Novel approaches for modelling changes in phytoplankton diversity and lake ecosystem function

Ecosystem function represents the collective outcome of many different processes. Function may be interrupted by events that originate from outside a system, influencing biological diversity dynamics. Difficulties in expressing how a system is functioning originate firstly from being able to define a normative status for a dynamic system and secondly from the accuracy of common metrics of biodiversity changes. In this thesis, I used a numerical model and high-frequency ecological observations to express functioning of a system. Chapter 2 used biogeochemical parameter perturbations in a lake ecological model to identify seasonal parameter sensitivity variabilities. A set of internal process parameters of calibrated shallow eutrophic Lake Waahi DYRESM-CAEDYM ecological model was used to apply Monte-Carlo perturbation. Analysis was conducted by examining the collective results variability, a “spread” of the ensemble results from the iteration. The results showed that the spreads were small when lake inflows had high discharge, suggesting that lake internal dynamics had lesser effect on water quality and inflows dominated the system dynamics. Due to the simplicity of the methods, regular use of perturbation methods is suggested to assess model uncertainty and to better understand the model. Chapter 3 used interdisciplinary methods to identify changes in dissolved oxygen (DO) observations caused by biological processes. DO in lakes is a key indicator of ecosystem function. Methods used in this chapter included expert panel decision making, Symbolic Aggregate approXimation (SAX) analysis, and text classification. The use of an expert panel was motivated by the common practice of DO data visual assessment. Variability in experts’ boundaries for data quality were observed by data survey, reinforcing the necessity of robust and reproducible methods for unbiased analysis. Surface DO sensor data from 18 global lakes were used to create day-long data segments. The modelling framework successfully simulated the expert panel decisions on these segments, automatically labelling data to indicate when the signal is likely dominated by biological activities. In Chapter 4, species-neutral biological assemblage metrics were developed to account for phytoplankton changes associated with changes in species abundance. Every species’ population changes were converted into binary metrics (i.e., increases or decreases) to identify the “constituents” of species richness, to allow robust assessments of population dynamics. Four lakes (Lakes Annie, Feeagh, Esthwaite and Mendota) from different regions were analysed. The results showed several previously undocumented features. Species recruitment was proportional to the number of species that were increasing. The number of species that were decreasing did not immediately increase the number of species that went extinct. The rate of increase was logarithmically distributed from the fastest to the slowest growing species, with the distribution shape being strongly influenced by number of species that were increasing. Such species-neutral community metrics, along with abundance distribution and diversity, are helpful to assess mechanistic community ecology models. This thesis provides toolsets useful for future studies to understand relationships between forcing and functioning of ecosystems and changes in biodiversity, by providing means to assess ecosystem function and demonstrating examples of species-neutral community structural changes

LakeAnalyzer: Lake internal dynamics analysis software – fact sheet

LakeAnalyzer is a computer program used to calculate indices of mixing and stratification, which are critical to understanding biogeochemical cycles of lakes and reservoirs. Lake physical stability indices, surface mixing depth and thermocline depth are calculated according to established literature definitions and returned to the user in a time-series format. LakeAnalyzer was developed to analyse high-frequency data collected from instrumented lake buoys (Figure 1). It provides a way to compare mixing and stratification indices in lakes across gradients of climate, hydrophysiography, and time, and provides a basis for understanding of the resulting biogeochemical transformations at different spatial and temporal scales

A coupled hydrodynamic-ecological model to test management options for restoration of lakes Onoke and Wairarapa

