Nitrogen removal performance in roadside stormwater bioretention cells amended with drinking water treatment residuals.

Bioretention cells, a type of green stormwater infrastructure, have been shown to reduce runoff volumes and remove a variety of pollutants. The ability of bioretention cells to remove nitrogen and phosphorus, however, is variable, and bioretention soil media can act as a net exporter of nutrients. This is concerning as excess loading of nitrogen and phosphorus can lead to eutrophication of surface waters, which green stormwater infrastructure is intended to ameliorate. Drinking water treatment residuals (DWTR), metal (hydr)oxide-rich by-products of the drinking water treatment process, have been studied as an amendment to bioretention soil media due to their high phosphorus sorption capacity. However, very few studies have specifically addressed the effects that DWTRs may have on nitrogen removal performance within bioretention cells. Here, we investigated the effects of DWTR amendment on nitrogen removal in bioretention cells treating stormwater in a roadside setting. We tested the capacity of three different DWTRs to either retain or leach dissolved inorganic nitrogen in the laboratory and also conducted a full-scale field experiment where DWTR-amended bioretention cells and experimental controls were monitored for influent and effluent nitrogen concentrations over two field seasons. We found that DWTRs alone exhibit some capacity to leach nitrate and ammonium, but when integrated into sand- and compost-based bioretention soil media, DWTRs have little to no effect on the removal of nitrogen in bioretention cells. These results suggest that DWTRs can be used in bioretention media for enhanced phosphorus retention without the risk of contributing to nitrogen export in bioretention effluent.

Microplastics in composts, digestates, and food wastes: A review.

Diverting food waste from landfills to composting or anaerobic digestion can reduce greenhouse gas emissions, enable the recovery of energy in usable forms, and create nutrient-rich soil amendments. However, many food waste streams are mixed with plastic packaging, raising concerns that food waste-derived composts and digestates may inadvertently introduce microplastics into agricultural soils. Research on the occurrence of microplastics in food waste-derived soil amendments is in an early phase and the relative importance of this potential pathway of microplastics to agricultural soils needs further clarification. In this paper, we review what is known and what is not known about the abundance of microplastics in composts, digestates, and food wastes and their effects on agricultural soils. Additionally, we highlight future research needs and suggest ways to harmonize microplastic abundance and ecotoxicity studies with the design of related policies. This review is novel in that it focuses on quantitative measures of microplastics in composts, digestates, and food wastes and discusses limitations of existing methods and implications for policy.

Assessment of lime-conditioned dairy manure fine solids captured using dissolved air flotation for fertilization in horticulture.

Dissolved air flotation (DAF) has shown potential to substantially improve phosphorus (P) mass balance on dairy farms by capturing P associated with fine solids from liquid manure, enabling new management options. However, at <25% total solids, further dewatering is necessary to facilitate export of recovered fine solids off farm for use in bagged or bulk products. Physical conditioners such as quicklime (QL) and lime kiln dust (LKD) are commonly used to enhance mechanical dewatering of biosolids, but their effect on the properties and fertilization value of DAF-captured manure fine solids has not been documented. We generated plant foods using DAF-captured dairy manure fine solids conditioned with 3, 4.5, and 6% m/m QL or LKD and dewatered using a benchtop press for comparison with thermally dried fine solids. Tomato (Solanum lycopersicum L.) seedlings were grown in a soilless substrate amended with 6% v/v plant food and in an unamended control. Thermally dried and LKD plant foods produced significantly greater seedling biomass than QL plant foods and the unamended control. Quicklime- and LKD-conditioned fine solids contained approximately 30× and 10× less water-extractable P than thermally dried fine solids, respectively, likely due to precipitation of Ca-P minerals. The elevated pH (≥10) of the lime-conditioned fine solids could have also suppressed plant growth. These effects limit horticultural applications but could be beneficial in agricultural field settings where slow-release P is desirable. Research beyond this preliminary assessment is needed to determine the practicality and sustainability of the approach along with longer-term nutrient bioavailability.

Phosphorus removal, metals dynamics, and hydraulics in stormwater bioretention systems amended with drinking water treatment residuals.

