling through better representation of human feedbacks on hydrological processes

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

Adaptation tipping points of awetland under a drying climate

Wetlands experience considerable alteration to their hydrology, which typically contributes to a decline in their overall ecological integrity. Wetland management strategies aim to repair wetland hydrology and attenuate wetland loss that is associated with climate change. However, decision makers often lack the data needed to support complex social environmental systems models, making it difficult to assess the effectiveness of current or past practices. Adaptation Tipping Points (ATPs) is a policy-oriented method that can be useful in these situations. Here, a modified ATP framework is presented to assess the suitability of ecosystem management when rigorous ecological data are lacking. We define the effectiveness of the wetland management strategy by its ability to maintain sustainable minimum water levels that are required to support ecological processes. These minimum water requirements are defined in water management and environmental policy of the wetland. Here, we trial the method on Forrestdale Lake, a wetland in a region experiencing a markedly drying climate. ATPs were defined by linking key ecological objectives identified by policy documents to threshold values for water depth. We then used long-term hydrologic data (1978–2012) to assess if and when thresholds were breached. We found that from the mid-1990s, declining wetland water depth breached ATPs for the majority of the wetland objectives. We conclude that the wetland management strategy has been ineffective from the mid-1990s, when the region’s climate dried markedly. The extent of legislation, policies, and management authorities across different scales and levels of governance need to be understood to adapt ecosystem management strategies. Empirical verification of the ATP assessment is required to validate the suitability of the method. However, in general we consider ATPs to be a useful desktop method to assess the suitability of management when rigorous ecological data are lacking

Determining the probability of cyanobacterial blooms: the application of Bayesian networks in multiple lake systems

A Bayesian network model was developed to assess the combined influence of nutrient conditions and climate on the occurrence of cyanobacterial blooms within lakes of diverse hydrology and nutrient supply. Physicochemical, biological, and meteorological observations were collated from 20 lakes located at different latitudes and characterized by a range of sizes and trophic states. Using these data, we built a Bayesian network to (1) analyze the sensitivity of cyanobacterial bloom development to different environmental factors and (2) determine the probability that cyanobacterial blooms would occur. Blooms were classified in three categories of hazard (low, moderate, and high) based on cell abundances. The most important factors determining cyanobacterial bloom occurrence were water temperature, nutrient availability, and the ratio of mixing depth to euphotic depth. The probability of cyanobacterial blooms was evaluated under different combinations of total phosphorus and water temperature. The Bayesian network was then applied to quantify the probability of blooms under a future climate warming scenario. The probability of the "high hazardous" category of cyanobacterial blooms increased 5% in response to either an increase in water temperature of 0.8°C (initial water temperature above 24°C) or an increase in total phosphorus from 0.01 mg/L to 0.02 mg/L. Mesotrophic lakes were particularly vulnerable to warming. Reducing nutrient concentrations counteracts the increased cyanobacterial risk associated with higher temperatures

Developing predictive insight into changing water systems: use-inspired hydrologic science for the Anthropocene

Globally, many different kinds of water resources management issues call for policy- and infrastructure-based responses. Yet responsible decision-making about water resources management raises a fundamental challenge for hydrologists: making predictions about water resources on decadal - to century-long timescales. Obtaining insight into hydrologic futures over 100 yr timescales forces researchers to address internal and exogenous changes in the properties of hydrologic systems. To do this, new hydrologic research must identify, describe and model feedbacks between water and other changing, coupled environmental subsystems. These models must be constrained to yield useful insights, despite the many likely sources of uncertainty in their predictions. Chief among these uncertainties are the impacts of the increasing role of human intervention in the global water cycle – a defining challenge for hydrology in the Anthropocene. Here we present a research agenda that proposes a suite of strategies to address these challenges from the perspectives of hydrologic science research. The research agenda focuses on the development of co-evolutionary hydrologic modeling to explore coupling across systems, and to address the implications of this coupling on the long-time behavior of the coupled systems. Three research directions supportthe development of these models: hydrologic reconstruction, comparative hydrology and model-data learning. These strategies focus on understanding hydrologic processes and feedbacks over long timescales, across many locations, and through strategic coupling of observational and model data in specific systems. We highlight the value of use-inspired and team-based science that is motivated by real-world hydrologic problems but targets improvements in fundamental understanding to support decision-making and management. Fully realizing the potential of this approach will ultimately require detailed integration of social science and physical science understanding of water systems, and is a priority for the developing field of sociohydrology

Environmental flow requirements of estuaries: providing resilience to current and future climate and direct anthropogenic changes

Estuaries host unique biodiversity and deliver a range of ecosystem services at the interface between catchment and the ocean. They are also among the most degraded ecosystems on Earth. Freshwater flow regimes drive ecological processes contributing to their biodiversity and economic value, but have been modified extensively in many systems by upstream water use. Knowledge of freshwater flow requirements for estuaries (environmental flows or E-flows) lags behind that of rivers and their floodplains. Generalising estuarine E-flows is further complicated by responses that appear to be specific to each system. Here we critically review the E-flow requirements of estuaries to 1) identify the key ecosystem processes (hydrodynamics, salinity regulation, sediment dynamics, nutrient cycling and trophic transfer, and connectivity) modulated by freshwater flow regimes, 2) identify key drivers (rainfall, runoff, temperature, sea level rise and direct anthropogenic) that generate changes to the magnitude, quality and timing of flows, and 3) propose mitigation strategies (e.g., modification of dam operations and habitat restoration) to buffer against the risks of altered freshwater flows and build resilience to direct and indirect anthropogenic disturbances. These strategies support re-establishment of the natural characteristics of freshwater flow regimes which are foundational to healthy estuarine ecosystems

Identification of the Major Hydrological Threats for Two Clay Pan Wetlands in the South West of Australia

Abstract: This study presents the findings of a wetland ecohydrological model (WET-0D), used to recreate a historical water regime and predict the future water regime for two clay pan wetlands in South West Western Australia. WET-0D simulates the major hydrological fluxes through three conceptual water storages including the open water/lake, and surrounding unsaturated and saturated zones. Groundwater -soil water balance -vegetation (GSV) dynamics are modelled with plant biomass simulated as three functional vegetation groups with differing water uptake strategies and dependence on water availability. The wetland model was driven by a simple catchment water balance model, using historical climate data from the Bureau of Meteorology (BoM). To simulate the potential impact of climate change on wetland ecohydrology, statistically downscaled output from a Global Climate Model (GCM), based on the IPCC SRES A2 scenario, was used to drive the models to predict potential future water regimes. This allowed us to gain an insight of the impact of projected drying climate on the clay pan ecosystems. Although both clay pan catchments experience very similar climates, differences in the partitioning of rainfall and subsequent flow generation, due to different vegetation, soil type and topography, results in dissimilar hydrological regimes. Differences in the hydrological regimes alter the way predicted climate change affects water flux and hydroperiod (period of surface flooding of a wetland) in both clay pan systems. Historically, the modelling predicts the lake level in the North East clay pan is more dependent on overland flow, while the South West clay pan is more dependent on shallow groundwater flow from a seasonal aquifer. Under a drying climate the modelling predicts, the South West clay pan will become increasingly overland flow dependent. However, the shallow groundwater inputs to the clay pan prolong inundation by reducing the rate of seepage from the clay pan. The partial clearing of the catchment area for the South West clay pan has maximised groundwater recharge efficiency allowing maintenance of ecological water requirements under a drying climate. The North East clay pan is under greater threat due to the reliance of surface water inflow and the lack of groundwater input due to differences in catchment characteristics