This report describes a modelling and remote sensing study of lakes Onoke and Wairarapa that seeks to determine water quality and ecological effects of specific management scenarios, and therefore inform the Ruamāhanga Whaitua Committee of potential water quality management options for lakes Onoke and Wairarapa. The study applied both one dimensional (1-D) and three dimensional (3-D) ecologically coupled hydrodynamic models to simulate current and scenario-based water quality variables. The Baseline model (calibration) simulates “current conditions” including management practices between 1992 and 2014. Business As Usual (BAU), SILVER and GOLD scenarios were all run using representative data catchment inflow and nutrients for mitigation taking effect in 2025, 2040 and 2080. Additional hydrodynamic scenarios were modelled (which also include catchment mitigations above). They were: deepening both lakes by 1 m, Ruamāhanga diversion back into Lake Wairarapa, and Lake Onoke summer outlet closed scenarios. These scenarios were provided by the Ruamāhanga Whaitua Committee. Within Lake Wairarapa, catchment mitigation-based scenarios showed considerable potential for the improvement of water quality. These mitigations simulated that the trophic state of the lake could change from the current supertrophic category, to the top of the eutrophic category (GOLD and SILVER mitigations). However, this still indicates poor water quality and high turbidity/low water clarity. In addition, these catchment mitigations did not move the lake from a NOF D category for total phosphorous (TP). Simulations indicated that larger reductions in TP (60%) (with SILVER2080 mitigations of other nutrients) could achieve a NOF C category for TP. Simulations that included the re-establishment of macrophytes also indicated NOF C category for TP (under SILVER2080), however only under a 1 m depth increase scenario, and under Ruamāhanga diversion scenario. These simulations indicated that the trophic status could move to the mid-eutrophic category. However, this is still indicative of poor water quality. Catchment scenarios had a greater influence on Lake Onoke trophic status compared to Wairarapa, due to the shorter residence time and low internal load (from the sediments) relative to external load. In effect, the composition of Onoke aligns closely with that of its inflows. Water quality in Lake Onoke is susceptible to changes in water quality in Lake Wairarapa, particularly in relation to chlorophyll a (chl a) and total suspended solids (TSS). High sediment resuspension events in Lake Wairarapa transport increased levels of suspended sediment to Lake Onoke. The very low residence time in Onoke does not allow adequate time for significant phytoplankton growth within the lake. However, 3-D simulations show higher phytoplankton concentrations at times in the western lake, relating to flushing and transport effects. The outlet-closed scenario in Lake Onoke simulated increased water quality in both 1-D and 3-D models However, we note that the risk of cyanobacteria blooms was low, but marginally increased. Also 1-D models suggested that the simulated TLI under SILVER2080 was almost identical to outlet closed SILVER2080. The 3-D model simulated lower chlorophyll concentrations and higher TSS under SILVER2080 outlet closed (compared to SILVER2080 and Baseline), largely due to changes in hydrodynamics and flushing. Therefore, these results show no conclusive evidence that water quality would be significantly increased or decreased in comparison to SILVER2080 under an outlet closed scenario. However, we note that in situ monitoring and expert opinion has indicated that under outlet closed conditions the lake is more susceptible to eutrophication

Facilitating rafting on the Kaituna River: The effect of manipulating Lake Rotoiti outflow on the function of the Ohau diversion wall

The University of Waikato was requested by Bay of Plenty Regional Council to quantify the effectiveness of the Ohau diversion wall when controlling the Kaituna River outflow during high and low flows. The Ohau diversion wall was constructed to divert nutrient-enriched water from Lake Rotorua away from the main basin of Lake Rotoiti and towards the Kaituna River outflow. Bay of Plenty Regional Council wished to determine whether controlling the Lake Rotoiti outflow to enable rafting on the Kaituna River would impact on the efficacy of the Ohau diversion wall. The Kaituna River is used for commercial and recreational white-water rafting and kayaking, and is a proposed venue for the 2013 World Rafting Championships. However, control of the Kaituna outflow to regulate the water level in the lake may conflict with the use of the Kaituna River for rafting, which requires discharge to be between minimum and maximum raftable flows (13 m³ s⁻¹ and 26 m³ s⁻¹, respectively). Outflow from the lake may be controlled so that flows in the river are within the raftable range for a number of hours a day, and then adjusted for the remainder of the day to prevent high or low water levels. However, it is possible that this may affect the efficacy of the Ohau diversion wall, leading to concerns that this mode of operation could impact on the water quality in Lake Rotoiti. To address these concerns, three-dimensional hydrodynamic modelling was used to quantify the transfer of water from the Ohau channel to Lake Rotoiti under scenarios that facilitated rafting operations. The model was set up so that a tracer (transported by water flow) would be released in the Ohau inflow for the duration of the simulation. Tracer concentrations were output from the model simulations as depth profiles for five stations in the lake to quantify the transport of water from the Ohau channel into Lake Rotoiti

Waikato shallow lakes modelling

The principal aim of this study is to apply a modelling approach to identify, evaluate and prioritise specific in-lake and catchment restoration options which could be applied to improve the water quality and ecological health of peat and riverine lake types across the Waikato Region. Four representative lakes have been selected as case studies for this work based on their social, cultural and ecological significance, as well as the availability of historical monitoring data and the potential transferability of the study findings to similar lake systems. The lakes include Rotomānuka, Ngāroto, Waahi and Waikare

The Global Lake Ecological Observatory Network (GLEON): the evolution of grassroots network science

Nine years later, with over 380 members from 40 countries, and 50 publications to its credit, GLEON is growing at a rapid pace and pushing the boundaries of the practice of network science. GLEON is really three networks: a network of lakes, data, and peopl

A Global lake ecological observatory network (GLEON) for synthesising high-frequency sensor data for validation of deterministic ecological models

