Algal blooms in freshwater ecosystems can negatively impact aquatic and human health. Satellite remote sensing of chlorophyll a (Chl-a) is often used to help determine the severity of algal blooms. However, satellite revisit flyover schedules may not match the erratic nature of algal blooms. Studies have paired satellite and ground-based data that were not collected on the same day, assuming Chl-a concentrations did not change significantly by the flyover date. We determined the effects of an increasing time window between satellite overpass dates and field-based collection of Chl-a on algorithms for Landsat 5, Landsat 8, and Sentinel-2, using 14 years (2006–2020) of Chl-a data from 10 Oklahoma reservoirs. Multiple regression models were built, and selected statistics were used to rank the time windows. The Sentinel-2 results showed strong relationships between Chl-a and satellite data collected up to a ±5-day window. The strength of these relationships decreased beyond a ±3-day time window for Landsat 8 and a ±1-day time window for Landsat 5. Our results suggest that the time window between field sampling and satellite overpass can impact the use of satellite data for Chl-a monitoring in reservoirs. Furthermore, longer time windows can be used with higher resolution (spatial, spectral) satellites.

Effective treatment options are needed for the management of aquatic invasive species. An herbicide treatment was used to control an invasive aquatic plant, yellow floating heart (Nymphoides peltata) in a 3350-acre drinking water reservoir. The purpose of this research was to document the success of the treatment in an individual cove of the reservoir using in-situ sampling and reservoir-wide using remotely sensed Sentinel-2 satellite imagery. We also determined if the dying vegetation negatively impacted biological oxygen demand and dissolved oxygen concentrations in the cove. The aquatic herbicide ProcellaCOR™ (active ingredient = florpyrauxifen-benzyl) was used to treat a 55-acre infestation of YFH at a rate of 3 Prescription Dose Units (PDU)/ac-ft by a certified applicator in July 2019. Total surface coverage of yellow floating heart in the reservoir was reduced by more than 90% within 15 days after the treatment, and to less than 3.0 acres within 50 days after the treatment. No blooming flowers were observed after treatment and the surface coverage was close to 0% within 17 days after treatment in the cove. The effect of the herbicide treatment also appeared to carry over into the following growing season as the total surface coverage of yellow floating heart in the reservoir was less than 8 acres one year after the treatment in July 2020. The herbicide treatment resulted in short term increases in biological oxygen demand and decreases in dissolved oxygen at some sites in the cove within 3-10 days after the treatment. Dissolved oxygen then increased and concentrations were greater 42 days after treatment than they were before the treatment. Our results show that ProcellaCOR™ has the potential to control yellow floating heart infestations with relatively short-term negative impacts on dissolved oxygen concentrations. We also show that Sentinel-2 satellite imagery can be used to monitor the success of herbicide applications over large spatial and temporal scales that would not be possible from ground based monitoring alone.

Agricultural runoff transports sediments and nutrients that deteriorate water quality erratically, posing a challenge to ground-based monitoring. Satellites provide data at spatial-temporal scales that can be used for water quality monitoring. PlanetScope nanosatellites have spatial (3 m) and temporal (daily) resolutions that may help improve water quality monitoring compared to coarser-resolution satellites. This work compared PlanetScope to Landsat-8 and Sentinel-2 in their ability to detect key water quality parameters. Spectral bands of each satellite were regressed against chlorophyll a, turbidity, and Secchi depth data from 13 reservoirs in Oklahoma over three years (2017–2020). We developed significant regression models for each satellite. Landsat-8 and Sentinel-2 explained more variation in chlorophyll a than PlanetScope, likely because they have more spectral bands. PlanetScope and Sentinel-2 explained relatively similar amounts of variations in turbidity and Secchi Disk data, while Landsat-8 explained less variation in these parameters. Since PlanetScope is a commercial satellite, its application may be limited to cases where the application of coarser-resolution satellites is not feasible. We identified scenarios where PS may be more beneficial than Landsat-8 and Sentinel-2. These include measuring water quality parameters that vary daily, in small ponds and narrow coves of reservoirs, and at reservoir edges.

Groundwater depletion is a serious issue in the southern and central parts of the High Plains Aquifer (HPA), USA. A considerable imbalance exists between the recharge process and groundwater extractions in these areas, which threatens the long-term sustainability of the aquifer. Irrigated agriculture has a major share in the economy, and it requires high pumping rates in regions vulnerable to large groundwater level declines. A literature review has been conducted to understand the state of affairs of irrigated agriculture in the HPA, along with the dynamics of groundwater decline and recharge using statistical and remote-sensing based datasets. Also, three irrigation management and technology-based approaches have been discussed from the perspective of sustainability. The southern and central parts of the HPA consist mostly of non-renewable groundwater formations, and the natural water storage is prone to exhaustion. Moreover, the aforementioned regions have comparatively higher crop water requirement due to the climate, and irrigating crops in these regions puts stringent pressure on the aquifer. The upper threshold of irrigation application efficiency (IAE) is high in the HPA, and could reach up to 95%; however, considerable room for improvement in irrigation water management exists. In general, the practices of irrigation scheduling used in the HPA are conventional and a small proportion of growers use modern methods to decide about irrigation timing. Among numerous ways to promote sustainable groundwater use in the HPA, deficit irrigation, use of soil moisture sensors, and subsurface drip irrigation can be considered as potential ways to attain higher lifespans in susceptible parts of the aquifer.

