Mark W. Clark

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...

Reflectance spectroscopy for routine agronomic soil analyses

Near-infrared reflectance spectroscopy is a demonstrated tool for quantitative analysis of numerous soil properties. Reported advantages include analytical precision, predictive accuracy, and reduced costs and processing times. A library (N = 1933) representing all major soil orders in Florida was assembled from samples submitted to the University of Florida Extension Soil Testing Laboratory for routine testing during 2004-2005. High-resolution diffuse reflectance spectra from each sample in the visible/near infrared were used to predict observations made using standard laboratory analytical procedures for soil pH, Mehlich-1-extractable P, K, Ca, Mg, Cu, Mn, and Zn, percentage of organic matter, and saturated hydraulic conductivity (Ksat). Calibrations were immediately applicable for organic matter and Al, based on relative performance determinant values (RPD = standard deviation/standard error of validation > 2.0). Models for pH, P, Ca, and Ksat showed moderate accuracy (1.5 < RPD < 2.0), whereas those for K, Cu, Mg, Mn, Zn, and Fe exhibited low efficiency (RPD < 1.5), indicating a need for further refinement before near-infrared reflectance spectroscopy is a viable alternate method to standard laboratory procedures. Prediction of soil fertility and productivity based on published Florida soil diagnostic categories showed effective discrimination for pH, P Mg, Mn, Cu (phytotoxicity), and Ksat. Our study showed that prediction efficiency is a strong function of mean nutrient/analyte concentration in the soil. We further demonstrated that near-infrared reflectance spectroscopy error rates were comparable to, and in some cases smaller than, laboratory analytical error rates, suggesting that the observed low spectral prediction efficiency may be substantially because of uncertainty in the laboratory data.

BIOGEOCHEMICAL INDICES OF PHOSPHORUS RETENTION AND RELEASE BY WETLAND SOILS AND ADJACENT STREAM SEDIMENTS

Eutrophication is still a water quality problem within many watersheds. The Lake Okeechobee Basin, Florida, USA, like many watersheds is impacted by eutrophication caused by excess phosphorus (P). To meet water quality criteria to reduce this impairment, several levels of information on P dynamics within the Basin are required. The use of biogeochemical indices to help determine P retention/release of different landscape units such as wetlands and streams provides useful information on P dynamics. The objective of our study was to determine P retention/release indices for a range of wetland soils and their adjacent stream sediments. We sampled several wetlands and adjacent streams within Okeechobee’s Basin, which represented a range of P impacted systems. Regression analyses suggest that a single incubation of sediment/soil equilibrated at 1000 mg P kg-1 was sufficient (> 96% of the time) to estimate maximum P sorption capacity (Smax). Using this single incubation, sampled wetlands had nearly twice the P sorption capacity (238 ± 21 mg P kg−1) of stream sediments (146 ±14 mg P kg−1). Stream sediments also had a greater P saturation ratio (PSR) than wetland soils, indicating that sediment had a greater potential to release P. Phosphorus sorption under ambient P conditions (soil equilibrated with ambient site water) covaried best with P concentrations in site surface water and, as concentrations increased, P sorption also increased. Finally, we used soil P storage capacity (SPSC) to help estimate the ability of soils and sediments to retain additional P loadings and found that wetland soils had a greater ability to retain P. Phosphorus sorption was predicted equally well (> 73%) using either ammonium oxalate or 1 M HC1 extractable Fe and Al. The use of indices to quantify P dynamics of different landscape units can inform watershed management and policies aimed at reducing P loads to receiving water bodies.

Phosphorus release and retention by soils of natural isolated wetlands

Hydrological restoration of historically isolated wetlands may mitigate phosphorus (P) loss. The objectives of this study were to quantify P in soil, and to determine the effect of (1) soil characteristics on P release, and (2) antecedent soil hydrological conditions on P dynamics. Humic/fulvic acid bound P and residual P accounted for majority of P (>78%) in surface soils. Soils with highest nutrient status and labile P fractions released most P during initial flooding. Phosphorus dynamics during additional flooding were dependent on soil characteristics, antecedent soil hydrological conditions, and P levels in the water. Phosphorus retention varied between 0.3 and 8 mg m-2 d-1.

Development of indices to predict phosphorus release from wetland soils.