Drinking water treatment residuals (DWTRs) are a promising media amendment for enhancing phosphorus (P) removal in bioretention systems, but substantial removal of dissolved P by DWTRs has not been demonstrated in field bioretention experiments. We investigated the capacity of a non-amended control media (Control) and a DWTR-amended treatment media (DWTR) to remove soluble reactive P (SRP), dissolved organic P (DOP), particulate P (PP), and total P (TP) from stormwater in a two-year roadside bioretention experiment. Significant reductions m SRP, PP and TP concentrations and loads were observed in both the Control and DWTR media. However, the P removal efficiency of the DWTR cells were greater than those of the Control cells for all P species, particularly during the second monitoring season as P sorption complexes likely began to saturate in the Control cells. The difference in P removal efficiency between the Control and DWTR cells was greatest during large storm events, which transported the majority of dissolved P loads in this study. We also investigated the potential for DWTRs to restrict water flow through bioretention media or leach heavy metals. The DWTRs used in this study did not affect the hydraulic performance of the bioretention cells and no significant evidence of heavy metal leaching was observed during the study period. Contrasting these results with past studies highlights the importance of media design in bioretention system performance and suggests that DWTRs can effectively capture and retain P without affecting system hydraulics if properly incorporated into bioretention media.

Balancing Hydraulic Control and Phosphorus Removal in Bioretention Media Amended with Drinking Water Treatment Residuals.

Green stormwater infrastructure like bioretention can reduce stormwater runoff volumes and trap sediments and pollutants. However, bioretention soil media can be both a sink and source of phosphorus (P). We investigated the potential tradeoff between hydraulic conductivity and P sorption capacity in drinking water treatment residuals (DWTRs), with implications for bioretention media design. Batch isotherm and flow-through column experiments were used to quantify the maximum P sorption capacity (Smax) and rate of P sorption for three DWTR sources. Smax values varied greatly among DWTR sources and methodologies, which has implications for regulatory standards. We also conducted a large column experiment to determine the hydraulic and P removal effects of amending bioretention media with solid and mixed layers of DWTRs. When applied to bioretention media, the impact of DWTRs on hydraulic conductivity and P removal depended on layering strategy. Although DWTR addition in solid and mixed layer designs improved P removal, the solid layer restricted water flow and exhibited incomplete P removal, while the mixed layer had no effect on flow and removed ~100% of P inputs. We recommend that DWTRs be mixed with sand in bioretention media to simultaneously achieve stormwater drainage and P reduction goals in green stormwater infrastructure.

Healthy diets can create environmental trade-offs, depending on how diet quality is measured.

BACKGROUND: There is an urgent need to assess the linkages between diet patterns and environmental sustainability in order to meet global targets for reducing premature mortality and improving sustainable management of natural resources. This study fills an important research gap by evaluating the relationship between incremental differences in diet quality and multiple environmental burdens, while also accounting for the separate contributions of retail losses, inedible portions, and consumer waste. METHODS: Cross sectional, nationally-representative data on food intake in the United States were acquired from the National Health and Nutrition Examination Survey (2005-2016), and were linked with nationally-representative data on food loss and waste from published literature. Survey-weighted procedures estimated daily per capita food retail loss, food waste, inedible portions, and consumed food, and were summed to represent Total Food Demand. Diet quality was measured using the Healthy Eating Index-2015 and the Alternative Healthy Eating Index-2010. Data on food intake, loss, and waste were inputted into the US Foodprint Model to estimate the amount of agricultural land, fertilizer nutrients, pesticides, and irrigation water used to produce food. RESULTS: This study included dietary data from 50,014 individuals aged ≥2 y. Higher diet quality (HEI-2015 and AHEI-2010) was associated with greater per capita Total Food Demand, as well as greater retail loss, inedible portions, consumer waste, and consumed food (P < 0.001 for all comparisons). Consumed food accounted for 56-74% of agricultural resource use (land, fertilizer nutrients, pesticides, and irrigation water), retail loss accounted for 4-6%, inedible portions accounted for 2-15%, and consumer waste accounted for 20-23%. Higher diet quality was associated with lower use of agricultural land, but the relationship to other agricultural resources was dependent on the tool used to measure diet quality (HEI-2015 vs. AHEI-2010). CONCLUSIONS: Over one-quarter of the agricultural inputs used to produce Total Food Demand were attributable to edible food that was not consumed. Importantly, this study also demonstrates that the relationship between diet quality and environmental sustainability depends on how diet quality is measured. These findings have implications for the development of sustainable dietary guidelines, which requires balancing population-level nutritional needs with the environmental impacts of food choices.

US county-level agricultural crop production typology.

OBJECTIVES: Crop production is an important variable in social, economic and environmental analyses. There is an abundance of crop data available for the United States, but we lack a typology of county-level crop production that accounts for production similarities in counties across the country. We fill this gap with a county-level classification of crop production with ten mutually exclusive categories across the contiguous United States. DATA DESCRIPTION: To create the typology we ran a cluster analysis on acreage data for 21 key crops from the United States Department of Agriculture's 2012 Agricultural Census. Prior to clustering, we estimated undisclosed county acreage values, controlled for acreage in other crop types, and removed counties with low agricultural production to produce proportional scores for each crop type in each county. We used proportional scores to control for the influence of county size in the cluster analysis and used internal and stability measures to validate the analysis. The final dataset features 2922 counties. Future research can leverage this typology as an input for county- or regional-level analysis.