A Global Lake Ecological Observatory Network (GLEON; www.gleon.org) has formed to provide a coordinated response to the need for scientific understanding of lake processes, utilising technological advances available from autonomous sensors. The organisation embraces a grassroots approach to engage researchers from varying disciplines, sites spanning geographic and ecological gradients, and novel sensor and cyberinfrastructure to synthesise high-frequency lake data at scales ranging from local to global. The high-frequency data provide a platform to rigorously validate processbased ecological models because model simulation time steps are better aligned with sensor measurements than with lower-frequency, manual samples. Two case studies from Trout Bog, Wisconsin, USA, and Lake Rotoehu, North Island, New Zealand, are presented to demonstrate that in the past, ecological model outputs (e.g., temperature, chlorophyll) have been relatively poorly validated based on a limited number of directly comparable measurements, both in time and space. The case studies demonstrate some of the difficulties of mapping sensor measurements directly to model state variable outputs as well as the opportunities to use deviations between sensor measurements and model simulations to better inform process understanding. Well-validated ecological models provide a mechanism to extrapolate high-frequency sensor data in space and time, thereby potentially creating a fully 3-dimensional simulation of key variables of interest

Multicenter retrospective study to evaluate the efficacy and safety of the double-flap technique as antireflux esophagogastrostomy after proximal gastrectomy (rD-FLAP Study)

AIM: As a result of the difficulty in effective prevention of gastroesophageal reflux, no standard reconstruction procedure after proximal gastrectomy (PG) has yet been established. The double-flap technique (DFT), or Kamikawa procedure, is an antireflux reconstruction procedure in esophagogastrostomy. The efficacy of DFT has recently been reported in several studies. However, these were all single-center studies with a limited number of cases. METHODS: We conducted a multicenter retrospective study in which patients who underwent DFT, irrespective of disease type and reconstruction approach, at each participating institution between 1996 and 2015 were registered. Primary endpoint was incidence of reflux esophagitis at 1-year after surgery, and secondary endpoint was incidence of anastomosis-related complications. RESULTS: Of 546 patients who were eligible for this study, 464 patients who had endoscopic examination at 1-year follow up were evaluated for reflux esophagitis. Incidence of reflux esophagitis of all grades was 10.6% and that of grade B or higher was 6.0%. Male gender and anastomosis located in the mediastinum/intra-thorax were independent risk factors for grade B or higher reflux esophagitis (odds ratio [OR]: 4.21, 95% confidence interval [CI]: 1.44-10.9, P = 0.0109). Total incidence of anastomosis-related complications was 7.2%, including leakage in 1.5%, strictures in 5.5% and bleeding in 0.6% of cases. Laparoscopic reconstruction was the only independent risk factor for anastomosis-related complications (OR: 3.93, 95% CI: 1.93-7.80, P = 0.0003). CONCLUSION: Double-flap technique might be a feasible option after PG for effective prevention of reflux, although anastomotic stricture is a complication that must be well-prepared for

津門川の感覚的環境評価 : アンケート解析および回答者に関する考察

The evaluation of river environment on the Tsuto River flowing through Nishinomiya City, Hyogo Pref., was performed by using the questionnaire based on human sensitivity. The survey was operated around the middle reaches of the river on July, 2004 and focused on the recognition and evaluation of the river by local residents. Valid responses were obtained from 613 residents. Three fourths of the respondents were women and two thirds were middle and older aged persons. About 70% of the respondents have lived in the neighboring area within a 30 min. distance from Nishinomiya-kitaguchi Sta. Of Hankyu Railway and 60% have lived over a long period of 5 years. Major subject groups were housewives and female students. As for the recognition of the river, basic and current information, such as location of riverhead, upstream migration of Ayu fish (Plecoglossus altivelis) and construction of fish-way, was less well known, however, local residents activities for environmental protection of the river were well known and highly valued. As for the evaluation of the river, average proportion of positive evaluation in 15 questions belonging to 4 categories, prodigality of nature, unity with community, beauty of landscape and disaster measures, was only 18.1%. Lower evaluations were particularly featured in the questions related to the categories of prodigality of nature and beauty of landscape. The cross-tabulation for the recognizability showed that the recognition of the river became lower in the responses from women, young people and persons in the distant area and short-period residence. Especially concerning to the distance of residence from the station and the number of residential years, the differences of recognition between the residents appeared clearly. The cross-tabulation for the evaluation indicated strong complaint against the landscape and administrative response from neighboring older persons in long-period residence. On the other hand, female students showed less interest in the environment of the Tsuto River even when they lived in the neighboring area and long-period residence