The U.S. Environmental Protection Agency created the Clean Water Action Plan to develop nutrient criteria for four water body types: lakes and reservoirs, rivers and streams, estuaries, and wetlands. Significant progress has been made in open water systems. However, only areas in and around the Florida Everglades have had numeric nutrient criteria set, due to the complexity, heterogeneity, and limited information available for wetlands. Our objective was to evaluate various soil tests to predict significant P release potential of soil in wetlands. A total of 630 surface soil samples (0-10 cm) were collected for this study from four southeastern states: Florida, Alabama, Georgia, and South Carolina. Soil samples were collected from the center of wetlands, the edge of the wetlands, and from adjacent uplands. The phosphorus saturation ratios (PSR), calculated using P, Fe, and Al molar concentrations from Mehlich 1 (M1-PSR), Mehlich 3 (M3-PSR), and oxalate (Ox-PSR) extractions and the amount of P extracted by different extractants were used to predict P loss potential from a soil. Total phosphorus (TP) concentration in wetland soils, estimated as the 75th percentile of the distribution of least impacted wetland soils as an example, was approximately 550 mg kg(-1). Based on this reference background condition, procedures for obtaining threshold values for P release to the surrounding water bodies were developed and threshold values calculated: M1-P = 24 mg kg(-1), M3-P = 44 mg kg(-1), Ox-PSR = 0.079, M1-PSR = 0.101, and M3-PSR = 0.067.

Kinetics of boron reactivation in doped silicon from Hall effect and spreading resistance techniques

In this work, a series of 13 boron implants were performed into Czochralski silicon substrates with doses of 2×1014–1.6×1015 cm−2 at energies of 10–80 keV. The boron was deliberately clustered with a 750 °C anneal of 10 or 30 min and the electrical activation of the boron implants was determined following a second anneal at 750 or 850 °C with a Hall effect system with certain samples also being analyzed with a spreading resistance technique. Analysis of the reactivation rates allows for the determination of the net energy to boron reactivation to be approximately 3.0 eV assuming the reactivation process is mediated by release of a boron interstitial with a migrational energy of 0.3 eV. This results in a critical binding energy of approximately 2.7 eV from the process limiting the dissolution of the most stable boron-interstitial cluster.

Evaluation of a Denitrification Wall to Reduce Surface Water Nitrogen Loads

Denitrification walls have significantly reduced nitrogen concentrations in groundwater for at least 15 yr. This has spurred interest in developing methods to efficiently increase capture volume to reduce N loads in larger watersheds. The objective of this study was to maximize treatment volume by locating a wall where a large groundwatershed was funneled toward seepage slope headwaters. Nitrogen concentration and load were measured before and after wall installation in paired treatment and control streams. Beginning 2 d after installation, nitrogen concentration in the treatment stream declined from 6.7 ± 1.2 to 3.9 ± 0.78 mg L and total N loading rate declined by 65% (391 kg yr) with no corresponding decline in the control watershed. This wall, which only comprised 10 to 11% of the edge of field area that contributed to the treatment watershed, treated approximately 60% of the stream discharge, which confirmed the targeted approach. The total load reduction measured in the stream 155 m downstream from the wall (340 kg yr) was higher than that found in another study that measured load reductions in groundwater wells immediately around the wall (228 kg yr). This indicated the possibility of an extended impact on denitrification from carbon exported beyond the wall. This extended impact was inauspiciously confirmed when oxygen levels at the stream headwaters temporarily declined for 50 d. This research indicates that targeting walls adjacent to streams can effectively reduce N loading in receiving waters, although with a potentially short-term impact on water quality.

P-sorption capacity estimation in southeastern USA wetland soils using visible/near infrared (VNIR) reflectance spectroscopy