Integrating anaerobic co-digestion of dairy manure and food waste with cultivation of edible mushrooms for nutrient recovery.

State-level policies in the New England region of the United States require diversion of organic materials away from landfills. One management option for food waste is anaerobic co-digestion with dairy manure. In addition to biogas, anaerobic digestion produces separated solid and liquid digestates. Solid digestates in the region are typically recycled as animal bedding before returning to the digester and liquids are used to fertilize local soils. Repeated land application of nutrients can contribute to eutrophication risk over time and alternative models are needed to convert digestates into valuable export products. We tested solid digestates derived from dairy manure and food waste as substrate ingredients in the cultivation of Pleurotus ostreatus. We show these materials can be used to offset non-local substrate ingredients while achieving mushroom yields comparable to commercial recipes. This strategy could help divert nutrients away from land adjacent to digesters and into safe, protein-rich food, while producing useful spent mushroom substrate.

Relationship between food waste, diet quality, and environmental sustainability.

Improving diet quality while simultaneously reducing environmental impact is a critical focus globally. Metrics linking diet quality and sustainability have typically focused on a limited suite of indicators, and have not included food waste. To address this important research gap, we examine the relationship between food waste, diet quality, nutrient waste, and multiple measures of sustainability: use of cropland, irrigation water, pesticides, and fertilizers. Data on food intake, food waste, and application rates of agricultural amendments were collected from diverse US government sources. Diet quality was assessed using the Healthy Eating Index-2015. A biophysical simulation model was used to estimate the amount of cropland associated with wasted food. This analysis finds that US consumers wasted 422g of food per person daily, with 30 million acres of cropland used to produce this food every year. This accounts for 30% of daily calories available for consumption, one-quarter of daily food (by weight) available for consumption, and 7% of annual cropland acreage. Higher quality diets were associated with greater amounts of food waste and greater amounts of wasted irrigation water and pesticides, but less cropland waste. This is largely due to fruits and vegetables, which are health-promoting and require small amounts of cropland, but require substantial amounts of agricultural inputs. These results suggest that simultaneous efforts to improve diet quality and reduce food waste are necessary. Increasing consumers' knowledge about how to prepare and store fruits and vegetables will be one of the practical solutions to reducing food waste.

Modeling impacts of sea-level rise, oil price, and management strategy on the costs of sustaining Mississippi delta marshes with hydraulic dredging.

Over 25% of Mississippi River delta plain (MRDP) wetlands were lost over the past century. There is currently a major effort to restore the MRDP focused on a 50-year time horizon, a period during which the energy system and climate will change dramatically. We used a calibrated MRDP marsh elevation model to assess the costs of hydraulic dredging to sustain wetlands from 2016 to 2066 and 2016 to 2100 under a range of scenarios for sea level rise, energy price, and management regimes. We developed a subroutine to simulate dredging costs based on the price of crude oil and a project efficiency factor. Crude oil prices were projected using forecasts from global energy models. The costs to sustain marsh between 2016 and 2100 changed from $128,000/ha in the no change scenario to ~$1,010,000/ha in the worst-case scenario for sea level rise and energy price, an ~8-fold increase. Increasing suspended sediment concentrations, which is possible using managed river diversions, raised created marsh lifespan and decreased long term dredging costs. Created marsh lifespan changed nonlinearly with dredging fill elevation and suspended sediment level. Cost effectiveness of marsh creation and nourishment can be optimized by adjusting dredging fill elevation to the local sediment regime. Regardless of management scenario, sustaining the MRDP with hydraulic dredging suffered declining returns on investment due to the convergence of energy and climate trends. Marsh creation will likely become unaffordable in the mid to late 21st century, especially if river sediment diversions are not constructed before 2030. We recommend that environmental managers take into consideration coupled energy and climate scenarios for long-term risk assessments and adjust restoration goals accordingly.

Changes in estuarine sediment phosphorus fractions during a large-scale Mississippi River diversion.

