Soil carbon sequestration resulting from long-term application of biosolids for land reclamation.

Investigations on the impact of application of biosolids for land reclamation on C sequestration in soil were conducted at Fulton County, Illinois, where 41 fields (3.6-66 ha) received biosolids at a cumulative loading rate from 455 to 1654 dry Mg ha(-1) for 8 to 23 yr in rotation from 1972 to 2004. The fields were cropped with corn, wheat, and sorghum and also with soybean and grass or fallowed. Soil organic carbon (SOC) increased rapidly with the application of biosolids, whereas it fluctuated slightly in fertilizer controls. The peak SOC in the 0- to 15-cm depth of biosolids-amended fields ranged from 4 to 7% and was greater at higher rates of biosolids. In fields where biosolids application ceased for 22 yr, SOC was still much higher than the initial levels. Over the 34-yr reclamation, the mean net soil C sequestration was 1.73 (0.54-3.05) Mg C ha(-1) yr(-1) in biosolids-amended fields as compared with -0.07 to 0.17 Mg C ha(-1) yr(-1) in fertilizer controls, demonstrating a high potential of soil C sequestration by the land application of biosolids. Soil C sequestration was significantly correlated with the biosolids application rate, and the equation can be expressed as y = 0.064x - 0.11, in which y is the annual net soil C sequestration (Mg C ha(-1) yr(-1)), and x is annual biosolids application in dry weight (Mg ha(-1) yr(-1)). Our results indicate that biosolids applications can turn Midwest Corn Belt soils from current C-neutral to C-sink. A method for calculating SOC stock under conditions in which surface soil layer depth and mass changes is also described.

Effect of long-term application of biosolids for land reclamation on surface water chemistry.

Biosolids are known to have a potential to restore degraded land, but the long-term impacts of this practice on the environment, including water quality, still need to be evaluated. The surface water chemistry (NO3-, NH4+, and total P, Cd, Cu, and Hg) was monitored for 31 yr from 1972 to 2002 in a 6000-ha watershed at Fulton County, Illinois, where the Metropolitan Water Reclamation District of Greater Chicago was restoring the productivity of strip-mined land using biosolids. The mean cumulative loading rates during the past 31 yr were 875 dry Mg ha(-1) for 1120-ha fields in the biosolids-amended watershed and 4.3 dry Mg ha(-1) for the 670-ha fields in the control watershed. Biosolids were injected into mine spoil fields as liquid fertilizer from 1972 to 1985, and incorporated as dewatered cake from 1980 to 1996 and air-dried solids from 1987 to 2002. The mean annual loadings of nutrients and trace elements from biosolids in 1 ha were 735 kg N, 530 kg P, 4.5 kg Cd, 30.7 kg Cu, and 0.11 kg Hg in the fields of the biosolids-amended watershed, and negligible in the fields of the control watershed. Sampling of surface water was conducted monthly in the 1970s, and three times per year in the 1980s and 1990s. The water samples were collected from 12 reservoirs and 2 creeks receiving drainage from the fields in the control watershed, and 8 reservoirs and 4 creeks associated with the fields in the biosolids-amended watershed for the analysis of NO3- -N (including NO2- N), NH4+-N, and total P, Cd, Cu, and Hg. Compared to the control (0.18 mg L(-1)), surface water NO3- -N in the biosolids-amended watershed (2.23 mg L(-1)) was consistently higher; however, it was still below the Illinois limit of 10 mg L(-1) for public and food-processing water supplies. Biosolids applications had a significant effect on mean concentrations of ammonium N (0.11 mg L(-1) for control and 0.24 mg L(-1) for biosolids) and total P (0.10 mg L(-1) for control and 0.16 mg L(-1) for biosolids) in surface water. Application of biosolids did not increase the concentrations of Cd and Hg in surface water. The elevation of Cu in surface water with biosolids application only occurred in some years of the first decade, when land-applied sludges contained high concentrations of trace metals, including Cu. In fact, following the promulgation of 40 CFR Part 503, the concentrations of all three metals fell below the method detection level (MDL) in surface water for nearly all samplings. Nitrate in the surface water tends to be higher in spring, and ammonium, total P, and total Hg in summer and fall. Mean nitrate, ammonium, and total phosphorus concentrations were found to be greater in creeks than reservoirs. The results indicate that application of biosolids for land reclamation at high loading rates from 1972 to 2002, with adequate runoff and soil erosion control, had only a minor impact on surface water quality.

Plant Uptake of PCBs and Other Organic Contaminants from Sludge-Treated Coal Refuse.

A field study of industrial organic contaminant uptake, in particular PCB uptake, by growing crops was conducted during 1990 at the St. David Coal Refuse Pile Reclamation Site, Fulton County, Illinois. The site had received one-time applications in 1987 of 785, 1570 and 3360 Mg ha-1 dry wt. of Chicago municipal sewage sludge. Corn (Zea mays L.), cabbage (Brassica oleracea capitata L.), and carrot (Daucus carota L.) were grown on the sludge treatments and soil (i.e., sludge treated coal refuse) and plant samples were analyzed. Mean PCB concentratious in the soils were ≤4 mg kg-1 dry wt. and there was no consistent effect on them of sludge application rate. Measurements on the 3360 Mg ha-1 dry wt. of sludge treatment soil indicated that several organochlorine pesticides occurred at concentrations ≤217 µg kg-1 dry wt. and several polynuclear aromatic hydrocarbons occurred at <1 to 3 mg kg-1 dry wt. Mean PCB concentrations in the plant materials were <300 µg kg-1 dry wt., however, there were differences among and within crops. Concentrations decreased in the order: carrot peels > carrot tops > cabbage wrapper and inner leaves > carrot core > corn ear leaf and stover > corn grain. There was insignificant PCB in corn grain. Except for cabbage wrapper leaves, the PCB concentrations in plant materials were not related to those in soil. Soil PCB concentrations accounted for 24% of the variance in cabbage wrapper leaf PCB concentrations and the bioconcentration factor (mg PCB kg-1 dry wt. of leaf/kg PCB ha-1 dry wt. of soil) was 0.0042. There was no detection of organochlorine pesticides in plant materials grown on the 3360 Mg ha-1 dry wt. of sludge treatment soil and, except for indole and isophorone, only trace amounts of a very few other organic contaminants were observed in the plant materials. Indole ranging from no detection to 52 mg kg-1 dry wt. may have been a natural constituent of cabbage. Isophorone ranging from 14 to 79 mg kg-1 dry wt. was observed in three samples of cabbage wrapper leaves and its source is unknown. Despite the very large rates of Chicago sludge employed in this study, findings indicated that they did not (i) result in high levels of organic contamination in the treated coal refuse, and (ii) represent a significant organic contaminant hazard to the quality for food and feedstuffs of crops grown on the treated coal refuse.