Lake Analyzer is a numerical code coupled with supporting visualization tools for determining indices of mixing and stratification that are critical to the biogeochemical cycles of lakes and ...reservoirs. Stability indices, including Lake Number, Wedderburn Number, Schmidt Stability, and thermocline depth are calculated according to established literature definitions and returned to the user in a time series format. The program was created for the analysis of high-frequency data collected from instrumented lake buoys, in support of the emerging field of aquatic sensor network science. Available outputs for the Lake Analyzer program are: water temperature (error-checked and/or down-sampled), wind speed (error-checked and/or down-sampled), metalimnion extent (top and bottom), thermocline depth, friction velocity, Lake Number, Wedderburn Number, Schmidt Stability, mode-1 vertical seiche period, and Brunt-Väisälä buoyancy frequency. Secondary outputs for several of these indices delineate the parent thermocline depth (seasonal thermocline) from the shallower secondary or diurnal thermocline. Lake Analyzer provides a program suite and best practices for the comparison of mixing and stratification indices in lakes across gradients of climate, hydro-physiography, and time, and enables a more detailed understanding of the resulting biogeochemical transformations at different spatial and temporal scales.
Lake Xingyun is a hypertrophic shallow lake on the Yunnan Plateau of China. Its water quality (WQ) has degraded severely during the past three decades with catchment development. To better understand ...the external nutrient loading impacts on WQ, we measured nutrient concentrations in the main tributaries during January 2010–April 2018 and modelled the monthly volume of all the tributaries for the same period. The results show annual inputs of total nitrogen (TN) had higher variability than total phosphorus (TP). The multi-year average load was 183.8 t/year for TN and 23.3 t/year for TP during 2010–2017. The average TN and TP loads for 2010–2017 were 36.6% higher and 63.8% lower, respectively, compared with observations in 1999. The seasonal patterns of TN and TP external loading showed some similarity, with the highest loading during the wet season and the lowest during the dry season. Loads in spring, summer, autumn, winter, and the wet season (May–October) accounted for 14.2%, 48.8%, 30.3%, 6.7%, and 84.9% of the annual TN load and 14.1%, 49.8%, 28.1%, 8%, and 84.0% of the annual TP load during 2010–2017. In-lake TN and TP concentrations followed a pattern similar to the external loading. The poor correlation between in-lake nutrient concentrations and tributary nutrient inputs at monthly and annual time scales suggests both external loading and internal loading were contributing to the lake eutrophication. Although effective lake restoration will require reducing nutrient losses from catchment agriculture, there may be a need to address a reduction of internal loads through sediment dredging or capping, geochemical engineering, or other effective measures. In addition, the method of producing monthly tributary inflows based on rainfall data in this paper might be useful for estimating runoff at other lakes.
Trophic state of lakes has been related to catchment land use, but direct links between phytoplankton taxa and land use are limited. Phytoplankton composition, represented by relative cell abundance ...of phyla, was measured over a period of 4 years in 11 lakes in the Rotorua region, New Zealand. The lakes differed in morphometry, trophic state and land use (as percentage catchment area). We tested whether relative proportion of land uses, indirectly representing relative nutrient loading, was the overarching driver of phytoplankton composition. Trophic state was correlated negatively with native forest and positively with pasture and urban area. Cyanoprokaryota were correlated negatively with native forest and positively with pasture and trophic state, Chlorophyta were correlated positively with native forest and urban land use and negatively with pasture and trophic state, and Bacillariophyta were positively correlated with dissolved reactive silica to dissolved inorganic nitrogen (Si:DIN) and Si to dissolved reactive phosphorus (Si:DRP) ratios. Lakes with higher nutrient loads had higher trophic state and Cyanoprokaryota dominance. Chlorophyta were negatively correlated with Cyanoprokaryota and Bacillariophyta, suggesting competition amongst these groups. Our results apply to lakes potentially subject to changes in catchment land use, which may have implications for trophic state, phytoplankton composition and Cyanoprokaryota blooms.
International studies point out that some freshwater policy objectives are not achieved. This study describes that this is in part caused by shortcomings that include: the lack of targeted monitoring ...schemes to measure impact; a too small range of specific technologies rather than a wider suite of integrated multiple technologies; a too tight focus on sub-sets of stakeholders instead of the involvement of the wider range of end users; and poor trust building and technology explanations to end users. As an example, the New Zealand government is addressing widespread concern over the deterioration of the national freshwater resource by supporting a diverse portfolio of land and riparian management actions. Efforts to assess the effectiveness of these interventions and establish an evidence-based framework for future policies are however limited by the existing regional-scale freshwater monitoring infrastructure. Such hydrometric networks were established largely to assess the broader-scale regional ‘state’ of the environment and are generally out-of-phase with freshwater improvement actions that are implemented more typically at edge-of-field, farm or sub-catchment scales. Recent and rapid evolution in sensor technologies have created new opportunities to deliver information tuned to the appropriate parameters and frequencies needed to evaluate improvement actions. Despite this, the necessary transformative change in freshwater monitoring has yet to gather pace. In this study we explore barriers and solutions with the objective to better understand what is needed for successful integration of innovative monitoring technologies in a transitional environmental policy setting, using recent New Zealand policy directives as a case study. We use expert surveys and scenario testing to explore barriers to adoption to more robust and comprehensive monitoring required to establish the success, or otherwise, of freshwater improvement actions. This process reveals that rather than further innovations in technology, change in the practice of environmental monitoring is limited instead by the development of defensible and accepted guidelines on the application and effective deployment of existing sensors and methods. We demonstrate that improved knowledge exchange between engineers, scientists and practitioners can be addressed and propose a new decision support and communication tool to enable the selection of monitoring technologies and solutions fit-for-purpose to evaluate freshwater improvement outcomes on multiple scales involving multiple stakeholders.