Globally, contamination of water bodies by microbial pathogens is a significant public health concern. Fecal indicator bacteria such as Escherichia coli (E. coli) typically identify the deterioration of water bodies. In order to determine water quality, monitoring E. coli concentrations is important. During collection, storage, and transportation of water samples, holding time can have a significant impact on the density of indicator pathogens. Although many studies have reported on the effects of holding time exceedances on water quality, there is a lack of comprehensive review of these studies. The objective of this work is to provide a complete review on the effects of holding time exceedances on water quality. The results of this study suggest that most E. coli samples can be analyzed beyond 8 hr and up to 48 hr after sample collection while still generating comparable data if the samples are stored below 10°C.

Grand Lake O’The Cherokees, the third largest reservoir located in northeastern Oklahoma, provides recreational services, water supply, hydroelectric power, and flood control to residents of Oklahoma and neighboring states. Grand Lake has experienced major problems with eutrophication, harmful algal blooms, and dissolved oxygen (DO) depletion during summer. To better understand the dynamics of DO depletion in the hypolimnion of Grand Lake, a three-layer steady state vertical DO model for summer-stratified conditions was used to investigate dissolved oxygen profiles both above and below the thermocline. The DO model was used to determine the relative effects of atmospheric reaeration and phytoplankton production as a source of DO and phytoplankton respiration, decomposition of organic matter, and nitrification as loss terms for DO. Additionally, the importance of sediment oxygen demand (SOD) for hypolimnetic oxygen depletion was investigated at the sediment water-interface under stratified conditions. Observed water quality data, kinetic coefficients from the literature, and physical, biological, and chemical data collected throughout 2013 and 2015 along the spatial gradient of riverine, transition, lacustrine zones and a site close to the Grand Lake Pensacola Dam were used in the pre-processing calculations to derive estimates of kinetic rates as input parameters to the model. The estimated predictions from the model showed reasonable agreement with the observed vertical profiles of DO. Conclusions from this study indicate that phytoplankton production, high light limitation, and phosphorus were the major terms that controlled DO production in the surface layer, while nitrification and organic carbon decomposition were the major sinks of DO consumption in the bottom layer. Interestingly, SOD did not play a significant role in DO depletion in the water column.

In the United States, many state and federally funded conservation programs are required to quantify the water quality benefits resulting from their efforts. The objective of this research was to evaluate the impact of conservation practices subsidized by the Oklahoma Conservation Commission on phosphorus and sediment loads to Lake Wister. Conservation practices designed to increase vegetative cover in grazed pastures were evaluated using Landsat imagery and the Soil and Water Assessment Tool (SWAT). Several vegetative indices were derived from Landsat imagery captured before and after the implementation of conservation practices. Collectively, these indicators provided an estimate of the change in vegetative soil cover attributable to conservation practices in treated fields. Field characteristics, management, and changes in vegetative cover were used in the SWAT model to simulate sediment and phosphorus losses before and after practice implementation. Overall, these conservation practices yielded a 1.9% improvement in vegetative cover and a predicted sediment load reduction of 3.5%. Changes in phosphorus load ranged from a 1.0% improvement to a 3.5% increase, depending upon initial vegetative conditions. The use of fertilizers containing phosphorus as a conservation practice in low-productivity pastures was predicted by SWAT to increase net phosphorus losses despite any improvement in vegetative cover. This combination of vegetative cover analysis and hydrologic simulation was a useful tool for evaluating the effects of conservation practices at the basin scale and may provide guidance for the selection of conservation measures subsidized in future conservation programs.

Problem statement: Wister Lake is located in the San Bois Mountains in southeastern Oklahoma, USA. The reservoir is primarily used as a water supply and flood storage to over 40,000 residents in the area. Due to high levels of phosphorus and sediment, Wister Lake is listed as a high priority basin for the State of Oklahoma. To help address these water quality problems, the Oklahoma Conservation Commission provided cost share funds for landowners in the basin to implement conservation practices. Approach: The objective of this study was to identify or target agricultural land that contributed disproportional pollutant losses, i.e. critical source areas. Results: Implementing conservation practice in these critical source areas allowed optimal placement conservation practices. The Soil and Water Assessment Tool (SWAT) model was used to identify critical source areas of phosphorus and sediment in the Wister Lake basin. SWAT predicted 57,000 metric tons a year of sediment and 84,000 kilograms a year of total phosphorus from upland areas in the basin. Eighty-five percent of the pollutant load originated from just 10% of the basin. Conclusion/Recommendations: This allowed the OCC to identify and contact specific agricultural producers to recruit into their water quality program, which optimized the use of limited cost share funds.

Areas with disproportionately high pollutant losses (i.e., critical source areas [CSAs]) have been widely recognized as priority areas for the control of nonpoint-source Pollution. The identification and evaluation of CSAs at the watershed scale allows state and federal programs to implement soil and water conservation measures where they are needed most. Despite many potential advantages many state and federal conservation programs do not actively target CSAs. There is a lack of research identifying the total CSA pollutant contribution at the watershed scale, and there is no quantitative assessment of program effectiveness if CSAs are actively targeted. The purpose of this research was to identify and quantify sediment and total phosphorus loads originating from CSAs at the watershed scale using the Soil and Water Assessment Tool. This research is a synthesis of CSA targeting studies performed in six Oklahoma priority watersheds from 2001 to 2007 to aid the Oklahoma Conservation Commission in the prioritized placement of subsidized conservation measures. Within these six watersheds, 5% of the land area yielded 50% of sediment and 34% of the phosphorus load. In watersheds dominated by agriculture, the worst 5% of agricultural land contributed, on average, 22% of the total agricultural pollutant load. pollutant loads from these agricultural CSAs were more than four times greater than the average load from agricultural areas within the watershed. Conservation practices implemented in these areas can be more effective because they have the opportunity to treat more pollutant. The evaluation of CSAs and prioritized implementation of conservation measures at the watershed scale has the potential to significantly improve the effectiveness of state and federally sponsored water quality programs.