The modelling community has identified challenges for the integration and assessment of lake models due to the diversity of modelling approaches and lakes. In this study, we develop and assess a ...one-dimensional lake model and apply it to 32 lakes from a global observatory network. The data set included lakes over broad ranges in latitude, climatic zones, size, residence time, mixing regime and trophic level. Model performance was evaluated using several error assessment metrics, and a sensitivity analysis was conducted for nine parameters that governed the surface heat exchange and mixing efficiency. There was low correlation between input data uncertainty and model performance and predictions of temperature were less sensitive to model parameters than prediction of thermocline depth and Schmidt stability. The study provides guidance to where the general model approach and associated assumptions work, and cases where adjustments to model parameterisations and/or structure are required.
•The General Lake Model (GLM) is stress tested against 32 globally distributed lakes.•There was low correlation between input data uncertainty and model performance.•Model performance related to lake-morphometry, light extinction and flow regime; deep, clear lakes had the lowest model error.•Predictions of temperature were less sensitive to model parameters than thermocline depth and Schmidt stability.
Coastal lakes, also known as temporarily open/closed estuaries or intermittently closed and open lakes and lagoons, are common worldwide, are typically sites of high biodiversity and often contain ...abundant macrophyte populations. Anthropogenic stressors such as increased nutrient and sediment loading have adverse effects on submerged macrophytes, and when closed, the lack of tidal flushing makes coastal lakes highly susceptible to eutrophication. Lake openings to the sea may occur naturally, but many coastal lakes are also opened artificially, often to reduce inundation of surrounding land. Here we used a coupled hydrodynamic-ecological model (DYRESM-CAEDYM), modified to include dynamic feedback between submerged macrophyte biomass and sediment resuspension, to explore the interactive effects of multiple disturbances (openings, eutrophication and climate change) on the dynamics of primary producers in a coastal lake (Waituna Lagoon) in South Island, New Zealand. Our results indicate that with exposure to high external nutrient loads, the frequent disturbances caused by artificial openings prevent sustained dominance by algae (algal biomass averaged 192 g C m−2 with artificial openings compared to 453 g C m−2 with no openings). However, under current nutrient loading, climate change is likely to enhance the effects of eutrophication on the system (algal biomass averaged 227 g C m−2 with climate change compared with 192 g C m−2 for current climate). The model provides a decision-support tool to guide lake management in setting limits for nutrient loads and managing the opening regime, in order to prevent eutrophication and the potential collapse of the macrophyte community.
•We explored the interactive effects of multiple disturbances on a coastal lake•Frequent openings mitigate eutrophication in a coastal lake•Climate change will exacerbate eutrophication in a coastal lake•Our model provides a decision-support tool to guide lake management
Anthropogenic activity has greatly enhanced the inputs of nitrogen (N) and phosphorus (P) to lakes, causing widespread eutrophication. Algal or cyanobacterial blooms are among the most severe ...consequences of eutrophication, impacting aquatic food webs and humans that rely on lakes for ecosystem services. In New Zealand, recent debate on the relative importance of N versus P control for limiting occurrences of algal blooms has centered on the iconic Lake Rotorua (North Island). Water quality in Lake Rotorua has declined since the late 1800s following catchment vegetation clearing and subsequent land-use intensification, as well as from sewage inputs. A multimillion dollar restoration programme began in the early 2000s, with key mitigation actions including nutrient load targets for the entire catchment and alum dosing in 2 tributaries. In this manuscript we analyse 2 water quality datasets (>10 yr) from Lake Rotorua and compare these with a global lake dataset. Generalised additive models predicted highly significant (p < 0.001) declines in total phosphorus (TP), total nitrogen (TN) and chlorophyll a (Chl- a) in surface waters between 2001 and 2015. Alum dosing had a negative (i.e., reducing) and highly significant effect on TP and Chl- a (p < 0.001). Correlations of Chl- a on TP and TN were highly significant, but the difference between the 2 correlation coefficients was not, indicating a need to control both nutrients to reduce algal productivity. This conclusion is reinforced by recent bioassay studies which show co-limitation by N and P. Collectively, our data and previous studies provide strong support for the current strategy of limiting both N and P loads to Lake Rotorua for effective eutrophication control.
