Sanjay Shukla

Paying for environmental services from agricultural lands: an example from the northern Everglades

There is growing interest in implementing market-like programs that would pay farmers and ranchers for producing environmental services (beyond those that generate food and fiber) from working agricultural lands. However, few examples exist of programs that pay directly for quantified services. Since 2005, a coalition of non-governmental environmental organizations, state and federal agencies, ranchers, and researchers has been developing a Pay-for-Environmental Services (PES) program that would compensate cattle ranchers in Floridas northern Everglades region for providing water storage and nutrient retention on private lands. We use our experience with this program to identify key challenges to PES program design, including identifying a buyer and defining the environmental services; agreeing upon credible, yet practical, approaches to quantifying the services provided; reducing programmatic costs in light of existing policies and complex regulatory issues; and maintaining an adaptive approach to progr...

Evaluating, interpreting, and communicating performance of hydrologic/water quality models considering intended use: A review and recommendations ☆

Abstract Previous publications have outlined recommended practices for hydrologic and water quality (H/WQ) modeling, but limited guidance has been published on how to consider the projects purpose or models intended use, especially for the final stage of modeling applications – namely evaluation, interpretation, and communication of model results. Such guidance is needed to more effectively evaluate and interpret model performance and more accurately communicate that performance to decision-makers and other modeling stakeholders. Thus, we formulated a methodology for evaluation, interpretation, and communication of H/WQ model results. The recommended methodology focuses on interpretation and communication of results, not on model development or initial calibration and validation, and as such it applies to the modeling process following initial calibration. The methodology recommends the following steps: 1) evaluate initial model performance; 2) evaluate outliers and extremes in observed values and bias in predicted values; 3) estimate uncertainty in observed data and predicted values; 4) re-evaluate model performance considering accuracy, precision, and hypothesis testing; 5) interpret model results considering intended use; and 6) communicate model performance. A flowchart and tables were developed to guide model interpretation, refinement, and proper application considering intended model uses (i.e., Exploratory, Planning, and Regulatory/Legal). The methodology was designed to enhance application of H/WQ models through conscientious evaluation, interpretation, and communication of model performance to decision-makers and other stakeholders; it is not meant to be a definitive standard or a required protocol, but together with recent recommendations and published best practices serve as guidelines for enhanced model application emphasizing the importance of the models intended use.

Rainfall Intensity-Duration-Frequency Relationships for Andhra Pradesh, India: Changing Rainfall Patterns and Implications for Runoff and Groundwater Recharge

Accurate and current rainfall characterization is an important tool for water-related system design and management. Updated rainfall intensity-duration-frequency (IDF) relationships in peninsular India were developed; impacts on runoff and groundwater recharge attributable to changes in rainfall characteristics are discussed. Two data sets were used from gage in Hyderabad city, the capital of Andhra Pradesh: hourly rainfall data for the 19 years from 1993–2011 and daily rainfall data for the 30 years from 1982–2011. Hourly data were used to develop updated rainfall IDF relationships; daily data were used for trend analysis of threshold-based rainfall events. IDF curves were developed for return periods of 2, 5, 10, 15, 25, 50, 75, and 100 years for 1-, 2-, 4-, 8-, and 24-h durations. The updated IDF relationships showed a significant change in rainfall characteristics compared with older relationships for the region surrounding Hyderabad, India; they showed greater rainfall intensities across all durations and return periods. Greater intensity storms may reduce groundwater recharge and increase runoff, making the surface storage of runoff increasingly important to enhance recharge and reduce flooding risks.

MIKE SHE: Model Use, Calibration, and Validation

MIKE SHE is a physically based, integrated water resources model that simulates both surface and subsurface water dynamics. These dynamics include interception, evapotranspiration, overland flow, channel flow, unsaturated flow, and saturated zone flow. The model can also simulate limited surface water quality processes using the advection dispersion equation and groundwater quality with a random-walk tracking method. This article is intended to describe the components of MIKE SHE and its calibration, validation, and applications. Given the deterministic, physically based characteristics of MIKE SHE and the large number of processes it simulates simultaneously, the number of parameters to calibrate can be large. A combination of user experience with the model, knowledge of the problem being solved, and an automatic calibration feature help in selecting the most sensitive parameters to calibrate. A case study describing the use of the MIKE SHE model, coupled with the hydraulic MIKE 11 model, to solve water flow in agricultural reservoirs in south Florida is presented. The problem required the use of the MIKE SHE model due to the high groundwater and overland flow interactions as well as the complex flow patterns inside the reservoir. The horizontal and vertical saturated hydraulic conductivities and the leakage coefficient were identified as the calibration parameters. The model was calibrated and evaluated for two reservoirs using two different time periods. Results showed matching between measured and simulated data for both reservoirs for the calibration and validation periods. The coupled MIKE SHE/MIKE 11 model has the capabilities to simulate complex hydrological processes and their interactions, which few other watershed models can match, and is suitable for current problems, such as the effects of climate change and land use change.