Observations by satellite sensors provide data on inland water systems at spatial and temporal coverage superior to current monitoring programmes. We derived an empirical relationship for Secchi ...depth using in situ data from eight lakes and data from the Landsat 5 Thematic Mapper, Landsat 7 Enhanced Thematic Mapper Plus and Landsat 8 Operational Land Imager between 1999 and 2018 in the Rotorua Lakes Region in New Zealand. This relationship was then applied to all Landsat data of 23 lakes in that region. A trend analysis on annual and summertime averages of Secchi depth revealed several statistically significant and positive trends, indicating improving water clarity. Our trends were in agreement with those based on in situ observations illustrating the opportunities of remote sensing time series data for lake monitoring and management.
Lake Heat Flux Analyzer is a program used for calculating the surface energy fluxes in lakes according to established literature methodologies. The program was developed in MATLAB for the rapid ...analysis of high-frequency data from instrumented lake buoys in support of the emerging field of aquatic sensor network science. To calculate the surface energy fluxes, the program requires a number of input variables, such as air and water temperature, relative humidity, wind speed, and short-wave radiation. Available outputs for Lake Heat Flux Analyzer include the surface fluxes of momentum, sensible heat and latent heat and their corresponding transfer coefficients, incoming and outgoing long-wave radiation. Lake Heat Flux Analyzer is open source and can be used to process data from multiple lakes rapidly. It provides a means of calculating the surface fluxes using a consistent method, thereby facilitating global comparisons of high-frequency data from lake buoys.
•Concise review of the recent advances in numerical modelling of lakes and reservoirs.•Coverage of model development, modelling methods and socio-economic perspectives.•Discussion of ways forward for ...the aquatic ecosystem modelling community.
Despite rapid growth in continuous monitoring of dissolved oxygen for lake metabolism studies, the current best practice still relies on visual assessment and manual data filtering of sensor ...observations by experienced scientists in order to achieve meaningful results. This time consuming approach is fraught with potential for inconsistency and individual subjectivity. An automated method to assure the quality of data for the purpose of metabolism modeling is clearly needed to obtain consistent results representative of collective expertise. We used a hybrid approach of expert panel and data mining for data filtration. Symbolic Aggregate approXimation (SAX) treats discretized numerical timeseries segments as symbolic indications, creating a series of strings which are literally comparable to human words and sentences. This conversion allows established text mining techniques, such as classification methods to be applied to timeseries data. Half‐hourly frequency surface dissolved oxygen data from 18 global lakes were used to create day‐long segments of the original time series data. Three hundred sets of 1‐d measurements were provided to a group of seven anonymous experts, experienced in manual filtering of oxygen data for metabolism modeling studies. The collective results were treated as expert panel decisions, and were used to rank the data by confidence level for use in metabolism calculations. While considerable variation occurred in the way the experts perceived the quality of the data, the model provides an objective and quantitative assessment method. The program output will assist the decision making process in determining whether data should be used for metabolism calculations. An R version of the program is available for download.
Lake water levels fluctuate at time scales ranging from minutes to many years. While extensive research has been devoted to seasonal and multiannual time scales, we examined water level changes at ...time scales of minutes to hours. By applying impulse response functions to Lake Biwa and its catchment, we demonstrated that it is possible to (1) identify the effects of natural oscillations governed by the shape of the lake, (2) determine the precipitation retention time at the surface (above the impermeable layer) of the catchment, and (3) estimate how long it takes precipitation falling in catchment areas to reach the lake. Between 2010 and 2012 we recorded water levels at high frequency in the South Basin of Lake Biwa and calculated response functions between precipitation and water levels. We categorized the delay time determined from the calculated response functions as direct precipitation on the lake, seiches, and river inflow (surface flow, return inflow). We then identified the runoff patterns of surface and return flows by considering the time scale of the delay. The method used in this study enables flood predictions in cases involving heavy rain and appropriate planning of preventive measures against flood damage. These results will be valuable for the development of management strategies to respond to climate change in lake catchment systems.
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