Algal Chlorophyll Concentration Research Articles

Prediction of algal blooms via data-driven machine learning models: an evaluation using data from a well-monitored mesotrophic lake

Abstract. With increasing lake monitoring data, data-driven machine learning (ML) models might be able to capture the complex algal bloom dynamics that cannot be completely described in process-based (PB) models. We applied two ML models, the gradient boost regressor (GBR) and long short-term memory (LSTM) network, to predict algal blooms and seasonal changes in algal chlorophyll concentrations (Chl) in a mesotrophic lake. Three predictive workflows were tested, one based solely on available measurements and the others applying a two-step approach, first estimating lake nutrients that have limited observations and then predicting Chl using observed and pre-generated environmental factors. The third workflow was developed using hydrodynamic data derived from a PB model as additional training features in the two-step ML approach. The performance of the ML models was superior to a PB model in predicting nutrients and Chl. The hybrid model further improved the prediction of the timing and magnitude of algal blooms. A data sparsity test based on shuffling the order of training and testing years showed the accuracy of ML models decreased with increasing sample interval, and model performance varied with training–testing year combinations.

Land-Use Pattern as a Key Factor Determining the Water Quality, Fish Guilds, and Ecological Health in Lotic Ecosystems of the Asian Monsoon Region

Land-use patterns influence water quality in lotic ecosystems worldwide; consequently, deteriorating water quality affects fish communities and composition and the ecological health of water bodies. This study aimed to evaluate how land use, stream order, and elevation regulate water quality and ecological health in 64 streams based on the following four land cover types: namely, forest, agriculture, urban upstream, and urban downstream regions. Spatial analysis revealed that urban downstream areas had higher nutrient concentrations [total phosphorus (TP) as follows: 117 µg/L; total nitrogen (TN): 5.57 mg/L] and organic pollutants [chemical oxygen demand (COD): 7.71] than other regions. Empirical analysis indicated that TP (R2 = 0.46) had a high relation with chlorophyll-a (Chl-a) compared to TN (R2 = 0.23) and TN:TP (R2 = 0.20). Elevation, stream order, and monsoon season significantly impact nutrients, organic matter, suspended particles, ionic content, and algal chlorophyll concentrations. The index of biotic integrity (IBI) was significantly positively correlated with elevation (R2 = 0.387), indicating that forest streams (high elevation) had better water quality and ecological health than lower-elevation streams. The proportion of insectivore species shows a significant negative relationship with biological oxygen demand (BOD) (R2 = 0.123) and TP (R2 = 0.155). The multi-metric index of biotic integrity (IBI) model suggested that the ecological health of forest streams was in fair condition. In contrast, agricultural streams were in poor condition, and urban upstream and downstream were in very poor conditions. The outcomes of this study indicated that land-use patterns and elevation largely regulate the water quality and ecological health of the streams.

Land Cover and Human Disturbance Impact on Water Chemistry and Ecological Health in an Asian Temperate Lotic System

The ecological integrity of lotic ecosystems is influenced by land cover type and human activity throughout the watershed. This study evaluated Nakdong River conditions in 2016 using two multi-metric models, the index of biotic integrity (IBI) and the water pollution index (WPI), and compared model outputs for four land cover types: predominantly urban, forest, barren land, and agricultural. The primary objective of this study was to determine whether the land cover type and human disturbance metrics effectively regulate water quality, fish communities, and ecological integrity in the Nakdong River basin. Predominantly forest sites had low nutrient, organic matter, suspended solids, ion, and algal chlorophyll concentrations. In contrast, these concentrations were higher in predominantly agricultural, urban, and barren land areas. Concentrations of nutrients, organic matter, ions, suspended particle loadings, and algal growth regulated by the intensity of the Asian summer monsoon. Model outputs indicated that total phosphorus (TP) was the most important factor in algal growth in agricultural (R2 = 0.25) and barren land (R2 = 0.35) sites, and evidence of P limitation was found, with TN:TP ratios >17 in ambient water. Fish community analysis indicated that tolerant species dominated the fish community in the agricultural (52%), barren land (85%), and urban sites (53%), and sensitive species were dominant in the forest sites (56%). Fish composition analysis indicated that two exotic species (Lepomis macrochirus (3.99%) and Micropterus salmoides (3.92%)) were identified as the fifth and seventh most abundant fish species in the watershed and labeled as “ecologically disturbing species” in Korea. Nutrient enrichment, organic pollution, and algal blooms enhanced the mean relative abundance of omnivorous and tolerant fish species. Mean WPI and IBI scores indicated fair or poor conditions in the agricultural (WPI: 22, IBI: 16), barren land (WPI: 21, IBI: 14), and urban (WPI: 21, IBI: 17) sites and good or fair conditions in forest (WPI: 28, IBI: 21) sites. The chemical (r = −0.34) and biological (r = −0.21) health of the river basin were negatively related to human disturbance metrics. The findings suggested that regional land cover, summer monsoon intensity, and human disturbance are important drivers of water quality, fish community, and ecological health. The resulting information suggested that agricultural diffuse pollution control, cutting-edge wastewater treatment technologies, and reducing the degrees of human disturbance could improve the Nakdong River’s ecological integrity.