Automated calibration of complex deterministic water quality
models with a large number of biogeochemical parameters can reduce
time-consuming iterative simulations involving empirical judgements of ...model
fit. We undertook autocalibration of the one-dimensional
hydrodynamic-ecological lake model
DYRESM-CAEDYM, using a Monte Carlo sampling (MCS) method, in order to test
the applicability of this procedure for shallow, polymictic Lake Rotorua (New
Zealand). The calibration procedure involved independently minimizing the
root-mean-square error (RMSE), maximizing the Pearson correlation coefficient
(r) and Nash–Sutcliffe efficient coefficient (Nr) for comparisons
of model state variables against measured data. An assigned number of
parameter permutations was used for 10 000 simulation iterations. The
“optimal” temperature calibration produced a RMSE of 0.54 ∘C,
Nr value of 0.99, and r value of 0.98 through the whole water
column based on comparisons with 540 observed water temperatures collected
between 13 July 2007 and 13 January 2009. The modeled bottom dissolved oxygen
concentration (20.5 m below surface) was compared with 467 available
observations. The calculated RMSE of the simulations compared with the
measurements was 1.78 mg L−1, the Nr value was 0.75, and the
r value was 0.87. The autocalibrated model was further tested for an
independent data set by simulating bottom-water hypoxia events from 15
January 2009 to 8 June 2011 (875 days). This verification produced an
accurate simulation of five hypoxic events corresponding to
DO < 2 mg L−1 during summer of 2009–2011. The RMSE was
2.07 mg L−1, Nr value 0.62, and r value of 0.81, based on
the available data set of 738 days. The autocalibration software of
DYRESM-CAEDYM developed here is substantially less time-consuming and more
efficient in parameter optimization than traditional manual calibration which
has been the standard tool practiced for similar complex water quality
models.
Transparency is a fundamental characteristic of aquatic ecosystems and is highly responsive to changes in climate and land use. The transparency of glacially‐fed lakes may be a particularly sensitive ...sentinel characteristic of these changes. However, little is known about the relative contributions of glacial flour versus other factors affecting light attenuation in these lakes. We sampled 18 glacially‐fed lakes in Chile, New Zealand, and the U.S. and Canadian Rocky Mountains to characterize how dissolved absorption, algal biomass (approximated by chlorophyll a), water, and glacial flour contributed to attenuation of ultraviolet radiation (UVR) and photosynthetically active radiation (PAR, 400–700 nm). Variation in attenuation across lakes was related to turbidity, which we used as a proxy for the concentration of glacial flour. Turbidity‐specific diffuse attenuation coefficients increased with decreasing wavelength and distance from glaciers. Regional differences in turbidity‐specific diffuse attenuation coefficients were observed in short UVR wavelengths (305 and 320 nm) but not at longer UVR wavelengths (380 nm) or PAR. Dissolved absorption coefficients, which are closely correlated with diffuse attenuation coefficients in most non‐glacially‐fed lakes, represented only about one quarter of diffuse attenuation coefficients in study lakes here, whereas glacial flour contributed about two thirds across UVR and PAR. Understanding the optical characteristics of substances that regulate light attenuation in glacially‐fed lakes will help elucidate the signals that these systems provide of broader environmental changes and forecast the effects of climate change on these aquatic ecosystems.
Key Points
Glacial flour contributed about two thirds of lake diffuse attenuation coefficients
Turbidity‐specific attenuation coefficients increased with glacier distance
Turbidity‐specific attenuation coefficients were similar across regions
The influence of the El Nino Southern Oscillation (ENSO) climate pattern on physical and chemical characteristics of surface waters at 77 river sites throughout New Zealand over the period 1989 2001 ...was investigated. The Southern Oscillation Index was used to characterize ENSO, and to examine the effect of climate variability on flow and water-quality variables, simple linear regression was performed of each variable on the Southern Oscillation Index for each site. Results suggested increasing flows in the north and decreasing flows in the south, and the pattern observed for river water temperature matched known ENSO effects on air temperature and sea-surface temperature around New Zealand. The temperature variation appeared to be relatively independent of rainfall flow variation. Variation in rainfall/flow associated with the Southern Oscillation Index was related to the patterns observed for conductivity, water clarity/turbidity, and total phosphorus levels, but no correlation was found with nitrogen species, dissolved reactive P, BOD, and river color.
