Long-Term Biosolids Application on Land: Beneficial Recycling of Nutrients or Eutrophication of Agroecosystems?

The impact of repeated application of alkaline biosolids (sewage sludge) products over more than a decade on soil concentrations of nutrients and trace metals, and potential for uptake of these elements by crops was investigated by analyzing soils from farm fields near Oklahoma City. Total, extractable (by the Modified Morgan test), and water-soluble elements, including macronutrients and trace metals, were measured in biosolids-amended soils and, for comparison, in soils that had received little or no biosolids. Soil testing showed that the biosolids-amended soils had higher pH and contained greater concentrations of organic carbon, N, S, P, and Ca than the control soils. Soil extractable P concentrations in the biosolids-amended soils averaged at least 10 times the recommended upper limit for agricultural soils, with P in the amended soils more labile and soluble than the P in control soils. Several trace elements (most notably Zn, Cu, and Mo) had higher total and extractable concentrations in the amended soils compared to the controls. A radish plant assay revealed greater phytoavailability of Zn, P, Mo, and S (but not Cu) in the amended soils. The excess extractable and soluble P in these biosolids-amended soils has created a long-term source of slow-release P that may contribute to the eutrophication of adjacent surface waters and contamination of groundwater. While the beneficial effects of increased soil organic carbon on measures of “soil health” have been emphasized in past studies of long-term biosolids application, the present study reveals that these benefits may be offset by negative impacts on soils, crops, and the environment from excessive nutrient loading.

Evaluation of Land Potential for Use of Biosolids in the Coastal Mediterranean Karst Region

The aim of this study was to evaluate the potential of agricultural land in the coastal Adriatic Karst region (Šibenik region, Croatia) for biosolids application by integrating spatial data from different sources: digital maps and remote sensing, parcel identification system, GIS field observations and measurements focusing on specific land and soil properties. Due to the rapid development of the wastewater treatment industry, excessive accumulation of sewage sludge (SS) in wastewater treatment plants is a growing problem worldwide. Management options for land application of biosolids require a comprehensive characterization of both SS and SS-amended soils. The assessment of agricultural land in the study area for SS disposal was based on EU and national legislation. The evaluation revealed that agricultural land in the study area accounts for only 10% of the total area (25,736 ha), but only a quarter of the existing land (6065 ha) is suitable for biosolids application. Furthermore, the data indicate that the sewage sludge can be safely applied to the soil in terms of soil metals according to the Croatian legislation. The short-term potential of the soil to sustain this ecosystem service, namely soil improvement with biosolids, should be used to determine the inherent long-term potential based on resistance to soil degradation and resilience. However, caution is needed and the long-term effects should be investigated before biosolids are continuously used for soil application.

Long-Term Biosolids Applications to Overgrazed Rangelands Improve Soil Health

Overgrazed rangelands can lead to soil degradation, yet long-term land application of organic amendments (i.e., biosolids) may play a pivotal role in improving degraded rangelands in terms of soil health. However, the long-term effects on soil health properties in response to single or repeated, low to excessive biosolids applications, on semi-arid, overgrazed grasslands have not been quantified. Using the Soil Management Assessment Framework (SMAF), soil physical, biological, chemical, nutrient, and overall soil health indices between biosolids applications (0, 2.5, 5, 10, 21, or 30 Mg ha−1) and application time (single: 1991, repeated: 2002) were determined. Results showed no significant changes in soil physical and nutrient health indices. However, the chemical soil health index was greater when biosolids were applied at rates <30 Mg ha−1 and within the single compared to repeated applications. The biological soil health index was positively affected by increasing biosolids application rates, was overall greater in the repeated as compared to the single application, and was maximized at 30 Mg ha−1. The overall soil health index was maximized at rates <30 Mg ha−1. When all indices were combined, and considering past plant community findings at this site, overall soil health appeared optimized at a biosolids application rate of ~10 Mg ha−1. The use of soil health tools can help determine a targeted organic amendment application rate to overgrazed rangelands so the material provides maximum benefits to soils, plants, animals, and the environment.