Merging bio-optical data from Biogeochemical-Argo floats and models in marine biogeochemistry

Abstract. New autonomous robotic platforms for observing the ocean, i.e. Biogeochemical-Argo (BGC-Argo) floats, have drastically increased the number of vertical profiles of irradiance, photosynthetically available radiation (PAR), and algal chlorophyll concentrations around the globe independent of the season. Such data may therefore be a fruitful resource to improve performances of numerical models for marine biogeochemistry. Here we present a work that integrates 1314 vertical profiles of PAR acquired by 31 BGC-Argo floats operated in the Mediterranean Sea between 2012 and 2016 into a one-dimensional model to simulate the vertical and temporal variability of algal chlorophyll concentrations. The model was initially forced with PAR measurements to assess its skill when using quality-controlled light profiles, and subsequently with a number of alternative bio-optical models to analyse the model capability when light observations are not available. Model outputs were evaluated against co-located chlorophyll profiles measured by BGC-Argo floats. Results highlight that the data-driven model is able to reproduce the spatial and temporal variability of deep chlorophyll maxima depth observed at a number of Mediterranean sites well. Further, we illustrate the key role of PAR and vertical mixing in shaping the vertical dynamics of primary producers in the Mediterranean Sea. The comparison of alternative bio-optical models identifies the best simple one to be used, and suggests that model simulations benefit from considering the diel cycle.

Chlorophyll Detection and Mapping of Shallow Water Impoundments Using Image Spectrometry

There exists a common perception that chlorophyll a concentrations in tidal coastal waters are unsuitable to be captured by remote sensing techniques because of high water turbidity. In this study, we use band index measurements to separate active chlorophyll pigments from other constituents in the water. Published single- and multiband spectral indices are used to establish a relationship between algal chlorophyll concentration and reflectance data. We find an index which is suitable to map chlorophyll gradients in the impoundments, ditches, and associated waterways of the Hackensack Meadowlands (NJ, USA). The resulting images clearly depict the spatial distribution of plant pigments and their relationship with the biological conditions of the waters in the estuary. Since these biological conditions are often determined by land usage, the methods in this paper provide a simple tool to address water quality management issues in fragmented urban estuaries.

Estimating chlorophyll‐a concentration using first‐derivative spectra in coastal water

This study was intended to apply the technique of derivative analysis to estimate algal chlorophyll concentration in Pensacola Bay, Florida. The data collection was conducted over the 16 sampling sites on three separate occasions. A portable field spectroradiometer was used to collect the upwelling radiance of water and reference panel at each sampling station. The instrument records a continuous spectrum in 512 bands ranging from 350 nm to 1050 nm, with 1.37 nm spectral resolution. The first derivatives were computed and correlated with the chlorophyll‐a concentration. The results indicated the first derivatives at 630–645 nm, 660–670 nm, 680–687 nm and 700–735 nm were correlated strongly with chlorophyll‐a. The R values reached 0.858 for the wavelength at 686.7 nm. The results support the hypothesis that derivative spectra are less impacted by wave effects and, therefore, are an effective tool for estimating chlorophyll concentration.

Water Quality Changes in Golf Course Irrigation Ponds Transitioning to Reuse Water

Irrigation ponds on nine golf courses in southern Nevada were monitored for water quality over a 1600-day period. Three of the golf courses were fresh water courses, three were courses scheduled to transition to reuse water during the study period and three were long term users of reuse water. Salinity [electrical conductivity (EC)], NO –3-N, PO4-P, pH, algal chlorophyll concentration, clarity, temperature, oxygen, and all major cations and anions were analyzed on a monthly basis. A selected fairway on each course was equipped with water meters to assess irrigation volumes on a bimonthly basis. Estimates of salt and NO –3-N loading on fairways were made by weighting irrigation volumes with concentrations of salt (assuming 700 mg·L–1 per dS·m–1) and NO –3-N measured in the irrigation ponds. Pond spectral reflectance measurements were obtained on a single monitoring day and correlated with water quality parameters. EC, temperature, NO –3-N, PO4-P, algal chlorophyll concentration and clarity all demonstrated significant changes in all irrigation ponds that transitioned to reuse water (p < 0.05). Multiple regression analysis revealed that as much as 75% of the variability in pH in some irrigation ponds could be accounted for based on water quality parameters measured, with higher R2 values associated with elevated HCO–3 concentrations. Spectral reflectance (individual wave bands and spectral indices) was shown to be correlated with pH, clarity and algal chlorophyll concentration (R2 = 0.66** to 0.82***) with a well defined threshold relationship between clarity and the spectral index R705/R670. Average yearly NO –3-N loads on fairways averaged 8.5 kg·ha–1·yr–1 on fresh water courses, 86.5 kg·ha–1·yr–1 on transition courses and 209.8 kg·ha–1·yr–1 on long term reuse courses (all significantly different at p = 0.05). Average yearly salt loads on fairways averaged 11,959 kg·ha–1·yr–1 on fresh water courses, 14,675 kg·ha–1·yr–1 on transition courses and 27,445 kg·ha–1·yr–1 on long term reuse courses (long term significantly different at p = 0.05). Such results indicate that significant attention must be given to irrigation strategies used on reuse irrigated golf courses to properly manage for higher nitrogen and salt loads.