Ongoing deterioration and loss of wetlands in the Mississippi River delta threatens the survival of Louisiana's coastal ecosystems and human settlements. In response, the State of Louisiana has proposed a $50 billion, 50-year restoration program. A central piece of this program is the reintroduction of Mississippi River water into the deltaic plain using managed diversions that mimic natural flood pulses. These diversions would transport critically needed sediment, but also deliver large nutrient loads. Coastal eutrophication is therefore a concern, particularly blooms of toxin-producing cyanobacteria. The Bonnet Carré Spillway (BCS) is an existing large flood diversion that protects New Orleans and provides an opportunity to investigate diversion nutrient transport. Here, we quantify sediment phosphorus (P) deposited by the BCS for the first time, and use a sequential P fractionation scheme to evaluate the likelihood of future sediment P release to the water column of the Lake Pontchartrain Estuary. In 2011, we collected sediment cores in the estuary for determination of P fractions before and after the discharge of 21.9km3 of river water through the BCS in just under 6weeks. We observed the greatest net increases in sediment total P, inorganic P forms, and more labile organic P in the region near the inflow. We estimate that the diversion deposited ≥5000 metric tons of P in the sediments of the Lake Pontchartrain Estuary. The sum of readily available inorganic P, Fe/Al-bound inorganic P, and more labile organic P equaled approximately 20-30% of post-diversion sediment total P. These fractions are more likely to be released to the water column than the other sediment P forms we quantified. Diversion designs that encourage sedimentation in coastal marshes versus open bays can likely reduce the chances that deposited particulate P creates eutrophication risk.

The phosphorus cost of agricultural intensification in the tropics.

Agricultural intensification in the tropics is one way to meet rising global food demand in coming decades(1,2). Although this strategy can potentially spare land from conversion to agriculture(3), it relies on large material inputs. Here we quantify one such material cost, the phosphorus fertilizer required to intensify global crop production atop phosphorus-fixing soils and achieve yields similar to productive temperate agriculture. Phosphorus-fixing soils occur mainly in the tropics, and render added phosphorus less available to crops(4,5). We estimate that intensification of the 8-12% of global croplands overlying phosphorus-fixing soils in 2005 would require 1-4 Tg P yr(-1) to overcome phosphorus fixation, equivalent to 8-25% of global inorganic phosphorus fertilizer consumption that year. This imposed phosphorus 'tax' is in addition to phosphorus added to soils and subsequently harvested in crops, and doubles (2-7 Tg P yr(-1)) for scenarios of cropland extent in 2050(6). Our estimates are informed by local-, state- and national-scale investigations in Brazil, where, more than any other tropical country, low-yielding agriculture has been replaced by intensive production. In the 11 major Brazilian agricultural states, the surplus of added inorganic fertilizer phosphorus retained by soils post harvest is strongly correlated with the fraction of cropland overlying phosphorus-fixing soils (r(2) = 0.84, p < 0.001). Our interviews with 49 farmers in the Brazilian state of Mato Grosso, which produces 8% of the world's soybeans mostly on phosphorus-fixing soils, suggest this phosphorus surplus is required even after three decades of high phosphorus inputs. Our findings in Brazil highlight the need for better understanding of long-term soil phosphorus fixation elsewhere in the tropics. Strategies beyond liming, which is currently widespread in Brazil, are needed to reduce phosphorus retention by phosphorus-fixing soils to better manage the Earth's finite phosphate rock supplies and move towards more sustainable agricultural production.

Spectroscopic measurements of estuarine dissolved organic matter dynamics during a large-scale Mississippi River flood diversion.

The Mississippi River Flood of 2011 prompted the opening of the Bonnet Carré Spillway (BCS) in southeastern Louisiana to protect the City of New Orleans. The BCS diverted approximately 21.9 km(3) of river water into the oligohaline Lake Pontchartrain Estuary over the course of 43 days. We characterized estuarine dissolved organic matter (DOM) dynamics before, during, and after the diversion in order to better understand the biogeochemical dynamics associated with these immense freshwater inflows. Dissolved organic carbon (DOC) exhibited a large degree of variability during and after the period of elevated primary productivity that occurred following the diversion. Furthermore, DOC analysis provides limited insight into carbon cycling during these dynamic periods. In order to overcome the limitations of DOC, spectroscopic methods were used to gain insights into chemical composition dynamics. Both ultraviolet visible (A254, A350, SUVA254, spectral slope, and normalized UV/Vis) and fluorescence spectroscopy (excitation emission matrices and fluorescence and biological indices) were used to study the compositional changes of DOM over time. Collectively, our results document a perturbation in DOM chemistry in Lake Pontchartrain due to the diversion and a subsequent return toward pre-diversion conditions. Immediate increases in A350 indicate that BCS freshwater contained elevated concentrations of lignin of terrestrial origin. Ensuing declines in A350, along with changes in the fluorescence and biological indices, indicate that DOM rapidly became more microbial in composition. Our results provide insights into estuarine DOM dynamics relevant to systems receiving flood pulses of freshwater due to either hydrologic manipulation or precipitation events.