Influence of a One Time Biosolids Application on Elemental and Nutrient Concentrations on Mine Tailings

Mine tailings are nutrient deficient, contain no organic matter, and have high metal concentrations preventing the long term establishment of vegetation. The use of organic amendments, including biosolids, can help the revegetation of mine tailings by adding organic matter and nutrients but can increase metals in the receiving soil. There is also uncertainty if biosolids provide a long term benefit, or if the benefits diminish with time. To test this, a study was conducted on two tailings storage facilities, a sand and a silt loam, on a copper mine in the southern interior of British Columbia, Canada. In 1998, biosolids were applied at rates between 50 and 250 Mg ha-1 and compared to a control and fertilizer treatment. Plots were sampled in 2000 and 2015 for total and available nutrients and metals. This study showed that 17 years after a one-time biosolids application at different rates, the tailing storage facilities that received biosolids had higher carbon, nitrogen, phosphorus, and biomass compared to tailings that did not receive biosolids or received conventional fertilizer. Many elements such as C did not change from 2000 to 2015 in biosolids treated plots indicating a long-term benefit to the tailings. Additionally, biosolids did not result in increased concentrations of metals above the national regulatory limits for agriculture. This study suggests that a one-time biosolids application can provide a long-term benefit to tailings, while proper application rates can reduce the risks of metal exceedances.

Vertical phosphorus migration in biosolids-amended soils : concentrations in soils and leachates.

The impacts of biosolids land application on soil phosphorus and subsequent transfer to aquatic ecosystems in the condition of the minimal slope were assessed. Soil, representing typical "Non response" Ontario soil, was amended with anaerobically digested biosolids at a rate of 8 tonnes/ha. Over five months, soil samples from two different depths were sequentially fractionated to determine various inorganic and organic phosphorus pools in order to evaluate phosphorus vertical migration within a soil profile. Soil leachate was analyzed for soluble reactive phosphorus and added to the aquariums mimicking receiving surface waters. Water from aquariums was tested for the presence of eutrophication. The results indicated that biosolids application did not significantly affect phosphorus concentrations in soil and did not cause phosphorus vertical migration. The concentrations of soluble reactive phosphorus also were not affected by biosolids. No signs of eutrophication were observed in receiving waters.

Phosphorus fractions in biosolids, biosolid-amended soils, runoffs and its impact on primary productivity in aquatic ecosystems

The impact of land application of biosolids on soil phosphorus (P) and subsequent transfer to aquatic ecosystems were assessed. Boxed reference soils were amended with two biosolids at a rate of 8 dry t/ha. Biosolids and soil samples taken over four months were sequentially fractionated to determine various inorganic and organic P pools. Also, within three weeks of biosolids application, four storm events were simulated and surface runoff and leachate from the soils were collected and analyzed for different P forms. The runoffs and equivalent inorganic nutrient were added to different mesocosms that mimicked stratified lakes. Samples from the mesocosms were periodically collected and analyzed for various physical, chemical and biological parameters. The results indicated that biosolids significantly affect different P pools in soils. Also, P loading from biosolids was expected to drive the mesocosms to hypereutrophication, yet the response was moderately eutrophic, followed by decline in chlorophyll a.

Vertical phosphorus migration in biosolids-amended soils : concentrations in soils and leachates.

The impacts of biosolids land application on soil phosphorus and subsequent transfer to aquatic ecosystems in the condition of the minimal slope were assessed. Soil, representing typical "Non response" Ontario soil, was amended with anaerobically digested biosolids at a rate of 8 tonnes/ha. Over five months, soil samples from two different depths were sequentially fractionated to determine various inorganic and organic phosphorus pools in order to evaluate phosphorus vertical migration within a soil profile. Soil leachate was analyzed for soluble reactive phosphorus and added to the aquariums mimicking receiving surface waters. Water from aquariums was tested for the presence of eutrophication. The results indicated that biosolids application did not significantly affect phosphorus concentrations in soil and did not cause phosphorus vertical migration. The concentrations of soluble reactive phosphorus also were not affected by biosolids. No signs of eutrophication were observed in receiving waters.

Phosphorus fractions in biosolids, biosolid-amended soils, runoffs and its impact on primary productivity in aquatic ecosystems

The impact of land application of biosolids on soil phosphorus (P) and subsequent transfer to aquatic ecosystems were assessed. Boxed reference soils were amended with two biosolids at a rate of 8 dry t/ha. Biosolids and soil samples taken over four months were sequentially fractionated to determine various inorganic and organic P pools. Also, within three weeks of biosolids application, four storm events were simulated and surface runoff and leachate from the soils were collected and analyzed for different P forms. The runoffs and equivalent inorganic nutrient were added to different mesocosms that mimicked stratified lakes. Samples from the mesocosms were periodically collected and analyzed for various physical, chemical and biological parameters. The results indicated that biosolids significantly affect different P pools in soils. Also, P loading from biosolids was expected to drive the mesocosms to hypereutrophication, yet the response was moderately eutrophic, followed by decline in chlorophyll a.