The health and well-being benefits of nature contact are inequitably distributed. Among other communities, persons with a disability have fewer opportunities to engage in nature contact in a ...self-determining way due to the presence of interlocking physical, informational, service, policy, and attitudinal barriers. The purpose of this project was to utilize accepted accessibility standards to document the state of accessibility in nature based tourism and recreation spaces across British Columbia. Following community-based research practices, a team of academic researchers and experts working in accessibility practice collected over 6,700 unique measurements documenting potential barriers across 124 outdoor tourism and recreation sites. Of the 974 infrastructure elements and features assessed, fewer than five percent met all required standards. This paper shares evidence about the categories of infrastructure that are most problematic from an access and inclusion perspective, as well as those that are comparable brightspots. Results demonstrate a considerable gap between Canada's policy goal to become barrier free by 2040 and the present state of accessibility in outdoor spaces across the nature continuum.
Organizations managing outdoor tourism and recreation spaces across the nature continuum in British Columbia, Canada are not meeting interrelated moral, legislative, and social demands for equitable access to nature. Management agencies should invest in data collection completed in partnership with the disability community to reveal the full suite of barriers that prevent access across the province. New capital investment programs are required to upgrade legacy infrastructure and realize new features and amenities that provide meaningful opportunities to all. To ensure accessibility does not diminish over time, changes in management practices like incorporating accessibility requirements into operational contracting, hiring for lived experience, and building accessibility monitoring into maintenance planning and operations are needed.
Gainsharing and comanagament programs are both successful means of achieving physician buy-in for all cost containment programs in Orthopaedic Trauma. Under comanagement agreements, physicians are ...reimbursed for their time and intellectual efforts in program and algorithm creation. The cost is minimal for the hospital in return for the millions of dollars in savings they achieve. Gainsharing models can incentivize physicians to quickly adopt cost-effective implant choices, care plans, and program development. Hospital systems keep the majority of the profits, patients, and insurance carriers benefit from the cost savings and physicians receive remuneration for their efforts. Careful attention must be paid to the legal issues surrounding the Federal Anti-Kickback Statute, the Civil Monetary Penalty Law, and the Physician Self-Referral Law when setting up these agreements. The keys to success for these programs are the presence of a physician champion, economic transparency for both physicians and hospitals, accurate data collection, and adequate economic incentive for physicians to drive change in practice patterns.
Distinct horizontal water column concentration gradients of nutrients and chlorophyll a (Chl a) occur within large, shallow, eutrophic Lake Taihu, China. Concentrations are high in the north, where ...some of the major polluted tributaries enter the lake, and relatively low in the south, where macrophytes generally are abundant. It is not clear, however, whether these water column concentration gradients are similarly reflected in spatial heterogeneity of nutrient concentrations within the bottom sediments. The main objective of this study was therefore to test if horizontal and vertical variations in the phosphorus and nitrogen content in bottom sediments of Lake Taihu are significantly related to (1) horizontal variations in overlying water column nutrient concentrations and (2) other sediment geochemical constituents. We measured the concentration of total phosphorus (TP) and total nitrogen (TN) in surficial sediments (0-2 cm) and TP, TN and Chl a concentrations in water column samples, collected from 32 sites in 2005. In 2006 sediment, TP, TN, carbon, iron and manganese concentrations were measured vertically at 2 cm intervals, extending to a depth of approximately 20 cm, at an additional eight sites. Linear correlation analysis revealed that surficial sediment TP concentrations across the 32 stations were related significantly, though weakly, to annual mean water column concentrations of TP, TN as well as Chl a. Correlations of surficial sediment TN with water column variables were, however, not significant (P > 0.05). Amongst the geochemical variables tested, the vertical variability of sediment TP concentrations was most strongly related to sediment manganese and carbon concentrations. A multiple stepwise linear regression revealed that the combination of sediment manganese and carbon concentrations explained 91% of the horizontal variability in sediment TP concentrations and 65% of the vertical variability.
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 process-based 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.
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