Estuarine ecosystem response to three large-scale Mississippi River flood diversion events.

Large inflows of nitrogen (N)-rich freshwater to estuaries can lead to expressions of eutrophication including harmful algal blooms of cyanobacteria (CyanoHABs). Lake Pontchartrain is a large, oligohaline estuary that occasionally receives episodic diversions of N-rich Mississippi River water via the Bonnet Carré Spillway to alleviate flood threats to New Orleans, LA. The extreme flood stage of the Lower Mississippi River in May 2011 prompted the tenth opening of the spillway since 1937. The 2011 opening occurred later in the season than the previous two lower discharge events (1997 and 2008) and was characterized by dissolved inorganic N loads 1.7 and 2.6 times greater than the 1997 and 2008 events, respectively. Rapid depletion of riverine nitrate (21 days) occurred post-spillway closure in 2011 with no associated CyanoHAB and was followed by an internal pulse of phosphorus (P) from sediments to restore N-limitation. Our analysis of recent spillway openings indicates that there is not a simple stimulus-response relationship between N loading and CyanoHAB formation. We investigate the systemic causal relationships that determine ecosystem response to these nutrient-rich freshwater inflows and highlight several important parameters including: external N loading, timing, magnitude, plume hydrodynamics, nutrient molar ratios, internal P loading, weather, and northern tributary discharge. Our results suggest that the turbulent, fluctuating environment and nutrient composition during diversions does not favor CyanoHAB formation and that the immense size and timing of the 2011 diversion may have resulted in near complete post-diversion CyanoHAB suppression by hydraulic flushing.

Nitrate flux into the sediments of a shallow oligohaline estuary during large flood pulses of Mississippi River water.

Lake Pontchartrain is a large, oligohaline estuary located in coastal Louisiana that receives episodic diversions of nitrogen-rich Mississippi River water via the Bonnet Carré Spillway to alleviate flood threats to the city of New Orleans. These events may be linked to expressions of eutrophication, and it is therefore important to investigate pathways of nitrate (NO) loss. Nitrate flux into the sediments of Lake Pontchartrain was investigated using two independent methods: (i) simulating high NO flood events under aerobic and anaerobic incubations in intact sediment cores collected during 2010 and (ii) in situ field measurements of the vertical profiles of dissolved inorganic nitrogen species at the sediment-water interface during the 2011 Bonnet Carré Spillway opening. Mean rates of NO flux into sediments based on mass transfer in intact cores collected in 2010 and in situ porewater measurements in 2011 were -17.4 and -1.4 mg NO-N m d, respectively, for water column NO concentrations observed in situ in 2011. During the laboratory incubations, there was no significant difference in NO flux between oxygen treatments. We estimate that NO flux into sediments accounted for up to 3.1% (309 Mg NO-N) of water column NO loss during the 2008 Bonnet Carré Spillway event. Sediment characteristics, field measurements, and results from the laboratory experiment suggest that denitrification is the primary pathway for NO reduction. Even though there is significant NO reduction occurring in Lake Pontchartrain sediments during Mississippi River diversion events, this pathway of NO loss from the water column plays a relatively minor role in the transformation of the very large amount of NO received during these times.

Municipal wastewater treatment in Mexico: current status and opportunities for employing ecological treatment systems.

The aim of this paper is to evaluate the current status of municipal wastewater (MWW) treatment in Mexico, as well as to assess opportunities for using ecological treatment systems, such as constructed wetlands. In 2008, Mexico had 2101 MWW treatment plants that treated only 84 m3/s of wastewater (208 m3/s ofMWW were collected in sewer systems). Unfortunately, most treatment plants operate below capacity owing to a lack of maintenance and paucity of properly trained personnel. The main types of treatment systems applied in Mexico are activated sludge and waste stabilization ponds, which treat 44.3% and 18% of the MWW collected, respectively. As in many other developing nations around the world, there is a great need in Mexico for low-cost, low-maintenance wastewater treatment systems that are both economically and environmentally sustainable. In 2005, 24.3 million Mexicans lived in villages of less than 2500 inhabitants and 14.1 million lived in towns with 2500-15,000 inhabitants. An opportunity exists to extend the use of ecological treatment systems to these low population density areas and considerably increase the percentage of MWW that is treated in Mexico. Small-scale and medium-size constructed wetlands have been built successfully in some states, primarily during the past five years. Several barriers need to be overcome to increase the adoption and utilization of ecological wastewater technology in Mexico, including: a lack of knowledge about this technology, scarce technical information in Spanish, and the government's concentration on constructing MWW treatment plants solely in urban areas.