Impact of Organic Amendments on Groundwater Nitrogen Concentrations for Sandy and Calcareous Soils

Experiments were conducted on calcareous and sandy soils to investigate the effects of organic amendments for vegetable production on groundwater nitrogen (N) concentration in south Florida. The treatments consisted of applying yard and food residuals compost, biosolids compost, a cocompost of the municipal solid waste and biosolids, and inorganic fertilizer. Nitrate nitrogen (NO3-N), ammonium nitrogen (NH4-N), and total N concentrations were collected for a period of two years for both soils. Statistical analysis results revealed that for the three species tested, there were no significant differences among treatments. NO3-N concentrations for all treatments remained less than the maximum contamination level (10 mg/L). NO3-N transport to groundwater was higher in calcareous soil (mean=5.3 mg/L) than in sandy soil (mean=0.6 mg/L). NH4-N concentrations ranged from 0 to 13.6 mg/L throughout the experiment. Calcareous soil had lower NH4-N concentrations (mean=0.1 mg/L) than sandy soils (mean=0.7 mg/L). Total N ranged from 0.4 to 21.7 mg/L for all treatments for both soils reflecting high adsorption of dissolved organic N in both soils. Overall, results indicated that all the compost treatments were comparable to inorganic fertilizer with regard to N leaching and N concentrations in the groundwater while producing similar or higher yields.

Effects of Composted Yard Waste On Water Movement in Sandy Soil

A two-year study was conducted in 2002-2003 (season one) and 2003-2004 (season two) at a seepage irrigated vegetable farm in south Florida to investigate the effects of soil organic amendment (composted yard waste) on movement of water in a sandy soil. Season one result showed that for the same water table depth, soil moisture content in the compost field was higher than the noncompost field in the root zone (top 20 cm). The increased soil moisture was attributed to the increased upflux due to increased capillary rise. Increased capillary rise was a result of increased organic matter content of the soil from compost application. After a rainfall event, soil moisture at 10 cm depth in the compost field responded rapidly, suggesting a higher extent of capillary fringe in the compost field compared to the noncompost field, which did not show the similar response. Another addition of compost further enhanced the soil moisture effect in season two. Season two results showed a higher difference between compost and noncompost soil moisture from the previous season. Results from the study showed that the addition of compost can help in maintaining the same level of soil moisture with a lower water table compare to the noncompost field. A lower water table in the compost field can result in higher retention of rainfall in the soil compared to the noncompost field, which in turn can reduce runoff, deep percolation, and seepage losses and achieve water conservation.

DESIGN, CONSTRUCTION, AND INSTALLATION OF LARGE DRAINAGE LYSIMETERS FOR WATER QUANTITY AND QUALITY STUDIES

Six large drainage lysimeters (4.85 × 3.65 × 1.35 m) were designed, constructed, and installed for quantifying crop coefficients and water quality impacts of drip and seepage irrigated watermelon in south Florida. Monitoring systems designed for the lysimeters included water quantity (irrigation, rainfall, runoff, drainage, soil moisture, and water table depth) and quality (nutrient concentrations in the root zone, saturated zone, drainage, and runoff). Lysimeters, made of mild steel plate, containing two plastic mulch plant beds and an irrigation ditch, were installed in a watermelon field. The soil profile (A and E horizons) was reconstructed using native soil from the field. Bi-weekly soil solution and saturated zone samples, and event-based drainage and runoff water quality samples were collected and analyzed for nitrogen (NH4-N, NO3-N, TKN) and total phosphorus. The watermelon crop was planted on plastic mulch beds. Four lysimeters received drip irrigation and two received seepage irrigation. Preliminary data for the first six weeks of watermelon crop for the drip and seepage irrigation systems indicated that lysimeters were working properly. Seepage lysimeter systems had higher ETc compared with drip irrigated lysimeters due to wetter soil and high evaporation losses during irrigation. Water quality data showed that total dissolved nitrogen discharges from the seepage lysimeters were higher than the drip lysimeters. Lower nitrogen loadings for the drip lysimeters were mainly attributed to higher soil water storage capacity and fertigation. The design and installation described in this study will be helpful for future studies with large lysimeters.