Phosphorus (P) is frequently the limiting nutrient in aquatic ecosystems, so wetland P attenuation is of particular landscape importance. Providing reliable knowledge about the capacity of wetlands to provide P sequestration is limited by knowledge of soil sorption capacities. We examined P-sorption in wetland soils using samples (n = 326) collected from 171 wetlands across three southeastern ecoregions, stratifying by land use intensity (reference vs. impacted), vegetation (forested vs. herbaceous), and hydrologic setting (riverine vs. non-riverine). Single-point isotherm values ranged from −73 to 990 mg P kg−1 (mean = 462.7 ± 295.2 mg P kg−1). Using a mixed-effects ANOVA, no significant P-sorption differences were observed for vegetation or condition, and only a moderate effect of hydrology (p = 0.01). We observed a strong ecoregion effect (Regions IX ≈ XIV > XII; p < 0.001) and a strong interaction between ecoregion and condition (p < 0.001). Site-level and within-site random effects were both significant (p < 0.001 and p = 0.04, respectively), though the latter were small. The overall model explained only 29% of observed variance, suggesting limited generality for prediction. Given increased sample density requirements for assessment of P-sorption, pedotransfer functions (PTF), which estimate hard-to-measure properties from more readily observable properties, may be useful. We developed and validated two PTF models by relating observed sorption with 1) biogeochemical P-sorption covariates (total P/C, water extractable P, oxalate extractable Fe/Al/P/Ca/Mg) and 2) visible/near-infrared (VNIR) diffuse reflectance spectra. Advantages of VNIR for predicting soil properties include low cost, high sample throughput, minimal sample preparation and reagent waste, and high analytical precision. Standard error of prediction (SEP), r2, and relative performance determinant (RPD) values were compared between PTF models for hold-out validation data. Models were of comparable utility; with SEP values of 144.1 vs. 157.2 mg P kg−1, r2 values of 0.61 vs. 0.69, and RPD values of 1.61 vs. 1.88 for the biogeochemical vs. VNIR models, respectively. Given other advantages of using VNIR spectra, it appears to be a useful tool for mapping and monitoring P sorption in wetland soils.

Evaluation of Legacy Phosphorus Storage and Release from Wetland Soils.

To better manage legacy phosphorus (P) in watersheds, reliable techniques to predict P storage and release from uplands, ditches, streams, and wetlands must be developed. Techniques such as the P saturation ratio (PSR) and the soil P storage capacity (SPSC), originally developed for upland soils, are hypothesized to be applicable to wetland soils as well. Surface soils were collected from eight beef ranches within the Lake Okeechobee Watershed, FL, to obtain a threshold PSR value and to evaluate the use of PSR and SPSC for identifying legacy P storage and release from wetland soils. Water-soluble P (WSP) was determined for all soils; the equilibrium P concentration (EPC) was determined for selected soils through the generation of Langmuir isotherms. The threshold PSR for wetland soils, calculated from P, Fe, and Al in a Mehlich 1 solution, was determined to be 0.1; SPSC, calculated using the threshold PSR, was found to be related to WSP. When SPSC was positive, WSP and EPC were minimal. However, both WSP and EPC increased once SPSC became negative. Organic matter (OM) varied from 0.4 to 90 g kg for both positive and negative SPSC, suggesting that OM in wetland soils does not have any effect on P retention and release below the threshold PSR. Moreover, when a wetland or drainage ditch is heavily P impacted, it could be a P source; wetland vegetation may no longer be able to assimilate additional P, resulting in P loss from the soil. This study suggests that the PSR-SPSC concept could be a valuable tool for evaluating legacy P release from wetlands.

Greenhouse Gas Emissions Under Different Drainage and Flooding Regimes of Cultivated Peatlands

Globally, approximately 10–20 % of peatlands have been drained for agricultural purposes. A strategy to protect peatlands and mitigate carbon dioxide (CO2) emissions, while continuing agricultural production, is the use of intermittent flooding and drainage. A potential drawback of this strategy could be increases in methane (CH4) and nitrous oxide (N2O) emissions. The objective of this study was to compare greenhouse gas (GHG) emissions from peatlands under various flooding-drainage cycles. A laboratory study was performed using intact soil cores subjected to different durations of flooding and drainage for 6 months. Average daily emissions of CO2 and N2O were significantly higher (P < 0.001) under drained (667 ± 37 mg CO2-C m-2 d-1 and 135 ± 19 μg N2O-N m-2 d-1) than flooded conditions (86 ± 6 mg CO2-C m-2 d-1 and 48 ± 2 μg N2O-N m-2 d-1). Methane emissions were not influenced by drained/flooded conditions, with an average rate of 116 ± 11 μg CH4-C m-2 d-1. Peaks of CH4 and N2O emissions were observed after flooding events and lasted less than 24 h. The peak emissions were approximately 8 and 19 times higher than the mean CH4 and N2O emissions, respectively. Carbon dioxide was the dominant component of GHGs, irrespective of hydrologic regime, accounting for more than 92% of overall global warming potential (GWP). Global warming potential was inversely proportional to the flooding period, indicating that prolonging the flooding period of peatlands would help mitigate soil oxidation and GHG emissions, and enhance sustainability of these agricultural peatlands.