Relationship between Algal Chlorophyll Concentration and Spectral Reflectance of Inland Water

Relationship between Algal Chlorophyll Concentration and Spectral Reflectance of Inland Water

Survival of rice during complete submergence: effect of potassium bicarbonate application

The effect of potassium bicarbonate application to floodwater on the survival and growth of submergence-tolerant (FR13A) and -intolerant (IR42) rice cultivars during complete submergence was investigated. Potassium bicarbonate, applied at different rates to enhance floodwater carbon dioxide concentrations, increased the floodwater oxygen concentration. The treatment that had CuSO4, added alone to reduce algal growth showed the lowest O2 concentration at the time of submergence and after 10 d of submergence. Potassium bicarbonate at higher rates tended to maintain the floodwater pH near neutrality while copper sulfate affected pH increase during a 10-day period of complete submergence. Potassium bicarbonate addition led to 100% survival of tolerant FR13A. Potassium bicarbonate, even at 0.01 mol m–3 enhanced the survival of intolerant IR42 to 69% and at 0.1, 0.5 and 1.0 mol m–3, the survival was above 85%. Dry weights of submerged plants showed increases in both rice cultivars in floodwater treated with potassium bicarbonate. The dry weight and leaf chlorophyll concentration of both cultivars increased with increasing rates of potassium bicarbonate. Algal chlorophyll concentration of floodwater treated with potassium bicarbonate was comparable to that of the control without copper sulfate. The findings suggest a possibility of environmental manipulation of floodwater by potassium bicarbonate application to enhance the survival and growth of rice cultivars during complete submergence.

Comparison of NIR/RED ratio and first derivative of reflectance in estimating algal-chlorophyll concentration: A case study in a turbid reservoir

The objective of this research was to test the use of the well-documented ratio of near-infrared (NIR; 705 nm) to red (670 nm) reflectance in estimating chlorophyll content in a relatively turbid midwestern reservoir. The results were compared with those obtained by analyzing the first derivative of reflectivity near 690 nm. Data were collected in three different months over a 2-year period, and the characteristic spectral features of surface reflectance associated with algal chlorophyll were analyzed. Results indicated that the NIR/red ratio was not an effective predictor of algal-chlorophyll concentration in our case, except on one occasion. The first derivative of reflectance, on the other hand, was better correlated with chlorophyll concentration than the 705/670 band ratio. The highest correlation between the first derivative and chlorophyll was at 690.7 nm.

Production and utilization of dissolved organic carbon during an experimental diatom bloom

Stable isotope measurements of carbon were used to study the transfer of carbon from phytoplankton to bacteria during an experimental diatom bloom. A large-volume tank was filled with 900 liters of 10-µm-filtered seawater from Woods Hole Harbor, and N, P, and Si nutrients as well as 13C-enriched NaHCO3 were added. This resulted in a high nutrient system with an isotope label of +85‰ in the dissolved inorganic carbon pool. Algal growth depleted nutrients to near-zero concentrations midway through the 2-week experiment with little net dissolved organic C (DOC) accumulation; algal chlorophyll concentrations peaked at 38 µg liter−1 near the time of nutrient depletion. Decline of the algal peak was associated with diatom sedimentation to the bottom of the tank and rapid accumulation of DOC. In 3 d, DOC increased from ∼ 130 to 250 µM C. The C : N ratio of this new DOC was > 22 vs. 14 in background harbor water. 13C labeling showed that bacteria preferentially assimilated the newly produced DOC in both the rapid growth and postbloom phases of the experiment, while DOC measurements indicated that very little if any of the background DOC from Woods Hole Harbor was metabolized by bacteria during the experiment. Overall, the experiment showed rapid DOC release following algal blooms, selective use of newly produced DOC by bacteria, and that DOC released during blooms is not rapidly or completely turned over following algal blooms.

Carbon‐14 assimilation, chlorophyll, and particulate organic matter in steady state systems at Lake Tahoe1

Eight large outdoor tanks (~8,000 liters) were brought to a steady state algal population by the constant addition of Lake Tahoe water alone or combined with 0.1 and 1.0% additions of secondary or tertiary sewage effluents. 14C assimilation rates and chlorophyll concentrations were related to growth rate and limiting nutrient. This result would be expected from the kinetics of a steady state (chemostat) system. Radioactive carbon fixation values underestimated the productivity of the phytoplankton as measured by the weight of the particulate organic matter produced per residence time. 14C assimilation rates were highly correlated with algal chlorophyll concentration but poorly correlated with particulate organic matter concentration in the tanks at steady state.