SIMULATING WATER DYNAMICS IN AGRICULTURAL STORMWATER IMPOUNDMENTS FOR IRRIGATION WATER SUPPLY

The hydrology of an impoundment in an agricultural grove in southern Florida was studied to assess its potential use as a water supply source. The MIKE SHE/MIKE 11 integrated hydrologic model was used to simulate the various hydrologic processes and their interactions. The model was calibrated and validated for water levels inside the impoundment and in a ditch outside the impoundment. Model evaluation results showed that the model could be used for assessing water retention alternatives with root mean square error (RMSE) values ranging from 0.03 to 0.25 m. Several structural and managerial alternatives were identified and evaluated to increase water retention volume and time. The alternatives include lining the impoundment, lining only the embankment and the inner distribution canal with 15 and 30 cm liner thicknesses, and pumping water regularly from the surrounding ditch to the impoundment. All alternatives were compared to the present condition. Lining the entire impoundment with clay provided ten weeks of additional irrigation from September to May. Lining the embankment and the inner canal of the impoundment provided up to four weeks of additional irrigation. Extending the regular pumping for a month after the wet season resulted in the reservoir being filled to full capacity during that month. The modeling study shows that clay-lining impoundments could provide an additional source of irrigation.

Water and nitrogen management effects on water and nitrogen fluxes in Florida Flatwoods.

The effects of water and fertilizer best management practices (BMPs) have not been quantified for groundwater nitrogen (N) beneath seepage irrigated vegetable fields with shallow water table environments. This effect was evaluated by a 3-yr study conducted in the Flatwoods of south Florida for watermelon ( cv. Mardi Gras and Tri-X 313) and tomato ( cv. BHN 586) using three treatments of water and inorganic fertilizer N (N) rates: (i) high fertilizer and water rates with seepage irrigation (HR), (ii) recommended fertilizer and water rates (BMP) with seepage irrigation (RR); and (iii) RR with subsurface drip irrigation (RR-SD). These treatments were implemented on six hydraulically isolated plots. The N rate treatments for high (HR) and recommended (RR and RR-SD) were based on a grower survey and BMP recommendations, respectively. Water applied, water table depth, and soil moisture content were regularly monitored for each treatment. Plant, soil, and groundwater N sampling and analyses were conducted for each season of the 3-yr study. The average water applied in HR (187 cm) was greater than RR (172 cm) and RR-SD (94 cm). Soil N maintained in crop beds for HR was significantly higher than RR and RR-SD. Soil solution analyses showed that N leached beneath HR (112 mg L) was greater ( = 0.053) than RR (76 mg L) and RR-SD (88 mg L). Shallow groundwater concentrations of dissolved inorganic nitrogen (NH-N + NO-N) were higher ( = 0.02) in HR (37 mg L) compared with RR (15 mg L) and RR-SD (19 mg L). Decreased N and water table levels can improve groundwater quality by reducing N leachate in shallow water table environments with seepage irrigated vegetable production systems.

Groundwater Phosphorus and Trace Element Concentrations from Organically Amended Sandy And Calcareous Soils of Florida

The effects of organic amendments on vegetable crop production, phosphorus (P), and trace element (Zn, Cu, Mn, B, Cd, Pb, Ni) concentrations in groundwater were investigated on calcareous and sandy soils in south Florida. Treatments consisted of applying yard trash and food compost, biosolids compost, a cocompost of municipal solid waste and biosolids, and inorganic fertilizer. A randomized complete block design with four replications was used at both study sites. Total Kjeldahl phosphorus (TKP) and soluble reactive phosphorus (SRP) were periodically measured in grab samples collected for two years for both soils from wells above and below the spodic horizon at Ft. Pierce and from one depth at Homestead. Treatments were similar (P > 0.05) except on two sampling dates from the deep wells in the sandy soil at Ft. Pierce, one for SRP and one for TKP. Phosphorus concentrations for all treatments averaged < 1.2 mg SRP L−1 at Ft. Pierce and 0.04 mg SRP L−1 for the calcareous soil at Homestead. From solely a P consideration, organic P sources could be used to offset all or a portion of P required to satisfy vegetable crop nutrient requirements. This statement is consistent with crop yields at Ft. Pierce where yields from the three organic sources were equal to or exceeded inorganic fertilization yields. Micronutrient and trace element concentration responses to organic treatments were more pronounced at Ft. Pierce, perhaps due to soil chemical conditions including lower soil pH. The cocompost should be used cautiously to avoid contamination problems, especially when application rates are based on N fertilization as in this study. Due to the calcareous soil at Homestead, trace element concentrations in the groundwater were considerably lower than Ft. Pierce concentrations. However, the cocompost source was elevated for lead (Pb) (P < 0.05) compared with all other treatments, although higher concentrations were observed only on one sampling date. Results from this study indicated that, combined with the environmental benefits of recycling waste, the use of these organic amendments is a viable alternative to inorganic P fertilizers in the sandy and calcareous soils of peninsular Florida. The compost treatments were comparable to inorganic fertilizer with regard to P concentrations in the groundwater while producing similar or higher vegetable crop yields.